Forest management and natural variability: The dynamics of landscape pattern in mountainous terrain.

摘要

Understanding the range of variability in patterns and processes that have historically shaped forest landscapes is of key importance to maintaining biodiversity in managed forests. My objectives in this study were to: (1) develop methods for incorporating topographic influence into landscape pattern analysis; (2) assess options for representing range of natural variability (RNV) in natural disturbance dynamics and landscape pattern and determine the feasibility of the RNV concept for evaluating the effect of timber harvesting and guiding forest management; and (3) assess the suitability of British Columbia forest inventory maps and Landsat Thematic Mapper imagery for the analysis of landscape pattern and reconstruction of historical disturbance dynamics. Study areas were the adjoining Stein River and Cayoosh Creek valleys, located on the eastern flank of British Columbia's Coastal Mountain Range, and the Arrow Timber Supply Area, located in the Selkirk Mountains of southeastern British Columbia.; Topography, especially natural fragmentation of the forest mosaic due to topographic features, was a predominant landscape-shaping factor especially in the Stein-Cayoosh area. In landscapes with steep topographic relief, topography should be given careful consideration, especially when results from focal studies are extrapolated to formulate management guidelines for areas with different topographic characteristics. Efforts to reconstruct historical disturbance dynamics from the standing age structure were substantially hampered by the error inherent in forest inventory age, as well as lack of information on the pre-harvest age of logged areas and age-specific susceptibility to disturbance. Managers and researchers should be aware that assumptions about disturbance dynamics and uncertainties in the data can significantly influence the outcomes of such analyses. In both study areas, harvesting has resulted in loss of old forest, as well as reduced connectivity and reduced interior patch area free of edge influence. However, whereas in the Arrow harvesting impacts could be reduced by changing harvesting pattern, in the Stein-Cayoosh area reducing harvesting impacts would have to entail primarily a reduction in harvesting rates. Thus, adjustments in harvesting pattern to more closely emulate natural disturbances may not be appropriate or sufficient under all circumstances, and successful landscape management will require careful attention to the local context.