Print PageThe ability of forests to adapt to climate change will be limited by the ability of tree species to migrate at the same pace as the geographic range of their suitable habitat contracts or expands. Tree species migration is in turn limited by a range of factors including source strength (the presence and number of mature trees that contribute to the seed rain), suitable habitat, fragmentation, and competition from extant forests. Competition can inhibit migration through shading (particularly for shade intolerant or mid-tolerant species) and by reducing available growing space and source strength. We have studied the factors which enhance or limit tree species migration in landscapes in Minnesota, Wisconsin, and Massachusetts. We simulated climate change effects using a consistent forest landscape modeling framework (LANDIS-II), although each landscape is unique and varies by disturbance regimes, degree of fragmentation, ownership patterns, and tree species.
Results/Conclusions
In northeastern Minnesota, simulations of climate change over 100 years indicate that the expansion of maple (Acer spp.) may cause widespread homogenization and loss of diversity. Forest management using a historic range of variability approach exacerbated the loss of forest by limiting establishment and migration. Despite planting, the migration of more southerly species was limited by seed dispersal and disturbance. Only an aggressive planting of southerly species outside their historic range will allow sufficient climate adaptation. In northwestern Wisconsin, simulated tree migration was limited by both fragmentation and competitive exclusion. The net result was a decline in aboveground biomass and diversity over time. Finally, in Massachusetts, simulations indicate few shifts in species composition due to climate change alone as the primary process dictating forest composition will be a continued shift towards late-successional species following agricultural abandonment circa 1900. In combination, these studies suggest that forest migration will likely be much slower than the projected changes in climate and climatically-suitable habitat. Historic patterns of forest conversion and/or recovery as well as successional limitations and disturbance regimes may all contribute to this lag. Forest management options may be limited given the scale and uncertainty of the projected change.
