Curious About … Plant Recovery After Fire?

I’m pleased to introduce my good friend, Ellen Kuhlmann, as my guest blogger. Her piece highlights how native plant are adapted to a landscape frequented by fire. Ellen worked as a botanist for the Okanogan Wenatchee National Forests and for the Wenatchee Forestry Sciences Lab. She led the Seeds of Success native seed collection team, a program managed by Rare Plant Care and Conservation. She studied fire ecology at Western Washington University and is the coauthor of Trees and Shrubs of the Pacific Northwest. Ellen lives in Bellingham, Washington.

Plants are closely attuned to the places they live, their habitat. Plant species differ in their ecological amplitude to respond to changes to their habitat. They grow successfully in places within their tolerance levels for environmental factors such as cold, shade, or drought combined with abiotic factors such as soil type and geographic locale. In addition to usual fluctuations in the growing conditions habitat can be altered, at times dramatically, by disturbances such as fire or flood.

Wildland fires naturally start from lightning when extreme heat connects with fuel, causing the material to combust due to reaction with oxygen in the air. Fires in natural areas burn vegetation and heat the soil while releasing particulate-laden gases into the air.

Historically, arid habitats often had more fires than wet places as vegetation with lower moisture levels burns more easily. If the area also experiences storms with lightning strikes during the dry season, the scene is set for recurrent fire. The East Cascade Wenatchee Mountains and the Okanogan are two of many areas with both dry summers and lightning storms. The plant communities found here have long coexisted with fire.

Over time, exposure to a stressor such as fire can result in the evolution of traits advantageous to species survival or even result in dependence on fire. Some traits developed for one reason, like grazing, may be adaptive towards other stresses such as fire as well. What we sometimes view as a static landscape is in motion, although the rate of change may be slower than the rate usually recognized by our human perspective.

Fire is a dramatic change agent that is easily noticed. After fire burns through an area it may appear barren, blackened with little if any vegetation remaining.

Nature is full of ingenuity, and plants have developed a variety of ways to cope with and even thrive with periodic fire. Some species have burn resistant physical or morphological features, while others have seeds that respond to fire. Depending on the fire severity, climate, and vegetation type, burned areas may quickly show signs of revitalization.

Fire Resistance. Some adaptations increase the ability of individual plants to weather a fire. The thick bark of ponderosa pine (Pinus ponderosa) and Douglas-fir (Pseudostuga menziesii) protect vulnerable phloem and xylem tissues (that transport water and other nutrients) located beneath the bark. The protective bark resists burning and retards transfer of heat, limiting damage to the tissues.

Resprouting. Many shrubs, grasses, and wildflowers grow new stems after the shoot is killed by fire. They resprout from buds near the root crown or from other underground structures. Bigleaf maple (Acer macrophyllum), aspen (Populus tremuloides), and pinegrass (Calamagrostis rubescens) are among the many plants with the ability to resprout after a burn.

Seed Germination. Species can experience high mortality on burned sites but remain part of the postburn plant community through germination of seed present in the soil. Plants also return to burned areas through dispersal of seed from nearby unburned areas. These may be new additions to the plant community or one that was part of the preburn community. In addition, fire creates bare soil patches where seeds can germinate more easily.

Seeds can remain dormant (viable but not germinating) for long periods of time, germinating only after the dormant state is broken. Heat from fire can break seed dormancy by cracking the seed coat, allowing water to enter, and releasing chemicals that maintained dormancy. Fire can affect seed dormancy in other ways such as by reacting with smoke or due to the duration of soil heating. Two species that show fire-stimulated seed germination are longsepal globemallow (Iliamna longisepala) and snowbrush (Ceanothus velutinus), both of which have long-lived seeds with hard seed coats.

A common component of postfire communities is the aptly named fireweed (Chamerion angustifolium). Fireweed can resprout from rhizome-like roots and has lightweight wind-disseminated seeds that readily travel through the air, dispersing into burned areas.

Sun and Soil Effects. Fire also brings changes to burned areas through increasing light levels reaching the ground and altering soil nutrients. One species that responds increased light is pinegrass. It rarely flowers except after fire, when it often blooms profusely. This trait both saves the energy spent on producing flowers and seed until needed and enhances the chance of the seeds germinating successfully.

Heating changes soil texture and composition, removing organic matter and volatilizing nutrients such as nitrogen. Lupines (Lupinus spp.) are less reliant on soil nitrogen level due to a symbiotic relationship with bacteria. The bacteria convert atmospheric nitrogen into a bioavailable form that is absorbed by roots that house the bacteria in nodules. Several years postfire lupines are often more abundant on a site than before as they grow well in nitrogen poor soils.

The interactions between fire and plants are complex, varying by species and fire severity.

The adaptations discussed here are only a few of  the ways they adapt to the presence of fire in their environment. Learning about these responses can teach us much about how organisms fit into the places they live. By examining how plants respond to fire we can learn how to better manage fire prone landscapes, fostering increased resiliency and health of these beautiful natural places.

Suggested Resources

Arno, S.F., and S. Allison-Bunnell. 2002. Flames in our forest: disaster or renewal?  Island Press. 227 pages.

Brown, J. K. and J.K. Smith, eds. 2000. Wildland fire in ecosystems: effects of fire on flora. Gen.Tech. Rep. RMRS-GTR-42-vol. 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 257 pp. Available: https://www.fs.fed.us/rm/pubs/rmrs_gtr042_2.pdf

DeBano, L.F. 1990. The effect of fire on soil properties. Symposium on Management and Productivity of Western-Montane Forest Soils, Boise, ID. Available:  https://forest.moscowfsl.wsu.edu/smp/solo/documents/GTRs/INT_280/DeBano_INT-280.php

Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Missoula Fire Sciences Laboratory (Producer). Available: https://www.fs.fed.us/database/feis/

Fireworks Educational Program. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Modeling Institute (Producer).

Check out many wildfire Resources available on this Wenatchee Naturalist webpage. Teacher and parents can explore a variety of wildfire ecology lessons and curricula (scroll to the bottom on the webpage.).