2.1 Study site
This study was conducted from July 2017 to October 2017 at six study sites, which extend from 28°4′ to 29°36′N latitude and from 106°28′ to 108°57′E longitude and are located in three typical karst districts of southwestern China (Youyang (YY) in southeastern Chongqing; Yinjiang (YJ) in northern Guizhou Province; and Beibei (BB) in northwestern Chongqing) (Fig. 1 and Table 1). The three districts are separated by approximately 100~250 km and are characterized by a typical subtropical monsoon climate, with mean annual precipitation and evaporation of 1200 and 1177 mm, respectively, and the average temperature ranges from 6.4 °C in the coldest month (January) to 29.1 °C in the warmest month (July), with a mean annual temperature of 18.5 °C.
The six study sites, which include two shrublands (YY1 and YY2) and four woodlands (BB1, YJ1, YJ2 and YY3), where elevation ranges between approximately 470-857 m asl, are located on a gentle slope of typical karst mountains where the slope, aspect and inclination are basically the same. The vegetation in these areas was strictly protected with the same ways especially after 1998. The shrubland is dominated by drought-tolerant plants, and the most common species includeRhus chinensis Mill.,Rubus coreanusMiq.,Rosa cymosa Tratt.,Berchemia sinica Schneid., and Rubus lambertianus Ser. The dominant tree species in woodland areas are Pinus massonianaL.,Ligustrum lucidum Ait., and Myrsine africana Linn. For nomenclature of the species recorded, see the Flora of China (Wu et al. 2013).