Tree-ring evidence for the historical cyclic defoliator outbreaks on Larix potaninii in the central Hengduan Mountains, SW China

Abstract

Dendrochronological methods have been used to reconstruct insect outbreaks, yet the application has been scarce in the high Asia. We compiled tree-ring data from 4 host (Larix potaninii) and 4 non-host (Abies and Picea) sites in the central Hengduan Mountains, southwestern China. We assessed site-specific growth-climate responses and applied two methods to detecting larch insect defoliation events during the past 250 years. Compared with the non-host chronologies, larch trees (host) showed periodic reduction in radial growth, which may be associated with outbreaks of a larch defoliator. Synchronously, growth reductions was found for three low-elevation sites, such as during 1783–1790, 1846–1850, 1860–1865, 1873–1878, 1900–1909, 1939–1945, 1965–1970 and 1981–1986. However, these periods of outbreaks differ from those of a high-elevation site. With spectral analyses, we found 11–13 years frequency domains for three low-elevation larch chronologies, while 7–9 year peaks presented one high-elevation site. Contrastively, no significant frequency domains within the same periodicity were found in ring-width chronologies of co-occurring non-host species. We provide tree-ring evidence that larch trees growing in the central Hengduan Mountains have been infected by insect defoliators repeatedly. We suggest that appropriate approaches should be applied to correct insect-defoliation signals when using larch tree-ring data as a climatic proxy.