DOI: 10.5061/dryad.05qfttf30
title: Regeneration biomass (AGB & BGB), age, NSCs and light: F. sylvatica and Acer spp.

description: Being able to persist in deep shade is an important characteristic of
 juvenile trees often leading to a strong dominance of shade-tolerant
 species in forests with low canopy turnover and disturbance rate. While
 leaf, growth and storage traits are known to be key components of shade
 tolerance, their interplay during regeneration development and influence
 on juveniles’ survival time remains unclear. We assessed the ontogenetic
 effects of these three traits on survival time of beech  (Fagus
 sylvatica), Norway and sycamore maples (Acer pseudoplatanus, Acer
 platanoides) in a primeval beech forest. Biomass allocation, age and
 content of non-structural carbohydrates (NSC) were measured in stems and
 roots of 289 seedlings and saplings in high and low vitality classes.
 Saplings experience a trade-off between absolute growth rate (AGR), and
 storage (NSC) at decreasing leaf area ratio (LAR) with biomass
 development. High LAR but slow AGR and low NSC confer beech with a marked
 ability to persist in deep shade awaiting canopy release. In turn, a
 comparably small LAR in combination with fast AGR and higher storage
 (NSC), as observed in Norway maple and sycamore maple, reduces their
 survival time, thus offering an explanation for beech dominance and maples
 disappearance in the undergrowth of old-growth beech forests.
description: 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 (<i>Coolpix 4500, Nikon,
 Japan</i>).  <em>Biomass
 processing</em>: 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
 (<i>Petiole, version 2.0.1, Petiole Ltd. 2019</i>) 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. <em>NSCs analysis</em>:
 Fresh pieces of 5 cm length from the stem at the level of the root collar
 and from the coarse roots (diameter &gt;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. <em>Dendrochronological
 analysis</em>: 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
description: Seedlings and saplings were growing at very low light levels
 (mean 2-3% of ISF) in the prime beech-dominated forest.