Practical and theoretical implications of a browsing cascade in Tasmanian forest and woodland
Alister Hazeldine A and Jamie B. Kirkpatrick A B
+ Author Affiliations
- Author Affiliations
A Discipline of Geography and Spatial Sciences, School of Land and Food, University of Tasmania, Private Bag 78, GPO Hobart, Tas. 7001, Australia.
B Corresponding author. Email: j.kirkpatrick@utas.edu.au
Australian Journal of Botany 63(5) 435-443 https://doi.org/10.1071/BT14334
Submitted: 8 December 2014 Accepted: 31 March 2015 Published: 29 April 2015
Abstract
Browsing cascades have strong implications for biodiversity conservation and fire management. The associational resistance and associational susceptibility hypotheses suggest different mechanisms. We tested the veracity of these two hypotheses by using small dry eucalypt forest and woodland trees. At 67 sites, we measured the height of the browse line and estimated the proportion of foliage remaining below it for all adult individuals of small trees within a 50 × 50 m area, recorded scat numbers, browsing damage to tree seedlings by species and environmental data. The 110–130-cm browse line, and strong relationships between macropod scat numbers and the remaining foliage below the browse line, suggested that Bennetts wallabies (Macropus rufogriseus Shaw) were the main cause of umbrella-shaped trees. The browsers preferred Exocarpos cupressiformis Labill. and Bursaria spinosa Cav. At the other extreme, adult Acacia dealbata Link suffered no browsing damage. All species were browsed as seedlings. Associational resistance occurred in some species and associational susceptibility in others, with the degree of difference in palatability between alternative sources of browse possibly resolving this apparent contradiction. Low browsing pressure is likely to cause woody thickening, an increase in fire hazard and a decrease in biodiversity. Extremely high browsing pressure had no such effects.
Additional keywords: associational resistance, associational susceptibility, eucalypt, macropod, rabbit, small trees, wombat.
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