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

is by the musterer’s hut at the mouth of Gladstone Stream (block 26), where a few
contorta trees were planted over 50 years ago. They were felled in the early 2000s (the
oldest at age 50), but by then they had parented an area of fairly dense wildings over
some hectares to the south. Many of these had been allowed to reach coning age before
they were felled.
2000s. The most obvious increase in wilding numbers on Pukaki Downs has taken
place since 2000. This is largely due to progeny of the outliers which arrived in the early
1990s becoming very obvious – mostly as fringe spread ‘islands’ but also in the form of
same-aged outliers beyond the ‘island’ borders. An NL slide of the Little Rhoboro Hills
east-facing scarp slopes (block 14) taken in 2003 shows the first of the larger fringespread
‘islands’ starting to become very obvious. The direction of spread of the fringe
wildings out from their parent trees strongly indicates a wind-flow pattern from the north.
On Pukaki Downs, there are two origins of this northerly wind – one from down the lake
and the other, on the western side of the Rhoboro Hills, from the Twizel river headwaters.
Spread in the upper Twizel river catchment is generally north to south, but on the western
side and on top of the Little Rhoboro Hills ridge it has more of a south-easterly flow as the
taller Rhoboro Range mountains to the north drop sufficiently to allow an eddy of wind to
the east. Along the ridge of the Little Rhoboro Hills, the Twizel River and lake wind flows
meet and move together to the south.
Age classes of wilding conifers. A feature of wilding spread on Pukaki Downs
and Ferintosh is the uniformity of wilding ages. The commonest age is 5-6 years – trees
which are progeny of the outliers which arrived in the early 1990s. The uniformity of tree
age is particularly striking where relatively closely-spaced parent trees were felled, often
when they were 10-12 years old. This ‘flush’ of new wildings which appears to occur after
parent-tree felling, has been observed on Pukaki Downs (and elsewhere) for some time.
The reason for this ‘flush’ is not clear. As contorta can first start to cone at age 5-6 years
of age, and there are many of this age-class present, there is obviously a great risk of a
new wave of wildings appearing in the near future – although the viability of seed
produced before age 10 is thought to be lower than when the trees are more mature.
Coning age. A summary of age of significant coning per species is given in Table
1. A small minority of trees will always start coning earlier. However, there is strong
suspicion that the earliest produced seed does not have as high viability as seed
produced later. Work is underway to confirm this. It is also known that the first obvious
appearance of wildings often occurs quite a few years after the first seed is produced. For
instance, on Pukaki Downs it seems that significant numbers of wilding contorta do not
appear much before age 10, even though cones are often produced from age 5-6.
Prevailing wind flows. As explained above, the direction of wilding appearance
out from a parent tree indicates the direction of the most common seed dispersing winds.
On Pukaki Downs these winds blow from the north. They are also the warmest, which is
important for wilding spread, as the cones open in warm conditions. As the Rhoboro Hills
are oriented north-south, the wind blows down both sides of the range, with the Twizel
river flow diverting more to the east before joining the lakeside flow over the Little Rhoboro
Hills and heading on south. Even though there is strong evidence for this wind flow
pattern, there is also evidence that the occasional strong winds can blow more from the
north east. Such a wind was responsible for the major spread event in the early 1990s,
which disseminated seed from the lakeshore parents to establish widely separated lone
wildings in and around the upper Twizel river flats
Frequency of spread events. The age of wilding trees enables any observer to
obtain a good estimate of when the seed arrived. However, in addition to the winds
needed to disseminate seed to a suitable site, successful seed germination and seedling
establishment requires a growing season without extremes of moisture stress and
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