Northern Prairie Wildlife Research Center
The effects of fire on most plant species in northern mixed prairie, particularly those associated with long-term burning, are not well known. Most of the available information has been based on short-term post-fire evaluations, (e.g. Dix 1960; Schripsema 1977; Wright and Bailey 1980; Kirsch and Kruse 1973).
The following are general observations of fire effects on certain plant species that we noted during recent field studies. They are based solely on observation and not empirical data.
Big bluestem, little bluestem, blue grama, Indian grass and switchgrass all increase in abundance with frequent spring (May-June) burns.
Composition and coverage of green needlegrass, needle and thread (Stipa comata), and porcupine grass (S. spartea) increased during the first few sequential (May-June) burns but often declined rapidly after a sequence of five or more spring fires on the same area. Spring burning to reduce Kentucky bluegrass will commonly reduce Stipa spp at the same time.
Kentucky bluegrass and quackgrass (Agropyron repens) apparently decline in abundance after several consecutive spring (May-June) fires. Fires at the time of seedhead emergence appear most effective. Too few observations have been made on fall burns to generalize.
Western wheatgrass increases in abundance after spring, summer, or early fall burns, but considerably more after late summer or early fall fires. Intermediate wheatgrass (A. intermedium), tall wheatgrass (A. elongatum), smooth brome grass (Bromus inermus), Junegrass, and spike oat (Helictotrichon hookeri) all responded well to spring fires and particularly to very early spring (March-April) burns.
Basin wild rye (Elymus cinereus) was unchanged with a 3-year rotation of May-June burns. Sweetgrass (Hierochloe odorata) responded most after August fires, but the sample of observations was small.
No changes to slight decreases occurred after periodic spring fires for white sage (Artemisia ludoviciana), fringed sage (A. frigida), wormwood (A. absinthium), Flodman's thistle (Cirsium flodmanii), western yarrow (Achillea millefolium), prairie coneflower (Ratibida columnifera), northern bedstraw (Galium boreale), western ragweed (Ambrosia psilastachya), stiff sunflower (Helianthus rigidus), and leafy spurge. Occasionally, notable decreases in wormwood have been seen when this species was about 6 inches (15 cm) tall at the time of the burn.
Silver-leaf scurf pea (Psoralea argophylla), lead plant, blue false indigo (Baptista australis), pasque flower (Anemone patens), many-flowered aster (Aster falcatus), lady slipper (Cypripedium spp), white camas (Zigadenus elegans), wild lily (Lilium philadelphicum), tall gayfeather (Liatris ligulistylis), Maximilian sunflower (Helianthus maximilianii), sweet clover (Melilotus spp), purple prairie clover (Dalea purpurea), and harebell (Campanula rotundifolia) increased in abundance following spring burns.
Pasque flower bloomed in August and September after a late July or early August fire. Silver-leaf scurf pea showed greater increases after August fires than spring fires, but we have limited observations for August burns.
Alfalfa (Medicago sativa) was favored by early spring burns, but substantial declines followed late summer or fall burns.
Dramatic increases in sprouts of western snowberry often occur after a first fire, particularly on areas that have been idle for several years. A sequence of spring fires on the same area will eventually reduce abundance. Significant reduction requires five or more fires in 10 years or less. One or two fires followed by a series of rest years will result in an increase of aerial coverage. Hot burns in late summer to early fall have caused severe root burns on western snowberry plants.
Buffaloberry does not occur in dense patches like western snowberry, nor is it as widely distributed. However, its response to spring fires is very similar. In a few instances, buffaloberry abundance has been greatly reduced with hot fires in early August.
Prairie wild rose, western wild rose, and willows (Salix spp) apparently survive frequent fires fairly well even though there appears to be a small reduction in plant abundance after repeated fires.
Stems of older plants of Juneberry, hawthorn (Crataegus spp) and choke cherry are often killed by hot spring fires, but they can survive cool or incomplete burns. Sprouting of new shoots occurs in all three species after either spring or fall burns but is less pronounced after late summer or fall burns. Resprouting has been seen on areas with histories of five or six fires over a period of about 15 years.