Reconstructing the Past to Protect the Future: Understanding the Historic Role of Fire in Shaping and Maintaining Forested Wetlands

Posted 11/1/18

Forested wetlands are an ecologically important ecosystem that make up over half of the freshwater wetlands in the United States. We lost over 250,000 hectares of these wetlands between 2004 and 2009, which could be detrimental to many wetland-dependent species of plants and animals, not to mention the importance of these systems for carbon sequestration. By collecting samples from stumps and trees in these areas and examining them for evidence of historical fire, Masters student Colleen Sutheimer is working to understand how fire has shaped these systems in the past and how it can be used to preserve them in the future.

Fire and wetlands are not concepts that we intuitively think about in conjunction with one another. Masters student Colleen Sutheimer is working to change that with the hope that her work will eventually inform future wetland management and conservation on a broad scale. By reconstructing the historic temporal and spatial scale of fires in forested wetlands in the upper Great Lakes region, Sutheimer believes her work will help managers make good decisions about the use of fire as a management tool in these extremely unique and important ecosystems.

Forested wetlands make up almost half of all freshwater wetlands in the United States, and forested wetlands declined by over 250,000 hectares between 2004 and 2009 alone. These areas are extremely important ecologically, though, as they are home to many unique plant and animal species, are important stores of organic carbon, and provide water filtration services. However, the historic role of fire in these systems is not well understood. Specifically, whether these systems developed with fire and how often fire happened in the past are questions Sutheimer is hoping to answer. “This is a really interesting time to be working on fire in the Great Lakes region, but especially in these wetland systems. A rigorous understanding of fire’s role in Wisconsin has not been achieved yet,” Sutheimer said of her research.

An example of a processed and dated remnant red pine stump. This tree originated in 1718 and was harvested around the 1850s. Each date corresponds to a different fire that scarred the tree while it was still alive.

Reconstructing historic fire regimes is not an easy job, however. In order to do it, Colleen and her colleagues at Wisconsin DNR target red pine stumps in forested wetlands that are remnants from the clear cut that took place over northern Wisconsin and the Upper Peninsula of Michigan in the 1800s. Using chainsaws, Sutheimer takes samples from these stumps and non-destructive samples from living trees and snags. These collected samples must then be dried, planed to create a flat surface, and finally sanded to smooth the surface and make the growth rings visible and ready for analysis. With a well-prepared sample, Sutheimer can determine the age of the tree, as well as examine fires scars as evidence of fire exposure in the growth rings of the tree. Targeting these old stumps allows Sutheimer to examine the frequency and intensity of fires that occurred up to 500 years in the past. Additionally, by taking samples at a large spatial scale, Sutheimer can get an idea of how intense specific fires were.

Sutheimer has already completed sampling at one of her study sites, near Betchler Lake in the Hiawatha National Forest, located in the upper peninsula of Michigan. At this site alone, Sutheimer took over 80 samples from both the periphery of the wetland as well as from “islands” of trees within the wetland. Using the samples she has collected from the Betchler Lake Area, Sutheimer will be able to reconstruct an entire fire history for this localized wetland area. Though Sutheimer has not aged these samples yet, a sample from another area yielded a tree that had originated in the 1500s, making Sutheimer optimistic that their sampling will successfully span a broad temporal range. This site is just the beginning. Sutheimer has plans to reconstruct fire histories for additional sites in the Hiawatha, Ottawa, and Chequamegon-Nicolet National Forests, giving her an unprecedented look at the history of fire in these wetland systems.

Location of where red pine stumps were sampled and peatland cores were taken within and around the Betchler Lake site.

Disturbances such as fire may be important shapers of forested wetlands by helping to stop vegetation encroachment and allowing them to continue to provide essential habitat to many amphibian and carnivorous plant species that are already threatened by other factors. These areas also serve as carbon sinks by storing carbon both in the trees and in the inundated organic soils. Threats like climate change make it even more imperative to understand past disturbance regimes to help scientists plan for future climate scenarios. Understanding the historic role and characteristics of the fire regime in these systems will allow Sutheimer not only to understand how fire has affected these systems in the past, but to provide recommendations for its use as a management tool in the future.

Story by Brunk, Kristin