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Mountain Ash:

Intense and Rapid Wildfire

Bushfire on a ridge
Bushfire on a ridge
Source - CFA

Regeneration of Mountain Ash requires a periodic hot and fast bushfire in a forest of trees of at least seed-bearing age. Mountain Ash forests naturally experience a crown fire possibly every 100-200 years-a fire that destroys the forest but results in dense regrowth. Such a crown fire is only possible after a number of years that result in dry fuel, low humidities and high temperatures.

The future succession of the sites will depend upon the frequency of subsequent fires. Fires less than 20 years interval (ie before trees are old enough to set seed) will see the elimination of Mountain Ash altogether and other species will dominate; fires every 2-3 years will result in domination by Pteridium esculentum; every 5-8 years, Cassinia aculeatum, and every 10-15 years, Pomaderris aspera.

Fire seldom penetrates the gullies colonised by the fire-sensitive Myrtle (or Southern) Beech. This absence of fire is the major determining factor in the Myrtle Beech range. Logging practices and clearing for other purposes also create major disturbance in the forest, yet it is to bushfire and occasional canopy disturbances with their more limited soil disturbance that the plants are adapted. As a result, logging and clearing results in a succession of flora which is different from that produced by bushfire.

Wildfire reduces ground-layer invertebrate activity by up to 90%; the number of different groups of these animals (taxa at the higher levels) is reduced by up to 60%. Yet groups such as spiders, mites, beetles, flies, ants and wasps are active after the fire. Some groups (eg ants) are more active after a fire than before. Although mammals and birds can escape from fires of low to medium intensity, this may be short-lived in the long term unless they survive in unburnt remnant vegetation. While an intense wildfire may kill all trees, the presence of dead and burnt stag trees for shelter is important for many animals such as the skink Pseudemoia spenceri.

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