Abstract:

Aims: This study aimed to identify areas of concentrated occurrence and priority verification units of the invasive plant Mikania micrantha under constrained survey coverage, and to provide spatial references for survey design, patch verification, and dynamic monitoring in protected areas. 

Methods: Spatial analyses were conducted in and around Xishuangbanna National Nature Reserve, China, using occurrence records of M. micrantha and survey tracks. A total of 336 occurrence records and 283 survey-track line features, with a cumulative length of 737.75 km, were integrated. Distances from occurrence records to the nearest survey tracks were calculated, and a 200-m buffer on both sides of the survey tracks was used to define the survey-supported spatial extent. Within this extent, relative occurrence intensity was estimated using Gaussian kernel density estimation with a 2-km bandwidth and 200-m raster resolution. Relative occurrence-risk zones were classified into low, medium, high, and extremely high classes using the P50, P75, and P90 thresholds of kernel-density values. High-occurrence-intensity nodes were identified using local maxima and proximity merging, and priority verification levels were assigned according to patch-area density within the local survey-supported extent of a 2-km node buffer. 

Results: All 336 occurrence records were located within 200 m of the nearest survey track, with a mean distance of 0.96 m and a maximum distance of 10.90 m. The survey-supported spatial extent covered 282.96 km². High- and extremely high-risk zones accounted for 25.01% of the extent but contained 74.11% of occurrence records. Extremely high-risk zones occupied 10.01% of the extent and contained 44.94% of occurrence records. Six high-occurrence-intensity nodes were identified. S4 and S1 were classified as Level I priority verification nodes, S3 as a Level II node, and S2, S5, and S6 as Level III nodes. 

Conclusion: Occurrence records of M. micrantha showed strong spatial correspondence with survey tracks. Defining a survey-supported spatial extent based on survey tracks enables relative occurrence-risk zoning and priority node identification without extrapolating risk to unsurveyed areas. This approach provides a spatial reference for survey planning and field verification of invasive plants under constrained survey coverage.

Key words: Mikania micrantha, survey-supported spatial extent, kernel density estimation, relative occurrence risk, priority verification nodes