Insect sampling and tree sampling
Beetle sampling was conducted using modified aerial collectors in the canopy and understory area of each forest plot at all sites. Aerial collectors, also called flight intercept traps (FITs), were constructed with two pieces of hard, transparent, plastic plates (50 × 35 cm, height × width) which were arranged crosswise and fixed upon a red or blue plastic bowl (35 × 30 cm, diameter × height). A piece of round, transparent, soft plastic plate with a diameter of 45 cm roofed the top of each FIT to prevent entry of too much precipitation during the rainy season. Within each plot, one trap was installed on canopy tree branches at a height of 10-30 m above the ground, and the second one was placed at the understory at a height of 2 m. The collecting basins of the FITs were filled with a liquid mixture of 75% alcohol and blue colored anti-freeze (ethanol-glycol) at 1:2 v/v. Ten FITs were used in each transect, totaling 90 FITs installed in all three investigated regions.
Owing to the large differences in climatic conditions among the three regions, the start time of collection from traps in each region differed slightly. Field work at Bubeng started in April, 2018 to end in April, 2019, and in Xujiaba and the Yulong mountain in May, 2018 to the end of May, 2019. Our insects sampling work last for 1 year at all plots, traps were emptied every 10 days during the collection periods with few exceptions where traps were destroyed by strong wind or collection was impossible owing to heavy rains. Despite the strict protective measures, we had a total of seven FITs destroyed by accident and the replacements were installed within the following 10 days. The collected specimen preserved alcohol and anti-freeze mixture were filtered and preserved in 70% ethanol liquid,after the first step of specimen cleaning (remove the trash and untargeted insects), we started the morphological classification and recorded the abundance and richness of longhorn beetles from each trap. The identification work was conducted with taxonomists experienced in Cerambycidae identification Voucher specimens of the collected beetles have been deposited temporarily at the laboratory in the Honghe University and they will finally be transferred to the National Zoological Museum of China, Institute of Zoology, Chinese Academy of Sciences, Beijing.
Collection of vegetation data was conducted in April and May of 2019. At each elevation transect, five 25 m × 20 m plots were set up and spaced around 40 m away from each other. These were the same as the plots mentioned above for insect sampling to install the FITs. Therefore, in all three regions, we censused woody plants in 0.25-ha plots using identical field methods at each elevation transect. All plots were established outside of large canopy gaps created by recent anthropogenic and natural disturbances. In each plot, we measured the abundance of each tree species (or morpho-species) ≧ 5.0 cm diameter at breast height (1.2 m). All sampling methods used in the present study comply with the instruction of the Center for Tropical Forest Science (http://www.ctfs.si.edu/) to assemble long term, large-scale forest data from the tropics (Condit, 1995) and the Chinese Forest Biodiversity Monitoring Network (http://www.cfbiodiv.org/). Voucher specimens were collected whenever necessary in the field for later identification with the help of experienced botanists. When establishing plots on slopes, we positioned the plot centerline perpendicular to slopes to minimize elevation gradients within plots. In addition, because sampling in all regions included a similar numbers of plots spanning small and large geographical distances, we were able to compare the potential influence of spatial limitation between regions at similar scales, including scales that encompass typical dispersal distances (seed shadows) from tropical to temperate vegetation (Clark et al. , 1999; Myerset al. , 2013).