Trees grow slowly in Finland. In southern Finland, it takes spruce at least 60 years to become sturdy enough for the final felling, and even longer in the north.
The climate is warming, and up north, it is warming much more strongly than the global average.
This presents a problem to forest regenerators: when sowing or planting a commercial forest, how do you choose species that will survive and thrive in a changing climate decade after decade?
According to Matti Haapanen, Senior Scientist at Natural Resources Institute Finland, climate warming as such is not a major problem for forest trees.
For research purposes, forest tree species have been planted far away from their origins. This has been done to test how different species succeed in climates colder or warmer than their original home environment.
“The result is very clear. A move to a warmer climate isn’t disastrous: trees mainly benefit from the added warmth.”
According to Haapanen, the risk of climate change mainly arises from the ensuing unpredictable changes in the habitats of trees. We have no way of knowing what all the seedlings planted now will have to endure in the coming decades.
Extreme weather conditions such as storms and long dry periods will probably become more common. New forest pests may also follow the warming climate farther north.
Better quality through forest tree breeding
As a result of long natural selection, forest tree species have adapted well to various diseases and changing weather conditions.
Nevertheless, properties refined by nature can still be improved. Forest tree breeding favours fast growth, high quality and resilience in different climate conditions.
The seeds of trees selected for breeding are grown into seedlings that are tested in experiments designed for various climate conditions and sites of varying fertility.
“Any developmental disturbances or quality defects detected in the experiments may be an indication of inadequate climate adaptation. Such individuals are excluded from breeding. Instead, individuals that offer good wood yield and quality in different test environments are retained. They will succeed best in future climate change.”
Frost also threatens in a warming climate
Climate change may expose spruce to increased risk of damage caused by spring frost. If frost destroys the slender light green annual growth, the entire year’s growth is lost.
Frost works somewhat counterintuitively: a warmer climate increases forest damage caused by the cold.
This is because although the growing season can begin at very different times in the spring, it ends around the same time every year in the autumn. In the spring, trees react more to changes in heat, and in the autumn, to changes in light.
As the climate changes, long warm periods may occur earlier and earlier in the spring, encouraging spruce trees to begin their annual growth. However, an early spring may be followed by a cold spell, or at least occasional night frost, destroying the annual growth.
“As spruce exhibits a strongly hereditary growth rhythm, we eliminate those individuals that begin their growth earlier in the spring from the breeding material. With time, this pruning improves the frost resilience of spruce seedlings grown from seed orchard seeds.”
The best individuals are selected for further breeding
Decades ago, trees exhibiting superior growth, quality and health were picked out in natural forests. They are known as plus trees. A short scion was cut off the top of these trees and grafted onto a small seedling. The grafts carrying the genetic material of these plus trees have been cross-bred under supervision.
The success of the crossbred progeny is studied in nature during multiyear field tests. Based on the results, the best individuals are selected for further breeding. In Finland, forest tree breeding is the responsibility of Natural Resources Institute Finland.
The plus trees selected in nature have also been used for seed production. They have been grafted and placed to grow in seed orchards, where they are freely pollinated.
Seed orchards produce seeds for tree nurseries, where they continue to grow into seedlings sold to forest owners. In Finland, the state regulates and supports seed production. Seed orchard activities are currently run by two commercial operators: Siemen Forelia and Tapio Palvelut.
New seed orchards coming
The Ministry of Agriculture and Forestry’s programme for the establishment of seed orchards was updated in the autumn last year. The programme spans four decades into the future, as indicated by its name The Seed Orchard Establishment Programme 2060.
The programme is based on projected trends indicating that the planting of pine and silver birch will increase while that of spruce will decrease. The seed orchard requirements for these most common tree species were specified accordingly.
The report also proposes seed orchards for less commonly used tree species. The advisory council for forest tree breeding and seed production was consulted to determine the order of importance. This resulted in the following list: larch, oak, black alder, wild lime, white birch, mountain elm, maple, Douglas fir, European white elm, curly birch and lodgepole pine.
“Don’t put all your eggs in one basket” is a good principle as climate change continues to progress. With no certainty about the direction of climate change and the tree species that the new climate will favour, it is justified to produce seeds of many different tree species.
However, as pointed out in the report, this also has its risks, since it means spending limited financial resources on tree species that may not be cultivated in the future.
Text Antti Kivimäki
Photo Vastavalo/Hannu Rämä
This text was published in Metsä Group’s Viesti 2/2024.