Southern Pine Beetle Infestation Development: Interaction Between Pine and Hardwood Basal Areas

Abstract

Abstract We evaluated the interactive effects of pine and hardwood basal areas on stand susceptibility to southern pine beetle during 2 yr. Low and high pine basal areas (12 vs. 25 m²/ha, respectively) and presence and absence of hardwoods (11 rs. 2 m²/ha, respectively) were represented in 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 adults from two infested trees into each experimental plot. Bolts were placed around a baited tree that provided a focus for attack. During both years the dense, pure pine treatment showed significantly greater infestation growth than the other treatments, killing an average of 9 trees during 1990 and 6 trees for the 2 yr combined. Infestations in the other treatments killed, on average, only the baited tree. These results demonstrated experimentally that thinned stands are less susceptible to southern pine beetle and that hardwoods apparently do not increase susceptibility but may interfere with infestation growth. Implications of these results for forest management are discussed. FOR. SCI. 39(2):201-210.