Direct and Indirect Analysis of the Elevational Shift of Larch Budmoth Outbreaks Along an Elevation Gradient

Philippe Rozenberg,Luc Pâques,Frédéric Huard,Alain Roques

doi:10.3389/ffgc.2020.00086

Abstract

Larch budmoth (LBM) periodically defoliates alpine stands of European larch during vast outbreaks occurring generally at 8-10 year intervals. LBM outbreaks recently declined and the ongoing global warming has been pointed out as a possible cause of this decline. We reconstructed the recent history of LBM outbreaks at different elevations along a larch altitudinal gradient in the French Alps using direct and indirect observations based on tree-ring width and density analysis, and compared it with local climatic data. We found that LBM outbreaks time-series were better reconstructed with latewood density than with ring width. We also found that there was a recent but limited altitudinal shift of LBM outbreaks from medium towards higher elevations. We suggest that this altitudinal shift is a consequence of the variable effect of the global warming at the different elevations. Winter warming is expected to affect differently the timing of LBM egg hatch as well as that of larch bud flush, larvae being at present susceptible to emerge whereas no needles are available as food at the former optimal altitude. A better synchronization between larch and LBM may exist at higher elevations.

Highlights

Larvae of larch budmoth (Zeiraphera griseana; Larch budmoth (LBM)) periodically defoliate alpine stands of European larch (Larix decidua) during massive outbreaks occurring most of the time at 8– 10 year intervals, with an optimum at 1800 m elevation (Dormont et al, 2006; Baltensweiler et al, 2008)
We found that LBM outbreaks time-series were better reconstructed with latewood density than with ring width
We suggest that this elevational shift is a consequence of the variable effect of the global warming at the different elevations

Summary

Introduction

Larvae of larch budmoth (Zeiraphera griseana; LBM) periodically defoliate alpine stands of European larch (Larix decidua) during massive outbreaks occurring most of the time at 8– 10 year intervals, with an optimum at 1800 m elevation (Dormont et al, 2006; Baltensweiler et al, 2008). The newly produced needles are shorter, as well as the needles produced in the following spring (Baltensweiler et al, 2008) Such radial growth reduction leaves a characteristic fingerprint in annual ring time-series used to retrospectively reconstruct LBM outbreaks (Weber, 1997; Rolland et al, 2001; Esper et al, 2007; Baltensweiler et al, 2008; Saulnier et al, 2017). A long-term dendrochronology study of larch trees in the Alps have discovered 123 outbreaks between 781 A.D. and 1981 (Iyengar et al, 2016).

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