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Comparing forest and harvested wood product carbon (C) stocks and accumulation among forest management treatments commonly applied in managed forests is needed to inform planning and policy decisions for C objectives. Therefore, pre- and post-harvest C stocks were quantified and C accumulation was projected over a 31-year period (to ∼2050) among forest management treatments that were applied on a subset (n = 3) of the Maine Adaptive Silviculture Network installations in northern Maine, USA. These installations included mature, second-growth forests composed of northern hardwood and hardwood-dominated mixedwood stands. Before treatments were initiated, average aboveground live tree C stocks ranged from 67.1 to 99.7 Mg ha−1. For the aboveground portions of live trees, dead wood and harvested wood products, the projected average annual net change in C (AAC) was 0.232 ± 1.164 Mg ha−1 year−1 (mean ± standard deviation). Models of projected AAC indicated that less biomass removal during harvests and greater representation of tree species with low tolerance of shade were associated with positive AAC values. The results emphasize the importance of leveraging multiple harvesting strategies to achieve C objectives, including consideration of forest reserves and using targeted yet operationally feasible silvicultural treatments that promote forest resilience relative to climate change. [ABSTRACT FROM AUTHOR]

Managed forests serve as a natural climate change solution through sequestration of C and long-term storage in harvested wood products, in addition to providing ecosystem services and wildlife habitat. Specifically, commodity products such as dimensional lumber and building materials, utilized from high-quality, defect free trees, provide greatest economic return and long-term C reservoir. Stem sinuosity is a noted deformity in juvenile coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) and can result in loss of value and degraded economic end-product. While the causal mechanisms have been of interest for decades, relatively little is known regarding the influence of tree improvement, silviculture, and local growing conditions. A network of experimental plots (n = 132) across six installations in the Pacific Northwest (PNW) were assessed to determine the effects of tree spacing, vegetation control, genetic gain, soil, site, and climate variables on stem sinuosity 10 years since planting. Sinuosity presence was greatest in wild genetic sources and on sites with low soil C and A horizon thickness. Severity increased with stem size and declined with concomitant gains in stand density and local windspeed. Findings suggest that site-specific deployment of genetic resources and silvicultural treatments may enhance Douglas-fir stem form in the PNW. • Stem sinuosity assessed on 13,250 Douglas-fir trees in the Pacific Northwest. • Genetics, silviculture, soil, and climate variables tested on presence and severity. • Sinuosity lowest in the medium and high genetic gain seed sources. • Detectable differences according to site characteristics and local windspeed. [ABSTRACT FROM AUTHOR]

We compared long-term C sequestration in the pools of aboveground portions of live trees, dead wood, and harvested wood products among highly contrasting forest management scenarios on a rotation (30-100 years) and 100-year basis. Average annual net change in C (AAC) and the cumulative sum of net changes in C were calculated using 65 years of data from permanent plots representing contrasting approaches to managing mixed-species stands dominated by shade-tolerant coniferous species on the Penobscot Experimental Forest in Maine, USA. Simulations of tree growth and mortality were used to estimate C pools to 100 years. On a rotation basis and for all pools combined, scenarios with selection cutting had greater AAC than those with shelterwood cutting followed by thinning or with diameter-limit cutting (p < 0.05). For combined pools, the cumulative sum of net changes in C for the unmanaged, selection, and guiding diameter-limit stands was positive for most of the study period. Our results suggest that strategies that maintain overstory stocking levels necessary to regenerate desired species and promote the development of sawlog-sized trees can enhance long-term C sequestration in mixed-species, naturally regenerated northern temperate forests. [ABSTRACT FROM AUTHOR]

Determining the optimal timing and type of entry in mid-rotation, unthinned stands can be complicated by a variety of economic and biological factors. In this analysis, long-term data from the Commercial Thinning Research Network was used to project spruce-fir (Picea spp.—Abies balsamea (L.) Mill.) stand growth on six different sites across Maine following six alternative thinning treatments (33% and 50% relative density removal paired with low, crown, and dominant thinning methods). Results showed that the low-thinning treatment performed best in terms of maximum net present value, stand age at time of maximum net present value, and average merchantable stem size. Although the low-thinning resulted in a 10% mean reduction in maximum net present value when compared to the control, the average merchantable stem size more than doubled. Overall, results of this analysis indicate that it may be financially responsible to commercially thin these stands using a low-thinning method and a light removal intensity, as the average merchantable stems size was increased and a mid-rotation financial return provided. [ABSTRACT FROM AUTHOR]

Dead wood pools are strongly influenced by natural disturbance events, stand development processes, and forest management activities. However, the relative importance of these influences can vary over time. In this study, we evaluate the role of these factors on dead wood biomass pools across several forest management alternatives after 60 years of treatment on the Penobscot Experimental Forest in central Maine, USA. After accounting for variation in site quality, we found significant differences in observed downed coarse woody material (CWM; ≥7.6 cm small-end diameter) and standing dead wood biomass among selection, shelterwood, and commercial clear-cut treatments. Overall, total dead wood biomass was positively correlated with live tree biomass and was negatively correlated with the average wood density of nonharvest mortality. We also developed an index of cumulative harvest severity, which can be used to evaluate forest attributes when multiple harvests have occurred within the same stand over time. Findings of this study highlight the dynamic roles of forest management, stand development, and site quality in influencing dead wood biomass pools at the stand level and underscore the potential for various outcomes from the same forest management treatment applied at different times in contrasting stands. [ABSTRACT FROM AUTHOR]

The overall goal of this study was to evaluate the correlation of multiple abiotic and biotic factors with organic-horizon (O-horizon) carbon (C) content on the Penobscot Experimental Forest in central Maine, USA. O-horizon samples were collected and their associated depths were recorded from stands managed with a range of silvicultural and harvesting treatments (i.e., selection, shelterwood, and commercial clearcut) and an unmanaged control. The overall mean for O-horizon C content from all samples was 25.6 ± 16.1 Mg ha −1 (mean ± SD). The samples were used to develop a pedotransfer function for predicting O-horizon C content from O-horizon depth ( R 2 = 0.47, RMSE = 1.6 Mg ha −1 ) so that an average of O-horizon C content could be calculated for permanent sample plots on which abiotic and biotic factors were quantified. O-horizon depth measurements recorded along transects on permanent sample plots were used to calculate plot average O-horizon C content. There were no significant differences in average predicted O-horizon C content among selection, shelterwood, and commercial clearcut treatments. However, variation in predicted O-horizon C content between stands where the same treatment was applied was statistically significant and was likely due to the timing of harvests and abundance of dead wood buried within O horizons. Depth to redoximorphic features, cartographic depth to water table or saturated zone, drainage class, fine woody debris mass, downed woody debris volume, tree basal area, and the relative basal area of conifer species were not significant predictors of predicted O-horizon C content at the plot level. When the individual predicted values of O-horizon C content were modeled, within-plot variation accounted for 83.8% of the variance. Bryophyte mass, which was predicted from bryophyte cover, only explained 1.2% of the variation in O-horizon C content at the microsite level. These results highlight the sizeable variability in O-horizon C content within and among these mixed-species stands with various forest management and natural disturbance histories. [ABSTRACT FROM AUTHOR]

Highlights: [•] We partition the variation in natural regeneration composition and abundance. [•] Contribution of biotic, abiotic, and disturbance explanatory factors were examined. [•] Overall explanation by regulatory factors was relatively low accounting for 26%. [•] Regeneration composition was structured by biotic factors, which accounted for 16%. [•] Controlling overstory composition is conducive to regeneration composition control. [ABSTRACT FROM AUTHOR]

Abstract: Snags are an important component of forest structure and a key carbon pool, but there is currently a limited understanding of their survival and decay in the Acadian region of North America. Using standing and fallen snag observations collected from permanent sample plot (PSP) remeasurements at a long-term, replicated silviculture methods experiment in central Maine, USA, the objective of this analysis was to develop quantitative models to better understand snag survival and decay dynamics. Species examined included the conifers Abies balsamea, Picea rubens, Thuja occidentalis, and Tsuga canadensis, and the hardwoods Acer rubrum and Betula papyrifera. Proportional hazards regression models that estimate the 5-year probability (Pr) of snag survival indicated that observed decay class (a measure of snag decomposition) could be used as a surrogate for years since death given the difficulties and errors associated with determining years since death for standing snags. Averaged across all species, Pr (5-year snag survival) estimated as a function of snag diameter at breast height (dbh) in decay classes 1, 2, 3, and 4 were predicted as 0.69±0.09 (mean±standard deviation), 0.36±0.09, 0.16±0.05, and 0.06±0.02, respectively. Where snag dbh was significant in estimating survival (3 of 6 species), hazard ratios indicated that snag survival would increase by as much as 24% for each 10cm increase in dbh, but was dependent on species. Probability matrices predicting the 5-year likelihood of snags transitioning to advanced decay classes or falling showed that T. canadensis and T. occidentalis snags were slowest to decay, as measured by the average time it takes for a snag to progress from decay class 1–4. Probability of snag height-loss, predicted using snag dbh and the harvest interval of the stand, was estimated to be highest for larger dbh snags found in stands with frequent harvest intervals (e.g. 40cm dbh and every 5years). Models predicting the amount of volume reduced in standing snags through time were related to the estimated total volume of a live tree with the same dbh, mode of death, and general decay stage (i.e. soft versus hard). When used together, these models quantifying snag dynamics and associated species and size differences can serve as tools for managers to estimating standing deadwood stocks in mixed-species stands found throughout the Acadian region. [Copyright &y& Elsevier]

Throughout the northeastern United States, thinning is a common management practice in stands of eastern white pine (Pinus strobus L.), but foresters lack clear information as to whether conventional B-line or low-density thinning will best achieve their growth and financial objectives. Conventional management consists primarily of light crown thinning, whereas low-density management uses heavy crown thinning to isolate selected crop trees. To better inform silviculturists of the effects of these thinning regimes on volume growth and taper of white pine, we compared the lower bole taper- quantified as Girard form class (GFC)-and volume growth between the two thinning regimes and a nonthinned control. Over the 17-year study period, GFC increased among all treatments from an overall average of 0.77 ± 0.01 (±SE) to 0.82 ± 0.00. Trees under the B-line thinning regime had the most taper (lowest GFC), owing to a thinning-induced growth response at breast height but not at the top of the butt log. Low-density thinning, on the other hand, resulted in substantially larger, less tapered butt logs with significantly higher growth rates at both breast height and the top of the butt log. The volume growth of low-density trees was significantly higher than that of trees in the other treatments. At the stand level, however, the overall volume growth of the low-density treatment was significantly lower than that of the B-line treatment. Thus, this study reveals that when implementing low-density thinning, there is a tradeoff between overall stand growth and larger, less tapered individual trees. [ABSTRACT FROM AUTHOR]

• Use of rare long-term data from multiple experimental forests across northeastern U.S. • Of all stand/site factors considered, stocking was most influential in managed stands. • C sequestration was highest a few years after harvest in managed stands. • Uneven-aged management tended to have positive effects on C sequestration in certain conditions. • Showcases the potential use of uneven-aged management regimes in climate mitigation. We compiled data from several independent, long-term silvicultural studies on USDA Forest Service experimental forests across a latitudinal gradient in the northeastern and north-central U.S.A. to evaluate factors influencing aboveground live-tree carbon sequestration and mortality. Data represent five sites with more than 70,000 repeated tree records spanning eight decades, five ecoregions, and a range of stand conditions. We used these data to test the relative influence of factors such as climate, treatment history (uneven-aged or no management), species composition, and stand structural conditions on aboveground live-tree carbon sequestration and mortality in repeatedly measured trees. Relative to no management, we found that uneven-aged management tended to have a positive effect on carbon sequestration at low stocking levels and in areas of favorable climate (expressed as a combination of growing season precipitation and annual growing degree days > 5 °C). In addition, losses of carbon from the aboveground live-tree pool due to tree mortality were lower in managed than unmanaged stands. These findings suggest that there may be conditions at which rate of sequestration in living trees is higher in stands managed with uneven-aged silviculture than in unmanaged stands, and that this benefit is greatest where climate is favorable. [ABSTRACT FROM AUTHOR]

• Tree growth and mortality responses to partial harvestings (PH) were examined. • The analysis was performed on ten major tree species of north-eastern USA. • Species response magnitude to PH was not dependent on shade tolerance. • High-intensity PH increased tree mortality irrespective of species. • Sugar maple displayed the highest growth and lowest mortality to PH. Silvicultural systems based on partial harvesting (PH) have become increasingly common in areas historically dominated by clearcut-based systems in response to ecological and social concerns. Current knowledge about the effects of PH is based primarily on stand responses from controlled experiments from limited number of sites. A broader scope of inference is needed to fully understand the effects of PH when applied operationally at a landscape scale. We used 835 permanent monitoring plots from the US Forest Service Forest Inventory and Analysis network to quantify the effect magnitude (EM) of low- (5–40% basal area removal) and high-intensity (41–80% basal area removal) PH on the periodic diameter growth and mortality of residual trees of ten major tree species in Maine, USA. Our results showed that the EM and timing of statistically significant effect (p < 0.05) of the two intensities of PH varies across species. Tree diameter growth responses to high-intensity PH was rapid and prolonged for sugar maple (Acer saccharum) and American beech (Fagus grandifolia), while other species did not show significant responses for at least five years. High-intensity PH increased mortality of American beech, balsam fir (Abies balsamea), red spruce (Picea rubens), northern white cedar (Thuja occidentalis), and red maple (Acer rubrum), but not for other tree species. No relationship was found between species shade tolerance and species-specific response magnitude to PH in terms of diameter growth and tree- or stand-level (absolute or relative) mortality. This result suggests that species shade tolerance does not always determine the type or magnitude of response that a given species has to increased resource availability following PH and that other functional traits may be more important. Overall, the findings provide strong evidence that subsequent tree responses to PH are not consistent among contrasting species for at least 15 years following harvest and longer-term regional assessments are needed. [ABSTRACT FROM AUTHOR]