Hello Fireshed community,
Happy Wednesday and a happy Thanksgiving to you and your family! This year we’re feeling particularly grateful for the beautiful landscapes of Northern New Mexico that we live and recreate in and the fire personnel that keep our ecosystems and communities safe. While we often share resources on how to prepare for or cope with wildfire, this week we wanted to share with you information regarding the ecological role of fire. The role of fire varies across landscapes and many ecosystems have evolved to have specific and beneficial relationships with periodic wildlife. Keep reading to learn more!
This week’s Wildfire Wednesday features information on:
How fire benefits ecosystems
Fire adapted species
Fire return intervals
Best,
Liz
How fire benefits ecosystems
Periodic, low-intensity fire can have many positive effects across ecosystems, keep reading to learn more or click on any of these sources to dive deeper: Benefits of Fire (Cal Fire); Fire Effects on Soil (NAU); Fire Ecology (BLM); Fire’s Natural Role (USFWS); The Ecological Benefits of Fire (National Geographic).
Photo credit: Sharon Hood
“Cleans” the forest floor
When low-intensity fire travels through the understory it removes the layer of dead or decaying plants. By removing this debris, it opens up space on the forest floor where growth of new plants is encouraged and it reduces the likelihood of high-intensity wildfire.
Returns nutrients to soil
Although overall some nutrients on-site are lost during a fire, fire actually increases the amount of available nutrients in an ecosystem. Soil fertility increases after low-intensity fire as the fire chemically converts nutrients in dead plants that would otherwise take much longer to decay and return to the soil.
Increases diversity
When a forest is without fire it leads to over-crowding, preventing sunlight from reaching the forest floor and creating intense competition for water and available nutrients. In the aftermath of low-intensity fire, gaps in the canopy are created allowing sunlight through and there is more available nutrients and water. Low intensity fires can also eliminate invasive/noxious weed infestations, allowing an opportunity for native plants to grow and establish. Some native species actually require fire for seed germination!
Creates new habitat
Fire removes thick brush, maintains open meadows, and thins out dense forests, all creating new habitat for animals and birds. Additionally, those trees that do not survive fire create new habitat for insects and cavity nesting birds and animals.
Kills pests and diseases
Fire kills populations of beetles, mites and other harmful pests which reduces disease and keeps forests healthier.
Photo credit: Harvey Mudd College
Fire adapted species
Many of our beloved plant species are fire-adapted, meaning that they have “life history traits that help them survive wildfire or to use resources created by wildfire.” There are different categories of fire-adapted plants based on the traits that allow them to survive or flourish with wildfire (from Fire Ecology by the Bureau of Land Management)
Ponderosa pines, an example of a “resister” fire-adapted species (Credit: John Marshall)
Resisters are the species that can survive moderate to low-intensity fires with little to no damage. Some adaptations of Resisters include: thick bark to shield them from fire; deep roots protected from fire; the shedding of their lower branches to prevent fire from climbing; and moist, short needles or leaves that are hard to burn. Some examples include: ponderosa pine, sugar pine, and Douglas-fir.
Aspen resprouting after a recent fire in Utah (Credit: Karen Mock)
Sprouters are the species that endure fire. Sprouters resprout from their roots, trunks, limbs, and/or crown after a burn. Many shrubs are sprouters. Some of these species also have hard shelled seeds relying on fire to crack them open. While the parent plant may be injured in a fire, the new sprouts are able to grow in nutrient rich soil and have less competition. Some examples include: oak, aspen, and madrone.
Lodgepole pines, an example of a “seeder” species, requires fire for their seeds to germinate.
Seeders are adapted to evade fire by shedding lots of seeds that sprout after fire. These sprouts thrive from the rich nutrients recycled into the soil. Right after a fire is a prime time for a plant to disperse its seeds and germinate because there is more space to grow and less competition for resources like sunlight, water, and nutrients. Many Seeders are dependent on fire to create the habitat needed for their seedlings to sprout and grow. Seeders are not invaders because they already inhabited the area before the fire and their population does not spread as rapidly as invaders. Some examples include: buckbrush, lodgepole pine, and manzanita.
Filling the “invader” niche, lupine will take advantage of recently burned areas (Credit: NPS)
Invaders take over recently burned areas. Their populations are either limited or unknown prior to fire. Invaders tend to have seeds that are highly dispersive by wind, animals, or people. Many invaders are noxious weeds that take over areas after disturbances such as a fire, flood, or development. Some examples include: star thistle, fireweed, scotch broom, and lupine.
White fir trees are “avoiders”, they tend to grow in areas where fire does not frequently occur.
Avoiders are least adapted to fire because they grow in areas where fire does not normally occur. They are typically found near water or in high elevations. Avoiders are a late successional species, thus they are not found in recently burned areas. Avoiders have thin bark, shallow roots, and lots of resin, which can help a fire spread. Few avoiders survive moderate to high intensity fires. Some examples include: white fir, vine maple, western red cedar, and western hemlock.
To learn more about the different traits plants develop to survive wildfire or use it to their advantage check out this Britannica article “Playing with Wildfire: 5 Amazing Adaptations of Pyrophytic Plants”
Fire Return Interval
A fire return interval is the (historical or natural) time between fires in a defined area, usually at the scale of a point, stand or relatively small landscape area. For example, fires in ponderosa pine communities burned naturally on a cycle of one fire every 5 to 25 years. This frequent fire burned the grasses, shrubs, and small trees, and maintained an open stand of larger ponderosa pine trees.
Check out this table from the Forest Service detailing fire regime characteristics for different ecosystem types in the Southwest.
Map showing the historic fire return interval in years for Arizona and New Mexico (Credit: HISTORIC FIRE RETURN INTERVALS FOR ARIZONA and NEW MEXICO: A REGIONAL PERSPECTIVE FOR SOUTHWESTERN LAND MANAGERS)