A trait‐based approach reveals the importance of biotic filter for elevational herb richness pattern

Abstract

Aim To evaluate how a biotic filter (overstorey cover [OC]) shapes an elevational herb richness pattern and to test whether intermediate elevations represent more suitable habitats for herb species due to the minimal biotic and moderate abiotic filtering that occured there. Location Dongling Mountain, China. Taxon Herbs. Methods We sampled herb richness along a 1,000‐m vertical transect (OC and elevation covary) and four horizontal transects (across the OC gradient with no change in elevation). Functional traits related to shade (leaf mass per area [LMA] and leaf stem ratio [LSR]) and freezing tolerance (leaf thickness [LT] and hair density [HD]) were collected based on vegetation sampling plots. We divided the richness data into below‐ and above‐timberline groups and then assessed the most important driver for each group. By estimating the variations in species richness and functional diversity along horizontal transects, we examined how these parameters responded to OC while controlling for associated differences in elevation. Results Herb richness showed a unimodal relationship with elevation, with a peak around the timberline. Below the timberline, herb richness was better predicted by OC and showed a positive relationship with the functional diversity of LMA and LSR. The frost period performed better in predicting herb richness above the timberline, and herb richness was positively related to the functional diversity of HD. Main conclusions The results support our hypothesis and highlight the importance of OC in shaping herb richness patterns. Below the timberline, OC acts as a filter, sorting species based on their ability to tolerate shade, whereas the frost period limits richness above the timberline and favours species that can tolerate low temperatures. Therefore, we suggest that biotic interactions, as well as environmental and geographical factors, should be considered the main drivers of elevational plant richness patterns.

Plant Diversity Along the Urban–Rural Gradient and Its Relationship with Urbanization Degree in Shanghai, China

“…This can be explained by intermediate disturbance hypothesis or other urban-related disturbances, similar to previous studies in Chinese cities [14,92,93]. In addition, the majority of the annual herbs we recorded are ruderal species, which evolve with different survival strategies to diverse habitats and multiple disturbances [94][95][96]. Exotic plant species richness exhibited a slightly negative quadratic relationship with urbanization degree, which means the introduction of an exotic plant could increase the total plant species richness associated with the urbanization process, which was also demonstrated by previous studies [75,97].…”

Forest community assembly is driven by different strata‐dependent mechanisms along an elevational gradient

“…Here, we found that overstorey functional diversity also had a negative effect on the functional diversity of understorey communities. This result suggests that overstorey trees could act as a biotic filter that structures understorey communities (Jiang et al, ). Meanwhile, canopy cover could be related to the composition and diversity of ground‐layer plant communities, because light conditions are generally thought to be an important resource in the forest understorey (Shigyo et al, ).…”

“…This result suggests that overstorey trees could act as a biotic filter that structures understorey communities (Jiang et al, 2018).…”

“…However, for understorey strata, apart from abiotic stress, overstorey species can act as a filter in the structuring of these communities by reducing resource availability (i.e. light, soil; Halpern & Lutz, ; Jiang, Ma, Liu, & Tang, ). Given this, we assume that phylogenetic or functional structure of the understorey should be more clustered compared to that of canopy trees.…”

Factors that shape the elevational patterns of plant diversity in the Yatsugatake Mountains, Japan

“…Elevation is a key factor that determines the patterns of plant diversity in mountainous areas (Jiang et al, 2018;Körner, 2007;Lee et al, 2013;Lee & La Roi, 1979). The patterns of plant diversity are often explained by several hypotheses for elevational diversity gradient such as the mass effect, mid-domain effect, and Rapoport's elevational rule.…”