Biological indices of soil quality: an ecosystem case study of their use

Soil quality indices can help ensure that site productivity and soil functi on are maintained. Biological indices yield evidence of how a soil function s and interacts with the plants, animals and climate that comprise an ecosy stem. Soil scientists can identify and quantify both chemical and biologica l soil-quality indicators for ecosystems with a single main function, such as agricultural lands and forest plantations. However, quantifying these in dices in complex ecosystems - that have multiple uses or goals such as main taining biodiversity, aesthetics, recreation, timber production and water q uality - is much more difficult. In an ecosystem context all components - p lants, animals and humans - interact with the soil differently, making soil quality indices variable. These interactions result in a combination of bi ological processes that make each ecosystem unique. We examined the soil an d site quality of five forest stands (xeric oak-pine; two mixed hardwood, c ove hardwood, northern hardwood), within the 2185-ha Coweeta Hydrologic Lab oratory. An initial rank of soil quality based on soil chemical and physica l properties was assigned. The ranking was then compared with four common g roups of soil biological indicators: (1) nitrogen availability; (2) litter decomposition; (3) soil microarthropod populations; and (4) carbon availabi lity. We also examined estimates of overstory productivity, overstory biodi versity and total aboveground productivity for each site as indices of site quality. We found that soil and site quality rankings varied with the indi cator, showing that the soil or site of greatest quality may change dependi ng on the use or goal of the ecosystem under examination. (C) 2000 Elsevier Science B.V. All rights reserved.