Preventing the effects of changing ground levels.
Carrying out various construction works, and above all earthworks, in the vicinity of trees often leads to disturbance of the surrounding ground level. Raising or lowering this level always has a negative effect on the course of a tree's life processes. It always violates the established relationship between soil conditions and the root system and can cause serious damage. Therefore, such work without damaging the tree can be performed to a limited extent or with the use of special safeguards.
Raising the ground level. Leveling Up, that is, the application of a layer of earth or other material, also called backfill, after all, it reduces the access of oxygen to the roots for everyone. Lack of oxygen may cause chemical processes to occur in buried soil, whose products are very often toxic to the root system. Root dieback occurs inside the oxygen deprived zone, the symptoms of which are visible after a short time in the form of e.g.. impaired growth, yellowing, drying and falling leaves, drying of shoots and branches, until the plant dies. These damages may sometimes be of a temporary nature, because the plant adapts to new conditions over time, but they can also lead to the death of the tree.
Drawing. Method of securing the root system of a tree in the event of increasing the level of the environment: a - sand; b - tubes; c - rubble; d - trunk cover.
The degree of physiological disturbance caused by elevated levels of the environment depends on the following factors: the species and age of the tree, overall health, thickness and quality of the embankment, and above all, the soil structure used for backfilling. They are particularly sensitive to burial: buki, oaks, tulipanowce, most conifers; suffer less from being buried: poplar, elms, willow trees, platany, clones and robins. Young trees always have a greater ability to adapt to higher levels than older trees. Sick trees, Broken, with rotten trunks suffer the most. Backfilling trunks with progressive wood infection may accelerate its decomposition. The larger the sprinkled layer is, the more serious are the consequences. Covering with clay has the worst effects, even a layer of several centimeters of which can be completely impermeable to air.
However, backfilling may not have a clearly detrimental effect on the plant, if soil or other material with a loose structure has been used for this, providing access to air and water. Adding a 20-30 cm layer of lumpy garden soil can be considered completely safe, because it creates the conditions, to which the roots can adapt very easily. Even increasing the layer thickness to 50 cm may be the case in certain cases, e.g.. on looser soils, however, this requires a 10 cm layer of coarse gravel first, and then the earth, loosened by adding 30-50% of gravel or coarse sand. In such a case, the trunk must be covered with stones or a layer of crushed stone. Should be added, that even short-term storage of piles of sand or similar materials in the vicinity of trees or shrubs may adversely affect their root system. If it is necessary to raise the level of the tree surroundings, the protection described below can also be used, which gives a great guarantee, that the root system and the above-ground part of the tree will not be damaged. The soil under the tree should be dug at least within the crown, sow a mixture of mineral fertilizers, e.g.. Azofoska in the amount of 0.2-0.4 kg for each centimeter of the trunk diameter. This fertilizer is spread within the reach of the crown. Next, drainage pipes with a diameter of 10-12 cm are arranged in a circular pattern around the tree, at the border of the reach of the crown and radially in 6-8 rows. Such pipes should be laid on a 5 cm layer of coarse sand. Several of these rows should extend outside the circular system 3–5 m in line with the slope of the terrain, to create good drainage conditions. At the junction of the rows with the circle, the same or larger pipes should be placed vertically, to the height of the designed embankment level. The places of connection are showered with coarse crushed stone or covered with stones. It is arranged in a circular pattern around the trunk at a distance of approx 60 cm so-called. dry wall (i.e.. laid without mortar) from appropriately selected stones. The space between the wall and the trunk will be opened and will act as a ventilation channel for the pipe system. To the bottom, at the exit points of the radial rows of tubes, it is good to spread a 20 cm thick layer of gravel, which protects the ends of the tubes from clogging. All horizontally laid pipes should also be covered with a layer of crushed stone to ensure better air access to the soil. Vertical tube outlets, especially in public areas, it is good to wrap with pieces of galvanized or plastic mesh, with small meshes. Before the soil is covered, the crushed stone covering the pipes should be covered with a thin layer of straw or hay, in order to protect the space between the pieces of gravel from backfilling. The space between the trunk and the wall should be covered with an appropriate iron grate and periodically cleaned of leaves and similar materials accumulating there..
If there are several or a dozen trees on the site, the pipe system can be common - combined into one whole, facilitating air circulation in a larger space.