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The role of habitat, landscape structure and residence time on plant species invasions in a neotropical landscape

Haider, Julian Ananda, Höbart, Raphael, Kovacs, Nina, Milchram, Markus, Dullinger, Stefan, Huber, Werner, Essl, Franz
Journal of tropical ecology 2016 v.32 no.3 pp. 240-249
Hedychium coronarium, Hydrilla verticillata, Neotropics, agricultural land, data collection, ecological invasion, flora, habitats, herbaceous plants, indigenous species, invasive species, landscapes, linear models, lowlands, probability, shade, species diversity, vegetation, Costa Rica
Plant invasions in tropical agricultural landscapes have been poorly studied so far. Here, we use plot data collected in 2015 in the La Gamba valley in southern Costa Rica to analyse the spread of two invasive alien species (Hydrilla verticillata, Hedychium coronarium) on the landscape level. In total, we recorded the aquatic H. verticillata, which was locally introduced into the La Gamba valley in 2005, in 26% of all plots (size: 15 m²), while H. coronarium, which occurs along water courses, was recorded in 80% of all plots (size: 25 m²). Generalized Linear Models (GLMs) showed that the habitat type invaded and shading had no significant effect on H. verticillata presence and abundance. However, proximity to the point of local introduction and habitat diversity in the adjacent landscape did positively affect its presence. For H. coronarium, GLMs showed a significant correlation with the invaded habitat type. The probability of H. coronarium presence was highest in herbaceous vegetation and cover was higher compared with other habitats. There was no effect on native plant species richness and cover by H. verticillata, while H. coronarium exerted a negative impact on herbaceous plant species number and, in particular, cover. Hydrilla verticillata is a rather recent addition to the local alien flora, and thus dispersal limitation still restricts its local range. Compared with observed rates of spread in other regions, spread velocity within the first decade of its local presence was low. In contrast, H. coronarium has been locally present for a substantially longer time period. This species encounters suitable habitat conditions in herbaceous vegetation along water courses, where it builds up dense clonal stands which negatively affect herbaceous vegetation. Our results show that while both study species are invasive in Central American lowlands, their local abundance and impacts on native vegetation may differ profoundly.