Secondary disturbance following a deposit of volcanic tephra: a 30-year record from old-growth forest understory

Forest disturbance is usually described by effects on trees, and small disturbances to forest understory are seldom studied. Nevertheless, effective analyses of succession need consider both stand-replacing subsequent “secondary” in the canopy understory. We estimated characteristics 13 types secondary old-growth understory, as well change cover, after deposition tephra (aerially transported volcanic ejecta) 1980 from Mount St. Helens, Washington. sampled 100 plots (1 m 2 ) at each four sites for vegetation 10 different times 2010; we tree above plot 2016. The number gaps increased 23% mean gap dimension 68% over 36 years, mostly loss Abies amabilis (Douglas ex Loudon) Douglas Forbes. Secondary affected 1.4% stand area per year. areas soil woody litter were similar. Erosion, greater deep than shallow tephra, peaked 1981, whereas most litter-caused 2000. Less frequent litter-based covered area. Our results differ conclusions about nonvolcanic disturbances. variable, more study, likely affect many other systems.