“Pruning can extend the life of trees by tens of years,” said Cllr. Petr Štěpánek and also added that it is more advantageous than the classical revival, i.e. cutting the trees down and planting new avenues.
Greenery forms a city
Grown wood species in themselves represent a biotope, they have high aesthetic and urban value and what is more, they have a sanitary function – they reduce dust levels. Their pruning also has a safety function, as fractured and semi-dry branches can be a danger for people and their property. “Avenues also regulate the microclimate in the streets, meaning that they maintain higher humidity and bring down temperatures during hot summer days. In addition with grass, avenues can drop the temperature by ten to fifteen degrees,” said Štěpánek.
Quarter of a milliard for greenery
“This year, we increased the budget allocated to the cleanliness and greenery by a quarter of a milliard,” pointed out Štěpánek. As far as greenery is concerned, it is managed not only by TSK, but also by other organizations and institutions, e.g. Prague Forest Administration and individual municipal districts. However, a huge amount of trees and avenues are managed by TSK, which e.g. looks after tens of thousands trees along major roads.
We have been planning pruning for a long time,” said the spokesperson for TSK Tomáš Mrázek. “As for Národní Obrany Street, i.e. one of our extraordinary actions, another one was held in Patočkova Street. As far as TSK’s budget is concerned, we have 36 million CZK more for greenery maintenance than we had last. The overall sum is 127 million CZK,” added Mrázek.
Trees in Prague are treated by arborists, i.e. people with adequate qualifications. One of them is Ing. Pavel Wagner, whom we had a chance to interview.
“For instance, the avenue in Národní Obrany Street is specific for its diverse mix of trees, there are old trees as well as young ones, maples and lindens, each of the species requiring a different type of pruning. As far as new avenues are concerned, they are a great example how trees in the city should be planted and looked after. They have good foundations, there are watering probes, the roads are adjusted in such a way that cars do not get too close to the trees. Old trees are a bit of a problem, we have to cut off branches that are too close to houses, so that houses receive at least a little light. In the city, the early care of trees is crucial. Treetops should be balanced, i.e. have only one axis and no defective branching.”
You prune and otherwise maintain alleys. Is it possible to set right mistakes that have been made in old trees or is it better to replace them straight away with new trees?
Not everything can be set right with old trees. Old trees in Prague often lack a single axis and branches grow too close to houses. The situation in Národní Obrany Street is by no means dramatic, though. I think that a gradual renewal is better than one-time renewal, i.e. planting of a new avenue. Gradual exchange makes sense in places where there are individual solitaires. From the cultivation point of view, it does not matter if the neighbouring tree is new or not. However, if you do the same task in a single green belt, then it might be necessary to consider, whether it would not be better to carry out a one-time renewal.
Which tree is ideal for Prague?
In fact, it’s not so clear-cut. There are several stress factors in the city - dryness, firmness and salinization of soils and exhalation. Our national tree, linden, therefore faces problems, but it is relatively well tolerated by silver linden. In its natural habitat, the field maple usually grows in drier areas, so it is suitable for the city but it is not possible to plant field maples everywhere. It is good when there is a certain conception of planting. Generally speaking, it can be said that those trees and wood species that are the first to grow at dumps are suitable for the city. Among these is also rowan, which, however, has a relatively short life expectancy.
How about sycamores, which are now widely plante?
Sycamore adjusts well to the city. Let’s take Paris, where there are many of them. They grow fast and up to large sizes. Look at Koněvova Street, where they have been newly planted. When planting sycamores, it is important not to forget people’s property, as they can block the light that would normally get to the houses.
How long do trees in the city live?
In normal environment, the age of trees is genetically determined. This, however, does not apply to city trees. Do you know what has been happening in a single street over the last thirty years? How many times the underground services have been changed, how many times there has been building going on, or how many times has the surface of the road been changed? All this negatively affects the life of the trees. It is enough when we touch upon the root zone and it can bring down the life expectancy of the trees by tens of years.
When do we use pruning and when felling and planting new trees?
It depends on individual cases. If the whole street is being renovated and the trees in the street are not in a great condition, a total renewal can be a good thing. As for drastic street renovations (from the point of view of trees), it might be necessary to consider complete renewal even when the trees are in a relatively good condition, since after the intervention they might start dying out prematurely. It is sad that in good faith we are trying to save a tree, we fight for it, but in the end, the tree does not survive the intervention. In this case it would be better to plant a new tree? So each case really needs to be considered individually.
What is the perspective for threes in the state the city is today?
At present, several factors have come together. In the 1980’s the care of trees rapidly deteriorated, the 1990’s then brought complete renewals, so it was said that there will be no maintenance, that the old avenues would simply be replaced by new ones. This means that there was a period of 25 years where the trees maintenance was neglected, branches grew in places where cars parked and now it is quite complicated to sort the situation out. At present, we are trying to get over the damage caused over the 25 years. If the present maintenance keeps going in the same way for at least one decade, the trees in Prague will be perspective and we will not have to worry about them much for the next thirty years. But we must not neglect the maintenance anymore.
Tree care glossary:
The aim of a health cut is mainly securing a long term high-functionality of the tree while keeping it in the best possible condition. The cut can be repeated in several-year intervals with regards to the state of the tree. The intervals are usually 8 – 10 years. Health cuts get rid of dry, mechanically damaged, broken or mutually intersecting branches. Experienced arborists can tell, if some branches have been affected by various diseases and pests, and if so, these branches are removed as well.
Reduction cuts are cuts carried out in trees growing near houses, power lines and other obstacles. This type of cuts reduces the trees crown. Those branches that deflect the tree from its centre of gravity are removed as well. The cut has to be done with a lot of care, otherwise it could lead to an uncontrollable crown sprouting.
Pruning is not an easy task. Arborists try to maintain the natural habitat of the tree without permanent deformation. This can, however, prove extremely difficult in the cramped conditions of the city. Reduction cuts can help those trees which are placed in an inappropriate way – e.g. too close to a residential building, without respecting the biological needs of the tree.
Part of the reduction is also correction of branches that block traffic lights and signs or otherwise disturb road safety.
Branches are trimmed exactly following a given technique of a cut, which professional arborists master very well. If the branch needs to be cut off completely, it is done exactly at the border line of the trunk and the branch, so that the cut can heal. When trimming, the branch is cut crossways towards the side of the branch. The remaining branch has to be sufficiently thick to be able to feed the remaining part and to take over the leading function. Dry branches must be removed in such a way so that the living tissues are not damaged.
Binding branches can be very helpful as a preventative intervention, during which those branches that grow out of defective branching are tied together in the tree. Binding also prevents the branches from falling down in case they break. Binding is usually accompanied by the above mentioned reduction cut done to ease the lever acting on the branching.
