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 is tackled. For each of the plots per focal region, the core plot is divided in nine quadrants.For each of the plots per focal region, the core plot is divided in nine quadrants. In three quadrants (upper right, central, lower left), a vegetation subplot of 5 m x 5 m (as close as possible to the central quadrant; subplot in the central quadrant located in the upper half) is marked for identification and estimation of cover of understorey vascular plant species. Location of subplots exclude major heterogeneities at any scale of sampling (tree trunks, tracks and paths, streams and ponds, peaty pools, boulders and cliffs…). Thus, terricolous plants growing on mineral and organic soil of the undisturbed forest floor are represented. Within this subplot, understorey vegetation is identified (species, cover) and afterwards clipped in a zone of 0.5 m x 0.5 m (biomass subplot), where understorey vegetation is relatively abundant and where vegetation composition is representative for the whole subplot. Then, biomass is divided into 'woody' (woody juveniles, woody plants) and 'non-woody' (seedlings, 'green' herbs). The woody fraction is further divided into 'woody-woody' (woody part) and 'woody-leaf' ('green' part).The biomass samples are dried for 24 to 48h at 70°C . Then they are weighed and analysed for P, Ca, K, Mg, C, N (Forest & Nature Lab, Ghent University).

For each of the plots per focal region, the core plot is divided in nine quadrants. In three quadrants (upper right, central, lower left), a subplot of 5 m x 5 m (as close as possible to the central quadrant; subplot in the central quadrant located in the upper half) is marked for identification and estimation of cover of understorey vascular plant species (species, cover, maximum height, development stage). Within this subplot, understorey vegetation is identified (species, cover) and afterwards clipped in a zone of 0.5 m x 0.5 m, where understorey vegetation is relatively abundant and where vegetation composition is representative for the whole subplot. Then, biomass is divided into 'woody' (woody juveniles, woody plants) and 'non-woody' (seedlings, 'green' herbs). The woody fraction is further divided into 'woody-woody' (woody part) and 'woody-leaf' ('green' part). Preparation of biomass samples for chemical analyses: dried at 70°C, grinded using a sieve of 1mm 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,N: analysis is done using an Elementar analyzer, type Vario Macro Cube in configuration CNS, with Argon as carrier gas. Catalytic combustion of the sample (1.5g) is carried out at a permanent temperature of up to 1200°C. This is followed by reduction of the combustion gasses on hot copper in the refuction tube. The formed gasses N2, CO2, H2O, SO2 are separated via purge and trep chromatography and afterwards detected on a thermal conductivity detector (TCD). A connected PC computes the element concentration from the detector signal, and the sample weight on the basis of stored calibration curves.

Romania

summer 2012

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

warm, dry weather (extremely dry year from August 2011 until August 2012, might have influence the germination of a lot of species as soil was very dry and therefore very hard)