Dynamics of kanuka (Kunzea ericoides) forest on south Kaipara spit, New Zealand, and the impact of fallow deer (Dama dama)

Exclosure plots established in three separate areas of kanuka (Kunzea ericoides var. ericoides) forest on south Kaipara spit in 1983 to assess the impact of introduced fallow deer (Dama dama) were remeasured in 1993. Kanuka shared canopy dominance with mapou (Myrsine australis), houpara (Pseudopanax lessonii) and mahoe (Melicytus ramiflorus ssp. ramiflorus) in relatively old forest in Lookout Bush, Woodhill, and dominated exclusively in two younger stands at South Head; Coprosma rhamnoides dominated understories throughout. At Lookout Bush cohort senescence continued in kanuka and began in mapou and houpara during the period of the study. Seedling thickets of kanuka self-thinned and were also likely to have been smothered by other species. Massive recruitment of mahoe occurred inside the exclosure, and continued in houpara, mostly outside. Mahoe and another generation of houpara are replacing the existing canopy in the absence of deer, and another generation of kanuka and houpara elsewhere in a partially stalled succession; Canopies are still intact at South Head, and there were no major changes in populations of canopy species. However, similar successional pathways are likely to occur there in future. An influx of highly palatable shrubs, e.g., coastal karamu (Coprosoma macrocarpa) and hangehange (Geniostoma rupestre var. ligus Trifolium), into collapsing forest in the absence of deer, and their scarcity or absence elsewhere, indicates continuing impoverishment of the understorey as well as the canopy by deer. In the long term it is likely that a variety of broadleaved trees will invade these stands and that tall semi- coastal forest, similar to extant relies on the dunes, will develop. In the meantime, the high conservation value of these stands suggests that a major reduction in the deer population—sufficient to allow natural successional changes to proceed unhindered—should be a conservation priority for the region.