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Mortality and Self-thinning in Postfire Black Spruce

T. J. CARLETON and BRENDA A. WANNAMAKER
Annals of Botany
Vol. 59, No. 6 (June 1987), pp. 621-628
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/42761599
Page Count: 8
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Mortality and Self-thinning in Postfire Black Spruce
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Abstract

Using age-structure determinations on both living and dead stems in censused plots, coupled with stem analysis techniques, an historical picture of mortality and above-ground tree stem growth was recreated for ten stands dominated by black spruce in northeastern Ontario, Canada. No evidence of mortality was seen in any plot prior to 30 years following postfire initiation. Each of the eight oldest stands showed a linear decline in numbers for a 20-25 year period. The steepness of the mortality slope was proportional to initial live stem density within and among plots during this phase. The final 10-20 years was marked by a less steep decline in numbers. The log density vs log mean tree volume curves in the eight oldest stands were doubly asymptotic and were fitted to a logistic curve very tightly in each case. At the point of inflection the curves' slopes ranged from -2·14 to -3·89. However, log density vs log mean stem volume among stands at this point of inflection had a slope of -0·96. Reasons for the inconsistency between within-stand and among-stand self-thinning estimates are considered, as well as the poor fit to the -3/2 rule. Ecosystem processes related to the change in nutrient relations during stand growth are identified as a prime influence on self-thinning behaviour in natural black spruce stands.

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