Effects of woody species diversity and composition on individual plant growth and demography

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Competition for light is broadly recognised as a key factor determining plant growth. In woody species, crown, branch and leaf level traits all contribute to light harvesting efficiency, and thus growth. Although there are genetic and mechanical constraints to the expression of these traits in individual trees and shrubs, individuals have the ability to show plastic responses within certain thresholds as a reaction to local abiotic and biotic conditions. As a result, crown functional traits (CFT) show inter- and intraspecific variability.In particular, crown dimensions and architecture of individual trees and shrubs are known to respond sensitively to local neighbourhood interactions. However, to explain the spatial development of crowns in detail, information on single branches is needed, since the process of crown expansion depends on the spatial development of branches and branch demography.In the third stage this subproject will continue to address the influence of species richness on aboveground plant growth and branch demography at the individual and local neighbourhood level to test the hypothesis that the diversity effect at the plot level is the overall result of the diversity effects at the local neighbourhood level.Specific objectives are (i) to analyse the impact of tree and shrub species richness (regarding both the plot and local diversity level) on individual tree and shrub growth and mortality within and among species, (ii) to quantify local neighbour interactions in terms of growth rates and branch demography and to test whether diversity reduces competition, and (iii) to investigate how inter- and intraspecific variability of CFTs is affected by species richness. Repeated measurements of architectural traits (stem, crown, branches) of individual trees and shrubs and their local neighbours by both, conventional methods and 3D terrestrial laser scanning, will be continued in the Main Experiment (including the trees of the BEFmod experiment, set up on subplots on all VIPs) and the Comparative Study Plots. A wide range of variables will be measured or calculated, such as stem diameter, tree height, stem slenderness, crown base height, crown length, crown diameter, crown projection area, relative growth rate and crown efficiency (mean annual biomass growth per unit of crown projection area).These variables are then related to species richness (explanatory variable) and local site conditions (as covariables; including all variables determined by the ecoscape approach). In addition, jointly with SP3 this subproject will use the whole suite of traits, which have been measured by SP2 and in particular by SP3, for synthesis work. Important data provided by SP3 will be the analyses of the plasticity of key traits as a response to diversity levels, and the calculation of community weighted means as well as of functional and phylogenetic diversity patterns.