Insect and tree diversity estimation
For beetles diversity, both canopy and understory FITs within each plot were combined as the smallest sampling unit for diversity estimation, and trees diversity were recorded for each plot. The analyses of α-diversity were the number of species recorded in each sampling unit (Appendix 1 and Appendix 2). Because observed species richness values in field studies are typically an underestimate of the actual number of species occurring at a plot (Colwell and Coddington 1994), sampling completeness and estimated species richness were also calculated using the Chao1 (Chao 1984), Shannon 
and Simpson diversity estimator based on sample units.
The β-diversity was calculated using the package ‘vegetarian’ (Charney & Record, 2012) in R. The Horn similarity index was used as recommended by Jost (2007) as the only overlap measure that is not disproportionately biased toward rare or common species. This index is considered a true overlap measure that quantifies the overlap of effective species between sampling units (Tuomisto, 2010). The Horn similarity index is defined as:
1Dβ = (ln2-H βShan)/ln2
where H βShan is the Shannon entropy based on Hill numbers and β-diversity is thus independent of α-diversity (Jost, 2007). We visualized β-diversity as 1-1Dβ (i.e., compositional dissimilarity), such that values of 1 indicate complete species turnover between sampling units.
A second similarity matrix was created treating transects as the unit of sampling using the function ‘sim.table’ in the R package ‘vegetarian’. Additionally, geographic distance matrices were constructed at the plot and transect levels using the function ‘earth.dist’ in the R package ‘fossil’ (Vavrek, 2011). Given that we were computing and comparing turnover between identical sampling units in all cases, it is not necessary to consider the species accumulation curve to check whether sampling is adequate (Kemp & Ellis, 2017).
For the plant phylogenetic α and β diversity, the family and genus names of all the enumerated species (215 species in total) in the APG III system were obtained with the R package ‘plantlist’ (Zhang, 2018). Then, their phylogenetic relationships were examined using the online phylomatic tool (Webb & Donoghue, 2005) (www.phylodiversity.net/phylomatic/) based on the Angiosperm consensus tree from Davies et al. (2004). Further, similarity matrices were constructed for plant phylogenetic β-diversity (PhyloSor Index, Bryantet al ., 2008) with the function ‘phylosor’ in ‘picante’ in R (Kembel et al. , 2010). PhyloSor is a modified Sørensen similarity index which quantifies phylogenetic similarity of communities as the proportion of shared phylogenetic branch-lengths between two samples. And the phylogenetic α diversity were calculated with ‘pd’ in ‘picante’ in R (Kembel et al. , 2010). ‘pd’ is the sum of the total phylogenetic branch length for the sample.