An experimental field study of the effects of mammalian herbivore damage on Eucalyptus nitens seedlings

Tasmanian herbivores are known to damage commercially farmed eucalypt seedlings during their first year of growth. This damage is thought to reduce plantation productivity by reducing seedling growth, reducing seedling survival and promoting the development of multiple leaders. We report a study which quantified the effects of browsing damage on Eucalyptus nitens seedlings. Twelve months after planting, severity of browsing, net growth rate (daily change in height), survival and number of leading shoots was compared between fenced and unfenced seedlings at seven forestry plantations. Browsing damage significantly reduced net growth rate of unfenced seedlings at five plantations. The amount by which net growth was reduced was linearly related to a measure of browsing damage severity (r2=0.907, df=6, p<0.01). Significant reduction in growth occurred where mean browse score exceeded 0.88. Unfenced seedlings with intermediate levels of damage developed more leading shoots than fenced seedlings. Seedling survival was unaffected by browsing damage at 12 months. The findings of this study can be used by forestry managers to assign meaningful measures of loss in height growth to observed levels of browsing damage, and to specifically identify 'acceptable' levels of damage.