2006 Annual Meeting and Arctic Forum | Abstracts

Climate Warming Greatly Restricts Growth and Recovery of Lichens Following Heavy Grazing by Reindeer on a Bering Sea Island

David R. Klein^1
1Institute of Arctic Biology, University of Alaska Fairbanks, PO Box 757020, Fairbanks, AK, 99775-7020, USA, Phone 907-474-6674, Fax 907-474-6967, ffdrk@uaf.edu

Lush, lichen-dominated plant communities on St. Matthew Island in the northern Bering Sea were markedly altered by grazing pressure following introduction of reindeer there in 1944. The reindeer were introduced by the U.S. Coast Guard to provide an emergency food source for their personnel operating a Loran navigational aid station there during the latter part of World War II. The Coast Guard abandoned the island after the end of the war in 1945 and the reindeer increased from 29 animals in 1944 to 6,000 in 1963 in the absence of humans and other potential predators. By 1963, lichens, the primary winter food of the reindeer, had been virtually eliminated in the previously lichen-dominated plant communities on the island. In late January and early February of the following winter, an anomalous weather event of extreme cold and heavy snow fall resulted in a massive and near total die off of the reindeer, with less than 50 animals surviving. No viable males survived, thus in the absence of breeding by the few remaining females, extirpation of the population followed. By 1963, those plant communities that had been lichen-dominated prior to the population explosion of the reindeer had become dominated by vascular plants, mainly sedges (Carex spp.) and willows (Salix arctica). A factor contributing to the loss of lichens, in addition to grazing by the reindeer, was the strong winds common on the island that resulted in large amounts of lichens fractured by grazing and trampling being blown to sea, rather than potentially serving as living propagules for lichen re-growth. When the island was re-visited in 1985, little lichen recovery had occurred in the 22 years following the reindeer die-off. In vegetation plots established in 1957, re-growth of lichen biomass, primarily by "pioneering" species, accounted for less than 10% of lichen biomass in plant communities on adjacent and un-grazed Hall Island where "climax" lichen species predominated in the thick lichen mats. When these vegetation plots on St. Matthew Island were again examined in 2005, 42 years after the reindeer die-off, we were surprised to find no significant changes in lichen biomass as well as species composition within the vegetation plots. A major climatic regime shift in the northern Bering Sea in recent decades, accounting for warming, reduced summer fog, and associated drying is believed responsible for greatly reducing favorability for lichen growth on St Matthew Island. Thus, the warming climate has stabilized change in plant community structure brought about by the relatively short presence of a large herbivore species on the island.