StudyArea

MaterialsandMethods

Results

Cita4ons

Backgroundandaimofwork

ContactInforma4on

Conclusion

Stephan Pietsch Research Scholar IIASA, Laxenburg, Austria E: pietsch@iiasa.ac.at

Franziska Schier Student Employee GIZ, Eschborn, Germany E: schier.franziska@gmail.com

Characteristics, Structure & Tree Species Diversity of a Tropical Exploitation Forest in Regeneration

Life Sciences Vienna

Forest degradation affects the diversity and structure of the Congo Basin rainforests. Yet actual carbon and biodiversity implications of forest degradation are less well known than those of deforestation. Forest structure and diversity could play an important role in climate regulation as both could influence forest biomass production and hence, determine the forests' capacity for carbon storage. With regard to future carbon forestry projects, the understanding of long-term impacts linked to selective logging on the carbon storage and the forest restoration capability is important. Thus, this case study aims to   analyse the long-term effects of logging on key forest

characteristics, stand structure and tree-species diversity   examine the regeneration potential of an exploitation forest

and the benefits of conservation regarding forest biomass, carbon stocks and tree-species diversity recovery

Franziska Schier1,3 Stephan Pietsch2,3

1 Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) 2 IIASA International Institute for Applied Systems Analysis 3 BOKU University of Natural Resources and Life Sciences Vienna

Fig 1: Study site Forêt classée de la Mondah , Gabon Potential natural vegetation cover of the area is the coastal Guineo-Congolian evergreen rainforest. The Mondah forest has a long history of commercial timber exploitation lasting from the 18th century to the mid 60th. In 2011, the sampling area was restricted to the south-eastern part where forest resources use is prohibited and effective forest protection guaranteed by a watchmen since 1972 (see Fig 1, orange oval).

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The study analysis proved proceeding forest recovery. In 1993, AGB and TBC ranked 25% below the local potential. In 2011 estimates were similar to pre-logged conditions. Signs of selective logging persists in the vertical and horizontal stem structure. Forest «thickening» and «heightning» is proved by significant increases in dg and HL. Tree-species richness is reduced due to human disturbances (i.a. resource overuse) and ranks below the regional potential. There is no strict correlation between the development of forest biomass carbon and diversity. Most of the carbon in tropical forests is stored in stems, thus increasing timber volume directly results in carbon benefits. The study concludes that forest conservation is a promising option to bolster the forest recovery of a degraded forest ecosystem and to restore essential ecosystem functions and services comparable to primary levels. The results of this study contribute to the TmFO efforts, to broaden the knowledge base on responses of tropical forests to logging, in terms of biomass dynamic and changes in species diversity.

1Balinga M. (2006) A Vegetation Assessment of the Waka National Park, Gabon. Report. http://pdf.usaid.gov/pdf_docs/Pnadm952.pdf 2Brown S. (1997) Estimating biomass and biomass change of tropical forests. A primer. FAO Forestry Papers 134. FAO. Rome, Italy 3Corlett, R.T. and Primack, R.B. (2011): Tropical rain forests. An ecological and biogeographical comparison. Oxford: Wiley-Blackwell 5Finch V. (2011) Mapping a greener future. GABON. Autumn 2011. August 2011. http://carbon.jpl.nasa.gov32-35_GABON21.ENGLISH.carbonmap.v3.pdf 4Pietsch R. (2000) Untersuchungen zur Struktur und Dynamik eines exploitierten Naturwaldes am Beispiel des Forêt Classée de la Mondah in Gabun. Georg-August-Universität, Göttingen, DE. 207pp. 6Sassen, M. and Wan, M. (2006): Biodiversity and local priorities in a community near the Ivindo National Park Makokou, Gabon. http://www.cifor.org/mla/download/publication/MLA_Gabon_Report%20FINAL3.pdf 7Sunderland T., Walters G. and Issembe Y. (2004) A preliminary vegetation assessment of the Mbé National Park, Monts de Cristal, Gabon. Report. http://pdf.usaid.gov/pdf_docs/PNADM950.pdf 8Magurran, A.E. (2004): Measuring biological diversity. Oxford: Blackwell Publishing. 9Gautam, S. and Pietsch, S. A. (2012): Carbon pools of an intact forest in Gabon. African Journal of Ecology, 50: 414–427. doi: 10.1111/j.1365-2028.2012.01337.x

Tab 1: Changes in Stand characteristic from 1993 to 2011 Given are means ± standard deviation, the change from 1993 to 2011 in % and the results of one-sided t-tests with 45 degrees of freedom, where n.s., +, * and ** stand for non significant, significant at α = 0.1, significant at α = 0.05 and significant at α = 0.01, respectively. SC = stem number, dg = quadratic mean diameter, HL = Lorey’s height, BA = basal area, SV = standing volume, AGB and TB = above- and total biomass and AGC and TBC = above- and total biomass carbon content. aincluding lianas, bcalculated from mean values indicated in the study.

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Tab 2: Changes in tree-species diversity from 1993 to 2011 1Counted Value 2taken from the area-species-curve given in Pietsch 2000; 3values refer to the first hectare of the area-species-curve given in Pietsch 2000

Fig 2: Changes in vertical stem diameter distribution from 1993 to 2011

Datacollec)on

DataanalysisForest

characteris)csDiversitymeasures

Stateandregenera)on

Standstructure

Sample area 1ha

Minimum dbh≥1cm

Records:   dbh   top height   tree species

Data sets:   dbh≥10cm   1≤dbh<10cm

Processing:   MS Excel 14.0

Statistics:   SigmaPlot 10.0

  Stem number[N]  Basal area[m2]  Volume[m3]  Above ground biomass[Mg]  Above ground carbon[Mg]  Total biomass[Mg]  Total biomass carbon [Mg]

Stem diameter distribution:

  vertical   horizontal

  Richness [S]  Rare species  Shannon entropy measure [H’],  Simpson measure [D]  Pielou’s J [J’]

Benchmarking study results with reference values from   Literature   Regional Reports   Local Study 1993 (see Fig 1: local map black rectangle)

Significantincreasesinforestbiomassandcarbonbyconstantstemnumber.Forestes)matesarereboundingtolocalpoten)als.

 Understorey(>15m)contained25%morestems1

 Canopy(<31m)contained50%lessstems

 Heightningprocess Classes>20mheightcontainedlesstreesin2011 Classesbetween20m–38mcontainedmoretreesin20111seePietsch2000

 Thickening Classes>30cmdbhcontainedlesstrees Classesfrom30cm≤dbh60cmcontainedmoretrees1=1cm≤dbh<10cm,...9=80cm≤dbh<90cm...

 cmFig 3: Changes in horizontal stem diameter distribution from 1993 to 2011

1993

Mean ± s.d.

2011

Mean ± s.d.

! %

Sign. level

Reference Values

SC [N ha-1

] 487 ± 144 500 ± 148 + 2.7 n.s. 300-6003,4

dg [cm] 27.7 ± 7.3 31.7 ± 7.5 + 14.3 + 29-31a,b,1,6,7

HL [m] 21.8 ± 5.8 26.4 ± 8.6 + 21.6 *

BA [m2 ha

-1] 29.6 ± 13.9 41.6 ± 28.7 + 40.9 * 29-44

b,1,6,7

SV [m3 ha

-1] 412 ± 255 771 ± 361 + 87.1 *

AGB [Mg ha-1

] 282 ± 192 415 ± 257 + 47.1 + 3752

AGC [Mg ha-1

] 134 ± 92 197 ± 122 + 46.8 +

TB [Mg ha-1

] 322 ± 214 469 ± 285 + 45.9 +

TBC [Mg ha-1

] 153 ± 102 223 ± 135 + 45.6 + 200-2505

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Even though the diversity level is high, it does not changed significantly and ranks below the regional potential.

Diversity Measure 1993 2011 Annotaion Interpretation

Species [S ha-1] 782 85

1

Lower than in comparable

forests1,6,7,9

Singletons k [%] 313 32

1

Doubletons [%] 153 18

1

Heterogeineity is high

50% (extremely) rare species

Shannon [H’] 3.35 3.73 > 3,5 -> highly diverse8 Complementarity in species high

Simpson [D] 0.03 0.04 0 -> no dominance Single species dominance low

Shannon Evenness [J’] 0.77 0.84 1 -> absl. equality Even stem-species distriution

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I thank the organizers of the 2014 IUFRO World Congress to have been selected as recipient of the Student and Recent Graduate Scholarship Fund - F.S.