Fig 1.
Example of PU-specification of N2000 habitats.
A) Distribution of habitat 3260 “Water courses of plain to montane levels with the Ranunculion fluitantis and Callitricho-Batrachion vegetation” in Germany (upper left panel indicates the location of Germany within Europe) as reported by the German Federal Agency for Nature Conservation (BfN; BfN, 2013) on TK25 grid cell level (each grid cell is ~ 120 km2). B) Enlargement of a random area (grid size ~ 120 km2) to better visualize the partitioning of TK25 grid cells into four equal quadrants (PUs; area ~ 30 km2) as seen in C. D) Single, partitioned TK25 grid cell (in the centre in green) combined with the EUNIS habitat class which accounts for habitat 3260. The lower right PU was excluded from further considerations of habitat 3260 occurrence, since it does not contain any EUNIS habitat class accounting for habitat 3260. E) Single, partitioned TK25 grid cell and the EUNIS habitat class combined with occurrence data of plant species characteristic for habitat 3260 (yellow circles). Since in the lower left PU not a single characteristic plant species accounting for habitat 3260 occurred, this PU was excluded from further considerations of potential habitat occurrence. In this example, habitat 3260 most likely occurs only in the upper two PUs.
Fig 2.
Human footprint (HFP) map of Germany.
The HFP was used as a surrogate for highly humanized PUs for the Marxan analyses. A higher value indicates greater human impacts on a PU, i.e. a higher cost-penalty for adding a PU. HFP Values based on Sedac, 2016.
Table 1.
Overview of missing habitats in the four different scenarios.
The table shows for each scenario: the number of PUs considered as protected, the number of total missing habitats, the number of habitats protected sufficiently when considering the 17% target (maximum 85 habitats), and the mean number of PUs which have to be additionally protected for each habitat to reach the 17% target.
Fig 3.
The rate of protection of N2000 habitats.
Representation of the three habitat categories (proportion covered by Natura 2000 sites, mean ± SD) in the current N2000 network based on the four different scenarios (Scenario 25, scenario 50, scenario 75 and scenario 90). Rare habitats occur in less than 100 PUs (n = 18), intermediate in a range of 100 to 1000 PUs (n = 39), and common habitats occur in more than 1000 PUs (n = 28). The red dashed line indicates the 17% target.
Fig 4.
Sensitivity analysis for habitat target setting.
Total number of PUs (i.e. locked-in PUs plus the ones identified by Marxan) needed to reach the 1%, 5%, 10%, 15%, 17%, 20%, or 25% target. Targets where calculated as a percentage of the maximum number of PUs in which a certain habitat occurs. For example, the 5%, 10%, 20% targets for a habitat which occurs in 100 PUs were 5, 10, and 20 PUs, respectively. Dashed lines indicate the number of PUs in each scenario, which were considered as initially protected, i.e. covered by N2000 and therefore locked-in for Marxan analyses (Table 1).
Table 2.
Specifics on Marxan solutions.
Detailed information about necessities to protect 17% of each N2000 habitat in each scenario. HFPP = human footprint penalty.
Fig 5.
Best Marxan solutions for the five scenarios.
Spatial distribution of PUs considered as protected (i.e. locked-in in the optimization analyses) and PUs selected by Marxan to fulfil the 17% target for all habitat types for the five scenarios. All scenarios met the 17% target for all habitat types (n = 85). Note that we locked-in PUs (green) being part of the coastal areas of North and Baltic Sea for the free-choice scenario (see Methods).