The impact of interannual variability in temperature and precipitation on global terrestrial ecosystems is investigated using a dynamic global vegetation model, LPJ (Lund-Potsdam-Jena model), driven by gridded climate observations for the 20th century.  Contrasting simulations are driven either by repeated mean climatology or raw climate data with interannual variability included.   

Results/Conclusions

Interannual climate variability reduces net global vegetation cover, particularly over semi-arid regions, and favors the expansion of grass cover at the expense of tree cover, due to differences in growth rates, fire impacts, and interception.  The area burnt by global fires is substantially enhanced by interannual precipitation variability.  The current position of the central United States’ ecotone, with forests to the east and grasslands to the west, is largely attributed to climate variability.  Among woody vegetation, climate variability supports expanded deciduous forest growth and diminished evergreen forest growth, due to difference in bioclimatic limits, leaf longevity, interception rates, and rooting depth.  These results offer insight into future ecosystem distributions since climate models generally predict an increase in climate variability and extremes due to the enhanced greenhouse effect.