Low‐density aspen seedling establishment is widespread following recent wildfires in the western United States

Kreider, Mark R.; Yocom, Larissa L.

doi:10.1002/ecy.3436

Cited by 9 publications

(4 citation statements)

References 30 publications

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“…In our model, aspen only increased when serotinous pines started to decline. Consistent with our modeling results, recent studies showed that aspen and other deciduous trees could become more abundant with increased fire activity (Kreider & Yocom, 2021; Mack et al, 2021). However, of the three strategies, resprouters were most resilient, as their density declined the least as fire rotation declined and eventually was extirpated when fire rotation reached 6 years.…”

Section: Discussionsupporting

confidence: 92%

Regeneration strategies and forest resilience to changing fire regimes: Insights from a Goldilocks model

Ramiadantsoa

Ratajczak

Turner

2023

Ecology

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Disturbances are ubiquitous in ecological systems, and species have evolved a range of strategies to resist or rebound following disturbance. Understanding how the presence and complementarity of regeneration traits will affect community responses to disturbance is increasingly urgent as disturbance regimes shift beyond their historical ranges of variability. We define “disturbance niche” as a species' fitness across a range of disturbance sizes and frequencies that can reflect the fundamental or realized niche, that is, whether the species occurs alone or with other species. We developed a model of intermediate complexity (i.e., a Goldilocks model) to infer the disturbance niche. We parameterized the model for subalpine forests in Yellowstone National Park (USA) adapted to infrequent stand‐replacing fires and included the three major tree‐regeneration strategies: (1) obligate seeders that rely on ex situ seeding into burned areas (non‐serotinous lodgepole pine, Pinus contorta var. latifola), (2) obligate seeders that depend on in situ seedbanks (serotinous lodgepole pine, Pinus contorta var. latifola), and (3) species that can resprout from surviving roots following fire (quaking aspen, Populus tremuloides). Our results showed which regeneration strategies increase or decrease in prevalence as fire rotation declines. Non‐serotinous pines were extirpated when fire rotation was below 50 years in a monoculture and 100 years in a mixed forest; serotinous pines were extirpated when fire rotation was below 20 years; and aspen was extirpated when fire rotation fell below 6 years. The fundamental and realized disturbance niches pinpointed the key mechanisms limiting regeneration for each strategy, namely, increasing fire size for non‐serotinous pine (ex situ seeders), decreasing fire frequency for serotinous pine (in situ seeders), and interspecific competition for aspen (resprouters). In a mixed forest, the three regeneration strategies were complementary and each dominated at different combinations of fire size and frequency. Consequently, diversity of regeneration strategies enhanced forest resilience to declining fire rotations. Despite its simplicity, our Goldilocks model produced realistic dynamics and could be readily adapted to other disturbance‐prone ecosystems to explore the generality of these results. The disturbance niche is a key concept for anticipating community resilience to changing disturbance regimes.

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Section: Discussionsupporting

confidence: 92%

Regeneration strategies and forest resilience to changing fire regimes: Insights from a Goldilocks model

Ramiadantsoa

Ratajczak

Turner

2023

Ecology

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“…Although medium-sized fires had higher mean severity, large fires may have more negative ecosystem impacts, depending on the vegetation [64], because large fires include larger patches that burn at high severity which may cause delayed vegetation recovery. As well, dispersal and germination of seeds may be hampered over large distances, such as those present in large fire scars [65,66]. Notably, we detected large proportions of 'unchanged' severity in large fires, potentially indicating the presence of unburned refugia in the interior of many of fires.…”

Section: Large Fires Have More Variable Burn Severities Than Medium-s...mentioning

confidence: 73%

Fire Regimes of Utah: The Past as Prologue

Birch,

Lutz

2023

Fire

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(1) Background: Satellite monitoring of fire effects is widespread, but often satellite-derived values are considered without respect to the characteristic severity of fires in different vegetation types or fire areas. Particularly in regions with discontinuous vegetation or narrowly distributed vegetation types, such as the state of Utah, USA, specific characterization of satellite-derived fire sensitivity by vegetation and fire size may improve both pre-fire and post-fire management activities. (2) Methods: We analyzed the 775 medium-sized (40 ha ≤ area < 400 ha) and 697 large (≥400 ha) wildfires that occurred in Utah from 1984 to 2022 and assessed burn severity for all vegetation types using the differenced Normalized Burn Ratio. (3) Results: Between 1984–2021, Utah annually experienced an average of 38 fires ≥ 40 ha that burned an annual average of 58,242 ha with a median dNBR of 165. Fire was heavily influenced by sagebrush and shrubland vegetation types, as these constituted 50.2% (17% SD) of area burned, a proportion which was relatively consistent (18% to 79% yr−1). Medium-sized fires had higher mean severity than large fires in non-forested vegetation types, but forested vegetation types showed the reverse. Between 1985 and 2021, the total area burned in fires ≥ 40 ha in Utah became more concentrated in a smaller number of large fires. (4) Conclusions: In Utah, characteristic fire severity differs both among vegetation types and fire sizes. Fire activity in the recent past may serve as an informative baseline for future fire, although the long period of fire suppression in the 20th century suggests that future fire may be more active. Fire managers planning prescribed fires < 400 ha in forests may find the data from medium-sized fires more indicative of expected behavior than statewide averages or vegetation type averages, both of which are weighted to large fires.

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“…Our burned sites also experienced beetle-kill, so we cannot rule out whether the combination of wildfire and beetle kill, or just wildfire alone, was necessary for aspen seedling establishment. Yet, several other studies have documented the fire-facilitated establishment of aspen by seed, making it likely that wildfire was the primary catalyst of this upward range shift (Fairweather et al, 2014;Kreider & Yocom, 2021). Burn severity did not seem to impact aspen seedling abundance in this study as it has in others (Gill et al, 2017) emphasize that not all disturbance types are equal, supporting other studies documenting the key importance of particular disturbances, such as wildfire and forest harvesting, in facilitating range shifts of shade-intolerant species (Brice et al, 2020;Johnstone & Chapin, 2003;Landhäusser et al, 2010).…”

Section: Disturbances Vary In Their Impact On Species Range Shiftsmentioning

confidence: 99%

“…Aspen's life history traits suggest that range expansion at its leading edge may require a catalyst such as wildfire (Brown et al, 2006; Kulakowski et al, 2004; Romme et al, 2001). Aspen's primary mode of reproduction is asexual, via resprouting from its roots in response to canopy mortality; however, it also has small, wind‐dispersed seeds and studies have documented aspen regeneration from seed after disturbance events (Fairweather et al, 2014; Kreider & Yocom, 2021; Landhäusser et al, 2010; Quinn & Wu, 2001; Romme et al, 1997). Aspen seedling establishment is associated with moderate temperatures, high‐light environments, thin soil organic matter layers and microsites that capture moisture (Lafleur et al, 2015; Landhäusser et al, 2019; McDonough, 1979; Schott et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Wildfire catalyzes upward range expansion of trembling aspen in southern Rocky Mountain beetle‐killed forests

Nigro

Rocca

Battaglia

et al. 2021

Journal of Biogeography

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Aim Climate warming is expected to drive upward and poleward shifts at the leading edge of tree species ranges. Disturbance has the potential to accelerate these shifts by altering biotic and abiotic conditions, though this potential is likely to vary by disturbance type. In this study, we assessed whether recent wildfires and spruce beetle outbreaks promoted upward range expansion of trembling aspen. Location The San Juan Mountains of southern Colorado, USA (37°34′–37°50′N, 106°49′–107°21′W). Taxon Populus tremuloides. Methods We used aerial imagery to determine the upper elevational limit of adult aspen and conducted seedling surveys at and above this upper limit in burned and unburned areas, which had already incurred high canopy mortality due to spruce bark beetle (Dendroctonus rufipennis) outbreaks. We compared characteristics of burned versus unburned bark beetle‐killed sites and assessed microsite conditions related to aspen seedling establishment using generalized linear models and interaction indices. Results Aspen seedling establishment occurred upslope of its previous range within burns, but not in unburned areas, despite severe beetle‐driven canopy mortality across all sites before the fire. Aspen seedling establishment was associated more with the light and mineral soil created by fire than the presence of nearby seed sources. Aspen seedlings were associated with nurse objects such as logs and rocks at the highest elevations, where these objects may ameliorate a range of stressors associated with the high elevation range boundary. Main conclusions Not all disturbance types are equal in promoting tree species migrations at the leading edge. Range shifts can be highly localized, and microsites are important for driving local range expansions in transitional environments. The mosaic of future disturbances across the landscape will drive forest compositional shifts, depending on the disturbance types and the species they promote.

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Low‐density aspen seedling establishment is widespread following recent wildfires in the western United States

Cited by 9 publications

References 30 publications

Regeneration strategies and forest resilience to changing fire regimes: Insights from a Goldilocks model

Regeneration strategies and forest resilience to changing fire regimes: Insights from a Goldilocks model

Fire Regimes of Utah: The Past as Prologue

Wildfire catalyzes upward range expansion of trembling aspen in southern Rocky Mountain beetle‐killed forests

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