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Basal area growth impacts of dwarf mistletoe on western hemlock in an old-growth forest

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We investigated the effect of western hemlock dwarf mistletoe (Arceuthobium tsugense (Rosend.) G.N. Jones ssp. tsugense) on the 13year basal area growth of large (>45.7cm diameter at breast height) western hemlock (Tsuga heterophylla (Raf.) Sarg.) trees in an old-growth forest in southwestern Washington state. We controlled for spatial effects on tree growth by utilizing twenty-seven 0.4ha plots that had uninfected, lightly, moderately, and severely infected classes of trees present on each plot. Basal area growth was analyzed using analysis of covariance of a randomized block design that was a balanced design with four treatments (infection classes) and 27 replicates (blocks or 0.4ha plots), with initial diameter as the covariate. Basal area growth was found to be significantly different among the infection classes (F[3,77] = 10.09 and p< 0.0001). Growth of the light and moderate infection classes was not detectably different from growth of uninfected trees. However, severely infected trees grew from 16% to 46% (mean = 36%) less than uninfected trees of the same initial diameter over the period of study (1991–2004). The large trees in this stand did not show growth impacts until they were severely infected.

Nous avons étudié l’effet du faux-gui de la pruche (Arceuthobium tsugense (Rosend.) G.N. Jones ssp. tsugense) sur 13années de croissance en surface terrière de grosses tiges (>45,7cm de diamètre au DHP) de pruches de l’Ouest (Tsuga heterophylla (Raf.) Sarg.) dans une forêt ancienne du sud-ouest de l’État de Washington, aux États-Unis d’Amérique. Nous avons contrôlé les effets spatiaux en utilisant 27 placettes-échantillons de 0,4ha qui contenaient toutes des arbres non infectés ainsi que des arbres légèrement, modérément et sévèrement infectés. La croissance en surface terrière a été analysée au moyen d’une analyse de covariance avec un plan expérimental en blocs complètement aléatoires: un plan équilibré avec quatre traitements (classes d’infection) et 27 répétitions (blocs ou placettes-échantillons de 0,4ha) et le diamètre initial comme covariable. La croissance en surface terrière était significativement différente entre les classes d’infection (F[3,77] = 10,09 et p < 0,0001). Une différence de croissance n’a pas été détectée entre les classes d’infection légère ou modérée et les arbres non infectés. Cependant, les arbres sévèrement infectés ont eu une croissance 16% à 46% (moyenne de 36%) inférieure à celle des arbres non infectés de même diamètre initial au cours de la période d’étude (1991–2004). La croissance des gros arbres dans ce peuplement n’a pas été affectée tant qu’ils n’étaient pas sévèrement infectés.

Document Type: Research Article

Publication date: 2008-03-01

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  • Published since 1971, this monthly journal features articles, reviews, notes and commentaries on all aspects of forest science, including biometrics and mensuration, conservation, disturbance, ecology, economics, entomology, fire, genetics, management, operations, pathology, physiology, policy, remote sensing, social science, soil, silviculture, wildlife and wood science, contributed by internationally respected scientists. It also publishes special issues dedicated to a topic of current interest.
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