How do succession and the microhabitat interact to shape the mosaic of biocrust types in the Tabernas Desert (semi-arid Southeast Spain)? We hypothesize that succession (in human time scales) occurs only where the habitat allows it and can regress. Reviewing results from an extensive body of research conducted at the Tabernas region, we aimed (i) to show that crust types can be considered successional stages, (ii) to propose a succession model. We used two approaches: (a) direct, in situ monitoring of three sites (13, 17 and 11 years) and examination of unaltered micro-profiles of biocrusted soil; and (b) indirect assessment, by reviewing functional properties (e.g., ecohydrology, soil loss, physical–chemical properties, microbiota and gas exchange) of biocrust types hypothetically considered successional stages. Although differences among communities in these functions do not necessarily imply species replacement, they were consistent with the hypothetical successional order and the evidence of replacement from the direct approaches. Succession occurs at various speeds across space because it is controlled by habitat. Therefore, it is mainly observable in favourable habitats where the biocrust was altered, or in ecotones. We propose a succession model, including microclimatic controls, two early cyanobacterial stages and two later lichen stages, showing the regressive paths.

The last half of the previous century has seen an explosion in publications on biocrusts, communities of eukaryotic and prokaryotic organisms inhabiting the uppermost surface of predominantly dryland soils. Much of the early work emanated from the western United States, yet there have been few attempts to document the breadth of this work and its contribution to our understanding of the ecosystem roles of biocrusts. We used a structured literature search to extract the 868 publications on biocrusts published between January 1900 and July 2024, and explored the trends in publications in 12 subject areas over that time. We found that almost half of the 868 publications focussed on the ecological and physiological effects of biocrusts and that more recent research explored emerging fields such as restoration, monitoring and climate change impacts. Five authors comprised about 10% of all authors on these publications, and 5.5% of publications had 10 or more authors. The number of authors per publication tended to increase over time. We identified three main periods of research ranging from basic ecology and exploration of ecological mechanisms pre-2000 to biocrust function, physiology and climatic drivers up to 2020. The post-2020 period was characterized by a greater emphasis on molecular approaches, restoration and climate change impacts. Our literature review identifies knowledge gaps associated with the need for more trained taxonomists, and greater education on biocrust ecology and function. Potential developments in biocrust research include a greater use and recognition of biocrust species traits, the establishment of a dedicated international biocrust society, and the development of a global research and monitoring network to coordinate methods and provide a framework to answer critical knowledge gaps.

Acarospora dissecta (Bolivia) and Sarcogyne brunnea (Bolivia, Ecuador) are described as new to science. Acarospora trachyticola, a common effigurate species in Peru, is revised and reported as new for Argentina, Bolivia and Venezuela. Acarospora brasiliensis is considered as a later synonym of A. lorentzii, which is reported new for Peru. Sarcogyne terrena is revised. Silobia smaragdula is verified as occurring in Chile. Polysporina urceolata is reported new to South America from Bolivia.