Human-mediated forest transition shapes long-term occurrence patterns of pine caterpillar (Dendrolimus spectabilis)...

Both intrinsic and exogenous factors affect the population dynamics of forest insects. Time series analysis based on long-term data provides insights into the ecological processes driving their oscillation or fluctuation. This study investigated the long-term occurrence patterns of the pine caterpillar (Dendrolimus spectabilis) based on both historical records and recent monitoring data. Historical records were obtained from books compiled by ancient governments (918-1903) on the Korean Peninsula, while recent monitoring data were collected from 22 monitoring sites in South Korea during 1968-2005. Forest growing stock and air temperature were used as indicators of forest change (deforestation and reforestation) and climate change, respectively, which are the major drivers of forest ecosystems. Convergent cross mapping (CCM) was applied to infer potential causal effects of growing stock and air temperature on the abundance of pine caterpillar based on the recent monitoring data. The occurrence patterns of pine caterpillar in both historical and recent monitoring data were characterized using spectral and wavelet analyses. The CCM analysis indicated that increased growing stock (reforestation) was a potential driver of the decline of pine caterpillar outbreaks in the 1970s, while no clear evidence supported a causal influence of temperature on its density. Both short- and long-term occurrence periodicities were observed in both historical and recent monitoring data, ranging from several years up to more than a hundred years. Interestingly, the periodicities were primarily detected when the frequency of outbreak or the abundance of pine caterpillars was high, suggesting that the high occurrence of pine caterpillars in both historical and recent monitoring data was considerably associated with deforestation of the pine forest caused by human activities. These data reveal a possible role of human-mediated habitat transition in driving the outbreaks and dynamics of the pine caterpillar.