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A factorial trial was established to examine the effects of planting density and fertilization on the growth of western redcedar (Thuja plicata Donn ex D. Don) and western hemlock (Tsuga heterophylla (Raf.) Sarg.) on nutrient- poor (CH) sites and nutrient-medium (HA) sites. Two levels of NPK fertilization were crossed with three levels of planting density (500, 1500, and 2500 stems/ha). Fifteen years after establishment and 10 years after the last fertilizer application, height, individual stem volume increment, stand volume, 5 year periodic annual increment (PAI), and 5 year periodic height increment were all increased by fertilization. Fertilization of CH sites increased annual stand volume increment by 753%-2552% and 122%-209% for hemlock and cedar, respectively; fertilization of HA sites increased PAI by 94%-264%. Volume growth response to fertilization was greater on HA than on CH sites. Increasing stand density reduced height growth on CH sites but not on HA sites. These results suggest that competition for nutrients can be a significant growth-limiting factor even before canopy closure occurs and that treatment of ericaceous sites may not be justified by productivity increases. Un dispositif factoriel a ete mis en place pour etudier les effets de la densite de plantation et de la fertilisation sur la croissance du thuya geant (Thuja plicata Donn ex D. Don) et de la pruche de l'Ouest (Tsuga heterophylla (Raf.) Sarg.) etablis sur des stations pauvres (CH) et moderement riches (HA) en nutriments. Deux niveaux de fertilisation en NPK ont ete appliques dans chacun des trois niveaux de densite de plantation (500, 1500 et 2500 tiges/ha). Quinze ans apres l'etablissement et 10 ans apres l'application de la derniere fertilisation, la hauteur, l'accroissement en volume des tiges individuelles, le volume du peuplement, l'accroissement annuel periodique quinquennal (AAP) et l'accroissement periodique quinquennal en hauteur ont tous augmente a cause de la fertilisation. La fertilisation des stations CH a augmente l'accroissement annuel en volume du peuplement de 753 % a 2552% pour la pruche et de 122% a 209% pour le thuya. La fertilisation des stations HA a augmente l'AAP de 94% a 264%. A la suite de la fertilisation, la reaction de la croissance en volume des stations HA a ete superieure a celle des stations CH. L'augmentation de la densite des peuplements a reduit la croissance en hauteur sur les stations CH, mais pas sur les stations HA. Ces resultats indiquent que la competition pour les nutriments peut etre un facteur important pour limiter la croissance des arbres avant meme que survienne la fermeture de la canopee. De plus, il est possible que le traitement des stations a ericacees ne soit pas justifie par des augmentations de la productivity;. [Traduit par la Redaction], Introduction Reforestation of sites dominated by ericaceous shrubs such as heather (Calluna vulgaris (L.) Hull), sheep laurel (Kalmia angustifolia L.), and salal (Gaultheria shallon Pursh) can be particularly challenging (Mallik [...]

Presents a study that determined factors limiting the early survivorship of Thuja plicata on northern Vancouver Island, British Columbia. Method of the study; Results and discussion; Conclusion.

Discusses the improvement of understanding of the role of soil invertebrates in the break-down of litter, cycling of nitrogen, and growth of seedlings in forests of British Columbia. Presence of millipedes in the microcosms of forest floor; Increase of inorganic nitrogen release in the presence of fauna; Rate of breakdown of forest litter.

Reports that the rate of mass loss of three standard substrates (pine needle litter, aspen leaf litter, and forest floor material) was measured in forests and adjacent clearcuts throughout British Columbia to test the hypotheses that (i) rates of mass loss are greater in clearcuts than in forests and (ii) clear-cutting would stimulate decomposition most in colder zones. Range of mass loss; Mass loss from pine needles that was significantly slower in clearcuts throughout the incubation; Aspen leaf litter and forest floor material that lost mass at similar rates in forests and clearcuts; Effect of clear-cutting that did not vary between relatively cold and warm sites; Effect of clear-cutting that was not related to the size of the clearcuts.

Reports on the measured rates of decomposition at three sites representing the major mixedwood forest types of British Columbia: (i) boreal forests of white spruce (Picea glauca (Moench) Voss) and trembling aspen (Populus tremuloides Michx.), (ii) coastal forests of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and red alder (Alnus rubra Bong.), and (iii) a wet interior forest of Douglas-fir, paper birch (Betula papyrifera Marsh.), and lodgepole pine (Pinus contorta Doug. ex Loud.). Mass loss of litter of each species (both pure and in combination with the other species) that was measured in forests of each species to determine (i) if broadleaf litter decomposed faster than needle litter, (ii) if litter decomposed faster in broadleaf or mixedwood forests than in coniferous forests, and (iii) if mixing with broadleaf hastened decomposition of needle litter; Broadleaf litters that decomposed faster than needles during the first year but, thereafter, decomposed more slowly; Litter that tended to decompose faster in the broadleaf forests than in the coniferous forests; No evidence to indicate that the addition of broadleaf litter hastened decomposition of needle litter; Results that indicate that the mixing of needle litter with broadleaf litter is unlikely to hasten decomposition in mixedwood forests of British Columbia.

Reports on the incubation of forest floor samples from a three tree species (Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.), and paper birch (Betula papyrifera Marsh.)). Rates of N mineralization in the forest floors of Douglas-fir that was significantly greater than either birch or lodgepole pine; Douglas-fir forest floors that also mineralized more N per unit of either N or C than the other species; Nitrogen mineralization rates that were positively correlated with the N concentration of the forest floor; Nitrogen concentration of foliar litter that were poor predictors of N mineralization rates resulting from Douglas-fir litter having the lowest N concentrations in litter but the highest rates of net N mineralization in the forest floor; Nitrogen mineralization in the forest floor that was negatively correlated with the lignin concentration in foliar litter; Douglas-fir litter that had low lignin concentrations, which may allow more of the mineralized N to remain in inorganic forms rather than being bound in humus; Results that suggest that a component of Douglas-fir might improve N availability in coniferous forest floors.

Tests whether nitrogen (N) cycling in stands of a single tree species increased with increasing mineral soil nitrogen capital. Estimation of N cycling rates in nine stands of Douglas fir; Net N mineralization rate in forest floor; Estimation of carbon and N turnover rates from the litterfall and forest ratio floor.

Investigates long-term effects of nitrogen fertilization on nitrogen availability in coastal Douglas-fir in southeastern Washington. Nitrogen mineralization rates in forest floors; Estimates of nitrogen turnover rates from litterfall/forest floor ratio; Absence of nitrogen fertilization effect on nitrogen cycling.