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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>

Johnstone, Jill; Greuel, Ruth; Hart, Sarah; Truchon-Savard, Alexandre; McLoughlin, Philip — 2021-02-18 <p>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>

Aubin, Isabelle; Cardou, Françoise; Munson, Alison; Anand, Madhur; Arsenault, André; Bell, F. Wayne; Bergeron, Yves; Boulangeat, Isabelle; Delagrange, Sylvain; Fenton, Nicole J.; Gravel, Dominique; Hébert, François; Johnstone, Jill; Macdonald, S. Ellen; Mallik, Azim; McIntosh, Anne C.S.; McLaren, Jennie R.; Messier, Christian; Morris, Dave; Shipley, Bill; Sirois, Luc; Thiffault, Nelson; Boisvert-Marsh, Laura; Kumordzi, Bright B. — 2022-04-18 <p class="MsoPlainText">Intraspecific trait variability (ITV) provides the material for species adaptation to environmental changes. To advance our understanding of how ITV can contribute to species adaptation to a wide range of environmental conditions, we studied five widespread understory forest species exposed to both continental-scale climate gradients, and local soil and disturbance gradients. We investigated the environmental drivers of between-site leaf and root trait variation, and tested whether higher between-site ITV was associated with increased trait sensitivity to environmental variation (i.e. environmental fit).</p> <p class="MsoPlainText">We measured morphological (specific leaf area: SLA, specific root length: SRL) and chemical traits (Leaf and Root N, P, K, Mg, Ca) of five forest understory vascular plant<span style="font-family:KievitWeb , sans-serif;font-size:medium;"> </span>species at 78 sites across Canada. A total of 261 species-by-site combinations spanning ~4300 km were sampled, capturing important abiotic and biotic environmental gradients (neighbourhood composition, canopy structure, soil conditions, climate). We used multivariate and univariate linear mixed models to identify drivers of ITV and test the association of between-site ITV with environmental fit.</p> <p class="MsoPlainText">Between-site ITV of leaf traits was primarily driven by canopy structure and climate. Comparatively, environmental drivers explained only a small proportion of variability in root traits: these relationships were trait-specific and included soil conditions (Root P), canopy structure (Root N) and neighbourhood composition (SRL, Root K). Between-site ITV was associated with increased environmental fit only for a minority of traits, primarily in response to climate (SLA, Leaf N, SRL).</p> <p class="MsoPlainText">Synthesis. By studying how ITV is structured along environmental gradients among species adapted to a wide range of conditions, we can begin to understand how individual species might respond to environmental change. Our results show that generalizable trait-environment relationships occur primarily aboveground and only accounted for a small proportion of variability. For our group of species with broad ecological niches, variability in traits was only rarely associated with higher environmental fit, and primarily along climatic gradients. These results point to promising research avenues on the various ways in which trait variation can affect species performance along different environmental gradients.</p> https://creativecommons.org/publicdomain/zero/1.0/