Biocrusts are widely distributed in global drylands; however, their species composition and community assembly remain poorly understood within degraded karst ecosystems under subtropical humid climates. This study investigated six typical areas representing a degradation gradient in Guizhou (South China Karst), elucidating biocrust distribution patterns through comprehensive comparisons with global dryland literature. Results revealed a total of 22 unique biocrust species distributed across four major phyla: 12 moss species (phylum Bryophyta; 6 families, 9 genera), 2 lichen species (phylum Ascomycota; 2 families, 2 genera), and 8 algal/cyanobacterial species (6 families, 7 genera), which were heavily dominated by cyanobacteria (6 cyanobacterial species vs. 2 green algal species). Mosses formed the absolute dominant crust type, contributing to 75%–100% of the total surface coverage. Within moss communities, Hyophila rosea emerged as the ubiquitous absolute dominant species persisting across the entire degradation gradient, alongside extremotolerant co-dominants like Brachymenium exile and Trichostomum brachydontium. Conversely, cosmopolitan species such as Bryum argenteum acted as gap-filling associated taxa. Ecologically, biocrusts exhibited pronounced habitat preferences, being enriched in managed groves (e.g., Zanthoxylum bungeanum, Camellia oleifera) rather than croplands or natural grasslands. Network analysis confirmed that taxonomic overlap between degraded karst biocrusts and global drylands is extremely low (