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Does species' shade tolerance regulate natural regeneration abundance and composition when partial harvestings ([less than or equal to] 80% of basal area removal) are operated on a landscape scale? We examined this question using 835 permanent plots located across forested landscapes of Maine, USA. These plots were surveyed for regeneration growth, mortality, and recruitment before and after treatment application (i.e., partially harvested and unharvested). Our results showed that relative to unharvested stands, high-intensity partial harvesting (41%-80% of basal area removal) increased the number of seedlings (diameter at breast height (DBH) < 2.5 cm) recruited to saplings (DBH of 2.5-12.69 cm) and sapling diameter growth irrespective of species' shade tolerance over a 15-year period after treatment. However, high-intensity partial harvesting increased sapling mortality during the initial 5 years since harvesting, whereas low-intensity partial harvesting (5%-40% of basal area removal) maintained the natural regeneration dynamics (growth, recruitment, and mortality) of unharvested stands. We found that harvesting intensity, basal area, and seedling density by shade-tolerance group before harvesting are more important attributes than species' shade tolerance for determining the responses of natural regeneration to partial harvesting. The greater importance of preharvest stand attributes on postharvest regeneration may suggest an integrated overstory and understory manipulation approach for attaining the desired regeneration composition. Key words: light, natural regeneration, sapling growth, regeneration mortality, partial harvestings. Est-ce que la tolerance a l'ombre des especes influence l'abondance et la composition de la regeneration naturelle lorsque des coupes partielles (prelevement de moins de 80% de la surface terriere) sont effectuees a l'echelle du paysage? Nous avons etudie cette question a l'aide de 835 placettes permanentes distribuees dans les paysages forestiers du Maine, aux Etats-Unis. Dans ces placettes, nous avons suivi la croissance, la mortalite et le recrutement de la regeneration avant et apres l'application des traitements (c.-a-d. des peuplements partiellement recoltes ou non). Nos resultats montrent que par rapport aux peuplements non recoltes, la coupe partielle de forte intensite (41 a 80% de prelevement de la surface terriere) augmentait la transition de semis (diametre a hauteur de poitrine (DHP) < 2,5 cm) a gaules (DHP de 2,5 a 12,69 cm), et la croissance en diametre des gaules, peu importe la tolerance a l'ombre des especes, pendant une periode de 15 ans apres le traitement. Cependant, la coupe partielle de forte intensite a augmente la mortalite des gaules au cours des cinq premieres annees apres la recolte, tandis que la coupe partielle de faible intensite (5 a 40% de prelevement de la surface terriere) a maintenu la meme dynamique de regeneration naturelle (croissance, recrutement et mortalite) que celle des peuplements non recoltes. Nous avons constate que l'intensite de la recolte, la surface terriere et la densite des semis par groupe de tolerance a l'ombre avant la recolte sont des caracteristiques plus importantes que la tolerance a l'ombre des especes pour determiner les reactions de la regeneration naturelle a la coupe partielle. La plus grande importance des caracteristiques des peuplements avant la coupe sur la regeneration apres la coupe indique qu'il serait possible d'utiliser une approche integree de manipulation du couvert dominant et du sous-etage pour obtenir la composition souhaitee de la regeneration. [Traduit par la Redaction] Mots-cles : lumiere, regeneration naturelle, croissance des gaules, mortalite de la regeneration, coupes partielles., 1. Introduction Light (i.e., photosynthetically active radiation) is a basic requirement for plant growth and establishment (Valladares and Niinemets 2008). Changes in light availability have a greater impact on younger [...]

Increased soil nutrient availability can promote tree growth while drought impairs metabolic functioning and induces tree mortality. However, limited information is available about the role of nutrients in the drought responses of trees. A greenhouse experiment was conducted with sessile oak (Quercus petraea (Matt.) Liebl) and Scots pine (Pinus sylvestris L.) seedlings, which were subjected to three fertilization treatments in the first year and two water regimes in the second year. Old and newly fixed carbon (C) and nitrogen (N) allocation were traced by dual labeling with 13C and 15N tracers, respectively, at two time points. Leaf gas exchange, biomass, as well as N and nonstructural carbohydrate (NSC) concentrations of all organs were measured. Fertilization predisposed sessile oak to drought-induced mortality, mainly by prioritizing aboveground growth, C and N allocation, reducing root NSC concentrations and decreasing old C contribution to new growth of leaves. In contrast, fertilization did not additionally predispose Scots pine to drought, with minor effects of fertilization and drought on newly fixed and old C allocation, tissues N and NSC concentrations. The role of nutrients for drought responses of trees seems to be species-specific. Therefore, we suggest nutrient availability and species identity to be considered in the framework of physiological mechanisms affecting drought-induced mortality. [ABSTRACT FROM AUTHOR]

Variable retention (VR) and partial cutting are both considered important silvicultural tools of natural disturbance or ecosystem based forest management approaches. Partial harvesting differs from VR in that post-treatment growth responses and stand regeneration are the primary objective rather than the maintenance of biodiversity. This partial cutting study is undertaken in mixed poplar (Populus spp.)--white spruce (Picea glauca (Moench) Voss) stands in the eastern Canadian boreal mixed wood forest. It compares, at the tree level, absolute growth rates (AGR) and relative growth rates (RGR) of basal area (BA) and stem survival; and at the stand level, it also compares absolute BA growth, mortality, and sapling density 10 years following treatment. The completely randomized experiment was established with four intensities of partial cutting (0, 50%, 65%, and 100% of poplar BA). All partial cutting intensities had a significant and similar positive effect on AGR of residual spruce stems. Complete poplar removal resulted not only in the highest increase in RGR of suppressed and intermediate spruce stems, but also in higher spruce mortality. Removal of 50% of the initial poplar stand BA provided the best trade-off between positive residual stem growth of spruce and poplar and limited post-treatment mortality. Key words: boreal mixedwood, variable retention, relative growth, cutting intensity, sapling density. La retention variable et les coupes partielles sont considerees comme des outils sylvicoles faisant partie des approches d'amenagement ecosystemique. Au-dela du maintien de la biodiversite, la croissance et la regeneration post-traitement demeurent un objectif principal de la recolte partielle. L'etude est realisee dans des peuplements de peuplier (Populus spp.)-- epinette blanche (Picea glauca (Moench) Voss) dans la foret boreale mixte de l'est du Canada. L'experience realisee selon un dispositif completement aleatoire compare quatre intensites de coupe partielle (0, 50, 65 et 100 % de la surface terriere (ST) du peuplier). On y compare les taux de croissance absolus et relatifs de la ST et de la survie des tiges, et a l'echelle du peuplement, Revolution de la ST, la mortalite et la densite des gaules 10 ans apres les traitements. Toutes les intensites de coupe ont eu un effet positif significatif et similaire sur la croissance absolue des tiges d'epinette. Le traitement le plus severe a entraine la plus forte augmentation de la croissance relative des tiges de l'epinette ou des de l'epinette ou des epinettes supprimees et intermediates, mais egalement une mortalite significativement plus elevee des epinettes. Le prelevement de 50% de la ST de peuplier constitue le meilleur equilibre entre la croissance residuelle des tiges d'epinette et du peuplier et la mortalite apres traitement. Mots-cles: foret boreale melangee, retention variable, accroissement relatif, intensite de la coupe, densite des gaules., Introduction In the last 25 years, concerns regarding conventional (sensu Puettmann et al. 2015) and ubiquitous forestry practices such as clear cutting have led to a redefinition of what constitutes [...]

Introduction: European mistletoe, Viscum album L., is a hemiparasite that can infect various tree species, yet our understanding of its physiological interactions with host species is limited. Methods: Nine mistletoe-host pairs (i.e. V. album ssp. album growing on nine different broadleaf tree species) under different growth conditions in central Switzerland were selected to examine the carbon, water and nutrient relationships between mistletoe and its hosts. We measured leaf morphological traits, isotopic compositions (d13C and d15N), concentrations of non-structural carbohydrates (NSC) and specific compounds (i.e. mobile sugars and starch), and macronutrients (i.e. N, P, K, Ca, Mg, S) in leaf and xylem tissues of both mistletoe and its hosts. Results and Discussion: There were only non-significant relationships between NSC concentrations in mistletoe and in its host species across the nine mistletoe-host pairs, suggesting the carbon condition of V. album ssp. album is determined by both the heterotrophic carbon transfer and self-photosynthetic capacity among different mistletoe-host pairs. However, mistletoe leaf morphological traits (single leaf area and mass, and leaf mass per unit leaf area) did not change across the nine mistletoe-host pairs, and mistletoe leaf d13C, water content and macronutrient concentrations were linearly correlated with those in the host leaves. Macronutrients showed accumulations in mistletoe across the nine pairs. Further, tissue N concentrations were significantly higher in mistletoe grown on N-fixing hosts than on non-N-fixing hosts. Finally, leaf N:P in mistletoe was significantly correlated with the ratio in the host across the nine mistletoe-host pairs. Overall, our results indicate strong relationships between mistletoe and its hosts for water- and nutrient-related traits, but not for carbonrelated traits, which demonstrates that V. album ssp. album can adjust its physiology to survive on different deciduous tree species hosts and under different site conditions. [ABSTRACT FROM AUTHOR]

Radial stem growth dynamics at seasonal resolution are essential to understand how forests respond to climate change. We studied daily radial growth of 160 individuals of seven temperate tree species at 47 sites across Switzerland over 8 years. Growth of all species peaked in the early part of the growth season and commenced shortly before the summer solstice, but with species‐specific seasonal patterns. Day length set a window of opportunity for radial growth. Within this window, the probability of daily growth was constrained particularly by air and soil moisture, resulting in intermittent growth to occur only on 29 to 77 days (30% to 80%) within the growth period. The number of days with growth largely determined annual growth, whereas the growth period length contributed less. We call for accounting for these non‐linear intra‐annual and species‐specific growth dynamics in tree and forest models to reduce uncertainties in predictions under climate change. [ABSTRACT FROM AUTHOR]

Northern hardwood stands, notably those with American beech ( Fagus grandifolia Ehrh), sugar maple ( Acer saccharum Marsh.), and yellow birch ( Betula alleghaniensis Britton), are abundant across the forested landscapes of northeastern USA and southeastern Canada. Recent studies have reported an increasing dominance of American beech in the understory and midstory of these forests. Beech is a commercially less desirable tree species due to its association with beech-bark disease, and because it commonly interferes with the regeneration of other more desirable tree species. We examined hardwood regeneration characteristics nine years after application of a 3 × 4 factorial combination of glyphosate herbicide (0.56, 1.12, and 1.68 kg ha) and surfactant concentrations (0.0, 0.25, 0.5, and 1.0% v v) to release sugar maple regeneration from beech-dominated understories using three stands that received shelterwood seed cutting in central Maine. Measurements nine years after treatment showed that glyphosate rate increased both absolute ( AD) and relative density ( RD) of sugar maple regeneration, but not its height ( HT). In contrast, beech AD, RD, and HT were all significantly reduced with increasing glyphosate rate. Post-release browsing by ungulates and a high residual overstory basal area resulted in reduced sugar maple HT. Our results indicated that glyphosate herbicide applied in stands that have been recently shelterwood seed cut can significantly increase the abundance of sugar maple regeneration. However, subsequent browsing damage combined with the negative influence of the residual overstory cover can limit the longer-term benefit of understory herbicide treatments. Subsequent removal of the overstory and browsing-control measures may be needed to promote sugar maple regeneration over beech in similar northern hardwood stands. [ABSTRACT FROM AUTHOR]

Variable retention harvesting, with a focus on maintaining biological legacies on managed landscapes, has been practised in the trembling aspen (Populus tremuloides Michx.) dominated boreal mixedwood forests for about two decades. However, little attention has actually been given to the growth response of aspen to partial harvesting. This is the first study to report on tree-level volume growth response of aspen after partial or variable retention harvesting in the Canadian boreal forest. During the winter of 1998-1999, an uncut control, clearcut and two partial harvesting treatments - 1/3 partial cut (1/3PC, 33% BA removal using low thin); 2/3 partial cut (2/3PC, 61% BA removal using high thin) - were applied in 75 year old aspen-dominated mixedwood stands in a complete randomized block design. Twelve years after treatment application, 27 dominant and 27 co-dominant trees were collected from unharvested controls and the two partial cut treatments for stem analysis. Annual volume increment (AVI) of individual stems was analyzed as a function of treatment, tree social status, pre-treatment growth, time since treatment application (1-12 years) and neighborhood competition. The latter was estimated using a variety of neighborhood competition indices (NCI). There was no evidence of initial growth stagnation after partial harvesting applications. Only the most severe treatment of partial harvesting (2/3 PC) resulted in an increase in volume increment relative to trees in control stands. Annual increase in volume in the 2/3 partial cut was 25.6% higher than controls over 12 years. AVI of dominant trees was higher by 16.2 dm³' yr-1 than that of co-dominants and was proportional to pre-treatment volume growth. No interaction between treatment and social status or pre-treatment growth was observed. The overall results indicate that competition for resources in these stands is essentially size symmetrical. These results should contribute to the development of silviculture prescriptions that aim to maintain both stand productivity and biological legacies. [ABSTRACT FROM AUTHOR]

Over the last 25 years, greater understanding of natural dynamics in the boreal forest has led to the integration of forest ecosystem management principles into forest policy of several Canadian provinces and, in turn, to greater interest in developing silvicultural treatments that are grounded in natural stand-level dynamics – often referred to as natural disturbance-based silviculture. As a result, alternative silvicultural practices including variants of partial cutting are increasingly being applied in the boreal forest as an approach to balancing economic and ecological management objectives. While the numerous benefits of partial cutting reported in the literature are acknowledged, the objective of this paper is to provide an overview of factors or constraints that potentially limit the application of these practices in boreal Canada in the context of forest ecosystem management and natural disturbance-based silviculture. Among constraining factors, numerous studies have reported elevated mortality rates of residual stems following partial cutting, initial growth stagnation of residual trees, problems related to recruitment of desirable species and, on certain flat or lowland sites, risks of long-term decline in site and stand productivity. A number of operational challenges to partial cutting in the boreal forest are also presented and several avenues of research are proposed. [ABSTRACT FROM PUBLISHER]

Increased soil nutrient availability can promote tree growth while drought impairs metabolic functioning and induces tree mortality. However, limited information is available about the role of nutrients in the drought responses of trees. A greenhouse experiment was conducted with sessile oak (Quercus petraea (Matt.) Liebl) and Scots pine (Pinus sylvestris L.) seedlings, which were subjected to three fertilization treatments in the first year and two water regimes in the second year. Old and newly fixed carbon (C) and nitrogen (N) allocation were traced by dual labeling with 13C and 15N tracers, respectively, at two time points. Leaf gas exchange, biomass, as well as N and nonstructural carbohydrate (NSC) concentrations of all organs were measured. Fertilization predisposed sessile oak to drought-induced mortality, mainly by prioritizing aboveground growth, C and N allocation, reducing root NSC concentrations and decreasing old C contribution to new growth of leaves. In contrast, fertilization did not additionally predispose Scots pine to drought, with minor effects of fertilization and drought on newly fixed and old C allocation, tissues N and NSC concentrations. The role of nutrients for drought responses of trees seems to be species-specific. Therefore, we suggest nutrient availability and species identity to be considered in the framework of physiological mechanisms affecting drought-induced mortality., (© The Author(s) 2023. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permission@oup.com.)