Stable Isotopes in Tree Rings of Boreal Forests

Abstract

The boreal forests are widely expanded from subarctic forest to tundra, and from taigato forest-steppe zone (from 50 °N to 70 °N). We reviewed available stable isotope chronologies in tree-ring cellulose (δ13C, δ18O and δ2H) from 16 sites located in the Russian Federation; 4 research sites from Fennoscandia (Finland, Sweden and Norway); 5 sites from Canada, and 1 site from Alaska (USA) to evaluate impact of climatic changes from seasonal to annual scale across boreal forest ecosystems. Results of our review of carbon isotope data showed that droughtconditions (mainly high vapour pressure deficit) are prevalent for western and central regions of Eurasia, Alaska and Canada, while northeastern and eastern sites of Eurasian subarctic are showing water shortage developments resulting from decreasing precipitation. Oxygen isotopechronologies show increasing trends towards the end of the twentieth century mainly for all chronologies, except for the Siberian northern and southern sites. The application of the multiple stable isotope proxies (δ13C, δ18O, δ2H) is beneficial to study responses of boreal forests to climate change in temperature-limited environments. However, a deeper knowledge of hydrogen isotope fractionation processes at the tree-ring cellulose level is needed for a sound interpretation and application of δ2H for climate reconstructions, especially for the boreal forest zone where forest ecosystems are more sensitive to climatic and environmental changes.

Towards the Third Millennium Changes in Siberian Triple Tree-Ring Stable Isotopes

“…Positive correlations between δ 13 C and July air temperature as well as with sunshine duration and negative correlations with July precipitation and relative humidity were revealed. This type of correlation between δ 13 C and drought is well established from mechanistic studies investigating isotope fractionations during photosynthesis as well as field studies worldwide [12,39]. An increasing number of sunshine duration hours also impacts leaf temperature and evapotranspiration under air temperature increase [55].…”

“…The permafrost module within LPX-model has been compared to active layer thickness at 20 sites from the Circumpolar Active Layer Monitoring Network (CALMN), where 8 sites are in Russia and 3 of these sites are in Yakutia [49][50][51]. Modelled seasonal soil temperatures, thaw depths, δ 18 O in soil and leaf water and water vapour [39,53,54] have been compared to measurements at four stations in the circumpolar region. In our early study [50], we calibrated the LPX-model for the YAK site and tested inter-annual variability of thaw depth with data from a nearby Yakutsk site [53].…”

Dual Carbon and Oxygen Isotopes in Siberian Tree Rings as Indicator of Millennia Sunshine Duration Changes

“…The average tree-ring width (TRW) of living trees ranges from 0.15 to 0.26 mm, while for dead trees it ranges between 0.26 and 0.29 mm. Tree cores and discs from living larch trees and dead trunks were collected within 69 -70 • N and 139-148 • E during several expeditions (Hughes et al, 1999;Sidorova et al, 2008;Churakova (Sidorova) et al, 2016, 2023, Churakova et al, 2022a, 2022b) from 1994 to 2020 CE.…”

Climate impacts on tree-ring stable isotopes across the Northern Hemispheric boreal zone

“…Intra-annual climate variability is high for the subarctic region. Highly continental boreal sites experience an extreme range of air temperature characterized by harsh winters, with daily minimum -55 °C and annual average temperature -14 °C in Yakutia and rather short (up to 70-90 days) and hot summers, with daily maximum temperature, which can reach +45 °C and mean annual air temperature of 1.2 °C in Siberian transect at the southern boreal region in Khakassia (KHAK, Table 1), e.g., Köppen zones Dfc and Dwc, Abaimov et al, 1997;Knorre et al, 2006Boike et al, 2013;Churakova (Sidorova) et al, 2022a, 2022b. The sum of annual precipitation varies across high-latitudinal sites from 205 mm in eastern part up to 2035 mm /year in the western part of subarctic (Table 1).…”

“…Sunshine duration and cloud cover are rather variable across boreal regions. In summer, sunshine duration lasts longer at high latitudes than at the southern taiga and forest steppe zone (Young et al, 2012;Gagen et al, 2016;Churakova (Sidorova) et al, 2019, 2022a, 2022bChurakova-Sidorova et al, 2022).…”