Twentieth century changes of tree‐ring δ¹³C at the southern range‐edge of Fagus sylvatica: increasing water‐use efficiency does not avoid the growth decline induced by warming at low altitudes

Abstract

We aimed to gain knowledge on the changes in intrinsic water use efficiency (iWUE) in response to increasing atmospheric CO 2 concentrations and climate change over the last century. We investigated the variation in the iWUE of mature Fagus sylvatica trees located in the higher, central and lower altitudinal forest limits (HFL, CFA and LFL) of one of the southernmost sites of beech distribution in Europe, the Montseny Mountains in Catalonia (northeast Spain), during the last century by analysing the d 13 C of their tree rings. Pre-and post-maturation phases of the trees presented different trends in d 13 C, D 13 C, Ci (internal CO 2 concentration), iWUE and basal area increment (BAI). Moreover, these variables showed different trends and absolute values in the LFL than in the other altitudinal sites, CFA and HFL. Our results show the existence of an age effect on d 13 C in the CFA and HFL (values increased by ca. 1.25% coinciding with the BAI suppression and release phases, previous to maturation). These age-related changes were not found in the LFL, whose beech trees arrived to maturation earlier and experienced drier conditions during the suppression phase. In the last 26 years of comparable mature trees, the increase of iWUE deduced from the D 13 C analyses was ca. 10% in LFL, ca. 6% in CFA and not significant in HFL. These results show that climate change towards more arid conditions accounted for these higher D 13 C-values and increases in the LFL more than the continuous increase in atmospheric CO 2 concentrations. This increased iWUE in the LFL did not avoid a decline in growth in these lowest altitudes of this beech southern range-edge as a result of warming. Furthermore, since there was no apparent change in iWUE and growth in the beech forests growing in the more standard-adequate environments of higher altitudes in the last 26 years, the rate of sequestration of C into temperate ecosystems may not increase with increasing atmospheric CO 2 concentrations as predicted by most models based on short-term small scale experiments.

Black pine (Pinus nigra Arn.) growth divergence along a latitudinal gradient in Western Mediterranean mountains

“…8) is in accordance with tree growth decline caused by decreasing precipitation or warming temperatures observed along the Mediterranean (Jump et al, 2006a;Macias et al, 2006;Peñuelas et al, 2008;Piovesan et al, 2008;Sarris et al, 2007). Despite the general negative long-term trend of radial growth, analysis of individual black pine tree-ring series revealed two groups of trees with distinct growth patterns during the second half of the 20th century.…”

“…These results suggest that global change might cause divergent tree growth in different ecosystems such as Mediterranean Pisaric et al, 2007;Wilmking et al, 2004), whereas negative trends mainly appear in warmer climates where precipitation and high temperatures are limiting (e.g. Macias et al, 2006;Peñuelas et al, 2008;Sarris et al, 2007). The individual analysis of trees in our regions (located between those with these two major trends) allowed us to document the gradual latitudinal progression of divergence and the relative proportion of positive trenders.…”

“…II) are most limited by increasing summer warmth and drought stress (Barber et al, 2000). Most likely, improvement of WUE (if any) cannot compensate for the increase in temperatures and decrease in precipitation in SCA and CUE as shown for other species such as Scots pine (Martínez-Vilalta et al, 2008) and beech (Jump et al, 2006a;Peñuelas et al, 2008) in their southern distribution ranges.…”

The altitude-for-latitude disparity in the range retractions of woody species

“…Carbon sequestration can be reduced even in the absence of mass mortality events via tree growth decline and elevated mortality rates, as reported recently at the southernmost range edge of beech distribution in Europe [65,66], and in temperate trees across the western USA [31]. Furthermore, such alterations to carbon economy are occurring despite the predicted enhancement of water-use efficiency by increasing CO 2 and its expected fertilization effect (higher atmospheric CO 2 concentrations leading to higher plant productivity) [79].…”

Predicting the future of forests in the Mediterranean under climate change, with niche- and process-based models: CO2 matters!

“…and the species-specific capacities (e.g. Peñ uelas et al, 2008). Ultimately, species-specific responses may affect the structure and functioning of ecosystems (Peñ uelas & Filella, 2001) due to altered competitive relationships of key performance measures and the loss of synchronization of development (Fitter & Fitter, 2002;Gordo & Sanz, 2005).…”