Trees in urban areas have a great influence on creating a local microclimate, affecting humidity, temperature, level of sunshine, air circulation – all the factors that make up living conditions that are or are not advantageous for people.

A human being does not put up with long isolation from the nature, so creating ‘green areas’: parks, boulevards, avenues in cities improves living conditions and makes it easier for the inhabitants to relax.

Moreover, trees can be a valuable anti-erosive (from water and wind) protection and have water-retentive properties. They should be grown especially in these areas, that are bound to harmful processes: floods, heavy wind, landslides. Hardly ever do building investments, like roadways and underground works leave natural green areas. These areas are mainly created in the aftermath.

The natural habitat of trees is a forest, where they are subjected to plants and soil interactions, which result in their dynamic equilibrium with environmental factors: where the beneficial microflora is rich, plants grow quickly and healthy. The microorganisms of the roots zone are of the greatest importance: fungi and bacteria, which – throughout association and symbiosis with a plant – create beneficial interactions and support the growth and health of plants.

Urban habitats of trees are principally disadvantageous, or even hostile, for transplanted plants. This is because all the constructions and investments disturb the natural balance.

Benefits of growing trees – planning

Town hall officials are obliged with special acts to create and maintain urban green areas of recreational, pro-health and aesthetic functions. However, ‘caring’ for trees might often be abused, sometimes in such a way, that a tree dies in a few years’ time – this is a way to avoid inconvenient procedure of obtaining permissions for cutting down trees that stand in the way of construction sites.

Choosing species of trees

The main rule is to conform the species to environmental conditions and the plants that already grow in the area. This aims at reducing the level of necessary help and care in the following years.

A general rule is to be careful with introducing foreign species. It is highly recommended to grow rather home species as basic ones, which prepare a habitat and microclimate for more sophisticated and sensitive trees.

It is also beneficial to grow many plants that give out a lot of ethereal oils. However, the oils of coniferous plants have calming influence on human behavior, whilst of the leafy trees – stimulating effect. Similarly, it is recommended to grow plants that cause negative ionization, whose impact on human is advantageous – for example linden, birch and pine.

It is equally important to avoid growing trees or bushes with poisonous fruit in places that are available for children. Such plants include for example: Taxus baccata, lilac, Laburnum, Symphoricarpos albus, Daphne mezereum.

Most trees are tolerant of transplantation. These species include: linden, Platanus, spruce, fir, dwarf mountain pine, Taxus, willow, poplar, red oak. Much more difficult to transplant are: ash tree, Sorbus and oak. Trees that are most difficult to transplant are: pine, birch, robinia, metasequoia, rhus. This is the opinion of the DREWSMOL company (www.drewsmol.pl), which is most experienced in this matter in Poland.

Technology of transplantation – technical and natural conditions

When the upper layer of soil is destroyed, it lacks in nutrients available for plants. This effect escalates due to an autumn habit of removing fallen leaves and cutting the grass, which are a natural nourishment of microorganisms that mineralize organic matter and restore the level essential elements.

Mineral and organic fertilization is not successful as a long-term measure. The best solution is to provide a root system of a plant with an appropriate symbiotic microflora.

The most tangible are mycorrhizal fungi, which establish a connection with a host plant and are supported by association microorganisms. If such a system lives in the roots zone, healthiness and convenience is provided even in extreme conditions.

Why is mycorrhiza and other root microflora so important for trees, especially transplanted ones? The answer to this question must be a complex one, as mycorrhizal fungi have numerous functions. They:

• improve water absorption (due to an extra-root system of filaments the absorbing surface of the roots zone is increased even a few hundred times)

• improve nitrogen usage – also from organic compounds, normally unavailable for plants

• improve absorption of phosphorus, iron and microelements that are very hard to obtain for trees

• protect inertly (habitat competition, stimulation of the immune system) and actively (antagonisms) against pathogenic fungi

• stimulate growth of plants through more effective assimilation

• stimulate propagation through hormones

• increase resistance to frost

• provide better, “lively” looks, which is not an effect of over-fertilization

• improve conditions for growth, regardless of soil alkalinity or acidity

• increase resistance to saltiness of soil

• participate in the creation of soil structure

• have other functions, that are partly unknown and have something to do with detoxification and migration of heavy metals multi-ring aromatic hydrocarbons and in soil

Considering the above mentioned reasons we have to conclude, that mycorrhiza should be used in any kind of non-forest growing trees, particularly trees transplanted to urban areas. Nowadays, it is technically possible, so such tasks are fulfilled in order to save many trees (sometimes even natural monuments) from extinction.

Several rules need to be obeyed during performing such tasks in order to be sure that the transplanted tree will continue its vegetation in new environment.

• Timing
  
  Transplantation needs to take place between the beginning of the absolute rest time and the end of the relative rest time. For leafy trees this means the time between losing color of trees in autumn and creaking buds in spring. For coniferous this is from the end of August (Pinaceae only) after current annual increment in growth becomes a mature wood until the buds grow in spring (end of April).

• How large can a tree be?
  
  Modern technology allows almost every tree to be transplanted. The biggest tree transplanted by a Polish company had a trunk perimeter of 300 cm.

• Technology and the biologic viewpoint
  
  Trees which are going to be transplanted, especially the large ones, need to be prepared for this at least 2 years before. This is making the roots zone (the block that is meant to be taken out) denser. In order to achieve this, the roots that transgress the border of this block are gradually cut. This stage also can include mycorrhization with an appropriate inoculant.

• Remarks
  
  The details are obviously a subject of various scientific works, yet we can mention some things.
  
  A roots system that has been seriously cut is very sensitive, so after transplantation mineral fertilization should not be used. It is beneficial to transplant a tree when the roots zone is frozen.
  
  

Trees are often transplanted into artificial habitats, like urban areas or the green lines near the highways. They have a shock connected with the sudden change of environmental and soil conditions – the bigger the tree, the bigger shock is involved, in case of large, old trees it can last even a few years. In these conditions it is highly recommended to use home species, i.e. these species of trees, that naturally grow in these areas. They are usually better conformed, at least to the local climate. It is possible to help plants acclimatize to new conditions with biological methods, introducing advantageous microorganisms to the roots zone. We should now remind, that the vast majority of large trees transplanted to urban areas come from nurseries that do not mycorrhizate their seedlings. Neither are the trees mycorrhizated during the transplantation, even though they are then being deprived of a lot of their valuable roots. Most often, along with the small roots, mycorrhizal fungous spawn is also taken away, of course if there was any. For all these reasons, mycorrhizating a tree in this conditions might have a particularly beneficial impact on health of a plant.

Summary: outlook for mycorrhization and the use of new technologies It has been proved that all the trees without active, living mycorrhizae are more vulnerable to destructive stress after the transplantation than mycorrhizated ones. The opportunities for mycorrhization depend on the trees themselves:

• trees from nurseries should be mycorrhizated in the early stages of growth, as seedlings.

• if trees from nurseries have not been mycorrhizated, they can still be during transplantation

• trees transplanted to new habitats might have developed mycorrhizae, but in most cases they have not. It is also very important, that these trees are being deprived of more than 80% of their roots, so they also should be inoculated.

To sum up, the process of mycorrhization is particularly important for the transplanted trees. It is connected with all the functions of symbiotic fungous spawn that have been presented in this article. Using this opportunity results in better acclimatization and both active and passive protection against root pathogens.

As a result, chances for successful growth and vegetation increase rapidly, in spite of such disadvantageous conditions like in urban areas, communication lines etc.

Bibliography

1. 
   
   Czerwieniec M., Lewińska J. Zieleń w mieście (Green areas in cities) Inst. Gospodarki Przestrzennej i Komunalnej, Kraków 2000.
2. 
   Pokorski J., Siwiec A.: Kształtowanie terenów zieleni (Creating green areas) Warszawa 1998.
3. 
   Niemirski W.: Kształtowanie terenów zieleni (Creating green areas) Wyd. Arkady, Warszawa 1973.
4. 
   Siewniak M.: Drzewa w centrum miasta. Ogrody, ogródki, zieleńce – nr 1 (Trees in city centres. Gardens. – issue 1),1999; s. 76-83.
5. 
   Szczepanowska B.H.: Drzewa w mieście (Trees in a city) Wyd. Hortpress, Warszawa 2001

A letter from the Botanic Garden of the Jagellonian University in Cracow.

Ericaceous plants (Rhododendron, Calluna, Vaccinium, Erica itp.) are mostly advised to be provided with great amounts of high peat, because the basement soil must have a reduced pH of 4-4,5. It is also often suggested to dig holes and fill them with forest bedding, which is forbidden by the foresters. We have some more efficient ideas which we would like to share with ericaceous plants amateurs.

Having observed the growth and health of ericaceous plants in their natural habitat we can conclude that costly processes of reducing pH are not necessary. It is mycorrhizal spawn that has a weird ability to reduce the level of pH from too high to the optimal one. I can say with a total confidence that it is possible to refrain from digging costly holes and filling them with peat, which can be instead used to enrich the humus and improve the air-water conditions. In order to do this, we should mix the peat with the basement soil - why not to provide our plants with this kind of luxury?

These remarks are result of a few years of experience and our own observations. Obviously, where the plants cannot grow properly it is advised to provide them with natural mycorrhizal inoculum, not to make the soil more acidic through injecting some vinegar, as I have recently read in a newspaper. In their natural habitats, plants (berries in the forest, for example) do not have such problems, as the Mother Nature has provided them with the miracle of mycorrhiza. Should you have any doubts, I have the reference of science authorities who have checkd the pH in my garden.

The plants grow in the soil without additional "soil-enrichement".