Substrate - Fire Interactions

Authors: Randall Mitchels and Paul Bodalski

This case study is part of a collection of pages developed by students in the 2012 course, "Megafires: rare events or the new norm," in the Department of Earth Sciences, Montana State University. Learn more about this project.

While often overlooked, the ground beneath you may have much more to do with fire ecology than you think! Substrate is a crucial root of forest ecology and fire regimes.


Forest vegetation is dependent on several different factors. For example, amount of precipitation, climate, fuel types et cetera. However, a major factor that controls vegetation patterns is too often overlooked in the view of the public, is substrate composition.

Jump down to: Glacial Substrate | Rhyolite Substrate | Fire Effects on Soil | Learning Activities | References

Two different substrate compositions and comparing the vegetation environments that occur in each substrate environment. Knowing each type of vegetation environment in turn allows forest ecologists to determine the fire regime. We will also be looking at how substrate environments change following a fire event.

Pictured below are three different vegetation environments. We can look at the types of vegetation to determine fire regimes and substrate compositions. As you can see these are three completely different vegetation environments. Therefore they are three completely different substrate environments and in turn, three different fire regimes.

Substrate #1: Glacial Till/Glacial Outwash

Glacial till and glacial outwash form a substrate upon which grasslands and small shrubs are typically successful. Pictured below on the right is a portion of Paradise Valley just North of Yellowstone National park. This photo is courtesy of the authors. Glaciers advanced and then retreated in the area dropping sediment and cobble sized stones creating the substrate layer. Fires in this area would be high frequency, low intensity as there are no intermediate fuels or large trees to burn. This information was obtained through a Montana State University course ERTH 212: Yellowstone Scientific Lab taught by Dr. Dave McWethy. If interested in learning more about this course and when it is offered it can be found under MyInfo on

See related links for more information about glacial till and glacial outwash as a substrate

Substrate #2: Rhyolite

Rhyolite substrates typically form extremely harsh soil environments where lodgepole pine are usually successful. Very few other species of vegetation are capable of growing in such an environment due to rather acidic soil. Lodgepole pine grow in a way that most of their branches are kept high off the ground. Very little intermediate fuels are able to grow in the area. Therefore, fire regimes in this type of substrate environment are for the most part are low frequency, high intensity if the forest is dense as is pictured. This photo is courtesy of the authors. This information was obtained through a Montana State University course ERTH 212: Yellowstone Scientific Lab taught by Dr. Dave McWethy. If interested in learning more about this course and when it is offered it can be found under MyInfo on Montana State University's class search.

Fire Effects on Soil

Fire events, regardless of size and severity, always alter soil's physical and chemical composition. Burned vegetation releases nutrients, that are otherwise held up in living and dead plant material, back into the soil. The nutrient rich soils left behind after a fire promote the growth of new vegetation which speeds the recovery of the affected area. Some nutrients are lost due to increased erosion in the affected burn area. The loss of vegetation leaves soil exposed to rain/wind erosion which can drastically change a landscape over time. More severe can fires have greater impacts on soils. Hotter burning fires can burn away subsurface soil biota, killing burrowing insects, animals, and deep plant roots which are otherwise generally unaffected by low intensity ground fires. In conclusion, fire can alter soil and even substrate composition, which in turn changes vegetation patterns. This information was obtained through the British Columbia Ministry of Agriculture

See related links for more information about fire effects on soils.

Learning Activities

The related links will take you to outside pages where you can read more about soil/fire interactions.

Here is a interactive learning page for kids that includes four different games, forest facts, stories with Smoky the Bear and an email club for kids.

Interested in learning more!? Here are a few links and case studies regarding each substrate topic!

Substrate #1 Glacial outwash/till:

Here are two sites that go into detail about glacial till as a substrate: This site is about glacial and periglacial environments, a list of environmental glacial terminology provided Macquaire University in Sydney, Australia; here is a website about glacial tills and sediments that are formed or found in and around glaciers.

Here is a link to a case study published in the scientific journal, Quaternary Research, conducted by Dr. Linda Brubaker titled, "Postglacial Forest Patterns Associated with Till and Outwash in Northcentral Upper Michigan'.

Substrate #2 Rhyolite:

This site discusses Yellowstone forest ecology. Much of the soil is rhyolitic in Yellowstone National Park.

Dr. Cathy Whitlock has conducted extensive research in Yellowstone and Grand Teton National parks regarding post glacial climate and vegetation. Here is a link to one of her earlier studies in the Greater Yellowstone Ecosystem.

Topic #3 Fire Effects on Soil

The government of British Columbia produced this fact sheet that discusses the after-effects of fires on soil, such as physical properties, biota and soil moisture.


Whitlock, Cathy. 1993. Postglacial Vegetation and Climate of Grand Teton and Southern Yellowstone National Parks. Ecological Monographs, Ecological Society of America. Print.

Secret Yellowstone. 2010. "Plantlife". Website.

Kelsie Dadd. 1999. Glacial and Perglacial Enviornments.

Glacial Till: Direct Glacial Sediments. 2013.

Brubaker, Linda B. 1975, "Postglacial Forest Patterns Associated with Till and Outwash in Northcentral Upper Michigan" College of Forest Resources, University of Washington-Seattle. Web.

Bruhjell, Darren, and Tegart, Greg. (n.d.) Fire Effects on Rangeland Factsheet Series. British Columbia Ministry of Agriculture. Web.

Anderson, Loren D, et al.. 2001. Fire Effects Guide (now offline). National Wildlife Coordinating Group. Web.