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Genetic diversity is essential because it provides a basis for adaptation and resilience to environmental stress and change. The fundamental importance of genetic variation is recognized by its inclusion in the Montréal Process sustainability criteria and indicators for temperate and boreal forests. The indicator that focuses on forest species at risk of losing genetic variation, however, has been difficult to address in a systematic fashion. We combined two broad-scale datasets to inform this indicator for the United States: (1) tree species occurrence data from the national Forest Inventory and Analysis (FIA) plot network and (2) climatically and edaphically defined provisional seed zones, which are proxies for among-population adaptive variation. Specifically, we calculated the estimated proportion of small trees (seedlings and saplings) relative to all trees for each species and within seed zone sub-populations, with the assumption that insufficient regeneration could lead to the loss of genetic variation. The threshold between sustainable and unsustainable proportions of small trees reflected the expectation of age–class balance at the landscape scale. We found that 46 of 280 U.S. forest tree species (16.4%) may be at risk of losing genetic variation. California and the Southeast encompassed the most at-risk species. Additionally, 39 species were potentially at risk within at least half of the seed zones in which they occurred. Seed zones in California and the Southwest had the highest proportions of tree species that may be at risk. The results could help focus conservation and management activities to prevent the loss of adaptive genetic variation within tree species. [ABSTRACT FROM AUTHOR]

Abstract: A wildfire at Blacks Mountain Experimental Forest provided the opportunity to observe fire severity at the point of transition between treated and untreated stands. At several locations in the forest, the wildfire burned from a dense stand of largely pole-size trees, into an area that had been recently treated with combinations of thinning and prescribed fire. These treatment areas are part of a large-scale experiment designed to evaluate stand structure, grazing and prescribed fire in an interior ponderosa pine (Pinus ponderosa P.&C. Lawson) forest. Tree survival and damage were sampled on strip plots arranged perpendicular to the treatment plot boundary. Logistic regression was used to develop a model relating the probability of initial mortality (within 9 months after the fire) to distance from treatment plot boundary, and treatment history (thinning and prescribed fire). Fire behavior simulation was used to evaluate the effectiveness of the pre-fire stand treatments. The model shows that probability of survival was greatest in those areas that had both thinning and prescribed fire prior to the wildfire event. Survival was near zero for the untreated areas. Survival in thinned-only areas was greater than untreated areas but substantially less than the areas with both treatments. [Copyright &y& Elsevier]