Don’t stand so close to me

4 February 2021

Competition between radiata pine can be used to identify trees with desirable traits

Competition between plantation grown radiata pine can be used to improve heritability estimates for desirable tree traits by accounting for phenotypic variation not explained by environmental and spatial effects.

Competition from large trees can reduce the growth of their smaller neighbours. The size of a tree (diameter at breast height), the size of neighbouring competitor trees and how close they are, can represent competition and growth potential.

Using a stand of young radiata pine of planted as part of a genetics trial in the Kaingaroa Forest, central North Island of New Zealand, Scion scientists have used competition metrics to account for environmental variation in tree traits. The trees’ height, diameter at breast height, stem volume, infection by Dothistroma needle blight and wood stiffness (wood quality) were assessed from the ground and the area was laser scanned from the air.

“Airborne laser scanning data can be used to distinguish between individual tree crowns and give us information about tree size and spatial relationships to neighbours. From this, we can calculate metrics to represent tree to tree competition,” says Dr David Pont, lead author of the study. “We characterised individual trees to generate tree-level phenotypes and tree-to-tree competition metrics”.

“We then used the competition metrics to improve our ability to account for environmental variation and its relative importance on heritable tree traits.”

Including competition substantially reduced residual variance and improved estimates of the traits being studied. The reductions in residuals ranged from -65.48% for tree height to -21.03% for wood stiffness, and improvements in heritabilities from 39% for tree height to 14% for wood stiffness.

“Including an explicit competition term and a generic spatial term is a robust and effective way to account for environmental variation in tree traits,” says Dr Pont.

The researchers also found that the relative amounts of variation due to genotype, competition, and site were distinct by trait. Tree diameter at breast height and volume were strongly influenced by competition, while height was influenced equally by competition and site effects.

The ability to phenotype individual trees to quantify the interactions between genotype, environment, and management practices is critical to improve tree genetics though breeding, and to the development of precision forestry approaches to increase the efficiency and sustainability of managed forests.

Pont, D., Dungey, H. S., Suontama, M., & Stovold, G. T. (2020). Spatial models with inter-tree competition from airborne laser scanning improve estimates of genetic variance. Frontiers in Plant Science, 11, 2141.