Climatic data availability
To characterize the climatic conditions at each site, we extracted eight variables from the BIOCLIM database (Hijmans et al. , 2005; available online): BIO1 (mean annual temperature, °C; AT), BIO4 (temperature seasonality, expressed as the standard deviation of temperature across months; ST), BIO5 (maximum temperature of the warmest month, °C; MAXT), BIO6 (minimum temperature of the coldest month, °C; MINT), BIO12 (mean annual precipitation, mm; AT), BIO13 (precipitation of the wettest month, mm; WP), BIO14 (precipitation of the driest month, mm; DP) and BIO15 (precipitation seasonality, expressed as the standard deviation of precipitation across months; SP). These variables include annual climatic means, climatic extremes and seasonality aspects.
Soil physicochemical property measurements
To characterize the soil properties at each site, we collected six upper mineral soil cores (0–10 cm) from random locations within each quadrat and mixed them thoroughly to produce a composite sample. The soil samples were then stored at 4℃ for later analysis. Samples were first sieved through a 2-mm screen to remove stones and visible plant roots, before air-drying at 25℃. Soil pH and electrical conductivity (mc/cm; EC) were determined using a 1:5 (w/v) soil-to-water solution. Soil total carbon (mg/g; Soil C) and total nitrogen (mg/g; Soil N) were measured on ground soil samples using an elemental analyzer (Elementar vario MACRO cube, Germany). Soil water content (SWC, %) was determined gravimetrically by quantifying the weight lost after oven-drying 100 g of fresh soil at 105℃ for 48 h.