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Western redcedar (Thuja plicata Donn ex D. Don.) is an important North American tree species, but little information is available on its long-term responses to silvicultural treatments. Stand responses (mortality, ingrowth, basal area and volume growth, and distributions of trees by diameter and height classes) were followed for 25 years after thinning and fertilization treatments (alone and in combination) were applied to a naturally regenerated, low site quality western redcedar stand on the Olympic Peninsula in western Washington, USA. Mortality was low overall, but the densest stands experienced competition-related mortality. Thinning resulted in additional stem recruitment; after 25 years, the number of ingrowth trees exceeded the number of trees in the cohort left after thinning. Fertilization (with nitrogen and phosphorus) flattened size distributions and skewed them to larger size classes. Thinning plus fertilization resulted in the largest individual trees and the most large trees, but also many trees in a wide range of diameter classes. The recruitment of a second cohort did not result in a two-storied stand. Fertilization without thinning resulted in the greatest stand basal area and volume, as well as trees with fewer live lower branches. Le thuya géant (Thuja plicata Donn ex D. Don.) est une espèce d'arbre importante en Amérique du Nord, mais peu d'informations sont disponibles concernant sa réaction à long terme aux traitements sylvicoles. Les réactions à l'échelle du peuplement (la mortalité, le recrutement, la croissance en surface terrière et en volume, ainsi que la distribution des arbres par classes de diamètre et de hauteur) ont été mesurées pendant la période de 25 ans qui a suivi l'application de traitements d'éclaircie et de fertilisation (seuls ou combinés) dans un peuplement de thuya géant naturellement régénéré sur une station de faible qualité de la presqu'île Olympique dans l'ouest de l'État de Washington, aux tats-Unis. La mortalité était globalement faible, mais les peuplements les plus denses ont subi une mortalité induite par la compétition. L'éclaircie a provoqué le recrutement additionnel de nouveaux arbres; après 25 ans, le nombre d'arbres recrutés dépassait le nombre d'arbres de la cohorte laissée après l'éclaircie. La fertilisation (avec de l'azote et du phosphore) a aplani la distribution de la taille des arbres tout en l'étirant vers les classes constituées des plus gros arbres. La combinaison de l'éclaircie et de la fertilisation a produit les plus gros individus et la plus grande quantité de gros arbres, mais aussi plusieurs arbres distribués dans une large gamme de classes de diamètre. Le recrutement d'une deuxième cohorte n'a pas créé un peuplement bi-étagé. La fertilisation sans éclaircie a produit les plus grandes valeurs de surface terrière et de volume de même que des arbres avec le moins de branches vivantes dans le bas de la cime. [ABSTRACT FROM AUTHOR]

There is little information available on the long-term effects of managing western redcedar (Thuja plicata Donn ex D. Don). In a 15- to 20-year-old naturally regenerated second-growth redcedar stand on a poor site on the Olympic Peninsula of Washington, we tested crop tree (largest 250 trees·ha–1) response to precommercial thinning and fertilization in a replicated study. Fertilization treatments were N or N+P applied at study installation and year 13; precommercial thinning occurred at installation. Precommercial thinning without fertilization produced a sustained increase in periodic individual-tree basal area (BA) growth rate from years 3 through 25 posttreatment. However, through year 12, higher BA growth rates resulted from fertilization. During years 13 through 25, when intraspecific competition increased, the highest BA growth rate resulted from the combination of fertilization and precommercial thinning. Compared with the unthinned–unfertilized control, fertilization without thinning increased year-25 crop-tree height by 34% and BA by 137%; thinning without fertilization increased height by 11% and BA by 91%. Height to live-crown base was decreased by thinning but increased by fertilization, while thinning significantly increased stem taper on the lower bole. Treatment responses and foliar analyses indicate crop tree growth was substantially limited by nutrient availability. [ABSTRACT FROM AUTHOR]

Investigates disturbance events and changes in the composition of riparian forests on a small section of the Queets River floodplain in Olympic Peninsula, Washington. Impetus to the increase in Alnus rubra Bong; Account of the fires occurring in the region; Effects of floods and fire on riparian forests.