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

Abstract

Question In functional biogeography studies, generalizable patterns in the relationship between plant traits and the environment have yet to emerge. Local drivers (i.e., soil, land use, vegetation structure) can increase our understanding of the trait–environment relationship. What is the role of climate and local drivers in shaping abundance‐weighted trait patterns of forest understories at biogeographic scales? Location Italian forests. Methods We selected 201 sites that are statistically representative for the heterogeneity of Italian forests across three biogeographic regions (alpine, continental, and mediterranean). Understorey vegetation was recorded for each site on an area of 400 m2, together with 25 environmental variables related to climate, soil, land use and forest structure. Specific leaf area (SLA), plant height (H) and seed mass (SM) were obtained from databases. Community‐weighted mean (CWM) values were calculated. Variance partitioning was used to identify the relative role of groups of environmental variables on the CWM of traits. Generalized Additive Models were used to assess the relationship between traits and single variables. Results Climate alone and climate–soil interactions explained the largest proportion of the variation of all the traits (13.7% to 22.8%). Temperature‐related factors as well as soil N and P availability were the climatic and edaphic explanatory variables most correlated to trait variation. Forest structure and land use accounted for a smaller percentage of the variation in traits. Land‐use factors alone were important in explaining only SLA variation. Conclusions While climate plays a major role in trait–environment relationships in forest understories, our results highlighted the need to integrate at least soil properties as local drivers of trait variation in broad scale functional biogeography studies of these systems.

The leaf economic and plant size spectra of European forest understory vegetation

“…From an ecological perspective, mature forest understories can be seen as highly selective environments adapted to stable environmental conditions where shade tolerance affects plants' ability to cope with other stressors (Verheyen et al 2003, Su et al 2019). Trait variation across European forest understories, like across their tree layers, is strongly shaped by macroclimate (Chelli et al 2019, Vanneste et al 2019, Maes et al 2020) and soil nutrient availability at regional scales (Gilliam 2006, Hedwall and Brunet 2016, Chelli et al 2019). Furthermore, tree canopy cover and structure can also partially buffer climate variability (Zellweger et al 2020) and influence patterns of light availability (Dahlgren 2006), thus affecting understory traits related to resource acquisition and competition.…”

“…These two mostly independent principal functional trait spectra were computed from four plant functional traits: specific leaf area (SLA) and leaf dry matter content (LDMC) for LES and plant height and seed mass for PSS. Based on previous regional studies from European temperate and boreal forests (Perring et al 2018, Chelli et al 2019, Vanneste et al 2019, Maes et al 2020), we expected environmental harshness (i.e. more extreme temperatures and soil pH, increased climatic seasonality and reduced precipitation) to be associated with a more conservative resource‐use strategy of forest understory plants, and to a lower variation in leaf resource‐use strategies.…”

Intraspecific variability of specific leaf area fosters the persistence of understorey specialists across a light availability gradient

“…Higher SLA values are generally linked to enhanced ability to capture light (Poorter & Bongers 2006; Lohbeck et al 2013); light availability is indeed one of the main ecological constraints in mature temperate deciduous forests associated with complete canopy closure (Chelli et al 2019a; Blondeel et al 2020). This implies that forest floor communities are more acquisitive for light availability, especially when light is scarce ( i.e.…”

Community weighted mean trait data of Italian forest understories

“…We attributed to these species trait values obtained from available databases and literature (see Refs. [6,7]). Trait values were available for ∼75% of the species [6].…”