Development of predictive distribution models for Fagus crenata forests under a climate change scenario

Tetsuya Matsui

The objectives of this study are to clarify the relationships between the macro-scale distributions of Fagus crenata forests and underlying climatic conditions, to assess impacts of climate change on the F. crenata forest distributions. Tree-Based Models (TMs), evaluated as the most accurate predictive distribution models, were used for the analyses. The vegetation data set was extracted from the 3rd National Survey of the Natural Environment (NSNE), with a 1-km2 spatial scale. Four climatic variables (summer precipitation: PRS; winter precipitation: PRW; the minimum temperature of the coldest month: TMC; and warmth index: WI) were extracted from the 1-km2 climatic data set, and used as predictor variables.

Changes in the probability distributions of F. crenata forests by the 2090s under a climate change scenario were predicted, and the vulnerability and sensitivity of the forests to the simulated changes were assessed. TMs for F. crenata forests were developed with the four climatic plus five other variables (topography, surface geology, soil, slope aspect and inclination), which were extracted and modified from the Digital National Land Information database. Areas with the probability of occurrence (>50%) were predicted to decrease by 91% by the 2090s. Vulnerability indices suggest that Kyushu, Shikoku, the Pacific Ocean side of Honshu and southwest Hokkaido will have high numbers of vulnerable F. crenata forests by the 2090s, due to increased WI. F. crenata forests in southwest Hokkaido and the Sea of Japan side of northern Honshu are predicted to reduce their probability of occurrence considerably: indicating high negative sensitivity. The predicted potential forest distributions in Hokkaido shift northwards by the 2090s. However, the warmer and drier Ishikari Plain hinders F. crenata migration.

In terms of conservation management of F. crenata forests under the climate change scenario, intensive in-situ controlling of evergreen trees is necessary in the Pacific Ocean side, ecological corridors are effective in the Sea of Japan side, and protection of current natural vegetation from F. crenata northern migration is required in northern Hokkaido. Monitoring nationwide changes in the forest’s species composition and structure are also necessary.

It was therefore concluded that western Japan, the Pacific side of Honshu and southern Hokkaido will have many vulnerable F. crenata forests by the 2090s and effective conservation strategies for F. crenata forest need to be tailored.