Crust Cover Research Articles

Soil hydrology is independent of microphytic crust cover: Further evidence from a wooded semiarid australian rangeland

Rainfall simulation experiments were performed on 25 plots of varying microphytic crust cover in a wooded semiarid rangeland in eastern Australia. Under a rainfall intensity of 45 mm h‐1, steady‐state infiltration ranged from 5 mm h‐1 to 41 mm h‐1, but there was no effect of cover on this or any of the other soil hydrological variables measured. When disturbed plots with low cover (<15% cover) were excluded from the analyses, significant increases in time to ponding were associated with increases in crust cover. Despite some significant relationships, however, crust cover was an insignificant predictor of soil hydrological status at this site. We attribute this to the well‐structured nature of the soils at the site, which have not been subjected to grazing by domestic animals for almost 20 years. The results support earlier work suggesting that in the short term, crust cover is only an important moderator of soil hydrology when soils are degraded.

Assessment of erosion rates from microphyte-dominated calcareous soils under rain-impacted flow

Intact soil monoliths with surfaces of varying microphytic crust cover were collected from a calcareous earth soil in a semi-arid belah–rosewood woodland near Wentworth in south-western New South Wales. Monoliths were tested for their susceptibility to erosion by rain-impacted flow using a laboratory rainfall simulator. The erosive stress applied to each surface was controlled by varying the flow depth between 4 and 8 mm whilst maintaining a flow velocity of 25 mm/s using 2·7 mm raindrops falling 11·2 m at average rainfall intensities of 65 mm/h. Increasing the cover of microphytic crusts on the surface resulted in a significant (P = 0·001) reduction in sediment concentration. A linear model incorporating percentage cover and distribution of cover accounted for 46% of the variance in soil erosion. A significant relationship was also found between the coarse fraction (&gt;0·053 mm) and crust cover (P = 0·012) at the 4-mm depth. Management practices such as overgrazing, trampling, and fire, which reduce the cover of crusts in this landscape, will lead to increased erosion hazard.

What determines the spectral reflectance of the Negev-Sinai sand dunes

Abstract The difference in spectra reflectance between the north-western Negev desert and the adjacent Sinai sand dunes has attracted the attention of many scientists. Remote sensing analysis of three Landsat Multi-Spectral Scanner (MSS) images acquired in the summer of 1984, 1987, 1989, followed by intensive field work, indicate that the area is not homogenous and is undergoing a quick recovery from the intensive grazing that it suffered between 1968 and 1982. The outcome is a gradual decrease in the brightness of the Negev between 1984 and 1989 in all MSS bands except band 7 which shows very little or no change with time. This is due to the increase in biogenic crust and vegetation cover. The Sinai bare sand shows the opposite trend of little to no change in all bands but band 7, which shows an increase in reflectance with time. This is probably due to the effect of further destruction of vegetation in the Sinai after 1982. In the northern part of the area, dunes are low, have a high percentage of fines...

Distribution and Floristics of Terricolous Lichens in Soil Crusts in Arid and Semi-Arid New South Wales, Australia

This paper examines the distribution of terricolous lichens at a regional scale across seven landscape types over 60 000 km2 in western New South Wales. Data are also presented on the distribution of lichens within a geomorphic sequence of runoff and runon zones on a red earth soil near Cobar. On a regional scale, 48 taxa from 23 genera were collected from 282 sites in semi-arid and arid eastern Australia, Of these, 74% were crustose or squamulose, and the remainder (26%) were foliose. Six genera (Acarospora, Endocarpon, Catapyrenium, Diploschistes, Peltula and Xanthoparmelia) accounted for 57% of species. Landscape type was a poor predictor of lichen floristics or crust cover. Instead, a core group of species comprising Collema coccophorum, Heppia despreauxii, Endocarpon rogersii, E. simplicatum var. bisporum, E. pallidum, Psora decipiens, Peltula patellata ssp. australiensis, Catapyrenium squamulosum and Synalissa symphorea, occurred in all landscape types. Plains with red earths had the greatest mean number of species per site (11.2) and the greatest mean crust cover (27.7%). Plains of calcareous earths yielded the greatest number of species (38). Across all sites, crust cover was a poor predictor of lichen species richness. However, on landscape types with non-calcareous soils, mean crust cover explained 88% of the variation in mean number of species. Whilst there was no difference in total number of species across a sequence of geomorphic zones, crust cover was significantly greater in the interception zones (79.0%) compared with either the run-on (6.6%) or run-off (24.0%) zones. These distributional data are compared with other published and unpublished studies from similar areas in Australia. The role of terricolous crusts as indicators of ecosystem health, and the influence of land management on crust cover and subsequent landscape stability are discussed.

Influence of Microrelief, Aggregate Size, and Precipitation on Soil Crust Properties

The USDA-ARS is currently developing a new wind erosion prediction system (WEPS) to estimate wind-induced soil erosion on a daily basis. This new system will estimate several soil crust-related properties not used in previous wind erosion prediction methods. This study was conducted to determine the effects of selected temporally varying surface soil properties and cumulative rainfall on soil crust-related properties used in WEPS. Specifically, crust-related properties including percent aggregate cover, crust cover, loose erodible soil material cover (LEMC), loose erodible soil material mass (LEMM), and plant residue percent cover were measured on fallow, cotton and sorghum fields and related to random roughness, dry aggregate size, and cumulative precipitation. Measurements were made during 1989 and 1990 for replicated plots in fields on three different sandy soils. Mean aggregate cover over the duration of the study ranged from 32 to 33%, crust cover ranged from 56 to 63%, LEMC ranged from 19 to 40%, and LEMM ranged from 1.2 to 1.9 tonne/ha. Although sorghum fields had significantly greater residue than fallow or cotton fields in two out of three soils, management treatments generally did not produce significant differences (P = 0.05) in aggregate cover, crust cover, loose erodible material cover, and loose erodible material mass. Significant differences (P = 0.05) were found among sampling dates for all crust-related properties, indicating a dependence on factors that vary through time. Differences among sampling dates were attributed to the effects of microrelief, cumulative precipitation, and aggregate size. Analysis of variance and regression were used to investigate these effects. Aggregate cover percentage was positively related to random roughness and negatively related to cumulative precipitation. Aggregate cover was not significantly (P = 0.05) related to dry aggregate size. Crust cover percentage was negatively related to random roughness and positively related to cumulative precipitation. Crust cover was not significantly (P = 0.05) related to dry aggregate size. Loose erodible material cover percentage was positively related to dry aggregate size and cumulative precipitation. Loose erodible material mass was positively related for one soil and negatively related for another soil to dry aggregate size, and negatively related to cumulative precipitation. Neither loose erodible material cover nor mass was related to random roughness.

Effects of Grazing on Cryptogamic Crusts in Pinyon-juniper Woodlands in Grand Canyon National Park

-Previously grazed pinyon-juniper woodlands in Grand Canyon National Park, northern Arizona, were studied to determine the effects of past and present grazing. The occurrence and biomass of cryptogamic crust were compared for five sites in and around the Park along a continuum from never grazed to recently grazed. All sites were similar in soil characteristics, elevation and overstory dominants. Cryptogamic crust was quantified using visible cover estimates and the chlorophyll a content of the crust as an indicator of biomass. Visible crust cover was reduced almost 80% on grazed (5.2%) as compared to ungrazed (23.3%) sites. Crust biomass, as estimated by chlorophyll a content, was reduced on grazed (3.1 ,tg cm-2) compared to ungrazed (9.9 ,tg cm-2) sites. There were no significant differences in species presence and absence data. Significant correlations existed between cryptogamic crust cover and the composition of the respective vascular plant communities, marked by a reduction of grasses and an increase of bare soil.

Plant community patterns and soil moisture regime in gypsum grasslands of north central Mexico

Plant community patterns and seasonal changes in soil moisture were evaluated at grazed and ungrazed sites on semi-arid gypsum plains in northern San Luis Potosi, Mexico. Muhlenbergia purpusii was dominant on exposed gypsum soils with indurated surface crusts, while Bouteloua chasei was dominant on exposed gypsum soils with cryptogamic surface crusts. Shallow fine-calcareous alluvial surface soils with gypsum sub-soils were dominated by desert shrubland species. Soil surface characteristics apparently prevent shrubs from establishing on exposed gypsum soils. Gypsum sub-soils are favorable for wide-ranging shrub species as long as a shallow, alluvial surface layer is present. The grassland dominants are slow-growing endemics which appear to be excluded from alluvial surface soils by shrub competition and by the longer period of extreme soil moisture stress in alluvium. Gypsum grassland communities did not show reduction in basal area or invasion by shrubs under heavy grazing pressure, while desert shrubland showed no reversion to perennial grassland under grazing protection. Cryptogamic crust cover was reduced by grazing in all three community types. Grazing decreased mean moisture content in the shrubland soil, possibly by increasing evaporative loss from the surface horizons and forcing the shrubs to use water stored at depth. It increased moisture content in the Muhlenbergia grassland soil, apparently by lowering consumptive use loss.

Influence of grazing management on vegetation, soil structure and nutrient distribution and the infiltration of applied rainfall in a semi‐arid chenopod shrubland

AbstractThe experiment utilized a fenceline contrast in vegetation and soil condition that was clearly visible on Landsat imagery. Measurements of vegetation cover, soil structure and chemistry, and infiltration were made. The greatest vegetation change was at the soil surface where the loss of litter and lichen crust cover under heavy grazing accompanied the loss of perennial shrubs. Although grazing caused changes in soil structure and chemistry to less than 10 cm in depth, these changes are quite significant for plant growth. Consistent differences in the infiltration of applied rainfall at two intensities were measured between the grazed and ungrazed sites. At both intensities of application the absence of a lichen crust increased infiltration three‐fold on the heavily grazed site compared with the ungrazed site. The implications of these observations on the long‐term functioning of this landscape are discussed.

Effects of Long-Term Grazing on Cryptogam Crust Cover in Navajo National Monument, Ariz

The effects of long-term grazing (40 years) on cryptogamic crusts of Navajo National Monument were investigated. Both vascular and nonvascular communities were heavily impacted with the cryptogamic community showing the greatest reduction in cover. Lichens and mosses were the most damaged, while the algae were much more tolerant. Individual cryptogamspeeies were affected in similar patterns with all identifuble species showing reduced cover. Vascuhr plant species were also affected with grassesshowing the greatest reduction under grazing pressure. Throughout desert systems of western North America there is scant ground cover and often extensive open areas between the plants. In such open areas, soils are exposed to powerful erosive impacts. When soils are unprotected, erosion can be extensive and soil losses can be great. Of primary importance in the protection of desert soils are communities of nonvascular cryptogamic plants that grow upon or immediately beneath the soil surface. When well established and undisturbed such plants form a crust which plays an important role in soil stabilization (Fletcher and Martin 1948; Kleiner and Harper 1972, 1977; Loope and Gifford 1972; Anderson et al. 1982a, 1982b). Algae are the primary components of these crusts but they are often accompanied by lichens and mosses (Anderson and Rushforth 1977, Kleiner and Harper 1972). Algae are the most effective in binding the soil particles (Anantani and Marathe 1974, Anderson and Rushforth 1976). Where cryptogam crusts are well developed the soil surface is almost always highly stable. Research has been done on several aspects of the biology of soil crusts and cryptogamic communities. Ecological relationships have been studied by Anderson et al. (1982a) and Anderson et al. (1982b). Species composition and taxonomic relationships of crusts were studied by Anderson and Rushforth (1976). The role of such crusts in nitrogen fixation was studied by Rychert and Skujins (1974) and their effects on infiltrationand sedimentation by Loope and Gifford (1972). However, much is yet to be learned about the role of these crusts in desert ecosystems. The Navajo National Monument boundary (fenceline) provided an excellent opportunity to evaluate the effects of grazing on the cryptogamic soil crusts of the pinyon-juniper zone in northeastern Arizona. The objective of this study was to evaluate the effects of long-term grazing (40 years) on the cryptogamic soil cover of the pinyon-juniper zone in northern Arizona (Navajo National Monument).

CERTAIN GEOCHEMICAL CHARACTERISTICS OF THE FOREST-STEPPE LANDSCAPES IN THE COPPER DISTRICT OF THE SOUTHERN URALS

This is the Fourth of eight papers in the symposium on landscape -geochemical prospecting for chalcopyritic ores in the semi-arid environments of the Southern Urals. Significant variations and correlations are reported in the local geochemical background of Cu, Ni, Co, Cr, V, and other metals, typical of the copper ore bodies in the Greenstone Belt, in the landscape profiles, i.e., in bedrock, weathered crust, soil horizons, and vegetative cover. A landscape-geochemical map, one of the first ones of its kind, with its legend in full, shows the intricate three-dimensional geochemical background pattern of the test area. It is this background that is indeed a prerequisite of success in recognition and interpretation of the many types of geochemical anomalies, so essential in metallometric surveys. V. P. Sokoloff