Lethal pest threatens protected forests

The pine wood nematode Bursaphelunchus xilophilus is a dangerous invasive pest. Since its accidental introduction in Europe, near Lisbon, in 1999, it has spread to more than half of the Portuguese territory and currently represents a major threat to coniferous forests in Spain and, in the longer term, in other European countries.

This pest is capable of killing the tree it infects in a matter of weeks, if the climatic conditions are right, as is the case in most of the Iberian Peninsula.

This nematode, native to North America, has caused enormous losses over the last few decades in the forests of Asia, where it was introduced and spread many years ago.

The effects of this pest on economic losses in agriculture have been widely studied, however, the impact they cause on forest ecosystems has not been so well addressed. The effects of this deadly pest are of particular concern in protected areas, declared to ensure a favourable conservation status for native habitats and species, such as those included in the largest internationally coordinated network of protected areas, the Natura 2000 network in the European Union.

Now, a research by the Universidad Politécnica de Madrid in collaboration with the Joint Research Center (JRC) of the European Commission is evaluating some of the consequences that this species can cause, or are already causing, in the protected areas of the Natura 2000 Network in the Iberian Peninsula.

The study, published in the journal Forests, focuses on the impact that the pine wood nematode could cause in coniferous forests included in the Natura 2000 Network sites in Portugal and, in particular, in those habitats that, declared as a priority due to their uniqueness or scarcity by the European Union’s Habitats Directive (92/43/EEC), are currently particularly vulnerable to the potentially devastating effects of this microscopic organism.

A dangerous spread

The work also assesses to what extent the spread of this harmful pest could lead to a loss of connectivity between protected forest areas, i.e. limit the flow of native species and the genes, seeds and pollen they carry, from one area to another. This loss “would have a pernicious effect on the health and persistence of our ecosystems, especially in a changing context (due to climate change and other factors) in which species need to readjust their areas of distribution, moving through the territory, to adapt to these dynamics,” explains study leader Begoña De la Fuente.

The results of the study show that, to date (with data from the October 2016 infected areas in Portugal), almost half (49%) of the conifer forests in the Natura 2000 Network, and more than two thirds (68%) of those located in the priority corridors between protected forest areas are already within the nematode infected area.

These already very high percentages could be increased in the coming years in Portugal and even start to occur soon in protected areas in Spain. The study predicts that by 2022 the pest will colonise the Sierra de Gata, on the border of Castile and León and Extremadura, and will begin to spread towards the centre of the peninsula through the pine forests near the Central System.

Particularly fragile areas in danger

Finally, the study identifies the most critical and fragile areas within the priority corridors, the so-called bottlenecks, where the narrowness of the corridor and the degradation of land conditions in the areas adjacent to it (in the sense of being unsuitable for the movement of forest species) mean that the functionality of the corridor is at greater risk of being interrupted by the action of the pest if it causes the death of the scarce trees that support it.

The results show that the areas infected by the nematode already cover the majority of these critical areas (60%)b in Portugal, “which alerts us to the risk of weakening the entire ecological network and increasing the isolation of habitats and spaces such as those that provide protection to the coastal dunes”, assures the expert.

Thus, the study highlights the important impact that the pine nematode is already having within protected areas, “and even more so outside them, due to the infection of forest areas that play a fundamental role as corridors facilitating the movement of native species between protected forest areas, and that lack protection or specific management measures to ensure the continuity of this connecting function in the long term”.

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