Community assembly in a tropical cloud forest related to specific leaf area and maximum species height

Abstract

Question We tested whether co‐existing tree species in tropical dwarf forests were deterministically assembled along gradients of air temperature, relative humidity and light availability, according to two important functional traits, specific leaf area (SLA) and maximum species height (Hmax). Location Tropical montane cloud forest, Bawangling Nature Reserve, Hainan Island, south China. Methods Null model analyses were used in conjunction with trait and species composition data collected to test our hypotheses at four plot sizes (25 m2, 100 m2, 400 m2 and 900 m2), addressing whether the consistent importance of variation in SLA and Hmax extends to these unique forests, as well as theoretical predictions concerning how patterns change with plot size. Results Low SLA species were significantly over‐represented within forest communities for the two largest plot sizes, and taller‐growing tree species were over‐represented across all four plot sizes. Plot‐level analyses indicated that low SLA species were associated with lower temperatures. Conclusions Our results show that tropical dwarf forests are deterministically assembled with respect to these two traits, and are consistent with other studies indicating that SLA responds to abiotic filters. Co‐existing tree species were not significantly divergent for these two traits, indicating that variation in these two traits among trees does not contribute to niche differences (i.e. limiting similarity) and therefore co‐existence within forest plots. Finally, our study demonstrates that patterns of community assembly change with plot size; however, trait convergence did not increase with plot size as previously predicted.

Patterns of Understory Community Assembly and Plant Trait-Environment Relationships in Temperate SE European Forests

“…Assembly mechanisms have been widely studied [3,5], especially in non-forest vegetation types [5,14,19,23,32]. Regarding forest ecosystems, relevant studies have so far been either conducted in (sub)tropical forests [27,33] or have focused solely on tree species in the overstory layer [4,34], woody plant species [35] or tree sapling communities [17]. In recent years, there has been increasing research focus on understory (herbaceous) forest communities [18,21,24,30,36].…”

“…Apart from environmental effects on community assembly patterns, there has been an active debate among community ecologists about how the relative importance of community assembly mechanisms may depend on the spatial scale of observation [27,32,33,43]. When spatial scale, i.e., the unit of observation (e.g., plot size), is reduced, patterns of trait divergence can be enhanced [10].…”

Changes in Patterns of Species Co‐occurrence across Two Tropical Cloud Forests Differing in Soil Nutrients and Air Temperature

“…Species aggregation can be caused by microhabitat heterogeneity, such as the variability in forest-floor micro-relief (Armas et al 2012), light (Holz et al 2002) and soil properties (Roiloa & Retuerto 2006). In this study, however, species in TDF are under long-term air temperature stress (Table 1, Long et al 2011a andb, Long et al 2015). Species living under abiotic stress in TDF may survive and stably coexist by facilitative interactions that improve the abiotic and biotic conditions of neighbours (Choler et al 2001, Callaway 2007, Holmgren & Scheffer 2010, Long et al 2013.…”

“… and b, Long et al . ). Species living under abiotic stress in TDF may survive and stably coexist by facilitative interactions that improve the abiotic and biotic conditions of neighbours (Choler et al .…”

“…The importance of competition increased as soil resources decreased from TMEF to TDF, while the importance of facilitation increased with increasing air temperature stress from TMEF to TDF. In addition, variation in soil phosphorus and air temperature contributed to trait-based assembly rules related to specific leaf area and plant height in these forests (Long et al 2011a(Long et al ,b, 2015.…”