Following the near-obliteration of American chestnut (Castanea dentata [Marsh.] Borkh.) by the chestnut blight early in the last century, interest in its restoration has been revived by efforts to develop a blight-resistant form of the species. We summarize progress and outline future steps in two approaches: (1) a system of hybridizing with a blight-resistant chestnut species and then backcrossing repeatedly to recover the American type and (2) transformation of American chestnut with a resistance-conferring transgene followed by propagation and conventional breeding. Several decades of effort have been invested in each approach. More work remains, but results indicate that success is within practical reach. The restoration of C. dentata to its native habitat now appears to be less a matter of time and conjecture than ever before in 90 years of work by public and private entities. The difficult and protracted task of incorporating extraspecific genes for resistance into a tree species with lethal susceptibility to a naturalized pathogen represents perhaps the most extreme of restoration challenges. Its pursuit by a small non-governmental organization supported primarily by philanthropy and volunteers may serve as a model for other species threatened by exotic pathogens or insects.

Advance regeneration in 52 mature mixed-oak stands was analyzed and described. Red maple (Acer rubrum L.) was the most abundant species in the study area. Among oak (Quercus) species, northern red oak (Q. rubra L.) was the most abundant within the Allegheny Plateau physiographic province, whereas chestnut oak (Q. montana L.) was the most abundant within the Ridge and Valley physiographic province. Sixteen stands, for which data are available through the fourth growing season following harvest, were used to describe stand development. Cumulative height, a composite measure of size and density, was used to describe early stand development. Black gum (Nyssa sylvatica Marsh.) and black birch (Betula lenta L.) had dramatic increases in stand density and cumulative height after overstory removal. Cumulative height of northern red oak and chestnut oak showed a faster positive response to overstory removal than red maple. Oak retained its dominance in cumulative height for at least 4 years after harvest. Red maple nevertheless remained the most abundant tree species after overstory removal. Our results suggest that the principal advantage of red maple regeneration is its ability to accumulate in large numbers prior to harvest.

Understory plots in mixed-oak stands in the Ridge and Valley and Allegheny Plateau ecoregions of Pennsylvania were classified to summarize the range of understory conditions common to the region and to evaluate relationships between understory vegetation, overstory conditions, and advance tree regeneration. Factor analysis and cluster analysis were used to identify understory classes. Vegetation cover data including 15 variables (plant species, bare ground, and rocky ground cover) and 4 composite variables (plant species groups) were observed on 1,208 204-m² plots.The eight vegetation classes resulting from the analyses were associated with different overstory compositions and advance regeneration densities. The understory classes identified in this study may provide insight on the distribution and diversity of problematic and nonproblematic vegetation types.

Aim: Based upon species distribution models (SDMs), many studies have predicted that climate change will cause regional extinctions of tree species within the next 50–100 years. SDM‐based predictions have been challenged on procedural and theoretical grounds, but for tree species they are largely beyond the practical reach of direct experimental validation. Here we report the experimental consequences of moving seedlings from ~50 natural populations of each of two ash (Fraxinus) species to experimental sites spanning a range of 10°C colder to 10°C warmer (mean annual temperature) than home environments.Location: Eastern North America.Methods: We measured population‐by‐test‐site survival percentages and mean trunk diameters at an average age of 35 years. We then used linear, mixed‐effect models to develop transfer functions for each species and predict survival and mean annual growth as functions of fixed and random effects including, especially, the climatic distance (CD) between test site and home environment.Results: Survival and growth were highest at CD ≈ 0 and declined as populations were moved to warmer or colder environments, indicating that survival and growth were optimal when populations were in home‐like climates. However, variance around the model fit was substantial, and we could not statistically detect, even at α = .50, elevated mortality following displacements into environments 3.5°C (white ash) and 4.1°C (green ash) warmer in mean annual temperature. Survival rates of 80%–100% were common even within populations subjected to warming conditions greater than those predicted to cause meso‐scale extinctions in this century. We show that within‐population genetic variance, phenotypic plasticity and idiosyncratic aspects of the non‐climatic environment and its interaction with genotype each likely contributed to these unexpected responses to climatic displacement.Main conclusions: Results emphasize the uncertainty that underlies predictions of climate‐induced extinctions of long‐lived woody plants over time frames of 50 to perhaps 100 years into the future.