PARENT SESSION
Symposium #24: Adaptive Management Experimentation in Ponderosa Pine Forest Restoration.

Organized by: PZ Fule and PG Friederici
Wednesday, August 7. 1:00 PM to 4:30 PM. Maricopa Meeting Room, TCC.

Impacts of forest restoration treatments on tree-feeding insects and host suitability in Southwestern ponderosa pine forests.

Kolb, Thomas^*,1, McHugh, Charles², Skov, Kjerstin¹, Wagner, Michael¹, Wallin, Kimberly³, ¹ Northern Arizona University, Flagstaff, Arizona² Coconino National Forest, Flagstaff, Arizona³ Rocky Mountain Research Station, Logan, Utah

ABSTRACT- Insect herbivory can influence forests at scales ranging from individual tissues to landscapes. Effects of forest restoration treatments on insect herbivory are poorly understood and likely depend on relationships among tree host suitability, tree defensive mechanisms, and insect populations. We have studied these relationships for the last 10 years at several restoration experiments and fires located near Flagstaff, Arizona. Thinning presettlement-aged trees to create the open stand structure present prior to Euro-American settlement increased ponderosa pine foliage toughness with or without prescribed burning. This response suggests greater tree resistance against foliage-feeding insects in restored stands. However, descriptions of insect feeding in a recent experiment in the Flagstaff-Urban-Wildland-Interface experiment showed a positive relationship between thinning intensity and weevil feeding and a parabolic relationship for defoliation; this result suggests an important role of other factors on tree suitability for some folivores. Thinning young trees generally increases tree growth and carbon allocation to resin defenses, a key defense against bark beetles. Burning in restoration can have complex effects on tree suitability to bark beetles. Evidence from one study suggests that light surface fires which do not damage the tree canopy increase resin flow, a key defense against bark beetles. In contrast, fire damage to the canopy can reduce carbon allocation to resin, and thus increase tree susceptibility to bark beetles. Moreover, bark beetles and fire damage to the canopy interact to influence tree mortality. Predictions of future bark beetle outbreaks in both restored and non-restored Southwestern ponderosa pines forests are complicated by possible constraints on beetle performance from interspecific competition among insects, climate, and host suitability that are currently poorly understood.

KEY WORDS: Pinus ponderosa, restoration, bark beetle, herbivory