Regeneration biomass (AGB & BGB), age, NSCs and light: F. sylvatica and Acer spp.

The Uholka-Shyrokyi Luh reserve in Ukraine belongs to beech-dominated prime forests of Europe. Total 289 target seedlings and saplings of Fagus sylvatica (100), Acer platanoides (95) and Acer pseudoplatanus (94) were randomly selected and marked according to the following criteria: three species, two vitality classes (low and high) and 8 height classes (0-10, 11-20, 21-35, 36-60, 61-90, 91-130, 131-200, 201-500 cm). Regeneration plots were deliberately selected to have the lowest diffuse radiation possible. The following measurements were taken before tree excavation in May-mid Jul 2018: diameter at root collar (DRC), tree height, height of the crown base (height of the lowest foliage, excluding epicormic shoots) and crown area projection. Crown area projection was measured by two perpendicular crown diameters using a pendulum suspended from the outermost branches to the ground. Stem height increment was measured for the recent 5-10 years (until the last visible bud scale scar) to the nearest millimetre. Leaf area index (LAI) and indirect site factor (ISF), i.e. the proportion of diffuse solar radiation at a given location relative to that in the open, were assessed with hemispherical photos (Coolpix 4500, Nikon, Japan). Biomass processing: The sampled trees were separated at the root collar into aboveground biomass (foliage, stem, branches) and belowground biomass (root). All fresh leaves per tree were scanned with a smartphone (Petiole, version 2.0.1, Petiole Ltd. 2019) after calibration of the camera. Foliage, stems, branches, and roots were dried at 65 °C for three days until a constant weight and then weighed to the nearest 0.01 g. NSCs analysis: Fresh pieces of 5 cm length from the stem at the level of the root collar and from the coarse roots (diameter >2 mm) were cut for NSC analysis and placed in a microwave at 900 W twice for 15 s immediately after harvest. The coarse root sections of bigger saplings (2-4 cm DRC) were limited to 5 to 10 mm diameter and the harvested stem sections to 10 mm of wood directly under bark. Dendrochronological analysis: From each harvested tree, a stem disc was cut at the level of the root collar using a microtome to determine age and radial growth. The stained discs were photographed (Canon EOS 700D) and analysed with WinDENDRO™ (Regent Instrument Canada Inc.) under a microscope. The number and width of the rings were measured in 2-4 perpendicular directions because of the excentric tree piths, and then arithmetically averaged