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Mixed-species plantations have been suggested as ecologically and economically viable alternatives to monocultures. We examined the growth response of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) and western redcedar (Thuja plicata Donn ex D. Don in Lamb.) to different species mixtures (Douglas-fir : western redcedar mixtures of 1:0, 1:1, 1:3, and 0:1) and planting densities (500,1000, and 1500 stems*[ha.sup.-1]) in a dry maritime forest on eastern Vancouver Island, Canada. Twenty-two years postplanting, species mixture significantly affected diameter and height growth (p < 0.001), with stand diameter and height generally decreasing with increasing redcedar composition. Inherent variation in soil productivity across the plantation (carbon:nitrogen ratio) equally constrained stand growth. The widest spacing had larger diameter than the closest spacing (p = 0.025) but the least stand basal area compared with the other spacing treatments (p = 0.003-0.031). Stand volume was significantly affected by mixture x density interaction (p = 0.024) and generally declined with increasing proportion of redcedar and decreasing stand density. In the first decades after plantation establishment, inherent species growth traits and soil fertility were most important in dictating stand productivity. Because of the differences in resource utilization of both species, stand dynamics may change as competition for light and soil resources increases. Evaluation of silvicultural recommendations regarding mixtures of both species will continue with plantation development. Key words: Douglas-fir, western redcedar, species mixtures, stand productivity, soil fertility. Les plantations plurispecifiques ont ete proposees comme alternatives ecologique et economique viables aux monocultures. Nous avons etudie la reaction de la croissance du douglas de Menzies (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) et du thuya geant (Thuja plicata Donn ex D. Don in Lamb.) a differents melanges de ces deux especes (douglas: thuya : 1:0, 1:1, 1:3, and 0:1) et a differentes densites de plantation (500,1000 et 1500 tiges*[ha.sup.-1]) dans une foret maritime seche de l'est de l'ile de Vancouver, au Canada. Vingt-deux ans apres la plantation, le melange d'especes a significativement influence la croissance en diametre et en hauteur (p < 0,001); la hauteur et le diametre du peuplement diminuaient generalement avec l'augmentation de la proportion de thuya. La variation inherente de la productivite du sol a travers la plantation (rapport carbone:azote) limitait egalement la croissance du peuplement. L'espacement maximum etait associe a un plus gros diametre que l'espacement minimum (p = 0,025) mais a la plus faible surface terriere du peuplement que les autres espacements (p = 0,003-0,031). Le volume du peuplement etait significativement influence par l'interaction entre le melange et la densite (p = 0,024) et diminuait generalement avec l'augmentation de la proportion de thuya et la diminution de la densite du peuplement. Durant les premieres decennies apres l'etablissement des plantations, les caracteres de croissance inherents a chaque espece et la fertilite du sol etaient les facteurs determinants de la productivite du peuplement. A cause des differences entre les deux especes dans l'utilisation des ressources, la dynamique du peuplement peut changer a mesure que la competition pour la lumiere et les ressources du sol augmente. L'evaluation des recommandations sylvicoles en ce qui a trait aux melanges des deux especes se poursuivra avec le developpement des plantations. [Traduit par la Redaction] Mots-cles: douglas de Menzies, thuya geant, melanges d'especes, productivite du peuplement, fertilite du sol., Introduction Plantations constitute an important part of forest management globally (FAO 2001). In Canada, intensification of forest management is expected to continue through plantation forestry over the coming decades (MacLean [...]

This study was conducted to quantify growth responses of three major commercial conifer species (lodgepole pine (Pinus contorta Douglas ex Loudon var. latifolia Engelm. ex S. Watson), interior Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. glauca (Beissn.) Franco), and spruce (white spruce (Picea glauca (Moench) Voss) and hybrid spruce (Picea engelmannii Parry ex. Engelm. x Picea glauca (Moench) Voss x Picea sitchensis (Bong.) Carriere))) to various fertilizer blends in interior British Columbia, Canada. Over 25 years, growth-response data were repeatedly collected across 46 installations. The fertilizer blends were classified into three groups: nitrogen only; nitrogen and sulfur combined; and nitrogen, sulfur, and boron combined. The growth responses for stand volume, basal area, and top height were calculated through absolute and relative growth rate ratios relative to a controlled group. Fertilizer blend, inverse years since fertilization, site index, stand density at fertilization, and their interactions with the fertilizer blend were used as explanatory variables. The magnitude and significance of volume and basal area growth responses to fertilization differed by species, fertilizer-blend groups, and stand-condition variables (i.e., site index and stand density). In contrast, the response in top height growth did not differ among fertilization blends, with the exception of the nitrogen and sulfur fertilizer subgroup for lodgepole pine. The models developed in this study will be incorporated into the current growth and yield fertilization module (i.e., Table Interpolation Program for Stand Yields (TIPSY)), thereby supporting guidance of fertilization applications in interior forests in British Columbia. Key words: fertilization gain, growth and yield model, Pinus contorta, Pseudotsuga menziesii, Picea glauca, Table Interpolation Program for Stand Yields (TIPSY). Cette etude visait a quantifier la reaction de croissance de trois importantes especes commerciales de coniferes (pin tordu latifolie (Pinus contorta Douglas ex Loudon var. latifolia Engelm. ex S. Watson), douglas de Menzies bleu (Pseudotsuga menziesii (Mirb.) Franco var. glauca (Beissn.) Franco) et epinette (epinette blanche (Picea glauca (Moench) Voss) et epinette hybride (Picea engelmannii Parry ex. Engelm. x Picea glauca (Moench) Voss x Picea sitchensis (Bong.) Carriere)) a divers melanges de fertilisants appliques dans la zone interieure de la Colombie-Britannique, au Canada. Les donnees de reaction de croissance ont ete recoltees de facon repetee sur une periode de 25 ans dans 46 installations. Les melanges de fertilisants ont ete classes en trois groups : azote seul, azote et soufre combines, et azote, soufre et bore combines. Les reactions de croissance en volume, en surface terriere et en hauteur dominante du peuplement ont ete calculees en valeurs absolues et en rapports de taux de croissance relatif a un groupe temoin. Les variables explicatives etaient le melange de fertilisants, l'inverse du nombre d'annees depuis la fertilisation, l'indice de qualite de station, la densite du peuplement au moment de la fertilisation et leurs interactions avec le melange de fertilisants. L'ampleur et la significativite statistique des reactions de croissance en volume et en surface terriere a la fertilisation differaient selon l'espece, le groupe de melange de fertilisants et les variables d'etat du peuplement (c.-a-d. l'indice de qualite de station et la densite du peuplement). Par contre, la reaction de croissance en hauteur dominante n'a pas varie en fonction des melanges de fertilisants, a l'exception du melange d'azote et de soufre combines dans le cas du pin tordu. Les modeles mis au point dans cette etude seront incorpores au module actuel de fertilisation pour la croissance et le rendement (c.-a-d. TIPSY) de facon a appuyer les directives pour les applications de fertilisants dans les forets interieures de la Colombie-Britannique. [Traduit par la Redaction] Mots-cles : benefices de la fertilisation, modele de croissance et rendement, Pinus contorta, Pseudotsuga menziesii, Picea glauca, Programme d'interpolation tabulaire pour les rendements des peuplements (TIPSY)., Introduction Forests are one of the most important natural resources in British Columbia (BC), Canada, and are closely connected with the industry, economy, and culture of BC communities. Climate change [...]

Temperate rainforest soils of the Pacific Northwest are often carbon (C) rich and encompass a wide range in fertility reflecting varying nitrogen (N) and phosphorus (P) availability. Soil resource stoichiometry (C : N : P) may provide an effective measure of site nutrient status and help refine species-dependent patterns in forest productivity across edaphic gradients. We described the nature of soil organic matter for mineral soil and forest floor substrates across very wet (perhumid) rainforest sites of southwestern Vancouver Island (Canada), and employed soil element ratios as covariates in a long-term planting density trial to test their utility in defining basal area growth response of four conifer species. There were strong positive correlations in mineral soil C, N and organic P (Po) concentrations, and close alignment in C : N and C : Po both among and between substrates. Stand basal area after five decades was best reflected by soil C : N but included a significant species-soil interaction. The conifers with ectomycorrhizal fungi had diverging growth responses displaying either competitive (Picea sitchensis) or stress-tolerant (Tsuga heterophylla, Pseudotsuga menziesii) attributes, in contrast to a more generalist response by an arbuscular mycorrhizal tree (Thuja plicata). Despite the consistent patterns in organic matter quality we found no evidence via foliar nutrition for increased P availability with declining element ratios as we did for N. The often high C : Po ratios (as much as 3000) of these soils may reflect a stronger immobilization sink for P than N, which, along with ongoing sorption of PO4-, could limit the utility of C : Po or N : Po to adequately reflect P supply. The dynamics and availability of soil P to trees, particularly as Po, deserves greater attention as many perhumid rainforests were co-limited by N and P, or, in some stands, possibly P alone. [ABSTRACT FROM AUTHOR]