The humus form is the expression of the equilibrium between litter production, litter decomposition and humification in a forest ecosystem, resulting from the biological action of bacteria, fungi, and soil fauna. The observed humus form reflects a certain combination of ecological factors as climate, soil, tree species composition and management. In a site with constant climate and soil the effect of tree species composition on humus form becomes determining. The effect of tree species mixtures is less well understood and so far mainly studied in microcosm experiments. The idea is to quantify the mass of the ectorganic horizon and to describe the humus form. These features can be further related to variables as microbial activity, litter decomposition and earthworm biomass and diversity. All (30 x 30) m² plots are divided in nine (10 x 10) m² subplots. In every plot, an ectorganic sample (25 x 25 cm) and humus form classification is done in the middle subplot. The ectorganic sample is taken and humus form classification is done nearby (± 1m) the earthworm sampling location. Ectorganic samples are taken to the lab to get air-dried.

For every plot of the focal region, plots (30 x 30) m2 are divided in nine (10 x 10) m2 subplots. In every plot, an ectorganic sample and humus form classification is done in the middle subplot. In principle, within every middle subplot, the sample is taken nearby the earthworm sampling location, but samples are not taken close to tree stems. On an estimated 30 by 30 cm square ground vegetation is removed in order that an ectorganic sample (25 x 25 cm) can be taken. Only the ectorganic forest floor material (OL, OF and OH, but not OLn and the mineral soil) is sampled in a bag. Later samples are transported to the lab where they can be air-dried in an oven to constant weight (75°C). Half a meter away from this sampling an observation trench (50 cm long and 20 cm deep) is dug in order to make the humus form description following the European Humus Form Reference Base (Zanella et al. 2011). Four places along the trench are observed in order to make a sound humus form identification. At least one photo of the humus profile per plot is made. The ectorganic sample is taken and humus form classification is done nearby (± 1m) the earthworm sampling location.

North Karelia, Finland

Spring 2012

Forest ectorganic horizon