Patch-burn grazing at Tallgrass Prairie National Preserve

Tallgrass Prairie National Preserve burns a different third of its pasture every year and lets cattle choose where to graze. The method, patch-burn grazing, is meant to restore a shifting patchwork of burned and unburned ground like the one fire and grazing once made across North American prairies.

Why fire and grazing

North American prairies developed under fire, of natural and human origin, and grazing. Those disturbances let grasses and herbaceous forbs dominate. Some native wildlife prefer recently burned areas, others rely on dense, undisturbed vegetation and litter, and others need both at different times of their lives. At the preserve, and across much of the Kansas Flint Hills, fire and grazing are key management tools, and the preserve aims for more natural patterns of both, yielding a healthier and more diverse ecosystem in plant composition and structure.

The article stresses heterogeneity, meaning variation in vegetation structure, composition, density and biomass. It influences wildlife diversity and ecosystem functions and has been called the root of biological diversity, so it should be the foundation of conservation.

Burned and unburned tallgrasses; note the lighter unburned grass and the darker green of new growth after a burn. NPS.

How it works

Patch-burn grazing is gaining favor among biologists, ecologists and range managers because it approximates the natural interaction between fire and native grazers. Typically one-third of each pasture burns every year, on a three-year rotation.

1. Fire shapes grazing. Animals prefer recently burned ground because the new growth is more palatable.
2. Grazing shapes fire. Grazers avoid unburned patches, so vegetation builds up there and becomes fuel for later fires.
3. The interaction produces a shifting mosaic of plant communities. Experts believe similar fire and grazing interactions shaped the pre-settlement Great Plains and other grasslands with large grazers and long histories of fire.

The larger fuel loads also give more intense burns, which may help keep trees and shrubs from encroaching on the prairie, and the technique may prove effective against invasive plants.

Sample patch-burn plan for a pasture. Each area burns once every three years, producing the patchwork of burned and unburned areas typical of patch-burn grazing. NPS.

Wildlife

The varied grassland structure supports a broad range of wildlife, including the greater prairie chicken and Henslow’s sparrow. Plants and animals respond differently to fire and grazing: some birds nest in recently burned areas with little cover, others in unburned areas with tall plants and old litter. Many species use all of the treated areas at different stages of life. A greater prairie chicken may boom (the male mating display), nest, rear young, forage and seek cover across all the vegetation structures patch-burn grazing provides.

At the preserve

The Nature Conservancy works closely with the preserve’s cattle grazing lessee and partners with the National Park Service to put the method in place in suitable areas. To help, managers removed 1.7 miles of cross fence between two pastures, making a single large grazing unit. Fire breaks and the natural lay of the land let specific areas burn while taller “old growth” prairie plants are left standing, making a more random and more natural landscape.

Monitoring

The National Park Service and The Nature Conservancy treat sound resource management as a top priority. The National Park Service’s Heartland Network Inventory and Monitoring Program and others have gathered baseline data on plant and animal communities, and the network will keep monitoring indicators of ecosystem health. Trend analysis will show how patch-burn grazing changes structural and biological diversity, and warn of unexpected impacts so managers can fine-tune their practices.

Sources

• National Park Service, Tallgrass Prairie National Preserve, “Patch-Burn Grazing”; the artist’s rendering credited to the Missouri Department of Conservation, the monitoring-network collage and the opening photograph are left out; rewritten in hubnx's own words.