Landscape Transformation of Degraded Shrublands to Pine Forestations Increases Biological Soil Crust Cover and Creates Small-Scale Soil Heterogeneity

Abstract

Efforts to reverse dryland degradation and desertification promote the transformation of rangelands to forestations. Biological soil crusts (biocrusts), a structural and functional component of drylands, have been primarily studied in rangelands, and seldom in other land-use types. The fate of biocrusts following tree afforestation remains unclear, limiting the understanding of the impacts of plantations on soil biota and functioning. In a grazed steppe with pine forestations, both land-use types were compared evaluating the influence of vegetation features and a regional precipitation gradient on biocrust community structure. The contribution of biocrusts to small-scale heterogeneity in soil properties (moisture, nutrients, carbon, and pH) within the forestations was also quantified. Biocrusts covered 16.5% of the forestation ground surface, a value one order of magnitude higher than in the natural vegetation (2.1%). Differences in species relative abundance suggested that biocrusts under pines represented an earlier succession stage compared to those in the natural vegetation. The precipitation gradient significantly modulated biocrust development in both land-use types. Within the forestations, biocrust cover was favored in partially opened canopy patches, with a relatively thin litter layer. Biocrusts had no significant effect on soil properties, which were mostly enhanced in deep needle-litter layer patches, and were modulated by the regional precipitation gradient. Our results provide novel evidence suggesting that pine forestations act as reservoirs and effective restoration agents for biocrusts in long-term grazed landscapes. Management practices of land-use mosaics should aim to enhance biocrusts in the forestations, as these actions could contribute to preserving dryland biodiversity and integrity.