High latitude ecosystems are projected to experience the greatest rise in temperatures (IPCC, 2013), and correspondingly this could result in an increase in the evaporative demand leading to enhanced drought stress for plants (Angert et al., 2005 Dai, 2013 Williams et al., 2013). 0.5 petagrams of carbon per year, and storing approximately one-third of the global terrestrial carbon (Bradshaw & Warkentin, 2015 Bradshaw et al., 2009 Pan et al., 2011).īoreal forests are experiencing rapid climate change including rising temperatures (Choi & Kim, 2018 Price et al., 2013), altered precipitation patterns (Kjellström, 2004), and an increased frequency of summer drought stress (Ma et al., 2012). Boreal forests also play a critical role in the global carbon cycle (Goodale et al., 2002) sequestering ca. Given their wide distribution, boreal forests regulate water and energy fluxes over a vast area and thus play an important role in global hydrology and climatology (Baldocchi et al., 2000 Bonan, 2008 Chalita & Le Treut, 1994 Chen et al., 2018 Price et al., 2013). They are located between 45° and 70° north latitude, with two-thirds of all boreal forests located in Eurasia (Larsen, 1980). Globally, boreal forests cover approximately 12% of the earth's surface (Launiainen et al., 2019), representing the second largest biome behind tropical forests (Bonan, 2008). The historical 2018 drought registered across Central and Northern Europe, and considered the most severe in the last 250 years (MSB, 2017 Schuldt et al., 2020), had major impacts on northern boreal forests, including severe tree-level stress, record low stream flows, and changes in water and carbon fluxes (Gómez-Gener et al., 2020 Hari et al., 2020 Lindroth et al., 2020 Schuldt et al., 2020). This study highlights unique species-specific responses to drought, which are additionally driven by a codependent interaction among tree size, relative topographic position, and unique regional climate conditions. Despite lower Q DZ during severe drought, drought spells were interspersed with small precipitation events and overcast conditions, and Q DZ returned to pre-drought conditions relatively quickly. Overall, Q DZ reductions (using non-drought Q DZ as reference) were less pronounced in larger trees during severe drought, but there was a species-specific pattern: Q DZ reductions were greater in pine trees at high elevations and greater in spruce trees at lower elevations. In general, pine showed a greater Q DZ control compared to spruce during periods of severe drought (standardized precipitation–evapotranspiration index: SPEI < −1.5), suggesting that the latter are more sensitive to drought. We monitored 30 Pinus sylvestris (pine) and 30 Picea abies (spruce) trees distributed across a topographic gradient in northern Sweden. ![]() More specifically, we examined how tree species, size, and topographic position affected drought response in high-latitude mature boreal forest trees. Here, we tested how daily whole-tree transpiration ( Q, Liters day −1) and Q normalized for mean daytime vapor pressure deficit ( Q DZ, Liters day −1 kPa −1) were affected by the historic 2018 drought in Europe. However, most drought-related studies on high-latitude boreal forests (>50°N) have been conducted in North America, with few studies quantifying the response in European and Eurasian boreal forests. Trees in northern latitude ecosystems are projected to experience increasing drought stress as a result of rising air temperatures and changes in precipitation patterns in northern latitude ecosystems.
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