Fire has been a recurrent environmental factor on grasslands from their beginning, as has drought.
Many grassland ecologists have retained the belief that grassland ecosystems can be managed with fire because they have accepted the observational concept that fire prevents the intrusion of shrubs and trees into grasslands (Weaver 1954, Humphrey 1962, Daubenmire 1974, Stoddart, Smith, and Box 1975, Wright and Bailey 1982). However, the presence of fire does not prove that grasslands need or are caused by fire.
The existence of a shrub component in a grassland is not a ecologically beneficial relationship as shrubs and grasses are adversarial inhibitive competitors. They compete for sunlight, mineral nitrogen, other essential elements, and soil water.
Fire in grasslands cannot prevent the invasion of, or cause the removal of, shrubs and trees that are able to reproduce by vegetative secondary suckers. Almost all deciduous woody plants reproduce vegetatively, except big sagebrush (Artemisia tridentata).
Seedlings of trees, shrubs, weedy forbs, and introduced grasses cannot become established in grasslands containing grasses with full nutrient resource uptake competitiveness. Intrusive seedlings can only be established after a grassland has been degraded by poor management practices.
Repeated prescribed fire can modify the composition of the aboveground vegetation in degraded grasslands which have been invaded by shrubs. The composition of introduced cool season grasses may change, and early succession and weedy forbs, and shrub aerial stems decrease temporarily after four repeated prescribed fires.
However, the fundamental problems of weak nutrient resource uptake, reduced water use efficiency, nonfunctional compensatory physiological mechanisms, impaired vegetative reproduction by tillering and diminished biogeochemical processes will remain in the degraded grassland ecosystem following repeated fire events. None of the biological, physiological, or asexual mechanisms within grass plants and none of the rhizosphere microbes or biogeochemical processes they perform are activated by fire.
Prescribed fire on grasslands cannot activate the grass plant growth mechanisms or the ecosystem biogeochemical processes because these practices remove too much of the leaf area preventing adequate quantities of carbon energy to be fixed through leaf photosynthesis. Stored carbohydrates are not mobilized for compensatory replacement growth following defoliation events.
Almost all of the essential elements in the aboveground herbage are volatilized when a grassland is burned, and if the soil is dry, some of the belowground essential elements are also lost. When the losses of essential elements are greater than the quantity of captured essential elements, the result is further degradation of the grassland.
Fire does not improve grassland ecosystems biologically or ecologically and fire cannot replace the partial defoliation achieved by grazing graminivores in managing health and productive grassland ecosystems.
For More Information Go To:
