Over the past 60 years, tree improvement has capitalized on the genetic diversity of valuable tree species to enormously increase wood production per hectare.
For example, Monterrey pine (Pinus radiata), introduced to New Zealand from the US, had rapid growth but poor form. An intensive selection and breeding programme was initiated, and after just one generation, trees had almost uniformly straight well-formed stems (Burdon and others 2008). This was possible because in this species and other conifers, the shape of the trunk is strongly controlled by a small number of genes. Even if most of the trees have poor form, experience in New Zealand and elsewhere has shown that when the small proportion of straight trees are selected and interbred, the offspring have straight, well formed trunks for generations to come. This alone has greatly improved the value of some tree species that have been brought into intensive cultivation for wood production.
The other characteristic that is a common focus of selection and breeding efforts is growth: the volume of wood produced over a given period of time. Gains have not been so dramatic as with form – often 10-15% in the first generation and approximately double that by the end of the second generation. This is because many genes are involved in growth, and environmental conditions play a big role. Nevertheless, second or third generation trees produced in a breeding programme generally grow significantly faster than their natural forest relatives.