Question: How do climate and landscape structure affect plant invasion process in south Brazilian natural grasslands?Location: Natural grasslands across Rio Grande do Sul state, southern Brazil.Methods: We selected 20 plots (2 km 9 2 km each), situated in ten different grassland types in southern Brazil. In each grassland type, one plot was located in a region with remnant grassland cover <30% (not conserved landscapes) and another in a region with remnant grassland cover >60% (conserved landscapes), in a paired design. In each plot, we surveyed the presence and cover of the four most important invasive species of grasslands in Rio Grande do Sul (Cynodon dactylon, Eragrostis plana, Senecio madagascariensis and Ulex europaeus). We used 12 variables related to climate and landscape structure (i.e. composition and configuration) for testing causal models of plant invasion using Akaike's information criterion for path analyses.Results: Empirical evidence on how climatic conditions and landscape structure can cause plant invasion in subtropical grasslands was provided through six causal models validated with path analysis. The models indicated that increased water deficit, higher density of roads and losses in natural grassland cover caused an increment of invasive plant cover. Further, invasion differed between plots located in conserved vs not conserved landscapes, resulting in not conserved grasslands having a higher level of invasion. E. plana, a perennial grass from South Africa, was the most important invasive species in the grasslands, in terms of frequency and cover.Conclusions: Our results identified the general conditions that promote successful population growth of invasive plants in subtropical grasslands: water deficit, road density and land use, highlighting the effects of climate, landscape structure and human activity in the level of invasion across grassland types.

No abstract

Summary Invasive species spread on natural ecosystems is one of the most important causes of biodiversity loss. To disentangle the invasive plant impact on communities it is essential to combine experimental and observation approaches, which enable the correct interpretations of results and lead to the right decisions for management. We examined the invasion of southern Brazil's grasslands by Eragrostis plana, which is currently the most problematic invasive species in the region. By means of an experiment on invaded communities complemented by observation of non‐invaded communities, we assessed E. plana impact on vegetation, evaluated community response to its removal and discussed the effectiveness of removal methods. Fifty permanent 1 × 1 m plots were located on natural grassland that was partially invaded by E. plana. Removal was done annually from 2012 to 2015 and consisted of five treatments (n = 10): (i) clipping above‐ground biomass on one occasion; (ii) clipping above‐ground biomass periodically; (iii) herbicide and (iv) hand‐pulling, plus (v) control treatment with no‐removal. In addition, 10 plots located in an adjacent non‐invaded area were monitored. All removal treatments reduced E. plana cover across years, but were not enough to eradicate it. Our results revealed not only differences between invaded and non‐invaded communities, but also an effect of E. plana removal on resident species richness and total cover. At the local scale, we demonstrated the impact of E. plana invasion on grassland vegetation, suggesting a reduction in resident species richness and total cover. Invasive species removal changed communities differently from invaded ones, but not resembling non‐invaded references, suggesting that community recovery may need more time for reestablishment or that some restoration strategies are required. Synthesis and applications. This study demonstrated the impact on vegetation of the most important invasive species in southern Brazil's natural grasslands. We highlighted the advantages of combining observations of non‐invaded communities and experimental studies on invaded communities, with and without invasive removal, to help infer causal relationships in ecological invasion research.

No abstract

No abstract