Abstract
The relationship between tree height and tree vigor was examined in order to test the hypothesis that increased height results in a reduction in photosynthate availability for growth due to an increase in respiratory load of the sapwood. Various vigor indices were measured on black spruce [Picea mariana (Mill.) B. S. P.] trees on a wide range of sites and ages. The relationship between these vigor indices and tree height and site quality were then evaluated through correlation and regression analyses. Vigor indices based on meristematic activity such as specific volume increment and height growth rate were generally more strongly correlated than foliage based indices (i.e. Waring vigor estimates). Both tree height and site index were found to have a significant effect on specific volume increment and height growth rate. However the height effect decreased with a decrease in site quality, and became insignificant (P <0.05) on the poorer sites. The full regression model, allowing the height effect to vary between different site quality groups, explained 82% and 72% of the variability in specific volume increment and height growth rate, respectively. The results support the hypothesis that increases in the ratio of respiration to photosynthesis in trees as they increase in size is largely a function of tree height. Possible explanations for the decreased height effect on poor sites are also discussed.
Published Version
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