Abstract
Species- and trait-environment linkages in forest plant communities continue to be a frequent topic in ecological research. We studied the dependence of floristic and functional trait composition on environmental factors, namely local soil properties, overstory characteristics, climatic parameters and other abiotic and biotic variables. The study area comprised 50 monitoring plots across Slovenia, belonging to the EU ICP Forests monitoring network. Vegetation was surveyed in accordance with harmonized protocols, and environmental variables were either measured or estimated during vegetation sampling. Significant predictors of species composition were identified by canonical correspondence analysis. Correlations between plant traits, i.e. plant growth habit, life form, flowering features and CSR signature, were examined with fourth-corner analysis and linear regressions. Our results show that variation in floristic composition was mainly explained by climatic parameters (mean annual temperature, mean annual precipitation), soil properties (pH) and tree layer-dependent light conditions. Trait composition was most closely related with tree layer characteristics, such as shade-casting ability (SCA, a proxy for light availability in the understory layer), tree species richness and tree species composition. Amongst soil properties, total nitrogen content and soil texture (proportion of clay) were most frequently correlated with different species traits or trait states. The CSR signature of herb communities was associated with tree layer SCA, soil pH and mean annual temperature. The floristic composition of the studied herb-layer vegetation depended on temperature and precipitation, which are likely to be influenced by ongoing climate change (warming and drying). Trait composition exhibited significant links to tree layer characteristics and soil conditions, which are in turn directly modified by forest management interventions.
Highlights
Herb-layer vegetation harbours the highest diversity of vascular plant species in temperate forests (Gilliam 2007; Thrippleton et al 2016)
Temperate forest understories are inhabited by plant species with distinctive life-history strategies that manifest as functional traits adapted to local environmental conditions (Durak and Durak 2021)
mean annual temperature (MAT) was most strongly correlated with the first axis (r = - 0.92), whereas mean annual precipitation (MAP) (r = 0.76), tree layer shade-casting ability (SCA) (r = 0.49) and soil pH (r = 0.58) exhibited a stronger correlation with the second correspondence analysis (CCA) axis (Fig. 2)
Summary
Herb-layer vegetation harbours the highest diversity of vascular plant species in temperate forests (Gilliam 2007; Thrippleton et al 2016). Not directly targeted during forest management interventions, this forest stratum plays a key role in the functioning of forest ecosystems (Landuyt et al 2019). It may serve as a good ecological indicator and its species composition results from a complex interplay between numerous environmental drivers and spatiotemporal resource gradients Species composition and diversity and the cover of herb-layer communities might be filtered by other environmental stressors, such as low nutrient availability on silicate bedrock or a water deficit on drier sites (lower soil moisture and air humidity) (Catorci et al 2011). Growth and reproduction in resource-limited conditions can be achieved by a broad spectrum of ecological strategies, spanning from long-living organisms (trees) to annual herbaceous species (Silvertown et al 1993)
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