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Open AccessArticle

Shifts in Growth Responses to Climate and Exceeded Drought-Vulnerability Thresholds Characterize Dieback in Two Mediterranean Deciduous Oaks

1
Depto. Sistemas Físicos, Químicos y Naturales, University Pablo de Olavide, Crta. Utrera km. 1, E-41013 Sevilla, Spain
2
Instituto Pirenaico de Ecología (IPE-CSIC), Avda. Montañana 1005, E-50059 Zaragoza, Spain
3
School of Agricultural, Forest, Food and Environmental Sciences, University Basilicata, I-85100 Potenza, Italy
4
Department of Plant Biology & Ecology, University of Seville, Av. Reina Mercedes s/n, 41012 Seville, Spain
*
Author to whom correspondence should be addressed.
Co-first authors.
Forests 2020, 11(7), 714; https://doi.org/10.3390/f11070714
Received: 9 May 2020 / Revised: 21 June 2020 / Accepted: 23 June 2020 / Published: 27 June 2020
(This article belongs to the Special Issue Dieback on Drought-Prone Forest Ecosystems)
Drought stress has induced dieback episodes affecting many forest types and tree species worldwide. However, there is scarce information regarding drought-triggered growth decline and canopy dieback in Mediterranean deciduous oaks. These species face summer drought but have to form new foliage every spring which can make them vulnerable to hotter and drier conditions during that season. Here, we investigated two stands dominated by Quercus frainetto Ten. and Quercus canariensis Willd. and situated in southern Italy and Spain, respectively, showing drought-induced dieback since the 2000s. We analyzed how radial growth and its responses to climate differed between non-declining (ND) and declining (D) trees, showing different crown defoliation and coexisting in each stand by: (i) characterizing growth variability and its responsiveness to climate and drought through time, and (ii) simulating growth responses to soil moisture and temperature thresholds using the Vaganov–Shashkin VS-lite model. Our results show how growth responsiveness to climate and drought was higher in D trees for both oak species. Growth has become increasingly limited by warmer-drier climate and decreasing soil moisture availability since the 1990s. These conditions preceded growth drops in D trees indicating they were more vulnerable to warming and aridification trends. Extremely warm and dry conditions during the early growing season trigger dieback. Changes in the seasonal timing of water limitations caused contrasting effects on long-term growth trends of D trees after the 1980s in Q. frainetto and during the 1990s in Q. canariensis. Using growth models allows identifying early-warning signals of vulnerability, which can be compared with shifts in the growth responses to warmer and drier conditions. Our approach facilitates establishing drought-vulnerability thresholds by combining growth models with field records of dieback. View Full-Text
Keywords: dendroecology; tree-rings; VS-lite; Quercus frainetto; Quercus canariensis; tree rings dendroecology; tree-rings; VS-lite; Quercus frainetto; Quercus canariensis; tree rings
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Sánchez-Salguero, R.; Colangelo, M.; Matías, L.; Ripullone, F.; Camarero, J.J. Shifts in Growth Responses to Climate and Exceeded Drought-Vulnerability Thresholds Characterize Dieback in Two Mediterranean Deciduous Oaks. Forests 2020, 11, 714.

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