Before the summer holidays, when I was looking for forest sites for autumn events, I visited a forestry experimentation area in Pirkanmaa, established by Natural Resources Institute Finland. After nearly 40 years of experiments, the area offers an excellent demonstration of the importance of thinning in periodic cover forestry. While the unmanaged stands were populated by thin, broken and fallen trees, the stands thinned in a timely manner were now home to stately pine trees.
Forest management is a chain of measures in which the actions – or omissions – of the previous phase always affect the forest's next growth phase. Forest thinning should not therefore be considered only as the removal of trees but also as the development of a future forest. In thinning, some trees are removed to give the remaining trees more room to grow. By reducing competition between trees, more light, nutrients and water can be made available for the remaining trees. Increased growth space improves trees’ vitality, and climate change further emphasises the importance of this.
Thinning boosts the growth of valuable log wood
Thinning accounts for the vast majority of felling in our forests. Of all the measures in periodic cover forestry, first thinning is the first to generate income for the forest owner. Above all, first thinning should be considered a forestry measure with far-reaching impacts. It is therefore important to perform first thinning in time to ensure the crowns of the trees do not shrink too much due to competition. First thinning mainly generates pulpwood. Although the income from first thinning accounts for only a small share of the total income earned during the forest rotation period, the timeliness of first thinning is crucial to tree development and the forest owner’s subsequent wood trade income.
Thinning generates raw material for various bioeconomy products that can be used to replace materials made from fossil-based resources. Although an unthinned stand may generate more wood in terms of cubic metres, some of it is lost through natural removal due to competition. After thinning, fewer trees grow per hectare, but they develop into sturdy valuable log wood more quickly. This means the trees remaining in the forest will be more valuable in future felling. In addition, the carbon stored in log wood remains in the wood and the long-lasting wood products such as construction materials made from it for decades or even centuries, also promoting climate change mitigation.
Through their choices, forest owners can influence the future of their forests – not just economically but also ecologically. In thinning, as in other forest management stages, it is important to consider biodiversity. It is therefore important to leave broadleaved trees to grow for the rest of the rotation period, to produce a continuum of decaying wood in the form of high biodiversity stumps, and to leave some of the trees as retention trees that are not removed – not even in regeneration felling. The Metsä Group Plus forest management model is a practical method that pays even closer attention to biodiversity in thinning as well.
My summer visit to Pirkanmaa showed me how big an impact timely thinning has on forest development in practice. Thinning really is an investment in the future – in terms of both forest health and economic return. When thinning is done in a timely manner, paying attention to biodiversity, it lays the foundation for a vibrant forest that generates income and provides value for future generations.