Ecological consequences of forest fragmentation in the Klamath region

We review the evidence for changes in species composition and population vi ability caused by forest fragmentation in one of North America's most biolo gically diverse regions, the Klamath region of northwestern California and southwestern Oregon. Our studies on small mammals and understory plant comm unities suggest that a number of species are restricted to, or closely asso ciated with, remnant patches of late-successional or old-growth forest. Lik ewise, we found evidence for changes in population sizes in species that we studied in-depth: California red-backed vole (Clethrionomys californicus M erriam) and western trillium (Trillium ovatum Pursh.). We also identified m any species that do not fit the island-ocean analogy that is often applied to habitat fragmentation. For example, some species were found mostly in re mnants, while other species were restricted to clearcuts, or were ubiquitou s across sites. Evidence from these studies suggests that the landscape mat rix can provide important habitat for many species. The conservation of bio logical diversity in this region will require not only knowing which specie s are adversely affected by fragmentation and what role remnant habitat pla ys in the viability of populations; it will also require a better understan ding of the role of matrix in providing both habitat and opportunities for dispersal of species between remnants. Studies of matrix conducted in the C ascade and Coast Ranges of Oregon and Washington provide relevant informati on, but there is a striking paucity of data concerning matrix in the Klamat h region, where we predict that the drier, warmer growing season is likely to result in different, species-specific responses to fragmentation. Resear ch on these responses would provide a vital contribution toward understandi ng how to conserve biological diversity in the Klamath region.