By Mariano Sanchez (CSIC)*
Starting from the premise, proven by science and known throughout the world, that the presence of trees in the city is healing, who can go against these living beings to the point of regularly pruning their branches or even cutting them down for a moment? here that infrastructure or hang the Christmas lights?
However, it seems that it is still necessary to stress that the treeswith its structure of branches and leaves, They are a healthy element for people and other living beings.like the birds that nest in them.
Trees to reduce heat islands
Trees in urban environments represent multiple benefits: reduce the heat island effect offering shade and evaporating water, which reduces the ambient temperature; provide oxygen and retain pollution in its leaves; sequester carbon in its branches, trunks and roots; hold the ground with their rootsavoiding avenues of water; increase biodiversity of birds and other associated plants; and embellish the walks with its chromaticism and its flowers.
As an example of the former, a modeling study carried out with data from 93 European cities estimated that a third of deaths attributable to heat islands could be avoided if trees covered 30% of urban space.
On the other hand, the vision of trees and vegetation from hospital windows shortens stays and improves healingas confirmed by studies carried out in the United States and by anyone who, during the pandemic, has leaned out of a window from home and had a tree nearby.
The importance of mature and adapted trees
Likewise, there is no doubt that large and mature trees provide us with more benefits, due to their large number of leaves, than young or smaller trees. Hence, as far as possible, they must be preserved in their integrity when works or pruning are carried out.
When talking about cutting down trees and adding the tagline “it’s that many more are going to be planted than there were” -it is an imitation of the well-known “what comes out for what comes in”-, there are many aspects that are not Those are considered.
One of the most notable is the cultural and human. With the felling, the benefits and the history of the 30 or 50 years that the trees lived in that place will have been lost.as well as the relationship that the citizens established with them during that time: the walks with talk, the meditation, the words lost among the pages, the readings, the glances and the memories.
In addition, at this time when, both in the CSIC’s Royal Botanical Garden and in many streets and gardens of Spanish cities, we detect that some species -such as the horse chestnut (Aesculus hippocastanus), the linden (Tilia platyphyllos), maple (Acer pseudoplatanus)- are losing vitality due to the change in rainfall and humidity in the Iberian Peninsula, having mature trees of 30 years or more, already adapted, is a privilege that cannot be renounced.
Mariano Sanchez (RJB-CSIC).
Better 50 mature trees than 250 young ones
On other occasions, especially when talking about logging, people usually talk about multiplying the number of plantations in the space already occupied by those trees that have been sentenced. It is about squaring the circle; if before there was room for 50, how is it possible that 100 or 250 can be planted in the same place?
Misleading figures are used trying to make it equivalent to changing 50 50-year-old trees for 250 10-year-old trees. However, in arboriculture and for our health, figures and mathematics do not work that way: 50 large, mature trees will always be better than 250 small, young ones.
When planting trees in cities, it must be taken into account that the specimens must be well separated so that, as adults, they do not bother each other. In this sense, the same reasoning that is used with vehicles and their parking lots must be applied: can buses use parking spaces for cars or motorcycles? It has to be coherent with the knowledge of the biology of the trees and, if the species is large, the separation must be great; if its size is medium, the space must be that of a car; and, if it is small, a motorcycle.
Works, felling and trees
For all these reasons, just as technical solutions are sought for certain infrastructures, solutions must also be sought for works that affect trees. From there that any work that impacts urban trees should have a mandatory and binding impact report.
and in any case mature specimens must remain because they represent a future won in front of some young trees that we do not know if they will acclimatize. In the event that they do not, we will have created, where there was none, an area exposed to the sun, which does not retain pollution or provide freshness in the increasingly hot summer months.
The keyword of the future is CONSERVE.
* Mariano Sanchez Garcia He is curator of the Royal Botanical Garden (RJB-CSIC).