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External Research 2002

Title:
Mixed Red Alder-Sitka Spruce Stands as a Silvicultural Approach to Prevent Damage By the Spruce-Tip Weevil (Pissodes strobi) in Riparian Ecosystems

Principal investigator(s); affiliations(s):
Dr. Robert I. Gara; University of Washington
Dr. Eric Turnblom; University of Washington

Award:
$36,886

Project description:
The overstory shade provided by red alder has been proven to significantly reduce infestation levels of spruce-tip weevil (Pissodes strobi) on Sitka spruce by reducing the high ambient temperatures required by the weevil for sexual maturation, feeding, mating, oviposition, and flight migration. At wide spacings, red alder allows spruce to emerge through the canopy and be constantly attacked by P. strobi; conversely, at narrow spacings, red alder suppresses Sitka spruce growth and development. The hypothesis of this research project is that, at some ideal spacing of overstory red alder, a balance can be achieved whereby acceptable levels of weevil incidence occur and leader growth is not drastically reduced. By studying the presence of spruce-tip weevil activity under a broad range of canopy closure densities, it is expected that this observational study will establish an ideal threshold of minimum damage versus maximum growth.

Project deliverable(s):