A multi-proxy assessment of dieback causes in a Mediterranean oak species.
Drought stress causes forest dieback that is often explained by two interrelated mechanisms, namely hydraulic failure and carbon starvation. However, it is still unclear which functional and structural alterations, related to these mechanisms, predispose to dieback. Here we apply a multi-proxy approach for the characterization of tree structure (radial growth, wood anatomy) and functioning (δ13C, δ18O and non-structural carbohydrates (NSCs)) in tree rings before and after drought-induced dieback. We aim to discriminate which is the main mechanism and to assess which variables can act as early-warning proxies of drought-triggered damage. The study was tailored in southern Italy in two forests (i.e., San Paolo (SP) and Oriolo (OR)) where declining and non-declining trees of a ring-porous tree species (Quercus frainetto Ten.) showing anisohydric behavior coexist. Both stands showed growth decline in response to warm and dry spring conditions, although the onset of dieback was shifted between them (2002 in SP and 2009 in OR). Declining trees displayed a sharp growth drop after this onset with reductions of 49% and 44% at SP and OR sites, respectively. Further, contrary to what we expected, declining trees showed a lower intrinsic water-use efficiency compared with non-declining trees after the dieback onset (with reductions of 9.7% and 5.6% at sites SP and OR, respectively), due to enhanced water loss through transpiration, as indicated by the lower δ18O values. This was more noticeable at the most drought-affected SP stand. Sapwood NSCs did not differ between declining and non-declining trees, indicating no carbon starvation in affected trees. Thus, the characterized structural and functional alterations partially support the hydraulic failure mechanism of dieback. Finally, we show that growth data are reliable early-warning proxies of drought-triggered dieback.
School of Agricultural, Forest, Food and Environmental Sciences, University of Basilicata, viale dell'Ateneo Lucano 10, 85100 Potenza, Italy.
Michele
M
Colangelo
Pyrenean Institute of Ecology (IPE-CSIC), Avda Montañana 1005, 50192 Zaragoza, Spain.
J Julio
JJ
Camarero
Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, Second University of Naples, Caserta, Italy.|École Pratique des Hautes Études (PALECO EPHE), Institut des Sciences de l'Évolution, University of Montpellier 2, F-34090 Montpellier, France.
Giovanna
G
Battipaglia
School of Agricultural, Forest, Food and Environmental Sciences, University of Basilicata, viale dell'Ateneo Lucano 10, 85100 Potenza, Italy.
Marco
M
Borghetti
Department of Agricultural Sciences, University of Naples Federico II, Portici (Naples), Italy.
Veronica
V
De Micco
School of Agricultural, Forest, Food and Environmental Sciences, University of Basilicata, viale dell'Ateneo Lucano 10, 85100 Potenza, Italy.
Tiziana
T
Gentilesca
School of Agricultural, Forest, Food and Environmental Sciences, University of Basilicata, viale dell'Ateneo Lucano 10, 85100 Potenza, Italy.
Francesco
F
Ripullone
D055864:Droughts; D065928:Forests; D007558:Italy; D029963:Quercus / Q000254:growth & development*; D014197:Trees / Q000254:growth & development; D014934:Wood / Q000254:growth & development*
Quercus frainetto; carbon and oxygen isotopes; climate warming; dendrochronology; non-structural carbohydrates; quantitative wood anatomy; southern Italy