Titre :
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In defence of the -3/2 boundary rule: A re-evaluation of self-thinning concepts and status
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Auteurs :
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N. Hamilton ;
C. Matthew ;
G. Lemaire
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Type de document :
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article/chapitre/communication
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Année de publication :
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1995
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Format :
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569-577
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Langues:
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= Anglais
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Mots-clés:
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self-thinning
;
-3/2 power rule
;
-3/2 self-thinning rule
;
boundary line
;
size-density compensation
;
regression methods
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Résumé :
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The -3/2 power rule, or -3/2 self-thinning rule, was accepted 10 years ago as an important generalization, but has recently been questioned by a number of authors. This paper assesses what remains of the rule. While it has been empirically established that size-density trajectories followed by self-thinning plant populations do not necessarily follow a -3/2 slope, a more general power rule describing a density-dependent upper limit to mean shoot biomass per plant (the ' -3/2 boundary rule') remains largely intact.Principal component analysis (PCA) overestimates the steepness of the thinning slope if y:x variance ratio is greater than 1:1. Lonsdale's (Ecology 71: 1373-1388) overall mean PCA slope of - 0.6 for biomass-density suggests a true mean slope close to the theoretical value of -0.5. Reduced major axis (RMA) regression appears a reasonable approximation for the -3/2 but not the -1/2 formulation of the rule. Fitting of a linear functional relationship (LFR) is a more appropriate slope estimation procedure, not previously used for data on thinning. None of these procedures estimates a boundary line that is not transgressed by any data point except through errors of measurement.Mortality due to overcrowding ensues when a small, suppressed plant no longer holds its leaves high enough in the canopy to maintain a positive carbon balance. It follows that LAI should remain constant during thinning, and that self-thinning theory should be developed in terms of maximum leaf area index and the biomass required to support it. A derivation is presented and some of its consequences are examined. (C) 1995 Annals of Botany Company
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Source :
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Annals of Botany - 0305-7364, vol. 76, n° 6
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