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Influence of Bushfire on Future Forest Growth

Although there are major nutrient losses from a forest during bushfire, mainly with smoke and washoff, there is little or no evidence that regrowth forests are less sustainable than the original mature forests.

Nitrogen, phosphorus and other nutrients contained in the standing biomass are essentially mobilised during fire, and flow into the air and water environment. Changes in soil chemistry occur, and microbiological and soil fauna activity is sharply altered. Re-establishment of understorey quickly restores this activity, and many native shrub species re-colonise the fertile ash-laden soils to replenish the soil with nitrogen.

By far, the greatest reserves of nutrients are usually contained in the soil well beyond the reach of fire effects. Regrowth forests can access these nutrients, as well as the flush of nutrients released into the ash layer by the fire (the "ash-bed effect"), resulting in prolific early growth. This cycle of fire, nutrient loss, the fixation of nitrogen by shrubs, and the weathering of parent rock materials allows the forest to recover through to maturity. Cycling of these nutrients between the litter, soil and the vegetation canopy then continues until it is interrupted again by fire. However, the quantity of nutrients involved in the cycle at any time is only a small fraction of the total available nutrient pool. Loss of the cycling nutrients therefore perturbs the nutrient balance in a minor way, and only temporarily. (Repeated forest burning for fire hazard reduction at short time intervals or regular forest harvesting may deplete these nutrient reserves in the long term; this is not considered here.)

Wildfire, to our knowledge, does not inhibit forest sustainability. But when combined with weather sequences that might favour establishment of a different ecosystem after the fire, or when closely-spaced fires alter seed production from vegetation, then changes in forest type may occur.

Key references:


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nutrient View Frequently Asked Questions     View Bibliography