Comparing dark diversity and α-diversity: Modulation by forest ecosystem vitality, management intensity, conservation strategies, and environmental conditions

Ongoing climate change and human impacts, such as forest management, are altering the distribution patterns of species and vitality of ecosystems around the world. The changing presence or absence of species is typically described using metrics that determine α-diversity, but it can also be assessed by estimating dark diversity (the absence of expected species). Therefore, we use defoliation as an indicator of forest vitality to study its impact on the presence or absence of plant species and how this interacts with management procedures, protection status, site characteristics, and soil characteristics. Our analysis is based on data of the second National Soil Condition Survey in Germany, which recorded species distribution, defoliation, forest stand and soil parameters on an 8 × 8 km national grid from 2006 to 2008. A third inventory was conducted from 2022 to 2024 and will allow for temporal, next to spatial, analyses. The large sample size enables us to develop separate models for the vitality and the presence or absence of species within each forest vegetation association. Preliminary results show that oak-dominated forests are more vital than montane beech forests, even when mixed with fir and spruce. However, defoliation is increasing over time for oak-dominated forests, while decreasing for montane forests. Overall, the vitality of trees and how it changes over time is more impacted by climatic conditions than by forest management procedures. Additionally, the results suggest that species that prefer open land increase in abundance in forest ecosystems with increasing defoliation (decreasing vitality) on protected forest sites. Since defoliation is higher in protected forest areas on average, it implies that the forest protection status is less effective for stands with decreasing vitality. We expect the upcoming analysis to confirm this community shift by showing a greater absence of forest indicator species as defoliation increases. Further, changes in community composition will be assessed using mean Ellenberg indicator values. By directly comparing dark diversity (species absence) and α-diversity, we aim to develop a more comprehensive understanding of the requirements for forest conservation practices and management procedures that are essential to maintaining vital forest ecosystems.