Mistletoes (Loranthaceae) in the Central North Island, New Zealand: Reproductive Ecology and the Effect of Possum (Trichosurus Vulpecula) Browsing, and Recovery Plan

Abstract

The reproductive ecology of five threatened, native loranthaceous mistletoes {Alepis flavida, Peraxilla colensoi, P. tetrapetala, Ileostylus micranthus, and Tupeia antarctica) in the Central North Island, New Zealand was investigated, including their response to possum {Trichosurus vulpecula) management. The five mistletoe species studied appeared to have stopped reproducing and recruiting in the study area prior to possum control. These mistletoes have become a high conservation priority in recent years due to an apparent decline in populations that were formerly widespread. Information on their reproductive ecology, and the effect of possum foliage browse on reproduction is required for the development of conservation management strategies. The aim of this study is to provide this information. The species studied occurred in and around Tongariro National Park and Lake Taupo, in the Tongariro/Taupo Conservancy of the Department of Conservation. This study was divided into three sections. The level of possum foliage browse on selected mistletoes of all five species were monitored pre and post various forms of possum management (banding and caging of mistletoes, and trapping and poisoning of possums) to establish if mitigation of possum foliage browse occurred, and if this improved the reproductive of the five species. Reproduction was studied by investigating flowering and pollinators, and fruiting and seed dispersers over two years following possum management. All five mistletoe study populations protected from possum browse by various management techniques showed decreases in possum foliage browse, post management. All species had decreases in possum browse post management, but this decrease was only significant for P. colensoi and P, tetrapetala. This was followed by a general trend of increases in size, health, and reproduction, but only P. tetrapetala and T. antarctica had statistically significant increases in reproduction, the other increases were non significant, and indicative only. More research is required to understand the implications of possum browse on mistletoes, especially at a regional scale. This study showed that flowering occurred primarily over the summer months (January - March) for A. flavida, P. colensoi, and P. tetrapetala. Fruiting occurred over the autumn and winter months (April - August). Native bird species were identified as pollinators and seed dispersers for two of these three mistletoes. There is also evidence for self-compatibility in these three species. Flowering in I. micranthus occurred primarily in spring (October - December), and fruiting occurred in autumn and winter (April - August). Native insect species were identified as pollinators, and native and introduced birds as seed dispersers. In T. antarctica, flowering occurred in spring (October) and fruiting in winter and the subsequent spring (July -September). Native insect species were identified as pollinators, and native bird species as seed dispersers of T. antarctica. All members of the Loranthaceae family in New Zealand are declining and one of them (Trilepidea adamsii) is presumed extinct. Many factors have contributed to their decline, principal among them are loss of habitat, declines in the native animal species involved with reproduction, and browse by mammalian pests. Active management is required to maintain existing populations and to prevent further declines and extinctions of these species. A recovery plan for these mistletoes is outlined, including management options and a work plan. Due to the cultural relationships New Zealanders have with these plants, promotion of public and iwi involvement with the management and conservation of these native mistletoes is a key element to the success of this plan.