Elevational differences in the timing and intensity of larch budmoth outbreaks in two valleys of the European Alps
Cyclic outbreaks of the larch budmoth (Zeiraphera griseana, hereafter referred to as LBM) have affected the growth of their larch host trees (Larix decidua) in the European Alps. These regular defoliation events have weakened since the 1980s, likely in response to climate change, but recured in 2018. Here, we investigate the LBM activity along two elevational gradients in the Swiss Alps using tree-ring width (TRW) and maximum latewood density (MXD) measurements from 15 sites between 1,400 and 2,300 m a.s.l. While the effect of the LBM events overall disrupted the tree-ring climate signal, correlations with instrumental JJA temperature recordings remain significant (p ≤ 0.001) for TRW (0.38 at 2,000 m and 0.64 at 2,300 m a.s.l.) and MXD (0.54 at 2,000 m and 0.74 at 2,300 m a.s.l) with the latter recovering quicker from the negative effects of LBM defoliation. Redfit and wavelet spectra as well as superposed epoch analysis of site chronologies reveal a maximum impact of LBM outbreaks at elevations around 1,900 and 2,000 m a.s.l. from where the signal gradually diminishes towards the upper and lower ends of the LBM distribution range. The timing of the growth response to LBM events varies between the two valleys but also between different elevations within the same valley.