Using centennial changes in plant, butterfly and bird diversity to inform restoration targets

Abstract Historical records reveal significant biodiversity loss, but over such long timespans that human minds gradually adjust to depauperated biotas. We used 19th and early 20th -century Danish records (100–180 years old) to address this blind spot and enhance our understanding of flora and fauna changes beyond mere richness gains or losses. By analyzing species’ traits, habitat affinities, and environmental indicators, we identified lost habitat types. Compared to the present, 19th-century Danish landscapes were more heterogeneous, featuring open, wooded pastures, now largely replaced by dense plantation forests. Historical data demonstrated that dark diversity is easily underestimated when based on contemporary data. Historical butterfly faunas were much more species-rich and had a stronger affinity for grazed ecosystems than current communities. Declining plant species of conservation interest were more light- and moisture-demanding and less nutrient-affiliated and competitive than persisting species. Declining butterfly species were linked to host plants with restricted national distribution. Declining bird species were typically carnivorous, migratory, and associated with open habitats, particularly grasslands, coastal areas, and freshwater wetlands.Our findings may guide the ambition level and direction of restoring efforts. The results suggest a restoration focus on open, heterogenous woodland, grassland and wetland ecosystems with low nutrient status and natural disturbance regimes, including populations of large herbivores near carrying capacity. This contrasts sharply with today’s timber-focused plantation forests and conservation area management governed by agricultural subsidies.