VEGETATION AND CLIMATE CHANGES BETWEEN THE LAST GLACIAL MAXIMUM AND TODAY: MODELISATION AND ANALYSIS WITH HADSM3- TRIFFID

A dynamic vegetation model (TRIFFID) developed at the Hadley Centre computes the distribution of vegetation types (broadleaf, needleleaf trees, grass, shrubs) as a function of their net primary productivity. Here, TRIFFID is used in conjunction with the coupled atmosphere-mixed layer model HadSM3 to interactively simulate the vegetation and climate at the Last Glacial Maximum (21,000 years ago). We also propose a method to analyse systematically the causes of the simulated vegetation changes.

The model reproduces reasonably well the vegetation of the last glacial maximum as depicted by palaeodata. Only grass survives North of 50 degrees North in Siberia. Although the removal of trees is primarily driven by the temperature decrease, we show that the drying of Siberia prevented its colonisation by shrubs. The drying occuring in most sub-tropical regions tends to favour the existing deserts, such as the Sahara and the Central Asian plateaus. Indian vegetation strongly declines as well. By contrast, water availability is simulated to increase in Mexico. Hence, the Mexican forest is maintained and even expands, but becomes dominated by needleleaf trees because of the colder temperatures of the last glacial maximum. The tropical rainforests are reduced, but to a lesser extent than suggested by data.