Büdel et al. 2009

Büdel B, Darienko T, Deutschewitz K, Dojani S, Friedl T, Mohr KI, Salisch M, Reisser W, Weber B. 2009. Southern African biological soil crusts are ubiquitous and highly diverse in drylands, being restricted by rainfall frequency. Microbial Ecology 57: 229-247.

These authors examined biological soil crusts (BSCs) along a 2000km transect running roughly north-south through Namibia and South Africa. A number of hypotheses relating to BSC composition, frequency, and succession were proposed and tested, with most hypotheses partly confirmed. In general, BSCs are an important and abundant component of these dryland ecosystems, and show patterns of biodiversity associated with biomass, as measured by chlorophyll-a concentrations and species counts.

The major finding of this study, as implied in the title, is that BSC distribution and composition is primarily controlled by patterns of rainfall, but not total rainfall. Species richness and successional stage of BSCs was highest in the winter rain zone, which has a shorter dry season though less total annual rainfall than the summer rain zone. This implies that most BSC organisms are limited by drought tolerance rather than annual water input.

This study is interesting to me for a number of reasons. First, it includes in the references a number of reviews of BSCs and methods to study them, such as protocols for measuring chlorophyll-a concentrations per square metre, and molecular methods for species richness estimation. Second, because BSCs are expected to be the major photosynthetic organisms in the polar desert, I need to know what patterns of their distribution and diversity I should expect. This paper’s Hypothesis 4, that biomass (and productivity) of BSCs increases with species richness, which was essentially confirmed, is of particular interest in this context, as it provides another layer of background expected pattern in addition to my general expectation of a species-richness gradient associated with latitude, particularly as one crosses Lancaster Sound north of Baffin Island. This paper provides some ideas for ways to measure species richness in BSCs, which (third) contribute strongly to the overall biodiversity of dryland regions and therefore will be interesting in their own right in studies of Arctic Biogeography.