It has been demonstrated that local species richness is jointly controlled by several interacting processes. However, the relative importance of forest attributes and topography on forest biodiversity across sites along latitude is unknown yet. Twenty two permanent stem-mapped forest plots covering a broad latitudinal gradient were chosen from CTFS-ForestGEO global network. Each plot was evenly divided into non-overlapping quadrats with the size of 20 m ×20 m. Three forest attributes, stand total number of stems, stand size variation and stand basal area were calculated for quadrats. For each forest plot, structural equation modeling (SEM) was implemented to quantify the relative contribution of these forest attributes and topography to species richness.
In 21 out of 22 forest plots studied, stand size variation positively influenced species richness in the majority of plots, with the exception of non-significant effects in three plots (BCI, Tyson and Wanang) and a negative effect in the Gutian plot. Stand total number of individuals consistently enhanced local biodiversity, with the mean standardized path coefficient 0.50 and the range from 0.212 in the SERC plot to 0.843 in the Jianfengling plot. In contrast, stand basal area displayed a divergent pattern: positive effects in eight plots, negative effects in six plots, and non-significant effects in the remaining eight plots. Total effects of topography summed up across the four topographic variables on species richness demonstrated a significantly negative change along the latitude, with the positive effects in tropical forests and the negative effects in temperate forests. The relative role of topography to stand size variation on biodiversity displayed a significant negative latitudinal gradient. The similar latitudinal gradient was observed when total effects of all three forest attributes considered. These latitudinal patterns indicated that the relative importance of topography and forest attributes on shaping local species richness varied with the latitude from tropical to temperate forests.