Effects of Disturbance on Fine Root Dynamics in the Boreal Forests of Northern Ontario, Canada

Wildfire and clearcutting are two main disturbances in North American forests, but whether root systems may respond differently to such disturbances is unknown. Here, we studied how the dynamics of fine roots (<2 mm in diameter) varied with stand origins in a boreal forest in northern Ontario, Canada. Fine root biomass increased with stand age, but did not differ between stands originating from fire and clearcutting. By contrast, fine root production, mortality and turnover rates were lower in 3- and 11-year-old clearcut-origin than fire-origin stands, but did not differ in 29-year-old stands of different stand origins. The lower rates of production, mortality, and turnover rates in 3- and 11-year-old clearcut-origin than fire-origin stands are attributable to a lower density of shrubs and herbs and larger nutrient pools after clearcutting than fire. The similarities among 29-year-old stands indicate that the effects of stand origin on fine root processes tend to converge at this time scale. Our results illustrate that time scale is critical for assessing ecosystem responses to disturbances.