This volume summarizes our current understanding of biological soil crusts (biocrusts), which are omnipresent in dryland regions. Since they cover the soil surface, they influence, or even control, all surface exchange processes. Being one of the oldest terrestrial communities, biocrusts comprise a high diversity of cyanobacteria, algae, lichens and bryophytes together with uncounted bacteria, and fungi. The authors show that biocrusts are an integral part of dryland ecosystems, stabilizing soils, influencing plant germination and growth, and playing a key role in carbon, nitrogen and water cycling. Initial attempts have been made to use biocrusts as models in ecological theory. On the other hand, biocrusts are endangered by local disruptions and global change, highlighting the need for enhanced recovery methods. This book offers a comprehensive overview of the fascinating field of biocrust research, making it indispensable not only for scientists in this area, but also for land managers, policy makers, and anyone interested in the environment.

In biological soil crusts (biocrusts)--communities of mosses, lichens, cyanobacteria, and heterotrophs living at the soil surface-- fundamental components of drylands worldwide, and destruction of biocrusts dramatically alters biogeochemical processes, hydrology, surface energy balance, and vegetation cover are present. Though there has been long-standing concern over impacts of physical disturbances on biocrusts (e.g., trampling by livestock, damage from vehicles), there is increasing concern over the potential for climate change to alter biocrust community structure. Using long-term data from the Colorado Plateau, in this paper we examined the effects of 10 y of experimental warming and altered precipitation (in full-factorial design) on biocrust communities and compared the effects of altered climate with those of long-term physical disturbance (>10 y of replicated human trampling). Surprisingly, altered climate and physical disturbance treatments had similar effects on biocrust community structure. Warming, altered precipitation frequency [an increase of small (1.2 mm) summer rainfall events], and physical disturbance from trampling all promoted early successional community states marked by dramatic declines in moss cover and increases in cyanobacteria cover, with more variable effects on lichens. Although the pace of community change varied significantly among treatments, these results suggest that multiple aspects of climate change will affect biocrusts to the same degree as physical disturbance. Finally, this is particularly disconcerting in the context of warming, as temperatures for drylands are projected to increase beyond those imposed as treatments in our study.

CD-ROM Water availability is one of the main limiting factors that control ecosystem functions and productivity in semiarid regions. Vegetation of these regions usually presents a patchy distribution where sparse plant cover is interspersed over a bare soil. During the few rainfall events, runoff is generated in non-vegetated areas and redistributed towards vegetation, which act as surface obstruction for water, sediments and nutrients. Thus, non-vegetated areas are more susceptible to water erosion processes. Non-vegetated areas from semiarid ecosystems around the world, are often covered by Biological Soil Crusts (BSCs). BSCs result from an intimate association between soil particles and cyanobacteria, algae, microfungi, lichens and bryophytes. These communities live within, or immediately on top of, the uppermost millimeters of soil, influencing soil surface properties involved in infiltration, runoff generation and water erosion. Several papers have demonstrated that BSCs are one of the most important soil stabilizing factors in drylands. There are, however, contradictory results on the role that BSCs play in regulating soil water fluxes. Some studies point BSCs as runoff sources that may increase downslope erosion or on the contrary may represent an additional supply of water for downslope vegetation allowing its survival. The impact of this additional runoff should be evaluated at less detailed scales than the patch and to analyze all interactions in terms of water, sediments and nutrients between areas covered by BSCs and vegetated patches in order to establish the real effects of BSCs on both runoff and erosion. Also, to correctly predict the impact of future climate changes or antropic disturbances on hydrological behavior and water erosion in systems dominated by BSCs their effects should be included on spatially distributed runoff and erosion models. Until now, the influence of BSCs on these processes has been addressed almost exclusively at patch scale, despite the fact some authors have pointed the need of upscaling their effects, and even more their influence on runoff generation and water erosion was never considered in spatially implicit medelling. The goal of this thesis is to determine BSC effects on runoff and water erosion from plot to catchment scale in a typical semiarid ecosystem. To achieve this objective, first direct and indirect effects of BSCs at patch scale must be clearly defined under natural rainfall conditions to solve the controversy about BSCs effects on runoff generation. To know the direct and indirect relationships among soil surface characteristics, BSC cover and type, topography, rainfall characteristics (duration, amount and intensity) and runoff, structural equation models (SEM) were applied. Our results reveal the critical importance of BSCs on runoff and water erosion. Both processes in biologically crusted areas are directly controlled by crust type and cover. BSCs also modified some soil surface properties involved in runoff generation and water erosion, such as microtopography, surface stability or water repellency. The final interaction of both, direct and indirect BSCs effects, determine the hydrological behavior of these surfaces under natural rainfall conditions. Moreover, the final effect of BSCs on runoff generation is strongly driven by rainfall properties, which determined the set of complex interactions among BSCs, type and developmental stage and soil surface properties: on one hand, during low intensity rains, BSC-induced microtopography increases the amount of surface micro-depressions, which act as temporal water sinks, reducing the connectivity among source areas, delaying runoff initiation and reducing runoff rates; on the other hand, during intense rainfall events, BSCs type and water repellency are the main factors determining runoff generation. When the effects of BSCs are analyzed at coarser scales, including all interactions among BSCs and vegetated areas on a whole catchment, our results reveal the importance of the interactions between areas with BSCs and areas with vegetation on runoff generation and water erosion. We show the capacity of vegetated areas to retain runoff waters generated by upslope biologically crusted areas as an important driver for the hydrological and erosional response at catchment scale. However, the capability of vegetated areas to trap and retain water and sediments is limited and can be exceeded during high magnitude events, increasing catchment connectivity, as well as runoff and water erosion at the catchment outlet. Even during high-magnitude events, when the runoff generated in BSC areas reaches the channel network, the local protection provided by BSCs also affects downslope areas and the catchment response. These results confirm that BSCs must be included in runoff and soil erosion models to obtain reliable predictions of the spatial pattern of runoff and water erosion in catchments with abundant BSCs. In order to correctly introduce the effects of BSCs in these models, it is necessary to have an accurate spatial characterization of BSCs. It is shown that a spectral mixture analysis is required for the precise characterization of the complex spatial distribution of BSCs, due to the intrinsic spatial heterogeneity of semiarid ecosystems and to the spectral similarities among BSCs, dry vegetation and bare soil. Due to the methodological and practical application problems of spectral mixture analysis when it is applied to spectrally complex areas or when some surface elements only appear in specific areas of the image, we needed to develop a novel methodology for BSCs classification and quantification (lichen and cyanobacteria-dominated CBS), based on hyperspectral images. Support vector machine classification was applied for spectral and ecological classification of homogenous areas to solve the mentioned problems inherent to spatial heterogeneity. Inmediately afterwards, spectral mixture analysis (SMA) was applied to each SVM class to quantify the proportion of each type of surface cover within each pixel. Relative abundance images obtained with this methodology achieve a relatively high accuracy for different types of BSCs, and have demonstrated to be an adequate source of spatially distributed information, to correctly characterize surface properties in biologically crusted drylands systems. Moreover, to have the spatial distribution of type and abundance of BSCs allows to increase the accuracy of modeled runoff and erosion. Thus, when BSCs effects are not included in the LISEM model, an important increase in modeled water erosion was observed in areas where BSCs was not considered.

Soils have been called the most complex microbial ecosystems on Earth. A single gram of soil can harbor millions of microbial cells and thousands of species. However, certain soil environments, such as those experiencing dramatic change exposing new initial soils or that are limited in precipitation, limit the number of species able to survive in these systems. In this respect, these environments offer unparalleled opportunities to uncover the factors that control the development and maintenance of complex microbial ecosystems. This book collects chapters that discuss the abiotic factors that structure arid and initial soil communities as well as the diversity and structure of the biological communities in these soils from viruses to plants.

Nearly one-third of the land area on our planet is classified as arid or desert. Therefore, an understanding of the dynamics of such arid ecosystems is essential to managing those systems in a way that sustains human populations. This second edition of Ecology of Desert Systems provides a clear, extensive guide to the complex interactions involved in these areas. This book details the relationships between abiotic and biotic environments of desert ecosystems, demonstrating to readers how these interactions drive ecological processes. These include plant growth and animal reproductive success, the spatial and temporal distribution of vegetation and animals, and the influence of invasive species and anthropogenic climate change specific to arid systems. Drawing on the extensive experience of its expert authors, Ecology of Desert Systems is an essential guide to arid ecosystems for students looking for an overview of the field, researchers keen to learn how their work fits in to the overall picture, and those involved with environmental management of desert areas. Highlights the complexity of global desert systems in a clear, concise way Reviews the most current issues facing researchers in the field, including the spread of invasive species due to globalized trade, the impact of industrial mining, and climate change Updated and extended to include information on invasive species management, industrial mining impacts, and the current and future role of climate change in desert systems