 Conference
1999
New Zealand Plants and their Story
Pest
Animals in Urban Forest Remnants
Ken
Wright
Biosecurity Department
Wellington Regional Council
Introduction
I work for the pest animals
section, Biosecurity Department of the Wellington Regional Council.
I'm responsible for the western half of our region, which covers,
four cities and one District Council. Our pests include possums,
rabbits, magpies, wasps, mustelids, rooks and feral goats.
This presentation will
focus on possums in urban forest remnants. I will mainly cover Wellington
City examples.
- Wellington City in
particular is clothed with a living cloak of forest with houses
inserted off streets on this steep hilly terrain.
- From a distance this
meshing of housing/urban life and the forest canopy is evident.
- This creates in effect,
a continuous habitat for animal pests such as possums. As you
can appreciate it creates special problems in controlling possums
and yet balancing issues of public safety.
- The most simple request,
from the public, involves pesky possums annoying householders
with their:
- blood curdling
shrieks at night
- taking up residence
in house walls, floors, ceilings or chimneys
- feeding on prime
garden specimens especially roses, just starting to grow at
this time of year
- balcony planter
boxes are also targeted
- possum droppings
are left behind on paths
These singular nuisance
problems are best treated with a Timms trap. The urban saviour
for possum control.
- However some possum
problems are on a large scale. Bush remnants, urban conservation
type parks are often surrounded by housing. Home owners rightfully
point out that the possums are coming from council land and it
is up to the council to control them. The four cities throughout
the greater Wellington area have these types of complaints. These
complaints are not efficiently treated with Timms traps on the
residential fringe. A complete possum control operation is required
to target possums through the reserve network.
- The Wellington Regional
Council's Biosecurity Pest Strategy has made provision for the
control of possums in the interest of environmental values as
well as the usual economic values, such as TB vector control,
forestry and horticulture.
It was realised that
possum control for conservation reasons is not a financially
rewarding undertaking for landowners. Therefore regionally funded
possum control in such ecosystems is justified.
Our pest strategy
makes provision for the control of possums for conservation
reasons under the Key Native Ecosystem (KNE) programme. This
involves surveying bush remnants using a scoring process and
developing a priority scoring to decide which areas are eligible
for regionally funded possum control.
The KNE Process
- The process starts
with a local landowner or council reserves officer approaching
us with a request to treat possums in a native forest remnant
or reserve.
We conduct a KNE
survey, assessing and scoring the following points:
- Recording all
plant and animal species present.
- Preparing comment
on protected status, fencing, previous surveys, vegetation
association, site specific issues.
- Allocating a
DoC score for plants.
- Allocating a
DoC score for animals.
- Allocating a
DoC score for vulnerability to possum damage.
- Allocating a
regional score based on public access and regional value.
- Following the final
KNE score, a decision is made on whether to fund possum control.
- Wherever possible
we try to involve the landowner in a partnership for possum control.
This ranges from half share of costs with city councils, to materials
and set-up provided by WRC with landowners providing their labour.
The information that
we gather during the survey is fed back to the DoC natural areas
database. On several occasions we have discovered endangered
or regionally rare species and a DoC "Species Record Sheet"",
is completed e.g. Gastrodia, Large Leafed Milk Tree,
Mistletoe, tree gecko etc.
- During the survey
process and from initial identification of potential KNE survey
sites, the Wellington Botanical Society has been excellent at
providing plant species lists and background information on management
areas. I commend this society for their supportive approach with
information sharing.
Actual Operation in
Urban Areas
Our constraints are:
- Continued public
access to reserves during operations
- Household pets, particularly
cats and dogs
- Child safety concerns
- Interference with
baits and bait stations, through to theft of traps.
Leg-hold Traps
There are various bylaws
for each city. Wellington City Council trapping bylaw requires us
to obtain a three month period permit to use approved leg-hold traps.
Conditions state no trapping within 200 metres of houses or within
20 metres of tracks. We must put up signs that indicate possum control
is in progress, advising people to stay on the tracks, but we don't
advertise directly that traps are being used to prevent them being
stolen. In some instances trapping is halted over school holidays
principally to reduce the chance of theft.
Poisons
Poisons are dispensed
from secured bait stations. Bait stations are laid out on a cut
grid pattern to ensure that the bait stations uniformly cover the
block and possums will readily encounter bait.
It is best to place bait
stations within 400mm of the ground so that possums will encounter
them promptly. However it is an option to put them higher in trees
where pets or children may have access. Using black bait stations
helps to make their presence less obvious.
We use anti-coagulant
poisons that have antidotes and are of less danger to principally
dogs. We can never assume that dogs will always be under constraint
by their owners, even though the law requires dogs to be kept under
control, and on a leash in most reserves.
Operational Process
- Initial KNE survey.
- Negotiate and plan
access with all landowners.
- Pre-operational trap
catch monitoring.
- Ministry of Health
approval.
- Public relations,
public notification.
- "Actual operation"
- traps, acute poison followed by chronic poison.
- Post-operational
trap catch monitoring.
- Public relations
follow-up.
Measuring Success
- Comparing pre-operational
possum trap catch with post-operational trap catch.
- Monitor predators
before and after the operation.
- Set-up canopy vegetation
assessment plots and measure before, and two years after control.
- Conduct bird surveys.
- Publicly advertise
the success to ensure political support for funding.
Wellington City Successes
- During 1998 bellbird
was heard in the suburbs of Karori and Wilton for the first time
since the 1950s.
- Otari - Wilton's
Bush treated in 1993/94 was re-measured in 1995 and the response
to vegetation was compared as good as occurs on off-shore islands
following possum eradication. Kohekohe fruit most notable.
- Wellington City Council
is now committed to an ongoing possum control programme in their
conservation value reserves.
- We are now moving
towards continuous areas of treated native forest. We are starting
to roll the possums back.
Case Study; Trentham
Memorial Park, Upper Hutt City
- This 17 ha bush remnant
was treated for possums in 1995
- After 3 months of
Brodifacoum applied from bait stations there were no possums left
and chances of invasion are extremely low.
- Gastrodia orchids
are noted in Jan 1996
- UHCC adopt a wandering
Jew weed eradication programme
- 1997 discover the
yellow mistletoe Ileostylus micranthus
- UHCC fence tracks
and forest margin, with posts and wire and chicken mesh to reduce
trampling of the under-storey
- The regionally endangered
plant, Teucridium pariflorum is planted in this restored
forest remnant.
Long-term Strategy
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