Prescribed fire is an important tool when it comes to managing Iowa’s prairie and woodland ecosystems. Having evolved under the influence of wild fire for thousands of years, native plant communities not only respond favorably to fire, but in many ways require it to thrive. Today, with so little native prairie left in Iowa (less than one tenth of one percent), wild fire has been removed from the equation. But the fragmented parcels of natural ecosystem still need fire to remain healthy – this is why we “prescribe” fire.
Fire removes excess leaf litter and duff (decaying organic matter) allowing more plants to flower, produce seed, and grow taller. It also increases available nutrients through indirect stimulation of microbial activity in the soil and releasing nutrients from the ash. Burning exposes the darkened soil and allows sunlight to warm the soil quicker and extend the growing season for warm season native plants. Fire favors native plants and helps control invasives. It suppresses many weeds (that would normally grow faster and outcompete the natives) and helps to control cool season invasive grasses like brome and reeds canary grass. It can also damage or kill woody invasive plants like bush honey suckle and autumn olive – both species that would otherwise quickly dominate a prairie system.
Conditions are most favorable for prescribed fire in the early spring (before ground nesting birds lay their eggs) and in the late fall. Linn County Conservation is watching weather conditions and planning for fall burns right now.
Fall burning has some benefits that spring does not. Fall burning is usually conducted after a hard frost when the plants have gone dormant. Burning when plants are dormant eliminates the possibility of damage to early forbs (wildflowers). Burning in the fall also allows for the seeds from forbs to contact the cold moist ground, by eliminating the thick layer of duff build up. Many forbs need a period of cold moist stratification to germinate and grow. Thus, fall burning increases the propagation of new forbs. Fall burning can also be better when trying to suppress certain invasives that may remain active and green later than native species. While fall favors the forbs, spring favors the tall grasses. For this reason, we alternate. We want the prairie to be as diverse as possible.
Whether we are using prescribed fire as a tool in the spring or the fall, we are careful to divide areas into approximately 1/3 sections. Rotating areas ensures habitat cover for wildlife and is not as stressful on insect populations.
The idea of using prescribed fire in woodland ecosystems is less familiar to most people, but like the prairie, the woodland native species derive many benefits. Most of Iowa’s woodlands historically were much more open than they are today, trees were more widely scattered with rich, diverse herbaceous plants growing underneath. The term “savannah” or “oak savannah” is often used to describe this native system. In the past 100 years the suppression of fire has changed the composition of our woodlands. They are more likely to be overgrown with invasive species and less desirable trees such as box elder, silver maple and elm. Many species of oak are built to survive fires of medium intensity. Their thick bark protects them. Less desirable trees and invasive species like garlic mustard are not conditioned to withstand fire and are removed. By removing undesirable plants in the understory of the woodland with fire, competition against native species is reduced and sunlight can penetrate to the forest floor. This aids in the growth of native herbaceous plants, wildflowers and the regeneration of oak trees. Linn County Conservation hopes to complete several woodland burns yet this year.
Dana A. Kellogg
Natural Resource Specialist