Mistletoe (Tupeia antarctica) recovery and decline following possum control in a New Zealand forest

The condition of 79 plants of the loranthaceous mistletoe Tupeia antarcticain a podocarp-hardwood forest in the central North Island, New Zealand, was monitored over 4 years during a period of increasing possum density, following previous possum control. Mistletoe comprised 1.2% of total possum diet during the three years following possum control. Incidence of possum browse on mistletoe plants increased from 2.6% of plants when the trap-catch index of possum density was < 3%, to 75.9% of plants when trap-catch rates reached 4.6%. Mistletoe foliage cover declined from 49.8% to 15.6% and mean plant size declined by about 55% over the same period. The mistletoe population was dominated by plants with large haustoria, located in heavily shaded locations in the lower crown of their Carpodetus serratus hosts. Most plants established more than 20 years ago, and the current potential for recruitment of new individuals into the population is severely limited by possum browsing and the senescent nature of the mistletoe population. Intensive management of host crowns and possum populations will be necessary to ensure the long-term viability of mistletoe at the study site.