Effects of Natural Disturbances Caused by the Siberian Moth, Dendrolimus Superans Sibiricus (Tschetverikov), and Fire on the Dynamics of Boreal Forests in Krasnoyarsk Krai, Russia.

Abstract

The effects of fire and Siberian moth, Dendrolimus superans sibiricus (Tschetverikov), (Lepidoptera:Lasiocampidae) defoliation on overstory and understory composition and structure, carbon flux, and conifer regeneration were examined in the boreal forests of Krasnoyarsk Krai, Russia to better understand the impact the Siberian moth may have if introduced in North American forests. Sampling was conducted in the following stand types: (1) undisturbed fir-spruce, (2) recent fire, five or fewer years ago, (3) severe defoliation by the Siberian moth in the 1995-97 outbreak with no fire, (4) severe defoliation by the Siberian moth in the 1995-97 outbreak, with a large post-outbreak fire scar, and (5) severe defoliation in the 1954-57outbreak that burned in the 1960’s. A steady state of forb domination between older defoliated stands and recently defoliated stands suggests that the Siberian moth may be responsible for a disruption of succession in Siberian boreal forests. No live conifer stems were sampled or observed in any of the recently defoliated and older defoliated stands. The implications for carbon flux in large areas with complete mortality caused by the Siberian moth and subsequently burning are significant. Stands defoliated in the 1950’s and burned in the 1960’s exhibited major differences in amounts of both downed and standing coarse woody debris compared to stands defoliated and burned in the 1990’s. This study found a loss of 23.8 Mg/ha of C in coarse woody debris in the approximately 50 year period separating these two disturbance types. Stands defoliated in the 1950’s and burned in the 1960’s had no regeneration. Stands defoliated in the 1990’s, burned or unburned, were comparable in the number of seedlings found but had significantly fewer seedlings than undisturbed stands. The stands enduring only recent fire appeared to have typical boreal forest regeneration. Reversion to fir-dominated stands after a severe Siberian moth outbreak may require several centuries of successive regeneration from conifer trees along the periphery of the disturbed area.