Eucalyptus species often show marked differences in morphology and ecophysiology between adult and juvenile leaves. Given these differences, it was hypothesised that juvenile and adult leaves would present different levels of resources to a herbivore, and potentially different levels of putative anti-herbivore defences. This hypothesis was tested in some eucalypts growing in native forest in south-eastern Australia.

There were no significant differences in levels of water, protein or carbohydrates (per unit dry weight) between mature adult and juvenile leaves. No difference was recorded in concentration of total phenolics between leaf forms, but more protein was precipitated (an estimate of tannin activity) in extracts from juvenile leaves. Cyanogenic glycosides were absent from mature leaves, but present in young leaves of both leaf forms in E. polyanthemos. No significant difference in concentration of any terpene was recorded between adult and juvenile leaves in E. nitens and E. regnans. Specific leaf area was lower in adult leaves, and fibre concentration was higher in adult leaves of some species, suggesting that resources in the adult leaf may be less accessible to a herbivore. However, there was no difference in leaf toughness between leaf forms, even though toughness per unit leaf thickness was higher in juvenile leaves. Hence, no major trends in resource concentration were apparent between the leaf forms, and of the defences investigated, only tannin activity varied significantly between the leaf forms.