Effects of a Dominant Species on the Functional Diversity of Coexisting Species in Temperate Deciduous Understorey

The herb layer plays a significant role in maintaining forest functions, and its community composition is determined by various abiotic factors and biotic interactions. This study attempted to investigate the interspecific plant–plant biotic interactions using a functional traits approach. Specifically, the effects of a dominant species coverage on the functional diversity of coexisting species in the temperate forest understory were studied. Species coverage and soil moisture data were collected using a 1 m2 quadrat couplet (2 × 1 m2) from six sites alongside a 20 m linear transect encompassing a cover gradient of Allium ursinum in southwest Hungary. Major plant functional dimensions i.e., aboveground, and clonal functional traits were considered. Linear and nonlinear mixed models to quantify the effects of biotic interaction on the functional diversity of every single trait and multiple traits were employed. Both aboveground traits and clonal traits of persistent clonal growth organs responded positively to the A. ursinum L., cover gradient. The coexistence of understory species in the presence of a monodominant species seems to be mainly influenced by aboveground traits as compared to the clonal traits suggesting, a role of niche differentiation. The consistent impact of A. ursinum coverage on coexisting species dynamics highlights a need for similar in-depth studies in various forest settings.

The Legacy of the Past Logging: How Forest Structure Affects Different Facets of Understory Plant Diversity in Abandoned Coppice Forests

Predicting how biodiversity affects ecosystem functioning requires a multifaceted approach based on the partitioning of diversity into its taxonomic and functional facets and thus redundancy. Here, we investigated how species richness (S), functional diversity (FD) and functional redundancy (FR) are affected by forest structure. Sixty-eight abandoned coppice-with-standards plots were selected in two mountain areas of the Apennine chain. We performed linear models to quantify the influence of structural parameters on S, FD and FR of clonal traits. Each diversity facet was affected differently by structural parameters, suggesting a complex interweaving of processes that influence the understory layer. Namely, tree layer density influences S, the height of the standards affects the lateral spread and persistence of clonal growth organs, and diameter of standards affects the FD of the number of clonal offspring. Opposite relationships compared to FD was found for the FR, suggesting how clonal traits play a key role in species assemblage. The observation that structural parameters exert opposite impact on FR seems to indicate a counterbalance effect on ecosystem stability. Multifaceted approaches yield a better understanding of relationship between forest structure and understory, and this knowledge can be exploited to formulate indications for more sustainable management practices.

Are clonal traits and their response to defoliation good predictors of grazing resistance?

Grazing resistance in plants, which can be defined as the ability to grow and reproduce under grazed conditions, is either associated to defoliation avoidance or tolerance. Clonal traits are often neglected when studying functional responses to grazing, despite frequent occurrence in grassland vegetation. We investigated whether clonal traits and response to defoliation were associated to increased grazing resistance. First, grazing resistance was estimated for eight clonal species using abundance patterns in a long-term field study. We then analysed its correlation with traits in undisturbed conditions and responses to defoliation in a garden experiment. A few traits were correlated to grazing resistance, though only one was a clonal trait (belowground clonal biomass). Grazing resistance was negatively correlated to shoot height and belowground clonal biomass and positively correlated to inflorescence biomass, suggesting that tall rhizomatous species investing little in sexual reproduction were at a disadvantage under grazed conditions. Both shoot height and belowground clonal biomass were negatively affected by defoliation but their decrease was significantly less for species that expressed the greatest grazing resistance in the field. Our findings show that incorporating clonal traits slightly improved predictions about field grazing resistance in the eight investigated species.

Spatial patterns in defoliation and the expression of clonal traits in grazed meadows

Clonal plant species dominate meadow vegetation where grazing can generate spatial heterogeneity at different scales and can select for species that express particular sets of clonal traits. This in situ study aimed to characterize fine-grained spatial patterns of defoliation (<1 m) induced by contrasting cattle grazing intensities and to link these spatial patterns with the abundance of species-specific clonal traits. Using correlogams and synthetic spatio-temporal indices, the heterogeneity of vegetation height and leaf damage was monitored along a cattle grazing gradient. Species were identified and their clonal traits retrieved from the database CLO-PLA3. Under moderate grazing, fine-grained spatial patterns of defoliation were not stable over time. Defoliation was heterogeneous during the first months of the grazing season and then became homogeneous. Intensive grazing generated homogeneous defoliation, regardless of the date. In the study meadow, grazing gave rise to communities containing a greater abundance of annual species. However, clonal traits assumed to enable clonal fragments to benefit from heterogeneity do not seem advantageous. Increasing grazing intensity promoted species with clonal traits expected to minimize costs associated with clonality (aboveground clonal growth forms, short-distance lateral spread, and (or) short-lived connections). Ungrazed conditions favoured species with clonal traits associated with a high competitive ability.