How Forest Structure and Management Impact on Forest Behavior

Forests are increasingly exposed to extreme events and disturbances like droughts, storms, fires, pathogens, and others. At the same time, forests are expected to act as important carbon sinks with the corresponding climate change mitigation capacity. What are the links between forest structure and ecosystem functional properties and the resilience against disturbances and extreme events? What are the options for forest management in this context?

Using data from flux towers and field experiments from 90 sites in 16 countries, mostly in Europe, and remote sensing observations, we investigate the role of forest structure as buffer of climate extremes; link light-use efficiency to stand characteristics and management; elucidate the role of climate effects of short-lived climate forcers and their feedback due to a warming climate, stress and disturbances, and evaluate the impact of extreme drought, fire disturbances and forest management on soil organic carbon (SOC) and nitrogen dynamics.

Combining GAMs with bootstrap-based variable importance analysis, we could show that there are associations between the means of selected Ecosystem Functional Properties of boreal and temperate forests, like photosynthetic capacity (NEPsat) or underlying water-use efficiency (uWUE), and structural complexity metrics, like Leaf Area Index or Near-Infrared Reflectance of Vegetation. With increasing drought stress, higher canopies, LAI and species number stabilizes the forest response both for NEPsat and uWUE.

Work on entangling the climate effects of short-lived climate forcers (SLCFs) is progressing with measurements of terpene concentrations and emissions and aerosol particle dynamics process modelling. Model evaluation of the climate effect from afforestation in the Nordic countries with coniferous trees on previous grassland shows that the climate cooling effect of increased terpene emissions and aerosol formation outweighs the warming effect due to the filtering of aerosol particles by trees.

Field experiments on Spanish sites indicate that drought (induced through precipitation exclusion) significantly reduces the litter decomposition rate, and that thinning increases SOC content; however, differences in SOC between management regimes are often masked by high spatial variability.

The work presented has emerged within the Work Package “Data assessment of processes and their impacts on biodiversity and climate effects on forests” of the CLIMB-FOREST H2020 EU project.