Modelling chestnut biogeography for American chestnut restoration

Aim Chestnuts (Castanea spp.) are ecologically and economically important species. We studied the general biology, distribution and climatic limits of seven chestnut species from around the world. We provided climatic matching of Asiatic species to North America to assist the range-wide restoration of American chestnut [C. dentata (Marsh.) Borkh.] by incorporating blight-resistant genes from Asiatic species. Location North America, Europe and East Asia. Methods General chestnut biology was reviewed on the basis of published literature and field observations. Chestnut distributions were established using published range maps and literature. Climatic constraints were analysed for the northern and southern distribution limits and the entire range for each species using principal component analysis (PCA) of fourteen bioclimatic variables. Climatic envelope matching was performed for three Chinese species using Maxent modelling to predict corresponding suitable climate zones for those species in North America. Results Chestnuts are primarily distributed in the warm-temperate and subtropical zones in the northern hemisphere. PCA results revealed that thermal gradient was the primary control of chestnut distribution. Climatic spaces of different species overlap with one another to different degrees, but strong similarities are shown especially between Chinese species and American species. Climatic envelope matching suggested that large areas in eastern North America have a favourable climate for Chinese species. Main conclusions The general biological traits and climatic limits of the seven chestnut species are very similar. The predictions of Chinese species climatic range corresponded with most of the historical American chestnut range. Thus, a regionally adapted, blight-resistant, introgressed hybrid American chestnut appears feasible if a sufficiently diverse array of Chinese chestnut germplasm is used as a source of blight resistance. Our study provided a between-continent climate matching approach to facilitate the range-wide species restoration, which can be readily applied in planning the restoration of other threatened or endangered species.