23 • 03 • 2021

The Importance of Forest Tree Selection is Growing

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In Latvia, the selection of forest trees began in the second half of the 1950s, when forest scientists started to search for and identify the best stands for the main tree species. Today, progeny testing plantations have been established on an area of more than 800 hectares, and almost a third of Latvia's forest stands are being restored with selected material, thus significantly increasing their future value.

True, the advantage of forest breeding can mostly be appreciated after several decades. However, the first results are already available, which confirm that if the forest owner has chosen to restore forest stands with selected planting material, a real, tangible benefit can be obtained already after 14 years. Forest tree selection plays and will continue to play an increasingly important role in mitigating the risks posed by climate change. Arnis Gailis, Researcher at the Latvian State Forest Research Institute “Silava”, talks about the latest findings in forest tree selection.

Scientists have calculated the benefit from fast-growing birches

The results and fruits of forest selection work take a relatively long time. The Latvian State Forest Research Institute “Silava” is also currently implementing the forest selection programme developed in 2008, the results of which will mostly be evident after 10, 20 and even more years. However, there is some good news for forest owners – the first results of the study, which were obtained in a large-scale birch free-pollinating family progeny test plantation, confirm that a tangible benefit from a selected birch forest can be obtained relatively quickly.

More than 600 progeny birch families (forest stands) grow on the test plantation on an area of about 30 hectares, and the first thinning was carried out when the plantation reached the age of 14. The diameter of the remaining trees after thinning was 10 cm, and the height was 14 metres; the diameter of the felled trees was 8 cm and the height was 13 metres. On average, 28 cubic metres of useful wood were prepared by cultivating one hectare of plantation. Having calculated the value of sawn wood, the scientists concluded that the value of wood of the fastest growing families exceeds the average value obtained in the same plantation by almost 300-400 euros. In turn, the selected trees exceeded the value of offspring of the slowest growing families by as much as 400-800 euros. Thus, already at the age of 14, the additional effect of the selection has covered the costs of forest stand restoration.

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Spruces reach the main felling point faster

Selection has a lasting long-term effect on stand productivity, characterized by improved growth of stands. Significant increase in productivity can be obtained if spruce stands are regenerated purposefully using the highest quality selection material. An example is the results obtained by measuring the plantations of lower thickness (sparser standing) spruce clones. In such plantations, spruces currently reach the diameter of the main felling allowed in laws and regulations in an average of 42 years and it is 30 years faster than the average in forest stands in Latvia (Forest Statistical Inventory data). The shorter growing time of the forest stand also ensures that trees are exposed to various risks such as diseases or strong wind effects for a shorter period of time. Forest selection in general provides an opportunity to increase the efficiency of land use, and it is the rapid growth of trees that increases the choice of felling time for the forest owner.

Vegetative propagation methods play an important role in forest selection research and transfer of the results. True, it must be taken into account that such planting material will be more expensive. When selecting the most productive genotypes for propagation, it is important to evaluate their quality characteristics. For example, in the spruce clone plantation, stem cracks and resin are very important properties influencing the quality of wood. The study concluded that these traits were genetically determined. Thus, in the selection process it is possible not only to select the most productive, fast-growing material, but also to promote its quality, thus increasing the value of the wood to be grown.

Selected forest stands – better prepared for climate change

In the future, the use of selected material will be increasingly important in reforestation. Given the effects of climate change on forestry, forest selection will contribute to the resilience of trees to a number of climate change risks.

In the future, climate change is expected to lead to temperature changes, stronger wind gusts and longer periods of drought. Already now, the Latvian State Forest Research Institute “Silava” is working to select genotypes that would be less responsive, for example, to a long period of drought. First of all, resilience must, of course, be recognized under controlled conditions (in the laboratory) by studying and comparing the expression of the response of different genotypes, but later breeding plants and materials could be evaluated using remote sensing capabilities.

Due to climate change, root rot, which is a common conifer disease, is also spreading more rapidly. In collaboration with forest phytopathologists, breeders and geneticists, it has been established that resistance to root rot is genetically determined – it is influenced by the composition of terpene in a particular plant or genotype. Therefore, it is possible and even useful to include the resistance index in the overall breeding index when evaluating the selection material of Scots pine.