population dynamics

Brushtail possums were studied over a period of four years by live-trapping, poisoning and kill- trapping on an altitudinal transect (455-1500 m a.s.l.) in beech (Nothofagus) forest in South Island, New Zealand. There was a single breeding season in autumn in which most females (including 80% of one-year- olds) panicipated. Trap-revealed ranges of adults were up to 1 km long and some immature males dispersed up to 10 km. Capture rates in live-traps were highest in beech/podocarp forest at 455-460 m a.s.l. and declined with altitude.

The data of Lloyd (1971) on the 'chosen tree' and 'chosen seedlings' in 5607 4 x 4 m plots in Russell forest are analysed using a simple transition matrix model. The most realistic analysis predicts little change in relative species composition, other than a slight increase in the softwoods. The virtue of the approach lies more in the questions it raises than in the predictions obtained. Before such models can be applied satisfactorily in New Zealand basic data on seedling survival, tree growth rates and average life spans are required for most indigenous species.

There has been considerable ongoing debate about the extent to which the impacts of introduced deer on native vegetation have replaced those of moa, and since the 1980s there have been major changes in thinking about the impacts of deer and ratites on ecosystems. Although it has long been known that deer caused a predictable sequence of changes in forest understorey composition, recent work has shown that the foliage of species preferred by deer contains lower concentrations of fibre – and decomposes faster – than avoided species.