Metacommunity dataset

The study covers a large area of natural forests in Northeastern China. The latitudinal and longitudinal ranges of the study region extend from 39–54°N (across 15 degree range) and 119–134°E (15 degree range), respectively. The climate varies from a middle temperate zone to a cool temperate zone. All these zones are characterized by strong seasonality with four distinctly different seasons. The main precipitation period is between July and September, and there is a harsh dry spring season.In the summer of 2017 and 2018, a total of 455 0.1-ha circlular (radius=17.84 m) forest plots were established in the region. All trees with a diameter at breast height (dbh) greater than 5 cm were identified, measured and mapped in each plot. To minimize the potentially bias resulting from uneven sampling coverage, we sampled a subset of plots to ensure even sampling coverage, leading to 300 plots.We used each of the forest plots and its nearest n neighbouring plots to define a particular regional community as a basis for calculating a species pool. In this study, the β-diversity is calculated in each regional community consisting of five to ten local plots (n=4, to 9, plus the focal plot in each case), respectively. Therefore, n+1 (i.e., 5 to 10) indicates the size of a regional community, and defines the spatial extent of each community (there are six extents: 5, 6, 7, 8, 9, 10 plots).