Disentangling juvenile growth strategies of three shade-tolerant temperate forest tree species responding to a light gradient

- Aboveground biomass allocation is strongly driven by tree species' identity.
- Growth analyses refine the quantification of tree species' shade tolerance.
- LAR and RGR are strong indicators for tree species' growth strategy and efficiency.
- Derivatives of growth variables help specify efficiency-related threshold values.

Light availability in forests is a strong driver for forest development and diversity. Tree species develop differently under varying levels of light. Understanding the reasons for the individual growth strategies of tree species is crucial to understand dynamics of forest communities. This study aims at further disentangling aboveground biomass allocation patterns and growth variables for saplings of the tree species sycamore maple (Acer pseudoplatanus L.), European beech (Fagus sylvatica L.), and European ash (Fraxinus excelsior L.). Plants were destructively sampled along a light gradient. European beech allocated more biomass to its branches and less to its stem, in comparison to the other two species. The relative growth rate (RGR) and leaf mass area (LMA) of all species increased towards an asymptote along the increasing light gradient, whereas the leaf are ratio (LAR) decreased. The rate of increase and decrease differed among the tree species. Net assimilation rate (NAR) and absolute growth rate (AGR) both also increased with light availability, but the distinction among the species was not as clear. This study showed varying reactions of all three species to light and allowed a quantitative distinction among the species regarding their shade tolerance (ash < maple < beech), whereas the individual reaction was not always the typical reaction associated with shade tolerance.