Boron and Tree Form
Because of a disastrous attempt to rectify boron deficiency in 1976 (which included tree death) through using a quick release granular borate , uneven application , and not understanding how boron affects the different soil profiles, the boron program for all state forests in Canterbury was halted until a better method was found.
However it wasn't until 1980 that operations resumed, but because of the fear of a similar disaster occurring, the plains forests were not treated, and only half of the foothills forests received an application.
The off shot from all this, is probably the best practical demonstration I have ever seen of the advantages of applying boron to plantation forestry. Because on one side of the road we have trees that were treated 20 years ago with boron, while on the opposite side of the road we have trees that were not treated and therefore are boron deficient.
After 18 years of growth, we are noticing striking changes in tree form within the treated and non treated sites.
The enclosed photographs below give good examples of this. These photographs were taken of treated, and non treated pines (P radiata & P muricata) within Ashley Forest. As can be seen from the untreated trees they grow into short fat dumpy specimens, ( very similar to the writer,) while the treated trees grow very tall with small branches, and good apical dominance.
Boron Deficient Sites
Lack apical dominance, Large branches
Boron Rich Sites
Boron Deficient Sites
produce weak wood
An independent study has shown that 18 years after a boron application, the site index increases from 24 to 29.5 ( site index = height of tree at age 20). Volume in the treated stands is 22% larger than the untreated. The incidence of stem wobble in the treated stand was 82% less than the untreated stand, and the incidence of sweep was 71% less in the treated stand to the untreated.
Probably the most striking difference between the two, is that in the boron treated stand branch diameters less than 6 centimetres, was 71% greater than in the untreated stand.
Pictures are indeed worth a thousand words, and what we have here is an excellent example of how to grow trees in Canterbury. In short if you choose not to apply boron you grow a short, fat, tapered tree, with large branches, resulting in a lot of wasted wood when sawn as well as a lot of lower grade sawn timber.
On the other hand if boron is applied, tree height is maximised, and because the tree can grow taller, it has no need to retain its terisary needles, and therefore branch diameter very seldom exceeds 4 centimeters in diameter.