Fitz, H.C., E.B. DeBellevue, R. Costanza, R. Boumans, T. Maxwell,
L. Wainger, and F.H. Sklar. 1996. Development of a general ecosystem
model for a range of scales and ecosystems. Ecological Modelling 88(1/3):263-295.
Abstract
We have developed a General Ecosystem Model (GEM) that is designed to simulate a variety of ecosystem types using a fixed model structure. Driven largely by hydrologic algorithms for upland, wetland and shallow-water habitats, the model captures the response of macrophyte and algal communities to simulated levels of nutrients, water, and environmental inputs. It explicitly incorporates ecological processes that determine water levels, plant production, nutrient cycling associated with organic matter decomposition, consumer dynamics, and fire. While the model may be used to simulate ecosystem dynamics for a single homogenous habitat, our primary objective is to replicate it as a "unit" model in heterogeneous, grid-based dynamic spatial models using different parameter sets for each habitat. Thus, we constrained the process (i.e., computational) complexity, yet targeted a level of disaggregation that would effectively capture the feedbacks among important ecosystem processes. A basic version was used to simulate the response of sedge and hardwood communities to varying hydrologic regimes and associated water quality. Sensitivity analyses provided examples of the model dynamics, showing the varying response of macrophyte production to different nutrient requirements, with subsequent changes in the sediment water nutrient concentrations and total water head. Changes in the macrophyte canopy structure resulted in differences in transpiration, and thus the total water levels and macrophyte production. The GEM's modular design facilitates understanding the model structure and objectives, inviting variants of the basic version for other research goals. Importantly, we hope that the generic nature of the model will help alleviate the "reinventing-the-wheel" syndrome of model development, and we are implementing it in a variety of systems to help understand their basic dynamics.
GEM manuscript
The manuscript which fully describes the GEM is published in Ecological Modelling as cited above 
GEM: Stella model
The GEM was initially developed using the Stella graphical modeling environment. If
you have Stella (Mac or Windows), you may want to download a version of the GEM.
Note that Stella is used primarily in the initial development and calibration
of the unit cell model (the GEM) for the spatially explicit landscape models.
The equations are later put into C code for integration into the spatial model.
The Stella unit model may also be used alone for non-spatial, homogenous ecosystem
models.
Download the model for Mac Stella v. 5.x (323 K, Stuffed and Binhexed).
Download the model for Windows Stella v. 5.x (258 K, PKZipped).
|
