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We compared three methods for estimating current-year spruce budworm (Choristoneura fumiferana (Clem.)) defoliation from 2014 to 2021 using a network of 99 permanent sample plots in central Gaspé Peninsula, Québec. Percent current-year defoliation was measured by assessing shoots from mid-crown branches, ocular ratings of all individual trees using binoculars, and provincial government aerial surveys. Ocular survey defoliation differed from branch sample defoliation in 5–6 out of 7 years, consistently underestimating defoliation, across the full range of defoliation severity observed. Nested mixed-effect models for fir–spruce combined, balsam fir, white spruce, and black spruce ocular survey defoliation bias resulted in marginal R2 of 0.40, 0.47, 0.82, and 0.86, respectively. Current defoliation severity and its interaction with previous year defoliation and weather conditions significantly affected ocular survey bias. Correspondence of aerial survey estimates and mean plot defoliation occurred in only 43% of all plot-years and ranged from 14%–58% in individual years. Differences between aerial survey defoliation and plot values mainly resulted from assigning an adjacent class (e.g., light <30% assigned as moderate 31%–70% defoliation) or misplaced defoliation polygon boundaries, suggesting that assignment of aerial survey defoliation to plots or specific ground areas needs ground truth sampling. [ABSTRACT FROM AUTHOR]

Defoliation level and site type are thought to influence tree response during spruce budworm (Choristoneura fumiferana (Clemens)) outbreaks. We determined the effects of four manual defoliation treatments (0%, 50%, 100%, and 100% + bud removal of current foliage) for 3 years on foliage production of balsam fir (Abies balsamea (L.) Mill.), black spruce (Picea mariana (Mill.) Britton, Sterns & Poggenb.), and white spruce (Picea glauca (Moench) Voss) trees on four site-quality classes. After 3 years of defoliation and 2 years of recovery, foliage biomass was reduced by 34%–98%. During defoliation, the number of shoots generally increased and shoot length of spruce generally decreased, especially on rich sites. During recovery, the number of shoots increased substantially, shoot length decreased, and bud destruction reduced the number of shoots by about 50% compared with that of trees that received the 100% defoliation treatment. Defoliation did not substantially affect needle length. Trees on rich sites had two- to fourfold greater foliage production than trees on poor sites. Effects of site and defoliation differed among species, but site quality, especially nutrition, played an important role in production of shoots and needles and the tree's ability to withstand defoliation. Black spruce had more limited ability to recover foliage biomass, only producing more shoots, whereas balsam fir and white spruce had stronger ability to recover needle and shoot length, respectively. [ABSTRACT FROM AUTHOR]

Predictions of defoliation are an important component of planning aerial insect control programs, especially for defoliators such as balsam fir sawfly (Neodiprion abietis (Harris)) that cause severe impacts on forest growth and yield. Currently, defoliation prediction is done manually based on field observations and experience, but it is a good candidate for a Bayesian network (BN), a flexible tool for combining available expert knowledge and empirical data. We created a BN model and linked it to a geographic information system to map predicted defoliation for balsam fir sawfly in western Newfoundland over an area of 5.7 million ha from 2001 to 2008. Based on expert knowledge, probabilistic influence of egg counts, previous defoliation, and stand characteristics (species composition, stand age, and management intervention) on subsequent-year defoliation was quantified. For validation purposes, maps created using the BN model were compared with manual defoliation predictions and with measured aerial defoliation survey maps. BN model defoliation prediction maps were found to be in moderate agreement (mean Kappa value of 0.59) with conventional manual prediction maps. Overall, the BN model showed similar accuracy to manual predictions, but with benefits of automating the process and of providing more spatial detail in predictions. [ABSTRACT FROM AUTHOR]

Spruce budworm (Choristoneura fumiferana Clem.) severely defoliates balsam fir (Abies balsamea (L.) Mill.) and spruce (Picea spp.) in large periodic outbreaks and represents one of Canada’s most damaging and widespread forest insects. We present a modeling framework that integrates stand-level spruce budworm volume impacts used in the Spruce Budworm Decision Support System (SBWDSS) into an industrial-scale timber supply model for the 209 000 ha Black Brook District in northwestern New Brunswick, Canada. This approach uses linear optimization of harvest scheduling, salvage, and insecticide application to minimize volume reduction. One hundred and ninety-five scenarios were simulated, including normal and severe spruce budworm outbreaks, beginning in 2002, with combinations of varying insecticide efficacy, timing, and spatial extent of protection. After simulated severe defoliation from 2007 to 2016, maximum harvest reductions of 35% were predicted for a normal outbreak for the 2012–2016 period, and 46% for a severe outbreak for the 2017–2021 period; these impacts were reduced to 25% and 34% using re-optimized harvest scheduling and salvage. Results suggest that combined optimized salvage and harvest rescheduling could reduce future harvest reductions by up to 12%. Spatial optimization of protected areas gave similar results to those obtained using protection priority assignments based on marginal stand-level volume reduction in the SBWDSS. [ABSTRACT FROM AUTHOR]

Defoliation reduces the growth and survival of trees, but this influence can be difficult to evaluate largely because of its interplay with various stand and site factors, especially for the highly dynamic defoliation of spruce-fir ( Picea- Abies) forests caused by spruce budworm (SBW; Choristoneura fumiferana (Clem.)), the primary tree defoliator in North America. In this study, we developed statistical models to evaluate the influence of SBW defoliation, while considering its interaction with various stand and site factors, on spruce-fir stand dynamics of annual volume net growth, mortality, and ingrowth. The data were collected at intervals of 1 to 3 years from 560 permanent sample plots during the last SBW outbreak (1970s-1980s) in Maine, USA, and New Brunswick, Canada. These data comprise a wide range of observations of cumulative defoliation, especially at relatively low levels, that have been largely overlooked in previous studies. Our results strongly demonstrated that even relatively low levels of cumulative defoliation were significantly related to stand-level mortality and ingrowth, while net growth was more competition driven. Additionally, these stand dynamics were found to be not significantly affected by any of the site factors evaluated. These findings were consistent for Maine and New Brunswick despite their differences in forest management and SBW outbreak histories. [ABSTRACT FROM AUTHOR]