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Abstract PremiseSouthern Africa is a biodiversity hotspot rich in endemic plants and lichen‐forming fungi. However, species‐level data about lichen photobionts in this region are minimal. We focused onTrebouxia(Chlorophyta), the most common lichen photobiont, to understand how southern African species fit into the global biodiversity of this genus and are distributed across biomes and mycobiont partners. MethodsWe sequencedTrebouxianuclear ribosomal ITS andrbcLof 139 lichen thalli from diverse biomes in South Africa and Namibia. GlobalTrebouxiaphylogenies incorporating these new data were inferred with a maximum likelihood approach.Trebouxiabiodiversity, biogeography, and mycobiont–photobiont associations were assessed in phylogenetic and ecological network frameworks. ResultsAn estimated 43 putativeTrebouxiaspecies were found across the region, including seven potentially endemic species. Only five clades represent formally described species:T. arboricolas.l. (A13),T. cf.cretacea(A01),T. incrustata(A06),T. lynniae(A39), andT. maresiae(A46). Potential endemic species were not significantly associated with the Greater Cape Floristic Region or desert.Trebouxiaspecies occurred frequently across multiple biomes. Annual precipitation, but not precipitation seasonality, was significant in explaining variation inTrebouxiacommunities. Consistent with other studies of lichen photobionts, theTrebouxia–mycobiont network had an anti‐nested structure. ConclusionsDepending on the metric used, ca. 20–30% of globalTrebouxiabiodiversity occurs in southern Africa, including many species yet to be described. With a classification scheme forTrebouxianow well established, tree‐based approaches are preferable over “barcode gap” methods for delimiting new species. 

Increases in the abundance of woody species have been reported to affect the provisioning of ecosystem services in drylands worldwide. However, it is virtually unknown how multiple biotic and abiotic drivers, such as climate, grazing, and fire, interact to determine woody dominance across global drylands. We conducted a standardized field survey in 304 plots across 25 countries to assess how climatic features, soil properties, grazing, and fire affect woody dominance in dryland rangelands. Precipitation, temperature, and grazing were key determinants of tree and shrub dominance. The effects of grazing were determined not solely by grazing pressure but also by the dominant livestock species. Interactions between soil, climate, and grazing and differences in responses to these factors between trees and shrubs were key to understanding changes in woody dominance. Our findings suggest that projected changes in climate and grazing pressure may increase woody dominance in drylands, altering their structure and functioning. 

Interactions among grazing pressure, climate, soil properties, and biodiversity affect ecosystem services provided by drylands.