There are several benefits to reducing the height of trees grown for short-rotation forestry or biofuels. This is the view of researchers at Oregon State University in the US, and it is an opinion that runs contrary to centuries of tree breeding, which has always tried to produce trees that grow larger and taller.
Forest genetics professor Steven Strauss believes that just as agriculture’s green revolution saw more food being grown on smaller, sturdier wheat plants, forestry could benefit from shorter trees. According to him, this would result in better wood growing, more efficient biomass production, less water use and even greenhouse gas mitigation.
“Research shows that genetic modification of height growth is achievable,” Strauss says. “We understand the genes and hormones that control growth in crop plants and in trees, and they’re largely the same.”
In a study published in Plant Physiology, researchers inserted genes into poplars, a species often used for genetic experiments, and valuable for wood and energy purposes. They described 29 genetic traits affected, including growth rate, biomass production, branching, water use efficiency and root structure. All of the changes were from modified gibberellins – plant hormones that influence growth and development.
The range and variation in genetic modification can be selected to grow trees of almost any height. For example, it would be possible to grow a miniature poplar for ornamental purposes. Strauss stresses that there is no chance these GM trees would take over in the wild, because all trees, in their need to seek sunlight, use height growth to compete against each other. Shaded by larger trees, the GM trees would ultimately die out.
Scientists could also produce trees with a larger root mass, which should make them more drought-resistant, increase water use efficiency, increase elimination of soil toxins and better sequester carbon. This would be useful for greenhouse gas mitigation, bio-remediation or erosion control.
According to Strauss, smaller trees with sturdier trunks could be selected for plantations, reducing the number of trees blown over by wind. And shorter, thicker and straighter trunks might create higher-value wood products.
“The main limitation is the onerous regulatory structure for genetically modified plants in the US,” he says. “Even beneficial trees are unlikely to be able to bear the high costs and red tape inherent in obtaining regulatory approval.”