Stem growth and respiration of young balsam fir trees in thinned and unthinned stands

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Abstract
Average respiration rate per square decimetre of stem surface area was greater in a thinned stand of balsam fir (Abiesbalsamea (L.) Mill.) than in an unthinned stand. While respiration rates of internodes were highly correlated to their rates of stem growth, the differences in respiration among internodes and stands could not be explained by the unequal use of respiration products to support synthesis alone. Maintenance respiration rates were greater for internodes with higher rates of stem growth, and consequently the efficiency of using photosynthates for growth was reduced in the thinned stand. In addition, breast-height internodes respired at higher rates than upper stem internodes with equal growth rates. It is argued that lower stem internodes expended more respiration products for translocation than upper stem internodes. The rate of stem growth per unit of foliar weight was less in the thinned than in the unthinned stand, indicating that the higher rate of respiration per unit of stem surface area counteracted the beneficial effects of thinning on the rate of photosynthesis per unit of foliar weight.