Determining the suitable distance thresholds for optimizing functional connectivity and identifying conservation priorities of meadow in Poyang Lake, China

Landscape functional connectivity and the contribution of individual patches for overall functional connectivity varies depending on species dispersal distance. Determining the suitable distance thresholds enables the detection of vulnerable landscape connections and the identification of key habitat patches. However, the selection of distance thresholds is often arbitrary, and the effects of threshold choice on the assessment of landscape functional connectivity and identification of conservation priorities for habitat patches remain largely unknown. Taking the meadow of Poyang Lake as the research object, this study firstly identified the spatial distribution of meadow at each water level. Then, functional connectivity and the importance of meadow patches were analyzed under different dispersal distances using the graph-theoretic connectivity indices and the delta value of the probability of connectivity (dPC). Finally, the suitable distance threshold was determined by means of the natural breakpoint method. Our results indicated as follows: (1) The meadow was inundated and divided by water, and its shrinkage coexisted with fragmentation as the water level rose. When the water level fell, the meadow emerged and spliced, and its expansion coincided with cohesion. (2) Landscape functional connectivity showed a positive relationship with species dispersal distance. Meadow functional connectivity increased progressively with increasing dispersal distance. A range of 600–1000 m can be selected as the suitable distance threshold for optimizing meadow functional connectivity in Poyang Lake. Within this range, meadow functional connectivity varied little, which facilitates the identification of small components and isolated patches with low resilience to environmental risks, as well as the timely detection of vulnerable landscape connections. (3) The importance of habitat patches for overall functional connectivity was highly sensitive to species dispersal distance. The importance of meadow patches exhibited spatial differentiation, with large meadow patches being highly significant and small meadow patches becoming less detectable as dispersal distance increased. A distance of 800 m was ultimately determined as the optimal threshold for identifying conservation priorities of meadow patches in Poyang Lake. At this distance, the distribution pattern of important meadow patches was stable, and both large and small meadow patches could be clearly highlighted, thereby facilitating the effective identification of key meadow patches that make vital contributions to maintaining overall functional connectivity. This study provides a scientific basis for landscape pattern optimization and habitat protection in lake areas. • Meadow shrinkage coexisted with fragmentation as the water level rose. • Meadow expansion co-occurred with cohesion as the water level fell. • Meadow functional connectivity and patch importance were highly sensitive to species dispersal distance. • A range of 600–1000 m was the suitable distance threshold for optimizing meadow functional connectivity in Poyang Lake. • A distance of 800 m was the optimal threshold for identifying conservation priorities of meadow patches in Poyang Lake.