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Contrasting response of native and alien plant species richness to environmental energy and human impact along alpine elevation gradients

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Abstract:

ABSTRACT Aim 

We tested whether the species–energy and species–human relationships vary between native and both naturalized and casual alien species richness when other environmental variables had been taken into account. Location 

Trento Province, a region (c. 6200 km2) on the southern border of the European Alps (Italy), subdivided into 156 contiguous (c. 37.5 km2) cells and ranging in elevation from 66 to 3769 m. Methods 

Data were separated into three subsets, representing richness of natives, naturalized aliens and casual aliens and separately related to temperature, human population and various environmental correlates of plant species diversity. We applied ordinary least squares and simultaneous autoregressive regressions to identify potential contrasting responses of the three plant status subsets and hierarchical partitioning to evaluate the relative importance of the predictor variables. Results 

Variation in alien plant species richness along the region was almost entirely explained by temperature and human population density. The relationships were positive but strongly curvilinear. Native species richness was less strongly related to either factor but was positively related to the presence of calcareous bedrock. Native species richness had a decelerating positive relationship with temperature (R2= 55%), whereas naturalized and casual aliens had a positive accelerating relationship explaining 86% and 62% of the variation in richness, respectively. Native species richness had a positive decelerating relationship with population density (R2= 42%), whilst both alien subsets had a positive accelerating relationship. Main conclusions 

Alien species richness was higher in areas with the most rich and diverse assemblages of native species. Areas at high altitudes are not especially prone to alien invasion due to energy constraints, low propagule pressure and disturbance, even considering a potential increased in temperature. Thus, if we consider future environmental change, we should expect a stronger response of aliens than natives in the currently warm, urbanized, low-altitude areas than in cold, high-altitude areas where human population density is low.

Keywords: Biological invasion; climate change; disturbance; elevation; exotic; homogenization; land-use change; propagule pressure; urbanization; weeds

Document Type: Research Article

DOI: http://dx.doi.org/10.1111/j.1466-8238.2009.00484.x

Affiliations: 1: Department of Environmental Agronomy and Crop Production, University of Padova, Viale dell'Università 16, 35020 Legnaro, Padova, Italy, 2: Department of Animal and Plant Sciences, Biodiversity and Macroecology Group, University of Sheffield, Sheffield S10 2TN, UK, 3: Museo Civico di Rovereto, Borgo Santa Caterina 41, 38068 Rovereto, Trento, Italy, 4: The Bio-Protection Research Centre, PO Box 84, Lincoln University, Canterbury, New Zealand

Publication date: November 1, 2009

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