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. In every plot, four ectorganic samples (25 x 25 cm) are taken and four humus form descriptions are done, in each case 2 in the 'no management' subplot (U) and 2 in the 'management' subplot (M). Ectorganic samples are taken to the lab to get air-dried.

All 16 plots where sampled. In every plot, four ectorganic samples (25 x 25 cm) are taken and four humus form descriptions are done, in each case 2 in the 'no management' subplot (U) and 2 in the 'management' subplot (M). In principle, within every subplot, the sample is taken nearby the earthworm sampling location, but samples are not taken close to tree stems. In the monoculture plots, sampling locations were located randomly in every subplot. In de mixed plots with 2, 3 or 4 tree species, sampling locations were, per subplot, located randomly on a 'crossing point' of respectively 2, 3 or 4 species. 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 horizon, but not OLn and the mineral soil) is sampled in a bag. Later samples are transported to the lab where they are weighed after they have been air-dried in an oven to constant weight (75°C). Half a meter away from these sampling points 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 observation trench is made.

BIOTREE Kaltenborn, Germany

Autumn 2011

Forest ectorganic horizon