Control over tree stability

In the management of urban public green areas, particular attention is paid to the periodic control of the tree heritage which takes place through the VTA method (Visual Tree Assessment, i.e. a technique for visual evaluation of the structural conditions of the tree).

The collection and analysis of available data on trees is an important step both to promote and improve public green spaces and to guarantee safety conditions for the community and individual users. The periodic control of trees has the aim of evaluating the phytosanitary conditions and stability of a tree, especially with regards to the risk of crashes or collapses.

The verification requires an important degree of specialization on the part of the technicians in charge with the use of elements of plant pathology, entomology, botany, statics and wood mechanics.

The felling of trees to ensure public safety represents a last resort option to be resorted to only when verified conditions of decay emerge which compromise the stability of the trunks with a high risk of falling.

Tree maintenance is carried out using the VTA method, an internationally recognized procedure for ascertaining the state of health of the trees present. This type of evaluation is widely used in the sector and guarantees adequate accuracy requirements. The VTA is the result of the studies carried out by prof. Claus Matteck at the Karlsruhe Research Center in Germany and from the experience gained in Forest Arboriculture by prof. Alex Shigo in the United States.

The methodology identifies and analyzes all the symptoms that the tree shows in the presence of anomalies in the foliage, trunk and root system, allowing the identification of trees at static risk. In this sense, the guidelines indicated by the protocol of the Italian Arboriculture Society are followed. 

The plants at greatest risk of falling are subjected to a series of instrumental analyzes thus obtaining quantitative indications and the localization of the damage to the internal tissues. For all trees checked by an agronomist and/or forestry technician, a risk class is assigned with the interventions to be carried out to ensure safety.

In any case, in the management of the urban arboreal heritage, the Municipality of Milan complies with the laws and regulations in force.

Class A

Trees that do not present structural defects are included in this class. The biometric form indicates the future checks and agronomic interventions to be carried out. The probabilities of entire trees or parts of them falling are linked to statistically unpredictable phenomena.

class B

Trees with mild structural defects are included in this class. The probability of falling and crashing can be traced back to class A. Please remember that the defects found may worsen over time and that it is therefore necessary to prepare and plan the necessary maintenance interventions.

Class C

The trees registered in this class have significant bearing and structural defects which can quickly worsen if the solutions identified such as pruning and consolidation are not implemented, thus moving to a higher risk class.

Class C/D

This class includes trees that have serious structural defects and in which the risk of crashing or overturning is very high. In this sense it is necessary to promptly resort to all technical-agronomic procedures aimed at reducing risks, placing the trees in a safe condition so as to bring them back to the lowest risk class. In any case, it is advisable to arrange periodic checks of a semi-annual or annual nature.

Class D

Those plants that present very serious morphological and structural defects belong to this class. The risks of falls and crashes are very high and the use of conservative and preservative techniques is considered impossible. Consequently, the plants must be cut down and replaced as soon as possible.


 

In the attachments to this page it is possible to download the list in PDF format of class D plants authorized for felling and pruning for safety purposes for the current month and for previous months and years. 

Based on the VTA (Visual Tree Assessment) methodology currently in use, trees included in phytostatic class D are characterized by such serious structural degradation that they do not guarantee their stability and anchoring to the ground as they are not agronomically correctable.

The green maintenance contractor will provide for the preventive posting of information signs, the identification with red paint of the plants to be removed, a preliminary investigation aimed at excluding the existence of birds/bats or other things in the cavities of the trunks and to ensure the presence of technical personnel on construction sites in order to provide any information to citizens. 

The removed plants, with the exception of those considered alien (trees, maples, locust trees, etc.) for which specific replacement will be carried out, will be replaced with new plants belonging to the same species during the current agronomic season, following the trend of the period of the year. 

Before proceeding with the felling, the agronomic technicians of the Municipality of Milan carry out a quality control on the verification activities carried out by the agronomists of the contractor entrusted with the green maintenance service. 

The replacement of felled trees with the installation of new ones takes place in the autumn-winter season because summer is not considered a suitable season for planting new trees.

The replacement is foreseen for all trees with limited exceptions which may concern the plane tree plants for which, if contagion of the fungus Ceratocistys fimbriata - colored cancer of the plane tree is ascertained, there is a ban on proceeding with the replacement for a period of time not less than two years after killing. 

A further exception concerns plants that in the past have been penalized by an excessively narrow geometric arrangement. If they were planted, in fact, they would have regular growth hindered by nearby plants that have greatly increased their foliage, taking away the growth spaces (a circumstance that sometimes occurs in street trees). 

The new trees will have, indicatively, minimum trunk circumference dimensions of no less than 20/25 cm and a minimum height of no less than 4 metres.

The felling operations are dictated solely by the need to intervene on potentially dangerous plants, ensuring the safety of people and things. It should be underlined that these are not intervention plans for the use of public green spaces for the construction of various types of construction such as underground car parks or buildings. 

The residual material from felled trees and that resulting from pruning operations becomes available to the contractor who disposes of it in compliance with current regulations.

In the case of material coming from plane trees affected by the parasitic fungus Ceratocistys fimbriata and by the parasitic woodworm of Anoplophora CLB, the residual traces must follow a particular procedure of delivery to authorized plants capable of guaranteeing the destruction of the pathogens, with the aim of avoiding contagion of free areas.  

The Green Area informs that, in implementation of Regional Decree No. 4379 of 27/04/2010, the territory of the city of Milan, characterized by the presence of the parasitic woodworm Anoplophora CLB, is affected by operations to fell infested plants.

All the felled plants will be replaced with new plants belonging to species not attacked by the parasite within the agronomic season following the felling.

Updated: 22/04/2024