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Title: Tree branch geometry : efficiency and design optimisation in Sitka spruce
Author: Farnsworth, Keith Douglas
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1994
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This study set up the hypothesis that branches are shaped so as to maximise total photosynthetically active radiation interception per unit of assimilate expended in branch structural material. Measurements of branch geometry, combined with computer modelling were used to develop a deeper understanding of form-function relations. The thesis seeks to discover whether light interception (as a measure of benefit) per unit invested material (as a cost) is maximised in natural branches by the optimisation of allocation of structural material among the shoots of branches. Thus a cost-benefit analysis paradigm is applied to the problem of structural carbon allocation among shoots. Topology of branches has been regarded as an invariant property of branch age, so providing an appropriate constraint. A topological classification scheme was devised for branch elements (links and shoots) so that form-function relations could be resolved. Geometric attributes of 125 individual branches from trees of Picea sitchensis Bong. (Carr.) were analysed to find evidence for form-function relationships. Multivariate differences in geometric design among genotypes were not considered sufficient to motivate form optimisation through a breeding program. Within branch shoot length distribution was related to position in the topology which may be a reflection of light interception potential. Diameters of branch elements were proportional to lengths, but proportionality constants varied with topological position. An allocation model based on mechanical design of shoots was more successful in explaining shoot allometry than one based on the pipe model. The mechanical load safety factor varied among branch elements according to their expected potential for light interception. Hydraulic (pine model) design of branches reinforced the pattern of distribution in mechanical safety factors. This provides possible support for the theory of shoot autonomy. It is concluded that tree branches are likely a result of competing optimisation goals acting within genetic and ontogenic constraints and that shoot size may be related to the potential for competition for light interception, with shoots that show greater potential taking a disproportionate share of resources within the branch.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available