Most of the plant diversity in European forests is found in the understorey, and despite its relatively low biomass compared to the forest overstorey, its functional importance is high (nectar source for pollinators, habitat for small mammals, affects tree regeneration, invasion resistance, decomposition and nutrient cycling (Gilliam 2007). Relationships between overstorey and understorey diversity and composition will be tackled. At the Biotree site in Kaltenborn-Germany, plots of 0.6ha were established in 2004, subdivided in an unmanaged part, a managed part and a managed part with additional species. The desired species mixture was achieved by patch planting (patches of 8mx8m). In the unmanaged part of each plot, 4 permanent vegetation monitoring subplots of 1m x 1m were established (see area maps) and permanently marked. Vegetation was first monitored in 2004 by the team of Michael Scherer-Lorenzen and afterwards in 2010 by the team of Helge Bruehlheide. In June 2011, these plots were relocated by Evy Ampoorter and Kris Ceunen in order to take a biomass sample of each subplot: within a frame of 1m x 1m (placed at the exact location of the permanent monitoring plot) a smaller frame of 0.5m x 0.5m was placed centrally within the bigger frame. All aboveground biomass within this smaller frame was clipped. Dead vegetation was removed from each biomass sample. The biomass sample was further divided into following groups: grass, Leguminosae, Achillea millefolium, other herbs. After removal of death vegetation and division into groups, the biomass samples were dried for 48h at 70°C (samples were quite wet). Then they were weighed and analysed for P, Ca, K, Mg (Forest & Nature Lab, Ghent University) and C and N (Institut für Walbau, Universität Freiburg).

Set-up was similar to set-up used for vegetation monitoring in 2004 and 2010. In each plot, 4 permanent monitoring subplots of 1m x 1m are marked (see maps). These plots were relocated and a frame of 1m x 1m was placed at the exact location. Within the frame of 1m x 1m a smaller frame of 0.5m x 0.5m was placed at a location where vegetation was relatively abundant and composition was representative for the bigger frame. All aboveground biomass within this smaller frame was clipped. Dead vegetation was removed from each biomass sample. Each biomass sample was also further divided into following groups: grass, Leguminosae, Achillea, other herbs. After removal of death vegetation and division into groups, the biomass samples were dried for 48h at 70°C (samples were quite wet when collecting). Then they were weighed and analysed for P, Ca, K, Mg (Forest & Nature Lab, Ghent University) and C and N (Institut für Walbau, Universität Freiburg). Preparation of biomass samples for chemical analyses: dried at 70°C, grinded using a sieve of 1mm (for analyses of P, Mg, Ca en K content) and afterwards further grinded with a ball mill (MM301, Retsch, Hahn, Germany) in Freiburg (for analysis of C and N). Before analyses of Ca, Mg, K en P-content, grinded biomass samples are 'destroyed' with HNO3/HClO4, diluted with demineralised water and filtered according to the method of Varian Instruments at work, AA-24 (McKenzie T., 1982. Automated multielement analysis of plant material by flame atomic absorption spectroscopy. Varian Instruments at work, AA-24). Analysis for Ca-content: destruction of biomass sample with the above mentioned method. Then the sample is diluted, 10% CsCI is added as modifer on the AAS (Varian SpectrAA 220) and calibrated to 5mg Ca/l and atomized in a nitrous oxide-acetylene flame, absorption is measured at 422.7nm. The analytical quality of the analysis is verified by repeated measurement of blanco and control samples. Analysis for K-content: destruction of biomass sample with the above mentioned method. Then the sample is diluted, 10% CsCI is added as modifer on the AAS (Varian SpectrAA 220) and calibrated to 1mg K/l and atomized in a air-acetylene flame, absorption is measured at 766.5nm. The analytical quality of the analysis is verified by repeated measurement of blanco and control samples. Analysis for Mg-content: destruction of biomass sample with the above mentioned method. Then the sample is diluted, 10% CsCI is added as modifer on the AAS (Varian SpectrAA 220) and calibrated to 0.5mg Mg/l and atomized in a air-acetylene flame, absorption is measured at 258.2nm. The analytical quality of the analysis is verified by repeated measurement of blanco and control samples. Analysis for P-content: destruction of biomass sample with the above mentioned method, then reaction of the destroyed biomass sample with metholsulphite, ammoniumheptamolybdate and sodiumacetate solution. Finally, measurement of the total P-content with a spectrophotometer type Varian Cary 50 at 700nm (Chemical analysis of plants and soils. Cottenie, Verloo,... Laboratory of analytical and agrochemistry, RUG). Analyses for C and N: C and N analysis is done by dry combustion with an elemental analyzer leco truspec™ (Leco, St. Joseph USA). 100-200 mg finely ground sample is wrapped in tin foil and burned with pure oxygen at 950°C. Tin foil rises temperature additionally throughout the burning process. Carbon is detected as CO2 with an infrared measuring cell, nitrogen is reduced to N2 and detected with a thermal conductivity cell. For prediction of C and N content with near infrared spectroscopy spectra are taken from finely ground material with a Tensor 37 spectrometer (Bruker, Ettlingen, Germany). The wavenumber range is 12000 to 3800 cm-1, Resolution is 16 cm-1 with 64 scans for each spectrum. Five spectra are measured for each sample. For at least 100 samples the dry combustion reference analysis is done. With Opus 6.5 software (Bruker, Ettlingen, Germany) spectral information is combined with the corresponding reference value and models to predict unknown samples are developed using PLS (partial least square) regression.

Kaltenborn, Germany: Biotree site

Spring 2011

understorey vegetation: woody and non-woody vascular species (herbs, seedlings) < 1.3m

Overall good weather (but a lot of dew in the morning making the biomass samples wet). Until 2008, mowing between rows. Mowing between trees within rows, until trees were higher than grass layer.