Rehabilitation of Mediterranean dwarf-shrub range-land with herbicides, fertilizers, and fire

Abstract

An experiment was conducted on a Mediterranean hill range dominated by communities of spiny dwarf-shrubs (mainly prickly burnet Sarcopoterium spinosum (L.) Spach) in order to determine the effects of P fertilizer application, shrub control and fire on the herbaceous and shrub components of the community. Herbicide (2,4-D) application eliminated almost all the shrubs in the first year and their regeneration was relatively slow: 6 years after the application, shrub cover was less than one-third of what it was at the beginning of the experiment. After fire, regeneration was rapid and original shrub cover was restored within 6 years. A single application of phosphorus fertilizer (4.5-9.0 g P m-2) significantly retarded regeneration of shrub cover and produced a three to five fold increase in herbaceous biomass production. The residual effect of the fertilizer application was still significant at the end of the 7-year monitoring period. The herbaceous vegetation in the P-fertilizer treatments was dominated by annual legume species throughout the experiment. The prolonged response of the herbaceous sward patches to a single P application appeared to be caused by the gradual release of phosphate from the applied fertilizer and also by the summer grazing system that facilitated recycling of soil nutrients on the site. Above-ground biomass on herbaceous sward patches increased not only as a consequence of nutrient amelioration, but also because of reduced competition from the lower shrub cover following fire or herbicide application. Shrub recovery that was dependent on the residual cover in the first year following fire and/or herbicide treatment, was further retarded by competition from the vigorous herbaceous vegetation that benefited from nutrient amelioration. The implications of these results for range improvement depend to a large degree on the economic conditions relevant to the grazing system.