The Effect of a Pine Looper Moth Outbreak on the Radial Growth Rate of Pine

Abstract

This study compares the 1945–2015 time series of the radial growth rate of pine Pinus sylvestris L. damaged by the 1974–1978 outbreak of the pine looper moth Bupalus piniarius L. and those of the undisturbed Krasnoturansk pine forest. It is proposed to employ regulatory characteristics of time series, including the order of autoregression (lag value n) and standard deviation of the amplitude of time series oscillation s (number of the first differences of radial growth s), to estimate differences between radial growth rates of trees in damaged and intact stands. These indicators allow for a quantitative assessment of the lag of the processes regulating the radial growth rate. Only the first differences of the series of radial growth rate are assessed, inasmuch as the regulatory characteristics can be correctly calculated only for the stationery time series. Trees exposed to insect outbreak either have no lag in the dynamics of the first differences of the series in the radial growth rate or they have high values of autoregression order n. At the same time, the oscillations of the current radial growth rate of damaged trees in relation to the age gradient are significantly larger than in undisturbed trees. We estimate the speed of the growth-rate recovery in damaged trees as a function of regulatory characteristics of time series of the radial growth rate before the damage. These data could be used to assess the pest hazard in the stands and recovery rates of forests damaged by insect outbreaks.