Spatio‐temporal patterns of tree growth as related to carbon isotope fractionation in European forests under changing climate

Abstract

Aim The aim was to decipher Europe‐wide spatio‐temporal patterns of forest growth dynamics and their associations with carbon isotope fractionation processes inferred from tree rings as modulated by climate warming. Location Europe and North Africa (30‒70° N, 10° W‒35° E). Time period 1901‒2003. Major taxa studied Temperate and Euro‐Siberian trees. Methods We characterize changes in the relationship between tree growth and carbon isotope fractionation over the 20th century using a European network consisting of 20 site chronologies. Using indexed tree‐ring widths (TRWi), we assess shifts in the temporal coherence of radial growth across sites (synchrony) for five forest ecosystems (Atlantic, boreal, cold continental, Mediterranean and temperate). We also examine whether TRWi shows variable coupling with leaf‐level gas exchange, inferred from indexed carbon isotope discrimination of tree‐ring cellulose (Δ13Ci). Results We find spatial autocorrelation for TRWi and Δ13Ci extending over a maximum of 1,000 km among forest stands. However, growth synchrony is not uniform across Europe, but increases along a latitudinal gradient concurrent with decreasing temperature and evapotranspiration. Latitudinal relationships between TRWi and Δ13Ci (changing from negative to positive southwards) point to drought impairing carbon uptake via stomatal regulation for water saving occurring at forests below 60° N in continental Europe. An increase in forest growth synchrony over the 20th century together with increasingly positive relationships between TRWi and Δ13Ci indicate intensifying impacts of drought on tree performance. These effects are noticeable in drought‐prone biomes (Mediterranean, temperate and cold continental). Main conclusions At the turn of this century, convergence in growth synchrony across European forest ecosystems is coupled with coordinated warming‐induced effects of drought on leaf physiology and tree growth spreading northwards. Such a tendency towards exacerbated moisture‐sensitive growth and physiology could override positive effects of enhanced leaf intercellular CO2 concentrations, possibly resulting in Europe‐wide declines of forest carbon gain in the coming decades.

Mountain treelines climb slowly despite rapid climate warming

“…Such responses of tree recruitment and growth to climate have been observed at alpine treelines in the Rocky Mountains (Elliott, 2012; Elliott et al., 2020), Sierra Nevada (Lloyd & Graumlich, 1997), central Himalayas (Sigdel et al., 2018), and the Spanish Pyrenees (Galván et al., 2015). In recent decades, water shortage has enhanced the synchrony of tree growth across Eurasian regions including treeline sites, and tree growth has become more limited by water demand almost worldwide (Babst et al., 2019; Jiang et al., 2019; Shestakova et al., 2019; Zhang et al, 2015). Tree recruitment at alpine treelines has also shown gradual declines at some drought‐prone sites (Camarero & Gutiérrez, 2004).…”

Assessing the response of forest productivity to climate extremes in Switzerland using model–data fusion

“…A diverse set of methods is currently used to quantify and project the impact of changing environmental constraints on forest ecosystem productivity, including extensive collections of in situ observations (Babst et al, ; Charney et al, ; Clark et al, ; Klesse et al, ; Shestakova et al, ), remote sensing data (Beer et al, ; Jolly, Dobbertin, Zimmermann, & Reichstein, ; Nemani et al, ; Piao et al, ), or dynamic vegetation models (DVMs, e.g., Huang, Gerber, Huang, & Lichstein, ; Rollinson et al, ; Zhang et al, ). These and other studies identified important differences in the response of forests to environmental constraints, depending on ambient climate conditions.…”

A triple tree-ring constraint for tree growth and physiology in a global land surface model

“…The enhanced information content obtained by combining multiple and complementary tree-ring variables has long been recognized in multi-proxy dendroclimatology (McCarroll et al, 2003;Loader et al, 2008;Hilasvuori et al, 2009;Daux et al, 2011;Schollaen et al, 2013;Loader et al, 2015) and dendroecology (Guerrieri et al, 2009;Savard, 2010;Leonelli et al, 2012;Shestakova and Martínez-Sancho, 2020), but its potential remained largely untapped in ecological modelling. Tree-ring widths provide a historical record of annual aboveground biomass increment (Clark et al, 2001;Bouriaud et al, 2005;Babst et al, 2018;Cernusak and English, 2015;Foster et al, 2016;Dye et al, 2016;Evans et al, 2017;Shestakova et al, 2019). The stable carbon isotope ratio of plant material, usually reported as δ 13 C, is related to the ratio of intercellular (c i ) and atmospheric CO 2 concentration (Farquhar et al, 1982).…”