Terrestrial Ecosystems Model (TEM) and the Global Land System Framework

The Terrestrial Ecosystems Model (TEM) has been developed by The Ecosystems Center at the Marine Biology Laboratory (MBL), and incorporated in the IGSM through cooperative efforts that have been ongoing since 1992.

The TEM has been used with the IGSM to examine the responses of terrestrial ecosystems to climate change, enhanced atmospheric CO2 concentrations, nitrogen availability and land-use change. Changes in natural ecosystems, as predicted by TEM, are used as a measure of terrestrial effects, or as inputs to analysis of the impact of climate change on agriculture. The version of TEM currently used in the IGSM also incorporates the influence of ozone on plant productivity and the influence of soil thermal regime on terrestrial carbon and nitrogen dynamics.

TEM is a process-based ecosystem model that simulates important carbon and nitrogen fluxes and pools for 18 terrestrial ecosystems. It runs at a monthly time step. Driving variables include monthly average climate (precipitation, mean temperature and mean cloudiness), soil texture (sand, clay and silt proportion), elevation, vegetation and water availability. The model incorporates a water balance model to generate hydrological input (e.g., potential evapotranspiration, soil moisture). For global extrapolation, TEM uses spatially-explicit data sets at a resolution of 0.5 degrees. The global data sets include long-term average climate, potential natural vegetation, soil texture and elevation.

Utilizing the IGSM's (Integrated Global System Modeling framework) climate predictions, TEM generates predictions of natural ecosystems states, including land vegetation changes, land CO2 fluxes, and soil composition, which feed back to the coupled chemistry/climate, and natural emissions models. The representations of ecosystem change produced by TEM are a crucial link to the estimation of economic and ecological effects. The change in carbon and nitrogen fluxes, and in carbon storage in vegetation and soils, are themselves useful indicators of climate change impact, and they provide a key step in the estimation of more specific models of effects on agriculture and natural ecosystems. With these linked components, the IGSM is used to study how climate-driven changes in the terrestrial biosphere affect climate dynamics through feedbacks on both the carbon cycle and the natural emissions of trace gases.

Changes in land ecosystems due to changes in climate are important considerations in policy discussions. In addition, climate-driven changes in the terrestrial biosphere affect climate dynamics, through feedbacks on both the carbon cycle and the natural emissions of trace gases.

The terrestrial component of the IGSM includes dynamically linked hydrologic and ecologic models in a Global Land System framework, as depicted in the diagram below.

Hydrologic processes and surface-heat fluxes are represented by the Community Land Model (CLM), which is based on a multi-institutional collaboration of land models. Within the IGSM, CLM is dynamically linked to the global Terrestrial Ecosystems Model (TEM), developed by The Ecosystems Center at the Marine Biology Laboratory (MBL). Within the IGSM, TEM is used to simulate the carbon dynamics of terrestrial ecosystems. Methane and nitrogen exchange are considered through the Natural Emissions Model (NEM), which is driven by dynamic inputs from both TEM and CLM. The coupled CLM/TEM/NEM model system represents the geographical distribution of global land cover and plant diversity through a mosaic approach, in which all major land cover types and plant functional types are considered over a given domain, and are area-weighted to obtain aggregate fluxes and storages.