How tree species, tree size, and topographical location influenced tree transpiration in northern boreal forests during the historic 2018 drought. (5th May 2021)

• Record Type: Journal Article
• Authors: Gutierrez Lopez, Jose; Tor‐ngern, Pantana; Oren, Ram; Kozii, Nataliia; Laudon, Hjalmar; Hasselquist, Niles J.
• Is Part Of: Global change biology. Volume 27:Number 13(2021)
• Page Start: 3066
• Page End: 3078
• Publication Date: 2021-05-05
• Subjects: drought -- Norway spruce -- sap flow -- Scotts pine -- topographic position -- tree size -- tree transpiration; Climatic changes -- Environmental aspects -- Periodicals; Troposphere -- Environmental aspects -- Periodicals; Biodiversity conservation -- Periodicals; Eutrophication -- Periodicals; 551.5
• DOI: 10.1111/gcb.15601
• Languages: English
• ISSNs: 1354-1013

Abstract

Abstract: 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. 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. 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. More specifically, we examined how tree species, size, and topographic position affected drought response in high‐latitude mature boreal forest trees. We monitored 30 Pinus sylvestris (pine) and 30 Picea abies (spruce) trees distributed across a topographic gradient in northern Sweden. 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. 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. 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. 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. Abstract : We studied whole‐tree transpiration ( Q, L day −1 ) response of Pinus sylvestris and Picea abies to the severe drought registered in Northern Sweden in 2018. We analyzed the effects of species, tree size, and topographic position. We observed species‐specific response to drought, and a strong codependence between tree size and the relative topographic position of the trees, which highlights the need for three‐dimensional approaches for scaling up Q to stand transpiration. We discuss the important role of local climatic conditions in high‐elevation boreal forests (>55°N), which can reset drought spell length, directly influencing how different tree species respond to drought.