Conservation of semi-arid gypsophile plant communities: The role of fragmentation and grazing

The consequences of ecosystem fragmentation have been documented in many regions of the world. In some of these ecosystems, grazing has been proposed as a dispersal agent preventing isolation of fragmented plant communities. In other fragmented plant communities grazing acts as a perturbation, together with fragmentation, in an additive or even synergistic way. The effects of fragmentation on plant communities and the possible role of grazing in fragmented arid and semi-arid ecosystems remain largely unstudied. Moreover, habitat-specialist plant species, frequent in arid ecosystems, can be particularly affected. We studied a fragmented semi-arid gypsophile shrubland, and the role of grazing in plant species composition of fragments. We hypothesize that fragments have lower plant diversity, while grazing could have a positive effect on plant diversity, acting as dispersal agent. We also hypothesize that the specialist gypsophile flora will be more negatively affected by fragmentation and grazing than common regional plant species. Results showed a decrease in diversity with fragmentation, mainly due to the dominance of plants that benefit from perturbed conditions in fragments. Propagule availability of annual plants increased with grazing, leading to an increase in annual plant cover as compared to fragments without grazing. As expected, the negative effect of fragmentation and grazing was larger for strict gypsophytes. We argue that fragmentation and grazing can alter the restrictive gypsum soil conditions, affecting strict gypsophytes more than common regional species. Conservation strategies for specialist plant communities in arid ecosystems should take into account their vulnerability in human-dominated landscapes.