Conifer expansion reduces the competitive ability and herbivore defense of aspen by modifying light environment and soil chemistry

Calder, W. John; Horn, Kevin J.; Clair, Samuel B. St.

doi:10.1093/treephys/tpr041

Cited by 60 publications

(56 citation statements)

References 35 publications

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“…In contrast, reduction in aspen regeneration growth with greater conifer dominance (Fig. 3) has been linked to changes in soil chemistry and shading to which aspen is sensitive (Calder et al 2011). These results suggest that the effects of facilitation and competition at the regeneration stage influence the development of mixed aspenconifer forests in two important ways.…”

Section: Discussionmentioning

confidence: 89%

Facilitation drives mortality patterns along succession gradients of aspen‐conifer forests

Calder

Clair

2012

Ecosphere

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Citation: Calder, W. J., and S. B. St. Clair. 2012. Facilitation drives mortality patterns along succession gradients of aspenconifer forests. Ecosphere 3(6):57. http://dx.doi.org/10.1890/ES12-00119.1Abstract. While it is well established that facilitation and competition are important structuring forces in plant communities, a clear understanding of the interactions between them and how they change through the life stages of plants and affect long-term plant community development is lacking. We have observed that conifer seedlings are rarely found growing in meadows but readily establish under adjacent aspen stands, particularly at the base of aspen trees, creating the potential for antagonistic interactions in later life stages. To examine these relationships and their potential consequences on forest community development, we characterized patterns of establishment, regeneration, and overstory mortality of aspen (Populus tremuloides) and subalpine fir (Abies lasiocarpa) along a stand composition gradient (aspen dominant ! mixed ! conifer dominant) that develops in seral aspen forests. We found strong stand effects on the establishment of both aspen and subalpine fir regeneration. Aspen regenerated into meadows from the forest boundary, reached peak densities underneath aspen stands, and decreased significantly in mixed and conifer dominated stands. In contrast, subalpine fir seedlings failed to regenerate in meadows, but established readily underneath aspen, mixed and conifer stands. Within stands, establishing subalpine fir seedlings were strongly aggregated around mature aspen trees, which increased the proximity of the two species 2-10 fold depending on subalpine fir age class and stand type. Both stand type and increased proximity of overstory aspen and fir trees drove mortality patterns of the two species in opposite directions. Overstory aspen mortality increased sharply along the stand composition gradient: aspen (7%), mixed (17%), conifer (49%), while subalpine fir wasn't significantly influenced by stand type. Proximity of overstory aspen and subalpine fir, was associated with increased (23) aspen mortality under all stand conditions but increased subalpine fir survival resulting in high aspen:fir mortality ratios that likely accelerate successional shifts toward conifer dominance. Our data suggest that environmental conditions that promote facilitator mortality may compromise the ability of facilitation-dependent forests to regenerate following disturbance. Maintenance of natural disturbance regimes appears to be critical in striking an ecological balance between facilitation and competition that promotes sustainability in succession-driven plant communities.

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Section: Discussionmentioning

confidence: 89%

Facilitation drives mortality patterns along succession gradients of aspen‐conifer forests

Calder

Clair

2012

Ecosphere

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“…Evidence from the literature suggests that the competitive interaction is driven through reductions in light and soil fertility associate with increasing conifer dominance (Stadt and Lieffers, 2000;Mallik et al, 2008). A recent study demonstrated that light reduction and shifts in soil chemistry that occur with increasing conifer dominance in aspen-conifer stands strongly impairs the physiology, growth potential and defense of aspen suckers (Calder et al, 2011).…”

Section: The Influence Of Successional Status On Aspen Regenerationmentioning

confidence: 99%

The influences of conifer succession, physiographic conditions and herbivory on quaking aspen regeneration after fire

Smith

O’Loughlin

Buck

et al. 2011

Forest Ecology and Management

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“…Aspen and conifer stands from semi-arid montane and subalpine forests differ considerably in soil microclimate [24][25][26][27], hydrology [24], litter quality [27,28], soil chemistry [27,29], soil microbial community structure [27] and SOC content and dynamics [25][26][27]. Woldeselassie et al [26] found that montane aspen stands in northern Utah had higher SOC stock (96.2 ± 26.7 Mg C ha −1 ) than adjacent conifer stands (66.9 ± 18.6 Mg C ha −1 ) in the top 60 cm of mineral soil.…”

Section: Introductionmentioning

confidence: 99%

Soil Organic Carbon Storage and Stability in the Aspen-Conifer Ecotone in Montane Forests in Utah, USA

Dobarco

Miegroet²

2014

Forests

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Abstract:To assess the potential impact of conifer encroachment on soil organic carbon (SOC) dynamics and storage in montane aspen-conifer forests from the interior western US, we sampled mineral soils (0-15 cm) across the aspen-conifer ecotones in southern and northern Utah and quantified total SOC stocks, stable SOC (i.e., mineral-associated SOC (MoM)), labile SOC (i.e., light fraction (LF), decomposable (CO 2 release during long-term aerobic incubations) and soluble SOC (hot water extractable organic carbon (HWEOC)). Total SOC storage (47.0 ± 16.5 Mg C ha −1 ) and labile SOC as LF (14.0 ± 7.10 Mg C ha −1 ), SOC decomposability (cumulative released CO 2 -C of 5.6 ± 3.8 g C g −1 soil) or HWEOC (0.6 ± 0.6 mg C g −1 soil) did not differ substantially with vegetation type, although a slight increase in HWEOC was observed with increasing conifer in the overstory. There were statistically significant differences (p = 0.035) in stable MoM storage, which was higher under aspen (31.2 ± 15.1 Mg C ha −1 ) than under conifer (22.8 ± 9.0 Mg C ha −1 ), with intermediate values under mixed (25.7 ± 8.8 Mg C ha −1 ). Texture had the greatest impact on SOC distribution among labile and stable fractions, with increasing stabilization in MoM and decreasing bio-availability of SOC with increasing silt + clay content. Only at lower silt + clay contents (40%-70%) could we discern the influence of vegetation on MoM content. This highlights the importance of chemical protection mechanisms for long-term C sequestration.

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Conifer expansion reduces the competitive ability and herbivore defense of aspen by modifying light environment and soil chemistry

Cited by 60 publications

References 35 publications

Facilitation drives mortality patterns along succession gradients of aspen‐conifer forests

Facilitation drives mortality patterns along succession gradients of aspen‐conifer forests

The influences of conifer succession, physiographic conditions and herbivory on quaking aspen regeneration after fire

Soil Organic Carbon Storage and Stability in the Aspen-Conifer Ecotone in Montane Forests in Utah, USA

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