Effects of stocking rate on the state transition processes of plant community in desert steppe

To investigate the state transition processes of plant community in desert steppe under different stocking rates, this study aims to systematically uncover the intrinsic characteristics of such transition processes and their underlying network-driven mechanisms across three hierarchical levels (i.e., species, functional group, and plant family). The findings are expected to provide a robust scientific basis for optimizing adaptive grassland management strategies and facilitating the restoration of degraded desert steppe ecosystems.

The study was conducted in Stipa breviflora desert steppe. Four grazing treatments were established: control (CK, no grazing), light grazing (LG), moderate grazing (MG), and heavy grazing (HG), with stocking rates of 0, 0.91, 1.82, and 2.71 sheep units·hm⁻²·half year⁻¹, respectively. Plant population height, coverage, and density were surveyed, and importance values were calculated. Based on species composition proportion and resource allocation proportion matrices, a Bray-Curtis state transition model was constructed.

The CK treatment exhibited the highest community self-stability. Species composition stability increased with increasing stocking rates (across the LG-HG gradient), while resource allocation stability decreased with increasing stocking rates below MG (CK > LG > MG). Grazing disturbance made grassland degradation easier than recovery. Restoring degraded grasslands requires a stepwise reduction grazing strategy: "from HG to MG to LG". State transitions across stocking rates occurred at multiple levels. Population proportion similarity showed bipolar differentiation, while resource dependence on grazing conditions exhibited a three-dimensional response. Perennial grasses (PG) showed significant resource output tendencies, perennial forbs (PF) acted as the core receiving center, and shrubs/semi-shrubs (SS) and annual/biennial plants (AB) served as intermediaries. Poaceae (POA) dominated resource output, while Asteraceae (AST) and Chenopodiaceae (CHE) functioned as key transfer hubs.

In summary, multiple stable states formed by grazing in desert steppe. The differentiation in species response strategies and reallocation among functional groups/families are the core mechanisms driving state transitions. For degraded grasslands, promoting recovery through stepwise reduce stocking rate is superior to fencing exclusion.