Defoliation and competition effects in a productivity gradient for a semiarid Mediterranean annual grassland community

Grazing and competition are two main factors shaping range plant communities; however, few studies have investigated their interaction. The current study aimed to investigate the effects of defoliation, competition and their interaction on production of annual grasses in semiarid Mediterranean areas. Competition treatments (absence/presence of neighbors) were combined with three defoliation intensities (0%, 30% and 60%) in a complete factorial design. Competition significantly reduced grass biomass. However, the role of competition was eliminated under heavy defoliation or under dry growth conditions. Defoliation showed variable results on final biomass (FB) and cumulative biomass (CB). While heavy defoliation (60% clipping intensity) reduced grass FB down to 80% during the two growing seasons, light defoliation (30%) significantly increased CB. Results showed that competition may limit the direct effect of defoliation on dominant grass species. Further, the relationship between site productivity and competition effect was best explained by a negative linear model. This hypothesized model may suggest that facilitation and competition alternatively affect grassland communities along a productivity gradient. The results suggest that light grazing may sustain or even enhance grassland productivity. The results also indicated the suitability of annual grass species to re-vegetate degraded rangeland in semi-arid climate. Further, optimum grazing practices to conserve biodiversity of Avena grassland may involve moderate stocking rate. Beweidung und Konkurrenz sind die zwei Hauptfaktoren, von denen Grünlandpflanzengemeinschaften geprägt werden. Ihre Interaktion wurde jedoch bisher in wenigen Untersuchungen betrachtet. Die vorliegende Untersuchung zielte darauf ab, die Auswirkungen von Blattverlust, Konkurrenz und ihrer Interaktion auf die Produktion von annuellen Gräsern in semiariden, Mediterranen Gebieten zu untersuchen. Die Konkurrenzvarianten (Anwesenheit/Abwesenheit von Nachbarn) wurden mit den drei Blattverlustintensitäten in einem vollständig, faktoriellen Design kombiniert (0%, 30% und 60%). Die Konkurrenz verringerte die Biomasse der Gräser signifikant. Die Rolle der Konkurrenz war jedoch bei starkem Blattverlust oder trockenen Wachstumsbedingungen eliminiert. Der Blattverlust zeigte variable Auswirkungen auf die Endbiomasse und die kumulative Biomasse. Während starker Blattverlust (60% Beschneidungsintensität) die Endbiomasse der Gräser auf 80% reduzier