Reading Past Fires in the Mud of a Denali Lake

The mud at the bottom of a lake keeps a record of the land around it. Pollen from nearby plants lands on the water and sinks; so does charcoal from nearby fires. Layer on layer, over thousands of years, the sediment holds a history of vegetation and past fires.

Why Denali

Little is known about the fire history and fire regimes of the front-country of Denali National Park and Preserve. To close that gap, the National Park Service's Alaska Regional Fire Ecologists and Dr. Nancy Bigelow of the University of Alaska Fairbanks wrote a joint research proposal, funded in 2023 by the Park Service's Fire Reserve Research Funds.

The goal: a better understanding of past fire regimes, vegetation and spruce bark beetle outbreaks, read from sediment records in lake and peat cores in and around the park.

The team prepares to build the raft platform, which is set up for stability so the sediment can be brought up without being disturbed. Photo: Sarah Stehn, NPS.

On the lake

In June, the NPS Alaska Western Area fire effects crew joined Dr. Bigelow and assistants from the University of Alaska to core a small lake just outside the park entrance. The crew:

• set up the coring equipment and rafts, then went out on the water;
• mapped the lake's depth and assessed the forest around it;
• pulled sediment cores while floating on the raft platform, and recorded data on each;
• packed the cores carefully for analysis at the university lab.

The team pulls up a core from the bottom of the study lake near the Denali National Park entrance. Photo: NPS.

In the lab

Each core is sliced, and each slice analyzed for the age of its carbon, its charcoal count and its pollen. Using macroscopic charcoal from well-dated sediment, the team will reconstruct how often fire burned, to assess the region's natural fire return interval over the past 1,000 years.

Packed cores wait for the trip to the lab, where they will be sliced for dating, charcoal counts and pollen. Photo: Sarah Stehn, NPS.

What it is for

The results will help park and fire managers write fire management and fuels treatment plans, and manage natural fire under future climates.

Sources

Based on "The story at the bottom of the lake: Detecting past fires through lake coring in Denali," National Park Service; a work of the United States government in the public domain. The source's diagram of how charcoal reaches lake sediment, credited to Dr. Phil Higuera of the University of Montana, is not reproduced.