دانلود رایگان مقاله ارتباط تنوع فلور بومی ناهمگنی پوشش زمین

ABSTRACT

Plant invasions and land cover changes are two important threats to biodiversity. River valleys, which are considered as hotspots of biodiversity, have been subjected to the both threats for centuries. Here we examined the impact of river bed proximity and land cover heterogeneity on the species richness of native, red-listed and invasive plants as well as the spatial associations between the three plant groups for alpha-, beta- and gamma-diversity. Surveys were conducted in 140 plots (1 km2 each) in the San River Valley (SE Poland). Our study showed that proximity to the river bed and land cover diversity was positively associated with both native and invasive plant species richness. The species richness of all three plant groups in the studied plots (alpha-diversity) was positively correlated across space. However, invasive plant species richness was negatively linked to beta- and gamma-diversity of native and red-listed species. In contrast, native plant species richness correlated neither with beta- nor with gamma-diversity of invasive species, thus, the hampering effect of high species richness on invasions was not confirmed. We conclude that studies of invasive plants should include multiple diversity levels as the effects may be hidden when evaluations are only made at the local spatial scale (alpha-diversity). Our study suggests that maintenance and restoration of forests close to the river may hamper alien plant invasions.

5. Conclusions Our study showed clearly the scale-dependence of the relationships between richness of native and invasive plants. The spatial co-occurrence of the species richness of native and invasive plants locally (i.e. alpha-diversity) suggests positive associations (simple correlations) or no associations with positive tendency (models incorporating detailed environmental data). Our study shows therefore that hotspots of native species in river valleys are simultaneously the most invasible. Thus, conservation strategies of riverine biodiversity need to take this co-occurrence into account by adjusting conservation measures. However, scaling-up the patterns to beta- and gamma-levels shows a negative relationship between invasive and native (or red-listed) species. Moreover, the proportion between nestedness-resultant and turnoverresultant components of beta-diversity also changes. We show, therefore, that the effects of invasions can be distinct at larger spatial scales but overlooked when investigations are only made at local scales. This stays in line with the recent recommendations of Socolar et al. (2016) that we need a deeper understanding of human impact on beta-diversity for interpreting alpha-scale studies. Invasions in river valleys are strongly related to land cover composition. Maintenance and restoration forest coverage close to the river in combination with reducing the coverage of urbanized and arable land may hamper invasions. We therefore suggest more careful evaluation of current flooding management, which in its present form in Poland and many other countries, leads to the deforestation of floodplains to facilitate water flow and thus may promote the spread of invasive plants.