Habitat protected potential and zoning

We assumed that the conservation potential of habitat can be determined by the importance of each grid in HQI, that is, if the habitat index in x grid contributes higher habitat quality to the total habitat quality in the municipality, it have higher potential for conservation in habitat quality. So we proposed HPI to reflect the potential value for conservation, and the higher HPI indicates more potential for habitat conservation (Table ​(Table3).3). The equation for calculating HPI is as follows:

where HPI_x denotes the potential index for habitat protection in grid x(%), HQI_x is the sum of habitat quality index on grid x, THQI represents the total value of habitat quality index in study area, and n is the total number of grids.

The criteria for habitat quality classification and its potential for habitat protection.

To access the spatiotemporal differences of habitat quality and habitat protection potential in Shanghai, we divided the HQI and HPI into five levels shown in Table ​Table33 according to their equidistant distribution, as well as previously reported study results and the actual situation of the study area^36,37. 0 is the poorest habitat quality or HPI as well as 1 represents the highest quality or HPI.

Habitat quality protected areas must effectively contribute to sustaining biodiversity, ranging from preventing species extinction to retaining the most intact ecosystems. The conservation importance of regional habitat mainly depends on the current habitat types and habitat quality variations. For example, the native habitat and rapid shrink habitat should be given priority for conservation and restoration. Therefore, we generated the zoning map in habitat protected areas by integrating the habitat quality in 2000 and 2017, as well as the variation in HQI between 2000 and 2017. The evaluation processes were: (1) extracting 20% and 40% of the study areas with the largest HQI values and dividing the areas into three grades based on relevant studies about assessing Ecological Conservation Redline and the actual situation in Shanghai^38,39. (2) Grading habitat quality variations from 2000 to 2017 by a criterion of [− 1 to 0.2), [0.2–0.8), and [0.8–1) considering the effectiveness of the ecological space construction and optimization projects in Shanghai between 2000 and 2017; (3) adding up all three index values in ArcGIS 10.8 and manually grade the total index value with consideration of their relative importance to maximize the representativeness and effectiveness of habitat conservation; (4) removing the fragmented patches with an area less than 10 hm², as fragmented habitats with an area less than 10 hm² are easier to influenced and filled by built-up land⁴⁰.