Restoration and Rehabilitation of Arid and Semiarid Mediterranean Ecosystems in North Africa and West Asia: A Review

Abstract

Mediterranean-type vegetation and ecosystems have undergone intense processes of degradation for decades, centuries, or millennia under heavy and prolonged pressure from human and livestock populations. An extensive literature on exclosures, afforestation, reafforestation, rehabilitation, and other regeneration operations over several million hectares in Mediterranean bioclimatic areas from the Atlantic Ocean to the Aral Sea, combined with 50 years of personal field experience, allowed us to draw a number of conclusions on the consequences of these efforts, constraints, and limitations: (1) Exclosure usually permits the restoration and biological recovery of vegetation structure, composition, biomass, and productivity in a time span of 3-5 years in steppic ecosystems and 25-30 years in coniferous or sclerophyllic vegeta tion areas. There are exceptions, however, when vegetation is so degraded to the level that it has reached a new metastable equilibrium, characterized, e.g., unpalatable range weeds, perennial dwarf ephemeroids, cryptogams, or soil surface sealing by raindrop splash or other physical or biological factors. (2) Controlled access and rationally managed utilization of the land may achieve similar and sometimes better results than full exclosure. (3) Afforestation and reafforestation are usually successful above the isohyet of 200 mm a-1 precipitation and, occasionally, at a lower annual precipitation, where the species introduced or reintroduced is appropriate and the causes for degradation have been discontinued or seriously mitigated. (4) Rehabilitation operations, including water and/or soil conservation, may quickly achieve spectacular results but at a higher cost and subjected to a number of constraints pertaining to the techniques utilized and adequate subsequent management. (5) The main constraint for success is the discontinuation of situations that have caused degradation. The most difficult to overcome usually are of a socioeconomic and/or sociocultural nature. The speed of biological recovery is commensurate (inter alia) with the rate to which this constraint is overcome. (6) The present land surface concerned with regeneration (restoration + rehabilitation) in this part of the world represents ca. 4 X 10 6 ha, representing some 6% of the actual ''forest and woodland'' in these areas. The National Regeneration Effort (NRE), a novel concept, is evaluated by using the ratio between the Annual Regeneration Expenditure (ARE) and both the Annual National Budget Expenditure (ANBE) and Gross National Product (GNP).