Curtailing succession: Removing conifers enhances understory light and growth of young aspen in mixed stands around Lake Tahoe, California and Nevada, USA

Berrill, John‐Pascal; Dagley, Christa M.; Coppeto, Stephanie A.; Gross, Shana

doi:10.1016/j.foreco.2017.06.001

Cited by 16 publications

(21 citation statements)

References 35 publications

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“…Prior research conducted at our study sites by Berrill and Dagley (2014) showed high within‐stand variability in stand density and tree species composition, and that regeneration was most abundant in areas of lower stand density with a higher proportion of aspen BA. Similarly, in a spatial pattern analysis, Pierce and Taylor () detected repulsion between aspen saplings (<5 cm dbh, >1.5 m height) and canopy trees, demonstrating the important role of understory light in the development of young aspen (Berrill et al ).…”

Section: Discussionmentioning

confidence: 85%

“…Permanent monitoring plots (1 ha in area) were installed over a 2‐year period in nine aspen‐conifer stands (4 plots in 2009, 5 plots in 2010) scheduled for conifer‐removal treatments. These stands surrounded Lake Tahoe, ranging in elevation from 1,900 to 2,260 m, with three located on the east side of the lake, three on the south, and three on the west (Berrill et al ). Aspen trees ≥10 cm dbh and conifer trees ≥20 cm dbh were mapped and measured pre‐treatment (Berrill & Dagley ).…”

Section: Methodsmentioning

confidence: 99%

“…On Lassen National Forest, Jones et al () found mechanical conifer removal treatments to be an effective strategy to stimulate aspen regeneration. A study reporting growth rates of aspen regeneration in the Lake Tahoe Basin found that restoration treatments with lower residual stand densities favored rapid regeneration of aspen and enhanced herbaceous vegetation cover (Berrill et al ). Less is known about other trees and plants found growing in association with aspen.…”

Section: Introductionmentioning

confidence: 99%

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Understory responses to restoration in aspen‐conifer forests around the Lake Tahoe Basin: residual stand attributes predict recovery

Dagley

Berrill

Coppeto

et al. 2020

Restoration Ecology

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The removal of conifers from aspen (Populus tremuloides) stands is being undertaken throughout the western United States to restore aspen for local-and landscape-level biodiversity. Current practices include mechanically removing conifers or hand thinning, piling, and burning cut conifers in and adjacent to aspen-conifer stands. To evaluate the effectiveness of restoration treatments, we examined tree regeneration and herbaceous vegetation cover in thinned, thinned and pile burned, and nonthinned control stands. Growth rates of small conifer saplings threatening to outcompete and replace aspen were also measured. Two to four years after pile burning, herbaceous vegetation cover within the footprint of burned piles (i.e. burn scars) was 35-73% of that in adjacent areas. Aspen was more likely to regenerate inside burn scars where fewer surrounding trees were true firs. Conifer seedlings were more likely to regenerate in burn scars where more of the surrounding trees were conifers (pine or fir) as opposed to aspen. Fir saplings had much slower growth than did aspen saplings. Overall, our findings show that restoration treatments are promoting desirable outcomes such as enhancing aspen regeneration but that follow-up treatments will be needed to remove numerous conifer seedlings becoming established after restoration activities. Eliminating conifers, while they are small, growing slowly, and contributing little to fuel loads may be an economical way to prolong restoration treatment effectiveness.

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Section: Discussionmentioning

confidence: 85%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Understory responses to restoration in aspen‐conifer forests around the Lake Tahoe Basin: residual stand attributes predict recovery

Dagley

Berrill

Coppeto

et al. 2020

Restoration Ecology

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“…This suggests that the lack of fire or other disturbance, which remove conifers and release aspen from competition is a driving cause for aspen decline in these areas. Restoration treatments found to promote aspen regeneration and growth include conifer removal alone [52, 37] or combined with prescribed fire [23]. Expansion between 1993 and 2017 was also affected by the percentage of conifers present in 1993 prior to burning.…”

Section: Discussionmentioning

confidence: 99%

“…Aspen are threatened by drought [35], climate change [36], and succession to conifer [37]. As conifers proceed to replace aspen throughout the west [12], aspen may be restricted to less favorable sites.…”

Section: Introductionmentioning

confidence: 99%

Multidecadal decline and recovery of aspen experiencing contrasting fire regimes: long-unburned, infrequent and frequent mixed-severity wildfire

Berrill

et al. 2020

Preprint

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Quaking aspen (Populus tremuloides) is a valued, minor component on western landscapes. It provides a wide range of ecosystem services and has been in decline throughout the arid west for the last century. This decline may be explained partially by the lack of fire on the landscape as aspen benefit from fire that eliminates conifer competition and stimulates reproduction through root suckering. Managers are interested in aspen restoration but there is a lack of knowledge about their spatial dynamics in response to fire. Our study area in northeastern California on the Lassen, Modoc and Plumas National Forests has experienced recent large mixed-severity wildfires where aspen was present, providing an opportunity to study the re-introduction of fire. We observed two time periods; a 54-year absence of fire from 1941 to 1993 preceding a 24-year period of wildfire activity from 1993 to 2017. We utilized aerial photos to delineate aspen stand size, location and succession to conifers. We chose aspen stands in areas where wildfires overlapped (twice-burned), where only a single wildfire burned, and areas that did not burn within the recent 24-year period. We looked at these same stands within the first period of fire exclusion for comparison (i.e., 1941-1993). In the absence of fire, all aspen stand areas declined and all stands experienced increases in conifer composition. After wildfire, stands that burned experienced a release from conifer competition and increased in stand area. Stands that burned twice or at high severity experienced a larger removal of conifer competition than stands that burned once at low severity, promoting aspen recovery and expansion. Stands with less edge:area ratio also expanded more with fire present. Across both time periods, stand movement, where aspen stand footprints were mostly in new areas compared to footprints of previous years, was highest in smaller stands. In the fire exclusion period, smaller stands exhibited greater changes in area and location (movement), highlighting their vulnerability to loss in the absence of disturbances that provide adequate growing space for aspen over time.

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Tree species composition and selection effects drive overstory and understory productivity in reforested oil sands mining sites

Xiao

Chen

2020

Land Degrad Dev

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Reforestation is a feasible option for the eventual restoration of biodiversity and ecosystem services on deforested oil‐sands mining sites. The associations between plant diversity and productivity spanning the different strata of restoration forests, in conjunction with specific factors that may impact these relationships, remain uncertain. We sampled 94 sites that encompassed conifer, mixed‐wood, and broadleaved overstory types as three exemplar substrates following the reforestation of oil‐sands mining sites in Alberta, Canada. We employed structural equation modeling to investigate the correlations between species diversity and aboveground biomass production spanning forest vegetation strata, while concurrently accounting for the effects of overstory composition, functional diversity/identity, soil fertility, and restoration age. We found that the relationships between species diversity and biomass were negative, or inconsequential across restoration forest strata. Overstory biomass was linked to the coniferous tree proportion and community‐weighted mean of leaf nitrogen, rather than the species and functional diversity of overstory trees. Further, overstory composition, diversity, and biomass were the key features involved in the diversity and biomass of understory strata. Our results demonstrated the importance of overstory tree species composition and selection effects toward driving overstory and understory productivity in restoration forests at post‐oil sands mining sites. Coniferous trees were observed to have lower leaf nutrient levels and negative impacts on the productivity and diversity of overstory and shrub layers. Therefore, it was recommended that a greater proportion of broadleaved trees should be incorporated to promote productivity and species diversity in restoration forests through the enhancement and utilization of available resources.

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Curtailing succession: Removing conifers enhances understory light and growth of young aspen in mixed stands around Lake Tahoe, California and Nevada, USA

Cited by 16 publications

References 35 publications

Understory responses to restoration in aspen‐conifer forests around the Lake Tahoe Basin: residual stand attributes predict recovery

Understory responses to restoration in aspen‐conifer forests around the Lake Tahoe Basin: residual stand attributes predict recovery

Multidecadal decline and recovery of aspen experiencing contrasting fire regimes: long-unburned, infrequent and frequent mixed-severity wildfire

Tree species composition and selection effects drive overstory and understory productivity in reforested oil sands mining sites

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