ICNF explains that it was “alert” by the environmental association Quercus and by the region's land owners of the situation that, in view of the symptoms detected, “appears as new”.

According to ICNF, the assessment is being carried out in collaboration with the National Institute of Agrarian and Veterinary Research, with competences in matters of forestry health, “there is still no data on the area or number of trees affected”.

Quercus warned on Tuesday of the drought and health problems in “thousands of black oaks” in the PNSSM, especially in the municipality of Castelo de Vide, in the district of Portalegre.

In a statement sent to Lusa, the regional nucleus of Portalegre da Quercus explained that, in August, it found that “thousands of black oaks (Quercus pyrenaica) were getting yellow and dry leaves.

"There is still no diagnosis that clearly points to the agent(s) that may be at the origin of the detected symptoms, which can be caused by different factors, either of a biotic nature (forest pests, aka pests and diseases that affect the arboreal specimens) or of an abiotic nature (physical, edaphoclimatic, water stress)”, explains the institute.

Also asked about the type of work being developed to solve this problem, the ICNF explains that monitoring actions are being promoted in the areas occupied by black oak, in the municipalities of Portalegre, Castelo de Vide and Marvão.

This action serves to prospect and identify harmful biotic agents (forest pests) and to assess/quantify the area of ​​incidence.

“As the cause has not yet been identified, there are no measures for its resolution yet”, he adds.

In the communiqué sent to Lusa, Quercus environmentalists say they suspect that “weather conditions have promoted the problem that affects this species”, by creating conditions for the development of an outbreak.

“It is probably an outbreak of an oak aphid which, according to specialists, in favorable conditions such as dry winters and, occasionally, summers with high humidity, can increase the attack of the pest”, they add.

According to the association, in the center and north of the country, "outbreaks occur punctually, with more incidence in situations with some degradation and imbalance of the oak forest ecosystem", which seems "to be an indicator of continued degradation of the oak forest due to human action".

In oak groves “of larger dimensions and better equilibrium conditions of the ecosystem, this does not occur or the incidence is low”, it is referred to.

Quercus also warned that, in the north of Alentejo, “black oaks appear in the cork oak system, so careful management is essential to avoid the decline of the ecosystem”.

The environmental association is waiting for an assessment and diagnosis of this situation, to clarify the owners and the rest of the community on the matter.

The black oak is a species that occurs mainly in the north and center of the country, but which has an “important nucleus” in the São Mamede mountain range, isolated from the other populations, he explains.