Bark beetle attacks on ponderosa pine following fire in northern Arizona

There is little quantitative information on relationships between insect attacks and fire damage for ponderosa pine, Pinus ponderosa Douglas ex Lawson, in the southwestern United States. Tree mortality and insect attacks were measured on 1,367 trees for three years after a spring wildfire (4 May 1996), a summer wildfire (20 June 1996), and a fall prescribed fire (9 September 1995) in northern Arizona. Western pine beetle, Dendroctonus brevicomis LeConte, mountain pine beetle, D. ponderosae Hopkins, roundheaded pine beetle, D. adjunctus Blandford, red turpentine beetle, D. valens LeConte, Ips species, and wood borers in the Buprestidae and Cerambycidae families were found in fire-damaged trees. The most frequently occurring insects, listed from most to least frequent, were wood borers, red turpentine beetle, Ips spp., western pine beetle, roundheaded pine beetle, and mountain pine beetle. Trees attacked by Dendroctonus and Ips spp. as a group had more crown damage from fire than unattacked trees. The percentage of trees attacked by Dendroctonus and Ips species was lowest during the fall fire (11%, 25 of 222 trees), intermediate during the summer fire (19%, 154 of 833 trees), and highest during the spring fire (41%, 127 of 312 trees). More than one-half of all wood borer colonization (58%) and attacks by western pine beetle (68%), roundheaded pine beetle (56%), and Ips spp. (66%) occurred in the first year after the fire. Measures of tree damage from fire and insect attacks were used to develop logistic regression models of tree mortality to quantitatively investigate factors that influenced tree mortality. Tree mortality 3 yr postfire was low until crown damage by fire exceeded 70-80% for unattacked trees, 40-50% for trees with partial attacks by Dendroctonus and Ips species, and 30-40% for trees with mass attacks. We concluded that several Dendroctonus and Ips species colonize fire-damaged ponderosa pines in northern Arizona and colonization is promoted by heavy crown damage from fire.