Research Journal of Agricultural and Environmental Management Vol. 2(10), pp. 277-288, October, 2013 Available online at http://www.apexjournal.org ISSN 2315-8719© 2013 Apex Journal International REVIEW Dryland Ecosystems: Their Features, Constraints, Potentials and Managements Haile Adamu Wale 1 *and Tatek Dejenie 2 1 Ethiopian Institute of Agricultural Research, Debre Zeit Agricultural Research Center, P.O. Box 32, Debre Zeit, Ethiopia. 2 Ethiopian Institute of Agricultural Research, Forestry Research Center, P.O. Box 30708, Addis Ababa, Ethiopia. Accepted 4 April, 2013 This paper has tried to review and discuss the characteristics, constraints and potentials and feasible management options of dryland ecosystems based on different authors’ point of views. Because dryland ecosystems are diverse in terms of climate, soils, vegetation, animals, and people’s activities, there is no practical characterization or definition of drylands that can be made. Drylands zones of the world have different features, constraints, and potentials like other ecosystems of the world. Certain features and constraints that drylands can be explained are aridity, climate, drought, soils, water, biodiversity, and in terms of socioeconomic. The overriding feature of dryland climates is the low average rainfall and the variability in rainfall patterns. Droughts are a normal feature of drylands. Soil salinity is the major constraint in drylands especially in the closed basins due to lack of surface water outflow. However, despite the fact that lots of authors wrote the desperate characteristics and constraints of drylands, there were many scholars that disclosed and advocated as dryland ecosystems had immense potentials that have been contributing for the present development of the world, and as they would be the future destiny and promising part of the globe too especially in the era of solar energy. Moreover, the fact that the current living organisms in drylands are living in line with the changing climate, it will be the promising ecosystem that could come up with many adaptive organisms to mitigate the changing climate. And therefore, the necessary due attentions shall be given to dryland ecosystems so as to maximize and exploit the present and future potentials. Key words: Drylands, features, aridity, salinity, climate, water resources, biodiversity constraints, droughts, cultural challenges, land tenure, potentials, era of solar energy, resources management. INTRODUCTION Drylands, and their global extents Drylands are defined by UNEP (1991) as those lands that have a precipitation (P) over potential evapotranspiration (PET) ratio of less than 0.65. This ratio is referred to as aridity index and is used to classify drylands as hyper-arid (ratio less than 0.05), arid (0.05 to 0.20), semi-arid (0.20 to 0.50) and dry sub-humid areas (0.50 to 0.65). Drylands cover approximately 41% of the continental land area. Two-thirds of the drylands are in Africa and Asia. According to UNEP (1991), out of 41% Africa occupies 13.1%, Asia (13%), Australia (4.4%), Europe (2.0%), *Corresponding author. E-mail: mamnaturepal@yahoo.com North America (4.9%), and South America (3.6%) in million Hectares. However, there is no universally accepted definition of drylands nor agreement on the delineation of the boundaries of dryland areas. The reason that Drylands are diverse in terms of climate, soils, vegetation, animals, and people’s activities, there is no practical characterization or definition of drylands that can be made. One binding feature of all drylands in the world, however, is aridity (Hassan and Degne, 1997). Arid regions are characterized by the precipitation that, most of the time, is insufficient to replenish losses of soil moisture by evaporation, transpiration, and other mechanisms. Many factors including solar radiation, temperature, humidity, wind, topography, vegetation affect soil moisture losses. Precipitation in arid regions usually is highly variable and, consequently, is unreliable.