Nutrient cycling in forest stands
The life cycle of a forest stand, from initiation to growth, senescence and finally decomposition, crucially depends on the availability of nutrients and water. The quality and amount of both are determined by geological substrate and soil properties, topography, land use history, deposition and climatic conditions. We are quantifying fluxes of water, nitrogen, carbon and major cations through measurements at the plot scale. Climate stations, tensiometers, lysimeters, and litter decomposition bags are among the equipment used. We investigate both episodic events and long-term trends to conclude on pollution (recovery), nitrogen status, the effect of different harvest intensities or additional fertilization (e.g. N and ash spreading), and climate change. The emphasis is on commercially relevant tree species and planted forests, but natural, unmanaged systems are of interest as well.
Root dynamics and decomposition
Though nutrient and carbon turnover in roots are known to be rather important, their proper quantification is notoriously difficult. We carry out lab experiments and field studies (minirhizotrons) to conclude on life expectancy, biomass and nutrient content of fine roots.
Ground vegetation and biodiversity
Species composition, spatial coverage and biomass of ground vegetation are sensitive indicators of recent stand history. Ground vegetation species exhibit rapid dynamics and are highly adaptive. Quantifying ground vegetation in small plots (1 m x 1 m) is a well-suited method to investigate the effects of tree harvest and stand treatment as well as soil nutrient status.
Soil carbon dynamics
Soils are the single most important carbon reservoir in boreal forest ecosystems. We quantify soil carbon and nutrient content by taking stratified samples from a set of representative forest stands. Using process-based models, we conclude on changes in soil carbon over longer time periods, and determine the source/sink strength of the whole forest ecosystem as a function of its age.