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FORESTRY MANAGEMENT

Fire prevention

 

When we speak of fire prevention, the removal of undergrowth, so-called “wood cleaning”, is the preventive measure that is popularly considered the most necessary. However, “cleaning” is a rather inappropriate term, as this often leads to confusion between typical dense, tangled Mediterranean vegetation and dirt and abandonment. In order to completely remove undergrowth, clearing would have to take place frequently, time after time, because the species involved are, basically, sprouting plants. Such action, besides entailing high economic costs, would generate amounts of plant waste that would be difficult to eliminate.

 

Generally speaking, undergrowth control in the Park is restricted to the sides of paths, the outskirts of urban areas and picnic areas, where the risk of fire is highest. These are the so-called buffer strips, in which the shrub layer and a certain number of trees are eliminated on either side of forest paths in order to reduce the mass of vegetation. The purpose of these buffer strips is not so much to actually stop the fire but to facilitate firefighting work, providing time to manoeuvre and escape.

 

Whilst it is true that to reduce biomass is to reduce combustibility, it is also true that it increases inflammability, that is to say, the ease with which vegetation can catch fire. By eliminating vegetation, we reduce the relative humidity of the air and increase luminosity in the zone. These new environmental conditions encourage the appearance of species that are better adapted to arid conditions, but which are also much more inflammable – aromatic plants, for example.

 

For the same reason, firebreaks are not provided, either. A firebreak can become a corridor along which fire can spread more quickly, as it finds little fuel but very high conditions of inflammability. In accordance with the same criterion, moreover, all the vegetation under high voltage cables is not eliminated, only that which exceeds a safe height.

 

Forestry management activities after fire are generally accompanied by a certain degree of controversy over whether or not dead tree trunks should be removed. We have at the Serra good examples of the regeneration of vegetation in zones where no forestry intervention has been carried out. For this reason, removing burnt trunks is not a priority action, less if we remember that it forces forest birdlife to move to another place. We should also bear in mind that forest regeneration takes place more quickly thanks to the dissemination of seeds by birds alighting on burnt trees.

 

Reforestation

 

The appropriateness or otherwise of repopulation is an issue that requires careful thought and consideration. In the 1940s, many areas of the Serra, particularly on the Barcelona side, were repopulated. In 1985, a new repopulation plan was implemented in which around 100 hectares were replanted, basically, with Italian stone pine (Pinus pinea).

 

Today, repopulation only takes place in burnt zones that had already been reforested previously. Thanks to the natural regeneration of Mediterranean vegetation, it does not require repopulation. Moreover, we should remember that a priority of environmental management is to maintain biological diversity and conserve and improve the patchwork of existent in the Serra.

 

Due to the physical separation between streams, which makes natural recolonisation of its habitat more difficult, riparian vegetation is the plan community that presents the greatest complication when it comes to regenerating lost areas. For this reason, in recent years, riparian vegetation has been replanted in certain areas.

 

Pest control

 

The pineprocessionary moth (Thaumetopoea pityocampa), which affects certain zones in the Serra cyclically, is the most important pest in the forest here. Since 1991, annual controls have been made of the flight of adult males using pheromone traps. From late-October on, and only when necessary, phytosanitary treatments are applied to young reforested areas and those most frequented by visitors as a preventive measure against cases of allergies.

 

Periodically, moreover, cases of pine shoot beetle (Tomicus destruens) may occur. The population of this species is controlled by visual inspection. During periods of the greatest incidence, the trunks of affected pines are felled and removed.

 

Observation of the holm oaks reveals that some of their branches are dry. This is due to a disease caused by two species of homopterous insects (Kermococcus vermilio and K. roboris), which dries their twigs, but does not endanger the life of the tree.

 

The disease whose effects can be most easily seen is that provoked by the fungus Ceratocystis ulmi, which causes Dutch elm disease. This begins by drying the tips of branches in late-spring and can lead to the death of the tree. The species that transmit this fungus are members of the bark beetle family (Scolytus sp.).

 

Finally, natural episodes of climatic origin (snowfalls, high winds, torrential rain and hail storms) can destroy large areas of forest in just a few hours. To this physical destruction of vegetation must also be added the effects of pests and diseases, which take advantage of the wounds opened in trunks and branches to multiply and increase the damage caused.

Consorci del Parc Natural de la Serra de Collserola
Ctra. de l'Església, 92. 08017 Barcelona. T: 932 803 552

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