We used a comparative approach to investigate heteroblasty in the Chatham Islands. Heteroblasty refers to abrupt changes in the morphology of leaves and shoots with plant height. Common on isolated islands such as New Caledonia and New Zealand, which once had flightless, browsing birds, heteroblasty is hypothesised to be an adaptation to deter bird browsing. The Chatham Islands are a small archipelago located 800 km off the east coast of New Zealand, which has clear floristic links to New Zealand.
The first deer to invade an area of forest on Secretary Island show an almost exclusive preference for bark of Pseudopanax colensoi var. ternatum. Young shoots of P. linearis and juvenile P. crassifolium are also sought. Intensive browsing is begun in areas of Asplenium bulbiferum and continued where Polystichum vestitum and bushes of Coprosma spp. are plentiful. The foregoing are the main species being killed by deer but others are being taken in increasing quantity.
New Zealand forests have been substantially modified by introduced red deer over the past century. New Zealand’s indigenous forest managers need to know if regeneration of palatable tree species can be restored following control or eradication of browsing ungulates. Aorangi Forest, Wairarapa, suffered dramatic changes in forest understorey composition by the 1950s after more than seven decades of colonisation by red deer (Cervus elaphus), feral goats (Capra hircus) and pigs (Sus scrofa).
This study uses data from forty-nine 20 m × 20 m permanent plots measured in 1976, 1982, 1989 and 1997-2002 in Wakatipu Forest, western Otago. We relate changes in red (Nothofagus fusca), silver (Nothofagus menziesii) and mountain beech (Nothofagus solandri var. cliffortioides) forest vegetation to the presence of fallow deer (Dama dama). Vegetation composition is likely to have been altered prior to plot establishment, and results show that there was little change in vegetation composition during the study.
Making use of existing fences as ready-made exclosures, this study aimed to assess the long-term effects of cattle grazing on forest margins. Results indicated: 1) that cattle browsing and trampling has an impact on vegetation species composition, structure and regeneration; 2) that the effects of a particular grazing regime may take many decades to dissipate; and 3) that the impacts of cattle change with stock intensity. Some plant species appeared to be highly palatable to cattle and only occurred on sites without cattle.
There are at least three hypotheses to account for the abundance of divaricating shrubs in New Zealand: 1) Ratites in the form of 11 species of moa, led to divarication for browse protection (Greenwood and Atkinson, 1977); 2) Divarication evolved as a microclimatic shield (McGlone and Webb, 1981); 3) Divarication evolved to aid leaves in light harvesting (Kelly, 1994). In Patagonia before human arrival, there were browsing mammals in addition to the ratite rhea.
The diet of the North Island kokako (Callaeas cinerea wilsoni) was studied in three central North Island habitats, Pureora, Mapara, and Rotoehu, for three years. Possum (Trichosurus vulpecula) diet was less intensively studied for part of the same time in Pureora and Mapara. A literature review was made of the diet of possum, red deer (Cervus elaphus), and feral goat (Capra hircus). There is considerable overlap between the diets of kokako and the three mammalian browsers; leaves and/or fruit of some species are eaten by all four, e.g.
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.
This study uses data from repeatedly measured forest monitoring plots (20 × 20 m) (n = 32) and nine ungulate exclosures (paired fenced and unfenced plots; 20 × 20 m) to show the effects of introduced ungulates on tree regeneration in Pureora Forest Park, central North Island, between 974 and 2002.