Assessment of Cryptogamic Crusts (Biological Soil Crusts) on Rangeland Soils of Semi-Arid Zones in Yobe State

Biological soil crusts, comprising cyanobacteria, mosses, lichens, and algae, play critical roles in soil stabilisation and nutrient cycling in semi-arid rangelands, yet their composition and condition in Yobe State, North East Nigeria, have never been systematically assessed. This study assessed the cover, species composition, and functional role of biological soil crusts in three rangeland sites across Yobe State representing a livestock grazing intensity gradient: heavily grazed, moderately grazed, and lightly grazed. Biological soil crust cover and composition were recorded in 0.25m2 quadrats at 50 systematically placed points per site. Cyanobacterial and algal components were identified microscopically from surface soil scrapings. Physical soil properties including infiltration rate, bulk density, and surface roughness were also measured. Biological soil crust cover declined significantly from lightly grazed (41% cover) to heavily grazed sites (9% cover). Cyanobacteria dominated all sites, with Microcoleus vaginatus being the most consistently occurring species. Moss cover was negligible except at the lightly grazed site. Infiltration rates were significantly higher in lightly grazed plots coinciding with higher biological soil crust cover (r = 0.77, p < 0.01). Bulk density increased with grazing intensity and was inversely related to biological soil crust abundance. The study concludes that overgrazing is severely depleting biological soil crusts in Yobe State rangelands, with negative consequences for soil function, and recommends rotational grazing management policies through the State Agricultural Development Programme. Keywords: biological soil crusts, cyanobacteria, semi-arid rangeland, grazing intensity, Yobe State