The Ecosystems Center, MBL

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Model Description

The Marine Biological Laboratory General Ecosystem Model (MBL-GEM) is a process-based plot-scale model of C-N interactions in terrestrial ecosystems.  The original structure of the model is described in detail in Rastetter et al. (1991).  Le Dizès et al. (2003) describe the latest version, MBL-GEM III, in detail.

The MBL-GEM III simulates, on an annual time step, plot-level photosynthesis and N uptake by plants, allocation of C and N to foliage, stems, and fine roots, respiration in these tissues, turnover of biomass through litter fall, and decomposition of litter and soil organic matter.  The model is generally calibrated to run on mean-July maximum and minimum daily air temperature, mean-July daily irradiance, total growing-season precipitation, mean-annual CO2 concentration, and annual N inputs in deposition.  A major feature of the model is that vegetation in the model acclimates to changes in the environment to maintain a nutritional balance between C and N.  For example, environmental changes that stimulate photosynthesis (e.g., increased CO2 or higher irradiance) result in an increase in the relative allocation of C and N to fine-root growth, which, in turn, stimulates N uptake.  Similarly, environmental changes that stimulate N uptake (e.g., increased available N) increase the relative allocation of C and N to foliage growth, which stimulates C uptake.  The C:N ratio of litter determines how it is partitioned among soil organic matter fractions that differ in relative turnover rates.  The rates of decomposition and N mineralization also depend upon soil temperature and moisture.

Recent modifications to MBL GEM include the incorporation of the Aggregated Canopy Model (ACM, Williams et al., 1997) as the photosynthesis submodel (MBL GEM III), and the conversion to a daily model including a water budget (MBL GEM VI).


Table 1: Key features of MBL GEM versions

MBL GEM Version

Key Feature


MBL GEM Version I

Original annual model

Rastetter et al., 1991

MBL GEM Version II

Modified growth equations

McKane et al., 1997a


Added ACM as photosynthesis submodel

ACM: Williams et al., 1997

GEM: Le Dizès et al., 2003

MBL GEM Version VI

Daily model, new growth and allocation submodel, daily water budget

unpublished, code available for download.


Figure 1: The General Ecosystem Mode (MBL GEM III, Le Dizès et al., 2003)


Clein, J. S., B. L. Kwiatkowski, A. D. McGuire, J. E. Hobbie, E. B. Rastetter, J. M. Melillo and D. W. Kicklighter. 2000. Modelling carbon responses of tundra ecosystems to historical and projected climate: A comparison of a plot- and a global-scale ecosystem model to identify process-based uncertainties. Global Change Biology Vol. 6, Supplement I:127-140.

Hobbie, J. E., B. L. Kwiatkowski, E. B. Rastetter, D. A. Walker and R. B. McKane. 1998. Carbon cycling in the Kuparuk Basin: Plant production, carbon storage, and sensitivity to future changes. Journal of Geophysical Research 103:29,065-29,073.

Le Dizès, S., B.L. Kwiatkowski, E.B. Rastetter, A. Hope, J.E. Hobbie, D. Stow, S. Daeschner. 2003. Modeling biogeochemical responses of tundra ecosystems to temporal and spatial variations in climate in the Kuparuk River Basin (Alaska). Journal of Geophysical Reseach D - Atmospheres 108(D2):8165. doi:10.1029/2001JD000960. (MBL GEM v3.3.6.5.b) (View PDF)

McKane, R. B., E. B. Rastetter, J. M. Melillo, G. R. Shaver, C. S. Hopkinson, D. N. Fernandes, D. L. Skole and W. H. Chomentowski. 1995. Effects of global change on carbon storage in tropical forests of South America. Global Biogeochemical Cycles 9(3):329-350.

McKane, R., E. Rastetter, G. Shaver, K. Nadelhoffer, A. Giblin, J. Laundre and F. Chapin. 1997a. Climatic effects on tundra carbon storage inferred from experimental data and a model. Ecology 78:1170-1187.

McKane, R., E. Rastetter, G. Shaver, K. Nadelhoffer, A. Giblin, J. Laundre and F. Chapin. 1997b. Reconstruction and analysis of historical changes in carbon storage in arctic tundra. Ecology 78:1188-1198.

Rastetter, E. B., M. G. Ryan, G. R. Shaver, J. M. Melillo, K. J. Nadelhoffer, J. E. Hobbie and J. D. Aber. 1991. A general biogeochemical model describing the responses of the C and N cycles in terrestrial ecosystems to changes in CO2, climate and N deposition. Tree Physiology 9:101-126.

Rastetter, E. B., R. B. McKane, G. R. Shaver and J. M. Melillo. 1992b. Changes in C storage by terrestrial ecosystems: How C-N interactions restrict responses to CO2 and temperature. Water, Air & Soil Pollution 64:327-344.

Rastetter, E. B., R. B. McKane, G. R. Shaver, K. J. Nadelhoffer and A. E. Giblin. 1997. Analysis of CO2, temperature, and moisture effects on carbon storage in Alaskan arctic tundra using a general ecosystem model, pp.437-451. In: W. C. Oechel, T. Callaghan, T. Gilmanov, J. I. Holten, B. Maxwell, U. Molau and B. Sveinbjörnsson (eds.), Global Change and Arctic Terrestrial Ecosystems.  Springer-Verlag, New York.

Rastetter, E.B., B. L. Kwiatkowski, S. Le Dízes, and J.E. Hobbie. 2004. The Role of Down-Slope Water and Nutrient Fluxes in the Response of Arctic Hill Slopes to Climate Change.  Biogeochemistry 69:37-62. (MBL GEMv3.3.6.5.d)

Williams, M., E. B. Rastetter, D. N. Fernandes, M. L. Goulden, G. R. Shaver and L. C. Johnson. 1997. Predicting gross primary productivity in terrestrial ecosystems. Ecological Applications 7:882-894.

This material is based upon work supported by the National Science Foundation under grants #OPP-9318529, OPP-9732281, DEB-9509613, and DEB-0108960 and the Environmental Protection Agency under grants RFQ-RT-00-00107 and QT-RT-00-001667. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation or the Environmental Protection Agency.

Last Updated: November 8, 2005