OSSERVARE NEL BOSCO

The wood hides many secrets and is one of the most complex ecosystems that we can find in nature. Walking in the forest we can observe many elements that characterize this habitat, whose protagonists are the trees, starting from their branches.

The leaves are essential for life on Earth: the organic materials they produce are vital both for insects and mammals. Thanks to chlorophyll the leaves can in fact combine sun’s energy, water and soil nutrients and carbon dioxide. They synthesize well the basic elements for the creation of living beings. This process is called photosynthesisa real production of renewable energy.

The waste substances of the leaves are oxygen and the water vapor that replenish the natural biochemical cycles.

Thousands of animal and plant species are interested in the leaves and leave delicate or destructive signs of their passage. The fall of the leaves in autumn is a strategy to protect from the cold as they fall before freezing: the leaf produces a separation layer between its stalk and the twig; when the wind makes the leaf drop it does not appear a wound but already a scar.

Every year an adult tree produces an average oxygen excess of 15-30 kg; breathing in an adult person consumes annually from 200 to 300 kg of oxygen, a quantity produced by approximately 12 trees.

The leaves are green because chlorophyll absorbs the red parts of the light spectrum: the green complementary color is reflected and it is the visible one. In autumn, however, when days are shorter and the temperature decreases, the plant gets back some precious substances contained in the leaves. The green chlorophyll is then replaced by other pigments, yellow, red, brown. The substances (sugars and proteins) are “stored” and used in spring to start growing when the leaves are not still active.

To know if a leaf is simple or compound is enough to know whether there is a bud at the base of its stem (stalk). If there is none it is not a simple leaf but the small leaf of a compound leaf (ash, rose hips, elderberry).

The branches are the forest framework, they are large and long and give the tree its particular shape, stretching every year with new sprouts; intertwining together they delimit the area of ​​the crown (phyllosphere), a protected space within which it develops that particular climate that characterizes the wood, a pleasant and sheltered environment. When you notice a tree without branches on one side it means that most likely it was once joined to another tree. Growing up so closely the branches that were between the two trees were deprived of light, and dried. Very often on the branches there are also bite marks: if the traces are thin it is likely they belong to small rodents while if they are wider they may belong to roe deer.

The bark is the tree skin, its protective armor. It protects the internal tissues of the plant from all kind of threats: cuts, aridity, attacks of fungi, insects or other parasites that breed within the tree. It contains and protects the elaborated lymph transport system that comes from the leaves.

This nutritional juice flows through a layer of cells placed against the wood and feeds all parts of the tree.

Each species has a different bark that changes its appearance over the years: in the beginning is smoother then it cracks, flakes apart or falls in pieces as the tree gets older. To determine the age of a bark you just have to count the circles on a piece of bark.

It is called “twisted fiber” when the wood fibers grow with a spiral shape. There are some insects that burrow mazes under the bark: this animal is the spruce bark beetle and it causes serious problems in the coniferous forests; instead when you notice holes around the trunk it is the woodpecker’s fault: it loves rough sap in early spring.

Observing logs and stumps along the trails you can discover so many curiosities: the annual rings are formed by light-colored spring wood that grows between April and June, and the dark-colored summer wood that grows from July to October. If you compare the thickness of the spring wood with the summer one you will see that in spring the tree grows quickly, in summer it strengthens the new sprouts and new ring and in winter it rests.

The rough sap goes up from roots especially through the latest rings. The elaborated sap instead goes down from the leaves to the roots to feed all living parts of the tree. During the night the photosynthesis process is interrupted due to lack of light. Trees continue to respire, consuming oxygen and expelling carbon dioxide. The nutrient elements produced during the day are distributed and stored in the various parts of the tree, which digests at night what assimilated during the day. When a tree bends the pressure inside the trunk is not uniform: there is a very strong compression on the lower half, while the upper part of the trunk undergoes a not less considerable traction. To resist and grow vertically in the most effective way, the coniferous trees produce wood and widen on the side subjected to compression, while the broad-leaved trees do it on the traction side.