Annual Pasture Legumes: A Vital Component Stabilizing and Rehabilitating Low-Rainfall Mediterranean Ecosystems

Abstract

Surveys of the distribution of annual legumes in low - rainfall Mediterranean areas show them to be a persistent element of ecosystems that exhibit great climatic and edaphic diversity and are present even when these systems have been substantially degraded by long - term human disturbance. Studies of the productivity of degraded grasslands in low - rainfall Mediterranean environments indicate that productivity is usually in the range of 2-5 kg mm-1 mean annual rainfall, i.e., well short of potential. It can be enhanced by a range of interventions that favor annual legumes. Effective strategies include control of grazing (both intensity and timing), input of exogenous nutrients, particularly phosphorus, and the addition of legume seed, or a combination of all of these. Recent studies have greatly increased understanding of the mechanisms leading to resilience of annual legume populations. This knowledge is useful in designing rehabilitation programs. It has become clear that the combination of a high level of seed coat impermeability and small seed size (1 mg) provides a very high degree of resilience. It is concluded that annual legumes have the attributes to be useful in practical programs to rehabilitate degraded ecosystems. Their initial status in ecosystems can vary over a wide range, demanding varying levels of intervention for effective rehabilitation. Effective rehabilitation requires technologically appropriate inputs for the prevailing socioeconomic circumstances.