The volume comprises 33 chapters and is divided into the following eight Parts:Part I: Taxonomic Composition, Ecology and Biogeography of Soil-Crust Communities * Part II: Heterotrophic Components of Biological Soil Crusts * Part III: Structure of Biological Soil Crusts: Microscale to Landscape * Part IV: Biological Soil Crusts as an Ecosystem Component: Carbon and Nitrogen Acquisition and Interactions with Vascular Plants * Part V: Soil Stability and Hydrology as Influenced by Soil Crusts * Part VI: Disturbance to Biological Soil Crusts: Resistance, Resilience and Restoration * Part VII: Monitoring and Management of Biological Soil Crusts * Part VIII: Conclusions.

Biological soil crusts : structure, function, and management

Water and nutrients are scarce resources in arid and semiarid ecosystems. In these regions, biological soil crusts (BSCs) occupy a large part of the soil surface in the open spaces surrounding patches of vegetation. BSCs affect physicochemical soil properties, such as aggregate stability, water retention, organic carbon (OC) and nitrogen (N) content, associated with primary ecosystem processes like water availability and soil fertility. However, the way BSCs modify soil surface and subsurface properties greatly depends on the type of BSC. We hypothesised that physicochemical properties of soil crusts and of their underlying soils would improve with crust development stage. Physicochemical properties of various types of soil crusts (physical crusts and several BSC development stages) and of the underlying soil (soil layers 0–1 cm and 1–5 cm underneath the crusts) in two semiarid areas in SE Spain were analysed. The properties that differed significantly depending on crust development stage were aggregate stability, water content (WC) (at −33 kPa and −1500 kPa), OC and N content. Aggregate stability was higher under well-developed BSCs (cyanobacterial, lichen and moss crusts) than under physical crusts or incipient BSCs. WC, OC and N content significantly increased in the crust and its underlying soil with crust development, especially in the first centimetre of soil underneath the crust. Our results highlight the significant role of BSCs in water availability, soil stability and soil fertility in semiarid areas.

/pdf/biological-soil-crust-development-affects-physicochemical-4co352gpa6.pdf

Biological soil crust development affects physicochemical characteristics of soil surface in semiarid ecosystems

Biological soil crusts (BSCs) are found in all dryland regions of the world, including the polar regions. They are also known to occur in the southern African region. Although there were a number of case studies on BSCs from that region, we did not know if they are a normal part of the vegetation cover or just a phenomenon that occasionally occurs here and there. In order to investigate diversity, distribution patterns, and the driving factors of both, we followed a random sampling system of observatories along a transect, stretching from the Namibian–Angolan border down south to the Cape Peninsula, covering seven different major biomes. Biological soil crusts were found to occur in six out of seven biomes. Despite the fact that soil-dwelling algae occurred in the Fynbos biome, crust formation was not observed for hitherto unknown reasons. Seven BSC types were distinguished on the basis of morphology and taxonomic composition: three of them were cyanobacteria-dominated, one with additional chlorolichens, two with bryophytes, one hypolithic type restricted to quartz gravel pavements, and the unique lichen fields of the Namib Desert. Besides 29 green algal species in 21 genera, one heterokont alga, 12 cyanolichens, 14 chlorolichens, two genera of liverworts, and three genera of mosses, these crusts are positioned among the most diverse BSCs worldwide mainly because of the unusual high cyanobacterial species richness comprising 58 species in 21 genera. They contribute considerably to the biodiversity of arid and semi-arid bioregions. Taxonomic diversity of cyanobacteria was significantly higher in the winter rain zone than in the summer rain zone (54 versus 32 species). The soil photosynthetic biomass (chlorophylla/m2), the carbon content of the soil and the number of BSC types were significantly higher in the winter rain zone (U
 27, 29 = 215.0, p = 0.004 [chla]; U
 21, 21 = 135.0, p = 0.031 [C]; U
 27, 29 = 261.5, p = 0.028 [BSC types]; excluding the fog-dominated Namib biome). The winter rain zone is characterized by a lower precipitation amount, but a higher rain frequency with the number of rainy days more evenly distributed over the year. The dry period is significantly shorter per year in the winter rain zone (U
 8, 9 = 5.0, p = 0.003). We conclude that rain frequency and duration of dry periods rather than the precipitation amount is the main factor for BSC growth and succession. Nitrogen content of the soils along the transect was generally very low and correlated with soil carbon content. There was a weak trend that an increasing proportion of silt and clay (<0.63 mm) in the soil is associated with higher values of BSC chlorophyll content (Pearson correlation coefficient = 0.314, p = 0.237). Furthermore, we found a significant positive correlation between silt and clay and the number of BSC types (Pearson correlation coefficient = 0.519, p = 0.039), suggesting that fine grain-size promotes BSC succession and their biomass content. Lichens and bryophytes occurred in BSCs with lower disturbance frequencies (e.g. trampling) only. Crust thickness and chlorophyll content increased significantly from crusts of the early successional type to the late successional crust types. From our results, we conclude that BSCs are a normal and frequent element of the vegetation in arid and semi-arid southwestern Africa, and that rain frequency and duration of dry periods rather than the precipitation amount are the key factors for the development, differentiation and composition of BSCs.

Southern African Biological Soil Crusts are Ubiquitous and Highly Diverse in Drylands, Being Restricted by Rainfall Frequency

In arid and semi-arid areas with sparse vegetation cover, the spatial pattern of surface soil properties affects water and nutrient flows, and is a question of considerable interest for understanding degradation processes and establishing adequate management measures. In this study, we investigate the spatial distribution of vegetation and surface soil properties (biological crusts, physical crusts, mosses, rock fragments, earthworm casts, fine root accumulation and below-ground stones) in a semi-arid Stipa tenacissima L. steppe in SE Spain. We applied the combination of spatial analysis by distance indices (SADIE) and geostatistics to assess the spatial pattern of soil properties and vegetation, and correlation analyses to explore how these patterns were related. SADIE analysis detected significant clumped patterns in the spatial distribution of vegetation, mosses, fine root accumulation and below-ground stone content. Contoured SADIE index of clustering maps suggested the presence of patchiness in the distribution of earthworm casts, fine roots, below-ground stone content, mosses and biological crusts. Correlation analyses suggested that spatial pattern of some soil properties such as biological crusts, moss cover, surface rock fragments, physical crusts and fine roots were significantly related with above-ground plant distribution. We discuss the spatial arrangement of surface soil properties and suggest mechanistic explanations for the observed spatial patterns and relationships.

/pdf/spatial-patterns-of-surface-soil-properties-and-vegetation-2mfiyd70gb.pdf

Spatial patterns of surface soil properties and vegetation in a Mediterranean semi-arid steppe

https://www.ntc.blm.gov/krc/uploads/643/Morphological%20Groups;%20A%20framework%20for%20Monitoring.pdf

Morphological groups: a framework for monitoring microphytic crusts in arid landscapes

Environmental factors relating to the distribution of terricolous bryophytes and lichens in semi-arid eastern Australia

A Practical Guide to Soil Lichens and Bryophytes of Australia's Dry Country

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Environmental factors relating to the distribution of terricolous bryophytes and lichens in semi-arid eastern Australia

A Practical Guide to Soil Lichens and Bryophytes of Australia's Dry Country