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

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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 5
temperature or unseasonal frosts, as well as light grazing/browsing pressure (from both domestic and wild animals). The evidence from many wilding spread areas throughout New Zealand is that this set of circumstances do not happen nearly as frequently as many people think - as wildings often appear in uniform age classes separated by many years. This is the case at Pukaki Downs. Even though the major seed source beside the lake has been producing contorta pine seed since the early 1980s, there appears to have been just one event (in the early 1990s) which allowed wildings to become established out to 10 km to the west (on the Twizel river flats). There is no certainty when such events will occur, but time and again this author has seen them happening between 15-20 years apart, sometimes earlier if contorta pine is involved. Susceptibility of land to wilding establishment. Wilding conifers establish most readily on lightly vegetated and lightly grazed land. They are least likely to establish where the vegetation cover is thick (herbaceous and woody) and/or where animal grazing is medium to heavy. Rabbit numbers can have a major negative effect on wilding establishment, and in the high country the arrival of rabbit haemorrhagic disease in 1997 heralded a significant rise in seedling numbers. However, sheep have been the main grazing influence on Pukaki Downs. Even a low stocking pressure of around 0.5 stock units per hectare will significantly decrease wilding establishment, but only while the seed rain is light and infrequent. Once the seed rain becomes heavy, higher animal stocking rates are required to prevent seedling establishment – they are especially difficult to remove with grazing once they become woody (usually at 2 years of age). Herbaceous growth following conifer felling. In the high country it is well known that after the felling of conifers, the growth of herbaceous species (particularly grasses) within the ‘carcass’ of the felled tree can be vigorous - as long as the slash is not too thick, preventing light from reaching the ground surface. This increase in vigour is due to a ‘flush’ of nutrients released from decaying needles and bark, combined with the sheltered microclimate created by the slash. The resulting vigorous grass growth can prevent the establishment of a new crop of wildings (or any woody species for that matter) for a number of years. And as conifer seed does not remain viable in the ground for more than a few years, the opportunity for wilding reinvasion can be lost – as long as there is no new outside seed source available when the grass vigour declines. Likely future spread with no further management Understandably, the incidence of wilding spread on Pukaki Downs would increase significantly if no further control was exercised. Relative to this three points deserve further mentioned: • Role of more intensive land use. Wildings will always have trouble establishing in the presence of improved pasture and/or higher stock grazing pressures. Although Pukaki Downs does not lend itself to large-scale pasture improvement, such areas do exist, the main one being in the southern mid and eastern zones (blocks 31 and 32), with a smaller area of thicker pasture swards on flat land to the west on the Twizel river flats (southern end of block 25). Parts of these areas are being worked up for an arable crop. These wilding-free areas can only be maintained if the more intensive management is continued, even if it may not be as cost-effective today to maintain the higher grazing levels of the past. It should also be noted that as seed rains get heavier (from higher seed production of adjacent trees) the likelihood of wilding invasion of less susceptible land increases. • Most susceptible land. The most susceptible land for further invasion is the western half of the property - that draining into the upper Twizel river catchment (blocks 25 to 29). This is the largest area with the 6
Page 1 and 2: Oral Submission Presentation by Bla
Page 3: 16. The responsibility the NZ carbo
Page 6 and 7: REPORT TITLE AUTHORS CLIENT CLIENT
Page 8 and 9: Recommendations On Pukaki Downs it
Page 10 and 11: Project and client In April, 2010,
Page 12 and 13: History of wilding spread Pre 1970s
Page 16 and 17: most depleted existing cover and it
Page 18 and 19: successfully on small trees close t
Page 20 and 21: ~ Herbaceous cover. Wildings have d
Page 22 and 23: event indicates that once the Twize
Page 24 and 25: Above. The clear corridor (pink-str
Page 26 and 27: Developments from Rural Delivery we
Page 28 and 29: We have sold the carbon credits thr

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

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