Tree selection for the high country

Press, 3 December 1982, Page 20

Tree selection for the high country

Three scientists employed by Government agencies doing research on fodder, forestry, and alternative crops spoke to the Twizel seminar on “Tree crops in the high country.” Dr Barry Wills, a scientist with the Water and Soil

Division of the Ministry oi Works and Development at Alexandra, described a number of tree and shrub species which are being used in forage and shelter trials in Central Otago. The trials are restricted to areas where the rainfall is less than 500 mm a year, and where there is potential for multiple use. Most of the shrubs are being tested in areas where the soil is of moderate to low fertilityareas of high fertility are considered best used for crops. Among the species discussed by Dr Wills were the tree lucerne (which is proving unexpectedly hardy in Central Otago), various acacias, sugar maples, a number of little-known Californian and Mediterranean shrubs, Caragana arborescens (the Siberian pea-tree which, as a legume, is capable of fixing nitrogen), and various poplars, willows, and oaks. Conifers would continue to be the dominant trees in high-country plantings in the foreseeable future, said Mr Nick Ledgard, a scientist from the Forest Research Institute at Rangiora. Mr Ledgard, who is attached to the Revegetation Section of the F.R.1., is leading a team which recently began a survey of trees growing in the high country throughout the South Island. He said that trees were likely to play an increasingly important role in the high country, especially if interplanted with other crops and fodder species. For the most exposed situations he recommended ponderosa or Corsican pines, or the European mountain pines, Pinus mugo and P. uncinata. Douglas fir, widely recommended for foothills planting, had grown very well in the research plots at Craigieburn but less well at Tara Hills, south of Omarama, and some other sites, he said. Frost often damaged Douglas firs on sites where air drainage was poor, and seedlings frequently showed uneven growth. The species preferred a high rainfall. Below 800 metres radiata pine outperformed all other species but good stock was essential for success with this tree, he said. Radiata was suspect in wet conditions and in areas where frosts were severe. Other conifers mentioned by Mr Ledgard as worthy of further trial included the wellingtonia (Sequoiadendron giganteum), and some spruces, cypresses, and firs? There might also be scope for growing pines with edible seeds, he said. Eucalypts were mostly marginal except on the most favoured sites, and though Eucalyptus pauciflora and E. gunnii had grown well in the high country, neither was of high value as a timber tree. Mr Ledgard also dealt briefly with a range of willows, poplar, birches, and other broadleaf trees which, he said, had proved themselves throughout the high country. One of the most

useful trees in the drier areas, such as the Mackenzie Country, seemed to be the silver birch, he said. Mr Ledgard listed the advantages of growing trees in the South Island high country, compared with corresponding sites in the North Island, as cheaper access, less competition from weeds, virtual freedom from pests and diseases, and relative closeness to export ports. Factors against tree growing were the slower growth rates, climatic risks, and longer rotation period in the South Island. Mr Ledgard also proposed guidelines, which he said had been prepared by the F.R.1., for high-country tree growers to prevent seed spread of conifers. Both runholders and environmentalists have recently expressed concern about the colonising ability of conifers in the New Zealand high country, and large sums have been spent to eradicate confers from some areas, for example the Amuri Range in North Canterbury, where Corsican pines seeded from the nearby Hanmer State Forest. Under the F.R.I. guidelines, landholders would be responsible for eradicating trees which seeded within 500 metres of their boundaries. Dr Keith Hammett, a scientist in the Horticultural and Processing Division of the D.5.1.R., Auckland, sounded a note of caution in describing his studies of chestnuts growing on sites throughout New Zealand. The edible chestnuts—species of the genus castanea, not to be confused with the non-edible horse chestnut—were among the earliest-planted trees in New Zealand, he said. This country was fortunate in being free of the major pests and diseases which . plagued chestnut plantations in many other countries, but there were problems with the quality of New Zealand chestnuts. However, promising genetic material had been found in Waikato, where many trees had a very high bearing capacity; in Taranaki, where some trees growing in a park seemed to be the best genetic material in the country; and in Marlborough and Queenstown. It was probable that the Taranaki trees had been imported as grafted specimens of named varieties, he said, but records of their origin had been lost. Some promising results ' were emerging at Lake Benmore, where chestnuts growing in poor, shingly soil were miserable-looking specimens compared with the large, leafy northern trees, but were fruiting very well. According to Mr New. the best seedling chestnuts at Benmore are producing nuts at the rate of 10 tonnes per hectare, making them potentially one of the most valuable' crops in the country. However. Dr Hammett noted that more extensive growth trials would have to be made before the potential of chestnuts could be confirmed.