Interspecific competition and livestock disturbance control the spatial patterns of two coastal dune shrubs
2012
AIMS: In spite of the important role played by herbivory in plant community structure and the fact that it constitutes one of the most important ecological disturbance processes in the dynamics of both natural and anthropic systems, few studies have concentrated on the consequences of browsing on vegetation spatial patterns. The main objective of this study was to examine the role of domestic livestock pressure in the spatial distribution pattern and interspecific competition of two sand dune shrubs: Retama monosperma and the endangered species Thymus carnosus. METHODS: We compared three areas featuring different intensities of livestock pressure. Two 25 × 25 m plots were established in each study area, and the crown heights, diameters and x, y coordinates of every individual in each plot were recorded. RESULTS: Livestock activity produced a considerable effect, not only on plant cover and size (larger and higher crowns of both species in non herbivory plots) but also on spatial pattern. Whereas light herbivory lead to a random spatial pattern for both species, high herbivory resulted in a repulsion one. CONCLUSIONS: Under high and no livestock pressure, T. carnosus is displaced by R. monosperma, creating a repulsion point pattern distribution between the two species. However, when livestock disturbance was low, our data reveal relatively higher T. carnosus cover values than in the other livestock pressure scenarios, along with a random distribution pattern.
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