Ecology is a very broad-ranging and complex topic, and even its definition lacks consensus. Thus, there are numerous concepts that fit within this discipline, and diverse manners in which the content can be arranged and studied. Several of the basic concepts of ecology include ecological units, the ecosystem, energy flow, nutrient cycles, species interaction, productivity, and ecological challenges.
The role fire plays in an ecosystem varies with the characteristics under which the ecosystem evolved. This role is the third concept of fire ecology, fire regime. The interactions of humidity conditions, fuels and ignition sources will 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 and are interdependent. Frequency of fire is largely determined by the ignition source(s) and the duration and character of weather which favors the spread of fire. Intensity of fire is determined by the quantity of fuel available and the fuels' combustion rates. The interaction between frequency and intensity of fires also will be influenced by wind and topography.
While some ecologists were studying the dynamics of communities and populations, others were concerned with budgets. In 1920 August Thienemann, a German freshwater biologist, introduced the concept of trophic, or feeding, levels (see ), by which the energy of food is transferred through a series of organisms, from green plants (the producers) up to several levels of animals (the consumers). An English animal ecologist, (1927), further developed this approach with the concept of ecological s and pyramids of numbers. In the 1930s, American freshwater biologists Edward Birge and Chancey Juday, in measuring the energy budgets of lakes, developed the idea of , the rate at which food energy is generated, or fixed, by . In 1942 Raymond L. Lindeman of the United States developed the trophic-dynamic concept of ecology, which details the flow of energy through the . Quantified field studies of through ecosystems were further developed by the brothers Eugene Odum and Howard Odum of the United States; similar early work on the cycling of was done by J.D. Ovington of England and Australia. (See ; and .)
The second concept of fire ecology is fire history. Fire history is described as how often fires occur in a given 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. These fire scars provide a record that scientists can use to determine when in history a fire occurred.