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Shifting States, Altered Fates: Divergent Fuel Moisture Responses after High Frequency Wildfire in an Obligate Seeder Eucalypt Forest

1
School of Ecosystem and Forest Sciences, Faculty of Science, the University of Melbourne, Baldwin Spencer Building, Parkville 3010, Australia
2
School of Ecosystem and Forest Sciences, Faculty of Science, the University of Melbourne, Burnley Campus, 500 Yarra Boulevard, Richmond 3121, Australia
*
Author to whom correspondence should be addressed.
Forests 2019, 10(5), 436; https://doi.org/10.3390/f10050436
Received: 25 April 2019 / Revised: 8 May 2019 / Accepted: 17 May 2019 / Published: 20 May 2019
(This article belongs to the Section Forest Ecology and Management)
High frequency wildfires can shift the structure and composition of obligate seeder forests and initiate replacement with alternative vegetation states. In some forests, the alternative stable state is drier and more easily burned by subsequent fires, driving a positive feedback that promotes further wildfire and perpetuates alternative stable states. Mountain Ash (Eucalyptus regnans (F.Muell.)) forests are highly valued for their biodiversity, water, timber and carbon. Fires are a natural part of the lifecycle of these forests, but too frequent fires can eliminate Mountain Ash and trigger a transition to lower stature, non-eucalypt forests which are dominated by understorey species. This study sought to better understand the fuel moisture dynamics of alternative stable states resulting from high frequency wildfires. A vegetation mosaic in the Central Highlands, Victoria created a unique opportunity to measure fuel moisture in adjacent forest stands that differed in overstorey species composition and time since fire. Specifically, we measured fuel moisture and microclimate at two eucalypt sites (9 and 79 years old) and three non-eucalypt sites (two 9 year old and one 79 year old). Fuel availability, defined here as the number of days surface fuels were below 16% and dry enough to ignite and sustain fire, was calculated to estimate flammability. Fuel availability differed between sites, particularly as a function of time since fire, with recently burnt sites available to burn more often (4–17 versus 0–3 days). There were differences in fuel availability between non-eucalypt sites of the same age, suggesting that high frequency fire does not always lead to the same vegetation condition or outcome for fuel availability. This indicates there is potential for both positive and negative flammability feedbacks following state transition depending on the composition of the non-eucalypt state. This is the first study to provide empirical insight into the fuel moisture dynamics of alternative stable states in Mountain Ash forests. View Full-Text
Keywords: alternative stable states; climate change; Eucalyptus regnans; fire regime; feedback; flammability; fuel availability; Mountain Ash; non-eucalypt alternative stable states; climate change; Eucalyptus regnans; fire regime; feedback; flammability; fuel availability; Mountain Ash; non-eucalypt
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Burton, J.; Cawson, J.; Noske, P.; Sheridan, G. Shifting States, Altered Fates: Divergent Fuel Moisture Responses after High Frequency Wildfire in an Obligate Seeder Eucalypt Forest. Forests 2019, 10, 436.

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