Biome-BGC Carbon Model

BIOME-BGC

Authors

Steve W. Running, Lars L. Pierce, Ramakrishna R. Nemani, and E. Raymond Hunt, Jr., School of Forestry, University of Montana, Missoula, MT 59812, USA

Links

http://www.forestry.umt.edu/ntsg/EcosystemModeling/BiomeBGC/

http://www.cgd.ucar.edu/vemap/abstracts/BGC.html

http://gaim.unh.edu/Structure/Intercomparison/EMDI/models/bgc.html

http://www-eosdis.ornl.gov/BOREAS/bhs/Documents/RSS08_biome_bgc.html

Description

The Biome-BGC (BioGeochemical Cycles) model simulates NPP for multiple biomes. Because NPP is computed as the difference between simulated GPP and autotrophic respiration, environmental controls operate on both the process of photosynthesis and respiration. Although nitrogen dynamics have been added, Biome-BGC relies primarily on the hydrologic cycle and how water availability controls C uptake and storage (VEMAP 1995). The response of NPP to elevated CO₂ is determined mainly by changes in transpiration associated with reduced leaf conductance, rather than feedbacks from nutrient cycling (Pan et al. 1998).

Model scale and resolution

Biome-BGC has a daily time step and no explicit spatial scale. The model has an intermediate number of vegetation (4) and litter/soil (3) pools.

Precursors

Biome-BGC is a multi-biome generalization of FOREST-BGC, a model originally developed to simulate a forest stand development through a life cycle (Running and Coughlan, 1988; Running and Gower, 1991). Biome-BGC combines Forest-BGC with MT-CLIM, which extrapolates meteorological driving variables from valleys to different slopes, aspects, and elevations (Running and Hunt 1993).

Inputs

Climate variables

1. Daily temperature (min, max in degrees C)
2. Daily total precipitation (cm)
3. Daily vapor pressure (Pa)
4. Daily total solar radiation (W/m²)
5. Daily total photosynthetically active radiation (W/m²)

Site variables

1. Soil depth with rock fraction removed (m)
2. Sand, silt, clay (% of rock-free volume)
3. Soil water content at field capacity and at critical water potential (m³/ha)
4. Slope and aspect (degrees)
5. Soil temperature at 20 cm depth (degrees C)
6. Elevation (m)
7. Latitude (decimal degrees)
8. Daylength (sec)
9. Shortwave albedo (dimensionless)
10. Total atmospheric nitrogen deposition (kg N/m²/y)
11. Total fixation of nitrogen (kg N/m²/y)

Lifeform variables

1. Precipitation interception coefficient (mm/LAI)
2. Light extinction coefficient (1/LAI)
3. Turnover coefficients for leaf, stem, and root (%/y)
4. Specific leaf area (m²/kg)

Initial conditions

The initial atmospheric CO₂ and the initial water in soil and snowpack are specified. Allometric relationships extrapolate from carbon (C) and nitrogen (N) in the leaf pool to initial stem, root, soil, and litter pools (Vitousek et al, 1988).

Testing and validation

Components of BIOME-BGC have previously undergone testing and validation, including the carbon dynamics (McLeod and Running, 1988; Korol et al, 1991; Hunt et al, 1991; Pierce, 1993; Running, 1994]) and the hydrology (Knight et al, 1985; Nemani and Running, 1989; White and Running, 1994). BIOME-BGC is sensitive to temperature.

References

Running, S.W. and J.C. Coughlan. 1988. A general model of forest ecosystem processes for regional applications, I. Hydrologic balance, canopy gas exchange and primary production processes. Ecological Modelling 42, 125-154.

Running, S.W. and E.R. Hunt, Jr.. 1993. Generalization of a forest ecosystem process model for other biomes, BIOME-BGC, and an application for global-scale models. Pp. 141-158 In J.R. Ehleringer and C.B. Field (eds.) Scaling Physiological Processes: Leaf to Globe. Academic Press, Inc. New York.

Churkina, G. and S.W. Running. 1998. Contrasting climatic controls on the estimated productivity of global terrestrial biomes. Ecosystems 1: 206-215.