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Baltzer, Jennifer; Degré-Timmons, Geneviève; Day, Nicola; Cumming, Steve; Turetsky, Merritt; Johnstone, Jill — 2022-06-23 <p style="margin-bottom:11px;text-align: justify;">Increased fire activity due to climate change may impact the successional dynamics of boreal forests, with important consequences for caribou habitat. Early successional forests have been shown to support lower quantities of caribou forage lichens, but geographic variation in, and controls on, the rates of lichen recovery have been largely unexplored. In this study, we sampled across a broad region in northwestern Canada to compare lichen biomass accumulation in ecoprovinces, including the Saskatchewan Boreal Shield, the Northwest Territories Taiga Shield and Northwest Territories Taiga Plains, divided into North and South. We focused on the most valuable <i>Cladonia</i> species for boreal and barren ground caribou: <i>Cladonia mitis</i> and <i>C. arbuscula</i>, <i>C. rangiferina</i> and <i>C. stygia</i>, <i>C. stellaris</i> and <i>C. uncialis</i>. We developed new allometric equations to estimate lichen biomass from field measurements of lichen cover and height; allometries were consistent among ecoprovinces, suggesting generalizability. We then used estimates of lichen biomass to quantify patterns of lichen recovery in different stand types, ecoprovinces, and with time following stand-replacing fire. We used a hurdle model to account both for the heterogeneous nature of lichen presence (zero-inflation), and the range of abundance in stands where lichen was present. The first component of the hurdle model, a generalized linear model (GLM), identified stand age, stand type and ecoprovince as significant predictors of lichen presence. With a logistic growth model, a measure of lichen recovery (time to 50% asymptotic value) varied from 28 to 73 years, dependent on stand type and ecoprovince. The combined predictions of the hurdle model suggest the most rapid recovery of lichen biomass across our study region occurred in jack pine in the Boreal Shield (30 years), while stands located in the Taiga Plains (North and South) required a longer recovery period (approximately 75 years). These results provide a basis for estimating future caribou habitat that encompasses some of the large variation in fire effects on lichen abundance and vegetation types across the range of boreal and barren ground caribou in North America.</p>

Baltzer, Jennifer; Day, Nicola; White, Alison; Reid, Kirsten; Degré-Timmons, Geneviève; Cumming, Steve; Mack, Michelle; Turetsky, Merritt; Walker, Xanthe; Johnstone, Jill — 2022-05-24 <p style="text-align:justify;"><span><span>Climate change is altering disturbance regimes outside of historical norms, which can impact biodiversity by selecting for plants with particular traits. The relative impact of disturbance characteristics on plant traits and community structure may be mediated by environmental gradients. We aimed to understand how wildfire impacted understory plant communities and plant regeneration strategies along gradients of environmental conditions and wildfire characteristics in boreal forests. We established 207 plots (60m²) in recently burned stands and 133 plots in mature stands with no recent fire history in comparable gradients of stand type, site moisture (drainage), and soil organic layer (SOL) depth in two ecozones in Canada’s Northwest Territories. <a name="_Hlk43198784">At each plot, we recorded all vascular plant taxa in the understory</a> and measured the regeneration strategy (seeder, resprouter, survivor) in burned plots, along with seedbed conditions (mineral soil and bryophyte cover). Dispersal, longevity, and growth form traits were determined for each taxon. Fire characteristics measured included proportion pre-fire SOL combusted (fire severity), date of burn (fire seasonality), and pre-fire stand age (time following fire). Results showed understory community composition was altered by fire. However, burned and mature stands had similar plant communities in wet sites with deep SOL. In the burned plots, regeneration strategies were determined by fire severity, drainage, and pre- and post-fire SOL depth. Resprouters were more common in wet sites with deeper SOL and lower fire severity, while seeders were associated with drier sites with thinner SOL and greater fire severity. This led to drier burned stands being compositionally different from their mature counterparts and seedbed conditions were important. Our study highlights the importance of environment-wildfire interactions in shaping plant regeneration strategies and patterns of understory plant community structure across landscapes, and the overriding importance of SOL depth and site drainage in mediating fire severity, plant regeneration, and community structure.</span></span></p> <p style="margin-bottom:11px;"> </p>

Ogden, Emily; Cumming, Steven G.; Smith, Sharon L.; Turetsky, Merritt; Baltzer, Jennifer L. — 2023-06-20 This dataset contains active layer thickness and normalized difference vegetation index (NDVI) data for 135 permafrost monitoring sites located across a 10° latitudinal transect of the Northwest Territories, Canada. Included are two .csv files that contain the yearly active layer thickness and NDVI values for each site and the rate of change through time for both of those variables at each site. The rates of change were divided into early and late time periods (Early, 1984 to 2000; Late, 2001 to 2019). Additional site characteristics and climatic variables are included in the data files. Active layer thickness data was derived from ground thermal and thaw tube data that was collected by the Geological Survey of Canada across the network of permafrost monitoring sites. An R script outlining the statistical analyses for the publication “Permafrost thaw induces short term increase in vegetation productivity in the northwestern Arctic-Boreal” is included, as well as a text file which includes the code used to calculate NDVI from a collection of Landsat images processed in Google Earth Engine.

Jorgensen, Alexis; Alfaro-Sánchez, Raquel; Cumming, Steven G.; White, Alison L.; Degré-Timmons, Geneviève É.; Day, Nicola J.; Turetsky, Merritt; Johnstone, Jill F.; Walker, Xanthe J.; Baltzer, Jennifer L. — 2023-06-01 This data was gathered to explore patterns of vegetation recovery after fire in the boreal forests of the Northwest Territories, Canada. Vegetation and environmental data was collected from a chronosequence of sampling sites ranging from one to 275 years after fire covering both the Taiga Shield and Taiga Plains Ecoregions.<p><p> The dataset is comprised of three data sheets:<p> <ol type="1"> <li> Jorgensen et al_SpeciesRelativeAbundance includes presence and absence data per plot for a selection of vascular plant and lichen species, as well as associated environmental variables and site information. Each species has a "presence" column and an "absence" column, adding to five, indicating the number of quadrats per plot where the species was found. </li> <li> Jorgensen et al_VegetationCommunityComposition includes abundance indices (from 1-5) per plot for all vascular and non-vascular species used in manuscript ordinations (excluded: species present in only one plot, species causing anomalies - see manuscript for more information). </li> <li> Jorgensen et al_SeedlingSaplingCounts includes counts of the number of seedlings and saplings <1.3m tall per sampling plot for black spruce (Picea mariana), paper birch (Betula papyrifera), and trembling aspen (Populus tremuloides). </li>

Avgar, Tal; Brown, Glen S.; Thompson, Ian; Rodgers, Art R.; Mosser, Anna; Fryxell, John M.; Patterson, Brent R.; Newmaster, Steven G.; Reid, Doug E. B.; Turetsky, Merritt; Hagens, Jevon S.; Reid, Douglas E. B.; Shuter, Jennifer; Baker, James A.; Kittle, Andrew M.; Mallon, Erin E.; McGreer, Madeleine T.; Street, Garrett M.; Turetsky, Merritt J. — 2016-01-20 1. Movement patterns offer a rich source of information on animal behaviour and the ecological significance of landscape attributes. This is especially useful for species occupying remote landscapes where direct behavioural observations are limited. In this study, we fit a mechanistic model of animal cognition and movement to GPS positional data of woodland caribou (Rangifer tarandus caribou; Gmelin 1788) collected over a wide range of ecological conditions. 2. The model explicitly tracks individual animal informational state over space and time, with resulting parameter estimates that have direct cognitive and ecological meaning. Three biotic landscape attributes were hypothesized to motivate caribou movement: forage abundance (dietary digestible biomass), wolf (Canis lupus; Linnaeus, 1758) density and moose (Alces alces; Linnaeus, 1758) habitat. Wolves are the main predator of caribou in this system and moose are their primary prey. 3. Resulting parameter estimates clearly indicated that forage abundance is an important driver of caribou movement patterns, with predator and moose avoidance often having a strong effect, but not for all individuals. From the cognitive perspective, our results support the notion that caribou rely on limited sensory inputs from their surroundings, as well as on long-term spatial memory, to make informed movement decisions. Our study demonstrates how sensory, memory and motion capacities may interact with ecological fitness covariates to influence movement decisions by free-ranging animals.