An objective-based prioritization approach to support trophic complexity through ecological restoration

We used species-rich European subalpine and alpine calcareous grasslands as a case study. These habitats are sensitive to disturbance, and impacted by ski resorts and other tourism activities, making them a target system for ecological restoration across European Natura 2000 sites (Garcia-Gonzalez, 2008, p.). We identified 176 plant species that frequently occur in the target ecosystem on a biogeographical scale as the potential regional and restoration species pool of interest (Ladouceur et al., 2018; Zobel et al., 1998). We used trait databases and literature to compile traits related to regeneration and relationships between the 176 plant species in our species pool and the insects, birds and mammals that are typical of these habitats and depend on particular plant species for various life stages. Hereafter, we refer to the traits and aspects of plant species that represent these relationships and characteristics of interest, as plant attributes. We compiled a list of the most frequent native species occurring in alpine calcareous grassland habitat types on a continental scale, using a synthesis of >1 million field surveys (Schaminée et al., 2016), reporting species frequencies in the habitat types of the European habitat classification system (EUNIS, www.eunis.org), directly assigned to habitat types of conservation concern (see Table S1). We identified native plant species that occur above a particular frequency (>5% of total occurrences) in calcareous alpine grassland habitat types on a European-wide scale. Expert opinion suggests that species below this frequency were found to be more typical of other habitat types. This resulted in a list of 176 native plant species that occur frequently in the calcareous alpine grasslands of continental Europe. We considered this to be the species pool of this habitat and we assumed all species can co-occur or can co-exist. Further, we consider all plant species in the pool as equal candidates for inclusion in seed mixes to meet prioritization objective targets. For the 176 plant species that were of interest for our goals, we collated traits related to dispersal, phenology, and nitrogen fixation available from the TRY plant trait database (Kattge et al., 2011), as well as associations with mammals, birds, and herbivorous and pollinating insects from additional sources (see Table 1). The list of associated faunal species was refined to keep only species that occur in this habitat. Plant species frequency of occurrence values were used to rank plant species’ relative abundance within the habitat type on a biogeographic scale, which we used to classify plant species dominance for a fixed species list for comparison with prioritized objectives (Table 1, see Table S1). We then grouped the 163 plant attributes into nine broad categories based on the ability to support specific ecosystem functions or services (Table 1): bird trophic diet, bird herbivory, bird shelter, seed dispersal syndrome, Lepidoptera relationships (species specific- pollination, herbivory), pollination syndrome, mammal herbivory, nitrogen fixation, and flowering month. For references listed here please see associated publication.