Seedling mortality and damage due to non-trophic animal interactions in a northern New Zealand forest

The importance of non-trophic animal damage (biting and uprooting without consumption) and mortality of canopy tree seedlings were investigated in a warm temperate forest, in northern New Zealand. Two hundred seedlings 10-30 cm in height were monitored at 4-6-week intervals for 2 years. Non-trophic animal damage accounted for more seedling mortality in the first year (37.5% of all mortalities) than any other cause. Of the seedlings damaged in non-trophic animal interactions 73% were bitten off close to the ground and left uneaten and the remainder were uprooted. In the second year all non-trophic animal damage and mortality ceased following the control of rabbits (Oryctolagus cuniculus), suggesting that rabbits were the major cause of this damage. Total annual mortality rates (6-8%) were low. However, measured seedling growth rates indicated an average time for seedlings to grow from 10 to 30 cm of 37 years. Therefore, in the absence of rabbit control, mortality due to non-trophic animal interactions (3% per year) can have an important cumulative effect. Non-trophic animal damage found in the present study before rabbits were culled (5% per year) was similar to that reported for two tropical forests, but much less than that reported for some other tropical and temperate forests.