yus carbon stocks report
TRANSCRIPT
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Lead Authors: Michelle Venter Wouter Dieleman David Gillieson Anurag Ramachandra Michael Bird
Carbon stocks of the YUS Conservation Area
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Contributing Authors: Bruce Beehler, Lisa Dabek, Will Edwards, Bega Inaho, Banak Gamui, Rigel Jensen, Andrew Krockenberger, Karau Kuna, Susanne Laurance, Stephen McKenna, Miriam Murphy, Tony Page, Timmy Sowang, Oscar Venter and Mark Ziembicki
Cover photo top to bottom:
a. Fallowed garden outside YUS Conservation Area b. Landholders measuring tree circumference during participatory biomass inventories in the YUS Conservation Area c. Anthropogenic grasslands adjacent to the YUS Conservation Area, fire set by passer‐by d. Landholder holding fruit of the Pandiumedule tree, in local Mato language the tree is named Matip e. (background) Aerial view of patches of forest and grasslands maintained by fire in the area surrounding the YUS Conservation Area Citation: Venter M., Dieleman W.I.J., Gillieson D., Ramachandra A., Bird M.I.1 (2012) Carbon stocks in the YUS Conservation Area. James Cook University, Cairns Australia
Contact Person: Michael Bird ([email protected])
School of Earth and Environmental Science and Centre for Tropical and Environmental Sciences James Cook University PO Box 6811 Cairns Queensland 4870 Australia Tel: +61 74042 1137
Disclaimer
The results of this report are part of an ongoing study of carbon stocks in the YUS area. As the study progresses,
information on identification of tree species, wood specific density and coarse woody debris, and possibly soil
carbon in non‐forest land‐uses, will serve to refine carbon stocks presented in this report. The carbon stocks are
based on the available data at the time of publication and may change in the future.
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ACKNOWLEDGEMENTS
This work was made possible by the funding provided by KFW Bankengruppe; we thank the organization and its staff
for the opportunity to carry out this work.
We would particularly like to thank the Landholders of the YUS area, for without their generosity, knowledge and
support, we would not have had such successful field campaigns. We would like to express our gratitude to all the
people of YUS who allowed us to work on their land, who worked as field assistants, and who provided
accommodation and food and shared their skills and knowledge. We thank the Community Based Organization (CBO)
of the YUS Conservation Area for promoting conservation and climate change initiatives and acting as a platform for
information exchange between the many actors and organizations in YUS.
We would like to give a special thanks to the team at the Tree Kangaroo Conservation Program (TKCP) for their
tremendous dedication and for providing advice and assistance with logistics; without their enthusiasm, hard work and
continuous engagement with YUS communities, our work there would have been impossible. We would also like to
thank Conservation International (CI) for providing technical support, access to 1ha permanent sample plots (PSP), for
their initiative in building bush camps and maintaining trails. Principally, we would like to thank Bruce Beeler for taking
the time to show us the bush ropes.
We would like to extend a special recognition to Timmy and Barbara Sowang for their ongoing commitment to the
project. Their dedication to the YUS Conservation Project, their hospitality and friendship has made our time spent in
the field enjoyable. Thank you Timmy for your help in training local landholders, for organizing the bush logistics and
for leading field teams during participatory biomass inventories. Also, thanks to the following people for help in the
field; Clant (Ray) Alok, Kylie Anderson, Kasbeth Evei, Richard Hopkinson, Bega Inaho, Banak Gamui, Anton Lata, Mireia
Torello‐Raventos and Oscar Venter; your help has been tremendous.
Special thanks to Bruce Beehler, Lisa Dabek, Will Edwards, Bega Inaho, Banak Gamui, Rigel Jensen, Andrew
Krockenberger, Karau Kuna, Susanne Laurance, Stephen McKenna, Miriam Murphy, Tony Page, Timmy
Sowang, Oscar Venter and Mark Ziembicki for your input in this report.
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TABLEOFCONTENTS
Acknowledgements ............................................................................................................................. 3
Abbreviations and definitions ............................................................................................................. 7
Executive summary ............................................................................................................................. 8
1. Introduction .............................................................................................................................. 13
2. Methods .................................................................................................................................... 16 2.1 Study sites ............................................................................................................................................ 16 2.2 Above ground biomass ......................................................................................................................... 20
2.2.1 Biomass inventories ............................................................................................................................... 20 2.2.3 Forest structure ..................................................................................................................................... 21 2.2.3 Wood density ......................................................................................................................................... 22 2.2.4 Allometric equations .............................................................................................................................. 22 2.2.5 Below ground living biomass ................................................................................................................. 23
2.3 Soil organic carbon ............................................................................................................................... 24 2.4 Total carbon stocks .............................................................................................................................. 29 2.5 Role of local landholders ...................................................................................................................... 30
3. Results and discussion ............................................................................................................... 31 3.1 Above ground forest carbon stocks ...................................................................................................... 31 3.2 Soil organic carbon (SOC) ..................................................................................................................... 36 3.3 Soil carbon storage in grassland and forest soils ................................................................................... 40 3.4 AGC and SOC along the elevation gradient ........................................................................................... 42 3.5 Standing C stocks for different land‐cover classes ................................................................................. 43
3.5.1 Carbon density across YUS ..................................................................................................................... 44 3.5.2 Land cover extent in YUS ....................................................................................................................... 47
3.6 Comparison of AGC with other PNG data sets ...................................................................................... 49 3.7 Options for carbon sequestration in YUS .............................................................................................. 50
3.7.1 Option 1: Protecting lowland primary forest ......................................................................................... 51 3.7.2 Option 2: Converting grasslands to forest by assisted natural regeneration ........................................ 53 3.7.3 Option 3: Converting non‐forest to shade coffee plantations .............................................................. 54
4. Concluding remarks ................................................................................................................... 57
5. Appendices ................................................................................................................................ 61 Appendix 1 Equations ................................................................................................................................ 61 Appendix 2 Mean wood density values in each elevation category ............................................................ 62 Appendix 3 Comparison of SOC in other elevation transects ...................................................................... 63 Appendix 4 Tree species in regrowth land cover (work in Progress) ............................................................ 64 Appendix 5 Aligning carbon sequestration options with Landscape Management plan in YUS ................... 65
6. References ................................................................................................................................. 66
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LISTOFFIGURES
FIGURE 1 YUS LANDSCAPE. GREEN DEMARCATES THE CONSERVATION AREA, DOTTED LINE DEMARCATES THE PROJECT LANDSCAPE AND THE RECTANGLE
DEMARCATES THE BROADER AREA OF INTEREST AS DEFINED BY CI .................................................................................................... 17
FIGURE 2 SCHEME OF A BIOMASS INVENTORY PLOT. STEM SIZES WERE RECORDED IN NESTED SUBPLOTS; LARGE STEMS (DBH ≥50CM) IN 20 X 50M,
MEDIUM STEM (DBH 20‐49CM) WITHIN 20 X 30M PLOTS AND SMALL STEMS (DBH 5‐10CM) WITHIN 10 X 10M PLOTS ............................ 21
FIGURE 3 SCHEMATIC REPRESENTATION OF SAMPLING LOCATIONS ALONG THE ELEVATIONAL GRADIENT. NINETY ONE FOREST LOCATIONS (54 IN 1HA
PLOTS AND 37 IN OTHER FOREST PLOTS) AND 14 GRASSLANDS SITES WERE SAMPLED. FOREST SAMPLING LOCATIONS ARE CLUSTERED
ACCORDING TO THE 1HA PLOT NUMBER (I.E. SITE 6 TO 14). ONE CLUSTER CONTAINS SIX LOCATIONS IN EACH HECTARE PLOT AND 3‐6
ADDITIONAL FOREST LOCATIONS WITHIN 200M ALTITUDE DIFFERENCE RELATIVE TO THE 1HA PLOT. GRASSLAND SITES ARE IDENTIFIED BY THE
NAME OF THE CLOSEST VILLAGE. ............................................................................................................................................... 26
FIGURE 4 SCHEME OF SOIL SAMPLING PROFILE ...................................................................................................................................... 27
FIGURE 5 TOPOGRAPHIC MAP OUTLINING THE TRANSECT FROM SEA LEVEL TO 3100M .................................................................................. 31
FIGURE 6 ABOVE GROUND CARBON VALUES FOR 179 PRIMARY FOREST PLOTS ACROSS A 3100M ELEVATION GRADIENT. AGB VALUES VARIED GREATLY
BETWEEN PLOTS. ................................................................................................................................................................... 32
FIGURE 7 ABOVE GROUND CARBON STOCKS IN PRIMARY FOREST AND HOW THEY VARY WITH ELEVATION. ABOVE GROUND BIOMASS WHERE HIGHEST AT
LOW ELEVATIONS AND AT MID‐MONTANE ELEVATIONS, UNEXPECTED DIPS OCCURRED BETWEEN 1400 AND 1800M. ERROR BARS ARE ONE
STANDARD DEVIATION OF THE MEAN ......................................................................................................................................... 34
FIGURE 8 ABOVE GROUND CARBON IN UNDISTURBED (RED BARS) AND IN SITES WITH NATURAL DISTURBANCES (GREEN BARS) ............................... 36
FIGURE 9 RELATIONSHIP BETWEEN SOIL ORGANIC CARBON (SOC) STOCKS AND TOPOGRAPHIC VARIABLES. DATA DISPLAYED ARE THE RELATIONSHIP OF
ALTITUDE WITH SOIL ORGANIC CARBON (SOC) STOCKS (A), OF ALTITUDE WITH SLOPE (B), OF SLOPE WITH SOC STOCKS (C), AND THE
RELATIONSHIP BETWEEN ALTITUDE AND SOC STOCKS FOR EAST ASPECT SITES (WHITE CIRCLES) AND WEST ASPECT SITES (BLACK DOTS).
SIGNIFICANT LINEAR CORRELATIONS AND ANCOVA DIFFERENCES FOR SLOPES AND GROUP MEANS ARE CONSIDERED SIGNIFICANT AT
P<0.05.AND SOIL CHARACTERISTICS (SOIL DEPTH, PH AND TEXTURE). MANY ENVIRONMENTAL VARIABLES WERE ALSO CORRELATED TO EACH
OTHER, INDICATING A STRONG COVARIANCE OF DRIVER VARIABLES ALONG OUR ELEVATION GRADIENT. ................................................... 39
FIGURE 10 RELATIONSHIP BETWEEN ALTITUDE AND SOIL C STOCKS FOR THE 100CM PROFILE IN GRASSLAND (RED CIRCLES) AND FOREST (WHITE
CIRCLES) PLOTS. THE P‐VALUE AND R2‐VALUE OF THE INDIVIDUAL LINEAR REGRESSIONS ARE GIVEN. SIGNIFICANT CORRELATION IS ASSESSED AT
P<0.05. P‐VALUES FOR ANCOVA ANALYSIS ARE GIVEN TO ASSESS DIFFERENCES BETWEEN MEANS AND SLOPES OF BOTH REGRESSIONS.
STATISTICAL DIFFERENCES ARE CONSIDERED AT P<0.05 ................................................................................................................ 40
FIGURE 11 RELATIONSHIP BETWEEN ALTITUDE AND BULK DENSITY CORRECTED SOIL C STOCKS FOR THE 30CM PROFILE IN GRASSLAND (RED CIRCLES)
AND FOREST (WHITE CIRCLES) PLOTS. THE P‐VALUE AND R2‐VALUE OF THE INDIVIDUAL LINEAR REGRESSIONS ARE GIVEN. SIGNIFICANT
CORRELATION IS ASSESSED AT P<0.05. P‐VALUES FOR ANCOVA ANALYSIS ARE GIVEN TO ASSESS DIFFERENCES BETWEEN MEANS AND SLOPES
OF BOTH REGRESSIONS. STATISTICAL DIFFERENCES ARE CONSIDERED AT P<0.05 ................................................................................. 42
FIGURE 12 AVERAGE CARBON STOCKS IN ABOVE GROUND POOL (GREEN) AND SOIL ORGANIC POOL (BROWN) AT NINE ELEVATION CLUSTERS ............ 43
FIGURE 13 YUS VEGETATION MAP DERIVED FROM 2009 SATELLITE IMAGERY (GILLIESON ET AL. 2011) .......................................................... 47
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LISTOFTABLES
TABLE 1 DESCRIPTION OF ENVIRONMENTAL FACTORS OF NINE ELEVATION CLUSTERS (FROM 50M TO 3100M IN THE YUS CA .............................. 19
TABLE 2 CORRELATION BETWEEN DIFFERENT LAND COVER CLASSIFICATION AND TYPE OF ASSESSMENT CARRIED OUT IN THE FIELD; ABOVE GROUND
CARBON (AGC) AND SOIL ORGANIC CARBON (SOC) ..................................................................................................................... 29
TABLE 3 NATURAL DISTURBANCES, MEAN STRUCTURAL PARAMETERS AND AGC VALUES FOR PRIMARY FOREST AT NINE ELEVATION CLUSTERS (50‐
3100M) IN YUS CA .............................................................................................................................................................. 33
TABLE 4 SUMMARY OF PAIRWISE LINEAR CORRELATION ANALYSIS FOR ALL CONSIDERED VARIABLES AFFECTING FOREST SOC STOCKS. CORRELATIONS
ARE CONSIDERED STATISTICALLY SIGNIFICANT AT P<0.05 ............................................................................................................... 38
TABLE 5 SUMMARY OF ABOVE GROUND AND SOIL ORGANIC STOCK ASSESSMENT FOR NINE LAND COVER TYPE IN THE YUS CONSERVATION AREA,
INCLUDING BELOW GROUND BIOMASS CARBON USING THE CAIRNS EQUATIONS .................................................................................. 45
TABLE 6 YUS LANDSCAPE CARBON STOCKS (OUTSIDE AND INSIDE CONSERVATION AREA) BY VEGETATION CLASS. EXTRAPOLATION OF PLOT‐LEVEL
ESTIMATES ACROSS THE YUS LANDSCAPE USING HIGH‐RESOLUTION FOREST MAPPING. MT MEANS MILLION METRIC TONNES. ..................... 48
TABLE 7 COMPARISON OF ABOVE GROUND CARBON FROM DIFFERENT STUDIES IN PNG ................................................................................ 49
TABLE 8 OPTIONS AVAILABLE FOR CARBON ENHANCEMENT ACROSS THE YUS LANDSCAPE .............................................................................. 51
TABLE 9 DEFORESTATION ACROSS THE YUS LANDSCAPE MODIFIED FROM BROOKS AND RAMACHANDRA (2012) ............................................... 52
TABLE 10 ALLOMETRIC USED TO CALCULATE ABOVE GROUND BIOMASS. AGB ABOVE GROUND BIOMASS IS DRY BIOMASS IN KG. AGC (CARBON)
VALUES ARE OBTAINED BY MULTIPLYING AGB VALUES BY 0.5 ......................................................................................................... 61
TABLE 11 MEAN WOOD SPECIFIC DENSITY AND STANDARD DEVIATION AT EACH ELEVATION. NOT ALL STEMS HAD DENSITY VALUES THIS TABLE
DEMONSTRATE THE PROPORTION OF STEMS THAT HAD AN ASSOCIATED VALUE. .................................................................................. 62
TABLE 12 COMPARISON OF SOC STOCKS IN OTHER TRANSECTS ................................................................................................................ 63
TABLE 13 COMMON SPECIES IN EACH LAND TYPE, IN ORDER OF HIGHEST BASAL AREA FROM EACH LAND USE TYPE .............................................. 64
TABLE 14 GOALS WITHIN YUS LANDSCAPE PLAN THAT POTENTIALLY OVERLAP WITH CARBON SEQUESTRATION ................................................. 65
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ABBREVIATIONS AND DEFINITIONS
AGB above ground biomass
Estimated dry mass of live and dead stems including trees, palms, lianas and tree ferns
AGC above ground carbon
Estimated carbon content of live and dead stems including trees, palms, lianas and tree ferns
C carbon
CBO community based organization
CI Conservation International
CO2 carbon dioxide
BA basal area
BGC below ground Carbon
Estimated carbon content of roots based on AGC
dbh diameter at breast height
ha hectare
LULUCF land use, land use change and forestry
m.a.s.l meters above sea level
MgC ha‐1 mega grams of Carbon per Hectare. A mega gram is a metric tonne
PNG Papua New Guinea
PSP permanent sample plot (1 ha)
REDD+ Reducing Emission from Deforestation and forest Degradation and enhancement of
SD standard deviation
SOC soil organic carbon
TKCP Tree Kangaroo Conservation Project
YUS CA Yopno‐Uruwa‐Som Conservation Area
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EXECUTIVE SUMMARY
Objective
The primary objective of this report is to assess carbon stocks across the different main land cover
types in YUS. These assessments will complement the remote sensing vegetation classification for the
region carried out by Gillieson et al. (2011). We aimed to provide representative carbon stocks by
sampling primary forests across a broad environmental cline. Additionally, we measured carbon stocks
in secondary forest, shade coffee plantation, fallowed gardens and anthropogenic grasslands to inform
future land‐use management for increased carbon sequestration.
Methods
Above Ground Carbon (AGC) and Soil Organic Carbon (SOC) were measured in primary forest at nine
elevation clusters from 50 to 3100m.a.s.l. To measure AGC, a total of 179 plots were set in four
primary forest types, 11 plots in fallowed gardens, 17 in secondary forests plots, and in 10 shade coffee
plantations. SOC stocks were sampled and assessed from 91 primary forest sites and in 14
anthropogenic grasslands sites in and around the YUS CA. To extrapolate total standing stocks in the
YUS conservation area, we used the mean AGC and SOC densities, including an estimation of below
ground living biomass (BGB), for each major land cover type.
Main findings
1. Above ground carbon forest stocks are extremely variable in YUS. This variability reflects the
rugged topography and the broad range of environmental conditions across the YUS landscape.
We recommend that unbiased stratified sampling at landscape‐scale be employed for future
monitoring of carbon stocks (section 3.1).
2. Large trees are an important carbon store in YUS. Even though large trees (dbh > 50cm) consisted
of only 4% of trees measured, they contained 58% of the above ground carbon overall and 65% in
Lowland forest. Safeguarding large trees within the conservation area could be a priority carbon
management strategy (section 3.1)
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3. Both above ground carbon and soil organic carbon are important components of the carbon store
in YUS. At the lowest elevation, 87% of the carbon is stored in above ground carbon, while at higher
elevation only 40% of carbon is found in above ground carbon, while the bulk of carbon is found in
soil organic carbon to 1m in depth. Because elevation had a strong but opposing effect on above
ground carbon and soil organic carbon, total carbon stocks did not change markedly with elevation
(Section 3.2 & 3.3).
4. We found that soil carbon stocks were higher in forest compared to grassland at similar elevations.
This finding is important because the effect of reforestation on grasslands on soil carbon is
debated, and in some cases can cause depletion in soil carbon (Guo and Gifford 2002). Whereas
reforestation of some grasslands in YUS might not only increase biomass carbon but also soil
carbon (Section 3.4)
5. Total carbon stocks were calculated by adding above ground carbon, soil organic carbon and
belowground carbon. We found that primary forest across YUS stored on average 341MgC ha‐1.
Lower montane forest (1000‐2000m.a.s.l.) had the lowest densities at 256 MgC ha‐1, while, at
396MgC ha‐1, mid‐montane (2000‐2800m.a.s.l.) forest stored the most carbon of any primary forest
(section 3.5.1)
6. Old secondary forests had above ground carbon stocks of 139MgC ha‐1, the highest amongst the
anthropogenic land‐uses. The young secondary forest had low AGC stocks (22MgC ha‐1). Shade
coffee plantations had relatively high above ground carbon densities (131MgC ha‐1), compared with
fallowed gardens that stored only 77MgC ha‐1 (Section 3.5.1)
7. The YUS landscape covers approximately 182,000ha, and 43% of this area is located within the
Conservation Area (77 500ha). Primary forest is the dominant land cover in the YUS landscape, and
both inside and outside the conservation area had an equal primary forest cover of 70% (section
3.5.2)
8. We estimated the stocks of the YUS landscape at 50.1 Million tonnes of carbon in 2009, and of that,
21 million tonnes of carbon were found inside the YUS Conservation Area. The bulk of the carbon
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was found in mid‐montane forests, they are the dominant land cover and they store more carbon
in total than all other land cover types combined (Section 3.5.3)
9. The forests of YUS contain higher above ground carbon stocks than all previous estimates reported
for PNG. To our knowledge, this is the first study to report forest carbon stocks across broad
environmental gradients and the first study to above ground carbon in upper montane forest
(Section 3.6).
10. The following options have been identified as the best strategies to reduce carbon emissions and
increased carbon sequestration in YUS (Section 3.7):
a) Forest protection: Although deforestation rates have been very low in the lowlands of YUS, on
average 4.8 ha per year from 1990‐2008 (Brooks and Ramachandra 2012), future threats from
logging are imminent and should not be ignored. The protection of forest from clearance
should be prioritized in the lowland forests of YUS. Lowland forests store the highest above
ground biomass (248 ± 140MgC ha‐1) and they are the most threatened by logging. At present
28% of lowland forest is gazetted under YUS Conservation Area, allowing for substantial
additional forest protection (up to 20,000ha containing about 5 million tonnes of above ground
carbon). There is thus great potential for further forest protection. As a measure to secure
significant carbon stocks, we recommend to plan for emissions avoidance on future threats
rather than on past emissions (section 3.5.1).
b) Assisted natural regeneration: Converting anthropogenic grasslands to forest through assisted
natural regeneration is an ambitious land management strategy but it may hold the greatest
potential for additional carbon sequestration in YUS. If 10% of grasslands were set aside and
managed for assisted natural regeneration, about half a million tones could be sequestered in
30 years, based on our calculations, this could incur benefits of about $170,000 per year for 30
years (section 3.5.2).
c) Shade coffee plantation in grasslands: although it this option will accrue lower carbon
sequestration benefits, this is probably the most broadly viable option for in YUS. It holds
multiple benefits and landholders have recently shown interest in establishing new coffee
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plantations. If 3000 hectare of shade coffee were planted in grasslands, c sequestration could
sustain additional benefits of $117,000 per year for 30 years based on our assumptions.
However, if existing forest area is cleared for coffee plantations, this will have an adverse effect
on carbon stocks in YUS; therefore we recommend thoughtful land‐use planning in close
collaboration with landholders (section 3.5.3).
11. For the moment, the best option for REDD+ in YUS might not come from reducing emission from
deforestation, as the deforestation rate are low in YUS compared to elsewhere in PNG.
Nonetheless there is ample scope to increase carbon sequestration in YUS. Our results have shown
that landscapes such as coffee plantations and secondary forests store significantly more carbon
than grasslands and there may be sufficient areas of grasslands suitable for reforestation. We
believe that the YUS Conservation Area and the landscape surrounding it holds potential for a
REDD+ project in PNG. The YUS area has set of unique conditions, coupled with land tenure
agreements, considerable capacity building and baseline research that might maximize the
circumstances to making REDD+ a viable option (Section 4).
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Photo 1 Lowland forest of YUS, found between 0‐1000m.a.s.l.
Photo 2 Lower montane forest of YUS, found on steep topography between 1000‐2000m.a.s.l
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Photo 3 Large tree found in mid‐montane forest of YUS, found between 2000‐2800m.a.s.l
Photo 4 Upper montane forest of YUS, found above 2800m.a.s.l
1. INTRODUCTION
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Tropical forests play an important, but complex, role in the global carbon cycle. On the one hand, they
store more carbon than any other terrestrial ecosystem (Dixon et al. 1994, Phillips et al. 1998, Pan et
al. 2011); on the other hand, tropical forest loss is responsible for 18% of anthropogenic carbon
emissions (van der Werf et al. 2009; Canadell and Raupach 2008; UNFCCC 2009). In the efforts to
include tropical forest in the fight to curb climate change, there is increasing support to protect forest
by giving a market value to the carbon stored within them. REDD+ (Reducing Emissions from
Deforestation and Forest Degradation, plus the conservation, sustainable management and
enhancement of forest carbon stocks) is so far the most promising (Venter and Koh 2011). The
objective of REDD+ is to provide support and incentives to reduce net forest C emissions in developing
countries. REDD+ has two basic strategies; the first is to reduce emissions by protecting forest, the
second is to increase forest carbon stocks through active management, such as reforestation or
afforestation. Both strategies require sound knowledge of carbon stocks in present or potential future
forests (Gibbs et al. 2007).
Papua New Guinea (PNG) could potentially benefit from REDD+ opportunities, given the importance of
the emissions from deforestation and forest degradation in the country. More than 40% of the
country’s anthropogenic carbon emissions are produced by logging alone (Bryan et al. 2010, CDIAC
2011). PNG contains ca. 28 million ha of primary tropical forests, covering about 70% of its land surface
(Shearman et al. 2009). PNG’s forests are part of one of the world’s largest remaining tracts of intact
tropical forest (Brooks et al. 2006, Keenan et al. 2011). Deforestation rates in PNG are estimated at 0.8
to 1.8% per year, resulting in the loss of 5 million hectares of forest in the past three decades
(Shearman et al. 2008). Moreover,
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However, PNG has had little on‐the‐ground assessment of the carbon stored within its forest (Bryan et
al. 2011). Therefore, major sources of uncertainty about tropical forest carbon stocks exist (Fox et al.
2010; Bryan et al. 2011). The realization of a sound carbon accounting scheme in PNG, as well as the
setting of priority areas for REDD+, will depend on an improved understanding of how carbon stocks
vary across landscapes as well as the potential for management actions to increase carbon stocks
within that landscape (Shearman et al. 2009, Bryan et al. 2010, Fox et al. 2010; Gibbs et al. 2007).
In PNG, landscapes are often mosaics with shifting boundaries between forest primary canopies,
secondary or degraded forests, low intensity agriculture (shifting agriculture), shade coffee plantations,
anthropogenic grasslands and small scale agroforestry (Hett et al. 2012). These different land covers
store carbon to different extents, as well as provide biodiversity and livelihood benefits of varying
degrees. As such, exploring the trade‐offs and synergies between various land management options is
essential. The successful implementation of REDD+ is reliant upon realistic management interventions,
that is, interventions that take into account conflicting objectives such as reducing emission from
forest loss and ongoing demands for food, timber and livelihood improvements.
The primary objectives of this report are to (1) sample representative biomass and soil carbon stocks in
major vegetation classes of the YUS landscape identified by previous remote sensing analyses (Gillieson
et al. 2011), (2) calculate YUS ecosystem’s carbon stocks by vegetation class and (3) to interpret this
information to help guide future land‐use management from increased carbon sequestration and to
explore realistic options for REDD+ projects in YUS.
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Photo 5 Village near the YUS Conservation Area
2. METHODS
2.1 Study sites
The study was conducted in the Yopno‐Uruwa‐Som Conservation Area (YUS CA) located in the
Saruwaged range in the Morobe province of PNG (6°04’S, 146°48’E) (Figure 1). The YUS CA, gazetted in
2009, covers 76, 000 ha of land and is composed of parcels of land that have been pledged by local
landholders and clans in the area for biodiversity conservation. The conservation area was previously
part of traditional hunting grounds that belong to five language groups. The pledged land is still under
customary ownership, but logging and hunting are now illegal under the PNG Conservation Act (1978).
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Figure 1 YUS landscape. Green demarcates the conservation area, dotted line demarcates the project landscape and the rectangle demarcates the broader area of interest as defined by CI
Tropical humid forest is the dominant ecosystem in the YUS landscape, covering 70% of the
conservation area and the YUS landscape. Forests are dominant from sea level to 3100m and alpine
grasslands are found above this elevation. Other land cover types in YUS include frequently burnt
anthropogenic grasslands, disturbed and secondary forests, and a mix of shifting and more intensive
agriculture, shade coffee plantations, cocoa plantations and small scale agroforestry plots.
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Photo 6 Mosaic of land‐cover types in YUS (photo by Tony Page)
Field campaigns were carried out between August 2010 and May 2012. Forest carbon stocks (AGC and
SOC) were assessed along a 3100m elevational transect. The transect follows a forested ridge that
changes from coastal alluvial forest and lowland hill forests (less 1000m m.a.s.l), to lower montane
forest (1000 – 2000 m.a.s.l), mid‐montane forest (2000‐2800) and upper montane forest (2800m‐3100
m.a.s.l; see Table 1). We also measured above ground carbon stores in secondary and disturbed forest,
shade coffee plantation, fallowed gardens and measured soil organic carbon in anthropogenic
grasslands.
The climate in YUS is perhumid, with only 2 months a year receiving less than 100 mm rainfall on
average. Mean annual precipitation ranges between 2600mm in the lowlands to 4200mm in the upper
montane forest (WorldClim; Hijmans et al., 2005). Mean annual temperatures decrease by about 5.4˚C
per 1000 m of elevation, ranging from 26˚C at 50m.a.s.l. to 6˚C at 3100 m.a.s.l. According to the
PNGRIS database (Bryan et al. 2008), soils at the lowland sites are classified as Hapludolls and
Rendolls, soils in lower montane forest are classified as Troporthents, and the upper montane forest
soils are classified as Cryorthents (Table 1). Some of the lower montane sites had relatively thin A‐
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horizons overlaying mixed layers of weathered mineral soil and regolith in the top 50‐70cm. At the
higher sites, evidence of B‐horizon formation was emerging. The bedrock consists of limestone and
mudstone, except on the alluvial plain (0‐100m.a.s.l.) where there is a limestone‐derived soil with a
50cm A‐horizon directly sitting on alluvial deposits.
Table 1 Description of environmental factors of nine elevation clusters from 50m to 3100m in the YUS CA
¥WorldClim ‐Hijmans et al. (2005); фPaijmans (1976); ¥PINGRIS database, Bryan and Shierman (2008) All sites have a limestone or mudstone parent material, except for at elevation 50m which are located on alluvial deposits
Elevation clusters (m.a.s.l)
Elevation sampled (m.a.s.l)
MAP (mm)¥
MAP driest quarter (mm)
MAT (˚C)
Minimum MAT (˚C)
Soil Type¥ AGC plots surveyed
SOC sites sampled
50 50‐ 111
2600 301 26 21 Hapludolls 14 9
600 475‐ 650
2800 270 23 19 Troporthents 15 10
800 650‐ 1031
2900 296 22 16 Rendolls 19 11
1400 1300‐1499
3200 314 19 14 Rendolls 18 10
1800 1750‐1930
3500 328 16 12 Rendolls 18 10
2200 2210‐2223
3650 331 14 11 Rendolls 25 10
2400 2244‐2500
3800 341 13 9 Troporthents 22 12
2800 2775‐2900
4100 362 11 7 Rendolls 30 10
3000 2911‐3100
4200 378 10 6 Dystropepts,Cryorthents
17 9
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2.2 Above ground biomass
2.2.1 Biomass inventories
Rapid carbon assessments to obtain AGC inventories were modified from LULUCF protocols in order to
include height and wood density measurements (Pearson et al. 2005). Plots of 0.1 ha were set at 179
locations in primary forests and 38 locations in production landscapes. Forest plots were selected at
random, using a stratified systematic approach. To measure the effect of slope and topography on
AGC, we stratified our sampling into four slope categories; (1) gentle slope (≤ 11˚); (2) medium slope
(12˚‐25˚), (3) steep slope (26˚‐45˚) and very steep (45˚‐90˚), also stratifying the sampling across three
topographic categories; (1) west facing aspect (2) east facing aspect and (3) ridge top. Slope angle was
measured with a LaserAce® Hypsometer. On very steep slopes, the same methods were applied but
rappelling equipment was used to access the plot. Once the site type was located (e.g. ridge) the start
point was selected by spinning a blindfolded person who then threw a stick and walked 12m north
from the landing. Plots were at least 120 m apart and had a minimum of 30% canopy cover. Other
land covers (old gardens, shade coffee, secondary forest and grasslands) were selected
opportunistically as they tend to be patchily distributed throughout the landscape.
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Plots of 20 x 50m were delineated with tape measures and nested for stem size class (Figure 2); large
stems (dbh ≥50cm) in 20 x 50m, medium stem (dbh. 20‐49cm) within 20 x 30m plots and small stems
(dbh 5‐10cm) within 10 x 10m plots.
Figure 2 Scheme of a biomass inventory plot. Stem sizes were recorded in nested subplots; large stems (dbh ≥50cm) in 20 x 50m, medium stem (dbh 20‐49cm) within 20 x 30m plots and small stems (dbh 5‐10cm) within 10 x 10m plots
2.2.3 Forest structure
Measures of forest structure were carried out by recording canopy and understorey cover. Tree
species identification was based on local knowledge and where possible, identification was cross‐
checked with species tagged in a series of 1 ha plots established in the same area by CI. Also, plant leaf
material was collected and dried on site with silica gel. These are being identified to species level at
the Australian Tropical Herbarium in Cairns, and will be reported elsewhere.
Within each plot, trees (including palms, tree ferns, pandans, tree‐like stranglers and woody lianas) of
5 cm dbh, at 1.3m, were measured with a dbh tape (Richter Measuring Tools, Speichersdorf, Germany).
Measurements were modified for stems of unusual shapes and trees with buttresses were measured
according to methods in Pearson et al. (2005). Diameters of trees with buttresses were measured at
50cm above the buttress using bush ladders (Condit 1998). Tree height was recorded using a LaserAce®
hypsometer, taking multiple measurements from each canopy and recording the highest value. Tree
heights were recorded for 100% of the trees above 50cm dbh, and for 82% of the other stems.
50m
20m
≥5 cm
Stem class (dbh)
≥20cm
≥50 cm
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Elevation specific height diameter modes were used to generate heights of the trees with no recorded
height.
2.2.3 Wood density
Wood density information is required to generate AGB estimates, as for a given volume the amount of
carbon stored in a tree is directly proportional to its wood density, which can vary widely by species
(Anderson et al. 2009). Wood specific gravity (density at 0% moisture content, hereafter called wood
density) information was gathered from an Asian rain forest dataset (IPCC. 2006) and Fox et al (2010)
supplemental material). For species with no wood density information or unidentified species, average
wood density at that elevation category was used. At the time of writing, 17% of the species had wood
density information. The mean wood density and standard deviations at each elevation are provided in
Appendix 2, Table 11 Mean wood specific density and standard deviation at each elevation. Not all
stems had density values this table demonstrate the proportion of stems that had an associated value.
2.2.4 Allometric equations
We used two allometric equations to calculate carbon stored in live trees in Primary forest (Chave et al.
2005). Equation (1) was used for sites below 1000 m.a.s.l (Moist Tropical Forest) and Equation (2) was
used for tropical forest that includes elevations above 1000m (Wet Tropical Forest) (Slik et al., 2010).
For non‐woody trees (e.g. palms, lianas, tree ferns & pandanus) we used the allometric equations
listed in Appendix 1.
0.0776 .
Eq 1. Above ground living biomass for a tree growing in wet tropical forest, where D is diameter in centimetres, H
is height in meters, and ρ is the wood specific gravity in grams per cubic centimetres (Chave et al. 2005)
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0.0509
Eq 2. Above ground living biomass for a tree growing in moist tropical forest, where D is diameter in centimetres, H is height in meters, and ρ is the wood specific gravity in grams per cubic centimetres (Chave et al. 2005)
Carbon represents about half of the weight of dry biomass, and therefore multiplied AGB data by 0.5
(equation 3). In each plot we summed the AGC values for all trees, and extrapolated our finding to a
per hectare basis. The unit for “tons of carbon per hectare” are denoted by MgCha‐1.
0.5
Eq. 3. Carbon (AGC) values are obtained by multiplying AGB values by 0.5
We calculated the carbon stored in dead standing trees that had no obvious signs of decomposition
using the same allometric equations as for live trees, but reduced values by 3% for hardwood and
broadleaf and 6% for softwoods and conifers (Pearson et al. 2005a). To estimate carbon in dead trees
with obvious signs of decomposition, we used Equation 5 using 0.307g cm‐3as a standard dead wood
density.
13 0.5
Eq. 4. Calculating carbon in dead trees with obvious sings of decomposition, where H=height in meter, r = radius at dbh in centimetre and is wood density gram per cm3
2.2.5 Below ground living biomass
Given the logistical difficulties of in the field destructive sampling, below ground living biomass
assessments were not undertaken. Instead, predictive relationships between below and above ground
biomass have been established based on extensive literature reviews (Cairns et al 1997, Mokany et al
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2006). In general, root biomass is typically estimated to be 20% of the aboveground forest carbon
stocks (e.g. Houghton et al. 2001, Achard et al. 2002, Ramankutty et al. 2007). For our application, we
used the relationship established by Cairns et al. (1997), which estimates below ground living root
biomass in tropical forests as:
exp 1.0587 0.8836 ln ∗ 0.5
Eq 5. Below ground biomass (Cairns et al. 1997)
Because the equations for Cairns et al. (1997) are for primary forest only, we were unable to calculate
BGC carbon for secondary forest, garden fallows and coffee plantation.
2.3 Soil organic carbon
All soils at our sites developed on limestone bedrock, with exception of the lowermost sites, at which a
limestone soil with a 50cm A‐horizon was sitting directly on alluvial deposits. With increasing altitude,
an increased degree of soil development and generally deeper soils were observed. The organic top
layer increased in thickness from the lowland sites towards the highest sites (up to 30 cm thickness),
and generally overlaid deep A‐horizons. Some of the lower montane sites had relatively thin A‐horizons
overlying mixed layers of weathered mineral soil and regolith in the top 50‐70cm. At the higher sites,
evidence of B‐horizons was present within the depth interval sampled. According to the PNGRIS
database (Bryan et al. 2008), soils at the lowland sites are classified as Hapludolls and Rendolls, lower
montane forest soils are classified as Troporthents, and the upper montane forest soil are classified as
Cryorthents (Table 1).
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Photo 7 Soil Sampling in YUS
In total, 297 soil samples and 54 litter samples were collected in the nine permanent 1ha plots. The
nine permanent 1ha plots were established by Conservation International as part of the YUS project in
2009‐2010. The 1ha plots were established along the ridgeline, and as a result slopes were often gentle
or flat, compared to the usually much steeper adjacent topography. In addition 209 soil samples and
38 litter samples were collected in 37 other forest plots along the elevational gradient to capture
natural variability, and 70 soil samples in 14 grassland plots were collected in order to compare soil C
stocks between forests and grasslands at different altitudes (Figure 3).
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Figure 3 Schematic representation of sampling locations along the elevational gradient. Ninety one forest
locations (54 in 1ha plots and 37 in other forest plots) and 14 grasslands sites were sampled. Forest sampling
locations are clustered according to the 1ha plot number (i.e. site 6 to 14). One cluster contains six locations in
each hectare plot and 3‐6 additional forest locations within 200m altitude difference relative to the 1ha plot.
Grassland sites are identified by the name of the closest village.
In each of the 1ha plots, soil profiles were sampled at 6 locations. At each location, litter was sampled
in three 20x20cm squares, located in line and 5‐10m from each other. These three samples were
bulked, weighed and a subsample retained for analysis. At the central litter sampling location, soil
samples were taken at 0‐10, 10‐20, 20‐30, 45‐50, 65‐70 and 95‐100cm depth. For each 1ha plot, this
resulted in a total of 18 (bulked to 6) replicates for the litter layer, and 6 replicates for all sampled
layers of the soil. A soil pit to 1m depth was excavated outside the hectare plots on a location
representative of the sampling locations.
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Figure 4 Scheme of soil sampling profile
In each of the other forest/grassland plots away from the 1ha permanent plots, soil profiles were
sampled at 3 locations. At each (forest) location, litter was sampled in three 20x20cm squares, located
in line and 5‐10m from each other. These three samples were bulked, weighed and a subsample
retained for analysis. At the central litter sampling location, soil samples were taken at 0‐10, 10‐20, 20‐
30, 45‐50, 65‐70 and 95‐100cm depth. At both other sampling locations, soil samples were taken at 0‐
10, 10‐20 and 20‐30cm depth. The three samples for the 0‐10, 10‐20 and 20‐30cm interval were
bulked, weighed and a subsample retained for analysis. For each sampling location, this resulted in a
total of 3 (bulked to 1) replicates for the litter layer, 3 (bulked to 1) replicates for the 0‐30cm layers and
1 replicate for the deeper layers of the soil.
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Soil cores were taken using metal tubes of 5cm in diameter and 10cm length, during fieldwork
between August and November 2010. The depth of the soil was estimated by pushing a wooden rod
through the base of the sampling hole to a maximum of two meters.
The wet weight of all samples was recorded in the field, and all samples were oven‐dried in the lab at
60°C. Dry mass was quantified and samples were crushed and sieved to remove all stones and roots
larger than 2mm in diameter. Samples were then reweighed, and a subsample was ground to estimate
organic C and N concentrations using dry combustion in an elemental analyser (Costech, Costech
Analytical Technologies, CA ‐ USA).
To remove possible inorganic C from the samples and make sure only measured organic C was
measured, a subsample of the 65‐70 and 95‐100 samples was treated with a 6N HCl solution and
assessed for presence of carbonates. Where carbonates were present, prior to analysis, samples from
the overlying layers were also treated with the acid solution until no response was observed.
Bulk soil densities were calculated sample dry weights and the sampling tube volumes. SOC and N
densities were then determined using the bulk densities for each layer. Total SOC and N stocks for the
30cm profiles were calculated by summing stocks for the individual 10cm layers. SOC and N stocks for
the 100cm profile were obtained by calculating sampling location‐specific relationships using the
stocks for the sampled layers, using both an exponential and a power function. SOC and N stocks for
the deeper layers, where not directly sampled, were then interpolated using these relationships, and
total 100cm profile stocks calculated by summing numbers for all layers. The mean and standard
deviation (SD) of the exponential and power function was used in the statistical analyses. Average
values and standard deviations for hectare plots were obtained by taking the mean of the 6 sampling
locations.
pH measurements for all individual samples were performed in a 0.01M CaCl2 solution. Soil textural
analysis was performed on pooled samples. A subsample of each sample at each sampling location was
taken to obtain 20g bulk samples for each layer at all hectare plots. Aggregates were dispersed by
submerging samples in a sonicator overnight. After sonication, 10g of sample was mixed into a 5%
sodium hexametaphosphate solution and left to stand overnight. The sample was then sieved at 63µm
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and dried in the oven at 60°C. The dried sample was used to calculate the proportion of sand‐sized
particles in the sample.
2.4 Total carbon stocks
The land cover mapping was produced by Gillieson et al. (2011) through classification of medium‐
resolution multispectral images (Landsat) into vegetation classes based on the Forestry Information
Mapping System (FIMS) (CSIRO 1995). Because remote sensing lacks sufficient resolution to distinguish
between certain vegetation covers, five vegetation classes were identified from satellite imagery while
nine vegetation types were assessed for carbon. Table 2 show the correspondence between each
cover‐type. Although alpine grasslands represent an important part of the YUS ecosystem, we did not
assess their C stock due to logistical constraints.
Table 2 Correlation between different Land cover classification and type of assessment carried out in the field; above ground carbon (AGC) and soil organic carbon (SOC)
Remote sensing Field assessment TKCP classification Assessment type
Medium canopy Lowland forest Lowland forest AGC +SOC
Small canopy Lower montane forest
Lower montane forest
AGC +SOC
Mid‐montane forest AGC +SOC
Very small canopy Upper montane forest Upper montane
forest AGC +SOC
Regrowth forest
Young secondary forest AGC
Old secondary forest AGC
Shade coffee plantation AGC
Fallowed gardens AGC
Grassland Anthropogenic grasslands SOC
Alpine grasslands Alpine grasslands SOC
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We separated the lower montane forest class (1000‐2800m) into lower montane (1000‐2000m) and
mid‐montane (2000‐2800m). We split up this class to reflect the extreme differences in carbon
densities and forest structure between these elevation ranges found in our results (Table 2). To inform
future management, we also split the ‘Regrowth’ class into the four land‐use categories that are
common in the YUS landscape. These categories are young and old secondary forest, shade coffee
plantation and fallowed gardens.
Total carbon stocks are calculated by adding AGC, SOC and belowground carbon (BGC) and
extrapolating these densities to land cover extent.In order to present biomass values measured on
slopes, they must be converted to values equivalent to those assuming a horizontal projection because
land‐cover maps measure horizontal area only. To make this correction, AGC measured on slopes
greater than 5° were transformed to values equivalent to a horizontal projection (Pearson et al. 2005).
The mean AGC and SOC densities for each major land cover type where used to extrapolate total
standing stocks in the YUS CA.
L Li S
Eq 4. Correcting for plots on slopes, where: L = true horizontal plot radius, Li = standard radius measured in the field along the slope, S = slope in degrees and, cos S= the cosine of the angle.
2.5 Role of local landholders
Because REDD+ methodology stresses the inclusion of the local people in the development,
management and monitoring of carbon offset projects, we devised a training module aimed teaching
local people with little formal education but extensive knowledge about the forest they live in all
carbon assessments. Local participation in the project was determined by a committee formed of clan
members (family line) who have pledged their land to conservation, known as “papa graun”. To
promote the exchange of knowledge, we requested that the teams consist of at least one person with
traditional knowledge of the forest and at least one young person who has little knowledge of the
forest and would be keen to learn.
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The two day training module follows LUCLUCF protocols (Pearson et al. 2005) for plot establishment,
complimented by the RAINFOR protocol (Phillips O.L. and Baker 2006). The first day of training had the
objective of making everyone familiar with the equipment (compasses, dbh tapes, clinometers, survey
tapes). Drill exercises were repeated until all team members were comfortable taking measurements
with each instrument. On the second day of training, the data collection was initiated and test plots
were established.
3. RESULTS AND DISCUSSION
Figure 5 topographic map outlining the transect from sea level to 3100m
3.1 Above ground forest carbon stocks
There are three major benefits of measuring AGC at the landscape scale and across broad
environmental gradients. The first is that this can improve the accuracy of forest C stocks estimates by
having a more representative sample. The second is that this enables a better understanding of how
environmental and biotic factors contribute to variations in above ground biomass (de Castillo et al.
2008). The third is particular to PNG, where the dearth of field measurements has increased the
difficulty of mapping forest C and led to a high degree of uncertainty in national forest C stock
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estimates (Bryan et al. 2010). In this section, we show how AGC stocks vary across YUS and examine
the potential biotic and abiotic drivers of this variation.
Variation in AGC stocks
In the forests of YUS, we measured a total of 7193 stems in 179 primary forests plots along a 3100m
elevation transect (Figure 5). In Figure 6, we show AGC values for all 179 forest plots in our study. It is
important to note that AGC varies considerably, not only across the 3000m elevation gradient but also
locally within any elevation cluster. For instance, in forest between 50‐110m, AGC variation between
plots was almost an order of magnitude, ranging from 55 to 514 MgCha‐1. In order to adequately assess
the above ground carbon of the heterogeneous forests of YUS, we therefore recommend setting many
plots and employing a stratified sampling design across major environmental gradients.
Figure 6 Above ground carbon values for 179 primary forest plots across a 3100m elevation gradient. AGB values varied greatly between plots.
Variability in AGC estimates can be attributed to a number of factors. Studies have shown that AGC is
affected by environmental and biotic factors that affect growth, plant establishment, mortality and
succession, as well as natural disturbances (Keeling and Phillips 2007, Asner et al. 2009). Major
environmental determinants include climate, substrate type, soil fertility, species composition and
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topographic relief (Laurance et al. 1999, Clark and Clark 2000, Girardin et al. 2010). In our study we
used a generalized linear regression model to test the relationship between elevation, minimum
temperature, annual rainfall, and a disturbance index, slope and aspect. We found that together these
factors explained 35% of the variation in AGC, with elevation being the strongest, though nevertheless
weak, predictor of AGC (p = 0.04, R2 = 0.23). Aspect also played a role at controlling AGC in our study;
forests on the sunnier northwest aspect had higher AGC (ANOVA df=3, N=179, p= 0.05), in
concordance with results from other studies (Mascaro et al. 2011; Laurance et al. 2010). AGC was not
affected by slope between 0 and 45°(Mn=179, df=3, P=0.67). Another possible variable that cannot be
tested at this point, but might explain part of the residual variation, is soil nutrient levels (Nitrogen and
Phosphorous in particular). A large number of previous studies have indicated that nutrient availability
and soil texture can exert control on plant biomass production in the tropics (Aragao et al. 2009;
Cleveland et al. 2011).
Table 3 Natural disturbances, mean structural parameters and AGC values for primary forest at nine elevation clusters (50‐3100m) in YUS CA
Elevation cluster (m.a.s.l)
AGC plots sampled
BA (m2ha‐1)
Height£
m Max HeightÐ(m)
Wood density (g.cm‐3)
Stems/ ha (>5cm dbh)
Stems/ ha (>50cm dbh)
AGC(MgC ha‐1)
SD (MgC ha‐1)
50 14 46 24 32 0.66 863 59 305 184
600 15 43 21 30 0.64 1109 45 251 104
800 19 36 19 27 0.58 802 40 192 104
1400 18 39 17 21 0.53 729 46 122 40
1800 18 46 18 21 0.42 1308 54 117 33
2200 25 63 19 28 0.49 1477 88 205 70
2400 22 65 18 27 0.50 1592 79 199 79
2800 30 67 13 16 0.50 2222 53 159 32
3000 17 57 13 18 0.47 1544 57 126 39
Average 18 53 18 25 0.52 1294 58 188 95
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£ Height of tree is the mean of all trees across sites, while Max height is the mean of the highest trees of each site.
Forest structure and AGC On average, basal area was 53 ± 20m2ha‐1, canopy height was 25 ± 9m, wood density was 0.52 ± 0.07g
cm‐3and mean AGC per plot was estimated at 188 ± 95MgC ha‐1 (Table 3). Mean canopy height
decreased with increasing elevation, from 24m with emergents to 65m tall in coastal forests, to 18m in
forests around 3000m in elevation. Wood density also decreased with elevation, with a greater
number of hardwoods at the coast and more softwood conifers at higher elevations (Table 3). In
contrast, stems per hectare as well as basal area of trees increased with elevation.
Figure 7 Above ground carbon stocks in primary forest and how they vary with elevation. Above ground biomass where highest at low elevations and at mid‐montane elevations, unexpected dips occurred between 1400 and 1800m. Error bars are one standard deviation of the mean
In Figure 7, an unusual trend in AGC values can be seen across elevation clusters. As expected, the
highest AGC was in lowlands (320 ± 185 MgCha−1). Above ground carbon then decreases until 1800m,
thereafter rising again to a secondary peak (205 ± 70 MgCha−1) at 2400m elevation. Other studies have
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shown that AGC generally decreases with elevation (Kitamaya and Aiba 2002; Girardin et al. 2012), and
some studies have also found that AGC can have a second peak at some intermediary elevations
(Marshall et al. 2012; Culmsee et al. 2012). What was most unexpected in our results was that our
lowest carbon values were at the mid‐elevations between 1000 and 2000m, and not at the highest
elevations, which is typically the finding of other studies. In our case, mid‐elevation forests stored less
AGC than forest growing above 3000m.
Photo 8 Upper montane forest in YUS Conservation Area, PNG (photo by David Gillieson)
Previous research has demonstrated that the size distribution of large trees and the frequency of
natural disturbances might influence elevational trends in AGC (Clark and Clark 2000). We found that
large trees (defined as those larger than 50cm dbh) constitute only 4% of all stems above 5cm, but
none the less they store over 58% of the all the above ground carbon in the study area and 65% in
lowland forest. We also found that natural disturbances had a strong effect on AGC stocks. Tree fall
disturbances were detected in 48 out of our 179 sites (Figure 8). The plots that experienced tree‐fall
disturbance contained on average 31% less carbon compared with undisturbed plots.
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Figure 8 Above ground carbon in undisturbed (red bars) and in sites with natural disturbances (green bars)
It is likely that several environmental factors are reacting simultaneously to influence AGC, either
limiting or promoting above ground biomass at different sites. We believe that the dip in AGC found
between 1000‐2000m is linked to the steep topography found across the YUS landscape at this
elevation range. Shallow soils in combination with steep topography may make forests more
susceptible to natural disturbances, such as landslides and windthrows. In the case of the second peak
in AGC between 2000‐2700m, we suspect that deep soils and high rainfall and more level topography
can support a high frequency of large trees due to increased potential longevity. At the highest
elevation where soils are the deepest and rainfall is the highest and topography is comparatively
gentle, it is probably low temperature that is limiting AGC.
3.2 Soil organic carbon (SOC)
Soil C stocks ranged between 48 ± 27MgC ha‐1 at the lowermost sites and 194 ± 28MgC ha‐1∙ at the
highest altitudes (Table 1). When categorized according to forest type, soils along the transect
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contained 64 ± 28, 112 ± 25, 152 ± 26 and 182 ± 29MgC ha‐1 in lowland, lower montane, and upper
montane forest respectively (Table 5).
In contrast, SOC stocks increased with altitude for both the top 30cm of the soil, as well as the total 1m
soil profile (data not shown). We found a clear linear relationship between soil C stocks with altitude
on our elevation transect, indicating larger SOC stocks at higher altitude (Figure 9a). No relationship
was found between SOC stocks and slope (Figure 9c), and SOC stocks were not significantly different as
a result of differing aspect along the elevational gradient (Figure 9d).
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Table 4 Summary of pairwise linear correlation analysis for all considered variables affecting forest SOC stocks. Correlations are considered statistically significant at P<0.05
Altitude MAP MAT soil depth pH soil texture root mass litter mass CN‐ratio
MAP <0.001
MAT <0.001 <0.001
soil depth <0.001 <0.001 <0.001
pH <0.001 <0.001 <0.001 <0.001
soil texture <0.001 <0.001 <0.001 <0.001 <0.001
root weight 0.09 0.1 0.15 0.62 0.1 0.03
litter weight <0.001 0.01 0.009 0.83 0.001 0.05 0.004
CN‐ratio <0.001 <0.001 <0.001 0.08 <0.001 0.28 0.014 0.24
SOC stocks <0.001 <0.001 <0.001 <0.001 <0.001 <0.001 0.21 0.004 <0.001
Along our gradient, we observed that climatic changes (temperature and precipitation) were of major
importance (Table 4): SOC stocks decreased with increasing temperatures, and increased with
increasing amounts of precipitation. In addition to climatic variables, soil characteristics also co‐varied
strongly with altitude (soil depth, pH and texture, Table 4) and thus likely played an important role in
explaining SOC stocks. Soil depth and pH were also closely correlated with each other, reflecting the
influence of the soil parent material. Soil C stocks were thus correlated to many environmental
variables (Table 4), indicating a strong dependence to climatic variables (MAP, MAT).
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Figure 9 Relationship between soil organic carbon (SOC) stocks and topographic variables. Data displayed are the
relationship of altitude with soil organic carbon (SOC) stocks (a), of altitude with slope (b), of slope with SOC
stocks (c), and the relationship between altitude and SOC stocks for east aspect sites (white circles) and west
aspect sites (black dots). Significant linear correlations and ANCOVA differences for slopes and group means are
considered significant at P<0.05.and soil characteristics (soil depth, pH and texture). Many environmental
variables were also correlated to each other, indicating a strong covariance of driver variables along our
elevation gradient.
Because so many variables co‐varied with altitude along our gradient (Table 4), we could not tease out
the main drivers behind the relationship with SOC stocks. Nevertheless, the individual correlations we
found agree well with existing hypotheses about SOC stocks at high altitudes: a warmer and drier
climate in concert with (close to) neutral pH at lower altitude provides favorable conditions for
microbial decomposition. In contrast, at higher altitudes, cold and wet conditions and an acidic soil
likely inhibited high microbial decomposition rates, and stimulated a buildup of a thicker organic layer.
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More controlled laboratory experiments will therefore be needed to identify sensitivity of SOC stocks
and decomposition of organic matter to different environmental changes along our gradient.
3.3 Soil carbon storage in grassland and forest soils
We found that there is generally no difference between forest and grassland SOC stocks at comparable
altitudes for soils to 1m depth (Figure 10). Because very often the grassland soils were shallow in our
study area, particularly on steep slopes and frequently burnt sites, an analysis for the top 30cm layer
was more appropriate here.
Figure 10 Relationship between altitude and soil C stocks for the 100cm profile in grassland (red circles) and forest (white circles) plots. The P‐value and R2‐value of the individual linear regressions are given. Significant correlation is assessed at P<0.05. P‐values for ANCOVA analysis are given to assess differences between means and slopes of both regressions. Statistical differences are considered at P<0.05
Soil C stocks in the top 30cm of the soil profile were higher in grassland plots compared to forest plots
(data not shown). The main reason for this difference in soil C stocks is the consistently higher soil bulk
density of the top soil layers in grasslands along the elevational gradient. A likely explanation for the
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higher soil compaction in grassland sites compared to forest sites might be associated with land‐ use
patterns.
Human‐induced fires and subsistence agriculture are common practice in the study area and have been
shown to induce stronger compaction of the top layers of soil (Prober et al. 2008; Schrumpf et al.
2011). We did not find a relationship between grassland SOC stocks or soil bulk density, or time since
the last burning event (data not shown), but this might be due to the relatively low amount of
grassland sites that were sampled.
In contrast to our findings for the YUS CA, forest conversion to grassland is generally thought to lead to
a reduction of soil C stocks (Don et al. 2011). In their review, Don and colleagues also point out that soil
bulk density changes with land‐use type, as was also found in our study. Therefore, SOC stocks need to
be corrected for differences in bulk density in order to directly compare SOC stocks on the same basis
of soil mass (Don et al. 2011). Based on ANCOVA results for a comparison of bulk density between
grassland and forest along the elevational gradient, we corrected soil C stocks for the grassland plots
with a factor BDcorr/BD (BDcorr = BD‐0.12 (difference between intercept of regression for grassland and
forest). As a result, we found lower soil C stocks for grassland compared to forest (Figure 11), and this
difference tended to increase with altitude. The marginally significant difference in slope is important
because it suggests that conversion of forest to grasslands at higher altitude sites might lead to a larger
loss of soil C than expected from land‐use change studies in Lowland areas.
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Figure 11 Relationship between altitude and bulk density corrected soil C stocks for the 30cm profile in grassland (red circles) and forest (white circles) plots. The P‐value and R2‐value of the individual linear regressions are given. Significant correlation is assessed at P<0.05. P‐values for ANCOVA analysis are given to assess differences between means and slopes of both regressions. Statistical differences are considered at P<0.05
3.4 AGC and SOC along the elevation gradient
Studies along elevation gradients are valuable as a natural model for studying temperature and
moisture effects under otherwise similar environmental conditions (Malhi et al. 2010). As mentioned in
section 3.1 to 3.3, above ground carbon generally decreases with elevation, driven largely by trees
becoming lower with colder conditions, whereas soil organic carbon generally increases with elevation
as the organic layer builds up because of slower decomposition in colder conditions (Girardin et al.
2010). Although a dip in the carbon stocks is obvious at 1400m.
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Figure 12 Average carbon stocks in above ground pool (green) and soil organic pool (brown) at nine elevation clusters
Because AGC and SOC pools respond in opposite trends to elevation, we found that the total C stocks
in YUS forests did not change much from lowland forests to forests at 3000m elevation, expect for a
dip at 1400m (Figure 12). At the lowest elevation, 87% of the carbon is stored in above ground stems,
while at 3000m only 40% of the carbon is stored above ground. Very often, forest C stock assessments
omit SOC measurements because of financial or logistical constraints. If we had omitted SOC in our
assessments, forest total C stocks would have been significantly underestimated, especially at higher
elevations.
3.5 Standing C stocks for different land‐cover classes
In this section we first look at the density of carbon stored in each land cover type, then we present
the extent of each land cover type as identified by Gillieson et al. 2011 and we finish by looking at the
total C stocks for each land cover, within the YUS CA and the YUS landscape. Combining carbon density
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measurements with vegetation extents from the remote sensing analysis to calculate carbon stocks is a
primary component of REDD+.
3.5.1 Carbon density across YUS
Summary of C stocks area found in Table 5. Carbon density was calculated by adding AGC, SOC and
belowground carbon (BGC). We found that primary forest in YUS stored on average 341MgC ha‐1.
Lower montane forest had the lowest densities at 256MgC ha‐1, while, at 396MgC ha‐1, mid‐montane
forest stored the most carbon of any primary forest.
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Table 5 Summary of above ground and soil organic stock assessment for nine land cover type in the YUS Conservation Area, including below ground biomass carbon using the Cairns equations
Land cover type Elevation (m.a.s.l.)
AGC plots (number)
SOC sites(number)
AGC ± SD (MgC ha‐1)
SOC ± SD (MgC ha‐1)
BGC (MgC ha‐1)
Total C (MgC ha‐1)
PRIMARY FOREST
Lowland 0‐1000 48 30 248 ± 140 64 ± 28 45 357
Lower montane 1000‐2000 36 20 120 ± 36 112 ± 25 24 256
Mid‐montane 2000‐2800 47 22 202 ± 74 152 ± 26 38 396
Upper montane 2800‐3100 47 19 147 ± 38 182 ± 29 29 358
“REGROWTH”
Secondary forest (15‐30 yrs.) 900‐1850 11 ‐‐ 139 ± 55
Shade coffee (5‐50 yrs.) 850‐1450 10 ‐‐ 131 ± 78
Fallowed garden (~15 yrs.) 1050‐1600 11 ‐‐ 77 ± 70
Secondary forest (<12yrs.) 750‐2450 6 ‐‐ 22 ± 16
ANTHROPOGENIC GRASSLANDS
50‐1747 ‐‐ 14 14* 105 ± 45 119
* (Hartemink 2001), from PNG grasslands, though IPCC default value is 6.2 used 112 MgC ha‐1 for SOC for all secondary land uses and 92MgC ha‐1 for AGC (average), BGC was calculated using equations in Cairns et al.(1997)
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Secondary forest, shade coffee, and fallowed gardens were only assessed for AGC. Old secondary
forest is defined as trees established for 12 years or more and having more than 30% canopy cover.
They are forests naturally regenerating on grasslands, in fallows or on lands that were previously
forested and are dominated by Trema sp., Ficus sp., Mallotus sp. and Macaranga sp. Old secondary
forests had AGC stocks of 139MgC ha‐1, the highest amongst the anthropogenic land‐uses. Young
secondary forests are defined as forest established in grasslands within the last 12 years and having
less than 30% canopy cover. The young secondary forest we measured was dominated by early pioneer
species such as Piper sp and Saurauria sp. and had low AGC stocks (22MgC ha‐1). Shade coffee
plantations had relatively high AGC densities (131 MgC ha‐1), compared with fallowed gardens that
stored only 77MgC ha‐1.
The primary factors controlling AGC in fallows and coffee plantation were the frequency shade trees,
their age and their ability to store carbon. Anthropogenic grasslands are maintained by frequent fires.
The above ground carbon component is therefore very volatile. Other studies that looked at AGC store
in grasslands of PNG found they store on average 14MgC ha‐1 (Hartemink 2001). Because the soil
carbon pool is more stable than the biomass pool, most of the carbon is found in the soil. We found
that grasslands store 105Mg Cha‐1, which is not different from the SOC of primary forests at the same
elevation (see section 3.3).
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3.5.2 Land cover extent in YUS
Figure 13 YUS vegetation map derived from 2009 satellite imagery (Gillieson et al. 2011)
The YUS landscape is the area outlined in Figure 13. It covers approximately 182,000ha, and 43% of this
area is located within the conservation area (77 500ha) (Table 6). Primary forest is the dominant land
cover in the YUS landscape, and both inside and outside the CA had an equal primary forest cover of
70%. Mid‐montane forest is the most extensive forest type, covering 45% of the YUS landscape.
Lowland forest covers 20% of the land outside the CA but only 10% inside the CA. The extent of
regrowth forest is between 6 and 7% in both areas. The majority of anthropogenic grasslands (17%)
were found outside the CA, around the areas where people live. In order to extrapolate our results
onto a vegetation map, we clumped the carbon values we measured in the field into the remote
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sensing vegetation classes and used the mean values carbon values for each (Table 6). 3.5.3 Carbon
stocks in YUS
Our estimates show that the standing stocks of the YUS landscape in 2009 were 50.1 Million tonnes of
carbon and that the YUS CA had a total C stock of 21 million tonnes of carbon. About 85% of the carbon
was stored in primary forest and 15% in anthropogenic landscapes. Mid‐montane forests store more
carbon in total than all other land cover types combined, both within the conservation area and for the
YUS area overall. Most additional carbon is stored in lowland forest. The importance of lowland and
mid‐montane forests in YUS is primarily due to their extent within the region, but also because of their
high carbon densities. An important caveat is that we do not have data on the SOC of regrowth forest,
and collecting these data should be a priority for future research in the area.
Table 6 YUS Landscape carbon stocks (outside and inside conservation area) by vegetation class. Extrapolation of plot‐level estimates across the YUS landscape using high‐resolution forest mapping. Mt means million metric tonnes.
Land cover C density (t/ha) Area in CA (ha) Area outside CA
(ha)
C stock Landscape, in+
out (Mt)
Lowland forest 357 7,863 20,467 10.1
Mid‐montane forest£ 326 41,756 41,016 27
Upper montane forest 358 4,030 10,703 5.2
Regrowth forest¥ 226 3,902 7,664 2.6
Grasslands 119 10,360 22,649 3.9
Alpine grassland 182§ 9,543 1,942 1.3
Total 77 500 ha 104 400 ha 50.1 Mt
£ Includes lower montane forest; ¥ includes fallowed gardens, disturbed primary forest, shade coffee, secondary forest; § No difference in SOC, therefore used same SOC value as upper montane forest (182MgC ha‐1) (Zimmermann et al. 2010) plus 8 MgC ha‐1 AGB from (Gibbon et al. 2010)
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3.6 Comparison of AGC with other PNG data sets
AGC estimates presented in this study are higher than global averages for tropical forests. Moreover, the AGC values found in this study are higher than all the previous estimates reported for PNG for all forest types (Table 7)
Table 7 Comparison of above ground carbon from different studies in PNG
Tropical forest type
Study MgC ha‐1
Location Sample size
Plot type
Forest average Saatchi et al 2011 115 Global ‐ Remote sensing
Forest average
This study 188 PNG 179 0.1 ha
Bryan et al 2010b 178 PNG 22 meta‐analysis
Saatchi et al 2011 153 PNG ‐ Remote sensing
FAO 39 PNG ‐ Remote sensing
Lowland
(0‐1000m)
This study 223 PNG 42 0.1 ha
IPCC default Value 180 PNG ‐ Remote sensing
Bryan et al 2010a 126 PNG 6 Bitterlichplotless
Fox et al 2010 106 PNG 10 1 ha Permanent plots
Bryan et al 2010a 96 PNG 6 Bitterlichplotless
Montane
(1000‐2800m)
This study 184 PNG 67 0.1 ha
Edwards & Grubb1977 155 PNG 1 0.24 ha destructive sampling
Fox et al 2010 141 PNG 2 1 ha Permanent plots
Upper Montane This study 137 PNG 28 0.1 ha
The biggest effort to quantify above ground carbon stocks in PNG come from a study by Fox et al. 2010.
That assessed AGC from network of permanent forestry plots they found that unlogged forest had AGC
values of 106 MgC ha‐1 (n=10) and selectively logged forests stored ~66 MgC ha‐1 (n=115). The study
benefited from a large sample size broadly distributed across the country. Although Fox et al (2010)
was criticized for the underrepresentation of undisturbed forest (Bryan et al 2011), their study remains
the largest inventory of lowland unlogged forest in PNG. Other considerable attempts were from Bryan
et al. 2010 (see table 7). Our study sampled 4.2 ha of lowland unlogged forest, and found substantially
higher values than Fox et al. (2010). Fox et al. (2010) attribute the low values found in their study to
the location of the permanent plots, which were often close to roads or villages, and therefore could
suffer from disturbances such as fire, landslides, and agriculture. Aside from the location and size of
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plots, our study used similar methods and the same allometric equations to calculate AGC as used by
Fox et al. (2010), and hence we believe that the differences between the two studies are real.
Our sampling effort was concentrated in montane forest in order to address the paucity of data from
these elevations in PNG, as well as to adequately sample the dominant forest type in YUS. Aside from
some early work in the late 1970s (Edwards and Grubb 1977), Fox et al. (2010) were the first to provide
AGB estimates for montane forests in PNG from on‐the‐ground measurements. We measured a total
of 6.2 ha (n=62) between 1000‐2800 m, and we measured a total 2.8ha above 2800m. This study is the
most extensive study of montane forest AGC in PNG, and represents the only study that has assessed
stocks above 2500m. Montane forests (>1000m) cover more than a quarter of PNG’s surface area
(Bryan et al. 2010), therefore this study should serve to improve national forest carbon stock
assessments.
3.7 Options for carbon sequestration in YUS
Photo 9 Vast areas of grasslands are maintained by frequent fires (RED), though some natural regeneration of forest is possible (white)
The options for carbon management in YUS include activities that protect forest carbon stocks and
activities that promote carbon stocks through enhancing biomass and soil carbon. There are a number
of important factors that determine the suitability of options for C management. This includes the type
and extent of land available for management, their ability to store and sequester carbon, and the cost
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of the management actions (Lamb 2011). Also, the best options for management will largely depend
on the desired outcomes or benefits to the landholders relative to the risks and costs of investment. In
Table 8 we outline three management options to enhance carbon stock in the YUS landscape and
discuss them further in this section.
Table 8 Options available for carbon enhancement across the YUS landscape
Option Obstacles/threats Management actions C benefits Other benefits
Protecting forest
Fire Illegal logging Fuelwood extraction
Fire management Protecting lowland
forest
Low now, High later
Biodiversity Full range of
ecosystem services
Converting grasslands to forest
Inappropriate fire regimes
Lack of seed stocks Weeds Altered hydrology
Fire management Nurseries for native
tree species Cutting weeds
High
Reduced risk of landslides
Fuelwood and timber supply
Shade coffee plantation
Access to markets Fire Suitable grasslands
Restoration of grasslands
Fire management Plantation of native
shade tree species
Medium *or adverse if replaces forest
Income habitat for
wildlife
3.7.1 Option 1: Protecting lowland primary forest
The lowland forests of YUS store approximately 10.1 million tonnes of carbon. They also house the
largest trees of the YUS CA. These trees grow up to 60m tall and 2m in diameter and we found that
they store the majority of the carbon in YUS; specifically, we found that large trees (dbh >50cm)
contained 65% of the above ground carbon in lowland forests. Carbon emissions from forest loss in
YUS have been minimal during the last 30 years (Table 9) (Brooks and Ramachandra 2012), and it
would seem that protecting forest from deforestation would only incur minimal carbon benefits. When
present, threats to forest carbon are located in three areas: 1) near villages, where trees are extracted
for timber and fuelwood causing forest degradation, 2) in coastal lowland forest, where small scale
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logging has caused some deforestation in the past 30 years and portable sawmills are responsible for
the clearing of 86.9ha of lowland forest between 2000 and 2008 (Brooks and Ramachandra 2011) and
3) in upper montane forest where fires caused by the 1997 El Niño event caused the greatest forest
loss in YUS in the past 15 years (Brooks and Ramachandra 2012).
Table 9 Deforestation across the YUS Landscape modified from Brooks and Ramachandra (2012)
Elevation
Deforestation (Ha) YUS Landscape
1990‐2000 2000‐2004 2004‐2008
0‐1,000m 0 52 34
[1,000m‐3,000m] 356 45 33
[> 3,000m] 1,430 1 25
Nevertheless in the rest of PNG, between 1990 and 2002 commercially accessible forests were logged
at 1.3 to 3.5 precent per year (Shearman et al. 2009). Based on the very high logging rates in PNG, and
on expected population growth in the Morobe province (Ningal et al 2008), threats from logging and
conversion to agriculture are imminent and should be taken seriously in YUS. For example, in the
Provincial Forest Plan for Morobe Province 2008‐2013, a proposed timber lease could target 28,000ha
of lowland forest for commercial logging (Brooks and Ramachandra 2012). Because carbon in biomass
is quickly released to the atmosphere and lowland forests contain the highest above ground carbon
(248 ± 140MgC ha‐1), the emission from forest loss in the lowlands would be higher than anywhere else
in YUS. Moreover, given that only 28% of the YUS lowland forest area is gazetted in the CA, allowing for
substantial additional forest protection (up to 20,000ha containing about 5 million tonnes of above
ground carbon). There is thus great potential for further forest protection. We recommend prioritizing
forest protection to the lowland and plan for emissions avoidance on future threats rather than on
past emission as a measure to secure significant carbon stocks.
Keeping primary forest standing has many additional non‐carbon benefits. Intact natural forests
provide ecosystem services that contribute to human well‐being. These services include the provision
of non‐timber forest products, the filtration of water and air (Sheil and Murdiyarso 2009), mitigation of
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floods (Bradshaw et al. 2007) and the provision of pollinators for adjacent farm crops (Ricketts et al.
2004). Natural forests also provide habitat for many species.
Photo 10 Mosaic of lowland forest and anthropogenic grasslands near coast in YUS
3.7.2 Option 2: Converting grasslands to forest by assisted natural regeneration
Converting anthropogenic grasslands to forests is an ambitious carbon sequestration strategy, but it
may hold the greatest potential for additional carbon sequestration in YUS. Anthropogenic grasslands
(excluding alpine grasslands) cover approximately 33,000ha or about 18% of the entire YUS landscape.
At 119MgC ha‐1 these grasslands store the least carbon per ha, moreover, only 14 MgCha‐1 are stored
in above ground carbon. Based on our carbon estimates, if 100% of the grasslands were converted,
above ground carbon storage could increase from 14MgC ha‐1 to 139MgC ha‐1 in 30 years, and 5 million
tonnes of carbon could be sequestered. If carbon were valued at $10 a tonne, this equals to about
$1.6K a year for 30 years. Although converting 100% of the grassland is unrealistic, converting 10% may
be achievable. If 10% of grasslands were set aside and managed for assisted natural regeneration,
about half a million tones could be sequestered in 30 years, based on our calculations, this could incur
benefits of about $170,000 per year for 30 years.
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Assisted natural regeneration involves management actions that help overcome barriers to forest
establishment, such as fire management, cutting weeds and promoting seedling propagation (Shono et
al. 2007). Grasslands in YUS are generally maintained by frequent anthropogenic fires, therefore
suppressing tree seedling establishment. If fire was suppressed, we can assume that most of the
landscape would eventually revert to forest, given that lands are not too degraded and that soil is deep
enough. However, under natural circumstances, this process would be limited by the rates of seed
dispersal, rates of seedling recruitment and their competition with weeds and could take centuries
(Young et al. 1987, Francis and Read 1994, Parrotta 1995). Assisted natural regeneration may hold the
greatest potential for carbon sequestration in YUS. The first step would be to identify favorable areas
for natural regeneration, and then most of the management actions could be carried out by
landholders, as the expertise for assisted natural regeneration already exists within the YUS
communities.
3.7.3 Option 3: Converting non‐forest to shade coffee plantations
At 131 MgC ha‐1, shade coffee plantations store similar above ground carbon to secondary forests
(139MgC ha‐1), but less than primary forests (188MgC ha‐1) and more than in grasslands (14 MgC ha‐1)
and fallowed gardens (77MgC ha‐1). Therefore converting grasslands into shade coffee plantation
would promote C sequestration, while converting forest to shade coffee plantation would generate
carbon emission.
Shade coffee plantations are probably the most viable option for increasing carbon sequestration rates
in YUS. Although shade coffee plantations have been part of the YUS landscape for over 50 years, they
were largely unprofitable until recently. In efforts to improve livelihoods of the people in YUS, TCKP
promoted the branding of YUS Conservation Coffee in search of niche Fair Trade markets that can
offset high transportation costs. In doing so, they have also aimed to improve silviculture and quality of
the coffee, and have run multiple workshops in YUS. This has reinvigorated the interest in coffee
plantations. Unfortunately, this may be having the undesirable effect of stimulating the conversion of
secondary forests for plantations, which results in net carbon emissions.
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From a climate change perspective, instead of expanding coffee into forests, it would be preferable to
convert grasslands. To determine how much land is available for coffee plantation, we calculated the
area of grasslands that have suitable growing conditions for coffee. Suitable conditions were defined as
grasslands between 1100m and 2100m, at less than 4km distance from villages and on slopes less than
45°. We found that roughly 18,000 ha are available for plantation using these criteria. If shade coffee
plantation were established in grasslands, above ground carbon could potentially increase from 14MgC
ha‐1 to 131MgC ha‐1 in about 25 years. If carbon is worth $10 a tonne, roughly $720,000 could be
generated over 30 years. Given the availability of grasslands that could be converted to coffee, the
scope of this carbon management strategy is more likely to be limited by the area of coffee plantations
that can be realistically managed by the YUS communities. Therefore if 20 villages each planted 150
hectare, coffee plantations could sustain additional benefits of $117,000 per year for 30 years based on
our assumptions.
Additionally, we found that the carbon stock in shade coffee plantation was determined by the type of
shade trees present at a site. For example Casuarina oligodon is a tree that is native to PNG, is fast
growing and has a wood density of 0.95g cm‐3 (Bourke 1985). We found that Casuarinas were being
ring barked and replaced by Leucaena leucocephala in coffee plantations. This is a fast growing exotic,
with many good attributes for shade coffee but it has wood density of 0.30g cm‐3, and therefore the
same sized tree would store almost three times less carbon as a Casuarina oligodon. If C sequestration
becomes a management goal in coffee plantations, careful thought should be given to where
plantations should be established and the type of species that should be planted along with coffee as
shade trees.
Other options to increase carbon sequestration in YUS include the restoration of degraded forest and
the improvement of agricultural practices and establishment of agroforests. Restoring degraded forest
by planting timber of firewood species, as well as improving agriculture has been shown to reduce
pressure on existing forest (Niles et al. 2002, Albrecht and Kandji 2003). Unfortunately, the data we
collected was insufficient to make sound assessment of the capacity to increase carbon sequestration
in YUS using this option. In addition to their carbon benefits, restoring degraded forests, planting
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agroforests and improving agriculture might be a locally attractive option for food security and
fuelwood benefits.
Photo 11 AGC assessment in shade coffee plantation
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4. CONCLUDING REMARKS
Photo 12 View of the YUS landscape from the conservation area (2200m.a.s.l.)
The rugged topography of PNG gives rise to structurally diverse and complex forests that span from
grand lowland forest to cloud immersed forest up to 4000m of elevation. These tropical forests are
indeed an important carbon store, though little is known about how much carbon is stored in them.
Within the forest of the YUS landscape, there is a diversity of forest types, parent material and
disturbance regimes. As a result the demography of individual areas of forest is highly variable. This
study represents one of the first attempts to quantify the natural variation in carbon stocks in PNG, in a
large area of approximately 75,000 ha. It shows that the forests of the Huon Peninsula, and the YUS CA
in particular, are very important carbon stores at a national level. Total carbon stocks in the YUS
landscape are estimated at 50.1 million tonnes; this represents approximately 1% of PNG’s carbon
stocks in logged and unlogged forest (Bryan et al. 2010).
What we have learnt from our results:
This study is the first in PNG to compare carbon stocks on such a broad altitudinal scale. We learnt that
stocks vary tremendously with environmental conditions. Factors that affect above ground carbon
store include forest stand demography, species composition, disturbance regimes and topography. Soil
carbon shows clearer trends with altitude and seems to be less affected by vegetation type and
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disturbance regime. We conclude that although the current study has been well replicated more
investigation is needed to understand the environmental factors that create variation in above and
below ground carbon. If we had measured above ground carbon only, we would have seriously
underestimated the carbon stocks in montane forest. At the lowest elevations 87% of the carbon is
stored in above ground stems, while at 3000m only 40% of the carbon is stored above ground; the
majority is in the soil. Reliable estimates of soil organic carbon are needed to provide realistic
estimates of the total carbon store in any forest type at any elevation.
In general, the forests of the YUS conservation area support large carbon stores which fall of the high
range of values recorded in both tropical forests in Papua New Guinea and elsewhere in the humid
tropics. From our literature review on other biomass assessment carried out in the tropics, we believe
that the above ground carbon values for the upper montane forest of PNG contain are the highest ever
reported when compared to other forests at similar latitude and altitude. This emphasises the
importance of the YUS area and the need to support initiatives in community conservation currently
being carried out under the auspices of the Tree Kangaroo Conservation Project. Although extensive
forests remain throughout the YUS area, the protection of forest from further clearance should be
prioritised in the lowland forests. These forests store the highest above ground biomass, they are the
most threatened by logging and only 28% of lowland forest is gazetted under the YUS Conservation
Area. Although deforestation rates have been very low until now, future threats from logging are
imminent and should not be ignored.
The YUS Project seeks to conserve forest carbon, endemic biodiversity, and ecosystem services, and to
benefit local rural communities by providing income streams from sustainable activities that have low
impact on traditional ways of life. Integrating sustainable development models that have multiple
objectives is a major challenge in land use planning (Dewi et al. 2011). Within the YUS Conservation
Area there are already significant initiatives in community reafforestation, improved silviculture,
particularly coffee, and sensible land use allocation in which conservation is a core value.
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Why YUS might work as a REDD+ project:
Implementation of REDD+ could provide critical compensation to forest users for improved
conservation management practices in the absence of, or in combination with other economic
incentives (Nasi et al. 2011). In YUS there has already been substantial investment in community
capacity building, technical support to develop carbon inventory surveys, mapping and remote sensing
capacity and community and regional consensus building. A series of planning workshops have laid the
foundations for community consensus on land use planning and rational approaches to both nature
conservation and economic development. The absence of these factors generally works against
building rural development capability in Papua New Guinea.
In YUS, enhanced carbon sequestration is likely to be productive rather than avoided emissions from
deforestation. Detailed study of deforestation rates in yours indicates that overall rates are very, very
low and seem to be related to major El Niño events such as 1997. The absence of roads in the US area
has protected the forests until now. There are extensive areas of anthropogenic grasslands, and areas
close to existing villages might be usefully reforested. Local management practices, resulting in tree
extraction for firewood supply could be enhanced to support a wide range of species with attendant
gains in above ground carbon and conservation value. Converting anthropogenic grasslands to forest
through assisted natural regeneration is an ambitious land management strategy but may hold the
greatest potential for additional carbon sequestration in YUS.
Other options include the establishment of shade coffee plantations in grasslands. This is probably the
most broadly viable option in YUS, although it will accrue lower carbon sequestration benefits. It holds
multiple benefits and landholders have recently shown interest in establishing new coffee plantations.
If existing forest area is cleared for coffee plantations, this will have an adverse effect on carbon stocks
in YUS; therefore we recommend thoughtful land‐use planning in close collaboration with landholders.
Support is needed to set up the institutional infrastructure required to distribute REDD+ benefits and
implement the various incentive schemes; this might be most usefully achieved through the
community business organization (CBO) model with financial benefits being held in trust for approved
community activities. A performance‐based model for the distribution of REDD+ funds a local level is
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critical, nested within a provincial and national approach. This would need to support rigorous and
reproducible standards of measurement and verification, and would need to target specific areas of
forest.
Central to all of this would be land use planning strategies which focused integrating development and
conservation goals with carbon sequestration strategies. There is increasing pressure to clear forest for
agriculture to address increased regional demand for food. Livelihood landscapes, such as old garden
fallows, agroforestry systems or perhaps plantations, can sequester and store significant amounts of
carbon given associated sound management (Ramachandran Nair et al. 2010; Montagnini and Nair
2004). Therefore, best approach is one which is realistic, one that focuses on maintaining high carbon
stock with low carbon flows while achieving agreed development goals (Dewi et al. 2011).
Photo 13 Local Landholder that have pledge to land to the conservation area and who was part of the team that assessed above and below carbon stocks for this study
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5. APPENDICES
Appendix 1 Equations
Table 10 Allometric used to calculate above ground biomass. AGB above ground biomass is dry biomass in KG. AGC (Carbon) values are obtained by multiplying AGB values by 0.5
Biomass Category Allometric equation Source
Trees in tropical wet forest AGBwet= 0.0776 ∙ [(ρD2H)]0.940
Chave et al. 2005
Trees in tropical moist forest AGBmoist= 0.0509 ∙ ρD2H
Chave et al. 2005
Trees without H (not used) AGBnoH= 21.297‐ 6.953 ∙ dbh + 0.740 ∙ dbh2 Brown 1997
Palms and tree ferns AGB = 6.666+12.826 ∙ height05 ∙ ln(height) Pearson 2005b
Lianas AGB = exp (0.12=0.91 ∙ log (BA at dbh) Putz 1983
Shade grown coffee AGB = exp [‐2.719 + 1.991 (ln∙dbh)] ∙ log10dbh Segura et al. 2006
Banana AGB = 0.030 ∙ dbh2.13 Van Noordwijk et al. 2002
Fast growing trees Log10 AGB = ‐0.834 + 2.223 (Log10dbh) Segura et al. 2006
Below ground Carbon BGC =[ exp(‐1.0587 + 0.8836 ∙ ln AGB)] ∙0.5 Cairns et al. 1997
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Appendix 2 Mean wood density values in each elevation category
Table 11 Mean wood specific density and standard deviation at each elevation. Not all stems had density
values this table demonstrate the proportion of stems that had an associated value.
Elevation (m.a.s.l.) Mean ρ (g/cm3) ±SD # stems with ρ value Total # of stems % of stems with ρ value
50 0.66 0.10 45 313 14.4
600 0.64 0.07 45 365 12.3
800 0.58 0.10 44 423 10.4
1400 0.55 0.16 64 393 16.3
1800 0.42 0.14 36 486 7.4
2200 0.49 0.10 83 788 10.5
2400 0.50 0.09 149 699 21.3
2800 0.49 0.08 152 961 15.8
2800.5 0.52 0.05 178 519 34.3
3000 0.47 0.05 178 681 26.1
Dendawang 0.45 0.08 11 334 3.3
Secondary forest 0.41 0.09 241 956 25.2
Overall 0.50 0.12 1260 7335 17.2
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Appendix 3 Comparison of SOC in other elevation transects
Table 12 Comparison of SOC stocks in other transects
Reference Location Elevation range (m a.sl.)
Depth sample (cm)
Range of C stocks (MgC∙ha‐1)
Soil description of selected sites Slopes of selected sites
Kitayama & Aiba, 2002 Borneo 700‐3100 100 ca. 70‐280 sedimentary substrate (sandstone/mudstone), pH 4.1‐4.9 gentle (17°‐27°)
Borneo 700‐3100 100 ca. 80‐100 ultrabasic substrate (serpentinizedperidotite), pH 4.5‐5.4 gentle (11°‐24°)
Townsend et al., 1995 Hawaii 900‐1500 20 113.9‐153.6 allophanic soils (Udands), extremely similar along sites relatively level
Girardin et al., 2010 Peru 194‐3025 40 14‐70 all except one on Paleozoic shalesslates), below 1000m clay rich soils on alluvial sediments, lower at higher sites
ridgetop
Schaweet al., 2007 Bolivia 1700‐3400 100 220‐530 Ordovician metasiltstone, slates and sandstones, pH 3‐4.5 Steep (>25°)
Soetheet al., 2007 Ecuador 1900‐3000 110 131‐402 gleyicCambisols, Podzols at highest altitude plot, pH < 3.5 to 30cm depth
27°‐31°
Zimmermann et al., 2010
Peru 2994‐3860 90 mean of 118 HisticLithosol ‐
Schrumpfet al., 2001 Ecuador 1100‐3050 100 ca. 70‐350 mainly phyllites, partly metamorphic sandstones as well as quartzites, pH 3‐5
very steep (30°, maxima >60°)
Raichet al., 1997 Hawaii 290‐1660 50 5.1‐145 All on pahoehoe lava, consistently very acid gentle
Raichet al., 2006 Meta‐analysis of 6 transects
ca. 0‐4000 5 x 100, 1 x 50
ca. 60‐600
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Appendix 4 Tree species in regrowth land cover (work in Progress)
Table 13 common species in each land type, in order of highest basal area from each land use type
Land use Type Dominant Species§
Shade Coffee Casuarina oligodon, Leucaena sp,Persea sp (avocado) Entrolobium cyclocarpum, Coffee arabica, Caesalpinia sp,Trema sp, Areca catechu (betelnut), Drayadodaphne crassa
Fallowed Garden Areca catechu (Betelnut), Artocarpus utilis (breadfruit), Piper sp, Casuarina oligodon, Pandanus, Finchia rufa, Saurauria sp, Tetrameles nudiflora, Ficus sp,
Secondary Forest Saurauria sp, Trema sp, Ficus sp, Macaranga sp, Arctocarpus altilis, Podocarpus crassigenmis
§Species identification is not complete, species data may change
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Appendix 5 Aligning carbon sequestration options with Landscape Management plan in YUS
The YUS Project seeks to conserve forest carbon, endemic biodiversity, and ecosystem services, and to
benefit local rural communities by providing income streams from sustainable activities that have low
impact on traditional ways of life, in the Morobe Province of Papua New Guinea. Integrating
sustainable development models have multiple objectives is a major challenge in land use planning
(Dewi et al. 2011). Table 9 displays some goals within YUS Landscape plan that might overlap with
carbon sequestration objective mentioned in this report as a starting point for further partnerships.
Table 14 Goals within YUS Landscape plan that potentially overlap with carbon sequestration
Sector DSP 2030 Deliverables
4.3 Forestry 9.0 Promote the international initiative Reducing Emissions from Deforestation and Forest Degradation
(REDD+) to assist with mitigation adaptation measures in climate change
5.1 Population 1.0 Enhancement of skills and capacity to equip the labor force
5.6 Environment
1.3 Comprehensive range of natural resource management guidelines that addresses drivers of deforestation
1.5 Enhance management of land degraded by commercial extraction 4.0 Creation of systems of protected areas management at all levels and forest and biodiversity
conservation 4.5 REDD + and payment for ecosystems services (PES) 5.5 Introduce land zoning systems to increase agricultural production 6.0 Environmental data and information management for planning and dissemination
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