Tree breeders began improving the quality of forests by selecting seed from trees with desirable characteristics. The first radiata pine seed orchards were established in the 1950s. Since then, there have also been tree improvement programmes for cypresses, eucalypts and Douglas fir.
Bigger or better?
Early genetic improvement of radiata pine focused on reducing the number and size of branches, and on producing a large, straight trunk. In recent years tree-breeding programmes have focused on improving wood quality and disease resistance.
Also in the 1950s, trials began to test coniferous trees from different parts of the northern hemisphere. The growth rates of different species were compared between various sites to find the best species for certain regions.
When planting large areas, commercial growers wanted seedlings with uniform characteristics. Researchers experimented with vegetative propagation techniques, such as cuttings and tissue culture, to mass-produce trees without using seed.
Since 1990 New Zealand scientists have identified trees with superior genetic makeup by examining their DNA. This screening process avoids lengthy and expensive testing.
In 2000 the first New Zealand field trial of genetically modified trees began in Rotorua, after being approved by the Environmental Risk Management Authority. Because of public controversy about genetic modification, it is unclear whether modified trees will ever be grown commercially. Nevertheless, New Zealand researchers are recognised as international leaders in this field.
One of the most important advances in New Zealand forestry research has been the development of planting, pruning and thinning systems for radiata pine to produce optimum growth and wood quality. For example, researchers established that early pruning of the lower branches from trees produces logs that are free from knots. The resulting ‘clearwood’ fetches a higher price from manufacturers of products such as furniture.
Food for thought
Trees, pasture and food crops all need fertiliser to replace elements consumed by the plants. In the case of forestry, fertiliser requirements are much lower.
When crucial nutrients are lacking in the soil, they need to be added for trees to grow well. By studying nutrients in the soil, forestry researchers have identified fertilisers to correct the deficiencies in most regions of New Zealand. These fertilisers are usually applied aerially at the time of planting, and then at 10-year intervals.
Leaf analysis techniques developed by New Zealand researchers were used in a 1980s national forest study to identify regions and sites where various trace elements were likely to be deficient.