Daniel Hillel

Desertification in Relation to Climate Variability and Change

Ecosystems in semiarid regions appear to be undergoing degradation processes commonly described as desertification. We review the concepts, definitions, and processes pertinent to the problem. Focusing on the long-term drought in the African Sahel as a case study, we analyze the relationships among climatic, biophysical, and social factors. Hypotheses related to the causation and persistence of drought involve the roles of land–surface change, atmospheric dust, and ocean–atmosphere dynamics. Remote sensing techniques have made possible monitoring ecosystem changes on a regional scale. Where fresh water resources are available, irrigation can be an effective way to stabilize and intensify agricultural production, but water resource development needs to be accompanied by water conservation and salinity control. Key social factors include land tenure, institutional structures, and population growth. Projections derived from global climate models suggest that drought conditions in the Sahel may worsen in the coming decades. Given challenges facing semiarid countries, vulnerability to the intertwined effects of degradation and climate change appears to be high. Improvements of scientific understanding of climate phenomena and their interconnections over space and time offer opportunities for controlling destructive land-use practices, augmenting carbon sinks through better soil management, and enhancing resilience.

The Role of Biodiversity in Agronomy

Publisher Summary As long as human exploitation of the land and its biotic resources was restricted to small enclaves, the surrounding expanses of relatively undisturbed natural ecosystems could remain intact, with their biodiversity preserved. But, as the extent and intensity of human exploitation of the terrestrial domain increased, along with the increase of population, natural habitats were reduced and fragmented. Entire biomes are now threatened and numerous ‘‘wild’’ species have already been eliminated. Projections indicate that biodiversity loss will continue into the future, as expressed in declines in populations of wild species and reduction in area of wild habitats. All the plants whose products are utilized by humans, either directly or indirectly, were derived originally from biological diversity; that is to say, from wild ancestors. Traditionally, agricultural breeding has been done with the close genetic relatives of the relevant organisms. Genetic diversity is often considered a resource for future crop improvement. Agriculture depends on biodiversity through pollinators, birds, insect pests, disease control, and cultivated plants, and wild relatives. Numerous species in soil are directly involved in ecosystem processes and ecological services that contribute to sustaining agriculture. Soil biodiversity is determined by multiple factors: vegetation, soil physical and chemical properties, climate, and the interactions among soil organisms. N agro-ecosystem approaches strive to integrate farming and food production units into the larger environmental domain, which recognizes and preserves the role of native fauna and flora in their natural habitats. The potential impacts of climate change and climate variability on biodiversity need to be more fully characterized, because both agricultural and natural ecosystems will thereby be affected. The formulation and implementation of biodiversity policies is a global priority. National and international policies are needed to encourage the adoption on a wide scale of the agro‐ecosystem paradigm and thus the conservation of biodiversity in food-producing systems.