POTENTIAL EFFECTS OF CLIMATIC-CHANGE ON SOME WESTERN CANADIAN FORESTS, BASED ON PHENOLOGICAL ENHANCEMENTS TO A PATCH MODEL OF FOREST SUCCESSION

We enhanced the forest patch model, Zelig, to explore the implications of 2xCO(2) climate change scenarios on several forest regions in Brit ish Columbia and Alberta, Canada. In addition to the processes and phe nomena commonly represented in individual-based models of forest stand dynamics, we added some species-specific phenology and sire-specific frost events. The consideration of bud-break heat sum requirements, gr owing season limits, and chilling requirements for the induction of do rmancy and cold hardiness slightly improved the ability of Zelig to pr edict the present composition of B.C. forests. Simulations of the pred icted effects of future climatic regimes (based on the averaged predic tions of four general circulation models) include some major shifts in equilibrial, forest composition and productivity. Lowland temperate c oastal forests are predicted to be severely stressed because indigenou s species will no longer have their winter chilling requirements met. High-elevation coastal forests are expected to increase in productivit y, while interior subalpine forests are expected to remain stable in p roductivity but will gradually be replaced by species currently charac teristic of lower elevations. Dry, interior low-elevation forests in s outhern B.C. are likely to persist relatively unchanged, while wet int erior forests are expected to support dramatic increases in yield, pri marily by western hemlock. Northern interior sub-boreal forests are li kewise expected to increase in productivity through enhanced growth of lodgepole pine. Conversely, the precipitous collapse of spruce stands in the true boreal forests of northeastern B.C. is expected to be ass ociated with reduced productivity as they are replaced by pine species . Boreal-Cordilleran and Moist Boreal Mixedwood forests in Alberta are less likely to undergo compositional change, while becoming somewhat more productive. We believe these model enhancements to be a significa nt improvement over existing formulations, but the resulting predictio ns must still be viewed with caution. Model limitations include: (1) t he current inability of climate models to predict future variation in monthly temperature and precipitation; (2) sparse information on the p henological behaviour of several important tree species; and (3) a poo r understanding of the degree to which growth is constrained by differ ent suboptimal climatic events.