Objective  In order to provide scientific proposals and theoretical basis for the integration and optimization of protected areas (PAs) in Liaoning Province of northeastern China, we analyzed the spatial distribution pattern and overlapping status of 235 PAs of six categories in Liaoning Province qualitatively and quantitatively.

  Method  The nearest neighbor index analysis and kernel density analysis were used to evaluate the spatial distribution of the PAs. By calculating the proportion of overlap in each protected area mosaic, the overlap status of PAs in Liaoning Province was analyzed qualitatively and quantitatively. We also proposed a new method to calculate the overlap rate of multiple layers.

  Result  (1) The nearest neighbor ratio of PAs in Liaoning Province was 0.904, indicating the aggregation distribution pattern of PAs in Liaoning Province. (2) The PA in Liaoning Province mainly formed four aggregation regions: deciduous broadleaved forest in western Liaoning Province and northern Hebei Province, mixed coniferous and broadleaved forest in Longgang Mountains, grassland and cultivated vegetation in Liaohe Plain, northern part of wetland and deciduous broadleaved forest in Liaodong Peninsula. (3) The PAs with overlap accounted for 50.43% (by amount) and 8.63% (by area) of the total PAs in Liaoning Province. The overlaps mainly occurred between nature reserves and natural parks, with a total area of 134, 421 ha occurred in 107 PAs. (4) There were 82, 13, and one overlapped patche (s) with two, three and four overlapped layers, respectively in Liaoning Province. (5) Based on the concept of PAM, a total of 36 PAMs were recognized in Liaoning Province, of which eight had an overlap rate more than 50%, maximum of 81.34%; 6 less than 10%, minimum of 1.82%.

  Conclusion  The high overlap rate of PAMs indicated over evaluation of the area and conservation service function of the PAs. In this case, we suggested that the PA overlaps should be merged, and appropriate reduction of the total area should be permitted during the integration and optimization of the PA system in Liaoning Province. Furthermore, given the low protection effectiveness of some regions worthy of conservation, e. g., the coastal areas at the southern part of the deciduous broadleaved forest and wetland in Liaodong Peninsula, we suggested new PAs be established or expansion of the existing PAs to ensure the protection intensity and effectiveness of the PA system of Liaoning Province of northeastern China.