What can we do to support the successful growth of silver fir seedlings?
The silver fir used to be a very important tree in our forests, but starting from the 18th century, its numbers decreased significantly due to changes in land management and air pollution. However, the representation of this tree species in our forests is now increasing again. Recent improvements in the health and regrowth of the fir have been observed in Central Europe. Recent findings suggest that the silver fir is better at surviving dry periods compared to the previously dominant spruce.
Photo: Silver fir seedling, author Jan Řezáč
In many of our forests, there are few fruiting fir trees, and they are spread out like islands. This makes it difficult to naturally increase the number of fir trees in these areas.
As a result, we will need to use artificial methods to help more fir trees grow. To do this, we need good quality seeds. Fir seeds have a natural dormancy, so we have to prepare the seeds before planting them in the ground.
The collected seeds often contain a high percentage of empty seeds that cannot be separated from the full ones even with the use of modern technologies. In some cases, the lifespan or germination of dehulled seeds does not reach the values required by the ČSN 48 1211 standard.
Photo: Silver fir growing together with European beech in the game-proof fence, author Jan Řezáč
These issues during sowing lead to uneven emergence of seedlings, and can cause high losses during the dry season.
A possible solution is to use soil conditioners called hydroabsorbents, which can be applied to the soil or directly to the seeds. In the case of seedlings, they can protect the root system. These substances swell significantly in a water environment and create a stable gel.
They are seen as a promising way to increase water availability for plants. Some modern hydroabsorbents can absorb up to 400 times their weight in water. They release this water to the plants during dry periods and remain effective for several years.
The scientists from VÚLHM, v. v. i., conducted an experiment to test the effect of hydroabsorbent application on the germination of fir seedlings under three different irrigation regimes. They published their results in an article titled “Influence of a hydroabsorbent on the germination of silver fir seedlings” (Vliv hydroabsorbentu na vzcházivost semenáčků jedle bělokoré) in the journal Forestry Research Reports (Zprávy lesnického výzkumu) 2/2024.The article was part of the project NAZV QK1910292 “Procedures for the support of white fir in the forest management of the Czech Republic” („Postupy pro podporu jedle bělokoré v lesním hospodářství ČR“).
Photo: Silver fir successfully growing in a fence, by author Jan Řezáč
The researchers hypothesized that applying the hydroabsorbent under low irrigation doses or in the complete absence of irrigation would help maintain higher substrate humidity and lead to a higher germination rate of the seedlings. They observed a positive effect of the hydroabsorbent on the overall germination rate only in the variant without the application of dressing, where the germination rate was about 17% higher compared to the pure substrate.
When watering once or twice a week, the hydroabsorbent already had a rather negative effect, and the germination rate was 4-5% lower.
The highest germination rate was observed in a clean substrate when watered once a week. In this scenario, the substrate’s humidity did not drop below 50% during seedling emergence, which was apparently optimal for germination.
Watering twice a week resulted in excessively high humidity, even in a clean substrate, leading to a decrease in germination.
Photo: Silver fir is coming back to our forests, author Jan Řezáč
In conclusion, the scientists found that the positive effect of the soil conditioner on germination percentage in the variant without continuous watering (only initial watering at the beginning of the experiment) is a promising result, indicating the potential for managing drought conditions.
The presence of a hydroabsorbent in the growing substrate during seed germination leads to increased water retention. This is beneficial as it helps to prevent water runoff and evaporation, especially in dry conditions.
However, it’s important to avoid overapplication of the hydroabsorbent, as excessive swelling can displace the substrate and plant material. Adjusting the watering and the amount of the conditioner is necessary when using hydroabsorbents in the substrate.
The paper Influence of a hydroabsorbent on the germination of silver fir seedlings (Vliv hydroabsorbentu na vzcházivost semenáčků jedle bělokoré) can be downloaded here.
Authors of paper: Lena Bezděčková, David Dušek, Kamila Brožovičová, Pavel Kotrla, Josef Cafourek, Dušan Kacálek; VÚLHM, v. v. i., e-mail: bezdeckova@vulhmuh.cz
According to the original, prepared by Jan Řezáč, VÚLHM, v. v. i., e-mail: rezac@vulhm.cz