Biospheric Process Models: The Challenge of Integrating Ecosystem Dynamics and Land Cover Change A. David McGuire USGS and University of Alaska

Historically Two Approaches CO 2 and Climate Process-Based Ecosystem Models Landuse and Disturbance Book-keeping Models

Modeling Integration for Investigating Global Change in Terrestrial Ecosystems CLIMATE DISTURBANCE Physical Properties Ecosystem Structure Ecosystem Function Human Dimensions

McGuire and CCMLP Participants Carbon balance of the terrestrial biosphere in the twentieth century: Analyses of CO 2, climate and land use effects with four process-based ecosystem models Global Biogeochemical Cycles 15: Dargaville and CCMLP Participants Evaluation of terrestrial carbon cycle models with atmospheric CO 2 measurements: Results from transient simulations considering increasing CO 2, climate, and land-use effects. Global Biogeochemical Cycles 16, 1092, doi: /2001GB Dargaville, R., A.D. McGuire, and P. Rayner Estimates of large-scale fluxes in high latitudes from terrestrial biosphere models and an inversion of atmospheric CO 2 measurements. Climatic Change 55: Process Models and Atmospheric Constraints

Goal of Study: … to simulate the concurrent effects of cropland establishment and abandonment, increases in atmospheric CO 2, and interannual climate variability on terrestrial carbon storage between 1920 and 1992.

Simulating the Effects of CO 2, Climate, and Cropland Establishment and Abandonment by Terrestrial Biosphere Models (TBMs) CO 2 Concentration Climate (Temperature, Precipitation) Landuse Map TBM Carbon Pools NPP R H Conversion Flux Product Pools NET Fire Disturbance Product Decay Flux 1 yr 10 yr 100 yr

Driving Data Sets Historical CO 2 : based on Etheridge et al. (1996) and Keeling et al. (1995) Temperature: based on Cramer and Leemans climatology and Jones et al. (1994) temperature anomalies Precipitation: based on Cramer and Leemans climatology and Hulme et al. (1992, 1994, updated) precipitation anomalies Solar Radiation: based on Cramer and Leemans climatology Historical Landuse: based on Ramankutty and Foley (1998) Relative Agricultural Productivity: based on Esser (1990) Other Data Sets: vegetation and soils - model specific

Comparison between net fluxes simulated by terrestrial biosphere models with a long- term inversion analysis of terrestrial C exchange with the atmosphere Modeled terrestrial exchange is consistent (within the uncertainty) with the long-term inversion analysis.

Partitioning effects of CO 2, climate, and cropland establishment and abandonment on global terrestrial carbon storage for HRBM,IBIS,LPJ and TEM The models indicate that the effects of CO 2 and cropland establishment/abandonment play important roles in terrestrial carbon storage. The models agree that the effects of climate are small relative to the effects of CO 2 and land use, but disagree about whether climate variability tends to cause net uptake or release of CO 2.

gC m 2 yr HRBMIBIS LPJTEM Mean Annual Net Carbon Exchange for the 1980s (CO 2, Climate, and Land Use)

gC m 2 yr HRBMIBIS LPJTEM Mean Annual Net Carbon Exchange for the 1980s (Land Use)

McGuire et al Canada and Alaska. Csiszar, I., et al Land use and fires. Chapters 9 and 19 in Land Change Science: Observing, Monitoring, and Understanding Trajectories of Change on the Earth’s Surface. Dordrecht, Netherlands, Kluwer Academic Publishers. Zhuang et al Carbon cycling in extratropical terrestrial ecosystems of the Northern Hemisphere during the 20th Century: A modeling analysis of the influences of soil thermal dynamics. Tellus 55B: McGuire et al Environmental variation, vegetation distribution, carbon dynamics, and water/energy exchange in high latitudes. Journal of Vegetation Science 13: Regional Changes in Carbon Storage may be Caused by Responses that affect Ecosystem Physiology, Disturbance, and Land Cover Change

Biomass of Boreal Forest Ecosystems has been Changing in Recent Decades From Myneni et al. (2001)

Courtesy of K. McDonald Growing seasons are occurring earlier

8.0 –18.0 Weeks – Region – 28.0 Weeks – Region –37.0 Weeks – Region 3 Duration of Snow Free Period Snow Free Duration Anomaly (weeks) Weeks of Snow Free Duration ( ) MeanSDCV Region 1 TEM Dye* Region 2 TEM Dye Region 3 TEM Dye *D. Dye, Hydrol. Process., 2002 Based on TEM simulation for north of 30 o N

Observed and simulated atmospheric CO 2 concentrations at Mould Bay Station, Canada ( o W, o N) during the 1980s g C m -2 yr -1 Sink Source 90° 60° 30° Spatial patterns of change in vegetation carbon over the twenty year period spanning from as simulated by the Terrestrial Ecosystem Model (TEM) Strategy to evaluate seasonal exchange of carbon dioxide simulated by terrestrial biosphere models Incorporation of freeze-thaw dynamics into the Terrestrial Ecosystem model improves the simulation of the seasonal and decadal exchange of carbon dioxide exchange with the atmosphere (Zhuang, Euskirchen, McGuire, Melillo, Romanovsky)

After crown fires, boreal conifer forests are often replaced by less flammable deciduous broad-leaved vegetation

Fire in Canada has became more frequent after 1970

[CO 2 ] and [O 3 ] and N Deposition Climate (Temperature, Precipitation) TEM Carbon Pools NPP R H NCE Fire Emissions Fire regime (Severity, History) Simulation of the effects of changes in [CO 2 ], [O 3 ], N deposition, Climate, and Disturbance by the Terrestrial Ecosystem Model (TEM)

Long-term Fire Return Interval for Alaska

* Pre-historical Fire Return Interval (before 1950) ** Fire Return Interval ( ) Uptake Release JSC 7/23/02

The high latitude transects span significant variation in several environmental variables and provide a network for improving our understanding of controls over vegetation dynamics, carbon dynamics and water/energy exchange in high latitudes

Percent Area Burned in IGBP Transects

Ground fires are typical in fire regime of Scots Pine Forests in Central Siberia Courtesy of Doug McRae

Crown fires are typical in fire regime of Boreal Forests in Far East Siberia and North America Courtesy of Doug McRae

Comparison of the average change in Seasonal Severity Rating (SSR) for Canada and Russia using the Canadian General Circulation Model (GCM) under left) a 1 x CO2, and right) a 2 x CO2 climate (from Stocks et al. 1998). Severity rating ranges from extreme (red), high (orange), moderate (yellow) to low (green).

Joyce et al. Harvesting disturbances on U.S. forestland from 1600 to present. In preparation. McGuire et al. Historical changes in carbon storage of the eastern United States: Uncertainties associated with forest harvest and agricultural activities. In preparation. Regional Processes: The Challenge of Multiple Disturbances

Overall Goals Develop land use model that allows native ecosystems to convert to agriculture, harvest occurrence in forests, and the creation the age cohorts following harvest and cropland abandonment. Compare modeled age class distribution with independent inventory data on stand age distributions Use data sets on forest disturbance to drive the Terrestrial Ecosystem Model (TEM) and evaluate how assumptions about CO2 fertilization and depletion of soil N by agricultural activities influence estimates of changes in carbon storage of the eastern US

Methods to Estimate Harvest Area Anecdotal information prior to 1952 Used inventory data summarized by state/region from 1952, 1962, 1977, 1987, 1992, 1997, and to 1952 –Trend extrapolation based on state population –Assume no harvest disturbance prior to European settlement 1952 to 2002 –Model harvested area using inventory data (volume, removals, timberland and forest area) and the limited data available on actual harvested area –Linear interpolation between inventory years

Development of the Land Use Model Agricultural Land Use –If cropland increases, conversion draws from oldest native vegetation, with a preference for secondary growth. –If cropland decreases, the oldest cropland is converted back to native vegetation Forest Harvest –Harvest oldest native vegetation first, with a preference for primary forest

Modeled estimates of total forestland area follow the temporal dynamics of inventory forestland estimates and are within 6 to 10%.

Forest Harvest Area by Region and US FIA Data and Modeled Estimates

Summary: Estimating Harvested Area Development of a method to obtain nationally consistent estimates of harvested area from 1600 to 2002 Linked forest land use change with agricultural land use; resulting projections of forest land are within 6 to 10 percent of recent inventory Comparison with independent data on stand age is good where harvest is the major disturbance Where other disturbances such as fire, comparison of stand-age distributions are weak

Simulating the Effects of CO 2, Climate, Forest Harvest, and Cropland Establishment and Abandonment by TEM CO 2 Concentration Climate (Temperature, Precipitation) Landuse Map TEM Carbon Pools NPP R H Conversion Flux Product Pools NET Fire Disturbance Product Decay Flux 1 yr 10 yr 100 yr

Comparison of forest growth curves between TEM and Birdsey (1995)

Effects of Cropland Establishment and Abandonment on Soil Carbon and Nitrogen Storage

Northeast Region Forest growth as a function of stand age in the TEM simulations is sensitive to assumptions about the effects of agriculture on the depletion of ecosystem nitrogen stocks through time. When nitrogen lost in agricultural production is not replaced (maximum N loss), forest regrowth after agricultural abandonment is not able to achieve the biomass of forests that were never harvested. When the lost nitrogen is replaced immediately after lost (minimum N loss), forest regrowth after agricultural abandonment is able to achieve the biomass of forests that were never harvested.

Average annual vegetation C flux (Tg C) maximum N loss $ Birdsey and Heath* minimun N loss $ transient CO 2 $ Northeast Southeast constant CO 2 $ Northeast Southeast $ TEM simulations (forest cells only) * Birdsey and Heath posted on the web the carbon estimates in forest land for 1987, 1992, and 1997 by state at

Biospheric process models provide a mechanistic means of evaluating the relative role of different drivers of changes in regional carbon storage, but are poorly constrained by extant atmospheric data. At the regional scale, changes in carbon storage may be affected by responses to drivers that affect ecosystem physiology (e.g., CO 2, climate, O 3, N deposition) as well as changes that affect ecosystem structure (e.g., disturbance and land use). It is important to account for historical legacies associated with disturbance regimes like fire. Age class distributions are generally the outcome of multiple disturbances, and it is a challenge to identify all of the disturbances that need to be considered. Comparison with inventory analyses is useful, but may not resolve controversies about the relative role of different drivers of changes in regional carbon storage. Conclusions