Study site
The study site was located at the Xishuangbanna Tropical Botanical Garden (21°54′ N, 101°46′ E) in the Mengla County, Yunnan Province, China. The zonal vegetations here are tropical rain forests and monsoon forests, which is not only a critical region for China’s tropical rain forests, but also the northern limit for tropical rain forests in Southeast Asia. The Xishuangbanna region is an important part of the Indo-Burma global biodiversity hotspots, and harbor over 5000 vascular plant species, which account for 16% of vascular species across China (Cao et al. 2006). The rain forests here not only possess biodiversity that is important both nationally and globally, but also revealed one of the highest forest productivity across China (Fenget al. 1999) as a result of high energy and water availability. Climate in this region is controlled by northern tropical monsoon, with a mean annual temperature of 21.5 °C, and mean temperature in June and January of 25.5 °C and 14.8 °C, respectively. Annual precipitation averaged 1557 mm, of which 1335 mm (87%) occurred in the wet season (May to October), while precipitation during the dry season (November to the next April) accounts for only 13% of annal total. Relative humidity averaged around 80 %, and frost was never recorded in this region.
The dataset
The dataset was provided by the Xishuangbanna National Forest Scientific Observation and Research Station, available at the Chinese Ecosystem Research Network (CERN) (http: //www.cnern.org.cn/). The data we downloaded included: 1) repeated measurements of 10 permanent plots (50 m × 50 m) in the rain forests of Xishuangbanna, including different forest types from secondary to primary forests (Table 1); 2) allometric equations to estimate tree biomass for each forest type (Table S1). 3) Soil variables, including ten soil variables (soil organic carbon, pH, moisture, nitrogen, phosphorous and kalium concentrations, etc.) measured at three locations in each plot in the year of 2010. These 10 plots were established in 2004, each consist of 25 subplots (10 m × 10 m), which were investigated annually from 2004 to 2010. In each subplot by each year, tree species name and diameter at breast height (DBH, 1.3 m) for all individuals with a DBH ≥1.0 cm were recorded.
To examine the effect of grain size on the relative importance of diversity vs. stand factors on ecosystem functions and stability, we split each 0.25 ha plot into subplots with different sizes: i.e. 400 m2, 800 m2 and 1200 m2. As a result, we obtained 61, 30, 20, and 10 (sub)plots with an area of 400, 800, 1200 and 2500 m2, respectively.