No. 02 Choosing radiata pine tree stocks
NZFFA Information leaflet No. 2 (2005).
Most forest nurserymen offer a range of different tree stocks for sale, with some quite large price differentials between them, reflecting the cost of production of each of them. The main types, in increasing order of cost, are:
- Open-pollinated seedlings (GF 16 to 19)
- Control-pollinated seedlings (mostly GF 22 to 30)
- Bare-rooted stool bed cuttings
- Bare-rooted field (aged) cuttings
- Containerised cuttings
In addition, some nurseries also offer control-pollinated seedlings with long internodes or Dothistroma resistance, or other special characteristics such as high wood density, low spiral grain etc., and these latter are called GFPlus.
GF is a rating for growth and form of radiata pine seedlots, with more emphasis given to growth than to form. The higher the GF rating, the better the growth and form, which means on average there are more whorls of branches, and the branches are smaller. The rating is given to a seedlot, and is an average for that seedlot, but there is still a lot of variation between seedlings within a seedlot.
The Forest Research Institute have measured the following average performance of seedlots:
|Seedlot||Vol. gain %||% acceptable stems|
Open-pollinated seed is naturally wind pollinated, and only the female parent is known. It is much cheaper than control-pollinated seed, but the gains in growth and form are limited. Control-pollinated seed is produced by isolating female cones and applying pollen from a known parent. This is very labour intensive, and consequently seed is costly to produce and available in only limited quantities, but because both parents are known, much higher GF ratings are possible.
On hard sites where growth is naturally slow, most radiata seedlings grow into trees of good form, but on very fertile sites such as farmland that has had a long history of fertiliser application and grazing, form is often poor, with many trees having sinuous stems and heavy branches. On these fertile sites the much better form of high GF rated seedlots is well worth the extra cost of plants, and the enhanced growth of such seedlots means that trees can be grown on shorter rotations or grown to larger sizes, which is particularly important if the butt log has been pruned. On average sites, the better form of high GF seedlots means that fewer trees need be planted to obtain a satisfactory final crop.
On the other hand, where it is desired to have a high initial stocking, for example to suppress woody weeds or to keep branch diameters very small, cheaper open-pollinated seedlots are quite satisfactory. Farm forestry experience has shown that high GF rated seedlots often perform poorly on cold (high altitude) sites, and on very exposed sites, especially when planted as shelterbelts. In these situations, cheaper open-pollinated seedlots are much more cost effective.
The long-internode breed produces a much higher proportion of clear-cuttings between the nodes, which can greatly increase the value of unpruned logs.
However, the long internodes result in whorls of large branches, which means that stem straightness is poorer, and the tops of trees are more inclined to blow out on exposed sites or sites that are prone to snow damage.
It is recommended, therefore, that the long-internode breed be planted only on sheltered sites of moderate to low fertility. The Dothistroma-resistant breed is worth using on sites which are particularly prone to Dothistroma infection, such as fertile lower slopes in high rainfall country, especially if spraying to control infection is likely to be expensive (remote location, small size of plantation etc.).
The GF Plus seedlots carry a surcharge of $32/1000 plants and can be used for specialist timber production. At this stage, the most useful breed for farm foresters is likely to be the high wood density one, which can produce stronger timber, and this can be of particular value where trees are normally below average density, e.g. at higher altitudes and in Canterbury and Southland.
Cuttings can be produced either from stoolbeds in a nursery, or from young trees already established in the field. Stoolbeds are most commonly used as a means of bulking up scarce and expensive control-pollinated seed by hedging young plants in the nursery for several years, so that each plant produces many dozens of cuttings. Because the cuttings can be collected in bulk, they are cheaper than field cuttings. Field cuttings are taken from established trees in the forest up until they are 4 years old, but as the cuttings are taken from only the leading shoots of branches, relatively few can be collected from each plant.
Cuttings taken from 1 year old plants have little advantage over seedlings, but cuttings from 2 and 3 year old plants result in trees with:
- straighter stems
- less malformation
- lighter branching
- less stem taper
- greater wind stability, due to stronger root systems and lighter crowns
These advantages mean that fewer trees need be planted to obtain a satisfactory final crop, and pruning costs will be less. The only disadvantages are that plants are more costly, and the bark of cuttings is thinner, so that they are more susceptible to browsing damage by animals.
Containerised radiata planting stock is quite new on the New Zealand scene, and a great deal of experience has not yet been gained. In general, containerised stock is usually smaller than good bare-rooted stock and not as well conditioned, so good site preparation is more important. However, as the roots are little disturbed in planting, there is scope for planting at any time of the year, providing soil conditions are suitable.
As with so many things in life, it pays to buy the best quality you can afford, provided you have suitable sites. The price differential between treestocks reflects the cost of production, not their potential profitability, which usually increases with the more expensive treestocks. Remember, when planting high quality stock, not only do you need to buy fewer plants, but there are also fewer to plant and release, pruning costs will be lower, and you will end up with higher quality logs. When planting fertile farm sites, it is false economy to plant the cheaper treestocks. However, on very exposed or cold sites, or where high stockings are being used to suppress woody weeds, there is little or no benefit in planting the more expensive treestocks.
On sites which are not particularly fertile, but which have good height growth and are reasonably well sheltered, it is well worth considering growing the long internode breed, while the Dothistroma-resistant breed is certainly worthwhile where controlling this disease is a problem. For growers in the southern part of the country, particularly those with good sites who intend to intensively manage their stands, the high wood density breed offers an opportunity to improve the quality of wood produced.