Fig 1.
The European N2k network across nine biogeographical regions.
Dark green polygons represent terrestrial N2k sites analysed in this study [47]. Map generated in ArcGIS 10.6.1 (http://www.esri.com/software/arcgis/arcgis-for-desktop).
Table 1.
The N2k network across biogeographical regions of the EU.
Table 2.
In this study, we used open-access data to derive information on fragmentation within and around Natura 2000 (N2k) PAs, N2k PA locations within one of nine biogeographical regions, their locations within specific administrative units, and PA age.
Table 3.
Categories of effective mesh density (seff).
In contrast to the EEA [46], the fragmentation categories "anthropogenic" and "very high" were combined into one category “very high” due to the relatively small number of N2k sites within the anthropogenic category.
Fig 2.
Number of N2k sites and their surroundings per fragmentation category.
Fragmentation categories are based on EEA standards for effective mesh density (Table 3). Decimal numbers represent the relative amount of N2k sites which fall in one of the five fragmentation categories. The total number of N2k sites analyzed was 15390 (55.3% of N2k sites).
Fig 3.
Fragmentation within N2k sites (seffwithin) (A) and in their surroundings (seffsurrounding) (B) for NUTS-3 regions. The value for each NUTS-3 region was obtained by calculating the median of seffwithin (A) and the median of seffsurrounding (B) of N2k sites for each NUTS-3 region. The area-wide coloration on the map reflects only the degree of fragmentation within (A) or in the surroundings of (B) N2k sites rather than the area-wide fragmentation throughout the NUTS-3 regions. Map generated in ArcGIS 10.6.1 (http://www.esri.com/software/arcgis/arcgis-for-desktop).
Fig 4.
Fragmentation difference between N2k sites and their surroundings.
Each point represents the centroid of a N2k site: When calculating seffdiff = seffsurrounding—seffwithin, 58.5% of N2k sites are less fragmented than their surroundings (seffdiff > 0 meshes per 1000 km2) (A); 40.6% of N2k sites are more fragmented than their surroundings (seffdiff < 0 meshes per 1000 km2) (B); 0.9% of N2k sites are equally fragmented as their surroundings (seffdiff = 0 meshes per 1000 km2) (C); and independent from seffdiff, no or only marginal fragmentation within and in the surrounding of N2k sites (seffwithin and seffsurrounding ≤ 0.9 meshes per 1000 km2) exists for 6.9% of N2k sites (D). Map generated in ArcGIS 10.6.1 (http://www.esri.com/software/arcgis/arcgis-for-desktop).
Fig 5.
Size of N2k sites and fragmentation within N2k sites (seffwithin).
The value for each NUTS-3 region was obtained by calculating the median of seffwithin of N2k sites for each NUTS-3 region. The area-wide coloration on the map reflects only the degree of fragmentation within N2k sites rather than the area-wide fragmentation throughout the NUTS-3 regions. Large N2k sites are predominantly located in remote and mountainous regions, which tend to exhibit low fragmentation. Map generated in ArcGIS 10.6.1 (http://www.esri.com/software/arcgis/arcgis-for-desktop).
Fig 6.
Number and area coverage of N2k sites per fragmentation category.
Bars in light grey represent absolute numbers of N2k sites analyzed in this study. Bars in dark grey represent absolute area coverage in 1000 km2 of N2k sites analyzed in this study. Black decimal numbers represent the relative amount of sites for each of the five fragmentation categories. White decimal numbers represent the relative amount of area covered by N2k sites for each of the five fragmentation categories. The total number of N2k sites analyzed was 15390 (55.3% of N2k sites). The total area covered by N2k sites analyzed was 796637 km2 (79.5% of the total area covered by N2k sites). Fragmentation categories are based on EEA standards for effective mesh density (Table 3).
Fig 7.
Correlation between effective mesh density (seff) within and around N2k sites for the nine biogeographical regions of the EU.
seffwithin significantly correlates with seffsurrounding for all nine biogeographical regions. For each biogeographical region, the R2 value, the number of sites (n), and the linear regression formula with x = seffsurrounding are provided.
Fig 8.
Recently protected PAs within the N2k network are predominantly located in eastern European member states which joined the EU since 2004 (Status 2017) [55]. Map generated in ArcGIS 10.6.1 (http://www.esri.com/software/arcgis/arcgis-for-desktop).