The general directorate of Forests of the Generalitat has launched a first action at the headwaters of the Ter aimed at reducing the density of the forests as a strategy to increase the flow of the rivers. Now the density of many unmanaged forests makes them large consumers of water, which subtracts resources from the natural flows of streams and torrents. Not only do they block water runoff and prevent it from seeping into the subsoil, but leaves and tops intercept rainflow with the umbrella effect, so water ultimately evaporates, is lost, and less arrives flow to ground Catalonia’s forests consume approximately 70% of the water they receive from precipitation.
The need to act in certain forests to gain water flows stems from the realization that many of these masses of trees at the headwaters of the rivers have become part of the problem of insufficient water supply and that the its correct management is an “indispensable” solution to gain the necessary reserves, according to Anna Sanitjas, director general 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 populated with trees has not been the subject of silvicultural operations.
The first major action will be concentrated in the public forest of Espinavell (Molló, Ripollès), at the head of the Ter, a wooded area created from a repopulation about 50 years ago where the pines form a dense and aged mass.
The felling will reduce the excessive competition of trees for water resources. The Bac de Casassa estate, on the Molló mountain, has 200 hectares and work will begin on some stands totaling 61 hectares.
The trees to be felled were marked and selected for this purpose yesterday. The first area where intervention will take place has 2,090 feet per hectare and one out of every four trees will be removed, so there will be around 1,500 feet per hectare, Anna Sanitjas points out.
“In the densest forests, we can get up to 25% more water for the river”, points out the general director. Weak, diseased trees are removed after replanting and priority is given to the maintenance of species in the forest that have sprung up spontaneously 50 years later, such as ash trees, which among the pines of the replanting provide biodiversity.
As the number of trees is reduced, not only will water be gained, but there will also be a forest better conditioned against the risk of fires, healthier and with specimens of greater size and quality.
The work has been made possible thanks to the studies of the Forest Technology Center of Catalonia. The criteria that are applied will prevent erosion on the ground, for example as a result of the impact of a downpour that can wash away the land. This is why it is used in areas with a large volume of trees and not in sparsely populated areas or where there is a high risk of erosion.
The beneficial effects can be obtained shortly after the intervention, since, “even if it does not rain, the decrease in water consumption by the vegetation is immediate, and will leave more water available on the ground, which will increase the chances of this water ending up in the aquifer or the river”, says the technical document on which the plan is based.
The promoters of this initiative emphasize that this method of management does not lead to an increase in CO2 emissions, since the trees that are removed are mostly immobilized as wood products. Sanitjas insists that, “when the competition between the trees is reduced”, those that are preserved will grow in better conditions and will be less vulnerable to fires. In addition, these fellings, if done outside the reproduction and breeding stages, offer the opportunity to create new habitats.
Anna Sanitjas points out that studies and pilot tests have previously been carried out to confirm the knowledge acquired. The plan is being launched for the first time in this Ripollès forest “because it is a public forest and we want to set an example with this action”. Other forests in the Generalitat are being identified with suitability conditions to be able to apply this management.
