Projecting spatiotemporal changes in suitable climate conditions to regenerate trees using niche differences between adult and juvenile trees

Abstract

Assessing suitable climate conditions to regenerate trees over a large area is of great importance to investigate potential impacts of climate change. In this study, we developed a size-based species distribution model (SBSDM) to assess spatiotemporal changes in the tree regeneration niche separately from the growth niche in adults. Siebold’s beech (Fagus crenata) was selected as the target species. We projected (1) areas where adult and juvenile potential habitats (PHs) overlapped, (2)only-adult PHs, (3) only-juvenile PHs, and (4) non-habitats for 2080–2099 using the SBSDM, a distribution dataset from the Phytosociological Releve Database of Japan, and a future climatic dataset from 24 general circulation models (GCMs). We also projected juvenile PHs for all decades between 2011 and 2099 using four representative GCMs to assess potential lost decades of the regeneration niche. The SBSDM provided sufficient projections of adult and juvenile tree distributions as well as their niche differences under the current climate. Overlapping areas and only-adult PHs were projected to decrease by the end of this century. An increase in only-juvenile PHs was projected to occur in snowy regions, with juvenile PHs starting to decrease in warm and less snowy regions. Furthermore, juvenile PHs are expected to decrease widely around 2060 as well as at the end of this century due to considerable rapid warming around those times. We conclude that regeneration of F. crenata will start to decline in 2060, but snowy conditions will postpone the timing of the regeneration loss, causing an increase in only-juvenile PHs.