Geographic extension of an uneven-aged, multi-species matrix growth model for northern hardwood forests

The objective of this study was to update and extend the geographic range of a forest growth model for northern hardwoods, developed previously with data from the fourth Wisconsin inventory (Lin et al., 1996. Ecol. Model., 91: 193–211.). To this end, Lin’s model was recalibrated with data from the recent fifth inventory of Wisconsin and Michigan, and with the addition of a site variable to reflect variations in land productivity. After the introduction of site effects, there were still statistically significant differences between the equations of ingrowth, upgrowth, and mortality for Wisconsin and Michigan. Thus, two models were maintained, one for each state. Each model predicted well the growth of trees on post-sample plots, and simulated adequately the tree distribution in old stands in its own state. Applied to stands of the same initial distribution of tree species and size, the equations predicted faster early growth and higher basal area in the steady state in Michigan than in Wisconsin, with more marked differences on good than poor sites.