Recognizing Biological Soil Crusts in Southern California - A Field Guide for Soil Surveys.

Biological soil crusts are important components of arid and semiarid soil ecosystems with crucial ecological functions in the landscape. While not as continuous as crusts in the Colorado Plateau and Great Basin (cold deserts), biological soil crusts in southern California are common, forming distinct patches in various desert or chaparral habitats. Different ecological sites can favor certain crust organisms, which, when dominant, form recognizable morphological/functional crust types. These crust types can vary in ecological functions due to their different surface morphologies and distinct composition. A morphological crust type classification is commonly applied for biological soil crust surveys of the cold deserts and an official field guide is available. However, crusts in southern California are not lichen- and moss-dominated as are cold desert crusts, but consist mainly of various algal crust types. In addition, some biological soil crusts in southern California can be overlooked due to their cryptic appearance and because they are often embedded among and underneath surface gravel.

Based on biological soil crust investigations throughout southern California we have developed a crust-type classification tailored for use in ecological surveys in this area. For example, the NRCS ecological site protocol currently notes the presence of biological soil crusts, but the crusts are not further identified into morphological/functional groups. Further identification is important because different kinds of crusts may function quite differently with regard to surface hydrology and nutrient dynamics. Biological soil crust categories of our field guide include: embedded fungal/bacterial crust, incipient algal crust, unblackened algal crust, blackened algal crust, cyano-lichen crust, green-lichen crust, simple growing moss crust, intricate growing moss crust, liverwort crust. Our field guide could be included within soil survey protocols to distinguish between biological and non-biological crusted soil surfaces as well as to easily recognize crust types.