LOSSES OF RED-COCKADED WOODPECKER CAVITY TREES TO SOUTHERN PINE BEETLES

摘要

Over an 11-year period (1983-1993), we examined the southern pine beetle (Dendroctonus frontalis) infestation rate of single Red-cockaded Woodpecker (Picoides bo-realis) cavity trees on the Angelina National Forest in Texas. Southern pine beetles infested and killed 38 cavity trees during this period. Typically, within each cavity tree cluster, beetles infested only a single tree (usually the nest tree of the previous spring) during autumn and used the cavity tree as an over-wintering site for brood development. Seven (4 active and 3 inactive) cavity trees (out of 346 cavity tree years) died as a result of beetle infestation during the first five years of the study (1983-1987). In 1988, an intensive habitat management program was initiated on the forest to halt a severe population decline of the woodpecker. During the next six years (1988-1993), a much higher mortality rate was observed; 31 single cavity trees (out of 486 cavity tree years) were infested and killed (χ~2 = 8.8, P < 0.003). Southern pine beetle-caused mortality of cavity trees also was high on other Texas national and state forests during this period. This marked increase of beetle-caused cavity tree mortality during a period of increased intensity of necessary management is of extreme concern. As a result of high beetle-caused mortality of active cavity trees, 64% of active cavity trees being used by Red-cockaded Woodpeckers on the northern portion of the Angelina National Forest during 1993 were artificial cavities. Pines selected by biologists for cavity inserts may produce less resin than those selected by woodpeckers and not provide an adequate barrier against snakes. The relationship between infestation of single active cavity trees and the number of beetle infestations (spots) on the northern portion of the Angelina National Forest from 1984 to 1993 was inconclusive (r = 0.56, P > 0.09, N = 10); further research is needed for a definitive conclusion.