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

south to remain within Pukaki Downs. Movement to the west is
restricted by winds coming down the Twizel valley and eddying east
around the end of the Rhoboro Range. In addition, most of these
scarp slopes now have a dense cover of wildings, which would be
both expensive to remove and to retain free of trees.
Means of removal. If aerial herbicides are not to be used, the only
other option is physical removal. Much of the land is too steep and
uneven for machines, although a roller-crusher (as used to clear
scrub in the past by the NZ Forest Service) could be operated from
the top ridge. This could be followed-up by burning, as the slopes
lend themselves to easier fire containment - but the resource
consent proceedure required to carry out a burn could well be
onerous. Local DOC should be consulted on the most costeffective
technique and operators for physical removal.
Containment area. This area, within which trees would remain, ties in very closely with
the pink-coloured blocks on the map, with two exceptions:
• The striped-pink corridor north of DOC’s Dusky Reserve (running
between blocks 21/16 and blocks 17 / 22-24) should be included in the
containment area, as it is surrounded by wilding contorta pine forests,
and keeping it wilding-free would be a large and on-going
commitment. Even if it is improved for heavier grazing (which would
require fencing as well), the seed rain would be high and wilding
control will become increasingly difficult to maintain.
• As indicated elsewhere, the current wilding cover in western parts of
blocks 12, 13 and 19 is relatively light, and where this is the case,
could be removed. With the major seed disseminating winds coming
from the north, wilding reinvasion would not be frequent, despite the
proximity of these areas to contorta forests to the east.
Options for containing conifers within managed areas
The areas recommended above for the clearing of wildings were chosen to reduce the risk
of wilding spread outside Pukaki Downs, and also because they had a relatively low
wilding presence, which would not be too costly to remove. Other areas could also be
cleared (continuing the strategy of control from the north), but clearing them and keeping
them clear would be very expensive. Once the trees outside the containment area have
been cleared, there are management options for minimising the risk of reinvasion. These
are establishing a vegetation cover which is too dense for wilding establishment,
developing and maintaining pasture for more intensive grazing, and planting a
surrounding ‘shelter-belt’ of a less spread-prone tree species.
• Establishment of a dense vegetation cover.
This could be another woody crop (usually forest) or it might be a vigorous herbaceous
cover.
~ Woody crop – usually forest. Most of the invasive conifers are too light
demanding to be able to establish from seed under a closed canopy woody cover,
especially if it is tall, such as a forest. Hence, one wilding prevention option for Pukaki
Downs is to establish susceptible land in a new forest cover. If the area to be planted is
one from which seed could be disseminated elsewhere, then a non or less spread-prone
species should be chosen. This might be ponderosa or radiata pine, or a radiata x
Knobcone pine (P. attenuata) hybrid on the harsher sites, or perhaps a cypress
(Cupressus species, such as Leyland or Lawsons cypress) on the more benign sites,
depending on the objective of the planting (timber production or carbon storage). Where
the risk of spread off-site is less, then a more valuable species such as Douglas-fir could
be planted.
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