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Refuge Notebook: Fire (and moose) by the numbers

Posted: April 18, 2013 - 2:47pm  |  Updated: April 19, 2013 - 8:39am
The 26,300-acre Fox Creek Fire in 2005 was caused by lightning in spruce bark beetle-killed white spruce on the Kenai National Wildlife Refuge. This fire was deliberately allowed to burn for resource benefits (including moose) but was flanked to protect cabins outside refuge boundaries.  Kenai National Wildlife Refuge
Kenai National Wildlife Refuge
The 26,300-acre Fox Creek Fire in 2005 was caused by lightning in spruce bark beetle-killed white spruce on the Kenai National Wildlife Refuge. This fire was deliberately allowed to burn for resource benefits (including moose) but was flanked to protect cabins outside refuge boundaries.

Despite all the snow still on the ground, April 1 was the official start of the 2013 fire season in Alaska. For many years, the season started on May 1, but it was changed in 2006 largely because of the increasing threat of “pre-green up” grassland fires in the aftermath of the spruce bark beetle outbreak on the Kenai Peninsula. The year before, in 2005, the Tracy Avenue Fire near Homer started on April 29, burning 5,400 acres in what was described by the Division of Forestry’s director as the “earliest large complex fire in the state’s history.”

Since then, the peninsula has seen three other grassland fires that burned significant acreage. The Caribou Hills Fire began in June 2007 when sparks from a shovel being sharpened by a grinder ignited dry grass, eventually burning 55,400 acres and almost 200 cabins, homes and outbuildings. The 260-acre Homestead Fire near Clam Gulch burned 260 acres in May 2008. The Mile 17 Fire on East End Road near Homer torched over 1,000 acres and 8 structures in mid-May 2009 after a downed power line ignited dry brush. 

What these fires have in common is they were human-caused and started in grasslands, composed primarily of Calamagrostis canadensis, during spring. This is a significant departure from fire records kept over the previous half century that show mostly lightning-caused fires started in spruce forests in mid or late summer.

Based on radiocarbon-dated soil charcoal and tree-ring counts, we know (thanks to retired ecologist Dr. Ed Berg) that not all spruce on the Kenai burns with the same frequency. In the northern part of the Kenai National Wildlife Refuge, where black spruce predominates, a given acre has historically burned every 80 years, a statistic called the mean fire return interval (MRI). In the southern part of the refuge, where white and Lutz spruce predominate, the MRI is 400-600 years. The MRI for white and black spruce stands mixed with hardwood is 130 years. Sitka spruce, on the eastern side of the peninsula, has essentially no MRI because of the wet climate there.  

Understanding the MRI helps us understand the distribution of our moose populations today. Spruce stands convert to hardwood when fires are hot enough to burn to mineral soil, and these stands are favored by moose for winter browse 20 years post-fire.

The impetus to establish what-was-then the Kenai National Moose Range by presidential order in 1941 was the concern about declining moose populations at that time. Of course, the opinions of early miners, commercial guides, and game wardens at that time were colored by the human-caused fires (at least 106,000 acres) that burned the Tustumena Benchlands in the late 1800s, setting the stage for abundant subalpine willow and moose into the 1920s. The earliest population estimate we have of moose in this area was 3,100 in 1965; the most recent estimate is about 1,000 moose in 2001.

Current long-time residents on the Kenai Peninsula similarly have a view of moose populations that is an outcome of the MRI. The 310,000-acre Skilak Lake Fire in 1947 and the 79,000-acre Swanson River Fire in 1969, both caused by campfires, set the stage for abundant hardwood browse and moose north of Skilak Lake in the 1960s through 1980s. Populations in this area peaked at 5,300 moose in 1971 but are now less than 1,600. The good news for moose hunters is that we are now well within the statistical bounds of the estimated MRI and the likelihood of a landscape-scale wildfire increases with every passing year.

Conversely, wildfires south of Tustumena Lake were historically non-existent as far back as the late 1700s. Consistent with an MRI that spans centuries, it has only been in the last two decades that fires have started to burn in the white and Lutz spruce forests that were coincidentally hard hit by spruce bark beetles during the late 1980s through the 90s. Starting with the 2,800-acre Windy Point Fire in 1994, about 140,000 acres have burned on the peninsula, two-thirds of that south of Tustumena Lake. Not surprisingly, moose have increased in that area from 2,000 in 1992 to 3,200 in 2013.

On almost 1.3 million acres of the Refuge, the default management option is to allow a fire to burn. However, that sometimes proves difficult when fires threaten local communities. Since 1980, the Refuge has used prescribed burns (4,700 acres) and mechanical treatment (1,000 acres) to reduce fuel loads along the wildland-urban interface (WUI). Although 6,000 treated acres in the past 3 decades doesn’t sound like much moose habitat, that wasn’t the explicit intent of this management strategy. Rather, it was to reduce fuel loads in the WUI to increase the likelihood of allowing wildfires to run.  

But fires and the vegetative response to fires are changing. Roughly 50% of every acre burned in spruce on the Refuge has historically been converted to hardwood. Here on the Kenai, however, in the aftermath of the longest spruce bark beetle outbreak in North America, not all spruce is regenerating back to spruce or converting to hardwood. Much of what was mature white and Lutz spruce forest on the southern peninsula is now Calamagrostis grasslands with few spruce seedlings. This has prompted the local fire management community (All Hands/All Lands) to evaluate different treatments for reducing Calamagrostis in the WUI. 

We’ve begun to suspect that these spring fires in grasslands are not just putting cabins and houses along the WUI at risk on an almost annual basis. Consistent with our climate-envelope models that predict deforestation on parts of the Kenai, these spring fires may actually be the mechanism by which a new grassland ecosystem is maintained in what used to be a transitional boreal forest. The climate is changing and our expectations about fire and moose should as well. 

 

John Morton is the supervisory biologist at Kenai National Wildlife Refuge. You can find more information about the refuge at http://kenai.fws.gov or http://www.facebook.com/kenainationalwildliferefuge.

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