Wood quality. Can you imagine how many factors there are that affect it? It starts with the properties of the seeds, continues with a suitable habitat for the growth of the tree and does not end with the final processing into the form of the selected product. There are many of them and they also include a way to regenerate the forest. In this case, we mean two forms in particular: clear-cut and shelterwood.
The Czech Republic is still dominated by the clear-cut method of management, in which all trees in the defined area are eradicated at once and new trees are planted on clearings. On the contrary, during shelterwood renewal, the new generation is protected by the mother stand, which is gradually felled. And just different farming methods can lead to different wood properties.
Scientists from the Faculty of Forestry and Wood Sciences came to this learning when they studied the density of the wood of the Scots pine, our second most important tree species. The trees came from two localities, where both forms of restoration took place separately. The average samples of wood, the width of annual rings, the density of summer and spring wood and the proportion of summer wood in annual rings were determined on test specimens – 3-5 cm thick discs taken at a height of 1.3 m. All these parameters are important for the final quality of the material.
There was no difference in the width of the annual rings between the trees from the two mentioned forms of restoration. The share of summer wood and the density of annual rings was higher in the case of the shelterwood method, the density of summer and spring wood then showed higher numbers at clear-cutting. What does this mean in the end? The release of the canopy of the mother stand leads to an increase in the width of the annual rings, which usually results in a lower density of the wood and thus its lower quality.
Juvenile wood, which has, among other things, low density, less summer wood, more lignin and hemicellulose, and low cellulose content, plays an important role in clear-cutting. For the resulting quality, it is desirable to reduce its share in the trunks, which, according to some studies, could be achieved by adjusting the spacing between the trees in the stand. In the case of shelterwood regeneration, more trees and growth in the shade of the older generation leads to a smaller width of annual rings.
So which of the management methods is more advantageous? As a result, this cannot be said unequivocally. It is important to know that different forms of restoration produce wood of different qualities, and that the density of the wood can be affected by growing interventions in the stand. Therefore, it is necessary to always think about all the steps of forest management in advance and pay attention to the growth of trees over time in order to achieve the best possible results.
doc. Ing. Aleš Zeidler, Ph.D.
Mr. Associate Professor Zeidler is a member of the Department of Wood Processing and Biomaterials. He teaches subjects related to the construction and processing of wood. His scientific outputs are diverse: he compares, for example, the properties of wood between different tree species, including exotic species, the influence of management methods on the development of wood as a material or the impact of climatic factors on wood density.
Prepared by: Lucie Hambálková