The Klamath Region

The Klamath region (or Klamath Mountain Range) is located between southern Oregon & northern California. It connects the Sierras to the Cascades and joins the southern Coast range to the northern Coastal mountains. Geologically the Klamath Range is well known for its complexity. Ecologically it represents an important biographic region of high turnover, where many species reach their northern range limits. The Klamath Mountains are essentially the northern range limit of the California Floristic Province. Mimulus cardinalis (the scarlet moneyflower) is also in this pool of species & reaches its northern range limit in south/central Oregon (see figure - modified from original on Bonap).

Why do so many species reach their range limits at the margins of this ecoregion? Is this high turnover a result of climatic constraints (niche driven range limits), legacies of glacial refugia (dispersal limitation) or perhaps the high topographic & bioclimatic complexity creates suitable microsites allowing for small pockets of populations from southern populations to occupy this area. Of course combinations of these factors along with other mechanisms may be responsible for this tension zone. Over large regions, richness is expected to increase with the geological age of the landscape (more time for speciation - Whittaker (1961)). The challenge is decoupling these processes when transplant studies within and beyond the range cannot be carried out for each species.

The shared range limit for many species in the California Floristic Province and the underlying climatic gradient over the Klamath tension zone suggests climate is the predominant factor limiting these species distributions, but how many are limited by dispersal? Can we make climate change projections for the California Floristic Province as a whole? Will the ecological and topographic complexity of the Klamath region facilitate are restrict the northward migration of species with climate change?