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As forest managers increasingly seek to implement partial-harvest silviculture systems in complex forests, more data are required on the potential development of the residual stand following treatment. In this study, we present 25-year data from a long-term silvicultural study of tree- and stand-level responses to differing levels of basal area following partial harvest in a complex spruce-fir forest in central British Columbia, Canada. Reducing stand basal area elicited stronger basal area increment response in fir than spruce; however, spruce productivity was overall higher than fir across all treatments. Smaller trees increased their size proportionally more than larger trees, and thinning resulted in increased recruitment of smaller trees into larger diameter classes. At the stand-level, basal area reductions to well below 20 [m.sup.2]/ha resulted in higher volume and basal area growth over the length of this study, and suggest that optimum stand-level growth may be achieved at lower basal areas than suggested in prior literature. We also found a positive relationship between stand-level residual basal area and mortality. In central British Columbia, stand structure, species composition, and growth rates in complex spruce-fir forests can be maintained through partial-harvest silviculture treatments. Key words: basal area, uneven-aged, white spruce, subalpine fir, complex stand structure, partial-harvest silviculture systems, Introduction In many temperate to boreal ecosystems, forest managers are increasingly striving to enhance the ecological and structural complexity of managed stands and landscapes using different silvicultural and harvesting practices, [...]

As forest managers increasingly seek to develop and maintain mixedwood forests, more information is required on the potential facilitative and competitive interactions between tree species. We present data from a broadleaf thinning study established in a mixedwood stand in Central British Columbia, Canada, to examine how residual trembling aspen and paper birch competitively affect spruce growth after thinning but may also concurrently protect spruce from attack by the white pine weevil. Tree-level data collected at a stand age of 36 years, 19 years after broadleaf trees were thinned, show that spruce height and diameter growth declined with broadleaf competition, particularly from taller trees, resulting in a competition-related reduction in stand-level spruce volume yields. The fastest spruce growth occurred in treatments where all broadleaf trees were removed, but complete broadleaf removal also resulted in higher rates of weevil attack on spruce, which also caused height and diameter growth reductions. Our results suggest that maintaining a density of approximately 500 broadleaf trees per hectare may achieve a stand condition that balances spruce growth reductions from competitive interactions with broadleaf trees while providing some protection from white pine weevil attacks. [ABSTRACT FROM AUTHOR]

Aim: Globally, forests at the alpine‐treeline ecotone (ATE) are considered sensitive to warming temperatures; however, responses to recent climate change show high variability and many underlying processes remain unclear. This study aims to provide further insight into possible ATE forest responses to climate change by examining spatiotemporal patterns in recent tree regeneration and growth responses to climate across treeline forms. Location: This study is situated at the ATE in the Rocky Mountain and Columbia Mountain ranges in central British Columbia, Canada. Taxon: Gymnosperms – subalpine fir (Abies lasiocarpa Hooker (Nutall)). Methods: We collected tree and stand data from 48 plots across five study sites. Plots were distributed across three treeline stand types: (i) islands; (ii) abrupt; and (iii) fringes of regeneration adjacent to tree islands. We used a dendrochronological approach to analyse the ages of recently established trees in fringe stand types, detect long‐term trends in annual tree growth and quantify climate‐growth relationships. Results: Seedling recruitment adjacent to tree islands occurred over a period of approximately 40 years (1960–2000), with two regeneration "pulses" in the late 1970s and 1980s. Abrupt and fringe trees showed a similar age structure and annual radial growth has increased in most trees over the past 30 years. Across the study region and stand types, summer temperature has the strongest influence on radial growth. Over the past 70 years, growth in tree islands has become increasingly correlated with growing season temperature variables. Main Conclusions: Forest growth and structure have changed in coherent spatial and temporal patterns over recent decades at the ATE in central BC. Projections for sustained warming in this region will likely result in increased tree growth and potential continued expansion of forests into untreed areas below the treeline. These changes will have implications for hydrological regimes, wildlife habitat and carbon sequestration. [ABSTRACT FROM AUTHOR]

How climate change will affect tree growth across species' geographic and climatic ranges remains a critical knowledge gap. Tree-ring data were analyzed from 33 interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) stands spanning wide geographic and climatic conditions in the interior of British Columbia to gain insights into how within-species growth responses to climate can vary based on local environmental conditions over a broad climatic and geographic range, including populations growing at the species' range and climatic margins. Populations growing in relatively warm and dry climates had growth patterns correlated mostly with annual precipitation, whereas populations growing in high-elevation wet and cold climates had growth patterns correlated with snowfall, winter and annual temperatures, and ocean-atmosphere climate systems. Populations growing at climatic extremes (e.g., coldest, driest, warmest) in each study region had the strongest responses to climate. Projected climate change may negatively influence Douglas-fir productivity across most of its range, and populations growing near the species' climatic limits may provide early and strong indications of future responses. Resume: Il y a un manque crucial de connaissances concernant la facon dont les changements climatiques vont influencer la croissance des arbres partout dans l'aire de repartition climatique et geographique des especes. Des donnees dendrochronologiques provenant de 33 peuplements de douglas bleu (Pseudotsuga menziesii var. glauca (Beissn.) Franco) soumis a une grande variete de conditions climatiques et geographiques dans la zone interieure de la Colombie-Britannique ont ete analysees dans le but d'avoir une idee de la facon dont la reponse en croissance au climat peut varier au sein de l'espece sur la base des conditions environnementales locales couvrant un large spectre climatique et geographique, incluant des populations qui croissent a la limite de l'aire de repartition et des exigences climatiques de l'espece. Les populations croissant sous un climat relativement chaud et sec avaient des patrons de croissance correles avec la precipitation annuelle tandis que les populations croissant a haute altitude sous un climat froid et humide avaient des patrons de croissance corre- les avec la precipitation nivale, les temperatures hivernale et annuelle et les systemes climatiques ocean-atmosphere. Les populations soumis a des extremes climatiques (p. ex. climat le plus froid, le plus sec, le plus chaud) dans chaque region etudiee avaient la plus forte reponse au climat. Les changements climatiques anticipes pourraient influencer negativement la productivite du douglas bleu presque partout dans son aire de repartition et les populations qui croissent pres des limites climatiques de l'espece peuvent fournir des indications serieuses et precoces des reponses futures. [Traduit par la Redaction], Introduction Climate change is expected to cause substantial changes in tree growth by altering growing season length, growing degree-days, soil moisture availability, and other climate-related factors important to plant life [...]