Botanist Investigating Low Treeline In New Zealand

Press, Volume CI, Issue 29776, 20 March 1962, Page 10

Botanist Investigating Low Treeline In New Zealand

The tree-line in New Zealand is thousands of feet lower than in north temperate zone countries, and Dr. P. Wardle, of the Botany Division, Department of Scientific and Industrial Research, Lincoln, is trying to find out why. "The highest altitude of the treeline in this country is about 5000 ft, in Marlborough, while in other districts it is much less, falling to about 2000 ft in Stewart Island,” said Dr. Wardle yesterday. “Yet in some places in the northern hemisphere at a similar latitude the trees go to 10,000 ft. “The New Zealand mountains have been thrown up only recently, geologically speaking, and in fact are apparently still in building.” said Dr. Wardle. “It may be that no route has been available since the rise of the mountains for suitable tree species to colonise the country, while the local vegetation may not have had time to evolve the required types. “An equally strong possibility, however, is that some feature of the climate at middle to high altitudes in New Zealand is inimical to tree-growth. “There may be a pointer in the fact that in Australia, with a completely different set of tree species, the treeline is still relatively low—about 5000 ft to 6000 ft in New South Wales, for example. “My main work so far on the problem has been to make a survey of the state of the sub-alpine, forest and scrub areas, so that the present position may be known and future changes

noted. Little botanical attention has been paid to the subalpine flora, as New Zealand botanists seem to have concentrated to a great deal on the tops.” he added. The survey had been carried out in co-operation with members of the staffs of the Forest Service and of his own division. The sub-alpine vegetation was very important because it provided a large part of the cover in the upper valleyheads, where erosion was often a problem. Some of the vegetation was "in a pretty bad way,” especially the mountain-beech forests of Canterbury. On the other hand, the forest in other areas seemed in quite good shape. There was often no obvious reason why the forest in one area was doing well while that in a neighbouring district was not replacing itself, and one of the objects of his research was to account for these differences. To get the picture of present conditions in the subalpine forest. Dr Wardle has kept climatic records of places among the treeline. measured the growth rate of trees in the area, watched the regeneration of the plants after attack by animals or fire, and travelled widely to observe the state of the subalpine vegetation in watersheds all over the country. “One line of research, started three seasons ago. was to plant New Zealand mountainbeech seedlings above the treeline and watch how they got on. This has been done with the co-operation of Mr A. H. Macßae, of the Botany Division. The experiment is being carried out in the

Craigieburn Range, with seedlings at three levels—at the treeline, 800 ft above it. and 800 ft below it. “So far, of course, it has not been possible to get any firm result, but the growth of the seedlings above the treeline has been very slow I understand the New Zealand Forest Service has a project to observe the growth rate of northern upland species in our mountains.”

Interim results of the tree measurements showed a slow general growth-rate. Treering counts on pink pine in the mountains of Westland, for example, indicated that trees 15ft to 20ft High could be over 1000 years old, said Dr. Wardle, although the mountain-beech was not quite so slow-growing. There was some indication that the limiting factor in the growth of mountain-beech in Canterbury was the effective length of the summer. At heights close to the treeline, the beech seemed unable to get through its annual cycle, with the result that at the end of the summer the tree was left with a soft outer growth which should have hardened off before winter and which was soon killed by frosts.