BC’s Inland Rainforest – Conservation and Community
Assembling the biota of the interior wet belt: separate lines of evidence from paleoecology, phylogeography, and climate models
Daniel Gavin 1
The northern Rocky Mountains support many plant and animal species that are disjunct from their main distribution along the coast. The origin of these disjunctions, whether from recent dispersal from the coast or long-term persistence south of the ice-sheet in Idaho, is a classic biogeographic question. This question is also directly relevant to the sensitivity of this biota to projected climate change. I present, and attempt to reconcile, different lines of evidence from paleoecology (pollen, macrofossils and charcoal from sediments), paleoclimatology (paleoclimate computer simulations and direct reconstructions from sediments), and phylogeography (genetic relatedness of existing populations). I then present the results from paleoecological and paleoclimate studies from small lakes between Kaslo and the Upper Fraser valley. The dominant tree species, western hemlock and western redcedar, became abundant 4000 years ago near Wells Gray Provincial Park, and only within the last 2000 years at the northern and southern edges of the interior wet belt. The very recent vegetation changes in the southern wet-belt may be attributed to the effects of fire and landscape patchiness as much as increased moisture availability. In the northern wet-belt, a lack of sufficient paleoclimate data and detailed pollen records prevents reaching similar explanations. Together, the data suggest that rather than establishing in wave-like migration, hemlock and cedar relied upon pre-dispersed populations established earlier in the Holocene. However, it also suggests that much of the interior wet belt occurs near its climatic threshold and may be one of the most susceptible forest types in British Columbia to future warming. Large questions remain unanswered, including the role of a Pleistocene mesic refugium in northern Idaho, the possibility of early-Holocene eastward migration of plant species through central British Columbia, and the role of fire and landscape dynamics versus climate change as controls of the establishment of the cedar-hemlock zone. No single tool can completely answer these questions. Rather, only the combination of paleoecology, mapping present and past climates, and phylogeographic studies of the same species can address these myriad factors. Additional biogeographic methods may also contribute to understanding the history of individual species, including inventories of disjunct populations, age structures of stands, and zones or gradients of endemism. Comparative (among species) approaches will eventually reveal the rich history of how the interior wet-belt biota assembled.
1 Department of Geography, University of Oregon, Eugene OR 97403-1251. Email: firstname.lastname@example.org
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