SOUTHERN PINE-BEETLE INFESTATION DEVELOPMENT - INTERACTION BETWEEN PINE AND HARDWOOD BASAL AREAS

We evaluated the interactive effects of pine and hardwood basal areas on stand susceptibility to southern pine beetle during 2 yr. Low and h igh pine basal areas (12 vs. 25 m2/ha, respectively) and presence and absence of hardwoods (11 vs. 2 m2/ha, respectively) were represented i n a 2 x 2 factorial experiment replicated in four blocks of 30-40-year -old pine stands during 1989 and 1990. Infestations were initiated by introducing bolts containing southern pine beetle pupae and callow adu lts from two infested trees into each experimental plot. Bolts were pl aced around a baited tree that provided a focus for attack. During bot h years the dense, pure pine treatment showed significantly greater in festation growth than the other treatments, killing an average of 9 tr ees during 1990 and 6 trees for the 2 yr combined. Infestations in the other treatments killed, on average, only the baited tree. These resu lts demonstrated experimentally that thinned stands are less susceptib le to southern pine beetle and that hardwoods apparently do not increa se susceptibility but may interfere with infestation growth. Implicati ons of these results for forest management are discussed.