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There is an increasing interest in mixed conifer-broadleaf stands as a way to increase the diversity and productivity of managed forests. This study examined the impacts of varying densities of planted broadleaf trees on conifer performance, total stand productivity, and understory plant cover 20 years after stand establishment. The study took place in the Malcolm Knapp Research Forest in Maple Ridge, British Columbia. It used a randomized complete block design to compare treatments containing low, moderate, or high broadleaf densities added to a constant conifer density. Each block contained a conifer-only plot as a control. Conifers were composed of equal amounts of western hemlock, western redcedar, and Douglas-fir. Broadleaves were composed of either red alder or paper birch. We found that conifer volume was significantly lower in most broadleaf treatments relative to the control, due to lower hemlock and redcedar volumes. Douglas-fir, on the other hand, had a higher volume--albeit not significant--in the broadleaf treatments. There were no significant differences in total stand volume between any of the treatments and the control. Shrub cover was significantly higher in the low and high alder treatments relative to the control, but there were no differences in shrub cover between birch treatments and the control. The results suggest that low alder density provides a good balance of conifer yield and understory development. Key words: deciduous trees, plant diversity, ecosystem-based management, mixed species stands, multi-value forestry, ecosystem services, 1. Introduction Industrial forest management in North America and Europe has historically focused on maximizing wood production, with the result that managed second-growth forests often have a homogeneous and simplified [...]

We examined the performance of sweetgum (Liquidambar styraciflua L.), cherrybark oak (Quercus pagoda Raf.), and loblolly pine (Pinus taeda L.) in two-species pine-hardwood mixtures (sweetgum : loblolly pine and cherrybark oak : loblolly pine) at various planting densities (1482-1976 trees per hectare (TPH)) over 23 years in northern Louisiana, USA. Species were planted in alternating rows with hardwood establishment occurring 1 year prior to loblolly pine. Mixtures were also compared to loblolly pine monocultures at a common density (1482 TPH) to assess whether mixing improved productivity. Sweetgum exerted more competitive pressure on loblolly pine than cherrybark oak. At final measurement, sweetgum survival statistically exceeded that of loblolly pine across mixture density. Moreover, sweetgum cumulative basal area and volume growth nearly tripled that of loblolly pine in balanced high-density mixtures (1976 TPH, 50 pine : 50 hardwood). In contrast, cherrybark oak basal area and volume growth did not significantly exceed loblolly pine at any density. At a common density (1482 TPH), loblolly pine monoculture cumulative basal area and volume significantly exceeded those of mixtures with sweetgum and cherrybark oak by 19% and 24%, respectively. Collectively, these results indicate that growing loblolly pine in mixture with these two species did not produce complementary interactions and negatively affected stand-level growth. Key words: overyielding, loblolly pine, cherrybark oak, sweetgum, interspecific competition, mixed stands Nous avons examine la performance du copalme d'Amerique (Liquidambar styraciflua L.), du chene a feuilles en pagode (Quercus pagoda Raf.) et du pin a encens (Pinus taeda L.) dans des melanges de pins et de feuillus a deux especes (copalme d'Amerique : pin a encens et chene a feuilles en pagode : pin a encens) a diverses densites de plantation (1482 a 1976 TPH) pendant 23 ans dans le nord de la Louisiane, aux Etats-Unis. Les especes ont ete plantees en rangs alternes, l'etablissement des feuillus ayant lieu un an avant celui des pins a encens. Les melanges ont egalement ete compares aux monocultures de pin a encens a une densite commune (1482 TPH) pour evaluer si le melange ameliorait la productivite. Le copalme d'Amerique a exerce une plus grande pression concurrentielle sur le pin a encens que le chene a feuilles en pagode. Lors de la mesure finale, la survie du copalme d'Amerique a statistiquement depasse celle du pin a encens, quelle que soit la densite du melange. De plus, la croissance cumulative de la zone basale et du volume du copalme d'Amerique a presque triple par rapport a celle du pin a encens dans les melanges equilibres a haute densite (1976 TPH, 50 pins : 50 feuillus). En revanche, la croissance de la surface terriere et du volume du chene a feuilles en pagode n'a pas depasse de maniere significative celle du pin a encens, quelle que soit la densite. A une densite commune (1482 TPH), la zone basale et le volume cumules de la monoculture du pin a encens ont depasse de maniere significative ceux des melanges avec le copalme d'Amerique et le chene a feuilles en pagode de 19% et 24%, respectivement. Collectivement, ces resultats indiquent que la culture du pin a encens en melange avec ces deux especes n'a pas produit d'interactions complementaires et a affecte negativement la croissance au niveau du peuplement. [Traduit par la Redaction] Mots-cles : rendement excessif, pin a encens, chene a feuilles en pagode, copalme d'Amerique, competition interspecifique, peuplements mixtes, Introduction Maintaining productive forests is a global priority. Historically, monocultures have been established to maximize forest productivity (Rubilar et al. 2018). However, concerns over declining biodiversity, enhanced risk of species-specific [...]