Siberian silkmoth outbreaks surpassed geoclimatic barrier in Siberian Mountains

Abstract

Siberian silkmoth (SSM, Dendrolimus sibiricus Tschetv.) is the most important defoliator of Siberian pine (Pinus sibirica Du Tour) and fir (Abies sibirica Ledeb.) stands. Warming-induced SSM outbreaks are one of the major driving factors of successions within the taiga zone. It is suggested that climate change impacted the SSM range and life cycle. We analyzed the migration of alpine and northerly SSM outbreak boundaries in Siberia and the impact of the climate variables and topography on the outbreak dynamics. We used time-series scenes (multispectral data, and vegetation indexes EVI and NDII) in combination with field studies, climate variables, and GIS techniques. We found that SSM outbreaks in the area of alpine boundary shifted about 370 m uphill since the mid of 1950. The outbreak onset was promoted by increased dryness and active temperatures and decreased root zone moisture content in the spring-early summer period. The terrain topography strongly affected SSM outbreak onset and dynamics. Initially, the outbreak was located at the middle elevations on the gentle concave southeastern slopes, which are the favorable insect habitats between outbreaks. Then the outbreak expanded uphill and downhill, to steeper slopes, and both concave and convex terrains. Alongside with elevation range expansion, SSM surpassed its northern historical outbreak boundary: the potential outbreaks' boundary moved about 300 km northward. Climate warming contributes to SSM migration into former outbreak free conifer stands located in highlands and at northern latitudes.

Orographic Factors as a Predictor of the Spread of the Siberian Silk Moth Outbreak in the Mountainous Southern Taiga Forests of Siberia

“…The second factor is the position on the slope, which regulates the soil moisture reserves. Most of the previous studies mentioned that south-facing slopes were favorable for the D. sibiricus reserves due to greater insolation and higher ground surface temperature [3,5,6,13,19,20]. Such areas of dark coniferous forests are characterized by the most drained and warm conditions, where trees are growing on loose, relatively fresh, and porous soddy-podzolic soils with no signs of gleying [27].…”

“…A Landsat-8 30 m Ground Sample Distance (GSD) time-series obtained from the Earth Explorer data portal (https://earthexplorer.usgs.gov/) was used for the analysis. There are well-proven high-precision methods for classifying areas damaged by phytophagous insects using such images in modern studies [13,21,[28][29][30].…”

“…The D. sibiricus population in the study region reaches 800-900 m above sea level and is rarely encountered at higher altitudes [4]. According to other researchers [13,18,36,37], global warming changes pest's ecology, facilitating elevation range expansion.…”

“…This phytophage's permanent habitats within a natural complex are not accidental and are often confined to host-tree areas combined with specific temperature and humidity conditions [8][9][10][11]. The phytophage outbreaks are cyclical and periodically Lyamtsev N.I., Kondakov Yu.P., Kharuk V.I., Foster J.R., Singh A., Townsend P.A., and others [2,4,6,13,[22][23][24].…”

Potential of Climate Change and Herbivory to Affect the Release and Atmospheric Reactions of BVOCs from Boreal and Subarctic Forests

“…Areas with favorable temperature sums for the complete development of bivoltine populations of I. typographus (>1500 degree days (DD)) shifted northwards by an average of 450 km during the entire study period of 1960–2016 [ 26 ]. Massive 2.5 M ha outbreaks of the Siberian silk moth Dendrolimus sibiricus have shifted northward by up to 500 km in the Siberian boreal conifer forest during the last 40 years with the shift promoted by droughts and an increase in the temperature sum [ 81 , 82 ]. Higher winter temperatures and decreased summer precipitation are the main drivers of the range expansion of Mountain pine beetle, Dendroctonus ponderosae , towards the north in the USA and Canada [ 84 , 85 ].…”