Regional legacies of logging: Departure from presettlement forest conditions in northern Minnesota

Forests in the Great Lakes region of Canada and the United States have been important timber producing resources for more than 100 years. Logging and fire suppression have caused major, but unquantified change in those forests, which includes both the magnitude of compositional change and its spatial patterns. Hence, a spatially explicit regional-scale change analysis was conducted using General Land Office Survey records from the late 1800s and the 1990 U.S. Forest Service Inventory and Analysis Survey, for a 3.2 million hectare study area in northeastern Minnesota, USA. These data document altered species abundance, proportional basal area, and spatial distribution patterns. Regionally, the proportionally most abundant species shifted from the presettlement period (spruce, 21%; larch, 15%; and paper birch, 15%) to aspen (30%), spruce (16%), and balsam fir (16%) in 1990. In terms of proportional basal area dominance, white pine declined from 20% to 5%, birch from 16% to 13%, spruce from 14% to 9%, and larch from 12% to 2%, while aspen increased from 8% to 35%. Based on ordination of species abundance and proportional basal area, physiographic zones varying in geology and hydrology were characterized by different species composition in the 19th century and experienced largely parallel rather than convergent shifts in community composition since that time. Maps were developed for the regional Study area using a 10 X 10 kin spatial resolution to document spatial patterns of species proportional basal area. White pine co-dominated (was ranked first or second in proportion of basal area) 45% of the 253 100-km(2) presettlement zones, but none of the 1990 zones. Forest zones co-dominated by red pine, jack pine, and larch also largely disappeared. These forests were largely supplanted by aspen co-dominated communities, which accounted for 82% of the 1990 forest zones and represent diminished regional landscape diversity. Although the same I I species made up the 1990 as well as the 19th century forest, change in their relative abundance and dominance was profound such that 85% of the 253 zones now contain community types (i.e., dominant species pairs) that did not dominate anywhere in the presettlement era.