Burned Twice in Seven Years: How Alaska's Forests and Tundra Recover from Repeat Fires

Spruce forests in Wrangell-St. Elias normally go 150 to 200 years between fires, and in Interior Alaska the usual gap is 60 to 150 years. In 2016 the Steamboat Fire burned nearly 18,000 acres of Wrangell-St. Elias that had burned only seven years before, in the 2009 Chakina Fire. This is a summary of the monitoring and inventory section of the National Park Service Alaska Region's 2017 fire ecology annual report, by Jennifer L. Barnes and Jennifer L. Hrobak. It covers two projects: the repeat-fire plots in Wrangell-St. Elias and a long-running set of tundra fire plots in Noatak.

Fire ecology monitoring gives the park fire management program feedback on activities such as fuels treatments and builds understanding of what wildfire does to the landscape. The report tallies the fire and fuels plots the Alaska parks have established since 2003; in 2017 the program measured plots in the area that recently burned twice and re-measured long-term tundra plots in Noatak.

Two fires in the same spruce forest

Fire managers wanted to know what had burned in 2016 and what a seven-year return interval might do to the land. Plots set up to monitor the severity and effects of the 2009 fire gave them a baseline. In summer 2017, Alaska Region fire ecology staff and U.S. Geological Survey researchers measured 42 plots in once-burned and twice-burned areas. They wanted to learn what fuels and vegetation carried the second fire and how once-burned and twice-burned sites differ in recovery, by tracking plant cover, tree seedling establishment, tree density by size class, and active layer depth and soil temperature. The plots were of two types before the fires: upland white spruce and mesic black spruce.

A white spruce forest burned in 2009 by the Chakina Fire, in Wrangell-St. Elias National Park. Left to right: before the fire (1998), one year after (2010), eight years after (2017) (NPS photo).

After the first fire. One year later, live tree cover was nearly zero. Most of the late-successional feathermosses were consumed, and early-successional mosses and liverworts, along with some fireweed, were moving in. Eight years after, the white spruce plots had dense fireweed (27% average cover) and willow (26%), with aspen and young white spruce coming up beneath. The black spruce sites had more horsetails (22%) and Labrador tea (4%) than the white spruce sites. Dwarf shrub cover dropped at both.

What fed the second fire. Fallen trees and the dead thatch of the previous year's fireweed likely provided the fuel. The second burn consumed much of the smaller dead and down wood and, at some sites, some of the larger logs too. At many twice-burned sites the ground was carpeted with early-successional mosses, fireweed seedlings and re-sprouts were common, and some willows and aspen re-sprouted. A year after the second fire there was more plant cover, vascular and non-vascular, than a year after the first.

A white spruce forest burned in 2009 by the Chakina Fire and again in 2016 by the Steamboat Creek Fire. Left: one year after the first fire (2010). Right: one year after the second (2017) (NPS photo).

Point intercept vegetation cover, averaged by life form, from the Chakina-Steamboat Creek fire plots in Wrangell-St. Elias (chart from the National Park Service).

Seedlings. Seedlings decide what the next forest will be. None of the seven plots sampled in 2010 had any seedlings a year after the first fire. Eight years on, the white spruce sites were dominated by deciduous regrowth, mainly aspen, at an average of 44,642 aspen "seedlings" per hectare, with white spruce seedlings averaging 2,730 per hectare. The black spruce sites had many white spruce seedlings, plus black spruce and aspen. After a second burn, some black spruce seedlings survived or regenerated, but re-sprouting aspen dominated, at an average of 6,824 per hectare on the white spruce sites and 2,017 on the black spruce sites. The report cautions that spruce seedlings are hard to identify to species, so some may be wrong, and that its analysis is preliminary.

Tundra plots that span forty years

Charles Racine and colleagues set up tundra fire plots in two Alaska parks, Bering Land Bridge and Noatak, in the late 1970s and early 1980s. The set is the longest record of tundra fire effects in Alaska.

• Bering Land Bridge: in 1978 the team set up 8 permanently marked plots on Nimrod Hill, in a 1977 fire, with pre-fire data from a 1973 soils and vegetation survey. They were re-measured in 1979, 1981, 1983, 2001, 2002 and 2009.
• Noatak: in 1981 and 1982 they set up eight sites on tundra burned in 1972, 1977 and 1982, from 4 weeks to 10 years after the burn. The Arctic Network Inventory and Monitoring Program and NPS fire staff re-measured them in 2005 and again in 2017. Some sites have burned again since.

At each plot the crews sampled ten 1-meter-square quadrats, recording the cover of vascular and non-vascular species, shrub height and stem density, tree density, the depth of the active layer above the permafrost, and photographs. The aim was to detect major changes in vegetation structure and composition over time.

Preliminary Noatak results compare unburned, once-burned and twice-burned plots:

• Unburned sites had the lowest cover of forbs and the greatest cover of shrubs.
• Once-burned sites had more grasses and rushes in the early years, which dropped sharply by 20 years after the fire.
• Shrubs and dwarf shrubs increased by 20 years after the fire in both once- and twice-burned sites, reaching about the cover found in unburned plots.
• Twice-burned plots appear to have more cover of tussock-forming sedges than the other plots.

The Kungiakrok burn site in the Noatak plots. It was first monitored a few weeks after a small fire in 1982 (upper left) and re-measured in 2005 (upper right), when tussocks and shrubs had recovered 23 years after the fire. It burned again in 2012 and was photographed one year after (lower left) and in 2017, five years after (lower right). By then tussocks dominate, while dwarf and low shrubs are returning (NPS photo).

The Noatak plots are now part of the Arctic Network's long-term monitoring protocols. Data from all 2017 projects were entered into FFI, a plot-level monitoring software tool for collecting, storing and analyzing ecological information, and archived on the NPS Data Store.

Sources

• National Park Service, Alaska Region, Fire Ecology Annual Report 2017 - Monitoring and Inventory, by Jennifer L. Barnes and Jennifer L. Hrobak, part of the NPS Alaska Region Fire Ecology Annual Report for 2017; rewritten in hubnx's own words.