Biocrust research: A critical view on eight common hydrological‐related paradigms and dubious theses

Abstract

Although being relatively young, research on biocrusts has already yielded numerous paradigms and/or dubious theses. The very existence of these “truths” may lead to erroneous conclusions and/or hinder research on these topics. In the current summary, eight paradigms and dubious theses are examined: (a) Biocrusts require physical crusts for establishment; (b) plant establishment is necessary for biocrust establishment on dunes; (c) developmental stages of biocrusts are often regarded as successional stages; (d) climate‐driven crust morphology determines crust hydrology; (e) infiltration (and subsequently run‐off) over biocrusts is determined by soil pores; (f) run‐off in dryland may stem from hydrophobicity; (g) exopolysaccharides trigger infiltration; and (h) mosses impede infiltration and subsequently the growth of perennial plants. During this summary, reasons that lie behind these paradigms and dubious theses are examined using data and/or rationale for a critical analysis. Experimental data, mostly gathered from the Nizzana research site of the Hallamish dune field (Negev Desert, Israel), and published material (mainly from the Tabernas and Tengger deserts) are used. It is argued that most of the paradigms were either based on improper techniques or never thoroughly investigated. The argument presented herein does not necessarily imply that none of the paradigms may take place under very specific conditions but that their acceptance as general “truth” is questionable.

Character, Rates, and Environmental Significance of Holocene Dust Accumulation in Archaeological Hilltop Ruins in the Southern Levant

“…Similarly, Baruch and Goring-Morris [82] reported that the Negev was covered by more mesic and denser woody vegetation during the Terminal Pleistocene, due to higher humidity. Denser vegetation would more efficiently trap sand particles [83]. This probably includes some sand from weathering of the underlying sandstones in the Petra region.…”

Composition of Modern Dust and Holocene Aeolian Sediments in Archaeological Structures of the Southern Levant

“…The hilltop ruin soils from the Petra region (the triclinium JF site 124/1 and Umm Saysaban, no. [67][68][69][70][71] are chemically similar and cluster in the lower center of the diagram, with negative values of PC2 and values of PC1 around 0. In contrast, samples from the sandstone terrace (samples Jh site 33, no.…”

“…This seems due to a contribution from nearby sandstone cliffs: proximity to such local sources leads to higher supply of sediment, in this case, rich in medium sand. In addition, the agricultural use of the monastery garden, probably with cistern-based irrigation, could have led to stronger presence of vegetation, which has been found to favor the trapping of sand [70].…”

Hydrological function of rapidly induced biocrusts

“…On the Colorado Plateau, well-developed lichen, moss, and dark-pigmented biocrusts tend to have greater levels of aggregate stability and surface roughness than biocrusts dominated by lightpigmented cyanobacteria (Fischer et al, 2010;Warren, 2001), which are often considered early successional (Belnap et al, 2013, but see Kidron, 2018). The most notable differences between plots with stabilizer and others were the significantly higher levels of both EPS and aggregate stability ( Figure 2), variables that were highly correlated (R 2 = 0.58, p = .002).…”

“…On the Colorado Plateau, well-developed lichen, moss, and dark-pigmented biocrusts tend to have greater levels of aggregate stability and surface roughness than biocrusts dominated by lightpigmented cyanobacteria (Fischer et al, 2010;Warren, 2001), which are often considered early successional (Belnap et al, 2013, but see Kidron, 2018). The enhanced roughness and stability of welldeveloped biocrusts likely counteract the effects of hydrophobicity and pore clogging on infiltration by biocrust biomass (as both filamentous cyanobacteria and other organisms are abundant in these biocrusts), but this may depend on rainfall intensity (Rodríguez-Caballero et al, 2013).…”