文档介绍：Global ChangeBiology (2000) 6, 445±458
Modelling the recent historical impacts of atmospheric
CO2 and climate change on Mediterranean vegetation
C. P. OSBORNE*, P. L. MITCHELL*, J. E. SHEEHY² andF. I. WOODWARD*
*Department of Animal and Plant Sciences, University of Shef®eld, Shef®eld S10 2TN, UK, ²International Rice Research
Institute, PO Box 933, 1099 Manila, The Philippines
Abstract
During the past century, annual mean temperature has increased by °C and preci-
pitation has shown marked variation throughout the Mediterranean basin. These his-
torical climate changes may have had signi®cant, but presently unde®ned, impacts on
the productivity and structure of sclerophyllous shrubland, an important vegetation
type in the region. We used a vegetation model for this functional type to examine cli-
mate change impacts, and their interaction with the concurrent historical rise in atmo-
spheric CO2. Using only climate and soil texture as data inputs, model predictions
showed good agreement with observations of seasonal and regional variation in leaf
and canopy physiology, net primary productivity (NPP), leaf area index (LAI) and soil
water. Model simulations for shrubland sites indicated that potential NPP has risen
by 25% and LAI by 7% during the past century, although the absolute increase in LAI
was small. Sensitivity analysis suggested that the increase in atmospheric CO2 since
1900 was the primary cause of these changes, and that simulated climate change alone
had negative impacts on both NPP and LAI. Effects of rising CO2 were mediated by
signi®cant increases in the ef®ciency of water-use in NPP throughout the region, as a
consequence of the direct effect of CO2 on leaf gas exchange. This increase in ef®-
pensated for limitation of NPP by drought, except in areas where drought
was most severe. However, while water was used more ef®ciently, total canopy water
loss rose slightly or remained unaffected in model simulat