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Title: Computer modelling of agroforestry systems
Author: Anderson, Thomas R.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1991
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The potential of agroforestry in the British uplands depends largely on the ability of system components to efficiently use resources for which they compete. A typical system would comprise conifers planted at wide spacing, with sheep grazing pasture beneath. Computer models were developed to investigate the growth of trees and pasture in a British upland agroforest system, assuming that growth is primarily a function of light intercepted. Some of the implications of growing trees at wide spacing compared to conventional spacings, and the impact of trees on the spatial and annual production of pasture, were examined. Competition for environmental resources between trees and pasture was assumed to be exclusively for light: below-ground interactions were ignored. Empirical methods were used to try and predict timber production in agroforest stands based on data for conventional forest stands, and data for widely-spaced radiata pine grown in South Africa. These methods attempted to relate stem volume increment to stand density, age, and derived competition measures. Inadequacy of the data base prevented successful extrapolation of growth trends of British stands, although direct extrapolation of the South African data did permit predictions to be made. A mechanistic individual-tree growth model was developed, both to investigate the mechanisms of tree growth at wide spacings, and to provide an interface for a pasture model to examine pasture growth under the shading conditions imposed by a tree canopy. The process of light interception as influenced by radiation geometry and stand architecture was treated in detail. Other features given detailed consideration include carbon partitioning, respiration, the dynamics of foliage and crown dimensions, and wood density within tree stems. The predictive ability of the model was considered poor, resulting from inadequate knowledge and data on various aspects of tree growth. The model highlighted the need for further research into the dynamics of crown dimensions, foliage dynamics, carbon partitioning patterns and wood density within stems, and how these are affected by wide spacing. A pasture model was developed to investigate growth beneath the heterogeneous light environment created by an agroforest tree canopy. Pasture growth was closely related to light impinging on the crop, with temperature having only a minor effect. The model highlighted the fact that significant physiological adaptation (increased specific leaf area, decreased carbon partitioned below-ground and changes in the nitrogen cycle) is likely to occur in pasture shaded by a tree canopy.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available