Induction of chemical defences in response to browsing: Effects of artificial and natural browsing by introduced Rusa deer on the eucalypt Corymbia gummifera

Plants have an array of chemical and physical characteristics, which affects their vulnerability to consumption by herbivores; mammalian and invertebrate. Plants respond to herbivory, and become less palatable after browsing due to changes in primary and secondary chemistry, this is known as induced resistance. Such induction has been related to foliage loss directly, but also as a chemical response initiated by the saliva of the herbivores during feeding. There have been a number of studies investigating induced defences in northern hemisphere plants but induction of resistance to mammalian herbivory is much less well understood in Australian ecosystems. Eucalypts comprise the dominant tree species of the forests and woodlands of eastern Australia, and are prone to herbivory by a range of native and introduced herbivores. We had three aims (1) to test the effects of artificial browsing and application of extract from deer salivary glands on levels of leaf phenolics of C. gummifera trees growing in their natural environment, (2) to determine the change in leaf phenolics of C. gummifera seedlings over time in the nursery, in response to artificial defoliation and application of deer salivary gland extract and (3) to quantify preferences of deer for C. gummifera seedlings that have been previously browsed, in relation to the level of induced defences. Preliminary results indicate a difference in response between young and older foliage.  Older leaves appear not to show any induced changes in chemistry with respect to any of the treatments, whereas younger leaves changes consistent with induced responses by grazing. These results will be discussed in the context of changes in the mammal herbivore populations as a result of introduced species