Land managers want to understand the effects of fire on grasslands because fire, as a disturbance process, is an integral part of ecosystem management and restoration ecology. Fire initiates changes in ecosystems that affect the composition, structure, and patterns of vegetation on the landscape. It also affects the soil and water resources of ecosystems that are critical to overall ecosystem functions and processes.

Grasslands collectively are the largest ecosystem in the world, covering 40.5% of the land surface of the Earth (excluding Greenland and Antarctica). They are not entirely natural, because they have formed and developed under the influence of anthropogenic disturbances like prescribed fire, wildfire, livestock grazing, woody vegetation clearing, over-sowing with pasture grass, and others.

Grasslands provide a variety of ecosystem services. A critical function of grasslands in global carbon circulation is their subsoil storage of organic matter for long periods of time. Grasslands soils are classified as Mollisols, soils with deep, organic matter horizons. This characteristic makes grasslands almost as important as forests for carbon fixation and storage; grassland soils are organic matter sinks on the same order of magnitude as tree biomass.

Although wildfires have always been a constant part of prairie fire regimes, wildfire numbers and area burned have surged in the 21st Century due to drought. The general effects of fire on soil physical properties range from very minor to serious. Since grassland fires often move rapidly with the wind and have much less fuel than brush and forest fires, soil heating is significantly lower, and therefore physical damage is much less than what occurs during crown, surface, or smoldering fires in forests and woodlands.

Key Findings

• The number of wildfires in the Great Plains of North America increased from 33.4 per year in 1985 to 116.8 per year in 2014.
• The total burned area in grassland fires grew by 400% over the same time period.
• Comparisons of wildfire and prescribed fire in grassland ecosystems show little differences in physical impacts due to the low fire severities of both types of fire, the narrow flame fronts, and rapid spread rates.
• Physical effects of fire include alterations in soil physical properties, development of water repellency, and erosion.