The effects of drought and grazing pressure on the physiology and morphology of the protégé species A. cytisoides in South-east Spain.

Climate models predict a decrease in precipitation and prolonged dry seasons in large parts of the Mediterranean. Combined with grazing pressure these prolonged dry seasons impose high levels of stress on plant communities within arid ecosystems. This stress may cause loss of biodiversity due to a lack of adaptability within plant species. Interspecific facilitation may increase the sustainability of these communities. However, high stress levels may induce competition as well. The phenological and physiological changes that these interactions cause under such conditions, may provide useful information on the evolutionary development of plant communities. To determine these phenological and physiological changes we conducted a field experiment on the morphology and physiology of a protege species. We tested this effect using the protege species Anthyllis cytisoides and a facilitating species Artemisia barrelieri. Furthermore, a combination of treatments was applied using different grazing intensities, additional water and presence of a nurse to examine the physiological and phenological alterations of the protege. From these treatments we found that protege plants get a significant temporal boost in water and nitrogen content as a consequence of adding water. Grazing pressure and presence of a nurse did, however, not affect physiological traits. Furthermore, we found no direct effects of the added water on morphological traits of the proteges. Height of the proteges was found to be negatively correlated to grazing intensity, while diameter was not. In general, conditions have been exceptionally dry which we expect to have caused the facilitator to become a passive factor within the interspecific interactions leading to a decreased facilitative and competitive ability. The results we found are signals of the incapability of plant communities to cope with the extended drought periods. This may cause biodiversity loss if environmental conditions fail to improve.