Regional-scale environmental drivers and thresholds of under-canopy biocrusts in the Sandland

Biocrusts play vital roles in arid ecosystems, yet their responses to environmental change remain poorly understood, especially for biocrusts sheltered beneath vegetation canopies. This study aimed to identify critical environmental drivers and thresholds shaping under-canopy biocrust distribution and development across the Mu Us Sandland in northwestern China.

We measured biocrust characteristics (cover, thickness, shear strength) and environmental variables (vegetation, soil, topography, climate, disturbance) at 44 sites. Relationships were analyzed using correlation analyses and regression tree models.

Vegetation cover emerged as the primary driver, with total biocrust cover increasing markedly above 56% canopy cover and moss dominance above 71%. Moss crusts thrived under moderate temperatures (15–17 °C) and higher soil potassium content (> 14 g/kg), while cyanobacterial crusts dominated on steeper slopes (> 10°) with lower composite topographic index (< -0.079) and higher soil pH (> 8.7). Moderate grazing disturbance (0.41–0.7 hoofprints m⁻²) promoted biocrust development under specific conditions.

Our findings reveal complex environmental controls on under-canopy biocrusts and their potential responses to climate change. The identified thresholds provide valuable guidance for developing evidence-based conservation strategies to enhance ecosystem resilience in vulnerable drylands worldwide.