Ice storms cause periodic disturbance to temperate forests of eastern North America. They are the primary agents of disturbance in some eastern forests. In this paper, a forest gap model is employed to explore consequences of ice storms for the long-term dynamics of Tsuga canadensis-northern hardwoods forests. The gap model LINKAGES was modified to simulate periodic ice storm disturbance in the Adirondack Mountains of New York. To adapt the gap model for this purpose, field data on ice storm disturbance are used to develop a polytomous logistic regression model of tree damage. The logistic regression model was then incorporated into the modified forest gap model, LINKADIR, to determine the type of damage sustained by each simulated tree.
The logistic regression model predicts high probabilities of bent boles or severe bole damage (leaning, snapping, or uprooting) in small-diameter trees, and increasing probability of canopy damage as tree size increases. Canopy damage is most likely on gentle slopes; the probability of severe bole damage increases with increasing slope angle.
In the LINKADIR simulations, tree damage type determines the probability of mortality; trees with severe bole damage are assigned the highest mortality rate. LINKADIR predicts Tsuga canadensis dominance in mesophytic old-growth forests not disturbed by ice storms. When ice storms are simulated, the model predicts Acer saccharum-dominated forests with higher species richness. These results suggest that ice storms may function as intermediate disturbances that enhance species richness in forested Adirondack landscapes.
Nomenclature: Magee & Ahles (1999).
Abbreviation: GDD = Growing degree day.