Sampling design
A spatially nested sampling approach referring to the design described in Kemp & Ellis (2017) was followed. To compare the role of elevation effects on β-diversity of beetle species distribution within the three different regions, we established three elevation transects at each region close to the above mentioned large permanent plots with the same range of elevation gradient covering almost 400 m in height. Each transect included five forest plots with the intermediate grain size of 25 × 20 sq. m established for the installation of beetle collection devices. Anthropogenic and natural disturbances, such as large canopy gaps in the plots, were avoided. All five forest plots at each transect were oriented parallel to respective contour lines and arranged with the least distance being 40 m away from each other. Each sampled transect is described below.
The tropical transects were located in Bubeng, Xishuangbanna (21.61° N, 101.58° S). This area borders Myanmar on the south-west and Laos on the south-east. Mean annual temperature and rainfall are 22 °C and 1500 mm, respectively. The rainy season ranges from May to October and dry season ranges from November to April. Approximately 80% of annual precipitation occurs in the rainy season. Three transects at different elevations (600, 800, and 1000 m) were selected based on current vegetation and topography conditions. The shortest distance between the three transects was around 0.5 km.
The subtropical transects were located in Xujiaba of the Ailao mountains (24.53° N, 101.03° S), which was about 329 km away from Bubeng (Fig. 1). The mean annual temperature and rainfall are 11 °C and 1900 mm, respectively, with a dry season between December and April. This area encompasses a large tract of evergreen broad-leaved forests primarily dominated by Lithocarpus and Castanopsis at mid elevation (ca. 2200-2600 m a.s.l.) with dense or sparse understory of bamboo, andRhododendron dwarf forests toward higher elevations. Three transects at different elevations (2200, 2400, and 2600 m) were selected based on the vegetation and topography conditions, with an average distance of around 1.7 km between the three transects.
The temperate transects were located in the Yulong mountains of Lijiang (27.14° N, 100.23° S). The climate of this area has an average temperature of 5.5 °C, with average annual rainfall around 1600 mm. This area encompasses a large tract of temperate coniferous forests primarily dominated by Berberidaceae , Caprifoliaceae, andRosaceae as the understory. Both Pinaceae andFagaceae plants dominate the canopy and have a relative higher importance value. Similar to the transects in tropical Bubeng and subtropical Xujiaba, three elevation bands (3200, 3400, and 3600 m) were selected for insect sampling and vegetation inventory, with an average of around 1.4 km between the three transects.