Natural regeneration 10 years after a Douglas-fir tussock moth outbreak in northeastern Oregon.

Abstract

A survey of natural regeneration 10 years after severe grand fir mortality caused by an outbreak of Douglas-fir tussock moth was conducted in the Wenaha-Tucannon Wilderness in the Blue Mountains of northeastern Oregon. Seedling stocking was only moderate, but seedling density was adequate where present. Grand fir is dominating both preoutbreak and postoutbreak regeneration, but ponderosa pine has increased substantially over preoutbreak levels. The largest seedlings are larch, spruce, and pine. These species have the fastest juvenile growth rate and also were not severely defoliated during the outbreak. Certain environmental factors affecting regeneration did not produce strong correlations other than some obvious relations like distance to nearest seed tree. There was a weak positive relation of regeneration density with the presence of litter. Given the past and present management regimes for this area, the pattern of gradual stand dominance by grand fir is the result of natural succession and lack of ground fires. Within a hundred years, history will probably repeat itself with a severe tussock moth outbreak that again reduces the grand fir component of the stand.

Citation

Wickman, B.E.; Seidel, K.W.; Star, G. Lynn. 1986. Natural regeneration 10 years after a Douglas-fir tussock moth outbreak in northeastern Oregon. Res. Pap. PNW-RP-370. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 15 p