Experimenting with new species
As early as 1897, the state established plantations of exotic trees to provide for New Zealand’s future timber needs. To explore the growth rates of exotic species in New Zealand, there were experimental plantings at Whakarewarewa in the North Island and Hanmer in the South Island.
Eucalypts and redwoods were planted first, followed by a range of pines. By 1909, 5,140 hectares had been planted with more than 60 introduced species.
Radiata pine (Pinus radiata) was recognised as the best species for plantation forestry because it grew quickly and its timber was versatile. After the establishment of the State Forest Service in 1921, extensive exotic forests were planted, mainly in the central North Island.
Planting trees as crops
At first, little was known about how to grow trees as a crop. New Zealand researchers devised methods for propagation, planting and silviculture that influenced plantation forestry practices throughout the world.
The first challenge was to reduce the high cost of planting trees. Every detail, including the shape of the spade and the depth of the planting hole, became the subject of scientific research.
Foresters developed a pit planting technique to improve tree survival rates. This involved digging a pit into hard ground and making sure the tree’s roots were surrounded with loose soil, which could absorb and retain more moisture than compacted ground.
Young trees of uniform size and quality were needed to ensure high survival and maximum early growth rates. In the 1970s Forest Research Institute scientists developed a precision seed sower, a lateral root pruner and a seedling lifter that greatly improved mass production of seedlings.
Preparing planting sites
Preparing land for planting was hard labour, but in the 1970s machines for ripping and mounding the soil were developed. Improvements were also made in distributing fertiliser from aircraft.
To ensure trees become properly established, shrubby weeds, such as broom, gorse and blackberry, must be controlled during the first few seasons of growth. Scientists conducted research on herbicides to find the safest, most cost-effective ways of controlling forest weeds.
In the 1970s and 1980s there were trial plantings of trees on farms, including the Tikitere trial near Rotorua, which was jointly established in 1973 by the Forestry Research Institute and the Ministry of Agriculture and Fisheries. Other trials were conducted at Whatawhata and Invermay research stations.
Trees were thinned to wider than normal spacings so that pasture could be grown between them. However, trees in fertile farmland often grew too fast, resulting in poorer wood quality. In addition, the spacing between trees meant branches were very large, further reducing the quality of the wood unless early pruning took place.
Although agroforestry seemed promising, and tree planting on farms was briefly popular, combining forestry with grazing has fallen out of favour.
New Zealand researchers have developed models to predict how forests are likely to grow in a given place. Growth modelling uses data collected from a permanent sample plot system, established in New Zealand forests in the 1980s. Growth rates of different tree species are regularly measured at around 12,500 plot locations. With this information, planners are able to predict and regulate future wood production to take advantage of market movements.