Ecological status of American chestnut (Castanea dentata) in its native range in Canada

Abstract

American chestnut (Castanea dentata (Marsh.) Borkh.) was once a dominant tree in eastern deciduous forests of North America and is now endangered in Canada, primarily because of the introduction of a fungal pathogen (Cryphonectria parasitica (Murrill) Barr) causing chestnut blight. A recovery plan is being developed, and more accurate information on the status of this species in its native range in southern Ontario is needed to assist in the restoration and management of this species. We conducted a 2-year inventory of the distribution and size of trees throughout southern Ontario, and characterized the habitat and incidence of blight. In total, 682 trees were sampled, 601 of which were not planted. Individuals were statistically most likely to occur in deciduous forest habitats with high canopy cover (>50%), gentle slopes (0°–10°), and acidic (pH 4–6), sandy (>75%) soils. Most trees were small (80% were <20 cm diameter at breast height (DBH)) and nonreproductive (86%). Blight cankers were visible on only 25% of trees. Of six habitat variables measured, canopy cover was positively related to tree size (height, DBH) and incidence of blight. Litter depth was also a good predictor of cankers and virulent cankers in particular, but not healing and (or) healed cankers. The presence of Acer and Quercus spp. in the canopy was associated with reduced incidence and number of cankers per tree but increased frequencies of healing and (or) healed cankers, while Carya was correlated with increased incidence and number of cankers per tree. The abundance of American chestnut and the number of blight-free trees in southern Ontario is higher than previously known. The importance of canopy density and associated species in the habitat for tree health will contribute to the development of further research programs and management strategies for the restoration of this endangered species.