Plant functional trait response to environmental drivers across European temperate forest understorey communities

Abstract

Functional traits respond to environmental drivers, hence evaluating trait-environment relationships across spatial environmental gradients can help to understand how multiple drivers influence plant communities. Global-change drivers such as changes in atmospheric nitrogen deposition occur worldwide, but affect community trait distributions at the local scale, where resources (e.g. light availability) and conditions (e.g. soil pH) also influence plant communities.• We investigate how multiple environmental drivers affect community trait responses related to resource acquisition (plant height, specific leaf area (SLA), woodiness, and mycorrhizal status) and regeneration (seed mass, lateral spread) of European temperate deciduous forest understoreys. We sampled understorey communities and derived trait responses across spatial gradients of global-change drivers (temperature, precipitation, nitrogen deposition, and past land use), while integrating in-situ plot measurements on resources and conditions (soil type, Olsen phosphorus (P), Ellenberg soil moisture, light, litter mass, and litter quality).• Among the global-change drivers, mean annual temperature strongly influenced traits related to resource acquisition. Higher temperatures were associated with taller understoreys producing leaves with lower SLA, and a higher proportional cover of woody and obligate mycorrhizal (OM) species. Communities in plots with higher Ellenberg soil moisture content had smaller seeds and lower proportional cover of woody and OM species. Finally, plots with thicker litter layers hosted taller understoreys with larger seeds and a higher proportional cover of OM species.• Our findings suggest potential community shifts in temperate forest understoreys with global warming, and highlight the importance of local resources and conditions as well as global-change drivers for community trait variation. Hansen et al., 2001;Walther, 2010;De Frenne et al., 2011;Bernhardt-R€ omermann et al., 2015;Bjorkman et al., 2018). Important global change drivers affecting temperate plant communities include increased temperatures, changes in Plant Biology 22 (2020) 410-424

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

“…Trait-based approaches are useful for inferring the underlying mechanisms responsible for shaping understory plant assemblages. Disentangling the relative importance of the different processes involved in community assembly (e.g., abiotic filtering, limiting similarity, dispersal limitation) is not only interesting in itself but also crucial for understanding how communities will behave under future environmental scenarios, e.g., temporal changes in understory vegetation due to global environmental change or increasing impacts of disturbances [84,85].…”

“…The inclusion of clonal and bud bank traits, which are associated with vegetative propagation and the re-sprouting ability of plants [8], might be insightful in this context. Similarly, below-ground traits and traits associated with root system properties, including mycorrhizal status, are likely to play an important role in the understory composition of mature forest stands [85].…”

“…Data on the Ellenberg Indicator Values (EIVs; [80]) were incorporated to estimate the mean environmental conditions in each plot. Bioindication with EIVs has been widely used by vegetation scholars to indicate species preferences in their realized niche, which may characterize the environmental conditions in the absence of directly measured parameters [81][82][83][84][85]. We calculated a presence/absence based mean community EIVs from all vegetation, including the tree, shrub and herb layer.…”

Trait-based responses to land use and canopy dynamics modify long-term diversity changes in forest understories

“…SLA is a succession trait, which increases in response to shading (Dahlgren et al, 2006) , whereas LDMC has probably decreased because of its negative covariance with SLA as part of the community-level leaf economics spectrum (Bruelheide et al, 2018) . The negative correlation between canopy SLA and field layer SLA was surprising, since we would have expected canopy leaf traits to correlate positively with field layer leaf traits via litter decomposition-mediated resource availability effects (Maes et al, 2019) . Low canopy SLA is an indicator of relative abundance of Picea abies , an evergreen species with long-lived leaves.…”

“…Some of these management practices, such as ditching and harrowing, directly affect understories by manipulating the soils they inhabit. On the other hand, the tree-layer is a major modulator of resource availability in the understory, as light availability and the amount and quality of litter directly influence growing conditions in the field-layer (Maes et al, 2019) . More information is needed about how different forest management practices affect understories in the long-term (Su et al, 2019) , but differentiating between direct and canopy-mediated effects of management requires long-term concurrent monitoring of canopies and understories in both natural and managed forests.…”