GLOSSARY Abiotic - The non-living parameters of an ecosystem. Advection - The process of transport of an atmospheric property solely by the mass motion of the atmosphere. Aeration (Soil) - Oxygen content of the soil. Albedo - Reflectivity. The fraction of incident radiation at a given wavelength (or wavelengths) reflected by a surface or body. Annual Plants - Plants which germinate, grow, set seed, and die in a single year. Desert annuals are short-lived mesophytes that live only when soil moisture is present and produce seed before the onset of soil drought. Arid - An ecosystem which receives from 60-100 mm to 150-250 mm annual precipitation, depending on whether a majority of the precipitation occurs in the season of low evaporitivity (winter) or high evaporitivity (summer), respectively. Azimuth - The angle between true north and the projection of the sun's rays onto the horizontal. At solar noon the azimuthal angle is 180° (true south). Bajada - Alluvial fan. Biomass - Weight of living material, usually expressed as a dry weight, in all or part of an organism, population, or community. Commonly expressed as weight per unit area. Biota - The living components of an ecosystem. Biotic - Variables pertaining to the biota of an ecosystem. Bulk Density - The dry weight of a given volume of undisturbed soil. Bunch Grass - Tall, perennial grass characteristic of the tallgrass prairie. Differs from annual and short statured perennial grasses. Clay - Soil in which the average particle size is less than .002 mm. Community - An association of interacting populations, delimited by their interactions or by spatial occurrence. Desert Pavement - Desert surface structure common on arid watersheds in which a relatively impervious cemented layer of coarse particles is formed due to the loss of finer particles in runoff water. Desertification - The process of succession of large ecosystems, or biomes, into "deserts". Desiccation - The loss of water by a body to its environment. Detritivores - Organisms which- feed mainly or exclusively on detritus. Detritus - Freshly dead or partially decomposed organic matter. Diffuse Radiation - That portion of solar radiation that reaches the earth's surface after having been scattered from the direct beam by molecules or suspensoids in the atmosphere. Also termed sky radiation.
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