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US Fish & Wildlife Service FieldNotes

Alaska Fire Management: Taking a Closer Look at What Fuels Fire

Region 0, April 26, 2013
Gathering vegetation samples.
Gathering vegetation samples. - Photo Credit: n/a
Logging vegetation samples collected.
Logging vegetation samples collected. - Photo Credit: n/a
Weighing samples before drying.
Weighing samples before drying. - Photo Credit: n/a
Vegetation with moisture removed.
Vegetation with moisture removed. - Photo Credit: n/a

By Lisa Saperstein
Alaska Region Fire Ecologist

 

How can we predict if and where a wildfire might occur? Sometimes it requires getting outdoors and getting your hands dirty.

The amount of moisture in various types of vegetation can determine if a fire is likely to start and how it might behave once ignited. The less moisture in vegetation, the more easily it can ignite and more rapidly it can burn.

For many years, fire managers in Alaska have relied on data collected from weather stations around the state and on formulas established in the Canadian Forest Fire Danger Rating System to determine fire danger. A statewide, interagency effort is now underway to determine just how accurately that system is predicting fire danger in Alaska.

For that reason the staff of the Fish and Wildlife Service Fire Management Program in Alaska will soon head outdoors armed with clippers and containers. They will travel to sites chosen for their representative sampling of the vegetation types likely to burn in that area. Once there, the fire staff will collect samples of these “live fuels” – grasses, shrub leaves and small twigs, spruce twigs, and herbs.

They will also collect “duff plugs” that consist of moss and the dead, decaying material – duff – between the live moss layer and the mineral soil. Moss – especially feather mosses – can dry quickly and carry a fire through the forest understory. Duff retains moisture better than moss, but even the lowest duff layers can dry if there are extended periods without rain, allowing a fire to smolder in the forest floor and sometimes to overwinter and flare up again after the snow melts.

Each sample collected is placed in an airtight container and transported to a lab where it is carefully weighed before being placed in a drying oven at 200° F. The live vegetation is dried for 24 hours while the duff is dried for 48 hours. Once dried, each sample is again weighed to determine its dry weight; the difference between wet and dry weights provides an estimate of how much moisture the plant contained in the field.

This vegetation collection effort will occur roughly every two weeks throughout the fire season at sites in Anchorage, Fairbanks, Denali National Park, Tok, McGrath and Galena. In addition to the Fish and Wildlife Service, the National Park Service, Bureau of Land Management, and State of Alaska are participants in the project. More than just an opportunity to get a few hours in the fresh air, the effort will provide valuable data for fire managers.

The project has several objectives: One is to track moisture levels in different fuel types from early spring – before the vegetation greens up – to the end of fire season in fall. Another is to verify that fire danger indices calculated from weather station data actually represent the moisture status of common fuels. A third objective is to provide data on live fuel moisture for use in fire behavior models. These models are used by firefighters during wildfires or to plan prescribed burns. In addition, the data collected are entered into a national database for live fuel moisture.

While it’s too early to draw year-to-year conclusions, preliminary data indicates that fuels in the Anchorage area have a higher moisture content throughout the fire season than those fuels sampled in areas farther north. The data gathered so far also appears to confirm that there is a dip in moisture content in all areas in the spring. In addition to continuing the project at current sampling sites, organizers hope to expand the effort to different areas of the state – and into tundra vegetation – in coming years.

Contact Info: Maureen Clark, (907) 786-3469, Maureen_Clark@fws.gov