A month after the storm of December 17, when an early morning of climatic fury made the City wake up with more than 900 fallen trees, branches that crushed cars, destroyed house fronts, threw high voltage cables and cut 400 streets, the evaluation of those damages today allows us to propose changes in the Buenos Aires trees.
But in order to be better planted in the face of the next event, which is "expected", due to the effect of climate change, we are not going to look at the forest but at the tree. It will go to precision.
The decision-making on the trees that were left standing and those that will grow in the future, will be de-leafed from solutions applied in the capitals of Europe, and the issue will be well underpinned by the Buenos Aires native.
As confirmed to Clarín by the Ministry of Public Space and Urban Hygiene, 10% of the 958 fallen specimens still need to be removed. If we talk about branches, the figure rises to 5,000, and 3,000 had significant damage.
Agronomía, Palermo, Villa Pueyrredón, Chacarita, Villa Ortúzar and Saavedra are among the most affected neighborhoods.
The destruction left by the storm on Avenida del Libertador and Kennedy.Photo: Guillermo Rodríguez Adami
One Tree at a Time
The City has a detailed plan for remediation of lost species, depending on the type of tree and the best time of year for planting. But what was actually triggered was a strong process of reviewing, analyzing, and "balancing-compensating" the damaged trees. One at a time.
"The modification, to reduce the impact in future storms, would be some kind of change in the maintenance of the trees, not in the species, which we already have defined in the tree plan and we know how they behave. We didn't make a mistake with them," Jorge Fiorentino, manager of maintenance of Buenos Aires public trees, told Clarín.
Three species grow mainly in the City, and none of the three is native.
There is the ash tree (American, it is the one that marks the most presence), the banana (guilty of spring allergies) and the linden tree (with its yellowish and very fragrant inflorescences).
Why won't there be a change in the type of trees? The fact is that its prominence among the falls, explains the expert, "was a quantitative question", not a qualitative one.
An image of the hours after the storm in the City of Buenos Aires. Photo: Télam
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All three species had an acceptable response in the storm. And while ash and banana accounted for more declines (for a matter of numbers), linden much less. It's a tree that turned out to be a champion. Something that surprises and gratifies us, because we are committed to having a significant number of lime trees in the City," says Fiorentino.
What does this (world) champion tree look like? It is a hybridization of the American species with the tomentose subspecies (Petiolaris), thus, it does not have a natural place of origin. It grows very slowly while young, and in its adulthood it exceeds 20 meters in height.
The decisive factor in deciding whether to plant more is the way in which it grows upwards. It has a conical, subglobose, broad, compact crown, with upper branches obliquely ascending and erect, and lower branches inclined downwards, is the technical description.
"We are going to keep the banana tree at the current level, and we are going to reduce the ash tree little by little from the plan, because there are too many in the city and there are better species," says Fiorentino.
Among the species that generate the most incidents – as in 2012, when a tornado affected 8,9 trees in communes 4 and 000 – are paradises and maples.
Now they are looking for the trees to be better balanced to avoid the so-called sail effect. Photo: Télam
"These are trees that have not been planted for several years. They don't perform well. They hollow out, they don't resist diseases, like fungi that eat wood. We are removing them, as far as possible," he says.
The change in the porteño trees
As these three species are "well known", the change in the tree plan goes in another direction: towards the resilience of trees to climate change.
"Possibly, the change we make, in some situations, is to modify some pruning trend," says Fiorentino.
After the storm, "excessive pruning" was the cause pointed out by environmental and neighborhood associations such as Stop Mutilating Our Trees, which on Instagram detailed that most of the "green and young trees" fell because they had a typical Buenos Aires shape: "palm tree or feather duster", a slenderness that would not allow them to maintain balance in the face of strong winds.
So far, Fiorentino responds, the City's pruning system "seeks to intervene as little as possible in the trees, maintaining the canopy, which provides shade and provides all the prosystemic services (from increasing humidity due to tree transpiration, to absorbing polluting gases)."
By developing an excessive slenderness, the specialist remarks, if the crown "is too globose", the tree becomes unbalanced, which makes it very vulnerable to weather events.
"They are very high, the crown is very high, out of scale – because they were planted at a time when the urban reality was different – and that makes them more vulnerable to the sail effect (the movement of gusts that could knock them down)," he continues. In these cases: "Everything that needs to be intervened will be intervened."
But, he clarifies, the change in pruning (either intensifying or decreasing it) would be in certain urban areas, where trees grew under these "uncontrolled" conditions. The pruning system will not be modified in its entirety.
"We are going to go to specific cases, very detailed, with a scalpel. Tree by tree, to see where you stand. There are some that were left standing, such as the tipas, in the woods of Palermo, which are unstructured. Trees are very resilient, scrambling to survive almost anything. If they are standing, as also happened in Tres de Febrero Park, we have to go and see each one. To balance them, reformulate their cups," he concludes.
Tree Tolerance Levels
Each tree species has certain levels of tolerance to stress situations, such as extreme temperatures, droughts, floods or carbon dioxide concentrations. Ana Beatriz Guarnaschelli, assistant professor of the Chair of Forestry at the Faculty of Agronomy of the University of Buenos Aires and director of the Center for Trees and Urban Forestry, explains it to Clarín from the academy.
"Weather irregularities and severe storms alert us to the need to take immediate care of current urban trees and those we will have in the future. Under the prevailing environmental conditions (with the variations that occur in climate factors) it is appropriate to carry out evaluations of the behavior of the species that make up urban trees, paying special attention to their ability to acclimatize to the new scenarios and, on the other hand, to identify possible alterations that would lead to the need for replacement. says the agronomist.
Urban green cover levels, he says, "need to increase" and to do so "more trees need to be planted in better places. Trees must be managed from an early stage, improving the architecture and correcting the defects, which will lead to better specimens in their adulthood."
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