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Radiata pine

by  Peter Berg

When first introduced from its native California, radiata pine may have seemed like an unlikely tree to become a New Zealand national icon. But breeding programmes and the development of planting, pruning and thinning techniques, have made fast-growing radiata pine plantations the core of New Zealand’s forestry industry.


A Californian import

Radiata pine (Pinus radiata, also known as Monterey pine), is the world’s most widely planted softwood plantation tree. New Zealand, along with Chile and Australia, are the top growers of this species. Some 89% (1.6 million hectares) of New Zealand’s forestry plantations are radiata pine.

Natural habitat

On the coast of California this endemic pine grows in just three discrete populations, totaling about 8,000 hectares. It grows mainly in pure stands, but sometimes adjoins or mingles with other conifers, such as coast redwood (Sequoia sempervirens), Douglas fir (Pseudotsuga menziesii), ponderosa pine (Pinus ponderosa) and macrocarpa (Cupressus macrocarpa, also known as Monterey cypress).

In addition to the mainland Californian populations, distinctive forms of radiata pine grow on Guadalupe and Cedros islands off the coast of Baja California in Mexico.

Because radiata pine is not widely grown in its natural habitat, New Zealand foresters had to devise their own techniques to establish and manage plantations, and develop new technology to use the wood.

Fire

Fire is important in the natural ecology of radiata pine. Its cones, which hold 50–100 seeds each, open quickly when exposed to heat. Because they are fast growing and tolerant of full light, radiata pines can quickly occupy any open space created after a fire.


Plantations in New Zealand

Original plantings

Radiata pine was first introduced to New Zealand in the late 1850s to see if would be a good candidate for widespread planting. Its excellent growth rate prompted seed imports from California in the 1870s, mainly for shelter belts and woodlots.

By the first forestry planting boom in the 1920s and 1930s, it had been adopted as the species of choice. It proved to be versatile and grew well throughout New Zealand on a variety of soil types, including coastal sands, heavy clays, gravels and volcanic ash deposits.

Canterbury firsts

The first recorded planting of radiata pine in New Zealand was in 1859, at Mt Peel Station in South Canterbury. The first recorded use of radiata pine timber in New Zealand was in 1893 at Leslie Hills Station, near Culverden, when Duncan Rutherford milled some 20-year-old pines and used their timber for farm buildings.

Early plantations

The first New Zealand radiata pine plantations were grown from seed collected from farm shelter belts. In its raw, undomesticated state it was a coarse and highly variable tree. Although usually healthy and fast growing, it also tended to grow many branches and a forked trunk.

Genetic improvement

To improve the quality of radiata pine, a genetic research programme was started in the 1950s. Trees of superior growth and form were selected and propagated by grafting. The grafted pines were planted out at wide spacing in seed orchards away from other plantations, to prevent pollen contamination. The first improved radiata pines were planted in forests in 1970.

Improvement programmes have continued, with selection criteria becoming increasingly complex and the testing of parent stock more stringent. Through controlled cross-breeding, hybridisation and advanced plant propagation techniques, scientists have developed breeds that:

  • are adapted to particular climatic zones and soil types
  • are resistant to foliage diseases such as dothistroma needle blight
  • produce wood that is stronger or more durable.

Propagation and planting

Propagation

New forests can be propagated from seedlings or cuttings.

In the case of seedlings, the seed is sown in nursery beds (usually in October) and seedlings readied for planting the following winter (May to August). The seedlings’ roots are undercut during the seven- to nine-month growing period, which causes them to produce many fibrous roots near the soil surface. This increases their chance of survival when planted out.

With cuttings, seed is first sown to produce stock plants, which are cultivated to yield a multitude of young shoots. The shoots are removed as cuttings and planted in nursery beds or containers. It takes several months for the cuttings to form roots. Improved varieties planted from cuttings can come from just a single, superior clone or, more usually, a mixture of clones from several different, unrelated crosses.

Seedlings and cuttings are ready for planting when 25–30 centimetres tall.

Site preparation

Before planting, sites are prepared to create the best conditions for tree survival and growth. Preparations include spraying to kill weeds, ripping or ploughing the soil, or forming soil mounds.

Trees are normally planted by hand, using a spade to dig the hole. The number of trees planted per hectare can vary from 600 to 1,400. If the soil is lacking nutrients, fertiliser is applied.


Growing and harvesting the forest

Forest management

Managing plantations involves thinning and pruning, depending on whether the trees are being grown for high-value saw logs, or as lower-quality logs.

Thinning

With a harvest age of 25–35 years, and final tree numbers of around 300 stems per hectare, two thirds of the trees planted are usually cut down during the early stages of the growing cycle to make more room for the others. The felled trees are either left on the ground to rot, or sometimes harvested as posts, poles or pulpwood.

Pruning

About five years after planting, the best trees are usually pruned up to a height of 4 metres. At around seven years, the trees may be pruned up to 6.5 metres. At around nine years, when the trees are 16 metres high, all the unpruned trees are felled to allow the remainder room to grow. This system is designed to produce a substantial yield of valuable knot-free wood in the lower part of the trunk.

Some forest management systems aim to grow a high yield of logs with small knots – suitable for structural timber such as house frames, roof trusses and poles. In this case the trees aren’t pruned, and they are grown closer together (450 stems per hectare) to limit branch growth and keep the knots small.

Types of log

No matter what kind of management system is followed, the forest will yield a range of log types. For example, large pruned logs are used for clear timber and veneer, large knotty logs for structural timber, and small logs from the top of the trees for wood chips, wood pulp, fibreboard and particleboard.

Logging

Logging is done by teams who:

  • fell the trees using chainsaws or mechanical shears
  • pick up and move the logs using crawler tractors, wheeled skidders or overhead cable haulers
  • cut the branches off the logs
  • use cranes to load the logs onto trucks for transport to log depots, mills or ports for export.

The logs are carefully sorted into categories according to their intended use and value.

Production

The amount of wood a hectare can produce depends on the rotation (lifespan) of the trees, how many are grown to maturity, and the productivity of the site, which is related to soil depth and fertility, and climate. Under very good conditions, such as a deep pumice soil and mild climate, a hectare of trees may produce 840 cubic metres of wood when harvested at 28 years. This would give a mean annual growth increment of 30 cubic metres per hectare per year; the national average is around 23.


Multi-purpose plantations

The benefits of radiata pine plantations include providing shelter on farms, stabilising soil on erosion-prone hillsides, reducing the amount of sediment that ends up in rivers and streams, and absorbing water that could cause flooding.

‘Carbon sinks’

Because trees can store carbon, radiata pine plantations are useful ‘carbon sinks’. About 50% of the dry matter in the wood is carbon – largely cellulose (about 65%) and lignin (about 30%). Depending on growth rate and wood density, a hectare of pine trees locks up 4–7 tonnes of elemental carbon per year, which is equivalent to 15–26 tonnes of carbon dioxide absorbed from the atmosphere. A 1,000-hectare forest can absorb 15,000–26,000 tonnes of carbon dioxide per year.

Car-bon footprint

When burnt as fuel in a car engine, petrol releases 2.62 kilograms of carbon dioxide per litre. On this basis, a typical car produces 1 tonne of carbon dioxide for every 5,555 km driven, or 3 tonnes for an average year’s driving (16,666 km). This is equivalent to the amount of carbon dioxide that 33–60 pine trees absorb in one year.

Habitat for native species

For long periods while they grow, plantation forests are relatively undisturbed ecosystems, and provide habitats for many species of native plants and animals. For example, kiwi and falcons have found planted forests to be a suitable habitat and feeding ground.

Although the biodiversity of plantation forests is not as rich as indigenous forests, the number of native species that live there contribute to the biodiversity of the country.

Soil improvement

New Zealand’s radiata pine forests are mainly planted on soils that were not considered suitable for intensive agricultural use. Some examples are the large volcanic ash fields of the central North Island, drifting coastal sand dunes and shallow, less-productive hill-country soils.

Growing trees on these soils often improves them because organic material in the form of leaf, bark and woody litter adds nutrients. The trees also extract mineral nutrients from deep in the soil. Because of this, the second crop of trees on such sites will often grow better than the first. Some areas that have produced one or two crops of trees have, with fertiliser treatment, been successfully converted to agricultural land.

Protecting the forest

Radiata pine can suffer from pests, diseases, windstorms and fire. Dothistroma needle blight, a pathogenic fungus that attacks the needles of young pine trees causing reduced growth, is the most widespread disease. It is most serious in places with higher rainfall or prone to prolonged misty conditions. However, it can be controlled by spraying with a fungicide.

Strong wind is a hazard to forests in New Zealand and has sometimes caused severe damage to pine plantations. Young trees are sometimes toppled by wind on sites with puggy soils, and older trees can be uprooted completely or snapped off.

Fire is an ever-present risk, particularly during prolonged droughts.


The wood

A versatile wood

Radiata pine wood is even-textured and easy to slice, peel, mould, turn, sand, plane, glue, stain and paint.

When planed to a smooth finish, the wood is creamy-coloured, with stripes created by the contrast between wood grown early in the annual growth season (softer and paler) and that grown later (harder and darker). The wood darkens over time with exposure to light.

Multi-purpose bark

Bark from harvested pine trees was once viewed as a waste product, but is now used for fuelling kilns and dryers at wood-processing plants, and made into plant-propagating mixes, mulches and composts. An extract from the bark is even used in a dietary supplement, enzogenol.

Wood density

The wood is of medium density (350–450 kilograms of dry weight per cubic metre of green volume), which means that it is light in weight, relatively soft and not very strong. It is easily penetrated by preservatives and pulped by chemical or mechanical processes.

Wood density increases with tree age, and with the mean annual temperature of the site – leading to a regional differentiation in wood quality. The densest wood is from Northland, the lightest wood from Southland or high-altitude areas, such as the central North Island.

Undesirable heartwood

The core of older trees (heartwood) has some undesirable features that can cause structural weakness and warping.

Heartwood is dark, contains resins and is dry. It starts to develop in the centre of trees at around 10 years, and is usually confined to the five innermost rings. Radiata pine heartwood is not highly regarded as it causes colour problems in pulp, detracts from the appearance of natural finishing timbers, and is not readily permeable by preservatives.


Uses of pine timber

Radiata pine wood was originally regarded as suitable only for fruit boxes and boxing for concrete, but soon came into use as house-framing timber. This was made possible by timber grading, drying and preservation technologies.

Its knottiness was in contrast to the clear wood of native softwoods, so it was not at first thought fit for furniture, panelling, fittings, flooring, and house cladding. Now it is used for all those purposes.

Durability

Wood from radiata pine is susceptible to decay-causing fungi and insect borers. For permanent uses it must be kept dry and protected by drying, chemical preservatives, or a combination of the two.

Treated wood

Before the early 1940s pine wood was treated with creosote. That was replaced by tanalising – a system of pressure treatment with water-borne copper, chrome and arsenic. This extended the life of the timber for decades, even when in contact with soil.

New Zealanders are among the highest per capita users of wood and wood products in the world. Treated wood is widely used for posts and poles in the agriculture and horticulture industries, and for building housing, outdoor furniture, decks and rails.

Processed products

The New Zealand pulp and paper industry began in the 1950s at Kinleith and Kawerau in the central North Island. Mills produced newsprint, industrial paper, tissue and pulp.

Other wood-processing industries followed, producing:

  • fibreboard (hardboard and softboard)
  • particleboard
  • plywood
  • medium-density fibreboard
  • heavy-duty engineering timber
  • timber for furniture, house sidings and mouldings
  • laminated veneer lumber.

These products are sold locally and exported.

Hardwood from softwood

Radiata pine is a softwood and, although it produces a versatile timber, there is always demand for denser, harder woods. Robert Franich at the New Zealand Forest Research Institute developed a hardwood product by injecting the cells of pine timber with a cellulose solution. The resulting product, marketed as Greenseal or NuWood, is used for flooring.

Exports

Exporting logs is important, as the local market is too small to absorb the ever-increasing annual harvest. Logs are sold mainly to Korea, Japan, China and India, and the timber used in construction work (concrete boxing), packaging, pallets, car cases, and cable drums. In China, it is also used to make furniture or furniture components for export. New Zealand also exports logs and chips for wood pulp.


External links and sources

More suggestions and sources

More links and websites


How to cite this page: Peter Berg, 'Radiata pine', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/radiata-pine/print (accessed 24 October 2017)

Story by Peter Berg, published 24 Nov 2008