Effect of mosaic representation of vegetation in land surfaceschemes on simulated energy and carbon balances

[摘要] Energy and carbon balance implications of representing vegetation using acomposite or mosaic approach in a land surface scheme are investigated. Inthe composite approach the attributes of different plant functional types(PFTs) present in a grid cell are aggregated in some fashion for energy andwater balance calculations. The resulting physical environmental conditions(including net radiation, soil moisture and soil temperature) are common toall PFTs and affect their ecosystem processes. In the mosaic approach energyand water balance calculations are performed separately for each PFT tileusing its own vegetation attributes, so each PFT "sees" different physicalenvironmental conditions and its carbon balance evolves somewhat differentlyfrom that in the composite approach. Simulations are performed at selectedboreal, temperate and tropical locations to illustrate the differencescaused by using the composite versus mosaic approaches of representingvegetation. These idealized simulations use 50% fractional coverage foreach of the two dominant PFTs in a grid cell. Differences in simulated gridaveraged primary energy fluxes at selected sites are generally less than5% between the two approaches. Simulated grid-averaged carbon fluxes andpool sizes at these sites can, however, differ by as much as 46%.Simulation results suggest that differences in carbon balance between thetwo approaches arise primarily through differences in net radiation whichdirectly affects net primary productivity, and thus leaf area index andvegetation biomass.

[学科分类] 地球化学与岩石