CAN DISTURBANCE DETERMINE VEGETATION DISTRIBUTION DURING CLIMATE WARMING - A BOREAL TEST

Models of terrestrial vegetation distribution change during warming ha ve generally paid little attention to ecological disturbances such as fire, even though these have been shown to be vitally important. A mod el predicting regionally dominant terrestrial vegetation in catastroph ically disturbed landscapes is proposed: probability of a disturbance adapted species leaving progeny (P-r) is (1-1/M)(j)-(1-1/M)(s), where M is the mean return interval between disturbances, j is the age of or ganisms at onset of reproduction, and s is the age at which reproducti on ceases. For non disturbance-adapted species, the model simplifies t o (1-1/M)(j). The model was tested in fire-prone boreal forest landsca pes in Ontario, Canada (48 degrees 00'-52 degrees 00'N, 80 degrees 00' -95 degrees 30'W). A vegetation map whose classes and class geographic al distributions were predicted using the above model was compared wit h a standard vegetation map. Three upland vegetation classes: poplar-p ine, spruce-pine-poplar and spruce-fir were predicted, as well as an o rganic class representing non fire-prone vegetation on peat. These cla sses were almost the same as those in the standard map and the vegetat ion distribution was comparable (vegetation correctly predicted for 61 .4% of the area, chi square P < 0.005). Thus the model can predict dom inant vegetation in this system, implying that the distribution of bor eal biome subzones in central Canada is largely governed by fire occur rence. To predict climate warming impacts, fire in the model was incre ased to 1.5 and 5 times the 1926-75 area, with a resultant shift of pr edicted vegetation zones to the north and east.