Radial growth response and vegetative sprouting of aspen following release from competition due to insect-induced conifer mortality

Bretfeld, Mario; Doerner, James P.; Franklin, Scott B.

doi:10.1016/j.foreco.2015.03.006

Cited by 20 publications

(20 citation statements)

References 54 publications

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“…Even among the 13 aspen-conifer (subalpine fir) stands, fire evidence was lacking, 10 of these plots had >1:2 ratio of recruitmentsized suckers to overstory aspen, and few plots had many young firs (Appendix S3); suggesting a relative equilibrium between aspen and conifers (e.g., Zier and Baker 2006). Subalpine fir is slow growing (Alexander et al 1984) and periodic disturbance (e.g., windthrow, disease) in aspen-conifer stands can create canopy openings that enable recurrent aspen suckering (Smith et al 2011, Bretfeld et al 2015.…”

Section: Aspen Tree Age-and Size-class Distributions Indicate Fire Inmentioning

confidence: 99%

Climate and disturbance influence self‐sustaining stand dynamics of aspen (Populus tremuloides) near its range margin

Shinneman

McIlroy

2019

Ecological Applications

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Species that are primarily seral may form stable (self‐sustaining) communities under certain disturbance regimes or environmental conditions, yet such populations may also be particularly vulnerable to ecological change. Aspen (Populus spp.) are generally considered seral throughout the Northern Hemisphere, including P. tremuloides, the most widely distributed tree species in North America. Recent declines in aspen populations have occurred, especially along drought‐sensitive margins of its range and where fire exclusion and herbivory have promoted community transition. However, aspen also forms stable stands, and examination of the mechanisms that influence persistence can offer conservation insights, especially where populations are vulnerable to changing climate or altered disturbance dynamics. We sampled tree age and stand characteristics of isolated aspen forests in the arid Great Basin (USA) to determine if (1) aspen communities are more fire‐dependent and seral or fire‐independent and stable; (2) ungulate browsing inhibits aspen stability; and (3) temporal patterns of vegetative reproduction (i.e., ramet establishment or “suckering”) are correlated with climate. Aspen size and age class densities strongly fit negative exponential distributions, whether grouped geographically or by functional type, suggesting landscape‐scale persistence. Continuous age distributions and high proportions of recruitment‐sized to overstory trees suggest stability at stand scales, with exceptions including stands with higher browsing pressure. Few stands had evidence of fire, and relationships between dead tree size and variability in live tree size suggest a lack of fire dependency. Several 5‐yr averaged climate variables and one sea surface temperature index were correlated with aspen ramet establishment densities over time, with strongest relationships occurring ~5 yr prior to establishment year, often followed by inverse relationships ~1 yr after. Indeed, aspen establishment density for a recent 41‐yr period was reliably reconstructed using antecedent climate conditions derived from a single drought index. Temporally synchronized aspen ramet establishment across the study region may be due to climate‐driven storage of nonstructural carbohydrate reserves in clonal root systems later used for regeneration. Complex regeneration dynamics of these self‐sustaining aspen stands, especially sensitivity to climate variability, suggest they may serve as harbingers of ecological change in the arid Great Basin and in other aspen populations near their range margin.

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Section: Aspen Tree Age-and Size-class Distributions Indicate Fire Inmentioning

confidence: 99%

Climate and disturbance influence self‐sustaining stand dynamics of aspen (Populus tremuloides) near its range margin

Shinneman

McIlroy

2019

Ecological Applications

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“…Following repeated and heavy defoliation, trees may lose vigor and cannot acquire adequate amounts of carbohydrates to support radial growth (Deslauriers, Caron, & Rossi, 2015;Hudgeons et al, 2007;Kosola, Dickmann, Paul, & Parry, 2001). Where some trees die as a result of insect outbreaks or drought, reductions in competition levels could lead to increases in growth of surviving trees (Axelson, Alfaro, & Hawkes, 2009;Berg, Henry, Fastie, De Volder, & Matsuoka, 2006;Bretfeld, Doerner, & Franklin, 2015).…”

Section: Effects Of Insect Outbreaks On Forest Declinementioning

confidence: 99%

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

Chen

Huang

Dawson

et al. 2017

Global Change Biology

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Insects, diseases, fire and drought and other disturbances associated with global climate change contribute to forest decline and mortality in many parts of the world. Forest decline and mortality related to drought or insect outbreaks have been observed in North American aspen forests. However, little research has been done to partition and estimate their relative contributions to growth declines. In this study, we combined tree-ring width and basal area increment series from 40 trembling aspen (Populus tremuloides Michx.) sites along a latitudinal gradient (from 52° to 58°N) in western Canada and attempted to investigate the effect of drought and insect outbreaks on growth decline, and simultaneously partition and quantify their relative contributions. Results indicated that the influence of drought on forest decline was stronger than insect outbreaks, although both had significant effects. Furthermore, the influence of drought and insect outbreaks showed spatiotemporal variability. In addition, our data suggest that insect outbreaks could be triggered by warmer early spring temperature instead of drought, implicating that potentially increased insect outbreaks are expected with continued warming springs, which may further exacerbate growth decline and death in North America aspen mixed forests.

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“…A previous study reported that an outbreak of forest tent caterpillar in the 1980s contributed to severe decline in western Canadian aspen forest (Hogg & Schwarz, 1999). Consequently, in addition to the main driver of drought, it is very likely that a variety of factors such as insects and resource competition have been, more or less, related to this growth reduction and declination in aspen growth (DeByle et al, 1987;Hogg et al, 2002;Parry et al, 2003;Allen et al, 2010;Luo & Chen, 2013;Bretfeld et al, 2015).…”

Section: Relationship Between Growth and Temporal Variability Of Droumentioning

confidence: 99%

Drought causes reduced growth of trembling aspen in western Canada

Chen

Huang

Alam

et al. 2017

Global Change Biology

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Adequate and advance knowledge of the response of forest ecosystems to temperature-induced drought is critical for a comprehensive understanding of the impacts of global climate change on forest ecosystem structure and function. Recent massive decline in aspen-dominated forests and an increased aspen mortality in boreal forests have been associated with global warming, but it is still uncertain whether the decline and mortality are driven by drought. We used a series of ring-width chronologies from 40 trembling aspen (Populus tremuloides Michx.) sites along a latitudinal gradient (from 52° to 58°N) in western Canada, in an attempt to clarify the impacts of drought on aspen growth by using Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI). Results indicated that prolonged and large-scale droughts had a strong negative impact on trembling aspen growth. Furthermore, the spatiotemporal variability of drought indices is useful for explaining the spatial heterogeneity in the radial growth of trembling aspen. Due to ongoing global warming and rising temperatures, it is likely that severer droughts with a higher frequency will occur in western Canada. As trembling aspen is sensitive to drought, we suggest that drought indices could be applied to monitor the potential effects of increased drought stress on aspen trees growth, achieve classification of eco-regions and develop effective mitigation strategies to maintain western Canadian boreal forests.

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Radial growth response and vegetative sprouting of aspen following release from competition due to insect-induced conifer mortality

Cited by 20 publications

References 54 publications

Climate and disturbance influence self‐sustaining stand dynamics of aspen (Populus tremuloides) near its range margin

Climate and disturbance influence self‐sustaining stand dynamics of aspen (Populus tremuloides) near its range margin

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

Drought causes reduced growth of trembling aspen in western Canada

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