Comparative Structure of Physical and Biological Soil Crusts

Abstract

The presence of physical and/or biological soil crusts alters many charac- teristics of the soil surface, and thus can play a defining role in many eco- system functions (Greene and Ringrose-Voase 1994; Issa et al. 1999). The presence of a physical crust can seal and smooth surfaces, thus decreasing rainfall infiltration and increasing the volume and velocity of water runoff (Sumner and Stewart 1992). Physical crusts often inhibit vascular plant seed- ling establishment. Smooth biological crusts, like physical crusts, can also control local hydrology by smoothing and partially sealing soil surfaces (Kidron and Yair 1997). In contrast, soil surfaces roughened by biological soil crusts can increase rainfall infiltration, decrease water runoff volume and velocity, and retain seeds and organic matter (Loope and Gifford 1972; J. Belnap, unpubl.). Thus, understanding the factors that control the form of physical or biological soil crusts is essential in interpreting how the presence of these crusts may influence ecosystem functions (Mücher et al. 1988).