Outbreaks of the larch budmoth (LBM) in the European Alps are among the most documented population cycles and their historical occurrence has been reconstructed over 1200 years. Causes and consequences of cyclic LBM outbreaks are poorly understood and little is known about populations near the margin of the host's distribution range. In the present study, we quantify historical LBM outbreaks and associated growth reductions in host trees (European larch). Tree-ring data collected from 18 sites between approximately 500 and 1700 m a.s.l. in the Northern pre-Alps are compared with data from the Western Alps and Tatra Mountains, as well as with nonhost Norway spruce. Highly synchronized host and nonhost growth in the Northern pre-Alps shows that periodic LBM outbreaks are largely absent near the distributional limit of larch. By contrast, growth patterns in the Western Alps LBM core region are indicative of LBM events. Although climatic conditions in the Northern pre-Alps and Tatra Mountains would allow LBM outbreaks, low host plant abundance is likely the key driver for the absence of cyclic outbreaks in these regions. The results obtained in the present study suggest that, in addition to the climatic conditions, host-species abundance is critically important for the occurrence of periodic LBM outbreaks and the determination of the respective outbreak range.
Hartl-Meier, Claudia; Esper, Jan; Liebhold, Andrew; Konter, Oliver; Rothe, Andreas; B ntgen, Ulf. 2017. Effects of host abundance on larch budmoth outbreaks in the European Alps. Agricultural and Forest Entomology. 19(4): 376-387. https://doi.org/10.1111/afe.12216.