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Active tending of Silver fir young stands increases their vitality

Over the last century, silver fir has experienced significant fluctuations in vitality and health. Combined with inadequate management practices, this has resulted in a decline in its presence in forests, not only in our country but also in Spain, Italy, Romania, Slovenia, Croatia, and Slovakia. However, in recent decades, the health of the silver fir has been improving, particularly when compared to Norway spruce or Scots pine. One major factor hindering the fir’s faster return to its suitable habitat is severe damage caused by wildlife.

Photo: In artificially established gaps with fir trees, the height growth accelerates quickly. Without proper tending, there is a risk of thinning and crown shortening. The archive of VÚLHM, VS Opočno

The silver fir’s ability to tolerate shade is crucial for its silviculture. In forestry management, this characteristic can help identify young stands that have naturally emerged and developed beneath the canopy of the mature trees.

A similar approach can be applied when underplanting or undersowing fir trees beneath mature stands, such as spruce or pine, or in so-called preparatory stands like birch or aspen, as long as the shading is not too intense or sudden. In these mixed-species stands, the necessary tending measures may not be as urgent or costly.

Currently, there is a low representation of silver fir, particularly in mature stands. Therefore, we cannot depend solely on natural regeneration, underplanting, or underseeding. Direct planting in smaller, partially shaded areas is an essential alternative for increasing the presence of this tree species.

When stands are created by planting in gaps or small clearings, as well as in areas with quickly or sporadically developed growth, we can no longer depend on spontaneous differentiation. Therefore, neglecting active cultivation becomes a risky choice.

Photo: In the gaps created during the combined regeneration of silver fir, the absence of the mother stand leads to accelerated height growth. Without proper tending, there is a risk of thinning and shortening of the crowns. The archive of VÚLHM, VS Opočno

Silver fir grows very rapidly in thickness and height during its unscreened new growth phase, leading to increased competition among the trees. Similar to spruce, this intense growth raises the risk of crown shortening and thinning, thereby increasing the slenderness quotient.

For Norway spruce or Douglas fir, tending models that involve significant intervention during the crown formation period have been successful in the long term. However, these models disrupt not only the horizontal canopy but also the vertical canopy. This disruption is not suitable for fir trees due to their ecological requirements, necessitating a different approach for their tending management.

The goal of young fir trees tending is to maintain as much diversity as possible within the stand groups. Tending practices should focus on promoting the growth and health of promising individuals by ensuring they have adequate crown length and uniformity, while also preserving at least a partial vertical canopy.

Photo: In artificially established gaps with fir trees, the height growth accelerates quickly. Without proper tending, there is a risk of thinning and crown shortening. The archive of VÚLHM, VS Opočno

In artificially created gaps where fir trees are planted, height growth quickly accelerates. However, without proper tending, there is a risk of crown thinning and shortening. Conversely, neglected fir cultures exhibit significant crown shortening and thinning. The archive of VÚLHM, VS Opočno.

Experience with tending the youngest fir cultures in our area is currently limited due to their low representation. To address this, scientists from the Opočno Research Station, VÚLHM, v. v. i., established experimental plots at eleven locations. They monitored the development of these plots after various interventions to determine how tending affected the growth in thickness, slenderness quotient, and crown ratio of the trees that were released.

They published their findings in an article titled “Effect of first thinning on fir thickets” (Vliv prvního výchovného zásahu na jedlové mlaziny) which appeared in the journal *Forest Research Reports*, issue 4 of 2024. This study was conducted as part of the NAZV project QK1910292, entitled “Procedures for the support of silver fir in the forestry of the Czech Republic.”

A pair of plots was established at all experimental sites, with each plot containing 1,000 promising fir trees marked by the scientists. The criteria for selecting these promising trees included their good health, lack of damage or deformities, well-developed crowns, and an approximately even distribution across the plot. In one plot of the pair, the selected trees were released from 1-2 competing trees, while the other plot (the control) had no such release.

Photo: If the green crowns of promising individuals in a young stand are still sufficiently long at the time of intervention, competitors can be eliminated by shortening these trees to a height of 1.5 m. This method helps maintain the desired vertical canopy for silver fir. The archive of VÚLHM, VS Opočno

The initial results, evaluated 3-5 years after the tending intervention, indicated that these interventions in most locations led to an increased growth rate in the thickness of the released trees. This improvement was also evident in their stability, as shown by an enhanced slenderness quotient (the ratio of height to nominal thickness). Considering that the young trees are currently experiencing a phase of rapid height growth, it is likely that the differences between the monitored variants will become more pronounced over time.

The research findings highlight the significance of initial tending interventions in silver fir stands. These interventions promote thickness growth, enhance stability by reducing the slenderness quotient, and help maintain crown length. As a result, the desired vertical canopy of the young fir stand remains largely undisturbed.

For young silver fir cultures with a top height of 5 to 10 meters, growing outside the influence of the mother or preparatory stand (or those that have been prematurely screened), a suitable approach is to release dominant firs at a density of about one thousand per hectare. If the living crowns have not yet shortened significantly by the time of this intervention, release can be achieved by shortening competing individuals. This method can effectively support the maintenance of the desired vertical canopy in the coppice.

Based on the results obtained, tending interventions can significantly support growth and promote the desired differentiation of silver fir stands as an adaptation measure. This is especially true for mixed stands, where neglecting young growth often results in the loss of the fir component. Additionally, we cannot overlook the positive effects of early tending interventions, which also help to improve the stand environment, such as enhancing precipitation supply, among other benefits.

Paper „Effect of first thinning on fir thickets“ (Vliv prvního výchovného zásahu na jedlové mlaziny) can be downloaded here.

Authors: David Dušek, Jiří Novák, VÚLHM, v. v. i., VS Opočno, e-mail: dusek@vulhmop.cz

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