Contributions of insects and droughts to growth decline of trembling aspen mixed boreal forest of western Canada

Chen, Lei; Huang, Jian‐Guo; Dawson, Andria; Zhai, Lihong; Stadt, Kenneth J.; Comeau, Philip G.; Whitehouse, Caroline

doi:10.1111/gcb.13855

Cited by 59 publications

(38 citation statements)

References 101 publications

(149 reference statements)

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“…Importantly, we found that the temporal trends in net above‐ground biomass change varied spatially along the gradient of the long‐term average of climate moisture availability, with a pronounced temporal decrease in the dry plots, due to a stronger temporal increase in mortality than an increase in growth. Our results indicated that although rising CO 2 , warming and associated increases in growing season length could increase tree growth in boreal forests (Girardin, Bouriaud, et al., ; Pretzsch et al., ), these positive climate change drivers for growth could be constrained by limited water availability (Chen et al., ; Hogg et al., ; Wang et al., ).…”

Section: Discussionmentioning

confidence: 74%

“…In dry plots, warming had strong negative effects on net biomass change due to increased mortality and reduced growth. These negative effects of warming could reflect the coupling influences of direct heat stress and increased activity of insects (Allen et al., ; Anderegg et al., ; Chen et al., ; Hogg et al., ). With temporally decreasing climate moisture availability, which resulted from temporally increasing PET despite slightly increasing precipitation in the study area (Luo & Chen, ), net biomass change decreased in dry plots, due to a decrease in growth and an increase in mortality.…”

Section: Discussionmentioning

confidence: 99%

“…Therefore, ΔAGB was the difference between growth and mortality. Observed tree mortality resulted from endogenous processes such as competition and longevity (Luo & Chen, ) and biotic and abiotic stressors such as heat, droughts, diseases and insects (Chen et al., ; Hogg et al., ), but not from fire and logging since government agencies discontinued monitoring once a stand‐replacing disturbance occurred.…”

Section: Methodsmentioning

confidence: 99%

“…Further climate change‐induced declines in water availability may exceed the coping mechanisms of forests (Allen et al., ; Wang et al., ). Based on the limiting resource theory (Bloom, Chapin, & Mooney, ), forests under water stress may not benefit from these positive climate change drivers, even though rising CO 2 , warming and extended growing seasons may be beneficial to forest growth (Brienen et al., ; Chen et al., ; D'Orangeville et al., ; Hogg et al., ; Pretzsch, Biber, Schutze, Uhl, & Rotzer, ; Wang et al., ).…”

Section: Introductionmentioning

confidence: 99%

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Divergent temporal trends of net biomass change in western Canadian boreal forests

et al. 2018

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Forests play a strong role in the global carbon cycle by absorbing atmospheric carbon dioxide through increasing forest biomass. Understanding temporal trends of forest net above‐ground biomass change (ΔAGB) can help infer how forest carbon sequestration responds to ongoing climate changes. Despite wide spatial variation in the long‐term average of climate moisture availability (CMIaverage) across forest ecosystems, temporal trends of ΔAGB associated with CMIaverage remain unclear. We tested the hypothesis that the negative impacts of climate change on ΔAGB would decrease with CMIaverage using the data from permanent sample plots, monitored from 1958 to 2011, with stand ages varying from 17 to 210 years, in western boreal forests of Canada. We found that ΔAGB on average increased with CMIaverage. Temporally, ΔAGB declined sharply between 1958 and 2011 in plots with low CMIaverage owing to increased biomass loss from mortality accompanied by little growth gain, whereas ΔAGB changed little in plots with high CMIaverage. The temporal decrease of ΔAGB in drier areas was attributable to its negative responses to warming‐induced temporal decreases in climate moisture availability. Synthesis. Our results indicate that large‐scale changes in forest carbon functioning associated with climate change depend on the long‐term average of climate moisture availability. Our finding suggests a possible retreat of boreal biome at the drier distribution limits with predicted declines in water availability in the 21st century.

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Section: Discussionmentioning

confidence: 74%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Divergent temporal trends of net biomass change in western Canadian boreal forests

et al. 2018

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“…5) and drought intensity during the summer of the previous year (Fig. It has also been reported that FTC outbreaks are triggered by above-average early spring temperatures (Ives 1973, Chen et al 2018. In contrast, previous studies have tended to stress that outbreaks may be inhibited when low minimum temperatures lead to high mortality of eggs in winter or starvation of hatchlings in spring due to frost damage to foliage (Blais 1955, Cooke andRoland 2003).…”

Section: Cyclicity Of Outbreaks Through Timementioning

confidence: 93%

Drought and surface‐level solar radiation predict the severity of outbreaks of a widespread defoliating insect

Haynes¹,

Tardif

Parry

2018

Ecosphere

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2018. Drought and surface-level solar radiation predict the severity of outbreaks of a widespread defoliating insect. Ecosphere 9(8):Abstract. Defoliating insects are a major factor impacting tree growth in temperate and boreal forests, but the effects of climate change on the severity and frequency of outbreaks of these insects are not well understood. Dendrochronological reconstruction of forest tent caterpillar (Malacosoma disstria) outbreaks on trembling aspen (Populus tremuloides) in southwestern Manitoba, Canada, from 1851 to 2010 was used to examine the effects of changes in temperature, incident surface-level solar radiation, and drought severity on the cyclicity, frequency, and severity of outbreaks. Outbreak severity was determined by comparing the tree-ring widths of trembling aspen with those of white spruce (Picea glauca), which is not a forest tent caterpillar host. Wavelet analysis suggested the cyclicity of outbreaks increased after 1930. From 1930 to 2010, the dominant period length of outbreak cycles steadily increased over time from three to seven years, coinciding with long-term declines in drought severity. The strength of forest tent caterpillar suppression of trembling aspen growth in a given year was inversely related to incident solar radiation and drought severity during late spring (the larval feeding period) of the same year. The effect of late spring drought on the impact of forest tent caterpillar on ring growth differed from that of summer drought. There was a nonlinear relationship between growth suppression in a given year and summer drought severity in the previous year; slightly above-average drought severity was associated with reduced impacts of the defoliator, whereas severe drought was associated with intense growth suppression. Strong suppression of aspen growth observed during outbreaks from 1983 to 2010 may be partly explained by observed long-term trends of decreasing atmospheric transmittance of solar radiation (a phenomenon termed "global dimming") and increasing soil moisture availability during late spring. However, as the severity and frequency of summer droughts are expected to increase over the 21st century, the nonlinear relationship between summer drought severity and growth suppression the following year suggests a future in which summer droughts precede severe outbreaks that threaten the health of boreal forest hardwood trees.

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Current and projected cumulative impacts of fire, drought, and insects on timber volumes across Canada

Boucher

Boulanger

Aubin

et al. 2018

Ecological Applications

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Canada's forests are shaped by disturbances such as fire, insect outbreaks, and droughts that often overlap in time and space. The resulting cumulative disturbance risks and potential impacts on forests are generally not well accounted for by models used to predict future impacts of disturbances on forest. This study aims at projecting future cumulative effects of four main natural disturbances, fire, mountain pine beetle, spruce budworm and drought, on timber volumes across Canada's forests using an approach that accounts for potential overlap among disturbances. Available predictive models for the four natural disturbances were used to project timber volumes at risk under aggressive climate forcing up to 2100. Projections applied to the current vegetation suggest increases of volumes at risk related to fire, mountain pine beetle, and drought over time in many regions of Canada, but a decrease of the volume at risk related to spruce budworm. When disturbance effects are accumulated, important changes in volumes at risk are projected to occur as early as 2011-2041, particularly in central and eastern Canada. In our last simulation period covering 2071-2100, nearly all timber volumes in most of Canada's forest regions could be at risk of being affected by at least one of the four natural disturbances considered in our analysis, a six-fold increase relative to the baseline period (1981-2010). Tree species particularly vulnerable to specific disturbances (e.g., trembling aspen to drought) could suffer disproportionate increases in their volume at risk with potential impacts on forest composition. By 2100, estimated wood volumes not considered to be at risk could be lower than current annual timber harvests in central and eastern Canada. Current level of harvesting could thus be difficult to maintain without the implementation of adaptation measures to cope with these disturbances.

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Contributions of insects and droughts to growth decline of trembling aspen mixed boreal forest of western Canada

Cited by 59 publications

References 101 publications

Divergent temporal trends of net biomass change in western Canadian boreal forests

Divergent temporal trends of net biomass change in western Canadian boreal forests

Drought and surface‐level solar radiation predict the severity of outbreaks of a widespread defoliating insect

Current and projected cumulative impacts of fire, drought, and insects on timber volumes across Canada

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