Decay dynamics and avian use of artificially created snags
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The loss of standing dead trees (snags) from logging has led to artificial creation of snags to help maintain cavity-nesting species. We compared two methods of snag creation: cutting tops and girdling. A total of 1189 trees of 10 coniferous species was treated between 1991 and 1997 on timber sales in northeastern Washington, USA. We monitored 1108 trees at approximately 2 years intervals to determine degree of decay (on a nine-point scale), signs of foraging, and presence of cavities. Nearly 7% of the girdled trees were still alive after 4-7 years, whereas all but one topped tree died. Initial decline (i.e., reaching decay class 2) was faster for ponderosa pine (Pinus ponderosa) and western larch (Larix occidentalis) than for Douglas-fir (Pseudotsuga mensiezii). Western larch lost bark (decay class 4) earlier than other species. Topped trees declined more quickly than girdled trees, but girdled trees reached decay class 4 faster. The proportion of trees with evidence of foraging and cavities increased with decay class. Western larch was used more for foraging than other species, and there was no effect of treatment on foraging use. In contrast, topped Douglas-fir and grand fir were used more for foraging than girdled trees at later decay classes. Cavities were observed only in trees that were topped. Interspecific differences in presence of cavities were not observed before decay class 4; western larch had the lowest frequency of cavities, whereas grand fir had the highest. The use of specific treatments for creating snags and selection of species may make these habitat elements available over long time periods.