Effects of grass functional diversity on invasion success by exotic grasses in Cerrado grasslands

Abstract

Abstract Invasive species pose significant challenges to successful restoration efforts worldwide. A strategy to reduce invasions is to establish communities consisting of species with varied ecological strategies. These strategies typically align along the conservative and plant size axes, and more recently, along a below‐ground collaboration axis. However, we lack understanding of how the diverse ecological strategies of Cerrado grass species, their combinations and their interactions with soil conditions can mitigate invasions. Here, we investigated how native grass communities composed by species with different ecological strategies affect the invasion success in two soil types of abandoned pastures in the Cerrado. Specifically, we tested the hypothesis that greater above‐ and below‐ground functional diversity reduces exotic species invasion. We also evaluated whether the isolated effects of native species on invasion were positive or negative. We installed an experiment with species richness ranging from zero to eight native grass species. In November 2019, we sowed species combinations to create communities composed by species with different ecological strategies. We quantified the above‐ground biomass of exotic species as a measure of invasion. To characterize the species ecological strategies, we measured five functional traits. Functional diversity of maximum height and specific root length (SRL) had the highest predictive power; however, the most parsimonious model included only SRL diversity, which represents the collaboration axis. Native above‐ground biomass was also negatively related to exotic species biomass. Furthermore, invasion was greater in less stressful soil conditions but did not interact with diversity. The effect of native species varied from facilitation to competition, with the annual fast‐growing native species favouring invasion. Synthesis and applications. Our results show that greater functional diversity of combined above‐ and below‐ground traits reduces invasion success, shedding light on an underexplored role of specific root length diversity. The competitive and facilitative effects of different native species highlight the need for careful selection of the species to be used in restoration programmes. Furthermore, the absence of interaction between diversity and soil types highlights the need for an integrated management of the functional composition and edaphic factors to increase resistance to invasion in these Neotropical grass communities.