Site preparation, fungi and dormancy mechanism - what affects the birch?

Kinga Stolarek works with a research project at the Southern Swedish Forest Research Centre at SLU aiming to understand what factors contribute to a successful birch plant production and establishment, as well as how different management practices can increase growth and survival of artificially regenerated seedlings. The birch seedling experiments conducted in the project are unique because of the number of treatments and the novelty of using containerized birch seedlings on such a large scale.

Observations on birch seedling survival

Clear scientific conclusions can’t be drawn after this first growth season, since the experiments were established in Tönnersjöheden, Asa, Siljansfors and Vindeln experimental parks in 2023. Some very preliminary observations from the project however show that site preparation seems to be a very crucial practice in southern locations.

“For now, we see a tendency for soil inversion appearing to be the most suitable site preparation for the survival of birch seedlings. Also, there may be some interaction between the site preparation method and the seedlings' size during spring planting, where seedlings with a bigger volume (105 cm3) of container may survive more frequently than smaller (75 cm3) on plots without site preparation. However, we need more growing seasons under observation to confirm this”, says Kinga Stolarek.

Kinga Stolarek also found differences between the survival in southern and northern Sweden. 

“The survival of seedlings was much higher in the northern location (Vindeln, 98,8% of survival) than in the southern location (Asa and Tönnersjöheden, average 77%)”.

Drought and insects, such as two types of weevils, pine weevil (Hylobius abietis) and Strophosoma capitatum, were the main identified damage for birch seedlings in the southern locations of the experiment during the growing season of 2023. How the weather, climate, browsing and planting period affect the birch seedlings will also be investigated further on in the project.

Fertilization possibly effective

Fertilization with arginine phosphate may have positive effects on seedlings and a connection between the fertilization and site preparation treatments was found. The initial analysis showed that applying fertilization during spring planting may increase the growth of seedlings on plots prepared with the method of soil inversion.

“Fertilization treatment may positively affect seedlings' height growth, mainly for northern locations, which is fully expected because of the depletion of nitrogen in soils in the northern part of Sweden. However, we need longer-term measurement to confirm the effect of fertilization”, Kinga Stolarek says.

Fungi and frost tolerance assessment

Hoping to contribute to an increase in the germination of birch seeds intended for the production of containerized seedlings in Sweden, Kinga Stolarek and her fellow researchers also work on identifying potential plant pathogens that may inhibit germination and cause diseases to the seedlings.

“I plan to use different methods for fungi identification because using multiple methods increases the possibility of catching the overall diversity of fungi within seeds. This in turn, gives us better opportunities to identify potential plant pathogens that may contribute to seed germination or seedling health at later stages of the nursery production”, says Kinga Stolarek.

And what about the dormancy mechanism?

“Seedlings produced in the spring of one year may be stored in minus temperatures over winter to be planted next spring. Exposing seedlings, which are not dormant yet, to minus temperatures may bring significant losses at nurseries. Therefore, there is a need to understand the dormancy mechanism in birch”, Kinga Stolarek explains. 

She argues that this project, starting in the summer of 2024, may bring a lot of practical guidance regarding the nursery production of birch seedlings and increase the knowledge on how long birch seedlings can be stored in a freezer and when is the most optimal time to freeze the seedlings.