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Biological soil crusts (hereafter, “biocrusts”) dominate soil surfaces in nearly all dryland environments. To better understand the influence of water content on carbon (C) exchange, we assessed the ability of dual-probe heat-pulse (DPHP) sensors, installed vertically and angled, to measure changes in near-surface water content. Four DPHP sensors were installed in each of two research plots (eight sensors total) that differed by temperature treatment (control and heated). Responses were compared to horizontally installed water content measurements made with three frequency-domain reflectometry (FDR) sensors in each plot at 5-cm depth. The study was conducted near Moab, Utah, from April through September 2009. Results showed significant differences between sensor technologies: peak water content differences from the DPHP sensors were approximately three times higher than those from the FDR sensors; some of the differences can be explained by the targeted monitoring of biocrust material in the shorter DPHP sensor and by potential signal loss from horizontally installed FDR sensors, or by an oversampling of deeper soil. C-exchange estimates using the DPHP sensors showed a net C loss of 69 and 76 g C m −2 in control and heated plots, respectively. The study illustrates the potential for using the more sensitive data from shallow installations for estimating C exchange in biocrusts. [ABSTRACT FROM AUTHOR]

Abstract: Biological soil crusts (biocrusts) are ubiquitous in drylands globally. Lichens and mosses are essential biocrust components and provide a variety of ecosystem services, making their conservation and management of interest. Accordingly, understanding what factors are correlated with their distribution is important to land managers. We hypothesized that cover would be related to geologic and pedologic factors. We sampled 32 sites throughout the eastern Mojave Desert, stratifying by parent material and the age of the geomorphic surfaces. The cover of lichens and mosses on ‘available ground’ (L + Mav; available ground excludes ground covered by rocks or plant stems) was higher on limestone and quartzite-derived soils than granite-derived soils. Cover was also higher on moderately younger-aged geomorphic surfaces (Qya2, Qya3, Qya4) and cutbanks than on very young (Qya1), older-aged surfaces (Qia1, Qia2), or soils associated with coppice mounds or animal burrowing under Larrea tridentata. When all sites and parent materials were combined, soil texture was the most important factor predicting the occurrence of L + Mav, with cover positively associated with higher silt, very fine sand, and fine sand fractions and negatively associated with the very coarse sand fraction. When parent materials were examined separately, nutrients such as available potassium, iron, and calcium became the most important predictors of L + Mav cover. [Copyright &y& Elsevier]

Abstract: The natural landscapes of semiarid areas worldwide comprise a series of scattered patches of shrubs within a matrix of biologically crusted soils (BSC). As BSCs are considered ecosystem engineers the relationships between the BSC and the shrub patches determine system functioning. The objective of our study was to investigate long-term effects of agricultural practices on biological soil crusts and their influence on hydrological aspects of a semiarid ecosystem. During 1991, we experimentally simulated five of the area''s agricultural practices; 1) Scraping – the topsoil was removed to a depth of 2 cm, 2) Spraying – phototrophic organisms were chemically killed with herbicide, 3) Mowing – perennial vegetation was cut and spread to simulate grazing practices, 4) Car track – a heavy roller was used to simulate car-tracks, 5) Control – undisturbed natural plots. Sixteen years later, in 2007, these agricultural practices were found to have a long-term effect on the crusted soil surface and the related soil-surface properties. Mowing and car-track treatments led to decreased overland runoff and increased hydraulic conductivity, whereas scraping and spraying treatments led to increased overland runoff production and decreased hydraulic conductivity. We conclude that the practices had a long-term residual impact on BSC succession and related soil surface properties, which affected the hydrological processes and system functioning. [Copyright &y& Elsevier]

Abstract: Biological soil crusts (BSCs), composed of lichens, cyanobacteria, mosses, liverworts and microorganisms, are key biotic components of arid and semi-arid ecosystems worldwide. Despite they are widespread in Spain, these organisms have been historically understudied in this country. This trend is beginning to change as a recent wave of research has been identifying BSCs as a model ecological system. Many studies and research projects carried out in Spain have explored the role of BSCs on water, carbon and nitrogen fluxes, the interactions between BSCs and vascular plants, their dynamics after disturbances, and their response to global change, among other topics. In this article we review the growing body of research on BSCs available from semi-arid areas of Spain, highlighting its importance for increasing our knowledge on this group of organisms. We also discuss how it is breaking new ground in emerging research areas on the ecology of BSCs, and how it can be use to guide management and restoration efforts. Finally, we provide directions for future research on the ecology of BSCs in Spain and abroad. [Copyright &y& Elsevier]

Abstract: In Northern Mexico, long-term grazing has substantially degraded semiarid landscapes. In semiarid systems, ecological and hydrological processes are strongly coupled by patchy plant distribution and biological soil crust (BSC) cover in plant-free interspaces. In this study, we asked: 1) how responsive are BSC cover/composition to a drying/wetting cycle and two-year grazing removal, and 2) what are the implications for soil erosion? We characterized BSC morphotypes and their influence on soil stability under grazed/non-grazed conditions during a dry and wet season. Light- and dark-colored cyanobacteria were dominant at the plant tussock and community level. Cover changes in these two groups differed after a rainy season and in response to grazing removal. Lichens with continuous thalli were more vulnerable to grazing than those with semi-continuous/discontinuous thalli after the dry season. Microsites around tussocks facilitated BSC colonization compared to interspaces. Lichen and cyanobacteria morphotypes differentially enhanced resistance to soil erosion; consequently, surface soil stability depends on the spatial distribution of BSC morphotypes, suggesting soil stability may be as dynamic as changes in the type of BSC cover. Longer-term spatially detailed studies are necessary to elicit spatiotemporal dynamics of BSC communities and their functional role in biotically and abiotically variable environments. [Copyright &y& Elsevier]

Abstract: The composition of cyanobacteria, mosses, and lichens of biological soil crusts were correlated with soil characteristics and sun exposure along an environmental transect. The study was conducted in Zapotitlán drylands, a locality within the Tehuacán–Cuicatlán Valley, central Mexico, where a great variety of environments for crust development exist due to landscape fragmentation. Data were analyzed with redundancy and Sorensen analysis. Soil crusts consisted of different combinations of cyanobacteria (7 species), mosses (19 species), and lichens (8 species). The relative frequencies of these groups were positively correlated with soil apparent density and lichens were also positively correlated with soil pH. However, there were no significant correlations with sun exposure. [Copyright &y& Elsevier]

Abstract: Biological soil crusts provide habitat for microarthropods of various trophic groups in arid systems, but the community composition and functional role of microarthropods in these unique systems are not well characterized for many desert locations. This study examined the microarthropod community, including mites, collembolans, and tardigrades, associated with early- and late-successional stage biological soil crusts at two locations, Colorado Plateau (southeastern Utah) and Chihuahuan Desert (southern New Mexico). Most microarthropod groups were more abundant in Colorado Plateau than Chihuahuan Desert, and tardigrades were more abundant near the surface (0–10cm) than at depth (10–30cm). Although the microarthropod community composition differed between Colorado Plateau and Chihuahuan Desert, Aphelacaridae, Cosmochthoniidae, Micropsammidae, Nanorchestidae, Stigmaeidae, and Tydeidae were families common to both locations, both crust stages and both depths. Most families present were microphytophagous, either strictly or as facultative predators. These findings are compatible with the microfloral nature of biological soil crusts dominated by lichen, moss, and cyanobacteria. Occasional predation of nematodes and protozoa grazing on the crust flora is likely. Other groups identified included zoophages, necrophages and macrophytophages. Proposed is a ‘core community’ of five strict microphytophages, four facultative predators, two zoophages, and one necrophage family. [Copyright &y& Elsevier]

The dominant direct physical processes responsible for desertification are water erosion, wind erosion and salinization. Other threats that degrade the soil include loss of biodiversity, loss of soil organic matter, fire, changing water resources, soil compaction, soil sealing and contamination. Soil management inevitably combines human and physical effects. Climate, which is the most important driver of the physical systems, is now being rapidly modified by human action, and at a scale which is much coarser than any local remedial action. In a model of near-subsistence systems, productivity is limited by climate and available labour, with some options for additional inputs through improved seed, fertilizer or tillage equipment. Optimum solutions in a particular environment depend on both climate and access to markets. Agricultural surpluses, if any, allow investment in infrastructure – some of it directly supporting agriculture through irrigation and market systems, some less directly useful through, for example, warfare or pyramid building. Today some traditional drivers of desertification, based on subsistence agriculture and grazing, may have become less relevant, as land, particularly in the global South, is developed for intensive irrigated farming, and populations move into mega-cities. The dominant drivers may become soil sealing around cities and transfers of urban and irrigation water. In semi-arid areas this will lead to competition for the best land – for urban expansion and agricultural land with irrigation potential. Desertification then becomes an issue increasingly focussed on abandoned marginal land, maintaining biodiversity, managing regional water resources and controlling erosion in the face of global climate change. [Display omitted] • Desertification is discussed in the context of a mixed subsistence/cash economy. • A model estimates labour surplus as a function of climate, fertiliser and population. • The model is applied for both arable and pastoral economies. • Labour surplus provides for re-investment in the land or improving infrastructure. • Can arid lands be sustainably managed in an urbanising world? [ABSTRACT FROM AUTHOR]

Abstract: Biological soil crusts (BSCs) are an integral part of dryland ecosystems and often included in long-term ecological monitoring programs. Estimating moss and lichen cover is fairly easy and non-destructive, but documenting cyanobacterial level of development (LOD) is more difficult. It requires sample collection for laboratory analysis, which causes soil surface disturbance. Assessing soil surface stability also requires surface disturbance. Here we present a visual technique to assess cyanobacterial LOD and soil surface stability. We define six development levels of cyanobacterially dominated soils based on soil surface darkness. We sampled chlorophyll a concentrations (the most common way of assessing cyanobacterial biomass), exopolysaccharide concentrations, and soil surface aggregate stability from representative areas of each LOD class. We found that, in the laboratory and field, LOD classes were effective at predicting chlorophyll a soil concentrations (R 2=68–81%), exopolysaccharide concentrations (R 2=71%), and soil aggregate stability (R 2=77%). We took representative photos of these classes to construct a field guide. We then tested the ability of field crews to distinguish these classes and found this technique was highly repeatable among observers. We also discuss how to adjust this index for the different types of BSCs found in various dryland regions. [Copyright &y& Elsevier]

Abstract: Soil crust lichens can be the dominant vegetation in arid lands, yet their importance as habitat to secondary producers is relatively unknown. This study examines the distribution of arthropod communities in the northern Namib Desert to evaluate whether a lichen-rich area is more or less productive than adjacent habitats in terms of the consumers each supports. Arthropods are diverse and highly endemic in the Namib Desert and lichens dominate this desert''s extensive gravel plains. We sampled lichen-rich, dwarf shrub, and unvegetated sites and found distinct arthropod assemblages in the lichen-dominated sites, including species unique to lichen sites. Arthropod assemblages in two of the lichen sites were similar to those found in the dwarf shrub site. In a canonical correspondence analysis, crustose lichens and overall lichen cover were key in driving the variance in arthropod assemblages within the lichen sites. Furthermore, lichen morphotypes, overall lichen cover and species richness, were significantly correlated with the representation of arthropod subgroups and arthropod species richness. These findings provide evidence that lichen-dominated soil crusts in the Namib Desert are important supporters of secondary production, warranting more in-depth studies into the ecology and conservation of this lichen-rich habitat in warm deserts. [Copyright &y& Elsevier]

Crusts on soil surfaces are well recognized for wind erosion control in arid regions and mine tailings. In the last two decades, the use of microorganisms for crust formation on the soil surface has been developed. The topic here is to examine the durability of a biocrust created by Microcoleus vaginatus cyanobacterium and a biocemented sand crust induced by precipitation of calcium carbonate by Bacillus subtilis against wind erosion. To this aim, the crusts were subjected to three wind velocities and one sandblasting condition for three different periods in wind tunnel simulation. Also, the strength of the crusts was measured after each period of sandblasting by a penetration test. The results suggested that the biocemented sand crust has a comparatively stronger bonding and more coherent structure so that its strength did not change in sandblasting in contrary to that of the cyanocrust. Concerning the crusts' erodibility, the biocemented sand crust was more durable than the cyanocrust, and its erosion was not progressive at any conditions. • The biocemented sand crust is more durable than the cyanocrust against wind erosion. • The biocemented sand crust has a coherent structure. • The biocemented sand crust's strength does not change over time in sandblasting. • The cyanocrust suffers strength reduction and progressive erosion in sandblasting. [ABSTRACT FROM AUTHOR]

The Soil Crust International (SCIN) project was a multidisciplinary attempt to obtain a complete understanding of biocrusts communities across Europe, including among the monitored locations the Tabernas badlands in Spain, the driest habitat in the whole continent. Here we provide an overview in a Mini-Review format of our research about the functional performance of the more relevant biocrust forming organisms involved, looking for similarities and differences in the behavior of these communities in regions with contrasting environmental conditions, allowing a deeper understanding of habitat over biocrusts functioning. New unpublished results linked to SCIN are also included in order to reinforce or clarify some general ideas proposed within the text. The general perspective provided to the data through this unique multi-site comparison, will allow in depth studies of relevant functional traits that can shed some light over the possibility of biocrusts behaving as functional types under some circumstances. Poikilohydry is proposed as an essential driving force involved, at different extents, in all key traits ruling biocrusts ecophysiology. • Summary of biocruts functional performance across Europe. • Functional Type theory has been approached to biocrusts ecophysiology. • The environment is a regulator of several key functional traits in biocrusts. • Poikilohydry acts as a driving force in biocrusts functionality. [ABSTRACT FROM AUTHOR]