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Resource allocation, water relations and crown architecture examined at the tree and stand-level in northern conifers Open Access


Other title
Resource allocation
water relations
Type of item
Degree grantor
University of Alberta
Author or creator
Schoonmaker, Amanda L
Supervisor and department
Lieffers, Victor (Renewable Resources) / Landhausser, Simon (Renewable Resources)
Examining committee member and department
Caspersen, John (University of Toronto)
Hacke, Uwe (Renewable Resources)
Zwiazek, Janusz (Renewable Resources)
Silins, Uldis (Renewable Resources)
Department of Renewable Resources
Forest Biology and Management
Date accepted
Graduation date
Doctor of Philosophy
Degree level
Variation in quantity of light has driven plants to employ many strategies in order to persist in high and low light. It is also a primary driver of lower branch mortality and crown recession. Fine roots and leaves are complimentary tissues representing belowground and aboveground resource acquisition. This balance is likely to the influence forest stands as they age. The objective of my thesis is to understand how hydraulic architecture, crown form and resource allocation are affected by shading trees of opposing shade tolerance. Four tree species were examined: Pinus banksiana, Pinus contorta, Picea glauca and Picea mariana. The following are key findings of my thesis: • A reduced light environment alters the xylem vulnerability of shoots. Shaded shoots are not as drought resistant as those in high light. The effect of shade on hydraulic conductivity is likely tied to both the position of the shoots being examined as well as the quantity of light reduced. Evaporative demand in an understory environment is low, however, a rapid change into full light could be detrimental for shaded conifers. • Asymmetric shading (where part of the tree crown is fully illuminated while the other part is shaded) placed less-illuminated shoots at a greater disadvantage in terms of bud expansion and growth compared with uniform shading of the entire crown. Relative reductions in TNC appear to follow similar patterns to bud expansion and growth observations, suggesting that carbon dynamics or fluxes are playing a role in dictating physiological activity of branches. In all cases, responses to asymmetric shade were always more extreme in Pinus contorta compared with Picea glauca. This is likely due, in part, to different C storage patterns as Pinus contorta exhibited lower overall TNC concentrations and smaller (or non-existent) seasonal fluxes in TNC compared with P.glauca. • In a P.contorta chronosequence, fine root surface area is the first stand parameter to level-off while wood production increases for another 30 years and leaf area to age 100. During the period of peak wood production, a number of pressures are also converging including: light asymmetry (driving crown recession), crown friction and reduced soil resources.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Schoonmaker ALS, Hacke UG, Landhäusser SM, Lieffers VJ, Tyree MT (2010) Plant Cell Environ 33: 382-393

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