Warning Signals of Adverse Interactions between Climate Change and Native Stressors in British Columbia Forests

Woods, Alex; Coates, K. David; Watts, Martin; Foord, Vanessa N.; Holtzman, Erin I.

doi:10.3390/f8080280

Cited by 10 publications

(7 citation statements)

References 50 publications

(87 reference statements)

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“…With respect to the analysis, the results only focused on how changes in tree growth resonate through an otherwise stationary system; everything else, including recruitment, background mortality, and disturbance, were held constant. While this allowed us to isolate the effect of tree growth, it ignored environmental changes that are simultaneously influencing biomass-dense forests through changes in the rates of tree mortality [8,54,74,75]. As the simulations consisted of single-species stands, potential effects of tree growth stimulation on rates of succession were also not considered.…”

Section: Discussionmentioning

confidence: 99%

Low Tree-Growth Elasticity of Forest Biomass Indicated by an Individual-Based Model

Hember

Kurz

2018

Forests

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Environmental conditions and silviculture fundamentally alter the metabolism of individual trees and, therefore, need to be studied at that scale. However, changes in forest biomass density (Mg C ha −1 ) may be decoupled from changes in growth (kg C year −1 ) when the latter also accelerates the life cycle of trees and strains access to light, nutrients, and water. In this study, we refer to an individual-based model of forest biomass dynamics to constrain the magnitude of system feedbacks associated with ontogeny and competition and estimate the scaling relationship between changes in tree growth and forest biomass density. The model was driven by fitted equations of annual aboveground biomass growth (G ag ), probability of recruitment (P r ), and probability of mortality (P m ) parameterized against field observations of black spruce (Picea mariana (Mill.) BSP), interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco), and western hemlock (Tsuga heterophylla (Raf.) Sarg.). A hypothetical positive step-change in mean tree growth was imposed half way through the simulations and landscape-scale responses were then evaluated by comparing pre-and post-stimulus periods. Imposing a 100% increase in tree growth above calibrated predictions (i.e., contemporary rates) only translated into 36% to 41% increases in forest biomass density. This corresponded with a tree-growth elasticity of forest biomass (ε G,SB ) ranging from 0.33 to 0.55. The inelastic nature of stand biomass density was attributed to the dependence of mortality on intensity of competition and tree size, which decreased stand density by 353 to 495 trees ha −1 , and decreased biomass residence time by 10 to 23 years. Values of ε G,SB depended on the magnitude of the stimulus. For example, a retrospective scenario in which tree growth increased from 50% below contemporary rates up to contemporary rates indicated values of ε G,SB ranging from 0.66 to 0.75. We conclude that: (1) effects of warming and increasing atmospheric concentrations of carbon dioxide and reactive nitrogen on biomass production are greatly diminished, but not entirely precluded, scaling up from individual trees to forest landscapes; (2) the magnitude of decoupling is greater for a contemporary baseline than it is for a pre-industrial baseline; and (3) differences in the magnitude of decoupling among species were relatively small. To advance beyond these estimates, studies must test the unverified assumptions that effects of tree size and stand competition on rates of recruitment, mortality, and growth are independent of climate change and atmospheric concentrations of carbon dioxide and nitrogen.

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Section: Discussionmentioning

confidence: 99%

Low Tree-Growth Elasticity of Forest Biomass Indicated by an Individual-Based Model

Hember

Kurz

2018

Forests

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“…Thus, even though snow added to the wind action, this damage could not be separated from the wind impact alone and both were included as windthrow. Considering the future, we recommend improving the understanding the impact of wet and heavy snowfall events on tree mortality since it is expected that this kind of events will increase in a climate change context (Lute et al, 2015;Woods et al, 2017).…”

Section: Predictormentioning

confidence: 99%

Post-cutting Mortality Following Experimental Silvicultural Treatments in Unmanaged Boreal Forest Stands

Girona

Morin

Lussier

et al. 2019

Front. For. Glob. Change

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Partial cutting has been recommended as an alternative harvesting method to ensure the sustainable management of boreal forests. The success of this approach is closely linked to the survival of residual trees as additional losses through mortality could affect post-cutting timber production at harvest. To better quantify post-cutting mortality in previously unmanaged boreal forests, we addressed two main questions:(1) what is the level of mortality 10 years after cutting? and (2) what ecological factors are involved in this phenomenon? Even-aged black spruce [Picea mariana (Mill.) B.S.P.] stands in the Canadian boreal forest were subjected to three experimental shelterwood treatments, a seed-tree treatment and an untreated control. Tree status (live/dead) was recorded prior to cutting and 10 years after cutting. Dead trees were classified as standing dead, overturned or broken. Ten years after experimental seed-tree treatment, 60% of residual trees were dead, compared to 30% for the shelterwood cuttings. Windthrow (overturned and broken trees) represented 80% of residual tree mortality; only the amount of overturning was influenced by treatment. Broken trees were associated with small-diameter trunks, stands having high growth prior to cutting, younger stands or forest plots located near to adjacent cuts (<200 m). Overturning was associated with a high harvesting intensity and large-diameter trees. Standing dead mortality was the most difficult to explain: it was related to untreated plots having suppressed and small-diameter trees. Based on these results, applying intermediate levels of harvest intensity could reduce post-cutting damage. Understanding tree mortality after cutting is essential to reduce economic losses, improve silvicultural planning and stand selection and ensure ultimately the sustainable harvest of North American boreal forests.

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“…Formerly, silviculturists viewed lodgepole pine ecosystems as resilient and relatively problem-free. This perception has changed in the 21 st Century as BC's great mountain pine beetle (Dendroctonus ponderosae) outbreak (Shore et al 2004) coincided with other stresses on lodgepole pine forests, including a growing incidence of stem and foliar diseases (Woods et al 2017), large wildfires (Ghoussoub 2017) and timber supply shortages (Burton 2010), as well as regional declines in woodland caribou (Rangifer tarandus caribou) populations (Cichowski and Williston 2005). One outcome of the confluence of forest management challenges is that silvicultural practices in lodgepole pine forests are now subject to increased professional and public scrutiny.…”

mentioning

confidence: 99%

Site preparation severity influences lodgepole pine plant community composition, diversity, and succession over 25 years

Haeussler

Kaffanke²,

Boateng

et al. 2017

Can. J. For. Res.

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Lodgepole pine (Pinus contorta var. latifolia Engelm.) ecosystems of central British Columbia face cumulative stresses, and management practices are increasingly scrutinized. We addressed trade-offs between “light-on-the-land” versus more aggressive silvicultural approaches by examining plant communities and indicator species (non-natives, berry producers, epiphytes, mycotrophs, pine rust alternate hosts) across a gradient of five or six site preparation treatments at the Bednesti trial (established 1987). We tested whether more severe site preparation (i) caused plant community composition to diverge from a 35- to 46-year-old reference forest, (ii) accelerated succession by hastening crown closure, or (iii) delayed succession by promoting seral species. Nonmetric multidimensional scaling (NMDS) ordination showed all treatments converging toward the reference forest composition. At 10 years, succession was incrementally delayed by more severe treatments; at 25 years, only burned windrows were still delayed. Mixed-effects models based on site preparation severity were better than crown closure models for 11 of 13 variables tested, suggesting that mostly belowground processes drive succession in these infertile ecosystems. Invasive hawkweeds persisted on all treatments at 25 years. Limited, contradictory data did not support using mechanical or fire treatments to reduce alternate hosts of pine stem rusts. Long-term trials such as Bednesti highlight the need for ecosystem-specific strategies and diverse approaches to accommodate conflicting benefits and risks of disturbance in forests.

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Warning Signals of Adverse Interactions between Climate Change and Native Stressors in British Columbia Forests

Cited by 10 publications

References 50 publications

Low Tree-Growth Elasticity of Forest Biomass Indicated by an Individual-Based Model

Low Tree-Growth Elasticity of Forest Biomass Indicated by an Individual-Based Model

Post-cutting Mortality Following Experimental Silvicultural Treatments in Unmanaged Boreal Forest Stands

Site preparation severity influences lodgepole pine plant community composition, diversity, and succession over 25 years

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