The effects of environmental factors on components and attributes of a Mediterranean grassland

1. The associations of six environmental factors with vegetative attributes on a species-rich Syrian grassland were investigated during 2 years with contrasting climatic conditions using an unreplicated factorial experiment. The six factors were (i) phosphate supply (nil or 25 kg ha(-1) P2O5); (ii) grazing severity (0.8 or 1.7 sheep ha(-1)); (iii) pre-existing growth conditions as defined by initial biomass (low or high); (iv) preexisting stone cover (low or high); (v) final stone cover, modified by the addition or removal of stone to 20% or 80% stone cover; and (vi) experimental protection or non-protection from grazing. 2. 127 species were present, 56 of which were legumes, 21 grasses and 50 other species. The most common species were Trifolium campestre, T. tomentosum, T. stellatum and several species of Bromus and Avena. Overall, the frequency of only a minority of species was changed by environmental differences. 3. Initial growth conditions (as measured by initial biomass) most affected subsequent performance, although the effect was less marked in the second year. Pre-existing stone cover also resulted in large differences in subsequent growth, greater stone cover reducing growth, probably because it was associated with shallow soil and low soil fertility. Experimental addition of stones increased biomass, probably because the stones protected the vegetation from grazing. Individual species differed in their response to both pre-existing and added stone cover, the most frequent species being the most affected. High stocking rate reduced the biomass of most species, and application of P2O5 increased it. Protection from grazing increased plant cover but individual species differed in their response. An abundance of stones was not necessarily harmful, and some species were favoured by their presence. 4. It is concluded that Mediterranean grasslands are less fragile than they appear since they have mechanisms that buffer them from environmental change, These mechanisms include the presence of a long-lived seed bank and certain adaptations such as the production of abundant small seeds and early flowering, but continued over-grazing clearly results in degradation.