Genetic consequence of widespread plantations of Cryptomeria japonica var. sinensis in Southern China: implications for afforestation strategies under climate change

Cryptomeria japonica var. sinensis is a fast-growing coniferous species that is widely planted in southern China for landscaping and timber production. Large-scale afforestation is frequently associated with alien provenance invasion and could increase the likelihood of intraspecific hybridization, with potentially significant positive or negative effects on local forests. This study is the first investigation of the genetic background of planted C. japonica var. sinensis forests across their distribution. A synthetic approach integrating population genetics and species distribution modelling was used to evaluate the genetic consequences of widespread plantations and predict the species’ future distribution. We found comparable levels of genetic diversity in 11 planted populations and seven ancient tree populations. Plantations in the species’ native range in eastern China were sourced from nearby native forests or ancient trees, so clear genetic structure has been retained in this region. In colonized regions, planted materials were mostly introduced from Zhejiang province, the best-preserved habitat of C. japonica var. sinensis in China. Overall, the species has low genetic diversity compared to its conspecies, C. japonica , in Japan. Fortunately, Maxent modelling indicated that suitable habitats for this species will expand to the northeast and southwest gradually during the next 50 years, indicating promising applications in afforestation under climate change. However, seed transfer zones for the species should be delineated quickly to guard against risks of genetic pattern disruption and adaptation loss. Finally, our results show that rapidly increasing plantation of this species has a negligible impact on ancient trees and highlights an urgent need to conserve remaining genetic resources.