Southern pine beetle-induced mortality of pines with natural and artificial red-cockaded woodpecker cavities in Texas
Southern pine beetle (Dendroctonus frontalis) infestation is the major cause of mortality for red-cockaded woodpecker (Picoides borealis) cavity trees in loblolly (Pinus taeda) and shortleaf (P. echinata) pines. Recent intensive management for red-cockaded woodpeckers includes the use of artificial cavity inserts. Between 1991 and 1996 the authors examined southern pine beetle infestation rates of pines with natural versus artificial cavities in loblolly and shortleaf pine habitat on the northern portion of the Angelina National Forest. No significant difference existed in the rate at which southern pine beetles infested and killed pines with natural cavities versus those with artificial cavity inserts (c2 = 0.84, P > 0.05). Southern pine beetles infested and killed 20 natural cavity trees (25.6 percent) during the 5-year study (78 cavity-tree years) and 19 artificial cavity trees (18.8 percent; 101 cavity-tree years). Data for the entire Angelina National Forest indicate that 40 percent (25 of 62) of the cavity trees killed by southern pine beetles between 1984 and 1996 had been the nest tree during the preceding breeding season. The annual infestation rate of cavity trees appears to be related to southern pine beetle population levels of the surrounding forest. Use of artificial cavities is essential to maintain sufficient numbers of usable cavities for red-cockaded woodpeckers in Texas. Why southern pine beetles appear to preferentially infest active red-cockaded woodpecker cavity trees is still unknown, but may be related to southern pine beetle attraction to resin volatiles produced when woodpeckers excavate resin wells and/or changes in the levels of infestation-inhibiting tree volatiles as a result of cavity and resin well excavation.