Silver fir is best regenerated artificially at the edge of an established stand

Silver fir, with its unique growth strategy, is one of the most important conifer species in Europe and serves as an indicator of high ecological stability and forest ecosystem diversity. Historically, it was a significant tree species in Central Europe, but in the Czech Republic, its representation has diminished over time to the current level of just 1.3%.

Photo: Artificial regeneration of silver fir protected by an adult Norway spruce stand. Author Jan Řezáč

Silver fir is commonly found as a shade tree species and typically thrives in multi-storey, uneven-aged forest stands, especially in mixed forests. However, under certain conditions, silver fir can exhibit traits of a pioneer species, allowing it to colonise previously abandoned agricultural lands.

Based on its current distribution, silver fir is traditionally regarded as well-suited for humid continental climates, which are characterised by high moisture requirements throughout the year, specifically in areas with average annual precipitation ranging from 700 to 1,800 mm.

Silver fir can thrive in a variety of soil types, accommodating different nutrient levels and alkalinity. Its ideal growth occurs in the fifth level of forest vegetation, specifically in fir-spruce-beech environments. This tree prefers heavier loamy to clayey soils, including those that are sticky and somewhat waterlogged. Silver fir naturally regenerates well in the presence of sunlight, along with tree species such as pine, birch, and larch, as well as under spruce and mixed forest stands.

Photo: Artificial regeneration of silver fir at the edge of an adult Norway spruce stand. Author Jan Řezáč

The main factors affecting the natural regeneration of silver fir include habitat conditions and the proportion of this tree species within the stand. In silver fir stands, efforts for regeneration and repatriation are often severely limited or even impossible due to the impact of overpopulated ungulates. Currently, artificial regeneration is necessary to enhance the overall representation of silver fir. However, its application in clearings is constrained by the tree’s slow initial growth and its sensitivity to extreme climatic conditions.

Scientists from the Landscape Research Institute, the Institute for Global Change Research of the Academy of Sciences of the Czech Republic (Výzkumný ústav pro krajinu, v. v. i., Ústav výzkumu globální změny AV ČR, v. v. i., and Mendel University in Brno (Mendelova univerzita v Brně) conducted a study on the growth of silver fir following artificial planting. This research was part of the GAČR project 21-47163L titled “Physiological, Morphological, and Growth Response of Fir and Beech Along a Geographic Gradient – A Basis for Predicting Future Trends” (Fyziologická, morfologická a růstová reakce jedle a buku podél geografického gradientu – základ pro predikci budoucího vývoje trendů). The findings were published in the article “Growth and health status of open-grown and shaded silver fir (Abies alba Mill.) plantations in the Beskydy Mts.” (Růst a zdravotní stav výsadeb jedle bělokoré na slunečných a zastíněných stanovištních podmínkách v Beskydech), which appeared in the journal Reports of Forestry Research.

The objective of the study was to evaluate the artificial regeneration of silver fir in clear-cut areas. They examined both regeneration elements in stand gaps, which are characterised by the lateral cover of mature trees, and extensive clearings that lack protection from surrounding adult growth. Based on their findings, the researchers aimed to recommend optimal regeneration procedures, considering the implications of the ongoing bark beetle crisis and climate change.

Photo: Artificial regeneration of silver fir on a clear-cut area. Author Jan Řezáč

The scientists conducted research in the Moravian-Silesian Beskydy Mountains, near Frýdlant nad Ostravicí in the Čeladná district, where the land is owned by the Bishopric of Ostrava-Opava (Biskupství Ostravsko–opavské). The research area comprised 15 unsecured plots (referred to as “stands”) that were established between 2015 and 2018 through the artificial regeneration of silver fir. Bare-rooted seedlings, measuring 26 to 35 cm in height, were used as the planting material. The selected stands were categorised by their coverage as follows:

Shaded stands are characterised by having either length or width smaller than the average height of the surrounding adult stand. These stands benefit from protection against direct sunlight provided by the surrounding adult trees, which also influence the microclimatic conditions.

In contrast, sunlit stands are not shielded from direct sunlight by adjacent adult stands. These areas resemble calamity clearings and are always planted at a distance of at least two stand heights from the surrounding trees, exposing them to direct sunlight throughout the day. Given this spacing, it can be assumed that the influence of surrounding stands on the microclimate of the plantings is minimal.

In conclusion, the scientists summarised their findings. The artificial regeneration of silver fir in clear-cut areas, such as stand gaps and large clearings, demonstrated the following parameters:

• Trees that grew in shaded areas, except for the youngest plants, were consistently taller than those in open areas.
• In all plantings, the shock from transplanting likely occurred during the first year after regeneration; therefore, no significant differences in growth were observed between firs in sunny and shaded areas during that time.
• In the subsequent years, annual height increases were almost always greater for trees growing in shaded areas.
• The overall health of firs in all plantings was better, and the number of dead trees was lower for those that grew in shaded areas.

The only parameter unaffected by light was the ratio of crown width to individual height. In shaded areas, there was no evidence of plagiotropism, which is the growth of lateral branches towards the light.

The growth dynamics and health status of silver fir cultures indicate that the best approach for renewing fir trees is at the edge of the adult stand. This position offers protective benefits that promote faster regrowth of the culture, resulting in overall better health and a reduced incidence of plagiotropism.

The paper “Growth and health status of open-grown and shaded silver fir (Abies alba Mill.) plantations in the Beskydy Mts” (Růst a zdravotní stav výsadeb jedle bělokoré na slunečných a zastíněných stanovištních podmínkách v Beskydech) can be downloaded here.

Authors: Jiří Kadlec, Kateřina Novosadová, Radek Pokorný, Mendelova univerzita v Brně, e-mail: jiri.kadlec.uzpl@mendelu.cz

Prepared following the original by Jan Řezáč, VÚLHM, v. v. i., e-mail: rezac@vulhm.cz