Fire, The Most Ancient Landscape Tool

Every year humans use fire to clear forests, brush, and pastures. Even before humans, lightning, volcanoes, and other causes burned landscapes as well. And everyone knows that the grass comes back greener after a fire. Scientist and extension agents the world over tell everyone how useful fire is for plants. So it must be a natural, helpful tool, right?

Actually, very rarely is fire the useful tool for landscape restoration it has been made out to be. Natural fires are few and far between and burned much less acreage in the past than man-made fires do now given the widespread use and frequency of it. Mr. Savory believes that this frequency of use plus the loss of herding animals and their predators to disturb the soil and vegetation is a major factor in the growing desertification in brittle environments world-wide.

The lush grasslands of Africa, Australia, and North America were all created by a combination of fire, grazing, and predator-induced animal impact, not by fire alone. Much of the burning done now is either through habit or because government or private agents suggest it. Fire, like any other tool, must be evaluated in the terms of a clearly stated holisticgoal and the current state of the four ecosystem processes in relation to that holisticgoal.

Fire and its effects on Biological Communities

What does fire do to the various biological communities? Only after understanding the effects resulting from fire should the decision whether to burn or not be made. These effects will be varied depending on the brittleness scale and amount of annual precipitation.

Soil Surface

The removal of liter and vegetation by fire bares the soil surface and due to the importance of soil surface management on all four ecosystem processes, it must always be considered first. The ground is noticeably bare right after a fire, but the recovering depends on where on the brittleness scale the land lies, amount and pattern of precipitation, amount of grazing or overgrazing by livestock or wildlife gathering on the burned area, the amount of rest, or the degree and amount of animal impact.

In low rainfall, very brittle environments, fire has the greatest impact on time of soil cover return, due to the lower precipitation leading to less vegetation, which produces less litter. Compounded with the bare soil making the water cycle less effective by allowing what rain does fall to run off, burned areas in these environments can last for years or even decades. Should total or partial rest follow a fire, it takes even longer for soil cover to return.

Plants

Plants respond to fire in various ways, some perennial grass species disappear after a fire, some have adapted so they only establish after a fire. The majority of mature plants respond well when burned as the old oxidizing material is removed. Woody plants mirror these responses, some disappear, some thrive. Many of the less than desired species seem to respond best to a fire, multiplying the number of shoots that return compared to those killed in the fire. Trees, especially mature specimens, usually survive most fires. Some species may survive in shrub form in areas of frequent fires.

As with soil surface, plants need some type of soil disturbance after a fire in order to recover fully. The creation of a large area micro-environment favors the establishment of only a few species of plants, insects and other organisms adapted to that micro-environment. If only mature specimens remain after a fire, the new organisms do create a more diverse micro-environment, yet repetitive fires quickly diminish that complexity. Eventually only fire-tolerant species remain. In some cases, a near monoculture is created.

A corollary to this is that boundary areas between burned and unburned areas are incredibly complex. Therefore fires that produce a mosaic of patches and tongues differ greatly from uniform burns.

Areas of high amounts of dry material tend toward “hot burns”, in which large flames and intense heat are produced. Areas with limited materials are more prone to “cool burns”, in which the fire moves slowly with small flames. While the immediate effects are different, the long-term effects are very similar.

Animals

Animals, as well, have varied responses to fire. Some can not move fast enough to get out of the way, others can and do, while others place themselves to capture fleeing small animals or insects. Large animals do not necessarily panic and flee helter-skelter. While that behavior has been observed when humans use fire and noise to drive them, in natural situations they very often walk calmly out of the way and stop outside the burn line. Many seek out burned areas when the first regrowth returns.

Humans have made the mistake throughout history on noticing the initial response of animals and plants, basing their evaluation on adult/mature members of the population, not the long-term changes that may have occurred. Did the population drop, maintain, grow in the short-term? Long-term responses are rarely if ever noticed, much less studied, so that what may appear to increase populations of various species may in fact veil a long-term decline as fire is used more frequently.

Fire and Atmospheric Pollution

Annual deliberately set fires on one-half the world’s grasslands and savannahs (1.85 billion acres) releases approximately 3.7 million metric tons (metric ton = 2,200 pounds) of carbon into the atmosphere, or three times the amount released by burning forests. The majority of this burning takes place in Africa, but is common wherever range-lands and grasslands occur. Ozone, carbon monoxide, and methane from fires in southern Africa have been traced to Australia and Antarctica within weeks of the occurrence. In addition, methyl bromide released by fires in Siberia, California, and Africa, is 50 times more effective than CFCs (banned chloroflurocarbons) in destroying upper-level ozone.

While some scientists argue that the carbon dioxide released by burning is recaptured when the plants begin growing again, they do not consider the negative effects of fire on the soil cover, plant spacing and composition, water and mineral cycles, energy flow and community dynamics. These frequent burns generally lead to reduced biomass production and therefore reduced carbon dioxide capture.

Few people have worried about this aspect of using fire as a tool, and it is generally the first choice of range managers and government agencies. In fact, in many government acreages, only fire can be used to clear off old growth; animal impact at the density necessary is generally not allowed.

Fire and Extreme Environments

There will be times when fire is the best tool for the job. It depends on the holisticgoal and what one is trying to achieve. If other tools that do not expose the soil or create atmospheric pollution can be used, it is generally better to use them instead of fire. It is important to consider the entire communities’ population, not just the adults.

Depending on the brittleness scale fire manifests different effects. The following examples are at the scale’s extremes so environments with a brittleness of 7 or 8 will be closer to the very brittle ones and the 2-3′s would be closer to the non-brittle examples.

Very Brittle Environments

Community Dynamics – exposed soil in wide spaced plant populations; new cover develops slowly. While fire in the short-term increases species diversity, repeated fires reduces it. Fire stimulates adult woody plants, generally. Fire created mosaic patterns producing edge effects increases species diversity. Too frequent burning reduces grasslands’ ability to store carbon.

Water Cycle – Reduced effectiveness as soil is exposed and litter removed. The lower the rainfall the greater the tendency.

Mineral Cycle – Short-term increase through conversion of dead matter to ash. Carbon and other pollutants released into atmosphere. Exposed soil and changed micro-environment reduce support of organisms of decay leads to long-term slowing of mineral cycle. Tendency is inversely proportional to amount of rainfall, especially in frequent fire regimens.

Energy Flow – Fire may produce immediate increase in energy flow by removing old material allowing plants to grow easier. Energy flow could be reduced over long-term by soil exposure leading to decreased water and mineral cycling and plant community changes. As with the Water and Mineral cycles, the lower the precipitation the higher the potential damage.

Non-brittle Environments

Community Dynamics – Short-term effects with little long-term except atmospheric. Higher humidity inhibits fires, return to complexity following fire is rapid on undisturbed land. Close plant spacing in these environments minimizes soil exposure.

Water Cycle – Short-term damage due to soil exposure but effect temporary due to better annual distribution of precipitation and humidity and rapid succession of plants on bare surfaces.

Mineral Cycle – Appears to speed up nutrient cycling, but hides adverse effects by delaying biological decay necessary to maintaining carbon levels in soil. Cycle appears to recover rapidly, but slash and burn agriculture, mainstay for thousands of years, quickly falls apart due to inadequate mineral cycling if burns more frequent than 20 years before re-burning.

Energy Flow – Fire disrupts energy flow temporarily but recovers quickly with the return of the plant communities. Frequent fires in all environments damages all ecosystem processes. Forests converted to savannas through frequent fires take on the characteristics of brittle environments, unless rested for several years.

Savory, Allan and Jody Butterfield. 1999. Holistic Management, A New Framework for Decision Making (Washington, D.C: Island Press), 182-194.