Background

The Nature of Fire Disturbance in Forests

Natural forests and their ecosystems in Australia have evolved to use available rainfall in a way that allows them to survive. In each climate niche, naturally occurring fires (caused by lightning) are just as much part of the natural scene as the climate and its well-known variability. Wet periods and droughts as well as fires affect forests in the short term, but in the longer term (centuries), our forests are essentially stable, and shrug off any temporary disturbance.

In the short term, however, major consequences to water catchments following fire become apparent. These are caused by:

• Temporary loss of vegetation cover
• Temporary loss of litter cover on the forest floor
• Release of nutrients into ash and loss to the atmosphere
• Deposition of charcoal and ash on the forest floor
• Altered soil properties near the surface
• Altered biological processes in the soil
• Some permanent loss of mature trees
• Vigorous regrowth of new forest

These primary changes have, in the most part, been well documented following major fires in the past, although they vary in importance from one site to another.

More importantly, these changes affect the water cycle in forests, as explained here.