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. Only the monoculture and high diversity (4 species) plots where sampled, resulting in 20 sampled plots. In every plot, an ectorganic sample (25 x 25 cm) and humus form description is done. Ectorganic samples are taken to the lab to get air-dried.

Monoculture and high diversity (4 species) plots where sampled. 20 plots in total. In every plot an ectorganic sample and humus form description is done. In principle, within every plot the samples are taken randomly, but samples are not taken close to tree stems. In the monoculture plots, samples were located in the middle of the plots. In the high diversity plots, the sampling location was located randomly on a 'crossing point' of 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 can be air-dried in an oven to constant weight (75°C). Half a meter away from this sampling point 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.

FORBIO Zedelgem, Belgium

Autumn 2011

Forest ectorganic horizon