Global Systems Group School of Ecology
I. Colin Prentice:
Tel.: +46 46-222 4176
Fax: +46 46-222 3742
Remote Sensing Laboratory
Dept of Physical Geography
Tel: +46 46 222 4039
Fax: +46 46 143859
BIOME3, which employs a more explicitly mechanistic scheme for vegetation physiology and has been more thoroughly tested for the global scale has superseded BIOME2 that is described as part of the VEMAP project on this page.
BIOME3 is an equilibrium terrestrial biosphere model that has been implemented globally using a minimal set of just five woody and two grass plant types. In BIOME3, leaf area is expressed as leaf area index (LAI). A small number of ecophysiological constraints is used to select the plant types that may be present in a particular climate. The model then calculates a maximum sustainable LAI and NPP for each plant type.
Gross primary production (GPP) is calculated as a linear function of absorbed photosynthetically active radiation based on a optimized version of the Farquhar photosynthesis equation (Haxeltine and Prentice 1996a). GPP is reduced by drought stress and low temperatures. Respiration is calculated with a semi-mechanistic model which partitions whole plant respiration costs into leaf respiration, transport tissue respiration, fine root respiration and growth respiration.
A semi-empirical rule designed to capture the opposing effects of succession driven by light competition and natural distrubance by fire excludes grasses as a dominant plant type if soil conditions are too wet. Otherwise, the plant type with the highest NPP is selected as the dominant plant type.
Model output consists of a quantitative vegetation state description in terms of the dominant plant type, secondary plant types present and the total LAI and NPP for the ecosystem. As in BIOME2, this basic model output is classified into biomes for comparison with vegetation maps.
The photosynthesis and water balance schemes are mechanistically coupled through stomatal conductance, thus allowing the model to simulate the response of photosynthesis, stomatal conductance and leaf area to environmental factors including atmospheric CO2. Laboratory studies show that stomatal conductance decreases in response to increasing CO2 concentration. However, regional decreases in stomatal conductance would result in a regional-scale feedback on evapotranspriation, leading to a smaller decrease in transpiration than that obtained at the leaf level. To incorporate this potentially important feedback, transpiration is calculated in BIOME3 using a simple, but well-tested, equation to describe the process of "accomodation" between transpiring plant surfaces and the water vapour content of the planetary boundary layer (Monteith, 1995).
Abstract mainly from A. Haxeltine (Ph.D. thesis, Lund University, Sweden).
Haxeltine, A., & I. C. Prentice (1996a)
A general model for the Light-use efficiency of primary production. FunctionalEcology. 10: 551-561.
Haxeltine, A. & I.C. Prentice (1996b)
BIOME3: An equilibrium terrestrial biosphere model based on ecophysiologicalconstraints, resource availability and competition among plant functionaltypes. Global Biogeochemical Cycles. 10: 693-709.
Haxeltine, A., I. C. Prentice, and I. D. Cresswell (1996)
A coupled carbon and water flux model to predict vegetation structure.Journal of Vegetation Science. 7: 651-666.
Accomodation between transpiring vegetation and the convective boundarylayer, Journal of Hydrology 166 : 251-263.
Prentice, I.C., Cramer, W., Harrison, S.P., Leemans, R.,Monserud, R.A.& Solomon, A.M. (1992)
A global biome model based on plant physiology and dominance, soil propertiesand climate. Journal of Biogeography. 19:117-134.