11 results on '"MacLean, David A."'
Search Results
2. Modelling variation and temporal dynamics of individual tree defoliation caused by spruce budworm in Maine, US and New Brunswick, Canada.
- Author
-
Chen, Cen, Weiskittel, Aaron, Bataineh, Mohammad, and MacLean, David A
- Subjects
SPRUCE budworm ,TREE growth ,DEFOLIATION ,TREE diseases & pests - Abstract
Insect defoliation reduces the growth and survival of trees. Evaluating these effects on trees requires understandings of the variation and dynamics of defoliation, which has been limited by the coarseness of analytical scales. This is especially the case for defoliation caused by spruce budworm (SBW; Choristoneura fumiferana (Clem.)), the primary forest defoliator in North America. In this study, we developed Bayesian models based on a Markov chain Monte Carlo technique to evaluate patterns of SBW defoliation by predicting individual tree defoliation using stand-level measurements of defoliation that are potentially more efficient to obtain through remote sensing. Additionally, the temporal development of individual tree defoliation was also analysed by the same modelling approach. Data containing over 47 000 observations of individual tree defoliation collected during the last SBW outbreak in the 1970s–1980s from an extensive network of permanent sample plots in Maine, US and New Brunswick, Canada were used in model development. Our results demonstrated that the variation in individual tree defoliation was predominantly dependent on species, while all the other examined tree-, stand- and site-level characteristics had a more limited influence individually or even in combination. Despite significant species-specific differences in magnitude, defoliation of both balsam fir (Abies balsamea L.) and red/black spruce (Picea rubens Sarg. Picea mariana (Mill.) B.S.P.) developed towards their respective converged trajectories regardless of differences in initial defoliation, and other examined tree-, stand- and site-level characteristics. These findings were consistent between Maine and New Brunswick despite varying forest management history and species composition. Overall, the results highlight the high variability in SBW defoliation, while the developed modelling framework should be extendable to other regions and other forms of defoliation. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
3. Effects of Hardwood Content on Balsam Fir Defoliation during the Building Phase of a Spruce Budworm Outbreak.
- Author
-
Bo Zhang, MacLean, David A., Johns, Rob C., and Eveleigh, Eldon S.
- Subjects
BALSAM fir ,HARDWOODS ,FORESTS & forestry ,DEFOLIATION ,SPRUCE budworm - Abstract
Defoliation by spruce budworm(Choristoneura fumiferana Clem.) on balsamfir (Abies balsamea (L.) Mill.) is more severe in fir than in mixed fir-hardwood stands. Previous studies assumed that defoliation in fir-hardwood stands was reduced in proportion to percent hardwood regardless of outbreak severity. We tested the influence of stand composition on defoliation during the first 5 years of a spruce budworm outbreak near Amqui, Quebec, by sampling 27 fir-hardwood plots selected to represent three percent hardwood basal area classes (0%-25%, 40%-65%, and 75%-95%). Balsam fir defoliation was significantly lower (p < 0.001) as hardwood content increased, but the relationship varied with overall defoliation severity each year. Annual plot defoliation in fir-hardwood plots, estimated using: (1) defoliation in pure fir plots and the assumption that defoliation in fir-hardwood plots was reduced in proportion to percent hardwood; (2) a generalized linear mixed-effects model with defoliation in pure fir plots, percent hardwood, and interaction as fixed-effects; and (3) Random Forests prediction incorporating 11 predictor variables, resulted in r = 0.77, 0.87, and 0.92 versus measured defoliation, respectively. Average defoliation severity in softwood plots and percent hardwood content were the most important variables in Random Forests analysis. Data on average defoliation level in softwood stands, as an indicator of overall outbreak severity, improves prediction of balsam fir defoliation in mixed stands. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
4. Cross‐scale effects of spruce budworm outbreaks on boreal warblers in eastern Canada.
- Author
-
Drever, Mark C., Smith, Adam C., Venier, Lisa A., Sleep, Darren J. H., and Maclean, David A.
- Subjects
SPRUCE budworm ,WARBLERS ,BIRD breeding ,FOREST birds ,ANIMAL behavior - Abstract
Abstract: Insect outbreaks are major natural disturbance events that affect communities of forest birds, either directly by affecting the food supply or indirectly by changing the vegetation composition of forest canopies. An examination of correlations between measures of bird and insect abundance across different spatial scales and over varying time lag effects may provide insight into underlying mechanisms. We developed a hierarchical Bayesian model to assess correlations between counts of eight warbler species from the Breeding Bird Survey in eastern Canada, 1966 to 2009, with the presence of spruce budworm (Choristoneura fumiferana Clem.) at immediate local scales and time‐lagged regional scales, as measured by extent of defoliation on host tree species. Budworm‐associated species Cape May warbler (Setophaga tigrina), bay‐breasted warbler (Setophaga castanea), and Tennessee warbler (Oreothlypis peregrina) responded strongly and positively to both local and regional effects. In contrast, non‐budworm‐associated species, Blackburnian warbler (Setophaga fusca), magnolia warbler (Setophaga magnolia), Canada warbler (Cardellina canadensis), black‐throated blue warbler (Setophaga caerulescens), and black‐throated green warbler (Setophaga virens), only responded to regional effects in a manner that varied across eastern Canada. The complex responses by forest birds to insect outbreaks involve both increased numerical responses to food supply and to longer term responses to changes in forest structure and composition. These effects can vary across spatial scales and be captured in hierarchical population models, which can serve to disentangle common trends from data when examining drivers of population dynamics like forest management or climate change. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
5. Topkill and stem defects initiated during an uncontrolled spruce budworm outbreak on Cape Breton Island, Nova Scotia.
- Author
-
Virgin, Grant V J, MacLean, David A, and Kershaw, John A
- Subjects
SPRUCE budworm ,CHORISTONEURA ,DEFOLIATION ,REGRESSION trees ,REGRESSION analysis - Abstract
Spruce budworm (SBW; Choristoneura fumiferana [Clem.]) defoliation begins at the top of the crown, and often results in leader death, loss of annual height growth or gradual top dieback, known as topkill. We used regression tree analysis to examine topkill incidences during a severe SBW outbreak in Nova Scotia, Canada in the 1970s-1980s that resulted in 60-100 per cent mortality of merchantable balsam fir (Abies balsamea (L.) Mill.) volume, and re-examined surviving trees for defects 25 years later. At the study outset in 1979, 4-6 years into the SBW outbreak, stand level topkill ranged from 40 to 88 per cent of trees and mean individual-tree topkill probability was 7, 52, 79 and 87 per cent on trees with ≤25, 26-75, 76-90 and 91-100 per cent total defoliation (all age classes of foliage). By 1987, the SBW outbreak had ended and mortality probability of trees was 12, 59, 85 and 98 per cent for classes of peak total defoliation of ≤25, 26-75, 76-90 or 91-100 per cent. Most mortality occurred following 6-8 years of defoliation, but topkill peaked after 4-6 years, indicating that topkill required less cumulative defoliation than death. When the plots were remeasured in 2012, 25 years later, 90 per cent of the surviving trees with documented topkill during the SBW outbreak had stem defects, of which 26 per cent were crooks, 53 per cent forks and 21 per cent sweeps. From 32 to 88 per cent of stem length was located above the point of the defect, resulting in the long-term downgrading of topkill damaged logs. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
6. Balsam fir sawfly defoliation effects on survival and growth quantified from permanent plots and dendrochronology.
- Author
-
Iqbal, Javed, Maclean, David A., and Kershaw, John A.
- Subjects
BALSAM fir ,FIR diseases & pests ,SAWFLIES ,DENDROCHRONOLOGY ,DEFOLIATION ,DECISION support systems ,BAYESIAN analysis - Abstract
Balsam fir sawfly (Neodiprion abietis (Harris)) has become a serious pest of young managed balsam fir (Abies balsamea (L.) Mill.) stands in western Newfoundland, Canada. During 1991–2008, a total area of 561 000 hectares was moderate to severely defoliated. We quantified impacts (growth and survival) using data from permanent sample plots (PSPs) and dendrochronology and related these impacts to defoliation severity determined from aerial defoliation data, in order to provide input into a Decision Support System. We analyzed 67 Newfoundland Forest Service PSPs, selected based on severity of defoliation (classes 1–6), stand age and management interventions (pre-commercially thinned vs natural) and measured before and after defoliation (1996–2008). We used Bayesian statistics to combine information from different sources, each having their own limitations and associated uncertainty. No mortality was observed in immature plots 12 years after defoliation, but survival was 54 per cent lower in mature defoliated than in non-defoliated plots. Plots in defoliation class 1 (1 year of moderate, 30–70 per cent, defoliation) showed 22 per cent cumulative growth reduction and complete recovery to pre-defoliation growth increment after 5 years. Plots in defoliation classes 2–6 (one to three consecutive years of severe, 71–100 per cent, defoliation) had mean cumulative growth reductions of 26–40 per cent and did not recover to pre-defoliation levels even 9 years after defoliation ceased. Natural and thinned plots responded similarly to defoliation severity. These results suggest that proactive control measures need to be implemented since impacts are severe, even with only 1 year of severe defoliation. [ABSTRACT FROM AUTHOR]
- Published
- 2011
- Full Text
- View/download PDF
7. Economics of Early Intervention to Suppress a Potential Spruce Budworm Outbreak on Crown Land in New Brunswick, Canada.
- Author
-
Liu, Eric Ye, Lantz, Van A., MacLean, David A., and Hennigar, Chris
- Subjects
SPRUCE budworm ,BIOLOGICAL insecticides ,DECISION support systems ,LOGGING ,INSECTICIDES ,NET present value - Abstract
We investigated the potential economic impacts of future spruce budworm (Choristoneura fumiferana Clem.) (SBW) outbreaks on 2.8 million ha of Crown land in New Brunswick, Canada and compared an early intervention strategy (EIS) with foliage protection approaches. We coupled the Spruce Budworm Decision Support System (SBW DSS) with a Computable General Equilibrium (CGE) model to assess the impacts of EIS and foliage protection on 0%, 5%, 10%, and 20% of susceptible Crown (publicly owned) forest, under moderate and severe SBW outbreak scenarios. Cumulative available harvest supply from 2017 to 2067 was projected to be reduced by 29 to 43 million m
3 , depending upon SBW outbreak severity, and a successful EIS approach would prevent this loss. These harvest reductions were projected to reduce total economic output by $25 billion (CAD) to $35 billion. Scenarios using biological insecticide foliage protection over 20% of susceptible Crown forest area were projected to reduce losses to 6–17 million m3 and $0.5–4.1 billion. Depending upon SBW outbreak severity, EIS was projected to have benefit/cost ratios of 3.8 to 6.4 and net present values of $186 million to $353 million, both higher than foliage protection strategies. Sensitivity analysis scenarios of 'what if' EIS partially works (80% or 90%) showed that these produced superior timber harvest savings than the best foliage protection scenario under severe SBW outbreak conditions and generally superior results under moderate outbreak scenarios. Overall, results support the continued use of EIS as the preferred strategy on economic grounds to protect against SBW outbreaks on Crown land in New Brunswick. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
- View/download PDF
8. Positive Results of an Early Intervention Strategy to Suppress a Spruce Budworm Outbreak after Five Years of Trials.
- Author
-
MacLean, David A., Hennigar, Chris, Amirault, Peter, Amos-Binks, Luke, Carleton, Drew, Johns, Rob, and Régnière, Jacques
- Subjects
INSECT populations ,SPRUCE budworm ,EARLY medical intervention ,DEFOLIATION ,DECISION support systems - Abstract
Spruce budworm (Choristoneura fumiferana Clem.; SBW) outbreaks are one of the dominant natural disturbances in North America, having killed balsam fir (Abies balsamea (L.) Mill.) and spruce (Picea sp.) trees over tens of millions of hectares. Responses to past SBW outbreaks have included the aerial application of insecticides to limit defoliation and keep trees alive, salvage harvesting of dead and dying trees, or doing nothing and accepting the resulting timber losses. We tested a new 'early intervention strategy' (EIS) focused on suppressing rising SBW populations before major defoliation occurs, from 2014 to 2018 in New Brunswick, Canada. The EIS approach included: (1) intensive monitoring of overwintering SBW to detect 'hot spots' of low but rising populations; (2) targeted insecticide treatment to prevent spread; and (3) proactive public communications and engagement on project activities and results. This is the first attempt of area-wide (all areas within the jurisdiction of the province of New Brunswick) management of a native forest insect population. The project was conducted by a consortium of government, forest industry, researchers, and other partners. We developed a treatment priority and blocking model to optimize planning and efficacy of EIS SBW insecticide treatment programs. Following 5 years of over 420,000 ha of EIS treatments of low but increasing SBW populations, second instar larvae (L2) SBW levels across northern New Brunswick were found to be considerably lower than populations in adjacent Québec. Treatments increased from 4500 ha in 2014, to 56,600 ha in 2016, and to 199,000 ha in 2018. SBW populations in blocks treated with Bacillus thuringiensis or tebufenozide insecticide were consistently reduced, and generally did not require treatment in the subsequent year. Areas requiring treatment increased up to 2018, but SBW L2 populations showed over 90% reductions in that year. Although this may be a temporary annual decline in SBW population increases, it is counter to continued increases in Québec. Following 5 years of tests, the EIS appears to be effective in reducing the SBW outbreak. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
9. Spatial-Temporal Patterns of Spruce Budworm Defoliation within Plots in Québec.
- Author
-
Li, Mingke, MacLean, David A., Hennigar, Chris R., and Ogilvie, Jae
- Subjects
SPRUCE ,DEFOLIATION ,SPOTTED cucumber beetle ,BALSAM fir ,PLANT phenology - Abstract
We investigated the spatial-temporal patterns of spruce budworm (Choristoneura fumiferana (Clem.); SBW) defoliation within 57 plots over 5 years during the current SBW outbreak in Québec. Although spatial-temporal variability of SBW defoliation has been studied at several scales, the spatial dependence between individual defoliated trees within a plot has not been quantified, and effects of defoliation level of neighboring trees have not been addressed. We used spatial autocorrelation analyses to determine patterns of defoliation of trees (clustered, dispersed, or random) for plots and for individual trees. From 28% to 47% of plots had significantly clustered defoliation during the 5 years. Plots with clustered defoliation generally had higher mean defoliation per plot and higher deviation of defoliation. At the individual-tree-level, we determined 'hot spot trees' (highly defoliated trees surrounded by other highly defoliated trees) and 'cold spot trees' (lightly defoliated trees surrounded by other lightly defoliated trees) within each plot using local Getis-Ord Gi* analysis. Results revealed that 11 to 27 plots had hot spot trees and 27% to 64% of them had mean defoliation <25%, while plots with 75% to 100% defoliation had either cold spot trees or non-significant spots, which suggested that whether defoliation was high or low enough to be a hot or cold spot depended on the defoliation level of the entire plot. We fitted individual-tree balsam fir defoliation regression models as a function of plot and surrounding tree characteristics (using search radii of 3–5 m). The best model contained plot average balsam fir defoliation and subject tree basal area, and these two variables explained 80% of the variance, which was 2% to 5% higher than the variability explained by the neighboring tree defoliation, over the 3–5 m search radii tested. We concluded that plot-level defoliation and basal area were adequate for modeling individual tree defoliation, and although clustering of defoliation was evident, larger plots were needed to determine the optimum neighborhood radius for predicting defoliation on an individual. Spatial autocorrelation analysis can serve as an objective way to quantify such ecological patterns. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
10. Detection of Annual Spruce Budworm Defoliation and Severity Classification Using Landsat Imagery.
- Author
-
Rahimzadeh-Bajgiran, Parinaz, Weiskittel, Aaron R., Kneeshaw, Daniel, and MacLean, David A.
- Subjects
SPRUCE budworm ,FOREST pest control ,DEFOLIATION ,FOREST management ,LEAVES - Abstract
Spruce budworm (SBW) is the most destructive forest pest in eastern forests of North America. Mapping annual current-year SBW defoliation is challenging because of the large landscape scale of infestations, high temporal/spatial variability, and the short period of time when detection is possible. We used Landsat-5 and Landsat-MSS data to develop a method to detect and map SBW defoliation, which can be used as ancillary or alternative information for aerial sketch maps (ASMs). Results indicated that Landsat-5 data were capable of detecting and classifying SBW defoliation into three levels comparable to ASMs. For SBW defoliation classification, a combination of three vegetation indices, including normalized difference moisture index (NDMI), enhanced vegetation index (EVI), and normalized difference vegetation index (NDVI), were found to provide the highest accuracy (non-defoliated: 77%, light defoliation: 60%, moderate defoliation: 52%, and severe defoliation: 77%) compared to using only NDMI (non-defoliated: 76%, light defoliation: 40%, moderate defoliation: 43%, and severe defoliation: 67%). Detection of historical SBW defoliation was possible using Landsat-MSS NDVI data, and the produced maps were used to complement coarse-resolution aerial sketch maps of the past outbreak. The method developed for Landsat-5 data can be used for current SBW outbreak mapping in North America using Landsat-8 and Sentinel-2 imagery. Overall, the work highlights the potential of moderate resolution optical remote sensing data to detect and classify fine-scale patterns in tree defoliation. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
11. Simulation and Analysis of the Effect of a Spruce Budworm Outbreak on Carbon Dynamics in Boreal Forests of Quebec.
- Author
-
Liu, Zelin, Peng, Changhui, De Grandpré, Louis, Candau, Jean-Noël, Work, Timothy, Huang, Chunbo, and Kneeshaw, Daniel
- Subjects
SPRUCE budworm ,FOREST dynamics ,TAIGAS ,TAIGA ecology ,FOREST surveys ,DEFOLIATION ,CLIMATE change ,FOREST declines - Abstract
In a climate change context, the sequestration of atmospheric carbon (C) in forests is key for achieving emission targets. It is thus critical to understand how large-scale disturbances are affecting the overall forest C stocks. C dynamics in North American boreal forest ecosystems are strongly affected by the defoliation and mortality that occurs during a spruce budworm (SBW) outbreak. We used forest inventory geospatial databases, monthly climate data, spatially explicit defoliation sequence data, and the TRIPLEX-Insect model to simulate C dynamics with and without SBW disturbances in stands with different vulnerability to the SBW in the boreal forest of Quebec. Our results showed that SBW defoliation and related mortality decreased the average aboveground biomass and belowground biomass by 5.96% and 6.94% by 2017, respectively. At the same time, 21,046 km
2 of forest were converted from a C sink to a source. This study provides the first quantitative analysis of the effect of a SBW outbreak on carbon dynamics for three different boreal stand types (that is, fir, spruce, and mixed fir-spruce) at a regional scale. Our results suggested that younger fir forests lost less C than either fir-spruce or spruce forests during SBW attacks between 2007 and 2017 in Quebec. This highlights the importance of considering species composition when assessing vulnerability or resilience. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.