# Mowing Modulates the Biotic Filter of Expansive Species

## TL;DR

Mowing increases plant diversity in grasslands by counteracting the effects of expansive species, which reduce diversity by acting as a biotic filter.

## Contribution

The study reveals how mowing modulates the biotic filtering effect of expansive species on plant community diversity.

## Key findings

- Mown grasslands had higher alpha and beta taxonomic and phylogenetic diversity than abandoned ones.
- Expansive species cover reduced alpha diversity but had a weaker effect on beta diversity.
- Mowing intensified the filtering effect of expansive species, likely due to higher species richness.

## Abstract

Disturbance and competition are two strong drivers of plant community formation. Disturbances like mowing in semi‐natural grasslands enhance taxonomic and phylogenetic diversity by preventing the establishment of expansive species, which act as a biotic filter. However, how mowing and expansive species influence alpha and beta diversity, and how mowing may modulate the effects of expansive species on plant communities, remains largely overlooked. We sampled 61 (0.5 × 0.5 m) vegetation plots in abandoned and mown semi‐natural grassland in Central Italy characterised by varying degrees of cover of expansive species. We used Rao's Quadratic Entropy to quantify alpha and beta taxonomic and phylogenetic diversity and we performed multiple regression models to evaluate the effect of management types (mowing and abandonment), expansive species cover, and their interaction. Overall, mown grasslands hosted higher alpha and beta taxonomic and phylogenetic diversity than abandoned grasslands. Alpha taxonomic and phylogenetic diversity decreased with increasing expansive species cover, whereas for beta diversity, only the taxonomic facet is negatively affected. For all diversities except beta‐phylogenetic diversity, we detected a significant interaction between the effect of management types and expansive species cover, with their effects being stronger in mown than abandoned grasslands. Mowing represents a management type capable of counteracting homogenisation due to land abandonment at multiple spatial scales, by allowing a higher number of species with distinct lineages to persist locally. Expansive species acts as a biotic filter in reducing the plant diversity within the community, but its effect on homogenising plant communities was weaker. However, the intensity of this biotic filter was more intense in mown grasslands than in abandoned ones, probably due to higher species richness. Our findings highlight how complex these drivers are and that management can modulate the filterering effect of expansive species.

Management type and expansive species influence plant community diversity in complex ways. Overall increase of expansive species cover acts as biotic filter in reducing the alpha and beta taxonomic and phylogenetical diversity. However, the filtering effect is modulated by management type, being more intense under mown grasslands. Mowing helps counteract vegetation homogenization from land abandonment, but its positive effect diminishes at higher cover of expansive species.