The ecosystem effects of the biocontrol of heather (Calluna vulgaris) with the heather beetle (Lochmaea suturalis) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Zoology at Massey University, Palmerston North, New Zealand
The biological control of invasive plants has the ability to affect sustainable and targeted
control over large areas. Such biological control programs are an important tool in the control
of invasive plants in conservation areas. The ultimate aim for these programs is to provide a
net ecosystem benefit via the reduction of invasive plant densities. However, whether this aim
is fulfilled is rarely evaluated. Invasive plant control results in large scale disturbance to
ecosystems by removing the novel but often utilised habitat and resources provided by the
invasive plant. Biological control is also complicated by having a novel organism introduced
into the ecosystem with potential flow on effects for species and trophic level interactions.
This research evaluated the ecosystem impact of the heather (Calluna vulgaris) biological
control program using the heather beetle (Lochmaea suturalis) on the native tussock grassland
in the central North Island of New Zealand. This was achieved by comparing invertebrate
communities in a small scale experiment and over three large heather beetle outbreak sites.
This work provides an extension to Keesing’s (1995) research on the effects of heather invasion
Heather provides a novel and unsuitable food source to many native phytophagous insects,
may disrupt host finding behaviours of these insects, and alter habitat structure and
complexity affecting Araneae abundance. Changes in invertebrate community composition
following control were related to the removal of these effects. This outcome was consistent
with predictions from Keesing (1995) and in both small and large scale studies. Heather beetle
presence was found to have a positive effect on Araneae and Collembola abundance.
Heather control also had a positive for the common skink (Oligosoma nigriplantare
polychroma) Overall the biological control of heather caused invertebrate communities to
revert back to a composition resembling more closely those found in non-invaded habitats.
This suggests that the biological control of heather provides a net positive conservation benefit
to native tussock grasslands.