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Ann. For. Sci.
Volume 60, Number 6, September 2003
Page(s) 469 - 474
DOI http://dx.doi.org/10.1051/forest:2003040
Ann. For. Sci. 60 (2003) 469-474
DOI: 10.1051/forest:2003040

Root biomass distribution under three cover types in a patchy Pseudotsuga menziesii forest in western Canada

Andrew D. Richardsona, Catherine Bealle Statlandb and Timothy G. Gregoirea

a  School of Forestry & Environmental Studies, Yale University, 370 Prospect Street, New Haven, CT 06511, USA
b  Research Branch, British Columbia Ministry of Forests, PO Box 9519, Stn. Prov. Govt., Victoria, BC V8W 9C2, Canada

(Received 7 October 2002; accepted 21 March 2003)

Abstract - We investigated the relationship between cover type and root biomass distribution and allocation to different root size classes in a naturally regenerated, dry, Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca) forest in the southern interior of British Columbia, Canada. The site was selectively harvested 32 years previously; residual stems were 30 cm and 130-170 years old at breast height at the time of study. A total of nine pits (each measuring $1.0\ {\rm m}\times 1.0$ m) were excavated to a depth of 1.0 m under three different cover types: mature timber, grassy (Calamagrostis rubescens) openings (canopy gaps), and regeneration clumps. Total (all diameters) live root biomass ranged from 4.7 kg/m2 under the mature timber to 1.9 kg/m2 under both regeneration clumps and grassy openings. Thin root (0.1 cm < $\phi\leq 0.5$ cm) biomass was similar across all three cover types (0.8 kg/m2). We suggest that the similarity of thin root biomass across the three cover types is indicative of strong root competition at this resource-poor site: there appears to be no below-ground "root gap" corresponding to the canopy opening above the pinegrass-dominated patches.


Résumé - Distribution de la biomasse racinaire sous trois types de couvert dans une forêt irrégulière de Pseudotsuga menziesii du Canada occidental. Nous avons étudié la relation entre le type de couvert et la répartition de la biomasse racinaire entre différentes classes de dimension des racines, dans une forêt sèche régénérée naturellement de Douglas des Montagnes Rocheuses (Pseudotsuga menziesii var. glauca) située dans la zone intérieure méridionale de la Colombie Britannique au Canada. Cette station avait subi une coupe à la dimension 32 ans auparavant. Les tiges restantes, âgées de 130 à 170 ans, avaient, au moment de l'étude, un diamètre à hauteur d'homme de 30 cm. On a creusé neuf fosses mesurant chacune $1,0 \times 1,0 \times 1,0$ m sous trois types de couvert : peuplement adulte, clairières à graminées (Calamagrostis rubescens) et bouquets de régénération. La biomasse racinaire totale (tous diamètres) va de 4,7 kg/m2 sous peuplement adulte à 1,9 kg/m2 sous les bouquets de régénération et sous clairières à graminées. La biomasse des racines fines (0,1 cm < $\phi\leq $ 0,5 cm) était du même ordre sous les trois types de couvert (0,8 kg/m2). Nous suggérons que cette similitude des valeurs de biomasse de racines fines entre les trois types de couvert est l'indice de l'existence d'une forte concurrence entre racines, dans cette station pauvre en ressources. Les ouvertures dans le couvert forestier se traduisent par des clairières à Calamagrostis qui ne sont pas des zones sans racines.


Key words: Calamagrostis rubescens / Douglas-fir / gap / Pseudotsuga menziesii / root biomass

Mots clés : Calamagrostis rubescens / Douglas / trouée / Pseudotsuga menziesü / biomasse

Corresponding author: Andrew D. Richardson andrew.richardson@unh.edu

© INRA, EDP Sciences 2003

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