PARENT SESSION
Poster Session #2: Plant-Animal Interactions.
Monday, August 6, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Insect population and tree resistance responses to restoration thinning treatments in Ponderosa pine forests.

Wallin, Kimberly¹, Skov, Kjerstin¹, Kolb, Thomas¹, Wagner, Michael¹, ¹

ABSTRACT- We examined the effects of restoration thinning treatments of ponderosa pine forests on tree water stress and resistance to subcortical and folivorous insects within experimental plots in northern Arizona. Two thinning treatments (partial and heavy) and a control were established in 1999. Thinned treatments had different densities of post-settlement-aged trees in a spatial arrangement that resembled pre-EuroAmerican forests. Controls were dense pre- and post-settlement trees with no thinning. Natural and pheromone-mediated colonization by subcortical insects (Coleoptera: Scolytidae) were negatively related to thinning intensity. Overall colonization density was 23% and 34% higher in trees within controls than in partially and heavily thinned treatments, respectively. In June and August, resin production in response to wounding was greatest in partially thinned treatments. Defoliation caused by chewing insects was parabolically related to thinning intensity, 82% greater in August than June, and negatively related to leaf toughness. Tree pre-dawn water potential in June and August was positively related to thinning intensity. Thus, within two-years of thinning there was increased tree water availability and resistance to insect herbivores.

KEY WORDS: bark beetle, folivores, tree physiology, Ponderosa pine