Implications of early browsing damage on the long term productivity of eucalypt forests

Abstract

Seedlings of Eucalyptus nitens (Deane et Maiden) and Eucalyptus regnans F. Muell. were artificially defoliated at various times during their first growing season in order to simulate the effects of animal browsing. Results after 7 years indicated that there was no long term effect on the survival and growth of seedlings that were subjected to the removal of growing tips in the first spring and autumn following planting. The loss of half of the crown in autumn resulted in lower survival than for unbrowsed seedlings but the better growth rate of the surviving seedlings resulted in no loss of total volume production. However, seedlings subjected to the loss of half of the crown in spring produced 25% less total volume growth than unbrowsed seedlings. The complete removal of the crown resulted in long term volume losses of 71–97% as a result of very low survival and poor growth rates. The poor growth of heavily browsed seedlings was attributed to their failure to achieve dominance over the competing vegetation. Overall, the severity of defoliation had a greater effect on survival and growth than the timing of treatment, although browsing in autumn resulted in higher mortality than in spring. The results confirmed the need for eucalypt seedlings to be protected against severe browsing damage in order to achieve site occupancy and full growth potential.