Mike Carson, the Business Development Manager at Gemnetics and Managing Director of Forest Genetics Ltd, is writing a short article series about breeding topics arising from the perspective that he and Sue Carson have developed during their (combined) 79 years involvement in forest tree breeding.
Mike uses Gemview on a daily basis to track his trial breeding data and view trends and relationships in order to increase the productivity of the Forest Genetics breeding and clonal deployment program.
Mike's articles will be published on our Gem news page. If you would like to contact Mike to comment or share your own insights, please contact him through our contact us page, or directly through Mike's Linkedin profile.
Although tree breeders have a strong and continuing interest in understanding Genotype-by-Environment interaction (G X E), this can sometimes lead to neglect of the large substantial genetic gains in productivity that can be achieved by simply better matching genotypes to known site expression characteristics, or G + E. Wood density variation across sites for radiata pine in New Zealand provides a useful case study example of how effective G + E can be in increasing genetic gains from varietal forestry.
Figure 1- Site variation across NZ for wood density of radiata pine.
Figure 1 illustrates the wide range in average radiata pine wood density that varying latitude and elevation creates in NZ plantations –with a range from less than 340kg/m3 for some low elevation southern stands, to greater than 460kg/m3 in Northland. Increased wood density confers additional strength to both structural and clear timber, and is also associated with improved stiffness and dimensional stability. The wide range of average wood density across NZ can act to limit forest growers choices, in terms of what timber products they can grow with reasonable success –for example, some high-latitude and/or high elevation sites with low average wood density may only be suitable for growing stands dedicated to pruning for production of clear timber, since there will be very limited ability to achieve the necessary timber grading levels required for structural timber. In addition, the opportunity for growers to benefit from carbon credits from their stands will be similarly limited on such sites, since wood density is a major contributor to carbon yields.
Fortunately, the expression of average wood density in radiata pine is under strong genetic control and, as a selection trait in breeding trials it has been shown to:
1. Express little genotype rank change due to site (i.e. it has low G X E),
2. have consistently high heritability, and
3. to express a wide range of genetic variation on any given site –i.e. up to 80-100kg/m3.
Together, these characteristics make wood density a prime target for achieving G + E gains, through careful deployment of highly-selected genetic material.
As a result of intensive selection, some Forest Genetics Ltd clonal varieties are yielding gains of up to 60kg/m3 in wood density, in combination with increases in growth rate, stem form, and corewood stiffness. If careful genotype/site matching is used by growers to target problem sites with such varieties, it seems very likely that the latitudinal and elevational limits that currently apply for growing either structural timber or carbon will be stretched to enable substantially greater productivity and profitability to be achieved on such sites.