Model Description:

The Terrestrial Ecosystem Model (TEM) is a process-based ecosystem model that describes carbon and nitrogen dynamics of plants and soils for terrestrial ecosystems of the globe. The TEM uses spatially referenced information on climate, elevation, soils, vegetation and water availability as well as soil- and vegetation-specific parameters to make monthly estimates of important carbon and nitrogen fluxes and pool sizes of terrestrial ecosystems. The TEM operates on a monthly time step and at a 0.5 degrees latitude/longitude spatial resolution.

Improvements in computer resources have allowed us to examine ecosystem processes across the globe in more detail over time so that several versions of TEM have been developed over the past decade. At first, TEM only conducted equilibrium analyses of terrestrial carbon and nitrogen dynamics with hydrological inputs determined by an independent water balance model (WBM, Vörösmarty et al., 1989). This WBM used the same climatic data and soil-specific parameters as TEM. In version 4.0, the algorithms of the WBM were incorporated directly into TEM so that terrestrial carbon, nitrogen and water variables were determined concurrently. Then, we were then able to develop TEM 4.1 using relatively minor modifications of TEM 4.0 so that the model could conduct either equilibrium or transient analyses of terrestrial carbon and nitrogen dynamics.

Version	Type of Analysis	Major Modifications	Applications	References
1.0	Equilibrium	Original	Examined spatial patterns of long-term mean net primary production (NPP) in South America	Raich et al. 1991
2.0	Equilibrium	New feedback algorithm between C and N uptake by vegetation	Examined spatial patterns of long-term mean NPP across North America	McGuire et al., 1992
3.0	Equilibrium	Split vegetation N pool (N_V) into structural (N_VS) labile (N_VL) pools to inplement recycling of N within vegetation	Examined the responses of NPP and carbon storage to changes in climate and atmospheric CO₂ concentration at the global and continental scales	McGuire et al., 1993, 1995, 1996; Melillo et al., 1993, 1995; Melillo 1994; Joyce et al., 1995; McGuire and Joyce, 1995,; Perez-Garcia et al., 1997
4.0	Equilibrium	Redefined C_S pool to represent storage of reactive soil organic carbon instead of total soil organic carbon. Parameters for plant production, decomposition and N immobilization are now dependent on soil texture.	Examined the responses of NPP and carbon storage to changes in climate and atmospheric CO₂ concentration at the global and continental scales	VEMAP Members, 1995; Pan et al.,1996, 1998; McGuire and Hobbie, 1997; McGuire et al., 1997; Xiao et al., 1997, 1998a Schimel et al., 1997; Heimann et al., 1998; Cramer et al., 1999; Kicklighter et al., 1999a; Jenkins et al., 1999, 2000; Nungessor et al., 1999; Schloss et al., 1999
4.1	Transient	Incorporated water balance and leaf phenology algorithms. Allow study of transient dynamic of terrestrial carbon, nitrogen and water.	Examined interannual variations of NPP and net ecosystem production (NEP) in response to: historical CO₂ for the globe historical climate and CO₂ for the Amazon Basin historical climate and CO₂ for the conterminuous United States historical and future climate and CO₂ for arctic ecosystems future projections of climate and CO₂ change across the globe	Melillo et al., 1996; Kicklighter et al., 1999b Tian et al., 1998, 2000 Tian et al., 1999; Schimel et al. 2000 McGuire et al., 2000a, 2000b; Clein et al., 2000 Xiao et al., 1998b; Prinn et al., 1999; Reilly et al., 1999
4.2	Transient	Inplemented algorithms describing the effects of land-use change on terrestrial carbon dynamics.	Examined the time-dependent responses of terrestrial carbon storage and the net carbon exchange with the atmosphere as influenced by historical climate CO₂, and land use	McGuire et al., 2001
4.3	Transient	Incorporated algorithms describing the effects of ozone on plant productivity.	Examined the time-dependent responses of terrestrial carbon storage and the net carbon exchange with the atmosphere as influenced by historical climate CO₂, land use and ozone	Felzer et al., 2002
5.0	Transient	Incorporated algorithms describing soil thermal regime and the effects of soil temperature on plant productivity, decomposition and nitrogen availability.	Examined the time-dependent responses of terrestrial carbon storage and the net carbon exchange with the atmosphere as influenced by historical climate CO₂, land use and soil thermal regime	Zhuang et al., 2001, 2002 and 2003

NOTE: When TEM is run in "equilibrium" mode, all carbon and nitrogen fluxes within terrestrial ecosystems are assumed to be balanced and annual carbon and nitrogen inputs to the ecosystem are equal to annual losses. When TEM is run in "transient" mode, annual net ecosystem production (NEP) can increase or decrease in response to transient climate and atmospheric CO₂ concentration. In the absence of disturbances, annual NEP represents the net annual CO₂ flux between the atmosphere and the terrestrial biosphere. Terrestrial ecosystems act as a sink of atmospheric CO₂ when NEP is positive and act as a source of CO₂ when NEP is negative.

Projects:

NASA EOS: "Changes in Biogeochemical Cycles" PIs: Moore, Melillo, Peterson, Steudler
MIT: Joint Program on the Science and Policy of Global Change "Coupling the MBL Model with the MIT Framework" PI: Melillo
NSF ARCSS SIMS:Arctic Systems Science Synthesis, Integration, and Modeling Studies "The Role of High Latitude Ecosystems in the Global Carbon Cycle" PI: McGuire
NASA LC/LUC: Land Cover / Land Use Change "The role of land-cover change in high latitude ecosystems: implications for the global carbon cycle" PIs: McGuire, Armbruster, Melillo, Verbyla
BBSR:Bermuda Biological Station for Research "The Cycling of Anthropogenic Nitrogen Between the Terrestrial, Atmospheric and Oceanic Ecosystems" PI: Melillo

Model Comparison and Evaluation Activities

Reference	Name	Products
CCMLP Phase I Phase II	Carbon Cycle Model Linkage Project	Heimann et al., 1998; Kicklighter et al., 1999b; McGuire et al., 2000, 2001
GPPDI	Global Primary Production Data Initiative	Clark et al., 2001a, 2001b
PnET / TEM	Predicting the Effects of a Changing Physical and Chemical Climate on Primary Production, Nutrient Cycling and Water Yield for Forests of the Northeastern U.S.: A Comparison of Models and Scales	Jenkins et al., 1999, 2000
Potsdam 95	IGBP NPP Model Intercomparison Workshops	Bondeau et al., 1999; Cramer et al., 1999; Kicklighter et al., 1999a; Schloss et al., 1999
VEMAP Phase I Phase II	Vegetation / Ecosystem Modeling and Analysis Project	VEMAP Members, 1995; Pan et al.,1996, 1998; Schimel et al., 1997; Jenkins et al., 1999 Schimel et al., 2000

Last Updated 1 May 2001