Factors associated with woody alien species distribution in a newly invaded mountain system of central Argentina

Abstract

To help determine the major factors associated with alien plant in a newly invaded mountain range; we analyzed the distribution patterns of woody alien species along the altitudinal gradient of the Cordoba mountains, in relation to biotic, abiotic and anthropogenic factors. We selected 303 plots using a Geographic Information System (GIS) covering all the variability of these factors. In the field we registered woody alien occurrence in these 303 and in 303 additional neighbor plots. We used 12 biotic, abiotic and anthropogenic variables from the GIS to predict the probability of presence of alien species through a logistic model. Then, we analyzed if neighbor alien occurrences could explain some additional variance. We created a probability map with 4 categories of alien occurrence which was then validated by new field sampling. Occurrence of woody aliens was highest in the eastern slope (with longer history of species introduction), at low altitudes, near sources of propagule pressure (human settlements, roads and neighbor sites with established alien plants), and associated to sheltered topographies. In the upper belt of the Cordoba Mountains woody invasion is incipient and thus in a transient stage. Accordingly, propagule pressure seems to be the major factor at play, while the relevance of disturbance and biotic interactions is less clear.