10.5.1 Initial species choices and quarantine
Forest practices are most important in making the best use of the land, preserving and creating biodiversity, and in limiting disease and pest problems. The major initial decision is whether to grow a monoculture or to have a multi-species forest as is common in Europe and in natural rain forests (though the rubber tree Hevea brasiliensis has been grown as a monoculture in the tropics for well over a century). The widespread practice of planting monocultures of radiata pine and other species produces even-aged single species coniferous forests of a type which occurs naturally in many parts of the world, including British Columbia and Alberta where lodgepole pine dominates large areas. Tree mixtures are very useful in some countries and trees such as eucalypts, which produce naturally durable timber can be very valuable, but in New Zealand, and often elsewhere, chemical treatment is used to prevent rot when timber lacking natural resistance is in contact with the ground. If clear felling is adopted the size of the logging coupe (an area in a forest to be clear felled) must be appropriate to considerations of erosion, flooding, water quality and landscape values. Site preparation must be suitable; burning is easy but often has detrimental effects and windrowing (which heaps woody slash and litter in piles or rows) often depletes soil productivity for decades. Timber extraction (logging) and road construction cause major environmental problems in terms of erosion, loss of nutrients and soil compaction (Li, 2004; McIntosh and Laffan, 2005; Mieth and Bork, 2005).
Codes offorestry practice used in New Zealand and most other countries are intended to educate and act as guidelines, rather than being mandatory. The area demanding the utmost vigilance is that of quarantine: preventing a further worldwide spread of the pests and diseases which have already caused a great deal of damage, as Chapter 5 indicates. Carter (1989) reported that 212 insects and 92 fungi known or suspected to harm radiata pine had not yet entered New Zealand. A major advantage of planting exotic trees is that they usually do better than in their places of origin because they have left their pests and diseases behind them. In some ways New Zealand is very vulnerable to introduced pests. The possum already carries bovine TB in many parts of the country, and if wood-consuming termites ever became established they could cause havoc to the many wooden houses, apart from anything else.
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