Research to bring back the American chestnut
February 23, 2019
The American chestnut (Castanea dentata), which could once reach massive proportions, was described by some as the redwood of the east. It was a common tree in southern Ontario that supported a multitude of other species, some of which were highly dependent on it such as the chestnut ermine moth and the American chestnut moth. The American chestnut also gave rise to an important lumber industry and is well known for its burs comprised of edible fruit shielded by a dense, spiny husk.
In the early 1900s, a fungus causing blight disease was introduced from Asia resulting in massive die offs and a precipitous decline in chestnut populations. The population in southern Ontario is now only 0.1 percent of its former glory and is listed as endangered under Ontario’s Endangered Species Act, 2007. This means that the American chestnut still exists in the wild in Ontario but it is in danger of imminent extinction or extirpation.
Van Drunen et al. (2018) studied the relationship between blight and American chestnut in southern Ontario with the goal of supporting conservation and restoration activities and future research. They drew on data from earlier studies where approximately 600 American chestnut trees were surveyed in 2001 and 2002 (Tindall et al., 2004) and then surveyed again in 2014 and 2015 (plus some additional trees; Van Drunen et al, 2017). They recorded a number of variables from each tree relating to: incidence of blight in 2014-15, gain in blight (i.e., whether healthy in the 2001-02 study but infected in 2014-15), and tree health measured as presence of healing/healed cankers and tree mortality. These variables were then analyzed in conjunction with 14 environmental factors that could influence how the fungus causing blight interacts with American chestnut.
According to the results, the trees exhibiting one or more variables related to the occurrence of blight or tree health were clustered throughout southern Ontario into so called “hotspots”. These hotspots indicate that local environmental factors may be key in moderating interactions between the fungus and American chestnut. Specifically, blight occurrence was predicted by 9 of these factors while tree health was related to 5 environmental factors.
When broken down further, the results demonstrated that the likelihood of having or gaining blight increased with larger American chestnuts, higher elevation, silt soils, and higher temperatures during the growing season. Incidence of blight also increased with proximity of an American chestnut to the nearest stream and less forested area within a 100 m radius while flatter slope was a predictor of gain in blight. Some environmental factors were important when considered together such that precipitation and soil drainage were predictors of incidence of blight while precipitation with both mean growing season temperature and soil texture predicted gain in blight.
With respect to measures of tree health, the chance of finding healing or healed cankers increased with precipitation over the growing season and with greater forested area within 100 m of an American chestnut. Dead trees tended to be larger in size (and presumably older) and were more often associated with north-facing aspects and areas with higher precipitation during the growing season, especially if the tree was on poorly-drained soils. Conversely, American chestnuts with more forest area within 500 m were less likely to die.
This study demonstrates the complex interactions that may exist between the fungus causing blight and American chestnut. The information and data generated will be used to direct future management and recovery strategies of this celebrated and ecologically important endangered species. The team of researchers on this study have been in close contact with the Ontario Ministry of Natural Resources and Forestry, the Canadian Chestnut Council, and the Natural Heritage Information Centre in efforts to bring the American chestnut back from the brink of disappearing from the landscape altogether.
Read the full article (journal subscription required):
Van Drunen, SG, McCune, JL, and Husband, BC. 2018. Distribution and environmental correlates of fungal infection and host tree health in the endangered American chestnut in Canada. Forest Ecology and Management. 427:60-69. doi.org/10.1016/j.foreco.2018.05.051
Van Drunen SG, Schutten K, Bowen C, Boland GJ, Husband BC, 2017. Population dynamics and the influence of blight on American chestnut at its northern range limit: Lessons for conservation. Forest Ecology and Management. 400:375–383. doi.org/10.1016/j.foreco.2017.06.015
Tindall JR, Gerrath JA, Melzer M, McKendry K, Husband BC, Boland GJ, 2004. Ecological status of American chestnut (Castanea dentata) in its native range in Canada. Canadian Journal of Forest Research. 34(12):2554–2563.