Epidemic spruce beetle outbreak changes drivers of Engelmann spruce regeneration

Pettit, Jessika M.; Burton, Julia I.; DeRose, R. Justin; Long, James N.; Voelker, Steven L.

doi:10.1002/ecs2.2912

Cited by 11 publications

(17 citation statements)

References 82 publications

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“…Similarly, if it is a goal to preserve Engelmann spruce in areas threatened by climate change and increased bark beetles activity, management actions aimed at reducing drought stress are unlikely to directly affect spruce beetle susceptibility. However, management that maintains a diversity of age and size classes of trees (DeRose & Long, 2014), including small regenerating trees that are not susceptible to beetle attack, will be essential to keeping this species present on the landscape (e.g., Pettit, Burton, DeRose, Long, & Voelker, 2019), and allowing it additional time to adapt to climate change and/or migrate to nearby refugia.…”

Section: Discussionmentioning

confidence: 99%

Spruce beetle outbreak was not driven by drought stress: Evidence from a tree‐ring iso‐demographic approach indicates temperatures were more important

Pettit

Voelker

DeRose

et al. 2020

Global Change Biology

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Climate change has amplified eruptive bark beetle outbreaks over recent decades, including spruce beetle (Dendroctonus rufipennis). However, for projecting future bark beetle dynamics there is a critical lack of evidence to differentiate how outbreaks have been promoted by direct effects of warmer temperatures on beetle life cycles versus indirect effects of drought on host susceptibility. To diagnose whether drought‐induced host‐weakening was important to beetle attack success we used an iso‐demographic approach in Engelmann spruce (Picea engelmannii) forests that experienced widespread mortality caused by spruce beetle outbreaks in the 1990s, during a prolonged drought across the central and southern Rocky Mountain region. We determined tree death date demography during this outbreak to differentiate early‐ and late‐dying trees in stands distributed across a landscape within this larger regional mortality event. To directly test for a role of drought stress during outbreak initiation we determined whether early‐dying trees had greater sensitivity of tree‐ring carbon isotope discrimination (∆13C) to drought compared to late‐dying trees. Rather, evidence indicated the abundance and size of host trees may have modified ∆13C responses to drought. ∆13C sensitivity to drought did not differ among early‐ versus late‐dying trees, which runs contrary to previously proposed links between spruce beetle outbreaks and drought. Overall, our results provide strong support for the view that irruptive spruce beetle outbreaks across North America have primarily been driven by warming‐amplified beetle life cycles whereas drought‐weakened host defenses appear to have been a distant secondary driver of these major disturbance events.

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Section: Discussionmentioning

confidence: 99%

Spruce beetle outbreak was not driven by drought stress: Evidence from a tree‐ring iso‐demographic approach indicates temperatures were more important

Pettit

Voelker

DeRose

et al. 2020

Global Change Biology

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“…We used a model comparison and selection process (Burnham and Anderson, 2003) to assess the influence of light, climate conditions, and plant development on trait variation within species. We used a stepwise process to compare a limited number of plausible linear mixed effects models that added terms in order of their empirical support in previous studies (Burton et al, 2014;Pettit et al, 2019). We compared model AICc values, a bias corrected version of Akaike's information criterion (AIC) for small samples to determine best-fit models, using the R package "AICcmodelavg" (Mazerolle, 2020).…”

Section: Guided Stepwise Linear Mixed Effects Model Selectionmentioning

confidence: 99%

Montane Temperate-Boreal Forests Retain the Leaf Economic Spectrum Despite Intraspecific Variability

Hecking¹,

Zukswert²,

Drake³

et al. 2022

Front. For. Glob. Change

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Trait-based analyses provide powerful tools for developing a generalizable, physiologically grounded understanding of how forest communities are responding to ongoing environmental changes. Key challenges lie in (1) selecting traits that best characterize the ecological performance of species in the community and (2) determining the degree and importance of intraspecific variability in those traits. Recent studies suggest that globally evident trait correlations (trait dimensions), such as the leaf economic spectrum, may be weak or absent at local scales. Moreover, trait-based analyses that utilize a mean value to represent a species may be misleading. Mean trait values are particularly problematic if species trait value rankings change along environmental gradients, resulting in species trait crossover. To assess how plant traits (1) covary at local spatial scales, (2) vary across the dominant environmental gradients, and (3) can be partitioned within and across taxa, we collected data on 9 traits for 13 tree species spanning the montane temperate—boreal forest ecotones of New York and northern New England. The primary dimension of the trait ordination was the leaf economic spectrum, with trait variability among species largely driven by differences between deciduous angiosperms and evergreen gymnosperms. A second dimension was related to variability in nitrogen to phosphorous levels and stem specific density. Levels of intraspecific trait variability differed considerably among traits, and was related to variation in light, climate, and tree developmental stage. However, trait rankings across species were generally conserved across these gradients and there was little evidence of species crossover. The persistence of the leaf economics spectrum in both temperate and high-elevation conifer forests suggests that ecological strategies of tree species are associated with trade-offs between resource acquisition and tolerance, and may be quantified with relatively few traits. Furthermore, the assumption that species may be represented with a single trait value may be warranted for some trait-based analyses provided traits were measured under similar light levels and climate conditions.

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“…Following bark beetle outbreak, abundant advance regeneration and new seedling establishment suggest that many forest stands have the potential to return to a similar structural state within a few decades [99,103,104]. Still, the composition and density of post-outbreak stands are highly variable due to outbreak severity, topography, weather, local microclimatic conditions, and prior disturbance by fire or blowdown that influence regeneration dynamics [57,101,[105][106][107][108]. Many of these same factors can also cause differences in individuallevel growth [57], leading to broad-scale variation in rates of post-disturbance recovery that may influence susceptibility to future disturbance [27,109].…”

Section: Patterns Of Bark Beetle-caused Tree Mortality In the Srmmentioning

confidence: 99%

Effects of Bark Beetle Outbreaks on Forest Landscape Pattern in the Southern Rocky Mountains, U.S.A.

et al. 2021

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Since the late 1990s, extensive outbreaks of native bark beetles (Curculionidae: Scolytinae) have affected coniferous forests throughout Europe and North America, driving changes in carbon storage, wildlife habitat, nutrient cycling, and water resource provisioning. Remote sensing is a crucial tool for quantifying the effects of these disturbances across broad landscapes. In particular, Landsat time series (LTS) are increasingly used to characterize outbreak dynamics, including the presence and severity of bark beetle-caused tree mortality, though broad-scale LTS-based maps are rarely informed by detailed field validation. Here we used spatial and temporal information from LTS products, in combination with extensive field data and Random Forest (RF) models, to develop 30-m maps of the presence (i.e., any occurrence) and severity (i.e., cumulative percent basal area mortality) of beetle-caused tree mortality 1997–2019 in subalpine forests throughout the Southern Rocky Mountains, USA. Using resultant maps, we also quantified spatial patterns of cumulative tree mortality throughout the region, an important yet poorly understood concept in beetle-affected forests. RF models using LTS products to predict presence and severity performed well, with 80.3% correctly classified (Kappa = 0.61) and R2 = 0.68 (RMSE = 17.3), respectively. We found that ≥10,256 km2 of subalpine forest area (39.5% of the study area) was affected by bark beetles and 19.3% of the study area experienced ≥70% tree mortality over the twenty-three year period. Variograms indicated that severity was autocorrelated at scales < 250 km. Interestingly, cumulative patch-size distributions showed that areas with a near-total loss of the overstory canopy (i.e., ≥90% mortality) were relatively small (<0.24 km2) and isolated throughout the study area. Our findings help to inform an understanding of the variable effects of bark beetle outbreaks across complex forested regions and provide insight into patterns of disturbance legacies, landscape connectivity, and susceptibility to future disturbance.

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Epidemic spruce beetle outbreak changes drivers of Engelmann spruce regeneration

Cited by 11 publications

References 82 publications

Spruce beetle outbreak was not driven by drought stress: Evidence from a tree‐ring iso‐demographic approach indicates temperatures were more important

Spruce beetle outbreak was not driven by drought stress: Evidence from a tree‐ring iso‐demographic approach indicates temperatures were more important

Montane Temperate-Boreal Forests Retain the Leaf Economic Spectrum Despite Intraspecific Variability

Effects of Bark Beetle Outbreaks on Forest Landscape Pattern in the Southern Rocky Mountains, U.S.A.

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