Radiata pine is the world’s most widely planted softwood plantation species. It comes from California where it is known as the Monterey pine but its natural distribution is very limited.
Radiata pine grows faster in New Zealand than in any other country, but it is also one of the fastest growing trees in North America. It grows fast because, unlike almost all other trees from outside the tropics, its growth continues throughout the year. Most non-tropical trees only grow for a limited period during the year (e.g. 155 days). No matter how ideal the conditions are outside that period the trees will not grow. Radiata, on the other hand, will grow throughout the year whenever conditions are good.
Around the Bay of Plenty, radiata grows almost every day, especially near the coast. Height growth is greatest in the spring and least in the winter. The greatest diameter growth is in the summer. In colder areas, like Southland, radiata may stop growing for several weeks in the winter.
It might be expected that radiata would do best in those areas that have summer-like conditions the year round. But this is not so. Radiata does not grow as well in Northland as it does in the Bay of Plenty (even if all other conditions – soil, water, etc., are the same).
This is because radiata does not stop growing if the temperatures are warm. If the night temperature is high, the tree tries to keep growing but it then wastes the energy (and the potential wood) that it has produced during the day. The only areas in the tropics where radiata will grow are at very high altitudes where the evenings are cool.
This ability to grow whenever conditions are favourable has an important disadvantage – it means that radiata is not able to go into true dormancy (sleep) stage. While it can withstand mild frosts and even very unseasonal ones, it cannot tolerate severe winter frosts. Minus 12 degrees Celsius is about the minimum.
So, it can be calculated where radiata will grow successfully. The tropics are out, except for cooler highlands, and so are any areas with a continental climate with severe winter temperatures. That leaves the following favourable areas:
• New Zealand
• Central Chile
• Some areas of Australia
• South coastal strip of South Africa (where rainfall and soil
permit)
• North coast of Spain and Portugal
• Some coastal parts of Italy, Greece, Turkey
• Some areas of Ireland and England
• Some areas of coastal California.
Of all of these, the very best conditions are in New Zealand.
New Zealand’s ideal conditions for radiata pine:
• Warm days, cool nights
• Relatively fertile soil
• High rainfall evenly spread through the year
Radiata has proved to be a remarkable and versatile plantation species because of these characteristics:
• Easily collected seeds
• Rapid germination
• Simple nursery production of seedlings
• Good seedling survival
• Rapid growth after thinning
• Quick healing of pruning wounds
• Easily improved by selection of better form trees and
breeding from these
Click on the illustration to compare the average annual production of radiata in New Zealand with the average yield of commercial forests in the world’s major softwood growing regions. New Zealand’s forests grow, on average, seven times faster than Sweden’s, 13 faster than Russia’s and 20 times faster than Canada’s.
A Single Species
Almost 90% of New Zealand’s plantation forests are radiata pine. It is easily established and its growth rate means that competing vegetation is soon left behind. The timber has excellent properties for general purpose uses such as building, packaging, etc., and when treated it is more durable than many native timbers.
This reliance on a single species in stands of the same age has been criticised because:
• Pure, even-aged stands can be vulnerable to disease,
insect attack and changes in climate
• Introduced plantation species can be more sensitive to
disease and pests than natural forests
• Long-term growth of pine stands may reduce soil quality.
A careful evaluation of these risks has been published by Scion. It found that most criticisms were ill-founded. Pure, even-aged stands are common in many natural, healthy forests such as the Douglas fir forests of North America. Provided genetic variation is maintained in the plantation – as is the case in New Zealand radiata stands – there is no evidence to suggest that it will be more vulnerable than a mixed forest.
Plantation forest species may be healthier because they are established away from natural predators. New Zealand radiata is not affected by the western gall rusts that is a serious problem to the species in its native California.
Strict quarantine have been relatively effective in preventing pests from entering New Zealand and a large team of timber inspectors and forest health officers constantly checks imported material and stands.
New Zealand has a dedicated biosecurity authority run by the Ministry of Agriculture and Forestry. See Biosecurity.
Because radiata pine grows quickly in New Zealand, large volumes can be harvested from a relatively small plantation forest estate (7% of land area). Even so, the country is a very small producer of timber, supplying just 1.1 per cent of the world’s industrial wood.
Agroforestry
As a further extension of plantation forestry, agroforestry is now an established practice in New Zealand. Since 1990, more than 650,000 ha of land have been planted with trees for the first time, mostly on pasture and mostly by small-scale growers.
‘Agroforestry’ can be defined as agriculture and forestry working in close association. The planting of trees on farms can be considered agroforestry, even if livestock is not grazed under the trees.
Radiata pine is also the preferred species for this kind of planting but there is also interest in Douglas fir, cypresses and eucalypts.
There are three main kinds of agroforestry in New Zealand:
• Farm-based – trees planted on existing farms
• Forest-based – animals grazing in existing forests
• Timberbelts – shelterbelts on farms managed to produced
high quality timber.
The objective of agroforestry is to increase the total productivity and profit from the land, and to meet many non-economic goals such as erosion control, weed suppression, livestock welfare, aesthetic enhancement.
Forest-based Agroforestry
Substantial areas of second-rotation forest are being over-sown with a combination of nitrogen-fixing plants such as Lotus ‘maku’ and grasses in order to suppress problematic weeds. In many cases, these forests are not grazed, as livestock returns have been variable, but often quite low and outweighed by the difficulty of management – installation and maintenance of drinking water and fencing.
Agroforestry practices are very much influenced by the current returns for livestock and logs, balanced against the costs of the various management practices. If reimbursement for carbon credits becomes a reality, this would have a major impact on agrofroestry. There would be a shift in land use to growing trees rather than livestock grazing.
In some areas however, particularly where pampas is a problem, grazing with cattle continues to be the cheapest and most effective method of weed control.
Thinning, followed by pruning of all remaining trees, maximises the sunlight reaching the forest floor and stimulates the growth of understorey pasture. The maku provides nutrition, including protein, for grazing animals, and nitrogen for the trees.
Benefits of oversowing and grazing (in order of importance):
• Increased tree growth as a result of additional nitrogen
input
• Reduction of problematic weeds and improved access for
pruning and thinning
• Reduced risk of fire
• Improved appearance
• Income from livestock.
Farm-based Agroforestry
Most new planting in recent years has been on pasture. This provides enormous benefits in reduction of costs (little site preparation, existing roading infrastructure) and good growth rates. However, it can result in inferior tree quality if the silviculture is not adjusted to take account of the differences between the new farm and traditional forest sites. For instance, pruning lifts have to be more frequent and stocking rates must be higher to control branch size.
Choice of the type of planting stock deployed on fertile farm sites is critical, particularly on exposed sites. Branching can be heavy and overall tree form can be poor on sites with high nitrogen levels. On exposed sites there are the risks associated with tree loss due to topple and, also, log down – grading due to poor form in surviving trees. Tree toppling occurs before canopy closure, particularly 1-3 years after planting, and is associated with damage to the root system after wind-induced tree sway. Long-internode genotypes are not recommended for fertile and exposed farm sites. Also, there is good evidence that rooted cuttings from physiologically-aged material (from early adolescent donors) are more stable and less likely to topple compared with seedlings and juvenile cuttings. Physiologically-aged cuttings also have the advantage of finer branches on such sites.
If whole farms are planted by investment companies, then the trees may be left to grow without any understorey grazing. On the other hand, for a nominal transaction fee, grazing with sheep for the first few years of a crop rotation can provide benefits in terms of improved access for silviculture and reduced fire risk.
Grazing, in all agroforestry systems, should be undertaken with extreme care in the early years, as the forest crop can be devastated by a few days of neglect. Where parts of farms have been planted by farmers, or in association with farmers, then it is likely that understorey grazing will be an integral part of farm management.
Timberbelts
Timberbelts – shelterbelts managed for timber in addition to their shelter benefit – have become increasingly common in New Zealand. Pruned trees, perhaps in combination with unpruned trees of another species, are expected to yield better prices in future years. This management practice is still relatively new and there is not a lot of data yet on returns from timberbelts.