|Title||Ecosystem mediated succession in aspen-dominated forests of northern lower Michigan|
|Year of Publication||2002|
|Academic Department||School of Natural Resources and Environment|
|Degree||Master of Science|
|Number of Pages||132 pp.|
|University||University of Michigan|
|City||Ann Arbor, MI|
Forest composition and succession within a local landscape are strongly mediated by the physiographic and edaphic characteristics of landscape ecosystems. One hundred twenty years after harvesting and severe fires destroyed presettlement forests throughout northern Lower Michigan, rapid forest ecosystem change is eminent as the bigtooth aspen that dominates much of the upland landscape declines and gives way to later successional species. While considerable research has focused on broad successional trends, none has examined site-specific succession in landforms and ecosystem types. In this study, I compared successional trends across 7 landscape ecosystem types nested within 3 landforms by comparing vegetative composition in permanent sample plots (n = 64) at the University of Michigan Biological Station in northern Lower Michigan. Multivariate statistical analyses (discriminant analyses) integrating physiographic, soil, and ground-cover vegetation variables confirmed the distinctness of the ecosystem units. Significant differences in vegetative composition and successional patterns among landforms and ecosystem types were strongly related to differences in the physiographic and edaphic characteristics of ecosystem units. Within two ecosystems of a high-level outwash plain, eastern white pine (Pinus strobus L.) dominated in the understory and will likely succeed the bigtooth aspen (Populus grandidentata Michx.) and northern red oak (Quercus rubra L.) along with red pine (Pinus resinosa Ait.) in the more severely disturbed type 36 and red maple in type 37. On two moraine landforms identical long-term successional trends were identified in two sets of ecosystem types similar in physiography and soil. Despite the vastly different disturbance histories of an interlobate moraine (types 109 and 113) and a moraine at Colonial Point (types 110 and 111), beech (Fagus grandfolia Ehrhart) is more prevalent and seems likely to dominate in sandier, lower-nutrient ecosystems (types 109 and 110), whereas sugar maple (Acer saccharum Marsh.), a more nutrient demanding species, is more abundant in more loamy, higher-nutrient ecosystems (types 113 and 111), evidence that edaphic characteristics can exert a stronger influence on long-term successional patterns than severe stand-replacing disturbances. A moderate human-caused disturbance, selective harvesting of a bigtooth aspen overstory in a lower-nutrient moraine ecosystem (type 109), hastened succession to beech by 30-40 years; a clearcut in the same stand induced suckering and returned dominance to bigtooth aspen. The impending conversion of bigtooth aspen-dominated forests to pine and northern hardwoods in natural and managed stands is of concern to both researchers and resource managers alike. The landscape ecosystem approach can provide a framework for understanding the ecological processes and characteristics that drive ecosystem change at multiple scales (physiographic systems, landforms, and ecosystem types), as well as the flexibility to make decisions at a scale appropriate for research or management objectives.