The dependence of the productivity of a semi-arid mediterranean hill pasture ecosystem on climatic fluctuations

Abstract

The results of a 6-year grazing trial in open Tabor oak woodland, dominated by annual plants, were used for the determination of the dependence of productivity on climatic fluctuations. Stepwise multiple regressions between October–November, December–January and February–March rainfall and minimum December–January temperatures resulted in high correlation coefficients, explaining 76% of the variance in the unfertilized, and even 99% of the variance in the more intensively improved and fertilized, pastures. Legumes were more dependent on total rainfall but also highly responsive to N or P dressings, whereas grasses were more responsive to early rains, especially after N dressings. This is the first study in any mediterranean annual grassland where such close correlations between climate and productivity could be determined. In the drier years this productivity is typical of semi-desertic biomes but in more favorable rainfall years it is well within the range of the subhumid woodland-grassland biome. This great responsiveness to climatic fluctuations was apparently of large adaptive importance in the evolution of these grasslands and has contributed much to their striking resilience and persistence as dissipative structures, “creating order through fluctuation”. It was concluded that this great climatic dependence, as a major bottleneck for rational livestock production, can be overcome only by improving the efficiency of moisture utilisation by introducing deeper-rooted, drought resistant and summer-green folder shrubs and trees.