Increased biodiversity through mixed forests

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​Mixed forests effectively increase the biodiversity of forests, and they are also more resistant than forests consisting of a single tree species to damage caused by climate change and other factors.

On an appropriate site, they also grow at least as well and in some cases, even better, further enhancing carbon sequestration.

My schedule was suddenly cleared of both work and other trips because of coronavirus restrictions. Exceptionally, I’ve also had time for seedling management work in my own forest. The weather has been favourable for working in the forest, and at the same time, I’ve been thinking about how forest management has changed over the decades, and how the change is visible in the forests.

One of the most significant changes in forest management has been the switch to favouring mixed forests in commercial forests. When I was starting my career in forestry, Finnish forest management was seeking high efficiency and rationality, which led to the creation of forest stands with a single tree species for the most part. The main tree species, either spruce or pine, depending on the site, was favoured in seedling management and first thinning, and deciduous trees were only left in open spots.

The guidelines have since shifted to favouring mixed forests, and this is also already visible in practice in my own forest. I just completed clearing saw work on a seedling stand that I planted nine years ago. The seedling stand, which grows on lush ground, is already nearly five metres tall. I originally planted half spruce and half pine as mixed cultivation. In addition, after the seedling management work, naturally growing silver birches, as well as some aspens, alders and rowans, were left to grow in the stand. There are retention trees growing in a swampy depression at the edge of the stand; I left that area with its large aspens untouched. With the undergrowth, it has formed a fine protective thicket for animals.

The end result looks good – at least to me. I also believe that the young, well-growing mixed forest will become considerably more diverse and resistant than its predecessor, a single-species spruce stand that was planted in the 1960s in an alder grove serving as pasture for cows, and managed according to the guidelines of the time. The end result was a very sturdy and tree-heavy pure spruce stand, which began to suffer from snow and wind damage, as well as the bark beetles that followed. A few dried trunks still remain as reminders of the spruce stand.

Mixed forests effectively increase the biodiversity of forests, and they are also more resistant than forests consisting of a single tree species to damage caused by climate change and other factors. On an appropriate site, they also grow at least as well and in some cases, even better, further enhancing carbon sequestration. Growing a mixed forest isn’t difficult, and it enables the simultaneous use of both well-growing cultivation material for domestic tree species and naturally growing seedlings.


Source: Metsä Group