Dr. FOREST - Diversity of FORESTs affecting human health

Forest ecosystems are an important reservoir for biodiversity in human-dominated landscapes within Central Europe, and deliver many ecosystem services. They are also a popular location for recreational activities, especially near urban areas. However, forests can also harbour threats and diseases. The Dr. FOREST project quantifies four important pathways explaining how forest diversity can improve, or reduce risks to human mental and physical health: (i) provision of visual aesthetics and enjoyable soundscapes, (ii) provision of nutritional and medicinal forest products, as well as a comfortable microclimate for recreation, (iii) dilution or reduction of disease vectors, and (iv) reduction of air pollution. The project makes use of existing research infrastructures for functional biodiversity studies and relies on a rigorous experimental design that allows quantification of tree diversity effects on human health. The empirical work will be done in controlled tree diversity experiments as well as in natural forests of differing diversity adopting a comparative design. The sites are located in contrasting climatic regions of Central Europe (France, Belgium, Germany, Austria, Poland). In three Case Studies in urban forests the consequences of forest diversification schemes for health-related risks and benefits will be elaborated together with local stakeholders (Sonian Forest Brussels, Bois de Bordeaux, Auwald Leipzig). All Work Packages and Tasks are handled by teams composed each of both natural and medical scientists, ensuring cross-disciplinary collaborations and synergies. Interactions with stakeholders to refine research questions and to promote the human health impacts of biodiversity in forests, as well as formulation of management guidelines, will ensure high relevance for health policy and forest administration. A final symposium will communicate the projects findings to high-level stakeholders and will support evidence- based decision-making for forest biodiversity and human health co-benefits and risks.

This project showed that among tree species different amounts of particulate matter (PM) are captured, and that mixing tree species can increase the amount of PM captured. Air pollution is a great risk to human health worldwide. Especially in urban areas airborne PM causes negative human health effects that reduce life expectancy. The most harmful particles are those smaller than 2.5 micrometres. Trees and forests can bind PM and reduce pollutant concentrations in the air, thus positively effecting human health. To investigate how trees, bind PM, we analysed data from 57 publications from the years 1996-2021, the data covered 11 countries and 190 tree species. Trees were classified into four functional groups. These were evergreen conifers, deciduous conifers, deciduous broadleaves, and evergreen broadleaves. The analysis showed that evergreen conifers had the highest PM accumulation on leaves. Evergreen leaves, in general, accumulated more PM than deciduous leaves. This was shown for all class sizes of PM (PM0.2, PM2.5, PM10, PM>10). Leaves with high levels of surface wax, accumulated PM in this layer. This is advantageous as it prevents PM being resuspended in the atmosphere. Mixing of tree species, rather than growing only one species, is increasingly promoted as a potential adaptation to climate change. In an experimental site investigating tree species mixing (B-Tree), we investigated four tree species Norway maple, small leaf lime, common oak, and hornbeam grown in monocultures and in two and four species mixtures. The amount of PM on the leaves of these species was determined by washing and fractionation of the PM into PM2.5, PM10 and PM100 size classes using a filtering method. We carried out extensive studies to test the weakness in this method and develop a standard protocol. The amount of PM2.5 per m2 leaf area was significantly higher in lime compared to oak and maple. This difference in accumulation was related to the structure of the leaves. Trees growing in mixtures can have a greater number of leaves (measured as the leaf area index) and different crown shapes. In mixtures, higher amounts of PM were bound in the two species mixture of oak and hornbeam and in the mixture of all four species. This was due to a higher amount of leaves in the mixtures, but also due to structural changes in the canopy. To measure the accumulation of PM by trees across a wider geographical area we collected samples from DrForest sites in Austria, Belgium, France, Germany and Poland. The analysis showed that, the levels of PM accumulated by a tree species are similar over a wide geographical range. But also confirmed the initial literature analysis, showing that evergreen conifers have the higher PM capture.