herbivory

For tens of millions of years the ratite moa (Aves: Dinornithiformes) were the largest herbivores in New Zealand’s terrestrial ecosystems. In occupying this ecological niche for such a long time, moa undoubtedly had a strong influence on the evolution of New Zealand’s flora and played important functional roles within ecosystems. The extinction of moa in the 15th century ce therefore marked a significant event in New Zealand’s biological history, not only in terms of biodiversity loss, but in the loss of an evolutionarily and ecologically distinct order of birds.

Predators can indirectly structure local plant communities by altering the diversity and behaviour of herbivores. These ‘trophic cascades’ can be seriously disrupted by the local extinction of top predators. They can also be restored by the subsequent re-introduction of top predators by conservationists. Here, we investigated trophic cascades involving kākā, puriri moths and their host trees. New Zealand kākā (Nestor meridionalis, Nestoridae) are large parrots that were extirpated from most of its range in the 20th century.

Introduced mammalian herbivores are changing the structure and composition of New Zealand’s forest ecosystems and may modify forest succession after natural disturbances. We studied how introduced ungulates (red deer and feral pigs) and rodents (rats and house mice) affected the rate of recovery (i.e. the engineering resilience) of the forest understorey following artificial disturbance.

Introduced brushtail possums (Trichosurus vulpecula) are controlled over large parts of New Zealand to protect canopy trees. The condition of canopy trees is one of the cues used to trigger possum control, but selecting an indicator of canopy tree condition is difficult because many factors unrelated to possum browsing can affect canopy condition, and indices based on canopy scoring may not always quickly detect real changes in possum herbivory.

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.

Honeydew excreted by phloem-sap sucking scale insects (Ultracoelostoma sp.) living in the bark of beech (Nothofagus solandri:) trees growing at a high elevation (900 m) site in the Craigieburn range of Canterbury, New Zealand, was measured over four days during 1–10 May 1996. Average standing crop of honeydew sugar was 3.1 mg m-2, and ranged from 0.4 to 5.5 mg m-2. Daily production of honeydew sugar ranged from 0.2 to 1.5 mg insect-1 24 h-1, and 4.1 to 45.9 mg m-2 24 h-1.

The Australian brushtail possum (Trichosurus vulpecula) has been blamed for the decline of three native New Zealand beech mistletoe species (Alepis flavida, Peraxilla tetrapetala and Peraxilla colensoi, Loranthaceae), but there are few quantitative data on possum effects, and anecdotal evidence is often conflicting. We present results from two monitoring programmes that suggest possum control operations can improve mistletoe health.

This study provides the first quantitative comparison of methods for monitoring herbivory and growth of New Zealand beech mistletoes (Alepis flavida, Peraxilla colensoi and Peraxilla tetrapetala). Four monitoring methods-leaf maps, volume estimates visual estimates of browse and foliage density, and rePeat fixed-point photographs-were used to assess the health of 60 permanently tagged mistletoe plants in four South Island beech forests between February 1997 and February 1998.

Kawakawa (Macropiper excelsum) is an understorey, forest tree which sustains conspicuous and substantial herbivory from the larvae of a geometrid moth, Cleora scriptaria.. This study examined the relationship between leaf abscission and the amount of damage a leaf had sustained. In the field, kawakawa trees showed no increase in the rate of leaf shedding in response to experimental damage by C. scriptaria larvae or to artificial damage produced by a hole punch, even when 90% of the leaf area was removed.