| Summary: | Subalpine fir mortality and stand decline are increasingly evident in British Columbia (B.C.). This long-term study confirmed <i>Dryocoetes confusus</i> to be the major disturbance agent in high-elevation subalpine forests, killing over two-thirds of subalpine fir in eleven one-hectare study plots. <i>D. confusus</i> infestations in mature stands can be described as early-, mid-, or late-phase. The transition from the early- through late-phase is characterized by a lowered stem density as high levels of <i>D. confusus</i> attack and remove the largest trees, while other mortality factors kill smaller trees. Initially, live subalpine fir density and <i>D. confusus</i> activity varied among plots. By a final assessment, very little difference was observed in live stems per hectare. Mortality from all factors ranged from 0.5% to 5% annually, reaching as high as 80% in-stand mortality with >6 times more dead than live volume. When subalpine fir density was reduced to <400 sph, the <i>D. confusus</i> attack rate declined. Cumulative mortality increased the average gap size in plots from 11 m<sup>2</sup> to 18 m<sup>2</sup>. Our study also showed that <i>D. confusus</i> might be able to switch to a univoltine life cycle, taking advantage of warmer and longer growing seasons that, in part, could explain the rapid increase in mortality in stands.
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