Erica A. Howard Michelle Steen-Adams

FEM 875, Forest Landscape Change, Fall 2002

Boreal forest land-use change and its effects on carbon storage

Climate change & the carbon cycle

1. Motivation

*(Fluxes in billion tons C per year)

Increased COIncreased CO22 in the atmosphere is causing temperatures to in the atmosphere is causing temperatures to riserise

Why should we care about boreal forests?

Provide fresh waterSupport wildlife/biodiversityProvide timber, petro,

and mineral resourcesAllow for recreationSupport native peoplesRegulate climateStore carbon

1. Motivation

Boreal forests now store several hundred Pg of C

Boreal forests could store much more C in the future…

…or could release some of that C to the atmosphere

Boreal forests & C cycling

Boreal forests in a global perspective

Definitions:Forests between the summer & winter positions of the Arctic front (Landsberg & Gower 1997)

Forests between ~50-70NForests with a characteristic community compositionBoreal-temperate boundary at the -16ºC (avg monthly) isotherm (R&W 1998)

Boreal-”taiga-tundra” (boreal woodland?) boundary -- 1330 growing degree-days (R&W 1998)

The circumpolar range of the boreal forest. About two-thirds of the area is in Eurasia. The sector in eastern Canada lies farthest from the North Pole.

Boreal forests in a global perspective

Area:12-14 x 108 ha; ~25% of global forest cover. (L&G 1997; IPCC LULUC&F)

~20% is wetlands; much of this is peatlands (Lafleur et al. 1997)

The circumpolar range of the boreal forest. About two-thirds of the area is in Eurasia. The sector in eastern Canada lies farthest from the North Pole.

Boreal forests in a global perspective

Carbon content:~88-143 Pg C in aboveground vegetation (Schlesinger 1997; IPCC)

~203-471 Pg C in soil organic matter and surface litter. (Schlesinger 1997; IPCC)

FROM: http://www.fao.org/docrep/003/y0900e/y0900e06.htm#P20_4486“Source: Dixon et al., 1994; Schlesinger, 1997.Boreal forests account for more carbon than any other terrestrial ecosystem (26 percent of total terrestrial carbon stocks), while tropical and temperate forests account for 20 and 7 percent, respectively (Dixon et al., 1994).”

Regional boreal forests

RussiaScandinaviaChinaCanada Alaska

…These have very different histories.

2 %

65%

34%

% of Total b

oreal land area

% of boreal cleared 1700-1990

1%

22%

Mg C harvested / ha

44

22

26

n/an/a

Estimates of carbon balance at varied spatial and temporal scales

Regional estimates (for the present, or very recent years):

IPCC LULUC&F 2000: inverse modeling results (Rayner et al 2000; Bousquet et al. 1999) show sinks in Siberia and North America (but not necessarily boreal N.A.)

Myneni et al. 2001: remote sensing & forest inventory results show (for 1981-1999) increase in biomass woody C in Eurasian boreal, but losses in Canadian boreal forests except for fragments with gains in N. Saskatchewan & Alberta

Estimates of carbon balance at varied spatial and temporal scales

Stand-specific estimates:NEE uptake up to ~2.7 Mg C/ha/yr (eddy flux)

• Very few recently disturbed standsNEE emissions of ~ -2.5 Mg C/ha/yr in one managed stand (drained?)Need more data in disturbed systems -- there are some chronosequence and paired-site studies

Estimates change through time:Kurz & Apps find that Canada’s boreal forests switched from net sink to net source in the 70s or 80s as a result of changing fire frequency interacting with stand succession

Comparison of estimates of biomass and NPP of boreal forests

(Jiang et al. 2002)

Country Biomass NPP (kg C ha-1/yr) (Mg C ha-1)

Alaska, USA 43-181 250-1660Canada 26-214 1170-3800Russia, Europe 23-166 1270-3140Russia, Siberia 56-237 310-6750China 56-318 1810-7800

C balance depends C balance depends on disturbanceon disturbance

Historical boreal C balance: intimately tied to fire and pests

Future C balance: will also be influenced by logging

1. Motivation

“Land use, land-use change and forestry activities, also known as ‘carbon sinks’, can provide a relatively cost-effective way of combating climate change, either by increasing the removal of greenhouse gases from the atmosphere (e.g. by planting trees or managing forests), or by reducing emissions (e.g. by curbing deforestation). There are pitfalls, however…”

UN Framework Convention on Climate Change website: http://unfccc.int/issues/lulucf.html

Biophysical drivers of boreal forest landscape structure: disturbances

FireStand-replacing fire very common in Canada; intervals 30-200 yrs (L&G 1997)Low-intensity fire very common in Siberia (Schulze et al. 1999)

Larocque et al. 2000:Fires may be frequent enough to keep forest stands in early successional species (e.g., jack pine)…or fires may occur less frequently, allowing directional succession

Age-class dynamics and/or succession dominate landscape pattern in most unmanaged boreal landscapes

Biophysical drivers of boreal forest landscape structure: disturbances

Other non-anthropogenic disturbances:

WindthrowInsect/pest outbreak very common; dominant in Eastern Canada; can be low intensity or mortality inducing

Age-class dynamics and/or succession dominate landscape pattern in most unmanaged boreal landscapes

Biophysical drivers of boreal forest landscape structure:

abiotic/biotic templateLandform/drainage/soil texture:Soil moisture, temperature, nutrient availabilityGrowing season lengthDeciduous/evergreen habitMoss or lichen typesMicrobial biomass and species compositionSeed source

Land Uses of Boreal Forests:Pre-Industrial Era

Note: People and forests migrated into Canada concurrently since the last Ice Age - there is no real “pre-indigenous” boreal forest here

Agriculture and grazing, esp. in Scandinavia (Ostlund et al. 2002)Selective Logging, fuelwood extraction (e.g. late 19th c. Norway (Storaunet et al. 2000), also Canada (Weir and Johnson 1998)

Small-scale resource extraction: tar (late 18th-early 19th c. boreal Sweden and Finland; specific wood production—e.g. ax-handles; peatHunting/gathering (Ostlund et al. 2002)Medicine trees; Magical/ spiritual uses

Culturally-modified trees/ Forest land uses in boreal Sweden

(Ostlund et al. 2002)

Boreal Forest Structure characteristic of Pre-Industrial era

Dominant ecological processes/ driversDisturbance and succession

“Old-Growth” conditionsAge of oldest trees

Landscape structure: forest matrix and interspersed patchesMultiple age class stands -

But no “equilibrium” age class distribution?

Effects of pre-industrial era land use on boreal forest landscapes

In Scandinavia, impacts of human activities limited to local scales; biophysical processes, especially fire, drove landscape pattern.Mixedwood boreal forest, Canada (1883-1994): white spruce aspen and jack pine dominated forests.

Land Uses of Boreal Forests:Industrial Era

Mining/ DrillingRecreation/ Road buildingSettlement/ AgricultureForest Harvesting(Intensive) Forest management

ThinningHerbicide applicationLogging

Fire Suppression

Change in processes driving landscape pattern:

Fire Industrial logging (Axelsson and Ostlund 2001, Jiang et al. 2002)

Effects of forest management on forest structure

Changes in species composition:Decrease in the deciduous component of Scandinavian boreal forestsManagement in Canada sometimes favors deciduous trees (aspen)

Conversion of “old-age” forests to young forests

Changes in Patch structure: FragmentationUneven-aged even-aged stands **

Potential to reduce site productivity

Carbon Dynamics: Effects of landscape structure

•Succession and age class structure•recently disturbed stands are a net source

•(decomposition continues, NPP is suppressed)•recovering stands have highest NPP•older stands produce more litter (leaf and woody)•regeneration may be a problem following harvest or very high intensity fire

•Species distribution (conifer vs. broadleaf; understory type)•deciduous foliage decomposes faster than evergreen•deciduous broadleaf - more productive than conifers during summer, but shorter growing season•foliage decomposes faster than mosses, lichens, wood

Effects of Forest Harvesting on Boreal Forest Carbon Dynamics

China (Jiang et al. 2002--modelling study): Harvest/ disturbance levels influenced biomass, litter, and soil carbon stocksRotation length influenced C stocksSensitivity of soil carbon stocks relative to biomass and litter carbon stocks at short and long time-scales

Carbon Dynamics: Effects of landscape structure

•Disturbance affects amplitude of the annual C balance:

•Many forms of disturbance enhance both growing season productivity and winter respiration (in the short term) (Zimov et al. 1999)-species shifts (in both overstory and understory) from evergreen to deciduous habit may be one cause

-Since NPP and respiration are only partially correlated and may not vary linearly with the effects of disturbance, this may be a clue that big change in the C balance may be in store for the future

Key points

“The boreal forest is a patchwork of forest age-classes and plant assemblages resulting form the interaction among fire histories, insect outbreaks, and topography.” (Larocque et al. 2000)

Net ecosystem exchange (NEE) depends strongly on the vegetation compositionNet biome productivity (NBP) (or modified NEP) may be less than one 1/1000th of instantaneous NPP (Schulze et al. 1999). So disturbance is KEY.

Ways that human activities may influence carbon stocks and mean

annual carbon sequestration

Nitrogen depositionClimate change (temperature and precipitation)Increased CO2 concentration

Intensive forest management

Effects of climate change on boreal forests

In upland Scandinavia: Increased temperature and/ or CO2 did not significantly influence tree growth; Carbon sequestration may be less than expected. Rasmussen et al. (2002) Effects of increased temperature and nitrogen deposition: enhanced forest productivity and timber yield (model based on Finnish Scots pine stands) (Pussinun et al. 2002)

Increased temperature lower carbon stocks (Pussinun et al. 2002)

Limits to our Knowledge / Important Future Research

DirectionsEffects of alteration of forest landscape structure due to fire suppression

• How much do small landscape elements (like beaver ponds) matter?

Regeneration success: Do managed forests recover to the same level of productivity as unmanaged forests?

Present and on-going research questions

What factors limit ecosystem recovery?/ How long do human alterations persist on the landscape? What does “sustainable forestry” mean?: forestry for single species versus whole communities (Hanski 2002).How long does it take to achieve old-growth conditions in boreal forests?