Disentangling Mechanisms of Drought-Induced Dieback in Pinus nigra Arn. from Growth and Wood Isotope Patterns

Ester González De Andrés,Jesús Julio Camarero

doi:10.3390/f11121339

Ester González De Andrés, Jesús Julio Camarero

Open Access

https://doi.org/10.3390/f11121339

Copy DOI

Journal: Forests	Publication Date: Dec 16, 2020
Citations: 12	License type: CC BY 4.0

Affiliation: Instituto Pirenaico de Ecología

Abstract

The increased frequency and intensity of warming-induced droughts have triggered dieback episodes affecting many forest types and tree species worldwide. Tree plantations are not exempt as they can be more vulnerable to drought than natural forests because of their lower structural and genetic diversity. Therefore, disentangling the physiological mechanisms leading to growth decline and tree mortality can provide tools to adapt forest management to climate change. In this study, we investigated a Pinus nigra Arn. plantation situated in northern Spain, in which some trees showed canopy dieback and radial-growth decline. We analyzed how radial growth and its responses to drought events differed between non-declining (ND) and declining (D) trees showing low and high canopy defoliation, respectively, in combination with carbon (δ13C) and oxygen (δ18O) isotope ratios in tree rings. The radial growth of P. nigra was constrained by water availability during the growing season and the previous autumn. The radial growth of D trees showed higher sensitivity to drought than ND trees. This fact is in accordance with the lower drought resilience and negative growth trends observed in D trees. Both tree classes differed in their growth from 2012 onwards, with D trees showing a reduced growth compared to ND trees. The positive δ13C-δ18O relationship together with the uncoupling between growth and intrinsic water-use efficiency suggest that D trees have less tight stomatal regulation than ND trees, which could involve a high risk of xylem embolism in the former class. Our results suggest that different water use strategies between coexisting ND and D trees were behind the differences in growth patterns and point to hydraulic failure as a possible mechanism triggering dieback and growth decline.

Highlights

Increasing rates of tree mortality and dieback events have been reported worldwide, covering all major forested biomes on Earth [1,2,3,4,5,6,7]
TheThe long-term radial growth patterns ofofthe positivelyassociated associated with water availability at long timescales encompassing the previous autumn to early summer, and with water availability at long timescales encompassing the previous autumn to early summer, and the the positive effect of water availability on growth was stronger in declining trees than in nonpositive effect of water availability on growth was stronger in declining trees than in non-declining declining trees. declining
We argue that the onset of growth decline and dieback symptoms of D trees in our study plantation was triggered by successive severe droughts that would progressively impair physiological processes, in line with previous studies reporting canopy dieback and tree mortality in other natural and planted P. nigra forests [6,16,21,53]

Summary

Introduction

Increasing rates of tree mortality and dieback events have been reported worldwide, covering all major forested biomes on Earth [1,2,3,4,5,6,7]. These trends have been linked to warming and drought, sometimes co-occurring with insect outbreaks [1]. The impacts of climate change can be stronger in pine plantations that have been found to be more vulnerable to warming-related drought than naturally regenerated forests [12,13]. Pine plantations constitute ca. 7% of the total worldwide forest cover, and they amount to 10% in the Mediterranean

Methods

Results

Discussion

Conclusion