Alien Plants Homogenise Protected Areas: Evidence from the Landscape and Regional Scales in South Central Chile

Abstract

Protected areas are generally considered ‘remnant islands’ of relatively natural ecosystems and are thus less susceptible to plant invasions than the anthropogenic matrix. However, there is increasing evidence that some invasive species are capable of invading more isolated natural landscapes, higher elevations and relatively undisturbed ecosystems. With an increasing influx and establishment of alien species into protected areas, we should expect a decrease in biotic differentiation and a homogenization of plant communities. Protected areas of south-central Chile have been shown to contain a significant number of alien species and can serve as a good model to test for homogenization processes due to the broad latitudinal, elevational and disturbance gradients. In this chapter, we use a comprehensive floristic survey (n = 165), collected across ten protected areas of central and south central Chile, to test whether alien plant species have contributed to the homogenization of plant communities. We test this homogenization using changes in Jaccard similarity index with the addition of alien species at local and regional scales. By analysing this case study, we expect to shed light into broader questions about the effectiveness of protected areas in filtering out alien plant invasions and to provide recommendations for specific management actions to reduce the threat of plant invasions in protected areas. We found that distance to the road (roadside vs. interior), context (protected area vs. anthropogenic matrix) were the only factors significantly associated with alien species richness. Higher alien species richness was found in transects located in matrices as compared to those in protected areas. Roadside transects showed higher alien species richness both in protected areas and matrices. On the other hand, no significant association to any environmental variable was detected for native species. Delta similarity in the Jaccard index was positive, indicating homogenization, for most of the 165 transects at all scales of comparisons. Overall floristic similarity is higher when alien and native species are included in the composition matrix compared to the only-native species matrix. Our study highlights the importance of complete floristic surveys and inventories in protected areas and their surrounding matrices, and the value of establishing effective monitoring networks, which can facilitate the large management challenge of reducing the threat posed by alien species to protected areas biodiversity.