Forest changes due to prescribed burns and windstorms in Itasca State Park, Minnesota: A preliminary report.

Abstract

This report explores how the forests of Itasca State Park, Minnesota, have changed over a 35-year period, with particular emphasis on responses to management burns that were begun in 1995 with the goal of restoring the natural disturbance regime of the region over the next 50 years. The consequences of windstorms, a second natural element of the disturbance regime, were also examined, in the aftermath of a catastrophic storm in 1995. A network of permanently marked plots have been sampled periodically since 1965 by now-emeritus Professor Vilis Kurmis of the University of Minnesota's Department of Forest Resources. Now with post-fire and post-windstorm resampling conducted in 2000 and 2001, the changes over time at these sites can be interpreted in context of large disturbance events. Of great concern is the conservation of old growth pine ecosystems within the park. The dependence of the region's three species of pine upon fire was a major motivation for the new controlled burn program. We found that red pine, white pine, and jack pine populations have been declining throughout the 35 year period of study but that fire caused no further damage; burned plots had no more pine mortality than unburned plots. Moreover, in both burned and undisturbed plots, those pines that continued to survive were adding girth and biomass even as their populations thinned. However, windstorms are plucking out the tallest and oldest red and white pines where they extend above the main canopy. Fires have not yet triggered new pine regeneration, and repeated burns as well as herbivore controls may be necessary to achieve this goal. Fires thinned out some understory shrubs and trees, including the ubiquitous hazel and the scattered thickets of shade-tolerant balsam fir found in the spruce-fir forest type. In the maple-basswood forest type, fire correlated with a dip in sugar maple seedlings from superabundant to abundant, but also with a pulse of sprouting by ironwood, an understory tree. Prescribed burns did not damage the richness of the vascular flora. Those forests treated with controlled, spring-season fires did not differ significantly from unburned forests in their trajectories of plant species richness. This resistance to fire was seen in the diversity data for trees, tree seedlings, shrubs, and forbs (wildflowers and ferns). Unlike fire, windstorms did influence diversity in at least one cover type, the maple-basswood forest, where forb richness dropped after wind damage. Richness has varied greatly over time and amongst different forest types, with a general downward trend for shrub richness and an upward trend for forbs. Thus the current regime of management burns appears to be meeting objectives related to ecosystem restoration: favoring canopy pines, whose preservation and perpetuation is of primary concern, while thinning understory shrubs and shade-tolerant saplings without damaging the diversity of vascular plant species, although not yet generating new pine reproduction.