The story at the bottom of the lake: Detecting past fires through lake coring in Denali

How charcoal from wildfires can be deposited in lake sediments.

Dr. Phil Higuera, University of Montana

Sediment at the bottom of a lake can tell a story of past vegetation and disturbances. Over time, pollen from nearby vegetation is deposited on the lake and settles to the bottom. Charcoal from nearby fires can also be deposited in this way (Figure 1). The layered sediment contains a record of vegetation pollen and charcoal from past fires over thousands of years.

To address the limited understanding of fire history and fire regimes in the front-country of Denali National Park and Preserve, National Park Service Alaska Regional Fire Ecologists and University of Alaska, Fairbanks (Dr. Nancy Bigelow) developed a collaborative proposal that was funded by the National Park Service – Fire Reserve Research Funds in 2023. The goal of the research is to improve the understanding of past fire regimes, vegetation, and spruce bark beetle outbreaks using paleo-sediment records from lakes and peat cores in and around Denali Park.

The research team prepares to build the platform raft. The raft set-up is designed for stability and allows the team to carefully retrieve lake sediment without disturbing it.

Sarah Stehn, NPS

A research study was initiated to reconstruct both vegetation (pollen records) and fire history (charcoal deposits) using lake-sediment records. In June, the NPS Alaska Western Area fire effects crew joined Dr. Nancy Bigelow and assistants from the University of Alaska to core a small lake just outside the Denali Park and Preserve entrance. Technicians set up coring equipment and rafts, to collect the lake sediment cores (Figure 2), and then went afloat. The crew mapped the lake depth and assessed surrounding forest vegetation. They extracted sediment cores while floating upon the raft platform (Figure 3), recorded data about each core, then carefully packed cores away for analysis at the University lab (Figure 4). In the lab, the cores are sliced and analyzed for the age of carbon, count of charcoal and pollen in each layer. Using macroscopic charcoal from well-dated lake sediments, the research team will reconstruct the frequency of fire necessary to assess the natural fire return intervals in the region over the past 1,000 years. Knowledge gained will assist park and fire managers in developing park fire management and fuels treatment plans and manage for natural fire under future climates.

The team pulls up ‘a story of sediment’ ready to be told from the bottom of their study lake near the Denali National Park entrance.

NPS

Packaged lake sediment cores await transport to the lab for slicing. Each slice is analyzed for the age of carbon, count of charcoal and pollen composition.

Sarah Stehn, NPS

Last updated: November 22, 2023