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Tree diameter increment (∆DBH) and total tree height increment (∆HT ) are key components of a forest growth and yield model. A problem in complex, multi-species forests is that individual tree attributes such as ∆DBH and ∆HT need to be characterized for a large number of distinct woody species of highly varying levels of occurrence. Based on more than 2.5 million ∆DBH observations and over 1 million ∆HT records from up to 60 tree species and genera, respectively, this study aimed to improve existing ∆DBH and ∆HT equations of the Acadian Variant of the Forest Vegetation Simulator (FVS-ACD) using a revised method that utilize tree species as a random effect. Our study clearly highlighted the efficiency and flexibility of this method for predicting ∆DBH and ∆HT. However, results also highlighted shortcomings of this approach, e.g., reversal of plausible parameter signs as a result of combining fixed and random effects parameter estimates after extending the random effect structure by incorporating North American ecoregions. Despite these potential shortcomings, the newly developed ∆DBH and ∆HT equations outperformed the ones currently used in FVS-ACD by reducing prediction bias quantified as mean absolute bias and root mean square error by at least 11% for an independent dataset and up to 41% for the model development dataset. Using the revised ∆DBH and ∆HT estimates, greater prediction accuracy in individual tree aboveground live carbon mass estimation was also found in general but performance varied with dataset and accuracy metric examined. Overall, this analysis highlights the importance and challenges of developing robust ∆DBH and ∆HT equations across broad regions dominated by mixed-species, managed forests. [ABSTRACT FROM AUTHOR]

To overcome existing knowledge gaps regarding altering harvest activities in the mixed species and heavily forested USA state of Maine, we used continuous forest inventory data to develop statistical models that predict harvest probability of occurrence and intensity. Among the three modeling approaches examined, the first one directly predicted stand-level basal area removal as a percentage of initial total stand basal area. The second approach first predicted stand-level harvest probability and then the stand-level basal area removal of the harvested plots only. The third approach used the stand-level harvest probability equation of the second approach, while subsequently predicting individual tree harvest probability for only the harvested plots. Among the most influential stand-level attributes were quadratic mean diameter, stand density, elevation, and ownership type, while the most influential tree-level attributes were diameter at breast height, basal area in larger trees, and species. Differences in prediction accuracy between modeling approaches were small with the third approach performing slightly better. Our findings suggest that harvesting in Maine might be less opportunistic and short-term driven than generally perceived. Overall, the analysis highlights the complex array of factors that influence harvesting patterns and provides a framework for better representing contrasting harvest behavior in future wood supply projections. [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]

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Understanding private woodland owner (PWO) timber harvesting behavior is essential for predicting potential timber supply, as PWOs could be an increasingly important source. This evidence-based review synthesizes more than 100 peer-reviewed articles, government reports, and dissertations from 1970 to 2014 from North America and Europe. Our broad research question was "To what extent is actual PWO timber harvesting behavior understood?" Our objectives were to (1) identify how past research analyzed actual harvesting behavior, (2) describe the evolution of these methods, (3) determine the extent to which previous research linked landowners' stated intentions to actual harvesting behavior, and (4) evaluate the significant predictors of PWO timber harvesting. This evidence-based review found that parcel size, harvest price, and distance from residence were the most common significant predictors of harvesting intention. Many studies purportedly studied behavior, but most measure stated attitudes without measuring observable harvesting behaviors. A better understanding of PWO behavior will inform timber supply prediction and support forest management outreach. [ABSTRACT FROM AUTHOR]

Forest inventory is vital to all aspects of forest management and inventory methods can vary greatly in their accuracy, precision, efficiency and cost. In Maine, much of the forestland base has been managed using partial harvesting methods over the past two decades. These partial harvesting methods generally produce highly heterogeneous stand structures and composition. Consequently, it is currently unclear which inventory methods are best given the distinct spatial and structural heterogeneity that is created. We compared efficiency and stand-level inventory estimates using horizontal point, fixed area and horizontal line sampling measurement methods in 16 partially harvested stands across northern and central Maine. Some stand-level variables were sensitive to measurement method (e.g., volume, quadratic mean diameter and small stem density and basal area), while others were less sensitive (e.g., overall basal area and stem density). Efficiency, defined as a combination of precision of volume estimates and measurement time, varied among measurement methods at lower stand basal area values but was similar at higher basal area, with the exception of the fixed area method. Overall, horizontal line sampling proved to be a viable method in post-partial harvest stand conditions. Our results illustrate the trade-offs between precision and time costs involved in several measurement methods under a range of heterogeneous stand conditions. [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]

The volume increment of individual trees is often inferred from a volume or taper equation and predicted or observed diameter and height increments. Prediction errors can be compounded with this type of approach because of the array of equations used and differences in their accuracy. The consequences of several alternative approaches for indirectly or directly estimating individual tree volume increment were examined using an extensive stem analysis data set of Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) in southwest Oregon. The data were used to construct new stem volume, taper, and volume increment equations, which were then used to compare predicted and observed 5-year volume increments. The results of this analysis suggest that the indirect prediction of volume increment is sensitive to both the approach used for estimating stem volume and the use of actual versus predicted diameter and height increment, especially diameter increment. In addition, using the indirect method of volume and taper equations was found to have a slightly lower level of accuracy in predicting stem volume increment than the direct method. It was found that the use of local calibration procedures could help to mitigate possible problems with the bias incurred by using predicted rather than actual diameter increment. [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]

This study investigates the combined effects of climate and socioeconomic change on fiber supply and forest carbon in Maine, USA, for broad alternative futures. We conduct an econometric analysis to project forest resource use over the next 80 years under a range of shared socioeconomic pathways (SSPs) and representative concentration pathways (RCPs). Results show that continued forest successional dynamics – without any harvesting – contribute the most to Maine's aboveground carbon (AGC) accumulation, with 2100 AGC potentially increasing by 140% compared to 2020. On this basis, climate change could result in 2.44–2.64 times greater AGC in 2100 compared to today. Harvest activities are major drivers of forest C dynamics, resulting in 2100 AGC being only 16% >2020. Socioeconomic factors (SSPs) had much larger effects on total harvest and carbon stocks than climate change (RCPs). Harvest volume were projected to increase by 9–29% between 2020 and 2100 for favorable socioeconomic development scenarios (SSP1/SSP2/SSP5) and decrease by 3–29% for unfavorable socioeconomic development scenarios (SSP3/SSP4). Overall, Maine's forest C pools were projected to increase by end-century for RCPs x SSP1/SSP2. This study offers valuable insight on possible methods for region-specific socioeconomic and climate change assessments, particularly in areas with extensive and diverse working forests with mixed ownership. • Maine's future forest carbon is driven primarily by successional and harvest dynamics. • Climate change influences future carbon dynamics up to 16% for most severe conditions. • Socioeconomic factors are more important than climate change on Maine's future carbon. • Forest carbon only increases in medium and high socioeconomic development scenarios. [ABSTRACT FROM AUTHOR]