Spatial patterns and climate relationships of major plant traits in the New World differ between woody and herbaceous species

Abstract

Aim Despite several recent efforts to map plant traits and to identify their climatic drivers, there are still major gaps. Global trait patterns for major functional groups, in particular, the differences between woody and herbaceous plants, have yet to be identified. Here, we take advantage of big data efforts to compile plant species occurrence and trait data to analyse the spatial patterns of assemblage means and variances of key plant traits. We tested whether these patterns and their climatic drivers are similar for woody and herbaceous plants. Location New World (North and South America). Methods Using the largest currently available database of plant occurrences, we provide maps of 200 × 200 km grid‐cell trait means and variances for both woody and herbaceous species and identify environmental drivers related to these patterns. We focus on six plant traits: maximum plant height, specific leaf area, seed mass, wood density, leaf nitrogen concentration and leaf phosphorus concentration. Results For woody assemblages, we found a strong climate signal for both means and variances of most of the studied traits, consistent with strong environmental filtering. In contrast, for herbaceous assemblages, spatial patterns of trait means and variances were more variable, the climate signal on trait means was often different and weaker. Main conclusion Trait variations for woody versus herbaceous assemblages appear to reflect alternative strategies and differing environmental constraints. Given that most large‐scale trait studies are based on woody species, the strikingly different biogeographic patterns of herbaceous traits suggest that a more synthetic framework is needed that addresses how suites of traits within and across broad functional groups respond to climate.

Effects of climate, soil, forest structure and land use on the functional composition of the understorey in Italian forests

“…Temperature‐related variables were correlated with all three plant traits, which is in line with recent findings (Moles et al., ; Reich & Oleksyn, ; Šímová et al., ). In particular, temperature seasonality was an important driver of changes in understorey mean values of H and SLA: forest stands characterized by high temperature variation across seasons (thermophilous deciduous and broadleaved evergreen forests located in the Mediterranean Region of Italy) were characterized by shorter understorey communities with high‐SLA values, while forest stands with low temperature variation across seasons (forests of the hilly and mountainous belt of northern and central Italy) were characterized by taller understorey communities with low SLA values.…”

“…Numerous studies have assessed the relationships between the environment and key plant functional traits on a broad scale (Moles et al., , ; Šímová et al., ; Wright et al., , ) that reflect fundamental plant strategies [Leaf–Height–Seed traits (LHS); Westoby, ]. However, generalizable patterns have yet to emerge (Shipley et al., ): trait–environment correlations are often weak, and the strength and sign of these correlations vary across studies (Borgy et al, ; Moles et al., ; Šímová et al., ).…”

Late Quaternary climate legacies in contemporary plant functional composition

“…Biases in trait data coverage could spatially bias our maps of FMs and FD if botanical collecting effort in certain areas were focused on certain taxonomic or functional groups (Borgy, Violle, Choler, Garnier, et al, ). Because our maps of functional composition are broadly consistent with other estimates (Butler et al, ; Šímová et al, ; van Bodegom, Douma, & Verheijen, ), this is unlikely to be a major concern. Nevertheless, trait data and species occurrence are poor in some regions (e.g.…”

“…We derived gridded maps of contemporary FMs and FD (as convex hull volume (Cornwell, Schwilk, & Ackerly, )) across the Americas by merging species‐mean trait data with maps of species distributions. We used five plant functional traits that are representative of major ecological strategy axes (Díaz et al, ; Westoby & Wright, ), and predictive of species sorting along environmental gradients (Moles et al, ; Šímová et al, , ). We then coupled these estimates with contemporary and paleoclimate maps at timescales spanning the Last Interglacial (120 ka) to the present.…”

Robustness of trait connections across environmental gradients and growth forms

“…This suggests plant growth forms differ in their strategies to cope with environmental conditions. The lack of variation in the modulatory of non‐woody species across environments suggests they experience weaker environmental filtering compared to woody species (Šímová et al, ). Weaker environmental filtering in non‐woody species perhaps results from their shorter life span, dormancy (and other bet‐hedging) strategies and lack of long‐persisting, reinforced stems above ground, which in combination may allow them to avoid much environmental heterogeneity.…”