Light and warming drive forest understorey community development in different environments

Abstract

Plant community composition and functional traits respond to chronic drivers such as climate change and nitrogen (N) deposition. In contrast, pulse disturbances from ecosystem management can additionally change resources and conditions. Community responses to combined environmental changes may further depend on land‐use legacies. Disentangling the relative importance of these global change drivers is necessary to improve predictions of future plant communities. We performed a multifactor global change experiment to disentangle drivers of herbaceous plant community trajectories in a temperate deciduous forest. Communities of five species, assembled from a pool of 15 forest herb species with varying ecological strategies, were grown in 384 mesocosms on soils from ancient forest (forested at least since 1850) and postagricultural forest (forested since 1950) collected across Europe. Mesocosms were exposed to two‐level full‐factorial treatments of warming, light addition (representing changing forest management) and N enrichment. We measured plant height, specific leaf area (SLA) and species cover over the course of three growing seasons. Increasing light availability followed by warming reordered the species towards a taller herb community, with limited effects of N enrichment or the forest land‐use history. Two‐way interactions between treatments and incorporating intraspecific trait variation (ITV) did not yield additional inference on community height change. Contrastingly, community SLA differed when considering ITV along with species reordering, which highlights ITV’s importance for understanding leaf morphology responses to nutrient enrichment in dark conditions. Contrary to our expectations, we found limited evidence of land‐use legacies affecting community responses to environmental changes, perhaps because dispersal limitation was removed in the experimental design. These findings can improve predictions of community functional trait responses to global changes by acknowledging ITV, and subtle changes in light availability. Adaptive forest management to impending global change could benefit the restoration and conservation of understorey plant communities by reducing the light availability.

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

“…There was also a reasonably high posterior probability that deeper canopy shading (increased canopy cover, decreased canopy SLA) leads to field-layer communities with shorter species. These results supplement results from previous studies, in which average height of field layer vegetation in response to less light either remained stable (Maes et al, 2019) or decreased (Blondeel et al, 2020) . Decreasing plant height is an expected response if light is a limiting resource for plant growth, as is the case in forest understories (Blondeel et al, 2020) , especially in the case of herbaceous plants which cannot annually increment their heights.…”

“…Unlike dissimilarity metrics, changes in average functional traits are informative of changing selection pressures on vegetation (Violle et al, 2007) , and resulting ecosystem consequences (Lavorel & Garnier, 2002) . For example, increased light and nutrient availability due to recent forest cuttings should lead to understory communities composed of higher plants, since only taller species can reach the light in conditions of high resource availability (Blondeel et al, 2020) . Furthermore, trait-based results should be transferable between systems with different species pools, facilitating comparisons and meta-analyses that cross system borders (McGill et al, 2006) .…”

Effect of tree canopy on species composition, diversity and biomass of herbaceous vegetation and soil characteristics in semi-arid forests of the Aravalli hills

“…al., 2019). Increasing light availability followed by warming led to establishment of taller herb community in temperate deciduous forest (Blondeel et. al., 2020).…”

Biological Flora of the British Isles: Poa nemoralis

“…Ryser and Wahl (2001) found an SLA of 32 mm 2 /mg, a leaf dry matter content of 0.178 g/g and a leaf area ratio (LAR; area of CO 2 assimilating surface per plant dry mass) of 12.8 m 2 /kg. Blondeel et al (2020) recorded a mean of SLA of 52.5 ± 1.7 mm 2 /mg (PAR = 7.8 µmol s −1 m −2 ; 45 individuals) and 50.0 ± 2.3 mm 2 /mg (PAR = 31.8; 51) in P. nemoralis plants grown in experimental mesocosms in Aalmoeseneie Forest (Belgium).…”