How Bison Help Restore Burned and Damaged Grasslands

For thousands of years, American bison and North American grasslands evolved together in a symbiotic relationship that shaped the vast prairie ecosystems stretching from Canada to Mexico. Before European settlement, an estimated 30-60 million bison roamed these grasslands, serving as ecosystem engineers that influenced everything from soil composition to plant diversity. Their grazing patterns, physical disturbance of the soil, and nutrient cycling created a mosaic of habitat conditions that supported thousands of other species.

This ancient relationship was nearly lost when bison were hunted to near extinction in the late 19th century, with populations plummeting to fewer than 1,000 individuals. As bison disappeared, so did many of the ecological processes that maintained healthy grasslands. Today, as conservationists work to restore damaged prairie ecosystems, they’re rediscovering that bison play a crucial role in grassland recovery, particularly in areas affected by fire and other disturbances. The reintroduction of bison to these landscapes represents not just a conservation success story, but the restoration of an ecological relationship essential for prairie health.

Bison as Nature’s Firefighters: Post-Burn Grazing Preferences

One of the most remarkable aspects of bison behavior is their attraction to recently burned areas of prairie. Unlike cattle, which tend to avoid freshly burned patches, bison actively seek them out. Research conducted at the Konza Prairie Biological Station in Kansas has documented that bison spend up to 31% more time grazing in burned areas compared to unburned sections. This behavior, known as “pyric herbivory” (fire-driven grazing), creates a natural partnership between fire and grazing that has shaped grassland ecosystems for millennia.

Bison are drawn to burned areas because the fresh regrowth following fire is highly nutritious, containing higher protein content and fewer dead materials than unburned grass. Their selective grazing in these areas creates patches of shorter vegetation amid taller grasses, increasing habitat heterogeneity that benefits countless other species. By concentrating their grazing on burned patches, bison also reduce fuel loads in those areas, potentially limiting the intensity of future fires while allowing other areas to accumulate the biomass needed for periodic, beneficial burns. This natural fire management system helped maintain the historic fire-grazing dynamics of North American prairies.

Soil Regeneration Through Bison Disturbance

Bison contribute significantly to soil health in damaged grasslands through multiple mechanisms. As they move across the landscape, their hooves break up compacted soil and create small depressions that capture water, seeds, and organic matter. These “bison wallows” – depressions created when bison roll in dirt – become microhabitats that collect water and provide unique growing conditions for specialized plants. Studies have shown that a single bison herd can create hundreds of wallows across their range, each becoming a hotspot for biodiversity and soil development.

Additionally, bison excrement returns essential nutrients to the soil in a readily available form. A single adult bison can produce up to 50 pounds of dung daily, distributing nitrogen, phosphorus, and other nutrients across the landscape. This natural fertilization is particularly important in fire-affected areas, where nutrients may have been lost through volatilization during burning. The combination of physical disturbance and nutrient deposition creates ideal conditions for rapid vegetation recovery after fires, accelerating the restoration process in ways that few other interventions can match.

Seed Dispersal: Bison as Mobile Biodiversity Spreaders

Bison play a critical role in the dispersal of native plant seeds throughout grassland ecosystems, serving as living seed transport systems that help damaged areas recover their plant diversity. Their shaggy coats act as natural seed collectors, with studies documenting up to 16 different plant species being carried in the fur of a single bison. As they move across the landscape, bison can transport these seeds for miles before they fall off or are rubbed off during wallowing, effectively reseeding areas that may have lost their native plant communities.

Their digestive systems also contribute to seed dispersal. Many grassland plant species have evolved seeds that can survive passage through a bison’s digestive tract, emerging in dung piles with a ready supply of fertilizer to support germination. Research has demonstrated that seeds dispersed through bison dung often show higher germination rates than those simply dropped on the soil surface. This endozoochory (internal seed transport) is particularly valuable in burned areas, where the existing seed bank may have been damaged by intense heat. By bringing in seeds from unburned areas, bison help jump-start the recovery process with a diverse array of plant species.

Creating Habitat Heterogeneity in Recovering Landscapes

Bison grazing. Image via Openverse

One of the most valuable ecological services bison provide is the creation of varied habitat structures within grasslands. Their selective and patchy grazing habits result in a mosaic of vegetation heights and densities – some areas are grazed short while others remain tall and dense. This structural diversity is critical for wildlife that depend on different vegetation characteristics. For example, some grassland birds like Henslow’s Sparrows require tall, dense grass for nesting, while others such as Upland Sandpipers prefer shorter vegetation for foraging. By creating this patchwork of habitat types, bison support greater overall biodiversity than would exist in a uniformly structured grassland.

The habitat heterogeneity is particularly important in burned areas, which might otherwise regenerate with more uniform vegetation. Research at the Tallgrass Prairie Preserve in Oklahoma has shown that areas managed with both fire and bison grazing contain up to 25% more plant species than areas managed with either fire or grazing alone. This increased diversity creates resilience within the ecosystem, making it better able to withstand future disturbances such as drought or invasive species. The varied vegetation structure also influences soil moisture patterns, microclimate conditions, and nutrient cycling processes, creating a more complex and functional ecosystem overall.

Controlling Invasive Species Through Selective Grazing

Invasive plant species often gain a foothold in grasslands following disturbances like fire, potentially transforming diverse native prairie into monocultures dominated by non-native plants. Bison can help counter this threat through their selective grazing habits. Unlike cattle, which tend to be less discriminating, bison specifically target grasses over forbs (broad-leaved flowering plants), which helps maintain the balance between these plant groups. This selective pressure can give native plants a competitive advantage against certain invasive species, particularly invasive grasses that might otherwise dominate after a fire.

Studies at several prairie preserves have documented bison’s effectiveness against specific invasives. For example, at Konza Prairie in Kansas, bison have been observed preferentially grazing on invasive tall fescue and smooth brome in recently burned areas, reducing these species’ dominance and allowing native warm-season grasses to recover. Similarly, at the American Prairie Reserve in Montana, bison grazing has been associated with reduced cover of cheatgrass, an invasive annual that commonly increases after fires. This natural control mechanism is particularly valuable because it requires no chemical inputs and works continuously as bison move through the landscape, providing a sustainable approach to managing invasive plants in recovering grasslands.

Nutrient Cycling Acceleration Post-Fire

Fires in grassland ecosystems temporarily release nutrients locked in plant tissues, but much of this nutritional bounty can be lost to the atmosphere or washed away before plants can reestablish. Bison play a crucial role in capturing and recycling these nutrients before they’re lost from the system. When bison consume the protein-rich regrowth in burned areas, they process these nutrients and return approximately 90% of what they consume back to the soil through urine and dung. This efficient recycling system keeps nutrients within the ecosystem and makes them available for the next generation of plants.

The timing of this nutrient cycling is particularly important. Research has shown that bison dung and urine contain nitrogen in forms that are more readily available to plants than the original plant material would be if it simply decomposed naturally. Additionally, the concentration of grazing in burned areas means nutrients are redistributed in patterns that support the most actively growing parts of the ecosystem. Soil samples from bison-grazed burned areas show significantly higher levels of plant-available nitrogen, phosphorus, and potassium compared to burned areas without grazing, demonstrating how bison enhance the recovery process through accelerated nutrient cycling.

Temperature Regulation and Microclimate Effects

The grazing patterns of bison create microclimate conditions that can be beneficial for ecosystem recovery after fire. When bison selectively graze certain areas more heavily, they create patches with varying amounts of bare soil and vegetation cover. These differences in ground cover significantly affect soil temperature and moisture levels. Areas grazed short by bison typically experience higher soil temperatures during the day and greater temperature fluctuations, which can stimulate seed germination for certain species that require temperature cues to break dormancy.

Additionally, the physical disturbance created by bison hooves breaks up hydrophobic soil layers that sometimes form after intense fires. These water-repellent layers can prevent moisture from penetrating the soil, but bison activity disrupts them, allowing better water infiltration. The combination of varied vegetation height, soil disturbance, and altered moisture patterns creates a range of microhabitats within burned areas. This microclimatic diversity allows a wider variety of plant species to find suitable growing conditions, accelerating the recovery of plant community diversity compared to ungrazed burned areas. Long-term monitoring at sites like the Tallgrass Prairie Preserve has documented that areas with bison grazing recover more diverse plant communities following fire than comparable areas without bison.

Bison Versus Cattle: Comparative Impacts on Burned Grasslands

While cattle can provide some of the same ecological functions as bison, research has consistently documented important differences in how these bovines affect burned grasslands. Bison are more selective for grasses (consuming up to 98% grasses in their diet compared to 80-85% for cattle), which helps maintain higher forb diversity in bison-grazed areas. Bison also demonstrate stronger preference for recently burned areas than cattle do, creating more pronounced patch grazing patterns that increase habitat heterogeneity. Studies at the Konza Prairie have shown that plant species diversity is typically 10-15% higher in bison-grazed areas compared to cattle-grazed areas under the same burning regimes.

Behaviorally, bison spend less time near water sources and more time on uplands than cattle, resulting in more evenly distributed grazing pressure across the landscape. They also engage in more wallowing behavior, creating small depressions that capture moisture and seeds. The seasonal patterns of grazing also differ, with bison naturally reducing their food intake during winter months, giving grasslands periods of recovery. While well-managed cattle grazing can certainly benefit grassland ecosystems, the distinct evolutionary history of bison with North American grasslands makes them particularly effective partners in the restoration of burned prairies. Where conservation goals prioritize biodiversity and ecological function over maximum livestock production, bison often provide superior results.

Case Studies: Successful Bison-Assisted Prairie Restorations

The Tallgrass Prairie Preserve in Oklahoma provides one of the most compelling examples of bison-assisted grassland restoration. Established in 1989 on former ranchland, the preserve now spans nearly 40,000 acres with approximately 2,500 bison. Managers implement a patch-burn grazing system where different sections are burned each year, allowing bison to create the natural fire-grazing dynamic. Over three decades, plant diversity has increased by more than 35%, with rare species returning and invasive plants decreasing. Bird surveys show the preserve now supports over 210 species, including specialists like Greater Prairie-Chickens that had previously declined.

Another success story comes from Midewin National Tallgrass Prairie in Illinois, where bison were reintroduced in 2015 to degraded agricultural land undergoing prairie restoration. After just five years, areas grazed by bison showed significantly higher native plant diversity than comparable ungrazed restoration sites. Particularly notable was the faster recovery of sensitive forb species in bison-grazed areas, even following prescribed burns. At the American Prairie Reserve in Montana, researchers documented how bison grazing following a major wildfire in 2017 accelerated the recovery of native grasses while suppressing cheatgrass, demonstrating their value in post-fire restoration even in more arid mixed-grass prairie systems. These case studies, along with similar results from smaller preserves across the Great Plains, provide clear evidence of bison’s effectiveness as restoration partners.

Implementing Bison in Modern Conservation Strategies

For land managers considering bison as restoration tools, several implementation approaches have proven successful. The patch-burn grazing system, where small sections of prairie are burned on a rotating schedule and bison are allowed to graze the entire area, most closely mimics historical processes. This approach requires minimal fencing and management intervention while maximizing ecological benefits. For smaller properties, managers often use temporary electric fencing to concentrate bison impact in specific restoration areas before moving them to new sections, effectively creating a rotational system that prevents overgrazing while still allowing bison to influence vegetation recovery.

Partnerships between conservation organizations and tribal nations have created innovative models for bison restoration. The InterTribal Buffalo Council now helps manage over 20,000 bison across 69 tribal nations, many using traditional ecological knowledge to guide grazing practices on restored grasslands. Meanwhile, conservation ranching programs allow private landowners to manage bison for both ecological and economic outcomes, creating financially sustainable restoration models. These varied approaches demonstrate that bison restoration doesn’t require a one-size-fits-all methodology but can be adapted to different landscapes, ownership patterns, and management objectives while still delivering significant ecological benefits to recovering grasslands.

The Future of Bison-Assisted Grassland Restoration

As climate change intensifies, the role of bison in grassland resilience becomes increasingly important. More frequent and intense wildfires are predicted across many grassland regions, making post-fire restoration strategies critical for ecosystem maintenance. Bison-grazed landscapes have demonstrated greater drought resistance and faster recovery following extreme weather events, suggesting they may provide natural climate adaptation benefits. Scientists are currently studying how bison grazing interacts with changing precipitation patterns and rising temperatures to better understand how these animals might help prairie ecosystems weather coming changes.

Looking forward, expanded bison restoration faces both challenges and opportunities. Habitat fragmentation, genetic management concerns, and conflicts with agricultural interests remain significant hurdles. However, growing recognition of ecosystem services provided by healthy grasslands—including carbon sequestration, water filtration, and biodiversity support—is creating new funding mechanisms for restoration efforts. The emerging field of regenerative ranching also offers models where bison production can be economically viable while delivering ecological benefits. As our understanding of bison’s ecological impact continues to deepen, their role in restoring and maintaining North America’s grasslands is likely to expand, bringing these ecosystem engineers back to more of their historic range and rebuilding the ancient partnership between bison, fire, and prairie that shaped the continent for millennia.