Which pest is a severe defoliator of Douglas, fir, and other firs, with outbreaks that can last for years and may lead to stands switching to ponderosa?

Which pest is a severe defoliator of Douglas, fir, and other firs, with outbreaks that can last for years and may lead to stands switching to ponderosa?

• A. Douglas fir tussock moth
• B. Cypress tip moth
• C. Spruce spider mite
• D. Larch case bearer

Answer: (A)

This question is about identifying a pest that can cause heavy, multi-year defoliation of Douglas-fir and true firs and, in turn, push stand composition toward ponderosa pine. The Douglas-fir tussock moth is known for producing severe defoliation of Douglas-fir and true firs, with outbreak cycles that can last for several years. Repeated defoliation reduces photosynthesis, slows growth, and increases stress or mortality in trees, which in mixed stands can create openings that favor ponderosa pine and lead to a shift in species composition. The other pests listed either do not target Douglas-fir and true firs in such prolonged outbreaks or do not typically drive the same kind of stand composition change.

This question is about identifying a pest that can cause heavy, multi-year defoliation of Douglas-fir and true firs and, in turn, push stand composition toward ponderosa pine. The Douglas-fir tussock moth is known for producing severe defoliation of Douglas-fir and true firs, with outbreak cycles that can last for several years. Repeated defoliation reduces photosynthesis, slows growth, and increases stress or mortality in trees, which in mixed stands can create openings that favor ponderosa pine and lead to a shift in species composition. The other pests listed either do not target Douglas-fir and true firs in such prolonged outbreaks or do not typically drive the same kind of stand composition change.