Fire Ecology

Subject:
Life Science, Unifying Concepts & Processes

Theme:
All living and nonliving things are connected in every ecosystem.

OBJECTIVE

To provide an opportunity or reinforce understanding of basic ecological concepts and apply that understanding to fire ecology.

METHOD

After reviewing ecological concepts, students create a food web.

BACKGROUND

Ecology is the study of the interrelationships among all living organisms (biotic) and the nonliving elements (abiotic) in and affecting our world. Biotic components live and die; most abiotic components are in a continuous cycle of building up and being reduced. These ebbs and flows make life possible by seeking a balance among all components, living and nonliving.

Most plants utilize nutrients from the soil, air, and water combined in the presence of sunlight to produce food through the process of photosynthesis. While herbivores eat these plants, carnivores eat the herbivores, and omnivores eat some of both – forming food chains. In the end, decomposers break down all that dies, returning it to the land, water, and air for plants to again use as nutrients. Like a giant spider’s web, all of these components are linked to form food webs.

Each plant and animal has its own niche (the role it plays) in its habitat (life space.) Groups of plants and animals find similar habitats suitable; these associations are often called communities. A group of communities, including their biotic and abiotic components that are linked by energy and nutrient flow, are said to be an ecosystem.

Communities and ecosystems are constantly changing, evolving through the process of succession (one community reacting to and being replaced by another). Many disturbance forces, including fire, impact these changes.

Fire ecology is a branch of ecology that studies the origins of wildland fire and its relationship to the biotic and abiotic environment. Fire is studied as a natural process operating as a component of an ecosystem. To understand an ecosystem requires looking beyond the ecosystem’s present state. Full understanding includes an investigation of the ecosystem’s origin, the cycles the ecosystem progresses through, and possible future stages. Fire, similar to floods, earthquakes, storms, etc. can be viewed as one means of promoting changes in an ecosystem.

There are three key concepts important to understanding fire ecology – fire dependence, fire history and fire regime.

In the 1930’s, researchers began to challenge the negative notions about wildland fire and this new thinking prevails today. They argued that fire was essential to many plant and animal communities. For example, in drier ecosystems around the world where there is not enough moisture to help in the decay of dead plants, fire is required to break down and help recycle the nutrients. This concept is fire dependence and applies to natural communities that are adapted to and rely on the effects of fire to make the environment more hospitable for that community’s plants and animals. For example, fire kills some large plants and prepares the soil for seeding by making nutrients more available for plant uptake. As a result, competition is reduced from other species that would have absorbed needed nutrients or shade out sunlight the new plants require.

Fire history is described as how often fires occur in a geographical area. Trees actually record fire history. Each year a tree adds a layer of cells, increasing the width of its trunk. When a fire passes through a forest, trees may be only scorched. A layer of charcoal remains on a living tree and, in time, is enveloped by a layer of new growth creating fire scars. These fire scars provide a record of the tree's history that scientists can use to determine when a fire occurred. Fire scarred trees that are petrified often retain these fire scar records as fossilized charcoal or fusain.

The role fire plays in an ecosystem varies with the characteristics under which the ecosystem has evolved. This role is known as fire regime. The interactions of humidity, fuels, and ignition sources determine the fire regime for a particular land area. A fire regime is a function of the frequency of fire occurrence, the fire intensity, and the amount of fuel consumed. Both frequency and intensity of fire vary but are interdependent. Frequency of fire is largely determined by the ignition source(s) and the duration and character of weather that favor the spread of fire. The quantity of fuels available and the fuels’ combustion rates determine intensity of fire. Wind and topography influence the interaction between frequency and intensity of fires. The greater the wind velocity and the steeper the terrain, the more intensely the fire will burn.

Fire ecology is a major subject of study in a number of universities around the world. A student who is interested in becoming a fire ecologist must study physical, chemical, and biological sciences, and mathematics. The study of wildland fire also requires an understanding of the human dimensions of the issue. Students must become proficient in language arts and social sciences. Through creative arts, students gain skills in design, problem solving, and aesthetics. All subjects are important, especially for scientists who work with forces of nature as awesome as wildland fire.

MATERIALS

Poster board or flip chart

Large index cards, string, scissors, and markers

Pencil and paper

PROCEDURE

Define "ecology" on the board.

Review what students know about ecological concepts. Terms that should be discussed are: Abiotic, Adaptation, Balance, Biotic, Carnivore, Communities, Decomposers, Ecosystems, Food Chain, Food Web, Habitat, Herbivore, Niche, Nutrients, Omnivore, Photosynthesis, and Succession.

Explain the following concepts:

Fire Adaptation, Fire Dependence, Fire Ecology, Fire History, Fire Regime, Fire Scars, and Wildland Fire.

Create a food web/interdependence game based on a local plant community. Ask students to list plants and animals found in that community.

Each student should make a name card for one of the species listed and then hang the card around his/her neck.

Discuss each species’ niche and what each species depends on for food, shelter, etc.

Using one piece of string, connect all of the students to their interdependent partners (students may be connected to many different partners.)

Ask the students to explain what happens to their species in the case of a wildland fire. Discuss both the positive and negative impacts. Include issues of water, air pollution, and impacts on soils. Ask the students what they would expect to find more and less of after a wildland fire and have them explain why.

Ask students what they would need to study in school if they wanted to become a fire ecologist or wildland fire manager. List their responses and reinforce. Stress how each area of academic study prepares them for these important positions.

SOURCE

Wildfire – a study guide

Discovery Pictures