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Biological soil crusts, consisting of cyanobacteria, green algae, lichens, and mosses, are important in stabilizing soils in semi-arid and arid lands. Integrity of these crusts is compromised by compressional disturbances such as foot, vehicle, or livestock traffic. Using a portable wind tunnel, we found threshold friction velocities (TFVs) of undisturbed crusts well above wind forces experienced at these sites; consequently, these soils are not vulnerable to wind erosion. However, recently disturbed soils or soils with less well-developed crusts frequently experience wind speeds that exceed the stability thresholds of the crusts. Crustal biomass is concentrated in the top 3 mm of soils. Sandblasting by wind can...
Shrub encroachment in arid and semiarid rangelands, a worldwide phenomenon, results in a heterogeneous landscape characterized by a mosaic of nutrient-depleted barren soil bordered by nutrient-enriched shrubby areas known as “fertile islands.� Even though shrub encroachment is considered as a major contributor to rangeland degradation, little is known about mechanisms favoring the reversibility of the early stages of this process. Here we synthesize the interactions between fires and soil erosion processes, and the implications of these interactions for management of rangelands. The burning of shrub vegetation develops relatively high levels of soil hydrophobicity. This fire-induced water repellency was shown...
Desert grasslands, which are very sensitive to external drivers like climate change, are areas affected by rapid land degradation processes. In many regions of the world the common form of land degradation involves the rapid encroachment of woody plants into desert grasslands. This process, thought to be irreversible and sustained by biophysical feedbacks of global desertification, results in the heterogeneous distribution of vegetation and soil resources. Most of these shrub-grass transition systems at the desert margins are prone to disturbances such as fires, which affect the interactions between ecological, hydrological, and land surface processes. Here we investigate the effect of prescribed fires on the landscape...
The definition of desertification accepted in the ad hoc conference held by UNEP in Nairobi in 1977 and confirmed at the Earth Summit on Environment and Development held in Rio de Janeiro in 1992 is: ?arid, semi-arid and dry-subhumid land degradation?. There is no global long-term trend in any rainfall change over the period of instrumental record (c. 150 years), but there has been an increase of 0�5�C in global temperature over the past 100 years. This increase seems partly due to urbanization, as there is no evidence of it resulting from atmospheric pollution by CO2and other warming gases (SO2, NO2, CH4, CFH etc.). On the other hand, the thermal increase is uneven, increasing with latitudes above 40� N and S....
Land degradation in drylands is one of the major environmental issues of the 21st century particularly due to its impact on world food security and environmental quality. Climate change, shifts in vegetation composition, accelerated soil erosion processes, and disturbances have rendered these landscapes susceptible to rapid degradation that has important feedbacks on regional climate and desertification. Even though the role of hydrologic?aeolian erosion and vegetation dynamic processes in accelerating land degradation is well recognized, most studies have concentrated only on the role of one or two of these components, and not on the interactions among all three. Drawing on relevant published studies, here we review...
In this study, we investigate changes in ecosystem structure that occur over a gradient of land-degradation in the southwestern USA, where shrubs are encroaching into native grassland. We evaluate a conceptual model which posits that the development of biotic and abiotic structural connectivity is due to ecogeomorphic feedbacks. Three hypotheses are evaluated: 1. Over the shrub-encroachment gradient, the difference in soil properties under each surface-cover type will change non-linearly, becoming increasingly different; 2. There will be a reduction in vegetation cover and an increase in vegetation-patch size that is concurrent with an increase in the spatial heterogeneity of soil properties over the shrub-encroachment...
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Woody plant encroachment and overall declines in perennial vegetation in dryland regions can alter ecosystem properties and indicate land degradation, but the causes of these shifts remain controversial. Determining how changes in the abundance and distribution of grass and woody plants are influenced by conditions that regulate water availability at a regional scale provides a baseline to which compare how management actions alter the composition of these vegetation types at a more local scale and can be used to predict future shifts under climate change. Using a remote sensing-based approach, we assessed the balance between grasses and woody plants and how climate and topo-edaphic conditions affected their abundances...
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This dataset includes the cover of perennial grasses in 1989, 1995, 1999, 2005, and 2009 across southern Arizona. Cover was determined using sub-pixel classifications of two Landsat scenes from path 36, row 38 (centered on latitude: 31.7470, longitude: -111.3981) and path 37, row 38 (31.7470, -112.9431) that encompass Tucson, AZ.
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This dataset includes the cover of leguminous trees (Prosopis velutina, Parkinsonia microphylla, Parkinsonia florida) in 1989, 1995, 1999, 2005, and 2009 across southern Arizona. Cover was determined using sub-pixel classifications of two Landsat scenes from path 36, row 38 (centered on latitude: 31.7470, longitude: -111.3981) and path 37, row 38 (31.7470, -112.9431) that encompass Tucson, AZ.
Land degradation in drylands is one of the major environmental issues of the 21st century particularly due to its impact on world food security and environmental quality. Climate change, shifts in vegetation composition, accelerated soil erosion processes, and disturbances have rendered these landscapes susceptible to rapid degradation that has important feedbacks on regional climate and desertification. Even though the role of hydrologic–aeolian erosion and vegetation dynamic processes in accelerating land degradation is well recognized, most studies have concentrated only on the role of one or two of these components, and not on the interactions among all three. Drawing on relevant published studies, here we...
We compared short-term effects of lug-soled boot trampling disturbance on water infiltration and soil erodibility on coarse-textured soils covered by a mixture of fine gravel and coarse sand over weak cyanobacterially-dominated biological soil crusts. Trampling significantly reduced final infiltration rate and total infiltration and increased sediment generation from small (0.5 m2) rainfall simulation plots (p<0.01). Trampling had no effect on time to runoff or time to peak runoff. Trampling had similar effects at sites with both low and very low levels of cyanobacterial biomass, as indicated chlorophyll a concentrations. We concluded that trampling effects are relatively independent of differences in the relatively...
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This dataset includes the cover of creosote bush (Larrea tridentata)in 1989, 1995, 1999, 2005, and 2009 across southern Arizona. Cover was determined using sub-pixel classifications of two Landsat scenes from path 36, row 38 (centered on latitude: 31.7470, longitude: -111.3981) and path 37, row 38 (31.7470, -112.9431) that encompass Tucson, AZ.
    map background search result map search result map Data for Decadal shifts in grass and woody plant cover are driven by prolonged drying and modified by topo-edaphic properties Shifts in Perennial grass in southern Arizona, 1989 - 2009 Shifts in Creosote bush in southern Arizona, 1989 - 2009 Shifts in Leguminous tree in southern Arizona, 1989 - 2009 Data for Decadal shifts in grass and woody plant cover are driven by prolonged drying and modified by topo-edaphic properties Shifts in Perennial grass in southern Arizona, 1989 - 2009 Shifts in Creosote bush in southern Arizona, 1989 - 2009 Shifts in Leguminous tree in southern Arizona, 1989 - 2009