Long-term monitoring of vegetation change following tundra fires in Noatak National Preserve, Alaska

Racine, Charles; Allen, Jennifer; Dennis, JG

Fire is an important driver of change at the local and landscape levels in the tundra ecosystems of Noatak National Preserve. In July 2005, with support from the National Park Service Arctic Network Inventory and Monitoring program, we relocated and remeasured fire plots established in 1981–82 at eight sites in Noatak National Preserve to evaluate the long-term (25 to 30 years) effects of tundra wildfire on vegetation and permafrost. The tussock-shrub and shrub tundra sites originally established by Racine and Dennis included one site burned in 1972, four sites burned in 1977, one site burned in 1982, and two unburned control sites. Stakes placed in the ground in 1981–82 to mark sample plots were relocated at four of the eight sites. At the remaining sites we used photos and field notes to relocate plots as close to the original as possible. Visual cover estimates were made for each species in each 1 m x 1 m plot (10 per site). Thaw depths were measured at five points in each plot. To provide for future monitoring, all sites were restaked and GPS coordinates obtained. Our experience relocating and remeasuring plots established 23 to 24 years ago indicates that these plots are valuable tools for assessing fire disturbance on tundra ecosystems. At all four 1977 and one 1982 burned site (but not the 1972 burn) there has been an increase in vascular plant cover during the past 23 years from 1981–82 to 2005. This increase was mostly due to increases in shrub cover by as much as 65% on a shrub tundra site and 15 to 30% in tussock-shrub tundra. The shrub species involved in this increase were mostly deciduous shrubs of birch and willow. Grass and forb (mainly fireweed) cover has declined or disappeared. At two lightly burned shrub tundra sites there has been a net decrease in the number of forb species (from 21–24 species in 1981 to 14 species in 2005) during the past 24 years. Thaw depths in 2005 were similar to those measured in 1981–82 except for a site burned in 1972 and possibly again in 1984. This analysis of change from 1981 to 2005 following tundra fire has occurred during a remarkable period of warming in the North American Arctic, with evidence for the expansion of shrubs in tundra similar to that observed at our sites. It is difficult to partition the effects of fire from the effects of climate warming because they are linked and both can result in warmer soils and associated nutrient increase. More monitoring attention needs to be given to the establishment of unburned control plots paired with burned plots to evaluate change without fire compared to change with fire.

Long-term monitoring of vegetation change following tundra fires in Noatak National Preserve, Alaska

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