Impacts of multi-year drought on post-fire conifer regeneration

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The results of this study indicate that post-fire natural regeneration in the Blue Mountains over the last 20 years has generally been sufficient to maintain forest resilience. Recruitment differs dramatically, however, across sites. In burned areas with abundant surviving adult trees 100 m away or less and on north-facing slopes, hundreds or thousands of seedlings per hectare may establish within the first 10 to 15 years post-fire. In contrast, conifer densities in large high-severity burn patches (i.e., larger than 100 to 200 m in radius) with high overstory mortality, especially those on warmer sites, may be insufficient to meet local silvicultural guidelines or maintain forest ecosystem function without supplementary replanting. Some of these marginal sites may be susceptible to ecosystem state transitions to shrub or grasslands. The results of this study also suggest that as climate change causes temperatures to warm and increases the probability of growing season moisture deficits, Douglas-fir recruitment may decline in drought-prone sites. Ponderosa pine seedlings may be more resilient to warming conditions, though as warming continues they also will become vulnerable to drought stress.

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