It takes a few to tango: changing climate and fire regimes can cause regeneration failure of two subalpine conifers

Hansen, Winslow D.; Braziunas, Kristin H.; Rammer, Werner; Seidl, Rupert; Turner, Monica G.

doi:10.1002/ecy.2181

Cited by 106 publications

(98 citation statements)

References 116 publications

(247 reference statements)

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“…, Hansen et al. ). In the Alaskan boreal forest, for example, increased severity of large stand‐replacing fires (i.e., where all trees are killed) has caused regional transitions in postfire tree species composition from spruce to deciduous dominance (Johnstone et al.…”

Section: Introductionmentioning

confidence: 99%

“…, Hansen et al. ). Historically, subalpine forests followed an adaptive cycle (sensu Gunderson and Holling ) where forests burned, creating favorable conditions for seedling establishment, and succession led back to structurally and functionally similar mature forest (Romme , Turner et al.…”

Section: Introductionmentioning

confidence: 99%

“…State changes in forests are often difficult to identify because mature trees are long lived and tolerate a wide range of environmental conditions (Lloret et al 2012). However, large severe disturbances can catalyze rapid reorganization (Crausbay et al 2017, Hansen et al 2018). In the Alaskan boreal forest, for example, increased severity of large stand-replacing fires (i.e., where all trees are killed) has caused regional transitions in postfire tree species composition from spruce to deciduous dominance (Johnstone et al 2010, Mann et al 2012.…”

Section: Introductionmentioning

confidence: 99%

“…These systems are characterized by infrequent high-severity fires and are dominated by conifers, which must reestablish from seed. Early postfire tree seedling establishment shapes stand structure and species composition for decades (Turner et al 1997, Kashian et al 2005, making seedling establishment a critical determinant of postfire resilience , Hansen et al 2018. Historically, subalpine forests followed an adaptive cycle (sensu Gunderson and Holling 2003) where forests burned, creating favorable conditions for seedling establishment, and succession led back to structurally and functionally similar mature forest (Romme 1982, Holling 2001, Johnstone et al 2004, Allen et al 2014Fig.…”

Section: Introductionmentioning

confidence: 99%

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Origins of abrupt change? Postfire subalpine conifer regeneration declines nonlinearly with warming and drying

Hansen

Turner

2019

Ecological Monographs

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Robust tree regeneration following high‐severity wildfire is key to the resilience of subalpine and boreal forests, and 21st century climate could initiate abrupt change in forests if postfire temperature and soil moisture become less suitable for tree seedling establishment. Using two widespread conifer species, lodgepole pine (Pinus contorta var. latifolia) and Douglas‐fir (Pseudotsuga menziesii var. glauca), we conducted complementary experiments to ask (1) How will projected early‐ to mid‐21st‐century warming and drying affect postfire tree seedling establishment and mortality? (2) How does early seedling growth differ between species and vary with warming and drying? With a four‐year in situ seed‐planting experiment and a one growing season controlled‐environment experiment, we explored effects of climate on tree seedling establishment, growth, and survival and identified nonlinear responses to temperature and soil moisture. In our field experiment, warmer and drier conditions, consistent with mid‐21st‐century projections, led to a 92% and 76% reduction in establishment of lodgepole pine and Douglas‐fir. Within three years, all seedlings that established under warmer conditions died, as might be expected at lower elevations and lower latitudes of species’ ranges. Seedling establishment and mortality also varied with aspect; approximately 1.7 times more seedlings established on mesic vs. xeric aspects, and fewer seedlings died. In the controlled‐environment experiment, soil temperatures were 2.0°–5.5°C cooler than the field experiment, and warming led to increased tree seedling establishment, as might be expected at upper treeline or higher latitudes. Lodgepole pine grew taller than Douglas‐fir and produced more needles with warming. Douglas‐fir grew longer roots relative to shoots, compared with lodgepole pine, particularly in dry soils. Differences in early growth between species may mediate climate change effects on competitive interactions, successional trajectories, and species distributions. This study demonstrates that climate following high‐severity fire exerts strong control over postfire tree regeneration in subalpine conifer forests. Climate change experiments, such as those reported here, hold great potential for identifying mechanisms that could underpin fundamental ecological change in 21st‐century ecosystems.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Origins of abrupt change? Postfire subalpine conifer regeneration declines nonlinearly with warming and drying

Hansen

Turner

2019

Ecological Monographs

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“…Climate change is expected to directly alter the geographic distributions of tree species by affecting physiological processes that govern establishment, growth, and mortality, and indirectly by increasing the frequency and severity of disturbances (Dale et al 2001, Rehfeldt et al 2006, Lenoir et al 2008, Turner 2010, Walter et al 2017. Climate-mediated disturbances that are outside the range of historical variability may have profound impacts on species distributions through their effects on regeneration processes (Johnstone et al 2016, Hansen et al 2018.…”

Section: Introductionmentioning

confidence: 99%

Epidemic spruce beetle outbreak changes drivers of Engelmann spruce regeneration

et al. 2019

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Climate-mediated disturbances outside the range of historical variability can have severe consequences on vital, post-disturbance regeneration processes. High-elevation forests of the Rocky Mountains that are dominated by Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) are expected to be sensitive to climate change. Additionally, these forests have experienced recent epidemic spruce beetle (Dendroctonus rufipennis) outbreaks that have often resulted in >95% mortality of overstory Engelmann spruce. Therefore, the future distribution of Engelmann spruce forests depends largely on natural regeneration processes. We examined Engelmann spruce seedlings across gradients in soil moisture and stand structural conditions 20 yr post-disturbance on the Markagunt Plateau in southern Utah. All Engelmann spruce seedlings were mapped, measured, and aged, and aspects of stand structure and the microclimate were measured. The goal of our research was to infer processes affecting Engelmann spruce establishment by determining if patterns of advance regeneration that established before the outbreak (~60% of individuals) differed from seedlings that established during and immediately following the outbreak (combined into one group,~40% of individuals). A generalized linear multi-model approach identified that the density of advance regeneration (seedlings/saplings) was negatively influenced by historical competition with overstory trees. In contrast, post-outbreak regeneration was related to microclimate conditions, including positive relationships with climatic moisture deficit and July soil water content. All seedlings were not significantly clustered around Engelmann spruce snags; however, there was evidence of facilitation of post-outbreak seedlings by pre-outbreak seedlings at higher elevation sites with lower moisture deficit. Together, these findings suggest post-outbreak seedlings were not moisture-limited at lower elevations but instead encouraged by higher evapotranspiration. Moreover, facilitation at higher elevations likely resulted from how pre-outbreak seedlings modify snowpack and associated seedbed environments. Our study provides insight for managing Engelmann spruce after a beetle outbreak. In these forests, pre-and post-outbreak regeneration can increase resilience to climate-disturbance interactions, but are patchy and structured at different scales. Therefore, the presence of advance regeneration and the likelihood of post-outbreak seedlings depend on local environment (soil moisture and stand structure) and could be taken into account to most effectively plan post-disturbance planting activities.

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Can wildland fire management alter 21st‐century subalpine fire and forests in Grand Teton National Park, Wyoming, USA?

Hansen

Abendroth

Rammer³

et al. 2019

Ecological Applications

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In subalpine forests of the western United States that historically experienced infrequent, high‐severity fire, whether fire management can shape 21st‐century fire regimes and forest dynamics to meet natural resource objectives is not known. Managed wildfire use (i.e., allowing lightning‐ignited fires to burn when risk is low instead of suppressing them) is one approach for maintaining natural fire regimes and fostering mosaics of forest structure, stand age, and tree‐species composition, while protecting people and property. However, little guidance exists for where and when this strategy may be effective with climate change. We simulated most of the contiguous forest in Grand Teton National Park, Wyoming, USA to ask: (1) how would subalpine fires and forest structure be different if fires had not been suppressed during the last three decades? And (2) what is the relative influence of climate change vs. fire management strategy on future fire and forests? We contrasted fire and forests from 1989 to 2098 under two fire management scenarios (managed wildfire use and fire suppression), two general circulation models (CNRM‐CM5 and GFDL‐ESM2M), and two representative concentration pathways (8.5 and 4.5). We found little difference between management scenarios in the number, size, or severity of fires during the last three decades. With 21st‐century warming, fire activity increased rapidly, particularly after 2050, and followed nearly identical trajectories in both management scenarios. Area burned per year between 2018 and 2099 was 1,700% greater than in the last three decades (1989–2017). Large areas of forest were abruptly lost; only 65% of the original 40,178 ha of forest remained by 2098. However, forests stayed connected and fuels were abundant enough to support profound increases in burning through this century. Our results indicate that strategies emphasizing managed wildfire use, rather than suppression, will not alter climate‐induced changes to fire and forests in subalpine landscapes of western North America. This suggests that managers may continue to have flexibility to strategically suppress subalpine fires without concern for long‐term consequences, in distinct contrast with dry conifer forests of the Rocky Mountains and mixed conifer forest of California where maintaining low fuel loads is essential for sustaining frequent, low‐severity surface fire regimes.

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It takes a few to tango: changing climate and fire regimes can cause regeneration failure of two subalpine conifers

Cited by 106 publications

References 116 publications

Origins of abrupt change? Postfire subalpine conifer regeneration declines nonlinearly with warming and drying

Origins of abrupt change? Postfire subalpine conifer regeneration declines nonlinearly with warming and drying

Epidemic spruce beetle outbreak changes drivers of Engelmann spruce regeneration

Can wildland fire management alter 21st‐century subalpine fire and forests in Grand Teton National Park, Wyoming, USA?

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