PARENT SESSION
Oral Session #44: Disturbance ecology of forests: Animals, wind, gaps, edges. Presiding: S. Archer.
Wednesday, August 8, 2001. 8:00 AM to 11:45 AM. Hall of Ideas G.
Temporal and spatial interactions among root and stem insects, fungi, and predators in declining forests.
Erbilgin, Nadir1, Raffa, Kenneth1, 1
ABSTRACT- Declining red pine, Pinus resinosa, stands in the Great Lakes region are characterized by gaps of dead trees, surrounded by trees showing reduced growth. These zones spread progressively into surrounding asymptomatic trees. We sampled stem and root colonizing beetles in seventeen declining and healthy stands in Wisconsin from 1997-1999. We also conducted systematic field excavations and laboratory isolations of various root pathogens. Multiple funnel traps were baited with synthetic pheromones of Ips (Coleoptera: Scolytidae), lower-stem and pitfall traps were baited with a-pinene and ethanol. The major trends associated with stand condition were: 1) Predators of bark beetle were most abundant in stands with low tree mortality. Ips populations declined seasonally in stands with high predator abundance. Factors associated with forest structure contribute to predator abundance; 2) Belowground herbivory plays an important role. Root colonizing beetles, Hylobius and Hylastes, were more abundant in declining stands during their ovipositional periods. However, seasonal dispersal between overwintering and ovipositional sites appears important. Phloeophagous beetles colonizing lower stems were more abundant in declining stands; 3) Root staining fungi, Leptographium, were more prevalent in declining stands. Within-stands, infection was most frequent at the perimeters of tree mortality, but included trees not yet showing aboveground symptoms. These results suggest dispersal plays an important role in the interactions among herbivores, predators, and host plant condition, with specific spatial and temporal patterns contributing to forest decline.
KEY WORDS: forest decline, bark beetles and predators, belowground herbivory, root pathogens