The fascinating thing about trees and forests is that there are always rival opinions about them. This quip of forest historian Oliver Rackham becomes topical in the 1990s through various visions of our prehistoric landscape as a reference for “wilderness.” While some propose a park landscape with trees, others swear by a dense forest with holes. The hypothesis that the northern half of Europe was once covered with dark forests has already been questioned by ecologist Francis Rose in the 1960s. After all, he observes that many lichens only occur on freely grown trees. This contribution leaves the true face of our primeval landscape in the middle. She does discuss the natural value of trees that can grow and grow old in an open, light-rich environment.
Icons
Old, freely grown trees are today recognized as natural, cultural and literary icons. Conservationists are highlighting their importance for biodiversity, as is the case, for example, with the impressive, widespread oaks on some Swedish island groups. It is less known that pines can also develop into beautiful free-standing trees (see photo). Preventing such icons from being cut down or overgrown by other trees is an absolute priority for some. This popularity contrasts with a past in which open landscapes with free growing trees were converted into fields, grasslands, treeless heather and plantations of dense trees.
Large and domed crown
In principle, a free-growing tree can grow old and die without competition with other trees throughout its life. As an adult it usually has a relatively short and very thick trunk with branches that spread almost horizontally, especially in the lower part of the crown. In general, its crown is large and dome-shaped. In order to be able to develop from seedlings to a full-fledged free-growing tree, oaks or pines are planted at a distance of 30 to 40 m from each other. Sometimes even more space is created at a later stage by strategically removing sick and less vital specimens. Although trees can also grow up freely without human help. Sometimes due to a “lack” of human intervention and shelter from grazing by thorn bushes (Vera 1997, 2000).
Vast, deep and long living root system
The roots of a freely growing tree can extend to roughly twice the radius of its crown. Even at 50 meters from the trunk of a fairly grown oak, there may still be roots with a diameter of 2.5 cm. While the majority of the roots are in the top 12 inches of the soil, some can be looking for water in crevices ?? reach a depth of nine meters. Apart from that, a free-growing tree develops sizeable support roots in response to continuous exposure to the wind. The root system of a healthy oak can span a span of roughly 500 to 1000 years, spreading and contracting according to the age and quality of the environment.
Differences in architecture and wood volume
Let us dwell for a moment on the different architecture of freely grown trees and forest trees. Typical forest trees grow in a highly competitive environment and usually have a long, narrow trunk and crown. Nevertheless, they appear to be able to produce relatively large volumes of wood. The average volume of wood in the trunk of a forest tree is even greater than that in the trunk of a freely grown tree of the same age. A freely grown tree, however, has a larger total wood volume. Much of it is present in large, spreading branches. Such branches also provide larger and more varied surfaces compared to the narrower, more simply built forest trees. In addition, forest trees do not need strongly spread support roots as they support each other when standing close together.
Cooperation and competition in forest trees
Thanks to the coexistence with fungi and microorganisms, which bring in water and minerals from elsewhere, forest trees can settle for a small underground root zone. In addition, their intensely entwined roots can allow the exchange of water and nutrients between individual trees. Shade-tolerant forest trees appear in many cases to grow up just as well as free-growing, light-loving trees. Nevertheless, Forest Trees Turn Out In Times Of Stress ?? like prolonged drought ?? less able to maintain. The situation in the root zone of a group of forest trees is similar to that in their crown roof, where the individual crowns converge. In both cases, there is intense competition for each spot, possibly leading to reduced stress resistance.
Research on oak health
Oak health appears to be proportional to their distance from neighboring competing trees. Likewise, mortality is increasing with the competitive pressures of younger, neighboring trees. The growth of leaves and roots is significantly greater in a freely growing oak. This higher productivity is due to the efficiency of a domed crown. The larger the leaf surface, the more photosynthesis and the greater the leaf mass. Thanks to this reserve, a freely grown tree can recover better from drought stress or a temporary lack of food. Its increased root production, especially the growth of its supporting roots, creates places where all kinds of insects and fungi can thrive.
Releasing nutrients by digesting wood
The natural value of forest trees increases significantly when – in collaboration with invertebrates, fungi and micro-organisms – they are given the opportunity to produce rotting wood. This both through age and through competition with powerful neighbors. In dense forests with shade-tolerant trees, the closer together, the stronger the competition, the more death, the more dead wood, the more rot. And then: the greater the availability of nutrients that are released during rotting. In fact, you can replace the verb rot here with digest. After all, it is the digestion of wood by fungi, bacteria and other micro-organisms that ensures that mineral nutrients are released from the wood. In the absence of human intervention, which unfortunately often is not the case, this creates a sustainable source of nutrients for “the survivors”: from seedling to old tree.
Difference in rot, difference in habitats
A fallen forest beech of about one meter thick can disappear into the soil after 30 to 40 years due to rotting / digestion. The rotting wood of freely grown trees will also form the soil of tomorrow. However, dead wood in the open, windy and sunny environment of a freely growing tree breaks down much more slowly. The heartwood, dried by exposure to air, remains sturdy for a long time and the outer layer can even last for centuries. Even a fallen 60 cm thick oak branch, which mainly consists of the resistant heartwood, can still be present in open and sunny conditions after 50 to 100 years. The difference in speed at which forest trees and free-standing trees rot, creates a difference in habitats: the “habitats” to which certain plants and animals are bound.
Hollowing out with the help of insects
Both forest trees and freely grown trees can become hollow when fungi and micro-organisms start to break down the inner wood. We have already seen that such rotting processes are much slower in the open environment of free-standing trees. However, the hollowing out of partially dried out wood can be facilitated by bark beetles and forest ants. In warmer climates, that’s usually the job of termites.
Mini ecosystems in a hollow tree
Hollowing out does not only ensure the availability of nutrients in the wood. The droppings of bats and birds can also contribute here. The sheltered space of a thick hollow tree protects these nutrients from leaching from heavy rainfall. The nutrient-rich cavities of different sizes attract different organisms. This includes mini-ecosystems. that develop in water-filled cavities. This both in the trunk, in the larger branches and between the supporting roots of freely grown trees.
“Fly agarics” as a food source for animals
The fruiting bodies of long-lived (!) Fungi with which free-growing trees live together for a long time can also play an important ecological role. An example of this are the soft, fleshy mushrooms that fly out from when the weather is too harsh for most other insects. In this way they provide food for birds, bats and small rodents late in the year.
Old tree species
Some types of plants and animals are bound by an age-long continuity of forests or forest-related environments: with trees, shade, moisture and rotting wood nearby. Not only old forests, but also freestanding trees that have the chance to become very old can provide this. Such forms of continuity include opportunities for wingless forest beetles, which are difficult to move to other free-standing trees or forests due to their “disability”. In this context, people often speak of old forest species. But in fact it can also be old tree species that thrive thanks to the long life and special architecture of freely growing trees.
The fruits of a freely growing tree
The natural value of a tree that is allowed to grow freely is due to a long and healthy life, with hardly any neighbors stress, a good cooperation with long-lived fungi, slow decomposition processes and a diverse range of surfaces and cavities. . In addition, a freely grown tree usually bears much more fruit than its forest equivalent. Dense forests of fruit trees simply do not exist! Just look at the difficulty with which wild apple trees try to survive in old forests if they are not “exempted” by cutting down neighboring forest trees. For this reason alone, our ancestors must also have recognized the importance of freely growing trees.