Fine-scale characteristics of the boundaries between annual patches and perennial patches in a meadow steppe

Context Boundaries may have crucial influences on landscape patterns, processes, and dynamics. However, there is little understanding of mechanisms that govern changes in the location and composition of boundaries. At smaller scales, investigation of detailed soil and vegetation characteristics can clarify the linkages between soil properties and vegetation patterns. Objectives The aims were to examine the relationship between vegetation patterns and soil properties, and to explore mechanisms that govern changes in the location and composition of boundaries. Methods In a 50-ha grassland fenced for more than 10 years, where a recovery process had been initiated and annual grasses dominated in most saline–alkaline areas, we quantitatively characterized the spatial gradients across the visually identified physiognomic boundary between annual patches and perennial patches at a fine spatial scale. Results Fine-scale vegetation and soil boundaries were well-defined and statistically characterized by a high rate of change compared to immediately adjacent areas. Plant characteristics were markedly influenced by soil properties. The alteration of salinity and alkalinity were the most important factors explaining the plant patterns across patch boundaries. Successional processes of colonization were involved in perennial encroachment in the annual patches. Conclusions Underlying soil properties primarily determine the plant patterns of the boundary; plant succession caused by interspecific competition is superimposed on the plant–soil feedback loop maintaining soil nutrient conditions. These processes alter the characteristics and locations of patch boundaries in response to changing disturbance regimes. Our findings offer insight into how boundaries may respond to changes in environmental conditions and drive landscape-level dynamics.