Correlates of biological soil crust abundance across a continuum of spatial scales: support for a hierarchical conceptual model

Abstract

Summary1. Desertification negatively impacts a large proportion of the global human population and > 30% of the terrestrial land surface. Better methods are needed to detect areas that are at risk of desertification and to ameliorate desertified areas. Biological soil crusts are an important soil lichen-moss-microbial community that can be used toward these goals, as (i) bioindicators of desertification damage and (ii) promoters of soil stability and fertility. 2. We identified environmental factors that correlate with soil crust occurrence on the landscape and might be manipulated to assist recovery of soil crusts in degraded areas. We conducted three studies on the Colorado Plateau, USA, to investigate the hypotheses that soil fertility [particularly phosphorus (P), manganese (Mn) and zinc (Zn)] and/or moisture limit soil crust lichens and mosses at four spatial scales. 3. In support of the soil fertility hypothesis, we found that lichen-moss crusts were positively correlated with several nutrients [Mn, Zn, potassium (K) and magnesium (Mg) were most consistent] at three of four spatial scales ranging from 3·5 cm 2 in area to c. 800 km 2 . In contrast, P was negatively correlated with lichen-moss crusts at three scales. 4. Community composition varied with micro-aspect on ridges in the soil crust. Three micro-aspects [north-north-west (NNW), east-north-east (ENE) and TOP] supported greater lichen and moss cover than the warmer, windward and more xeric micro-aspects [west-south-west (WSW) and south-south-east (SSE)]. This pattern was poorly related to soil fertility; rather, it was consistent with the moisture limitation hypothesis. 5. Synthesis and application. Use of crusts as desertification bioindicators requires knowledge of a site's potential for crust cover in the absence of desertification. We present a multi-scale model of crust potential as a function of site properties. Future quantitative studies can use this model to guide sampling efforts. Also, our results suggest new directions in restoration research: enhancement of moisture residence time and fertilization with key nutrients (Mn, Zn, K and Mg). Re-establishment of soil crusts in desertified lands will help regain lost soil stability and fertility, and facilitate plant re-establishment.

Insolation and disturbance history drive biocrust biodiversity in Western Montana rangelands

“…Our soil pH and texture data had a low variance compared to the other studies and to our insolation data. In contrast, studies conducted in areas with a greater diversity of soil parent materials or weathering environments are likely to display strong edaphic control on biocrust abundance and structure (Bowker et al 2006). …”

“…Further complicating the matter, specific expressions of interdependent climatic, edaphic, topographic, and biotic forces vary by spatial scale (Ochoa-Hueso et al 2011;Bowker et al 2016). For example, water availability may correlate with biocrust abundance, composition and physical structure across regional precipitation and evapotranspiration gradients, local insolation gradients generated by topography, or fine-scale shade gradients generated by plant canopies and soil surface microtopography (Bowker et al 2006). Juxtaposed over the complex, scale-dependent environmental influences on biocrust communities are anthropogenic disturbance legacies.…”

Drivers of lichen species richness at multiple spatial scales in temperate forests

“…Epiphytic lichens are affected by several environmental factors whose relative importance may depend on the scale of the analysis (Bowker et al 2006;Will-Wolf et al 2006;Ellis andCoppins 2009, 2010). Hence, to provide effective conservation strategies to improve lichen diversity the influence of different environmental and management-related factors needs to be evaluated at multiple spatial and temporal scales (Crawley and Harral 2001;Willis and Whittaker 2002).…”

Analysis of environmental factors determining development and succession in biological soil crusts

“…Both K and Na contents restricting the emergence of lichens may be because these ions play an important role in regulating water content of lichen thalli (Stocker-Wörgötter and Türk, 1991). In addition, in other researches it has been reported that Mn and Zn (DTPA extracted) may also be the important limited nutrients for some lichen species (Bowker et al, 2005(Bowker et al, , 2006, while higher P availability and CaCO 3 support lower lichen coverage (Bowker et al, 2006).…”

“…Except for the soil microenvironments, climate and also vegetation appeared to have an effect on crust development and succession, because different crust species response variously to those influencing factors Bowker et al, 2006), among which some factors may directly affect crust metabolism (eg. solar radiation, although radiation also changes soil temperature and water content), while the others affect BSCs via changing the ambient soil microenvironments, such as soil water availability.…”