Factors Influencing Development of Cryptogamic Soil Crusts in Utah Deserts

Abstract

The relationofsomephysiallandchemicalsoilcharncteristicsto cryptogamic crust development was determined from sites in semidesert regions of southern Utah. The effects of grazing on eryptogamic crust development also wasexamined. Electrical conductivity, percentage silt, and soil phosphorus were found to he correlated with well-developed cryptogamic crusts. Both total cryptognmic cover and the number of cryptogamic species decreased under grazing pressure. Themsnagement ofmngelands, especially in arid regions, would bestrengthened by understanding the role of cryptogamic crusts and considering them in range management decisions. The vascular plants of many semidesert areas furnish a scant ground cover of discrete and widely spaced units. Between the plants are rather extensive open spaces exposed to the elements. Where soils are gravelly, a pavement of pebbles provides protection from erosive forces of wind and water. Another factor, less obvious but ofimportance in the controloferosionin theinterspaces, particularly where the gravel pavement is weak or absent, is a community of nonvascular or cryptogamic plants that grow upon or immediately beneath the soil surface. Where well established and undisturbed by trampling, the cryptogams form a recognizable crust (Fig. I). Algae are the primary components of these crusts, but in some environments, themorevisiblemacroscopiclichensand mossesare common members of the cryptogamic cover (Anderson and Rushforth 1977, Kleiner and Harper 1972). Even though they are small and often inconspicuous, cryptogamic species play an important role in soil stabilization in semideserts (Fletcher and Martin 1942). Algal filaments, fungal mycelia, and tissues of lichensand mosses are present throughout the surface few millimeters of many semidesert soils (Anderson and Rushforth 1977, Hunt and Durrell 1966). Where lichens and mosses grow in abundance, the stability of the soil surface is readily apparent, but the less obvious algae, especially the filamentous algae, are probably more effective in binding the surface soil particles (Anantani and Marathe 1974; Durrelland Shields 196l).Thethickgelatinoussheathsthatencase some of the algal species probably add strength and toughness to the felt-like web of filaments among the soil particles in the surface I or 2 millimeters of a well-established algal crust. Cryptogamic crusts are common in the arid regions of the westn and more importantly, lichen-free grasslands could be maintained through continous moderate to heavy grazing, suggesting cryptogams can be used to evaluate grassland management practices. Little has been done to incorporate the information known about soil crusts into range management considerations. It seems likely that our ability to manage ranges, especially in arid regions, would be strengthened by such an inclusion. The purposes of this study are two-fold: first, we seek to determine the relations of some physical and chemical soil factors to crust development, and second, we desire to evaluate the effect of grazing on cryptogamic soils crusts. Study Areas Five areas in the southern part of Utah were selected for study (Fig. 4). All are characterized by low precipitation, hot summers, and cold winters. The Desert Experimental Range (DER) of the USDA-Forest Service is located in western Utah and isthedriest of all the areas considered: precipitation averages I5 cm annually. Two study areas are along the Hurricane Fault in extreme southwestern Utah near St. George and Hurricane, which receive about 19 and 22 cm average annual precipitation, respectively. Virginia Park in Canyonlands National Park in southeastern Utah is the wettest site, receiving about 30 cm of annual precipitation, mainly during the warm season. The temperature extremes for all five areas are similar over the past IO years. Maximums are around 4CPC and minimums -14OC or lower (Holmgren 1973). Quite different vascular communities prevail at the study sites. Species of low shrubstypical ofthecolddesertdominatethestands at the DER. Hilaria (galleta) and Boutelouo (blue grama) are the most common grasses. Ephedra (Mormon tea) and Larrea (creosotebush) are the most common vascular plants at St. George, while Ephedra and Petalonyx (sandpaper plant) are the dominant vascular species at Hurricane. Hi/aria and Sripa (needlegrass) grasslands characterize Virginia Park. An additional collection was made north of Black Rock, Utah, in Atriplex (saltbush) and Chrysothomnus (rabbitbrush) communities. The St. George and Hurricane study sites are on gypsum outcrops and have sparse vascular cover and heavy cryptogamic cover of algae, lichens, and intermingled mosses characteristic of gypsiferous soils.