Undesirable Woody Establishment is Driven by Herbaceous Cover Phylogenetics and Abiotic Conditions

Abstract

Abstract Revegetation with herbaceous covers is widely used to inhibit tree encroachment in managed areas. However, most studies tend to focus on species selection for inclusion in seed mixtures, neglecting the effect of local contingencies such as soil conditions and native vegetation emerging from the seed bank. Here, we tested the joint effect of sown herbaceous mixtures and local site conditions on the encroachment of undesirable woody species. In a recently cleared right-of-way, we sowed mixtures containing either 3, 5, or 8 species. Over two consecutive years, we allowed spontaneous vegetation to be established. We measured three facets of its diversity: taxonomic, functional and phylogenetic. We also evaluated how woody encroachment was spatially structured and influenced by soil physico-chemical properties. Our study illustrates how successful revegetation strategies for inhibiting tree species should account for both mixture effectiveness in ideal conditions and their ecological versatility (i.e., their ability to regenerate and thrive in various soil types and climatic conditions). The inhibition of woody species also involved multiple mechanisms, with phylogenetic diversity metrics being the dominant predictors of tree encroachment in the first year. However, the significance of abiotic mechanisms intensified in the second year. This temporal shift added complexity to identifying the most effective vegetation management strategies for inhibiting invasive and undesirable species. Hence, an effective prevention of woody species establishment on bare soil sites linked to infrastructure projects necessitates a multifaceted strategy, incorporating not only sown diversity but also a comprehensive understanding of soil properties and resident vegetation diversity.