THE RELATIONSHIP BETWEEN HARVEST RATE AND CONFIGURATION ON FOREST FRAGMENTATION: AN ANALYSIS OF THE MAINE FOREST PRACTICES ACT
John M Hagan, III and Randall B. Boone
Manomet Observatory, Inc. (JMH)
81 Stage Point Road
P.O. Box 1770
Manomet, Massachusetts 02345
Maine Cooperative Fish and Wildlife Research Unit and the
Department of Wildlife Ecology (RBB)
5755 Nutting Hall
University of Maine
Orono 04469-5755
Fragmentation of habitats is a primary concern of conservation biologists and landscape ecologist that seek to conserve biological diversity. An important source of fragmentation in Maine is forest harvesting, especially clearcutting. There are many geometric patterns that may be used to harvest forest products (e.g., many small clearcuts, a few large clearcuts, small and large clearcuts, partial cuts of various sizes). Each pattern of harvest would yield a distinct pattern of fragmentation, with some patterns better ecologically than others.
In Maine, the geometric pattern of forest harvesting is being affected, in part, by a piece of legislation, the Maine Forest Practices Act (MFPA), implemented in 1990. The act placed restrictions of the size of clearcuts, and required that buffer strips and separation zones be associated with clearcuts over given size requirements (Fig. 1a, Fig. 1b, Fig. 1c). Forest product interests in Maine have reduced the size of clearcuts in response to the MFPA, and have conducted more partial cuts, to which the law does not apply.
To explore some potential long-term effects of the Maine Forest Practices Act on forest configuration, we simulated five harvest patterns in a generalized township. The township modelled was 36 square miles, initially with forest coverage of a uniform age. Each harvest practice was simulated for up to 150 years, with harvest rate varied across simulations. Harvests were modelled in accordance with the MFPA (except for rolling clearcuts), as much as possible (i.e., size categories, buffer distances, and separation zones were modelled, whereas regeneration standards were not). We modelled: 1) 35 acre clearcuts, representing forest practices observed since the MFPA was passed (Fig. 2a, Fig. 2b); 2) 100 acre clearcuts (Fig. 3a, Fig. 3b); 3) clearcuts between 35 and 500 acres, selected randomly from a uniform distribution (i.e., equal probability for any size from 35 to 500 acres) (Fig. 4a, Fig. 4b); 4) clearcuts selected from a distribution with many small (minimum 5 acres) and fewer large (maximum 500 acres) clearcuts (Fig. 5a, Fig. 5b); and 5) rolling clearcuts, illegal under the MFPA (Fig. 6). Similar geographic patterns were simulated, using partial cuts of from 10% canopy coverage removal to 50% removal.
The simulations were conducted on an IBM Risc 6000 25T, using a program written by one of us (RBB) in C, and incorporating the graphical features of the X Window System. The program FRAGSTATS (McGarigal and Marks 1994) was used to calculate landscape metrics. Results will be presented as a series of trends and fragmentation patterns.
