Rainforests: will they cope with a changing fire regime?

Cool Temperate Rainforests are remnants of some of the oldest vegetation in Australia. They comprise a dense canopy of Myrtle Beech, a midstorey of trees such as Southern Sassafras and Blackwood Wattle, and an open understorey of tree ferns and ground ferns, forming a cool, shaded environment along the margins of streams. Despite their name, the most potent factor that determines rainforest distribution over a broad scale is absence of fire, but as our climate warms, it is expected that fire frequency and severity will increase. Cool Temperate Rainforest may not be adapted to this changing fire regime, with implications for its long-term persistence.

ARI recently completed a research project for Parks Victoria which aimed to determine how Cool Temperate Rainforest in the O’Shannassy Catchment, part of Melbourne’s water catchment area, had fared after the fires of 2009.

Ten years post-fire, the key findings were:

• At the highest fire severity, non-rainforest (i.e. eucalypt) canopy recruitment was so prolific that around two thirds of the rainforest mapped pre-fire could no longer be classified as such and has been lost.
• At low fire severity, there was little invasion of eucalypts into the rainforest stands.
• Understorey changes were mostly as expected, with burnt plots having a higher cover of forbs, grasses and shrubs than unburnt plots. Burnt plots had substantially lower tree cover, but similar fern cover and the rainforest species Myrtle Beech and Southern Sassafras were resprouting from the bases of top-killed parent trees.