Multiple drivers of plant diversity in forest ecosystems

Abstract

Aim Theoretical and empirical studies have shown that climate is a major determinant of species richness, yet the importance of climate relative to local site conditions remains unclear in forest ecosystems across large regions. Furthermore, little is known about how climate and local site conditions affect species evenness and understorey plant diversity. Location Canadian forest (42°37′ to 68°14′ N; 53°25′ to 134°46′ W; 4 to 2170 m elevation). Methods Using national, broad‐scale forest inventory data, we tested the influence of growing degree days (GDD), climate moisture index (CMI), soil drainage class (SDC) and stand age (SA) on plant diversity across Canada's forests. Diversity was assessed on variable plot sizes from 125 to 500 m2 for canopy tree and total plant species, and from 100 to 400 m2 for understorey plants. Results Our models accounted for 47, 30 and 49% of total variation in canopy tree species richness, Simpson's dominance index and total plant species richness, respectively. After accounting for the effects of plot size and management history, canopy richness increased with GDD and CMI and peaked at intermediate SDC and SA. Simpson's dominance index decreased with increasing GDD and CMI and was lowest at intermediate SDC and SA. Total species richness was most strongly related to SDC and was highest on imperfectly drained soils. Climatic controls on species richness of understorey strata were generally weaker than those on canopy richness. Main conclusions Our results for canopy richness along a mainly longitudinal gradient demonstrate the positive effects of energy on tree species diversity and show evidence for the effects of local site conditions and secondary succession on diversity. Furthermore, our results show that the extent of the influence of climate and local site conditions on plant species diversity can strongly differ between vegetation strata.

Aboveground biomass of understorey vegetation has a negligible or negative association with overstorey tree species diversity in natural forests

“…For example, GDD positively promoted overstorey tree biomass, but had a negative impact on the understorey aboveground biomass. We speculate that differences in responses of different growth forms and strata may be cumulatively affected by environmental factors that influence the species diversity of each growth form and stratum (Zhang et al ., ), in conjunction with the filtering effects of available resources by overstorey tree layers on forest functions and services (Oberle et al ., ).…”

“…Specifically, the challenges of missing data and the partial incompatibility of definitions and classifications between provincial agencies (e.g. heterogeneity introduced by variability in sampling schemes between provincial agencies) (see Zhang et al ., ) as well as departures from normality, homogeneity of variance and the strong collinearity among predictors (http://onlinelibrary.wiley.com/doi/10.1111/geb.12392/suppinfo), prevent conventional parametric statistics from being effective. BRT analysis is an increasingly recognized statistical method that combines the advantages of regression trees through recursive binary splits and adaptive model averaging.…”

Latitudinal patterns and environmental drivers of moss layer cover in extratropical forests

“…Sandholt, Rasmussen, & Andersen, ). Indeed, temperature was shown to have a negative influence on species richness across Canadian forests, where latitudinal climatic gradients explained 19% of the variability, although lichens were pooled with mosses in that study (Zhang, Chen, & Taylor, ), potentially obscuring moss distribution patterns (cf. Cornelissen et al, ).…”

Individual size inequality links forest diversity and above‐ground biomass

“…; Zhang, Chen & Reich ). Moreover, we found that sites with medium soil nutrient regime, corresponding to well‐drained soils (Beckingham, Nielsen & Futoransky ) suited for most boreal tree species, have higher tree species diversity (Zhang, Chen & Taylor ) and thus tree size inequality (Fig. S3) and productivity.…”