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Thinning is expected to improve both individual tree- and stand-level growth efficiency since more environmental resources (growing space, light, water, and nutrients) become available to fewer trees. However, thinning can also promote asymmetric competition among residual trees, and potentially increase mortality and growth stagnation by creating an immediate and often dramatic change in stand micro-environments. To strengthen our understanding of stand-level responses to thinning, we used long-term and replicated experiments for the three most commercially important softwood forest types in the North America, including: shade-intolerant loblolly pine ( Pinus taeda L.), moderately shade-tolerant Douglas-fir ( Pseudotsuga menziesii Mirbel), and shade-tolerant red spruce ( Picea rubens Sarg.) and balsam fir ( Abies balsamea L.). The primary objectives of this study were to quantify the stand-level and dominant tree (100 largest trees ha −1 ) response to various thinning treatments in terms of relative ( RVG ) and cumulative volume growth ( CVG ), while evaluating the effects of stand conditions, timing/intensity of thinning, and key stand-level biotic factors. Our results showed relatively limited differences between the stand-level and dominant-tree responses. Thinning generally increased the RVG of all three forest types, but the effect was dependent on time since treatment for spruce-fir. When compared to unthinned stands, thinning increased the overall RVG , but the pattern of change over time since thinning was negative for both loblolly pine and Douglas-fir. CVG was generally higher in unthinned than thinned stands across the three forest types. Thinning intensity had a positive effect on the RVG of Douglas-fir and loblolly pine, but negative on RVG of spruce-fir forest type. Relative age (based on age of maximum periodic annual increment) and stand density at time of thinning had negative effects on the RVG of dominant trees for all species examined, except spruce-fir. Overall, our results highlight a range of responses to thinning among three distinct softwood forest types, and revealed that thinning does not always improve the growth efficiency of dominant trees, and that the responses are governed largely by a variety of stand characteristics at the time of thinning. [ABSTRACT FROM AUTHOR]

Questions What are the primary biotic and abiotic factors driving composition and abundance of naturally regenerated tree seedlings across forest landscapes of Maine? Do seedling species richness ( SR) and density ( SD) decrease with improved growing conditions (climate and soil), but increase with increased diversity of overstorey composition and structure? Does partial harvesting disproportionately favour relative dominance of shade-intolerant hardwoods ( PIHD) over shade-tolerant softwoods ( PTSD)? Location Forest landscapes across the diverse eco-regions and forest types of Maine, USA. Methods This study used USDA Forest Service Forest Inventory Analysis permanent plots ( n = 10 842), measured every 5 yr since 1999. The best models for each response variable ( SR, SD, PIHD and PTSD) were developed based on AIC and biological interpretability, while considering 35 potential explanatory variables incorporating climate, soil, site productivity, overstorey structure and composition, and past harvesting. Results Mean annual temperature was the most important abiotic factor, whereas overstorey tree size diversity was the most important biotic factor for SR and SD. Both mean annual temperature and overstorey tree size diversity had a curvilinear relationship with SR and SD. Average overstorey shade tolerance and percentage tolerant softwood basal area in the overstorey were the top predictor variables of PIHD and PTSD , respectively. Partial harvesting favoured PIHD but not PTSD. Conclusions This is one of the first studies to comprehensively evaluate a number of factors influencing naturally established tree seedlings at a broad landscape scale in the Northern Forest region of the eastern USA and Canada. Despite limitations associated with relatively small plot size, large seedling size class and lack of direct measurements of light, water and nutrients, this study documents the influence of these factors amid high variability associated with patterns of natural regeneration. The curvilinear relationship between mean annual temperature with SR and SD supports the argument that species richness and abundance usually have unimodal relationships with productivity indicators, whereas the curvilinear relationship between overstorey tree size diversity and SR and SD suggest that moderate overstorey diversity incorporates multiple species as well as higher seedling individuals. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ground vegetation responses to herbicide and thinning were compared at midrotation. [•] Aerial application of herbicide had no direct effect 23–33years after treatment. [•] Precommercial thinning had positive and long-lasting effect on cover and diversity. [•] The resulting overstory structure had a larger effect than overstory composition. [•] Thinning is an effective tool for the maintenance of ground vegetation diversity. [ABSTRACT FROM AUTHOR]

Abstract: Disturbance-based silvicultural systems generally seek to promote complex stand structures that are consistent with temporal and spatial patterns of natural disturbance while allowing for the sustainable harvest of timber. Gap-based harvesting systems are commonly used within this framework because they can be designed to approximate the frequencies and spatial patterns of a wide array of disturbance regimes. Patterns in stand-level growth, sapling recruitment and regeneration response were examined for one such gap-based system, the Acadian Forest Ecosystem Research Program (AFERP) in central Maine, that was designed to emulate the annual 1% disturbance frequency typical of the northeastern United States and Canada. A decade after treatment, stand-level differences in basal area growth and density between two gap-based treatments and an unharvested control were not statistically significant, largely due to low replication, but within-stand growth and regeneration responses differed strongly by spatial position relative to harvest gaps. Regeneration of shade-tolerant and intolerant species increased regardless of gap size, likely a response to increasing light availability from canopy openings due to harvesting and mortality. Further, there was evidence of gap size effects on sapling recruitment as large gaps (>1000m2) favored the growth and survival of mid-successional species such as red maple and white pine, while small gaps (<1000m2) favored late-succession species such as eastern hemlock and spruce. Overstory growth rates also differed by both species and position relative to harvest gaps with most species growing best in gaps and better along gap edges than in adjacent forest. Notably, overstory growth rates for white pine were not influenced by spatial position. These results suggest harvest gaps may have significant growth and regeneration impacts in adjacent, yet unharvested areas, which could lead to profound differences in forest development over the rotation. Obviously, longer-term studies of gap-based systems are needed to more clearly elucidate these responses. [Copyright &y& Elsevier]

In order to maintain biodiversity in forests, it has been recommended that harvests be designed after patterns of natural disturbance. Using a long-term study that includes harvest treatments designed to emulate tree-fall gap disturbances in Maine's Acadian forest, we examined how the species richness, abundance, diversity, and assemblage similarity of click beetles inhabiting coarse woody material (CWM) were affected by gap harvesting and CWM characteristics (diameter, degree of decay, and type of wood). There were few differences in beetle assemblages between 0.07 and 0.12 ha harvest gap treatments. Four of the most common species had higher abundances under a closed forest canopy than within harvest gaps. Species richness and total abundance were higher in CWM that had larger diameters and were more decayed. Species assemblages also differed with the degree of wood decomposition. Diversity was higher in CWM from softwood trees than hardwood trees. Results from this study suggest that small (<0.2 ha) harvest gaps with living trees retained throughout the gap can maintain click beetle assemblages similar to that of an unharvested forest. Forest managers also need to address the temporal continuity of CWM, including different types of wood (hardwood and softwood), a range of decay conditions, and a range of diameter classes, especially larger diameters (>35 cm). [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Forest Research is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Using inventory data from a long-term silviculture experiment in east-central Maine, spatial models were developed to analyze 28 years (1974–2002) of stand structural dynamics. Differences in spatial pattern, species mingling, height differentiation, and relative stand complexity index (rSCI) were compared among five treatments: commercial clear-cutting, fixed diameter-limit, 5 year single-tree selection, three-stage shelterwood (both with and without precommercial thinning), and unharvested natural areas. Regardless of treatment, regeneration events (whether induced by natural breakup of the overstory or by harvesting) increased aggregation in spatial pattern and reduced species mingling, more so in the commercial clearcut and fixed diameter-limit treatments where hardwood densities were highest. Regular spatial patterns were rare. Height differentiation values for individual trees and stand-level mean rSCI were generally highest in untreated natural areas and 5 year selection treatments, intermediate in commercial clearcut and fixed diameter-limit treatments, and lowest in three-stage shelterwood treatments. After a brief adjustment period, precommercial thinning in a shelterwood treated stand generally increased species mingling, height differentiation, and rSCI. Two untreated natural areas exhibited divergent pathways of structural development. Dynamics in uneven-aged selection treatments more closely resembled that of the untreated natural areas than did the shelterwood, commercial clearcut, or fixed diameter-limit treatments. En utilisant les données d’inventaire d’une expérience sylvicole à long terme dans le centre-est de l’État du Maine, aux tats-Unis, des modèles spatiaux ont été mis au point pour analyser la dynamique de la structure du peuplement pendant une période de 28 ans (1974 à 2002). Les différences de patron spatial, de mélange d’espèces, de différenciation de la hauteur et d’indice relatif de complexité des peuplements (ICPr) ont été comparées parmi cinq traitements : la coupe à blanc commerciale, la coupe à diamètre limite fixe, la coupe de jardinage par pied d’arbre selon une rotation de cinq ans, la coupe progressive d’ensemencement en trois étapes (avec et sans éclaircie commerciale) et des peuplements naturels non coupés. Indépendamment du traitement, l’établissement de la régénération (induit par la sénescence naturelle des arbres dominants ou par la coupe) augmentait l’agrégation des patrons spatiaux et diminuait le mélange des espèces et ce, de façon plus marquée dans la coupe à blanc commerciale et dans la coupe à diamètre limite où la densité des espèces feuillues était la plus forte. Les patrons spatiaux réguliers étaient rares. Les valeurs de différenciation de la hauteur des arbres individuels et d’ICPr moyen à l’échelle du peuplement étaient généralement plus élevées dans les peuplements naturels non traités et dans la coupe de jardinage selon une rotation de 5 ans, intermédiaires dans la coupe à blanc commerciale et dans la coupe à diamètre limite, et plus faibles dans la coupe progressive d’ensemencement en trois étapes. Après une brève période d’ajustement, l’application d’une éclaircie précommerciale dans un peuplement soumis à la coupe progressive augmentait généralement le mélange des espèces, la différenciation de la hauteur et l’ICPr. Deux peuplements naturels non traités montraient des trajectoires divergentes de développement de la structure. La dynamique dans les coupes de jardinage appliquées à des structures inéquiennes était plus près de celle des peuplements naturels non traités que ne l’étaient la coupe progressive d’ensemencement, la coupe à blanc commerciale ou la coupe à diamètre limite fixe. [ABSTRACT FROM AUTHOR]

Using a long-term silvicultural experiment, we(i) investigated how epiphyte and arthropod communities wereaffected by height on the stem, bark texture, and stem diameter of red maple(Acer rubrum L.) trees, (ii) examined howharvest gaps influenced epiphyte and arthropod communities on red maple boles,and (iii) explored whether these effects influenced therelationship between the epiphyte and arthropod communities. Arthropod andepiphyte assemblages dwelling on the bark of red maple trees located inundisturbed forest and harvest gaps varied with height. Bryophytes,Cladonia spp., and cyanolichens were most abundant near the baseof the tree, while noncyano, foliose lichens and fruticose lichens were mostabundant 4–6 m above the ground. Acari, Araneae, and Collembola weremost abundant near the base of the tree, while Diptera were most abundant above2 m. A previously undocumented assemblage of dipterans (flies), primarilyin the suborder Nematocera, was found. Gap harvesting reduced the abundance ofbryophytes, Collembola (springtails), Araneae (spiders), and total arthropodson the bark of red maple. Canonical correlation analysis revealed a positiveassociation between bryophytes, Collembola, and Araneae. A strong correlationbetween Collembola and Araneae suggested a possible trophic interaction thatmay be affected by gap harvesting through a reduction in bryophyteabundance. [ABSTRACT FROM AUTHOR]

Historical and future projected landscape patterns and changes caused by harvesting and silviculture were evaluated for a 189,000 ha, intensively managed forest in New Brunswick, Canada. We compared changes in species composition, age classes, and patch characteristics (area, size, density, edge, shape, and core area) between 1945, 2002, and projections to 2027 (based on the landowner's spatial forest management plan). In 1945, the landbase was 40% softwood, 37% mixed hardwood-softwood, 10% hardwood, and 9% softwood-cedar. From 1945 to 2002 and 2027, respectively, softwood forest area increased by 2 and 11%, mixedwood decreased by 19 and 20%, and hardwood area increased by 15 and 14%, and softwood-cedar increased by 6% and then decreased by 7%. In 1945, forest >70 years old comprised 85% of the landscape, but declined to 44% in 2002 and was projected to encompass 41% in 2027. Increased area harvested, decreasing harvest patch size, and protection against natural disturbances resulted in progressively smaller mean and less variable patch sizes from 1945 to 2002. Based upon the 25-year forest management plan, this trend was projected to continue, with the exception of nine patches >1000 ha created by 2027, eight of which were softwood plantations. Stand type successional dynamics were highly variable in both harvested and non-harvested areas, and in some cases were unexpected. Few of the 1945 stand types remained static by 2002, with 42 and 35% of mixedwood shifting to softwood as a result of harvesting, and to hardwood as a result of both harvesting and spruce budworm(Choristoneura fumiferana Clem.) outbreaks in the 1950s and 1970s. This study demonstrates the strong cumulative effect of forest management on landscape patterns, especially the socially mandated drive for smaller clearcuts resulting in the loss of large patches. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Forest Research is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Herbicide technology has evolved with forest management in North America over the past 60 years and has become an integral part of modern forestry practice. Forest managers have prescribed herbicides to increase reforestation success and long-term timber yields. Wildlife managers and others interested in conserving biodiversity, however, have often viewed herbicide use as conflicting with their objectives. Do herbicides increase forest productivity, and are they compatible with the objectives of wildlife management and biodiversity conservation? Results from the longest-term studies (10-30 years) in North America suggest that the range of wood volume yield gains from effectively managing forest vegetation (primarily using herbicides) is 30-450% in Pacific Northwest forests, 10-150% in the southeastern forests, and 50-450% in northern forests. Most of the 23 studies examined indicated 30-300% increases in wood volume yield for major commercial tree species and that gains were relatively consistent for a wide range of site conditions. Meeting future demands for wildlife habitat and biodiversity conservation will require that society's growing demand for wood be satisfied on a shrinking forestland base. Increased fiber yields from intensively managed plantations, which include the use of herbicides, will be a crucial part of the solution. If herbicides are properly used, current research indicates that the negative effects on wildlife usually are short-term and that herbicides can be used to meet wildlife habitat objectives. [ABSTRACT FROM AUTHOR]

We examined the dynamics of down coarse woody debris (CWD) under an expanding-gap harvesting system in the Acadian forest of Maine. Gap harvesting treatments included 20% basal area removal, 10% basal area removal, and a control. We compared volume, biomass, diameter-class, and decay-class distributions of CWD in permanent plots before and 3 years after harvest. We also determined wood density and moisture content by species and decay class. Mean pre-harvest CWD volume was 108.9 m3/ha, and biomass was 23.22 Mg/ha. Both harvesting treatments increased the volume and biomass of non-decayed, small-diameter CWD (i.e., logging slash), with the 20% treatment showing a greater increase than the 10% treatment and both treatments showing greater increases than the control. Post-harvest reduction of advanced-decay CWD due to mechanical crushing was not evident. A mean of 18.48 m3 water/ha (1.85 L/m2) demonstrates substantial water storage in CWD, even during an exceptionally dry sampling period. The U-shaped temporal trend in CWD volume or biomass seen in even-aged stands may not apply to these uneven-aged stands; here, the trend is likely more complex because of the superimposition of small-scale natural disturbances and repeated silvicultural entries. [ABSTRACT FROM AUTHOR]

Presents a study with the objective to understand the mechanism underlying nitrogen (N) and water competition between jack pine (Pinus banksiana Lamb.) and four boreal forest species. Large-leaved aster (Aster macrophyllus L.), Canada blue-joint grass (Calamagrostis canadensis (Michx.) Beauv.), trembling aspen (Populus tremuloides (Michx.), and red raspberry (Rubus idaeus L.) that were planted at a range of densities (0-8 plants/m2) with jack pine seedlings; Net photosynthesis (P[subn]), nitrogen-use efficiency (NUE), water-use efficiency (WUE) of each species that was monitored over three consecutive growing seasons; Changes in available soil N and water that were also measured. Jack pine P[subn], NUE, and WUE decreased as competitor density increased; Effects varied among species (p < 0.001) and over time (p < 0.001); Influence of density on jack pine P[subn] that decreased over time for aster and blue-joint grass and increased over time for aspen and raspberry (p < 0.001); Jack pine P[subn] that correlated with available soil N. Corelation between jack pine p[subn] and soil water that was rarely significant.

Differences in yield-density models derived from an additive experimental design were used to compare the relative competitiveness of nine early-successional boreal forest plants (aster, grass, fireweed, fern, raspberry, willow, alder, birch, and aspen) on jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana (Mill.) BSP). A randomized complete block split-split-plot design with three replications blocked on soil type was used. Initial density gradients were 0-4 plants/m2 for woody and 0-8 plants/m2 for herbaceous species. An a priori analytical approach that compared a full model (using linear regression analysis of 4th-year stem diameter of conifers under increasing cover and height of competitors) to various reduced models was used to assess competition. Increasing cover and (or)height of all competitors (except fern) significantly (P < 0.05) decreased conifer stem diameter. The final regression model (based on visual estimates of cover and differences in initial conifer size) accounted for 89% of the variation in stem diameter. During the years studied, both conifers responded similarly to competition, and herbaceous species were on average 28.9% more competitive than woody species. Under different growing conditions (e.g., a natural forest) the relative competitiveness of herbaceous and woody species may vary from these results. [ABSTRACT FROM AUTHOR]

Using critical-period analysis, we examined the temporal effects of interspecific competition from herbaceous vegetation on seedlings of jack pine (Pinus banksiana Lamb.), red pine (Pinus resinosa Ait.), eastern white pine (Pinus strobus L.), and black spruce (Picea mariana (Mill.) BSP) during the first 5 years after planting. The critical period is the time period during stand development when interspecific competition reduces tree growth. We found both similarities and differences in responses among tree species. Gains in stem volume index associated with increasing duration of vegetation control (expressed by weed-free curves) differed among species. In contrast, declines in stem volume index with increasing duration of competition after planting (expressed by weed-infested curves) were equal among species. Critical periods for stem volume index were shorter for shade-intolerant jack and red pine (1 and 2 years after planting) than for more shade-tolerant white pine and black spruce (1-3 years for spruce and 1-4 years for white pine). Intolerant species had greater absolute stem volume growth, but smaller relative declines from continuous association with herbaceous vegetation (85, 81, 78, and 67% for white pine, blackspruce, red pine, and jack pine, respectively). Herbaceous vegetation did not affect survival and had a variable influence on height growth of all species. [ABSTRACT FROM AUTHOR]

Forest managers require accurate and timely data that describe vegetation conditions on cutover areas to assess vegetation development and prescribe actions necessary to achieve forest regeneration objectives. Needs for such data are increasing with current emphasis on ecosystem management, escalating silvicultural treatment costs, evolving computer-based decision support tools, and demands for greater accountability. Deficiencies associated with field survey methods of data acquisition (e.g. high costs, subjectivity, and low spatial and temporal coverage) frequently limit decision-making effectiveness. The potential for remotely sensed data to supplement field-collected forest vegetation management data was evaluated in a problem analysis consisting of a comprehensive literature review and consultation with remote sensing and vegetation management experts at a national workshop. Among currently available sensors, aerial photographs appear to offer the most suitable combination of characteristics, including high spatial resolution, stereo coverage, a range of image scales, a variety of film, lens, and camera options, capability for geometric correction, versatility, and moderate cost. A flexible strategy that employs a sequence of 1: 10,000-, 1:5,000-, and 1:500-scale aerial photographs isproposed to: 1) accurately map cutover areas, 2) facilitate location-specific prescriptions for silvicultural treatments, sampling, buffer zones, wildlife areas, etc., and 3) monitor and document conditionsand activities at specific points during the regeneration period. Surveys that require very detailed information on smaller plants (<0.5-m tall) and/or individual or rare plant species are not likely to be supported by current remote sensing technologies. Recommended areas for research include: 1) digital frame cameras, or other cost-effective digital imagers, as replacements for conventional cameras, 2) computer-based classification and interpretation algorithms for digital imag [ABSTRACT FROM AUTHOR]

This study was designed to test the hypothesis that herbicide (glyphosate, active ingredient) application for conifer release would reduce species diversity (measured as richness, Simpson's index, and Shannon-Wiener index) of both plant and small mammal communities over a 5-year period in young sub-boreal spruce (Picea engelmannii Parry ex Engelm. x Picea glauca (Moench) Voss) forest. Four treated and four untreated (control) sites were studied near Prince George in central British Columbia, Canada. Crown volume index of shrub vegetation was reduced by herbicide application. Species richness of shrubs was reducedin the first year after treatment and remained lower on treated sites throughout the 5-year period. Both indices of shrub diversity, however, were not different over the 5 years. Herbicide treatment initially reduced crown volume index of herbaceous vegetation, but values quickly recovered to untreated levels by the second year after treatment. Herbaceous species diversity was not affected by herbicide treatment. Diversity of small mammal communities apparently was not affectedby herbicide application. In general, diversity of plant and small mammal communities seemed to be maintained, and hence, these treatmentsites may not lower overall diversity of a forested landscape. Silvicultural practices, such as conifer release with herbicides or alternative methods, may contribute to a diversity of stand structures and wildlife habitats if appropriately designed and implemented. [ABSTRACT FROM AUTHOR]