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Effects of Grizzly Bear Digging on Alpine Plant Community Structure

Abstract In Alaskan alpine tundra, grizzly bears excavate deep holes in search of ground squirrels, but few studies have tested the importance of grizzlies, or other large mammals, in maintaining plant community structure. We examined 43 bear digs, asking how they affect plant species richness and diversity, recolonization patterns, and plants with different clonal growth strategies. Bears remove most vegetation from digs, and recovering digs had lower species richness than adjacent mature tundra. Mature tundra alone, however, had significantly fewer species than mature tundra and bear digs combined, suggesting that bear digs contribute to the overall richness of tundra communities. Digs develop the highest plant richness and diversity at intermediate ages, but even in new digs the overall species composition is similar to adjacent tundra. Plants of different clonal growth forms reacted differently to bear digs. The two species significantly more common in digs than elsewhere have a nonspreading (phalanx) clonal habit, whereas five of six plant species significantly more common in mature tundra are capable of rapid, diffuse (guerrilla) clonal growth. Overall, bear digs cause less pronounced effects on community composition than mammalian diggings in some other systems, possibly because subarctic alpine tundra is already characterized by high levels of abiotic disturbance.