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Summary
In Australia, eucalypts frequently suffer defoliation due to insect herbivory or fire. Rapidly-applied ‘shock’ defoliation of eucalypts, characteristic of artificial defoliation experiments, is unusual under natural and plantation conditions, though the exception to this is defoliation by fire. The effect of 15 consecutive annual complete defoliations of jarrah (Eucalyptus marginata Donn ex Smith) saplings on diameter and survival of main stems is described. Within 3 y, this defoliation resulted in almost complete suppression of stem diameter growth. Despite up to 15 y of repeated defoliation, no plants died, although after 15 y about half the defoliated plants had died back to below 30 cm. Low mortality in E. marginata following complete defoliation is in contrast to effects on several other eucalypt species which have been subjected to defoliation experiments. Stem die-back did not appear to be related to less-than-usual winter rainfall in some years. Annual diameter growth of undefoliated plants was not correlated with preceding winter rainfall, probably due to the poor resolution of diameter measurements. The resilience to this defoliation, which is more severe than defoliation encountered in natural conditions, is evidence that understorey jarrah plants are capable of withstanding, for extended periods, defoliation by insects or fire. The degree and frequency of defoliation under current fire management regimes do not appear to threaten the persistence of jarrah saplings. Chronic defoliation by insect pests, while having a detrimental effect on growth, is unlikely to affect the persistence of jarrah saplings.