Topographic and vegetation drivers of thermal heterogeneity along the boreal–grassland transition zone in western Canada: Implications for climate change refugia

Abstract

Climate change refugia are areas that are relatively buffered from contemporary climate change and may be important safe havens for wildlife and plants under anthropogenic climate change. Topographic variation is an important driver of thermal heterogeneity, but it is limited in relatively flat landscapes, such as the boreal plain and prairie regions of western Canada. Topographic variation within this region is mostly restricted to river valleys and hill systems, and their effects on local climates are not well documented. We sought to quantify thermal heterogeneity as a function of topography and vegetation cover within major valleys and hill systems across the boreal–grassland transition zone. Using iButton data loggers, we monitored local temperature at four hills and 12 river valley systems that comprised a wide range of habitats and ecosystems in Alberta, Canada ( N = 240), between 2014 and 2020. We then modeled monthly temperature by season as a function of topography and different vegetation cover types using general linear mixed effect models. Summer maximum temperatures ( T max ) varied nearly 6°C across the elevation gradient sampled. Local summer mean ( T mean ) and maximum ( T max ) temperatures on steep, north‐facing slopes (i.e., low levels of potential solar radiation) were up to 0.70°C and 2.90°C cooler than highly exposed areas, respectively. T max in incised valleys was between 0.26 and 0.28°C cooler than other landforms, whereas areas with greater terrain roughness experienced maximum temperatures that were up to 1.62°C cooler. We also found that forest cover buffered temperatures locally, with coniferous and mixedwood forests decreasing summer T mean from 0.23 to 0.72°C and increasing winter T min by up to 2°C, relative to non‐forested areas. Spatial predictions of temperatures from iButton data loggers were similar to a gridded climate product (ClimateNA), but the difference between them increased with potential solar radiation, vegetation cover, and terrain roughness. Species that can track their climate niche may be able to compensate for regional climate warming through local migrations to cooler microsites. Topographic and vegetation characteristics that are related to cooler local climates should be considered in the evaluation of future climate change impacts and to identify potential refugia from climate change.

Oil sands restoration with warm‐adapted trees improves outcomes under moderate but not severe warming scenarios

“…Because an increase of 1°C in the temperature tolerance of local populations may not be sufficient to allow them to survive projected future climate changes, we also evaluated some even more southerly populations. We ran simulations based on theoretical populations for which tolerances were increased by 3°C (hereafter Pop+3) for P. banksiana and P. tremuloides , but not for P. glauca , as populations of this species are found only in warmer climates that are also significantly wetter (e.g., eastern Canada) or in locally sheltered conditions (e.g., shaded river valley slopes in southern Alberta, Estevo et al, 2022).…”

Topography influences diurnal and seasonal microclimate fluctuations in hilly terrain environments of coastal California

“…This difference in sunlight exposure is likely a key factor explaining the canopy effects observed exclusively during the summer season. These effects are pronounced due to variations in canopy cover, with summer showing a greater seasonality because of the trees providing more effective shading during this period [54,55]. A recent study at Pepperwood Preserve reported that site aspect was the most important determinant of species distributions of trees [42].…”

Topography‐driven microclimate gradients shape forest structure, diversity, and composition in a temperate refugial forest

“…Topographic variation can also drive shifts in forest structure, diversity, and composition along local gradients (Jucker et al., 2018 ; Marca‐Zevallos et al., 2022 ; Russo et al., 2005 ). Therefore, the structure of the forest canopy, coupled with fine‐scale heterogeneity in topography, can play a crucial role in buffering microclimate conditions (Estevo et al., 2022 ; Lawrence et al., 2021 ; Zellweger et al., 2020 ), maintaining climate‐change refugia as macroclimate changes (Dobrowski, 2011 ; Landuyt et al., 2019 ; Rita et al., 2021 ). We define microclimate buffering in the context of the northern hemisphere temperate growing season (approximately May to October) to include decreased air and soil temperatures and increased soil moisture and relative humidity that can occur due to the presence of the forest overstory (De Frenne et al., 2021 ), and due to underlying topographic features ( e.g.…”

“…Therefore, the structure of the forest canopy, coupled with fine-scale heterogeneity in topography, can play a crucial role in buffering microclimate conditions (Estevo et al, 2022;Lawrence et al, 2021;Zellweger et al, 2020), maintaining climate-change refugia as macroclimate changes (Dobrowski, 2011;Landuyt et al, 2019;Rita et al, 2021). We define microclimate buffering in the context of the northern hemisphere temperate growing season (approximately May to October) to include decreased air and soil temperatures and increased soil moisture and relative humidity that can occur due to the presence of the forest overstory (De Frenne et al, 2021), and due to underlying topographic features (e.g., elevational depressions or valleys, sheltered slopes, north-facing aspects) and hydrologic features (e.g., presence of groundwater springs and seeps) (Cartwright et al, 2020;Morelli et al, 2016).…”