Long-term recovery of vegetation on two experimental crude oil spills in interior Alaska black spruce taiga

Abstract

Vegetation was sampled on two black spruce taiga sites in interior Alaska, 15 and 20 years after crude oil was experimentally applied as low-volume sprays or high-volume point spills. Low volume spray spills that uniformly covered the ground caused initial damage to vegetation, but after 20 years recovery of the understory vegetation was almost complete, with dramatic recovery and expansion of fruticose lichens. High-volume point spills created small areas of surface oil saturation with dead vegetation and little sign of recovery but spread out mostly belowground with little or no apparent effect on the shallowly rooted vegetation above even after 15–20 years. Because winter point spills created a much greater area of surface oil, their effects were more damaging. After 15 years on the saturated surface oiled areas, only Eriophorum vaginatum tussocks survive and grow. At both sites with surface oil, black spruce mortality was high, with no evidence of long-term recovery and with continuing chronic effects after 15 years. However, from a long-term perspective the black spruce taiga ecosystem appears to be able to recover from low volume spray spills and to retain large amounts of crude oil from high-volume point spills belowground with minimal damage to the vegetation. Because of the permafrost, removal of crude oil from this ecosystem by soil excavation is undesirable. In situ acceleration of oil breakdown using fertilizers and bacteria is a possible option; seeding or planting of E. vaginatum on surface-oiled areas may also provide some cover and belowground biomass. Key words: oil spills, taiga, black spruce, interior Alaska, vegetation recovery.