Strong legacy effects of prior burn severity on forest resilience to a high-severity fire

Abstract

Legacy effects from one disturbance may influence successional pathways by amplifying or buffering forest regeneration after the next disturbance. We assessed vegetation and tree regeneration in non-serotinous Sierra lodgepole pine (Pinus contortavar. murrayana) stands after a 1984 wildfire which burned with variable severity and again after a high-severity subsequent fire in 2012. The legacy effects of the 1984 fire were amplified; seedlings and saplings were abundant in areas initially burned at low severity (1267 stems ha⁻¹) despite high reburn severity, but regeneration was low in areas twice burned at high severity (31 stems ha⁻¹). Our results suggest that the severity of the 1984 fire may have influenced post-2012 tree regeneration by creating variable fuel loading, which may have affected soils, litter cover and shade after the 2012 fire and therefore affected seedling establishment and survival. A canopy seed bank of unburnt cones from trees killed by the 2012 fire potentially contributed to a strong effect of prior burn severity on regeneration after the 2012 fire despite a lack of serotinous or resprouting tree species, although the influence of this canopy seedbank was likely limited to the year following the fire. Our results suggest that a low- to moderate-severity fire increases forest resilience relative to a high-severity fire even when the next fire burns at high severity.

Citation

Harris, Lucas B.; Drury, Stacy A.; Taylor, Alan H. 2020. Strong legacy effects of prior burn severity on forest resilience to a high-severity fire. Ecosystems. 113: 11770. https://doi.org/10.1007/s10021-020-00548-x.