The species specific growth patterns make plastic crown architecture respond in different manner to different environments modifying their influence to neighbours. The main aims of this thesis were to separate the effect of neighbour species identity from the abundance, size and proximity of the neighbours in between-tree competition and to link crown architecture with hydraulic architecture by identifying the associated within-tree variation of crown traits.
The empirical part of the work was based on digitising three-dimensional (3D) crown architecture and measuring xylem anatomy. Digitising allowed the development of crown architecture models for Betula pendula (Roth.) and Pinus sylvestris (L.). The models were further applied to simulate light transmission in mixed stands.
Crown architecture of the studied species responded to increased competition intensity primarily by reducing branch number and size. Proportional biomass distribution to foliage and main branches over the stem increased in young B. pendula with increasing competition intensity, whereas Pinus sylvestris used the opposite strategy. In addition to competition intensity, crown architecture of the studied species showed plastic responses to the species identity of neighbouring trees. Lower overall growth but added height growth indicating stronger competition was found in mixtures of B. pendula and Pinus sylvestris when a tree was surrounded by interspecific neighbours compared to trees surrounded by intraspecific neighbours. Both species-specific effects on resource gradients and non-resource signals remain plausible explanations for this result: B. pendula transmitted more light than Pinus sylvestris at simulated dense stands.
Hydraulic architecture was shown to be interlinked with crown architecture as the conduit diameter varied as a function of tree compartment, branching hierarchy, leaf area and distance from the apex. The results suggest that the use of detailed tree structure models and species-specific competition analysis is useful in predicting and understanding growth in mixed boreal stands.