Model Versions

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 (NV) into structural (NVS) labile (NVL) 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 CS 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:
  1. historical CO2 for the globe
  2. historical climate and CO2 for the Amazon Basin
  3. historical climate and CO2 for the conterminuous United States
  4. historical and future climate and CO2 for arctic ecosystems
  5. future projections of climate and CO2 change across the globe
  1. Melillo et al., 1996; Kicklighter et al., 1999b
  2. Tian et al., 1998, 2000
  3. Tian et al., 1999; Schimel et al. 2000
  4. McGuire et al., 2000a, 2000b; Clein et al., 2000
  5. Xiao et al., 1998b; Prinn et al., 1999; Reilly et al., 1999; Webster et al., 2003
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 and future climate, CO2, land use and ozone Felzer et al., 2002, 2004, 2005, 2007; Webster et al., 2009 Sokolov et al., 2005, 2008, 2009 Reilly et al., 2007a, 2007b; Webster et al., 2009
4.4 Transient Incorporated disturbance cohort structure to describe sub-grid effects of land-use change on terrestrial biogeochemistry. Examined the time-dependent responses of terrestrial carbon storage and the net carbon exchange with the atmosphere as influenced by future climate CO2, land use and ozone pollution Melillo et al., 2009a, 2009b;
5.0 Transient Incorporated algorithms describing soil thermal regime and the effects of soil temperature on plant productivity, decomposition and nitrogen availability. Does not consider ozone effects Examined the time-dependent responses of terrestrial carbon storage and the net carbon exchange with the atmosphere as influenced by historical and future climate, CO2, land use and soil thermal regime Zhuang et al., 2001, 2002, 2003, 2006, 2007; Lu et al., 2009; Xiao et al., 2009;
5.1 Transient Updated algorithms describing the effects of soil temperature on plant productivity and added algorithms to describe effects of wildfire. Does not consider ozone effects. Examined the time-dependent responses of terrestrial carbon storage and the net carbon exchange with the atmosphere as influenced by historical and future climate, CO2, wildfires, and soil thermal regime. Euskirchen et al., 2006; Balshi et al., 2007, 2009
TEM-Hydro Transient Updated algorithms describing plant physiology from TEM 5.0, but does not include soil thermal dynamics or their effects on terrestrial biogeochemistry. Examined the time-dependent linked responses of terrestrial water, carbon and nitrogen dynamics as influenced by future climate, CO2 fertilization, nitrogen limitation and ozone pollution. Felzer et al., 2009


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.