Environmental factors associated with the abundance of forest wiregrass (Tetrarrhena juncea), a flammable understorey grass in productive forests
Geofe O. Cadiz
School of Ecosystem and Forest Sciences, University of Melbourne, Burnley Campus, 500 Yarra Boulevard, Richmond, Vic. 3121, Australia.
Department of Biology and Environmental Science, College of Science, University of the Philippines Cebu, Gorordo Avenue, Lahug, Cebu City, 6000, Philippines.
Jane G. Cawson
School of Ecosystem and Forest Sciences, University of Melbourne, Burnley Campus, 500 Yarra Boulevard, Richmond, Vic. 3121, Australia
Trent D. Penman
School of Ecosystem and Forest Sciences, University of Melbourne, Creswick Campus, Water Street, Creswick, Vic. 3363, Australia
Alan York
School of Ecosystem and Forest Sciences, University of Melbourne, Creswick Campus, Water Street, Creswick, Vic. 3363, Australia
Thomas Duff
School of Ecosystem and Forest Sciences, University of Melbourne, Burnley Campus, 500 Yarra Boulevard, Richmond, Vic. 3121, Australia
Abstract
When flammable plant species become dominant they can influence the flammability of the entire vegetation community. Therefore, it is important to understand the environmental factors affecting the abundance of such species. These factors can include disturbances such as fire, which can promote the dominance of flammable grasses causing a positive feedback of flammability (grass–fire cycle). We examined the potential factors influencing the abundance of a flammable grass found in the understoreys of forests in south-east Australia, the forest wiregrass (Tetrarrhena juncea R.Br.). When wiregrass is abundant, its structural characteristics can increase the risk of wildfire ignition and causes fire to burn more intensely. We measured the cover of wiregrass in 126 sites in mountain ash forests
in Victoria, Australia. Generalised additive models were developed to predict cover using climatic and site factors. The best models were selected using an information theoretic approach. The statistically significant factors associated with wiregrass cover were annual precipitation, canopy cover, disturbance type, net solar radiation, precipitation seasonality
and time since disturbance. Canopy cover and net solar radiation were the top contributors in explaining wiregrass cover variability. Wiregrass cover was predicted to be high in recently disturbed areas where canopy cover was sparse, light levels high and precipitation low. Our findings suggest that in areas with wiregrass, disturbances such as fire that reduce canopy cover can promote wiregrass dominance, which may, in turn, increase forest flammability.
Additional keywords: canopy cover, disturbance, fire regime, grass–fire cycle, mountain ash.
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