Exposed-site diagnosis for the pine wobbles

Press, 25 February 1989, Page 26

Exposed-site diagnosis for the pine wobbles

Country Diary

Derrick Rooney

■ Speed wobbles: cheap roller : skates get them. Skateboards can get them. Powerboats can get them. Bicycles can get them — if . the wheels are not true. But trees with speed wobbles? I wouldn’t .have believed it if I hadn’t seen it. “Speed wobbles” is not the i official designation: the problem is “McLaughlan Syndrome,” so called because it occurred in a radiata pine shelter belt planted in 1982 on John and Mary-Jean McLaughlan’s farm west of Loburn. The trees are now about four metres tall. Over the last five years forestry scientists from various parts of New Zealand have looked at the curiously contorted leader growth, which showed up when the trees were about a year old. Every expert offered, with complete conviction, a different - explanation. One was convinced - the cause was copper deficiency. ..Another diagnosed boron defi- ' ciency. A third diagnosis was «lead poisoning — the paddocks

adjoin the Garry River bed, a long-time favourite rabbit-hunt-ing area. . • But the most likely explanation, according to Forest Research Institute staff at Rangiora, is simple and obvious: the climate. The site is one of the most exposed in North Canterfcry,

and is subject to frequent and severe nor’west gales. Twice this summer Mr McLaughlan’s irrigation unit has been — expensively — blown over. According to Pat Milne, of the F.R.1., it is the speed of those winds that caused the wobbles. This kind of over-exposure is one of the reasons why the F.R.I. selected the site for tree and shelter trials. On the riverbed adjoining the wobbled . pines is a key trial planting of macrocarpa, in which a range of silvicultural methods and spacings is being tested. Macrocarpa has been grown in New Zealand for shelter for more than 100 years, but only relatively recently has extensive interest been shown in its potential — and in ways of managing it — as a timber tree. Macrocarpa has different growth patterns from pines, and the silvicultural techniques that New Zealand foresters have developed to a fine art for growing radiata do not work at all well with macrocarpa.

During the last year a joint "Macrocarpa Action Group” has been initiated by the F.R.L and the Farm Forestry Association. However, the McLaughlan trial dates from before the action group was constituted, and reflects a long-term interest by some F.R.I. staff in. the cypresses as "alternative” timber species. During an inspection of the McLaughlan plantings, in the course of a tour of F.R.L projects in North Canterbury, the research field leader at Rangiora, Dudley Franklin, detailed some of the pruning methods being developed for macrocarpa. An important point, he says, is that the presence of small, green knots in macrocarpa logs does not lessen the value of the timber — even for boatbuilding. Since macrocarpa does not seem to respond well to clear pruning, the aim therefore is to maintain a balanced crown, and to restrict branch sizes by what he calls “pre-emptive pruning.” In a nutshell, so to speak, this involves early training.by remov-

ing vigorous branches from low on the stems of young trees, and shortening any others that look likely to grow too big to be removed in the following year. And the definition of a branch too big to be removed? Simply, one that cannot easily be cut through with conventional, medium-sized pruners. Since cypresses are subject to canker — a disease that can kill stems by girdling them — wounds on the trees should be kept to a minimum, says Mr Franklin. More detailed information, and finer points of the pruning technique, should emerge from the action group’s trials in due course. An uncommon sight last weekend, on the flats of the Rangitata River below Mount Potts, was a brown bittern, sheltering in the reeds in characteristic pose, erect with head thrown back. The bird seemed completely unfazed by the sound and sight of a* dust-covered Barry Crump ute containing three rather scnftfy trampers, and sat still for

a minute or more, enabling us to get a rare close look at it, before lifting off with slow, powerful wing-beats. This large, and now relatively rare, Australian bird is, like the pukeko and the white-faced heron, a self-introduced migrant from Australia. It has been here a very long time, and from all accounts was at one time fairly common in wetlands, which it needs to provide both its nesting sites — in raupo beds — and its diet, which consists of insects, eels, fish, frogs — and mice. Since European occupation New Zealand’s wetlands have been much reduced, and so have the bittern’s numbers. It was pleasing to see evidence that at least one population is surviving in the harsh, inland Canterbury climate. None of the three of us had seen a live bittern for many years. One member of the party, who farms above the Rakaia Gorge, used to have bitterns in swamps on his property, but they disappeared«*friany years ago.

Mount Potts itself, despite its proximity to the Main Divide, was a mild disappointment. In terms of the variety of species observed, it is less interesting than the peaks to its north-east: Somers, Taylor, Hutt. A very steep mountain, to which access was gained — with permission — via a ski-road that Barry himself might have thought twice about, Potts seemed to consist largely 'pf shattered rocks, one of which nit me on the knee. But the outlook, through the narrow, screen-sided gully to the vast Rangitata flats with the Sinclair range behind, was marvellous. And, near the top, we crossed a rocky ridge to face one of those cameos of breathless beauty often to be seen in our mountains: a large, clear tarn surrounded by snow tussock and lichen-coated boulders. There were a few notable plants, of which I would like to mentioh just two: Hectorella caespitosa and Raoulia youngii. These are tfco of the more

remarkable of New Zealand’s indigenous mountain plants. Both grow only at high altitudes, in quite specific habitats: rocky snow hollows with some loose grit. The former is a dense, green cushion — studded last Sunday with dainty white flowers — and the latter usually a loose carpeter, running around in the sharp grit and showing its silver-white shoots here and there. Both are plants more usually associated with the wetter mountains in and near the Main Divide, although the raoulia does come out as far as Mount Hutt, where it grows in close proximity to its curious cousins, the vegetable sheep. They are members of the daisy family and on Sunday on Mount Potts, many carpets of Raoulia youngii were liberally dusted with pure white flowers, each about the size of a 5c piece. Near the top there were, oddly enough, no vegetable sheep to be seen but we spotted some half-way down, on crags high above us. £