Prescribed fire can be healthy for an ecosystem and it can have unintended consequences. With a little information, one can support the positive and avoid the negative. For example, a 7-acre forb-heavy planting was wholly burned annually because it was believed seed production would increase. A few years of this intense burning and big bluestem crowded out the forbs. The manager then wanted to herbicide the tall grass to restore diversity. These are expensive and resource-heavy consequences that didn’t need to happen had science been at the forefront of their management plan.

Had managers understood these processes—along with the four elements described later—their plan would have been grounded in ecological science rather than this urgency where burning became a reflex rather than a well-thought-out plan. These crisis narratives oversimplify management by flattening the complex dynamics of the ecosystem converting complex biological processes into linear expectations. The results often produce the opposite effect of what is intended. In this case, the assumption that fire inevitably boosts flowering and seed production ignored the nuanced mechanisms by which fire actually operates. By assuming a linear outcome, this management overlooked how fire can actively strengthen dominant C4 grasses by stimulating mycorrhizal associations, which increases tillering and flowering [1], and by opening the canopy in ways that improve pollen movement for wind-pollinated grasses [2]. Together, these effects can intensify grass dominance.

Grasses and forbs respond differently to fire, especially frequent fire [3-7]. Management practices highly dependent upon fire cater to warm season grasses and suppress the less dominant species, such as forbs. The result: biodiversity is eroded [8-15].

Costly long-term mistakes can be avoided with knowledge. Understanding the biology and physiology of grass and how these factors interact with fire explains the oft-heard phrase “fire favors grass”.  Learning this science brings freedom from relying on others and gives landowners confidence achieving management goals specific to their land.

Grasses also produce tillers, which are additional stems that sprout from buds at the base of the plant. These buds—called apical meristems—are protected at ground level or below. When a fire passes through, it removes the dead leaves and stems aboveground but usually does not damage these basal growing points [15-17]. As a result, grasses can quickly resprout after fire.

In contrast, many wildflowers and shrubs grow from exposed above-ground growing points that are more easily damaged by fire. Because grasses can regrow rapidly from protected tissues, fire often gives them a competitive advantage following a burn [15,18]. In this way, grasses respond to fire much like resprouting woody plants—by using stored energy and protected buds to rebound quickly.

There are certain physical and chemical grass characteristics that cause them to burn easily. The small diameter, rigid stems and slender, rough leaves provides a high surface-to-volume ratio [19, 20]. In simple terms, this means more plant surface is exposed to air. The more exposed surface there is, the faster fire can move across it. These same features also cause grasses to dry out quickly after rain or dew, making them more flammable than plants with thicker stems or broad leaves that retain moisture longer.

Their chemical composition predisposes them to combustibility. Their tissues contain cellulose, silica, and other flammable chemicals such as terpenes and waxes [6,19,21]. Many grasses deposit microscopic silica particles in their leaves as a defense against grazing, which makes the leaves stiff and abrasive. In addition, grasses have a waxy outer coating that helps limit water loss. While this is beneficial for drought tolerance, waxes also increase flammability, allowing fire to ignite and spread more readily across grass fuels [5,22].

Because grasses both burn easily and recover quickly, they can create a self-reinforcing cycle. Fire favors grasses because grasses carry fire efficiently and repeated burning further increases grass dominance. Over time, this feedback can reduce wildflower diversity, simplify habitat structure, and make the system increasingly dependent on frequent fire to maintain its current state.

This fire–grass cycle can be desirable in some situations such as sustaining species that depend on dense grass cover. In this case, periodic fire reinforces the conditions managers are aiming for. However, the same cycle becomes problematic when frequent burning allows the tall C4 “bully” grass species to dominate at the expense of wildflowers, insects, and structural diversity. Once grasses take over, more fire is often required just to maintain the system, narrowing future management options and increasing dependence on burning.

Grasses have low quality litter that doesn’t provide the nutrients forbs require.

Because this litter layer will continue to thicken, it must be periodically removed through fire, grazing, haying or some other creative removal technique [24,25]. Interestingly, the removal creates another feedback cycle that enhances grass growth because of how they photosynthesize. Unlike most wildflowers, which use the C3 photosynthetic pathway, C4 grasses are highly efficient at capturing carbon under warm temperatures with lots of sunlight and open conditions—exactly the environment created after litter removal. When fire or grazing clears away litter, sunlight reaches the soil surface, temperatures increase, and C4 grasses rapidly increase growth and tillering. Studies show that grass productivity can increase by up to 60% following litter removal [11,18].

4. Use Nitrogen Efficiently

Warm-season (C4) grasses are especially efficient at using nitrogen, which also explains why they grow quickly and dominate after disturbance.

All plants need nitrogen to photosynthesize, in part because it is used to build Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase), the enzyme that captures carbon dioxide during photosynthesis. In most forbs and cool season grasses (called C3 plants), this process is inefficient under hot, sunny conditions. In hot, dry weather, cool-season (C3) plants shuts down their leaf pores (stomata) to save water. That limits how much carbon and oxygen they can take in because Rubisco normally grabs carbon dioxide to build sugars. When a plant closes its stomata, less CO₂ gets in and oxygen builds up inside the leaf. Under those conditions, Rubisco is more likely to grab oxygen instead of carbon dioxide, pushing the plant into photorespiration. When this happens, the plant is not building new plant tissue but rather its entered into a wasteful pathway that burns energy and loses both carbon and nitrogen. To compensate, C3 plants must produce large amounts of Rubisco, which requires more nitrogen [26].

C4 grasses avoid this wasteful cycle. Their photosynthetic pathway concentrates carbon dioxide around Rubisco, allowing the enzyme to work efficiently even in hot, bright conditions. Because less Rubisco is needed, C4 grasses require less nitrogen to achieve the same—or greater—photosynthetic output [27]. As a result, Rubisco accounts for only about 5–9% of leaf nitrogen in C4 grasses, compared to 20–30% in C3 plants [28].

This efficiency allows C4 grasses to rapidly convert sunlight into growth. They quickly expand their root systems and produce large amounts of aboveground biomass that is low in nitrogen [29]. The expanding root mass also occupies space and resources in the soil, leaving fewer opportunities for other plants to establish or persist.

A simple way of thinking of this is: C4 grasses run photosynthesis like a fuel-efficient engine. They get more growth out of less nitrogen, while many wildflowers need a much larger “engine” to keep up.

In addition, frequent disturbance that removes litter creates open, exposed conditions that favor fast-growing grasses [30] but leave forbs vulnerable to moisture stress, competition, and repeated setbacks to flowering and seed production. Over time, these pressures make it difficult for many forb species to persist or reestablish, even though the site may appear vigorous and productive. Without rest periods or additional management tools, the system can shift toward lower diversity, heavier litter production, and greater dependence on continued fire. The “bully” grasses such as Indian grass, big bluestem, and switchgrass set up a nice little feedback system for themselves. It’s as if they conspire to be a monoculture!

4. Grasses Use Nitrogen Efficiently

Warm-season (C4) grasses are especially efficient at using nitrogen, which also explains why they grow quickly and dominate after disturbance.

All plants need nitrogen to photosynthesize, in part because it is used to build Rubisco (Ribulose-1,5-bisphosphate carboxylase/oxygenase), the enzyme that captures carbon dioxide during photosynthesis. In most forbs and cool season grasses (called C3 plants), this process is inefficient under hot, sunny conditions. In hot, dry weather, cool-season (C3) plants shuts down their leaf pores (stomata) to save water. That limits how much carbon and oxygen they can take in because Rubisco normally grabs carbon dioxide to build sugars. When a plant closes its stomata, less CO₂ gets in and oxygen builds up inside the leaf. Under those conditions, Rubisco is more likely to grab oxygen instead of carbon dioxide, pushing the plant into photorespiration. When this happens, the plant is not building new plant tissue but rather its entered into a wasteful pathway that burns energy and loses both carbon and nitrogen. To compensate, C3 plants must produce large amounts of Rubisco, which requires more nitrogen [26].

C4 grasses avoid this wasteful cycle. Their photosynthetic pathway concentrates carbon dioxide around Rubisco, allowing the enzyme to work efficiently even in hot, bright conditions. Because less Rubisco is needed, C4 grasses require less nitrogen to achieve the same—or greater—photosynthetic output [27]. As a result, Rubisco accounts for only about 5–9% of leaf nitrogen in C4 grasses, compared to 20–30% in C3 plants [28].

This efficiency allows C4 grasses to rapidly convert sunlight into growth. They quickly expand their root systems and produce large amounts of aboveground biomass that is low in nitrogen [29]. The expanding root mass also occupies space and resources in the soil, leaving fewer opportunities for other plants to establish or persist.

A simple way of thinking of this is: C4 grasses run photosynthesis like a fuel-efficient engine. They get more growth out of less nitrogen, while many wildflowers need a much larger “engine” to keep up.

In addition, frequent disturbance that removes litter creates open, exposed conditions that favor fast-growing grasses [30] but leave forbs vulnerable to moisture stress, competition, and repeated setbacks to flowering and seed production. Over time, these pressures make it difficult for many forb species to persist or reestablish, even though the site may appear vigorous and productive. Without rest periods or additional management tools, the system can shift toward lower diversity, heavier litter production, and greater dependence on continued fire. The “bully” grasses such as Indian grass, big bluestem, and switchgrass set up a nice little feedback system for themselves.

It’s as if they conspire to be a monoculture!

The effect of fire depends on the grass species, their growth habits, and the region where they grow [6,18]. For example, research from Wisconsin, Missouri, Kansas, Illinois, and Oklahoma shows that tallgrasses like big bluestem (Andropogon gerardii) often respond strongly to fire, with stands nearly doubling after repeated burns [18,31]. Whereas, a 56-study in Kansas found little bluestem (Schizachyrium scoparium), a bunchgrass, may be less tolerant, and in some cases decline after repeated burning [32,33]. These responses also vary by location. In South Dakota, big bluestem production was little affected by fire, showing that local conditions—soil, climate, and existing plant community—matter just as much as species traits [18].

The tall C4s are more tolerant of fire than are little bluestem and other bunchgrasses [33]. Side oats has been shown to not increase after fire [34,35] and could decrease depending on whether it was a dry or wet year. For example, side oats was reduced by 51% when burned in a drought year but only 12% when burned in a wet year [36]. In contrast, side oats increased with mowing [37].

Fire can be a powerful tool to boost certain grasses, but its effects are not uniform on all C4 grasses. Knowing which grasses dominate your property or which you want to support means knowing how they respond to fire; in this way you can plan burns that support your management goals.

Timing of burns can affect grasses, forbs, and wildlife, but it’s not fully understood. Research is limited, and results vary by region, species, and site conditions. More long-term studies are needed to determine how different burn dates influence plant growth and diversity.

Late-spring burns, for example, can create conditions that strongly favor fast-growing C4 grasses. Removing litter and exposing soil in warm conditions boosts grass growth and tillering, which can help grasses dominate over slower-growing wildflowers. At the same time, late-spring burns can harm native reptiles and amphibians, which are emerging from winter nests after just a few warm days (around 50°F for three consecutive days). Even if you don’t see them, these animals are present and vulnerable. 

The same fires that stimulate grasses can inadvertently reduce forb diversity and impact wildlife. Timing, frequency, and intensity all interact—burn too often, too early, or too late, and grasses may gain the upper hand while wildflowers struggle. Carying the timing and planning patchy burns by leaving unburned refuges can help balance grass productivity with plant and animal diversity.

Fire favors grasses in multiple ways: it removes litter, exposes sunlight, and stimulates regrowth from underground buds. Warm-season C4 grasses are especially efficient—they convert sunlight into growth using less nitrogen, and expand rapidly after litter removal more than most wildflowers or bunchgrasses. Because of these traits, frequent burns can lead to grass-dominated landscapes, simplifying habitat, and removing the diversity that forbs provide.

Yet, not all warm-season (C4) grasses respond the same way. Tallgrasses like big bluestem thrive after fire, while bunchgrasses such as little bluestem may be more sensitive. Geographic variation also matters: a burn that boosts grasses in one state may have little effect in another. Timing adds another layer: late-spring burns can strongly favor grasses but may harm emerging reptiles and amphibians, and frequent burning can give grasses a long-term competitive edge over slower-growing wildflowers.

If diversity is your goal, you’ll want to balance fire with other tools. Overuse or misuse of fire as illustrated in the initial example can be prevented by learning the science. Fire is not one-size-fits-all—it’s a tool that works best when applied thoughtfully, with attention to species, site conditions, and management goals. Fortunately, there are various management techniques at our disposal. Keep the options to mow, graze, and hay in your toolkit.

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