Oral Submission Presentation by Blake Foster - New Zealand ...

most) to the north of a shelterbelt of those species. Therefore, some
seed may well fall to the north of the eastern section of the northern
boundary, but while seeding trees are growing nearby on Ferintosh
station (and presently there are many), they remain the most likely
origin of any new wildings which may appear.
• Eastern boundary. Apart from spread onto the road margin, which is
regularly controlled by contract spraying from the highway (SH80), the
risk of future spread here is very low. This is due to the presence of
the lake and the fact that much of the ‘LINZ’ land between the highway
and the lake is already well covered with forests. Even if these forests
are removed, the likelihood of reinvasion will not be high (due to heavy
branch slash and/or vigorous grass invasion) – unless there is
significant ground disturbance exposing large tracts of mineral soil.
• Southern boundary. Even though the prevailing wind flow is from
north to south, and there are mature seeding conifers just inside the
Pukaki Downs boundary, the risk of spread along the eastern section
of this boundary with Rhoboro Downs station (south ends of blocks 9
and 31) is low. This is because there is already closed-canopy forest
immediately over the boundary on Rhoboro Downs. However, it is
quite a different story along the western section of this boundary
(south end of blocks 25 and 26), where there are virtually no trees on
either side of the fenceline, and both the vegetation cover and grazing
pressure over on Rhoboro Downs is light. In the middle section of this
stretch, there is a high risk of spread to the south-west, from mature
coning contorta pine in block 9. Further to the west, along the
remainder of the southern fenceline (south end of blocks 25 and 26),
although the land is very susceptible to wilding invasion, there is a low
current risk, as no wildings are present close to the boundary and
seed spread from more distant sources to the north are infrequent.
However, the risk situation will change if conifers are allowed to seed
close to the boundary.
• Western boundary. Virtually all of this (blocks 26 to 28) bounds onto
DOC land. The vegetation cover is light and the grazing level zero, so
although the prevailing winds are more north-south than east-west,
there is a risk of spread in this direction. However, this risk of spread
from Pukaki Downs will remain low as long as the present scattering of
contorta (mostly present as fringe-spread ‘islands’) is removed soon
ie., not allowed to mature to significant coning age.
Priority control (wilding removal) areas
Based on the boundary risks outlined above, the major areas for control within Pukaki
Downs in order of priority removal (see map) would be:
• The upper Twizel river catchment - blocks 25-29. As explained
above, this area is not subjected to regular arrivals of conifer seed
from elsewhere. In addition, currently there are no mature trees
present. However, many of the ‘islands’ of spread have trees just
starting to cone, and unless these are removed in the very near
future, there is a high likelihood of much wider invasion.
Means of removal. Local DOC staff (based in Twizel) are very
experienced in wilding removal options and should be consulted
on this score. They are intending to use herbicides for much of the
removal of the same type of wildings on their land. If herbicides
are not favoured on Pukaki Downs, then the most obvious options
are mechanical or physical removal. Burning is not recommended,
due to the small size of the spread ‘islands’ and risk of the fire
spreading elsewhere. Mechanical mulching has been used
8