The thinning of forests is a natural process as much as it is an anthropogenic one. It has been carried out since the emergence of trees and forests as organisms and communities by the effects of wind. Wind plays an important and natural role in regulating the size and structure of many stands of trees. Human beings, either as individuals or on behalf of forestry agencies also play a role in the thinning of forest stands. There are several reasons for the practice of thinning forests by humans. These reasons, and the subsequent benefits of the practice are mirrored by the impact of natural, wind-blown trees.
1)Thinning increases the growth rate of trees.
In commercial forest plantations the juvenile trees, lets say for example Sitka Spruce, are planted very densely, perhaps as close as one meter apart. As they grow they compete with each other for nutrients from the soil and sunlight. As the stand increases in age and subsequent size, due to the competing nature of trees they will ultimately begin to grow with thinner girth but taller in height, henceforth competing to get the sunlight. This competition will leave commercial forestry operation with trees which do not have adequate girth to fulfill the needs of their markets, for example producing timber for building. This is obviously not in the best interests of forestry operators so thinning is seen as the best possible solution to getting rid of this problem.
Once the trees have been thinned this opens up the stand, allowing more space between individual trees and reducing competition. This will allow the trees to grow with increased girth and thereby increase their value and the health of the stand.
2)Thinning can lead to increased levels of nutrients in the forest.
The thinning of trees can lead to an increase in the available nutrients in the forest. If the brash (branches, stems, needles etc) is left on the forest floor, as is common practice in the U.K. this can allow the nutrients contained within to leach back into the soil, and therefore increase the fertility of the stand. The root system may also be left in the ground after the trunk of the tree has been harvested. This will also return large amounts of nutrients into the ground. In the case of whole tree harvesting, the tree, stems and root system are all removed, however, in order to prevent the whole sale removal of nutrients from the forest, the tree will be left in-situ in the forest in order to dry out, and therefore shed it’s branches and needles, allowing the return of vital nutrients to the forest.
3)Thinning can have beneficial impacts on levels of biodiversity.
Thinning in dense forest plantations or over grown natural plantations can have beneficial impacts on the levels of biodiversity within the forest. The Scottish Capercaillie, a large woodland grouse, is a prime example of a species that benefits hugely from the thinning of forests. The Scottish Capercaillie, only five years ago was critically endangered, with only an estimated 1,000 individuals remaining. The population crash, from 20,000 in the 1970’s to 1,000 at the turn of the millennium, can be attributed to poor breeding success due to the loss of habitat and increased predation. These factors were tackled by a conservation project, “Urgent Conservation Management for Scottish Capercaillie”. This project aimed to increase the amount of available habitat for adults and juveniles, included in which was the provision of shelter from predators. Thinning of the Capercaillie’s densely overgrown woodland home provided them with food and shelter.
The main food plant of the Capercaillie is the blueberry, which grows on the forest floor. The adults feed on the berries and the chicks feed on the insects to which the blueberry plant plays host to. In dense forest stands, not enough light can penetrate through the canopy to provide the right conditions for the growth of blueberry. This therefore removes a major source of food for the Capercaillie and their chicks. Without the insects which thrive on the blueberry plant, the chicks will not receive enough protein and will die, thereby decreasing breeding success. In addition, the rate of adult mortality can be increased by the birds flying into trees within dense forests. Thinning will open up the stand and reduce trees strikes and subsequent adult mortality.
The brash provided by thinning operations in dense forests will also be able to provide the Capercaillie and the chicks with shelter from both adverse weather conditions and predators, thereby increasing the chances of survival and breeding success.
The Capercaillie is what is known as an “Umbrella Species”. This means that the efforts to conserve the Capercaillie, be it through thinning or other habitat management techniques will also have beneficial impacts on many other species inhabiting the same environment, e.g. Red Squirrels and The Hairy Wood Ant to name but a few.
4) Thinning can keep people safe.
Thinning operations can also have beneficial impacts to humans also. The removal of some trees in a forest stand may reduce the likelihood of the spread of forest fire. Also, by the removal of dense stand growth there is also the reduction of the likelihood of injury being caused by the stems and branches of the trees. If the trees are competing for sunlight and nutrition, this means they will grow as tall, as quickly as possible. To do this the tree must sacrifice it’s expansion of girth in favour of height. In doing so the tree becomes taller and more susceptible to being blown over by the wind. A tree which is susceptible to being blown over by the wind is a threat to humans, be it through damage to homes, vehicles or personal bodily harm
Thinning is a necessary practice for all of these reasons. Any plant which is growing in a dense stand is going to be competing with those around it. Competition will mean that sacrifices will be made, which in turn may have detrimental impacts on the individual itself, not to mention the sheer quantity of nutrients being stripped from the forest soil. Thinning can have beneficial impacts on the well being of humans as well as forest health, in the form of the growth of trees, the nutrient level, the biodiversity.