Extensive surveys conducted in September 2019 found that brush-tailed possums were the only browsing animal found in densities high enough to present a risk to plant survival. Possums are particularly problematic as they target the most palatable plants, and habitually return to key browsing areas. New plantings are highly palatable for possums and are therefore vulnerable in this location. Over time, possums form trails through the landscape, which in turn guide other possums to desirable food sources and enable movement of introduced predators.
Annual surveys were used to map baseline and changing densities, browsing activity, and pest animal corridors to allow the best control methods to be planned. An initial possum toxin operation, followed by the establishment of a bespoke trapping network, have substantially reduced possum densities, suppressed re-invading possums, constricted the movement of other carnivorous predators, protected the establishing native plantings, and improved the overall ecological functionality of the area. Annual surveys indicate that the Boffa Miskell-led operation was able to dramatically change the browsing behaviour of the remnant possums, such that the centre of the control site is still devoid of possum movement and browsing impacts.
This project was carefully coordinated with other similar Boffa Miskell biosecurity projects on Lyttelton Port Company (LPC) land. This is a landscape-scale approach which is the most effective option for controlling high densities of possums in large inaccessible areas. Much of the control site is off-limits due to the risk of post-quake rock fall.
Continued control is needed in this area, as there are source possum populations nearby and predatory animals continue to be problematic.
When the three-year plant maintenance contract ended, Christchurch City Council (CCC) requested a more sustainable plan for continued browsing animal control. This would ensure the gains achieved were not lost over time. Boffa Miskell proposed and initiated a new, sustainable trapping network, allowing for continued protection of the native vegetation, while requiring minimal visits by staff for clearing and re-baiting traps. The solution offered saw the establishment of a new trap network upgraded with self-resetting tree-mounted traps that require allow for less frequent checking, which is particularly welcome in high-risk areas due to rockfall, while still providing the confidence that re-invasion corridors are being actively trapped.
