Trapping sites and VHF collar recovery locations for snowshoe hares.

<p>Hares were collared in Bonanza Creek Experimental Forest near Fairbanks, Alaska, from June 2008 to May 2012. Figure includes data previously published in Feierabend and Kielland [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0143543#pone.0143543.ref016" target="_blank">16</a>].</p

Relationship between estimated daily survival rate and body condition index for snowshoe hares.

<p>Estimates are shown for hares collared in the Conifer (black lines) and Deciduous (grey lines) trapping grids in July (solid lines) and November (dashed lines) (the months of highest and lowest snowshoe hare survival) in Bonanza Creek Experimental Forest near Fairbanks, Alaska, from June 2008 to May 2012. Estimates are based on the model <i>S</i> (Body Condition + Site + Month). Confidence intervals (95%, not shown) indicated some overlap between trapping grids within a season.</p

Estimated snowshoe hare densities in Bonanza Creek Experimental Forest near Fairbanks, Alaska, from June 2008 to June 2013.

<p>Estimates were based on live-capture of ear-tagged hares in June (J) and September (S) of each year. Error bars show SE.</p

Daily survival rate estimates for snowshoe hares.

<p>Hares were collared in the Conifer and Deciduous trapping grids in Bonanza Creek Experimental Forest near Fairbanks, Alaska, from June 2008 to May 2012. Estimates are based on the model <i>S</i> (Body Condition + Site + Month) and are reported for a mean body condition index of 10.4. Error bars represent 95% <i>CI</i>.</p

Proportion of snowshoe hare predation by predator species, season, and habitat type.

<p>Hares were collared in Bonanza Creek Experimental Forest near Fairbanks, Alaska, from June 2008 to May 2012. Habitat types are black spruce forest (BS), early successional forest (ES), and mixed forest (MIX). Only the habitats most frequently used by hares in our study are shown. Predators are goshawk (GOS), great horned owl (GHO), unidentified raptor (AVI), lynx (LNX), coyote (COY), and unidentified mammal (MAM). Sample size is given above each column.</p

Relationships between surface organic thickness and thaw depth (a) and surface organic thickness and volumetric soil moisture (b) across all sites (<em>n</em> = 18)

<p><strong>Figure 5.</strong> Relationships between surface organic thickness and thaw depth (a) and surface organic thickness and volumetric soil moisture (b) across all sites (<em>n</em> = 18). Solid markers represent unburned sites, open markers represent burned sites. Triangles=  sandy lowlands; circles=  silty uplands; squares=  rocky uplands.</p> <p><strong>Abstract</strong></p> <p>Discontinuous permafrost in the North American boreal forest is strongly influenced by the effects of ecological succession on the accumulation of surface organic matter, making permafrost vulnerable to degradation resulting from fire disturbance. To assess factors affecting permafrost degradation after wildfire, we compared vegetation composition and soil properties between recently burned and unburned sites across three soil landscapes (rocky uplands, silty uplands, and sandy lowlands) situated within the Yukon Flats and Yukon-Tanana Uplands in interior Alaska. Mean annual air temperatures at our study sites from 2011 to 2012 were relatively cold (−5.5 ° C) and favorable to permafrost formation. Burning of mature evergreen forests with thick moss covers caused replacement by colonizing species in severely burned areas and recovery of pre-fire understory vegetation in moderately burned areas. Surface organic layer thickness strongly affected thermal regimes and thaw depths. On average, fire caused a five-fold decrease in mean surface organic layer thickness, a doubling of water storage in the active layer, a doubling of thaw depth, an increase in soil temperature at the surface (−0.6 to +2.1 ° C) and at 1 m depth (−1.7 to +0.4 ° C), and a two-fold increase in net soil heat input. Degradation of the upper permafrost occurred at all burned sites, but differences in soil texture and moisture among soil landscapes allowed permafrost to persist beneath the active layer in the silty uplands, whereas a talik of unknown depth developed in the rocky uplands and a thin talik developed in the sandy lowlands. A changing climate and fire regime would undoubtedly influence permafrost in the boreal forest, but the patterns of degradation or stabilization would vary considerably across the discontinuous permafrost zone due to differences in microclimate, successional patterns, and soil characteristics.</p

Nonmetric multidimensional scaling (NMDS) ordination of plant community structure and correlations with selected vegetation characteristics (a) and environmental characteristics (b)

<p><strong>Figure 2.</strong> Nonmetric multidimensional scaling (NMDS) ordination of plant community structure and correlations with selected vegetation characteristics (a) and environmental characteristics (b). Points represent community structure at each site, and symbols differentiate between landscape types and treatment. Vectors show the direction and strength of the correlations. The ordination axes were rotated by the treatment variable (fire). The ordination axes represented 93% of the total variance in community structure, with 54% accounted for by Axis 1 and 39% by Axis 2.</p> <p><strong>Abstract</strong></p> <p>Discontinuous permafrost in the North American boreal forest is strongly influenced by the effects of ecological succession on the accumulation of surface organic matter, making permafrost vulnerable to degradation resulting from fire disturbance. To assess factors affecting permafrost degradation after wildfire, we compared vegetation composition and soil properties between recently burned and unburned sites across three soil landscapes (rocky uplands, silty uplands, and sandy lowlands) situated within the Yukon Flats and Yukon-Tanana Uplands in interior Alaska. Mean annual air temperatures at our study sites from 2011 to 2012 were relatively cold (−5.5 ° C) and favorable to permafrost formation. Burning of mature evergreen forests with thick moss covers caused replacement by colonizing species in severely burned areas and recovery of pre-fire understory vegetation in moderately burned areas. Surface organic layer thickness strongly affected thermal regimes and thaw depths. On average, fire caused a five-fold decrease in mean surface organic layer thickness, a doubling of water storage in the active layer, a doubling of thaw depth, an increase in soil temperature at the surface (−0.6 to +2.1 ° C) and at 1 m depth (−1.7 to +0.4 ° C), and a two-fold increase in net soil heat input. Degradation of the upper permafrost occurred at all burned sites, but differences in soil texture and moisture among soil landscapes allowed permafrost to persist beneath the active layer in the silty uplands, whereas a talik of unknown depth developed in the rocky uplands and a thin talik developed in the sandy lowlands. A changing climate and fire regime would undoubtedly influence permafrost in the boreal forest, but the patterns of degradation or stabilization would vary considerably across the discontinuous permafrost zone due to differences in microclimate, successional patterns, and soil characteristics.</p

Box plots of surface organic layer thickness (a), volumetric soil moisture (b), water stock (c), thaw depth (d), and net seasonal heat input (e) across landscape types and treatments (<em>n</em> = 17)

<p><strong>Figure 3.</strong> Box plots of surface organic layer thickness (a), volumetric soil moisture (b), water stock (c), thaw depth (d), and net seasonal heat input (e) across landscape types and treatments (<em>n</em> = 17). Note, one outlier from a low-severity burn in the rocky uplands was excluded. Two-way ANOVAs and post hoc tests (Tukey HSD and student's <em>t</em>-tests) were conducted. Significant differences (<em>p</em> < 0.05) between means are denoted by lowercase letters for treatment (unburned/burned) and uppercase letters for landscape type. Positioning of uppercase letters indicate the landscape-level means on the <em>y</em>-axes. Interactive effects of landscape and treatment (*<em>L</em> <b>×</b> <em>T</em>) are displayed when significant.</p> <p><strong>Abstract</strong></p> <p>Discontinuous permafrost in the North American boreal forest is strongly influenced by the effects of ecological succession on the accumulation of surface organic matter, making permafrost vulnerable to degradation resulting from fire disturbance. To assess factors affecting permafrost degradation after wildfire, we compared vegetation composition and soil properties between recently burned and unburned sites across three soil landscapes (rocky uplands, silty uplands, and sandy lowlands) situated within the Yukon Flats and Yukon-Tanana Uplands in interior Alaska. Mean annual air temperatures at our study sites from 2011 to 2012 were relatively cold (−5.5 ° C) and favorable to permafrost formation. Burning of mature evergreen forests with thick moss covers caused replacement by colonizing species in severely burned areas and recovery of pre-fire understory vegetation in moderately burned areas. Surface organic layer thickness strongly affected thermal regimes and thaw depths. On average, fire caused a five-fold decrease in mean surface organic layer thickness, a doubling of water storage in the active layer, a doubling of thaw depth, an increase in soil temperature at the surface (−0.6 to +2.1 ° C) and at 1 m depth (−1.7 to +0.4 ° C), and a two-fold increase in net soil heat input. Degradation of the upper permafrost occurred at all burned sites, but differences in soil texture and moisture among soil landscapes allowed permafrost to persist beneath the active layer in the silty uplands, whereas a talik of unknown depth developed in the rocky uplands and a thin talik developed in the sandy lowlands. A changing climate and fire regime would undoubtedly influence permafrost in the boreal forest, but the patterns of degradation or stabilization would vary considerably across the discontinuous permafrost zone due to differences in microclimate, successional patterns, and soil characteristics.</p

Monthly mean (±SE) soil temperatures at the surface (5 cm) and at depth (100 cm) for unburned (solid line) and burned (dotted line) sites by landscape type from September 2011 to August 2012 (<em>n</em> = 17)

<p><strong>Figure 4.</strong> Monthly mean (±SE) soil temperatures at the surface (5 cm) and at depth (100 cm) for unburned (solid line) and burned (dotted line) sites by landscape type from September 2011 to August 2012 (<em>n</em> = 17). Note, one outlier from a low-severity burn in the rocky uplands was excluded. Mean annual surface temperatures (MAST) and mean annual deep temperatures (MADT) are displayed in text boxes.</p> <p><strong>Abstract</strong></p> <p>Discontinuous permafrost in the North American boreal forest is strongly influenced by the effects of ecological succession on the accumulation of surface organic matter, making permafrost vulnerable to degradation resulting from fire disturbance. To assess factors affecting permafrost degradation after wildfire, we compared vegetation composition and soil properties between recently burned and unburned sites across three soil landscapes (rocky uplands, silty uplands, and sandy lowlands) situated within the Yukon Flats and Yukon-Tanana Uplands in interior Alaska. Mean annual air temperatures at our study sites from 2011 to 2012 were relatively cold (−5.5 ° C) and favorable to permafrost formation. Burning of mature evergreen forests with thick moss covers caused replacement by colonizing species in severely burned areas and recovery of pre-fire understory vegetation in moderately burned areas. Surface organic layer thickness strongly affected thermal regimes and thaw depths. On average, fire caused a five-fold decrease in mean surface organic layer thickness, a doubling of water storage in the active layer, a doubling of thaw depth, an increase in soil temperature at the surface (−0.6 to +2.1 ° C) and at 1 m depth (−1.7 to +0.4 ° C), and a two-fold increase in net soil heat input. Degradation of the upper permafrost occurred at all burned sites, but differences in soil texture and moisture among soil landscapes allowed permafrost to persist beneath the active layer in the silty uplands, whereas a talik of unknown depth developed in the rocky uplands and a thin talik developed in the sandy lowlands. A changing climate and fire regime would undoubtedly influence permafrost in the boreal forest, but the patterns of degradation or stabilization would vary considerably across the discontinuous permafrost zone due to differences in microclimate, successional patterns, and soil characteristics.</p

Topographic map of study area in interior Alaska

<p><strong>Figure 1.</strong> Topographic map of study area in interior Alaska. Dominant mineral soil textures are mapped with gray-scale symbology based on Karlstrom (<a href="http://iopscience.iop.org/1748-9326/8/3/035013/article#erl471090bib22" target="_blank">1964</a>) and Jorgenson <em>et al</em> (<a href="http://iopscience.iop.org/1748-9326/8/3/035013/article#erl471090bib20" target="_blank">2008</a>). The northern and southern boundaries of the discontinuous permafrost zone, from Jorgenson <em>et al</em> (<a href="http://iopscience.iop.org/1748-9326/8/3/035013/article#erl471090bib20" target="_blank">2008</a>), are represented with dashed lines. Study sites (<em>n</em> = 18) are indicated by open squares (rocky uplands), triangles (sandy lowlands), and circles (silty uplands). Fire perimeters and year of burn are shown for the recent fires studied.</p> <p><strong>Abstract</strong></p> <p>Discontinuous permafrost in the North American boreal forest is strongly influenced by the effects of ecological succession on the accumulation of surface organic matter, making permafrost vulnerable to degradation resulting from fire disturbance. To assess factors affecting permafrost degradation after wildfire, we compared vegetation composition and soil properties between recently burned and unburned sites across three soil landscapes (rocky uplands, silty uplands, and sandy lowlands) situated within the Yukon Flats and Yukon-Tanana Uplands in interior Alaska. Mean annual air temperatures at our study sites from 2011 to 2012 were relatively cold (−5.5 ° C) and favorable to permafrost formation. Burning of mature evergreen forests with thick moss covers caused replacement by colonizing species in severely burned areas and recovery of pre-fire understory vegetation in moderately burned areas. Surface organic layer thickness strongly affected thermal regimes and thaw depths. On average, fire caused a five-fold decrease in mean surface organic layer thickness, a doubling of water storage in the active layer, a doubling of thaw depth, an increase in soil temperature at the surface (−0.6 to +2.1 ° C) and at 1 m depth (−1.7 to +0.4 ° C), and a two-fold increase in net soil heat input. Degradation of the upper permafrost occurred at all burned sites, but differences in soil texture and moisture among soil landscapes allowed permafrost to persist beneath the active layer in the silty uplands, whereas a talik of unknown depth developed in the rocky uplands and a thin talik developed in the sandy lowlands. A changing climate and fire regime would undoubtedly influence permafrost in the boreal forest, but the patterns of degradation or stabilization would vary considerably across the discontinuous permafrost zone due to differences in microclimate, successional patterns, and soil characteristics.</p