Ecological consequences of forest fragmentation in the Klamath region

We review the evidence for changes in species composition and population viability caused by forest fragmentation in one of North America's most biologically diverse regions, the Klamath region of northwestern California and southwestern Oregon. Our studies on small mammals and understory plant communities suggest that a number of species are restricted to, or closely associated with, remnant patches of late-successional or old-growth forest. Likewise, we found evidence for changes in population sizes in species that we studied in-depth: California red-backed vole (Clethrionomys californicus Merriam) and western trillium (Trillium ovatum Pursh.). We also identified many species that do not fit the island-ocean analogy that is often applied to habitat fragmentation. For example, some species were found mostly in remnants, while other species were restricted to clearcuts, or were ubiquitous across sites. Evidence from these studies suggests that the landscape matrix can provide important habitat for many species. The conservation of biological diversity in this region will require not only knowing which species are adversely affected by fragmentation and what role remnant habitat plays in the viability of populations; it will also require a better understanding of the role of matrix in providing both habitat and opportunities for dispersal of species between remnants. Studies of matrix conducted in the Cascade and Coast Ranges of Oregon and Washington provide relevant information, but there is a striking paucity of data concerning matrix in the Klamath region, where we predict that the drier, warmer growing season is likely to result in different, species-specific responses to fragmentation. Research on these responses would provide a vital contribution toward understanding how to conserve biological diversity in the Klamath region.