Clarky's Comment - July 2011

In this issue of Wood Matters, I would like to discuss how to choose the right treestocks for your forest.

The genetics and performance of radiata pine in New Zealand have been steadily improved over the last 60 years through tree breeding. The trees planted today are better in growth, form and wood qualities than trees we planted 20 years ago. I have been around long enough to personally observe dramatic differences in tree growth and form on the same sites, with the only variable being genetics. I don't need to look at data to convince me of the value of genetics - but the data is there for those that do.

The increasing levels of genetic improvement in treestocks can be broken down into four types:

  1. Open-pollinated (OP) seeds were produced from purposely established seed orchards in the 70s and 80s using grafts of elite trees selected from intensive breeding programs. The seeds are GF™ certified and most OP treestocks planted today are GF 17 to GF 19. OP seeds are in short supply at the moment as most of the older OP seed orchards have been demolished and new generation OP seed orchards are still too young to produce seed.
  2. Stand-Select Open-Pollinated (SSOP) seeds are usually collected from GF 25 to GF 28 forest stands and are used to fill the market gap caused by the shortage of OP seed. The seeds are collected from trees that have excellent growth and form. Because SSOP seed is a new product and lacks trial data to support its performance, SSOP seed and seedlings produced from it are not GF™ or GF Plus™ certified.
  3. Control-pollinated (CP) seeds are also produced from purposely designed seed orchards. In controlled pollination, female conelets are bagged and pollinated using pollen from a donor clone so that both male and female parents are known. In this case, genetics can be recombined using the best of our knowledge to produce families with the most desirable traits. CP seeds are GF Plus™ certified and have indicative GF Plus values for six important traits - growth, straightness, branching, Dothistroma resistance, wood density and spiral grain. CP seeds are more expensive to produce and their price is higher than OP seed. However, CP seed can offer higher levels of genetic gain in the important growth, form and wood quality traits.
  4. Clonal treestocks are multiple copies of single trees that are first propagated by tissue culture, and are then further 'bulked-up' as rooted cuttings harvested from nursery stoolbeds. Trees of the same clone are initially generated from single seeds developed from CP crosses among top breeding parents. The clones are all stored in frozen condition (a process called 'cryopreservation') in order to maintain their juvenility. Copies of the clones are then grown in field trials designed to compare their performance for growth rate and wood quality against that of OP and CP seedlots. The best 1-5% of clones tested are selected and extracted from 'cryostorage' for nursery production. Trees of the same clone are genetically identical and clonal treestocks have the highest degree of uniformity and genetic improvement. Clonal trees are expected to receive GF Plus™ certification in the near future. Since clonal treestocks are very expensive to produce, their price is the highest.

Forest Genetics Ltd is a producer of high-quality treestocks of selected clonal varieties, and is rapidly developing these for sale in commercial quantities. The best clonal varieties are yielding substantial gains in growth rate and wood quality over CP treestocks in comparison trials, and several of the large forest growing companies are already establishing them across more than 25% of their estate. Since high gains in both growth rate and wood density are being achieved with Forest Genetics' varieties, they will also provide opportunities to substantially increase yields of carbon credits.

Treestocks can be grown as bareroot or container nursery stocks, and either as seedlings, or as cuttings harvested from nursery stool plants:

  1. Bareroot treestocks are grown in nursery beds and are usually larger in size and cheaper to produce. Because their roots, especially the nutrient-absorbing fine roots, are trimmed back during lifting, the trees spend their first year redeveloping their root systems after planting. Skilled planting (cultivate, open, drop and pull up) is required for planting bareroot treestocks. Due to their larger size and reduced root mass, bareroot treestocks should only be planted during the relatively wet winter season.
  2. Containerised treestocks are grown in a special medium mix in plastic containers. The root plug remains intact during lifting and as a result the root systems are not disturbed. Containerised trees are usually smaller but they continue to grow after planting without any setback. The planting season can be extended if containerised treestocks are used. PF Olsen has planted containerised seedlings as late as December with satisfactory results. Containerised treestocks produced in PF Olsen's nursery are also treated with ArborGuard™, a beneficial bio-protection agent that protects young trees in the field from harmful root diseases, such as Armillaria root rot.

Container grown treestocks are often smaller than bare-rooted treestocks, but retaining the integrity of their fine root systems lessens planting shock and susceptibility to drought.

Good genetics can give the tree good potential to grow but the actual growth and performance will also depend on site quality, as well as good establishment practice.

The rule of thumb in choosing treestocks is always to get those trees with the highest genetic potential available in the market. If this cannot be achieved due to market or financial constraints, one should always match trees with the best genetics to the highest quality site. If the site is prone to Dothistroma infection then high Dothistroma-resistance seedlots should be used.

In addition to growth, both wood density and timber stiffness are other key traits to consider when choosing treestocks. Treestocks with higher wood density and stiffness are available in GF Plus™ certified CP seedlings and also in clonal material. Forests established from high wood density seedlots not only have higher output of valuable structural logs at rotation end but also can have higher value by gaining more carbon credits.

Choosing the right treestocks and matching the right genetics to forest site and management objectives can be a daunting issue. At PF Olsen we have experts that can help our clients to make the right decision. Keep in mind that there is only one chance every 30 years to make the right call.