Ecology and Management of Aspen: A Lake States Perspective

Aspen has been an ecologically important, though relatively minor, component of the Lake States (Michigan, Wisconsin, and Minnesota) forests for millennia. General Land Office records from the 1800s indicate that aspen comprised a small fraction of the region’s eastern forests, but was more extensive on the western edge. Then Euro-American settlement in the 1800s brought land clearing, timber harvesting, and subsequent widespread wildfires that increased aspen-birch acreages considerably. Although aspen-birch acreage has declined since the 1930s, it remains the region’s second most prevalent forest type. Aspen management is probably the most contentious issue confronting forest managers in the Lake States. Concerns regarding the status of early successional forest communities have emerged nationally. Across the United States, many disturbance-dependent ecosystems including prairies, savannahs, barrens, and early successional forests have declined in recent decades. These declines are due in part to nearly a century of fire suppression, as well as land conversion, rural development, and grazing. However, loss of late successional communities is also of national concern. Thus, both ends of the successional spectrum, young early successional forests and old late successional forests, have declined due to human activities. Quaking aspen (Populus tremuloides) and bigtooth aspen (Populus grandidentata) are among the premier early successional species in the United States. Quaking aspen is the most widely distributed tree in North America (figure 1), whereas the distribution of bigtooth aspen is confined primarily to the northeastern United States and the Great Lakes Region (figure 2). These two species, and their less common eastern associates, paper and gray birch (Betula papyrifera and B. populifolia), are often characterized as the aspen-birch forest type. Aspen and aspen-birch forests occur in 27 states within the United States, extending from Alaska to New Mexico in the west and from Maine to West Virginia in the east. The greatest acreage occurs in the eastern states of Minnesota, Wisconsin, Michigan, and Maine, and in the intermountain and mountain states of Utah and Colorado. Combined, these six states have 86% of the aspen and aspen-birch acreage in the lower 48 states. Based on the most recent Forest Inventory and Analysis (FIA) inventories, there are approximately 20.3 million acres of aspen and aspen-birch forest types (predominantly aspen) in the lower 48 states. These types comprise 7% of the nation’s forest lands (298.1 million acres of land stocked at least 1⁄6 with trees) and 10% of the nation’s timberland (198.1 million acres of more productive forest land; Powell et al. 1993). The Lake States (Michigan, Wisconsin, and Minnesota) are notably the stronghold of the aspen-birch forest type, with 12.9 million acres, or 63%, of the total acreage, in the lower 48 states. Within the Lake States, there are 51.9 million acres of forest lands, of which 49.0 million acres are considered timberland. Recent FIA data indicate that the aspen-birch forest type covers 6.3 million, 3.4 million, and 3.2 million acres of