The Catalan Government has launched a first action at the headwaters of the Ter aimed at reducing the density of forests as a strategy to gain flow in the rivers. Now the density of many unmanaged forests makes them large consumers of water, and that subtracts water resources from the natural flows of streams and torrents. Not only do they block water runoff and prevent it from infiltrating the subsoil, but also leaves and crowns intercept the flow of rain with an umbrella effect, so that the water eventually evaporates, is lost and less flow arrives. down. It is estimated that Catalonia's forests consume 70% of the water they receive from precipitation.
The need to act in certain forests to gain water flows arises from the realization that many of these masses of trees in river headwaters have become part of the problem of insufficient water supply and that their correct management is a solution. “essential” to gain the necessary reserves, explains Anna Sanitjas, general director of Boscos.
In the main headwater basins of Catalonia, river contributions have decreased between 5 and 10% per decade in the last 50 or 60 years, according to the Catalan Water Agency (ACA), and 70% of the surface wooded area has not been the subject of silvicultural actions to clear the forest.
The first major action will be concentrated in the public forest of Espinavell (Molló, Ripollès), at the head of the Ter, in a wooded area created from a repopulation of about 50 years ago and where the pines form a dense mass and aged. The felling will reduce the excessive competition of trees for water resources. The farm in question (Bac de Casassa, in the Molló mountain) has 200 hectares and work will begin on stands that total 61 hectares.
The trees that will be felled began yesterday to be marked and selected for this purpose.
The first area where the intervention will be carried out has 2,090 feet per hectare and one in every four trees will be removed, so there will be about 1,500 feet per hectare.
“If we remove one in four trees in the densest forests, we can get up to 25% more water for the river,” explains the general director of Boscos.
By reducing the number of trees, not only will water be gained, but there will also be a forest that is better conditioned against the risk of fires, healthier and with larger and quality specimens. The work has been possible thanks to the studies of the Center Tecnològic Forestal de Catalunya.
“Trees consume water and, therefore, if we reduce their number we will reduce their consumption,” summarizes Anna Sanitjas when explaining the philosophy of the plan in progress, before highlighting the conditions of this premise. First, the forest that must be managed has to be really dense, with coverage of more than 80%, and, secondly, it must be located in geographical areas where the average rainfall exceeds 380 mm, since unnecessary deforestation must be avoided or that Soil erosion may be caused if more trees than necessary are cut in a less humid area.
Precisely, the forest management that will be carried out seeks to avoid soil erosion at all costs, especially as a result of the impact of a downpour, which can wash away soil and mud.
Hence, action is taken in areas with a large volume of trees. For this reason, the technicians will ensure, with technical criteria and limitations, that they will act in areas where there is soil stability, and those that are not very dense or have a high risk of erosion will be excluded.
The beneficial effects can be obtained immediately afterwards, "since even if it does not rain, the decrease in water consumption by the vegetation is immediate, and will leave more water available in the soil, which will increase the chances of this water running out." in the aquifer or in the river,” says a technical document supporting Boscos' plan.
The promoters of this initiative highlight that this management modality does not lead to an increase in CO2 emissions because “the trees that remain will be able to significantly increase their capacity to sequester carbon”; and on the other hand, those that are eliminated are mostly immobilized as wood products.”
Sanitjas also argues that it will also be beneficial for the forests, since "by reducing competition they will allow them to grow in better conditions" and "be less vulnerable to fires."
Another advantage of these selective fellings is that if they are done outside the reproduction and breeding stages they will offer the opportunity to create new habitats.
Previously, several studies and pilot tests have been carried out to cement the knowledge acquired. The plan is launched for the first time in this Ripollès forest “because it is a public and we want to set an example with this action,” she tells the general director.
However, other public forests of the Generalitat are being identified in which these same suitability conditions also exist to be able to replicate this same management model.
