The southern pine forest La Palma is in full decline. The gases vitiate the ecosystem, the humidity could be generating occasional episodes of acid rain and the ash prevents them from taking advantage of the sunlight. The landscape tinged with yellow that he volcano has left in the south of the island is, in the eyes of the biologist of the Institute of Natural Products and Agrobiology (IPNA-CSIC), Manuel Nogales, “Bleak”. But in this extreme situation, not all the flora is supporting the changes in the same way and, in the case of the pine forest, it is those younger specimens that are suffering the consequences to a greater extent.
These pines are the ones that flourished after the great fire that ravaged La Palma in 2016. Then 4,864 hectares of land burned (7% of the island’s land) and the fire cost the life of a forestry agent on the island. In areas where the fire caused the most damage, the pines did not re-bloom in the same way. “They have had a brush growth,” explains the biologist, who indicates that this way of calling it refers to the fact that its shape is very similar to that of the brushes used to clean toilets. In this type of formation, most of the needles emanate from the central trunk, instead of being distributed by the branches, which is normal.
Sulfur dioxide (SO2), chlorine or fluorine vitiate the atmosphere and become the only food for these trees, unable to digest them
This form of growth has allowed it to recover quickly from that devastating fire, but it has not given it enough tools to survive such harsh living conditions as those caused by the Palmero volcano. “They have managed to sprout, but they are not the strongest,” summarizes Nogales.
The main threat facing the pine forest is the continuous emanation of toxic gases and ash, which have already destroyed 8 kilometers of this ecosystem to the south of the volcano. The most damaging are acidic aerosols that stagnate in the atmosphere. Sulfur dioxide (SO2), chlorine or fluorine are found in such high concentrations that they become the only food for these trees that, in turn, they are unable to digest it. This produces that their needles end up totally yellow, which is the color that now stains the entire pine forest of La Palma.
Although the affection due to the volcano’s emissions reaches 80% of the pine forest of the southern municipalities, the destruction is occurring in high areas
The concentrations of these gases in height, especially in the exclusion zone, are so high that it has caused the occasional scare among the scientists who work there. “We went to the exclusion zone equipped with eight gas detectors that we have rented for the emergency,” says Nogales, who insists that safety for them has always come first. In his recurring visits, his devices have repeatedly warned that the amount of sulfur dioxide was high enough to cause damage to his health. Although its greatest concern is carbon monoxide (CO) since it does not warn of its presence and can be lethal in a matter of two hours if the concentrations are too high.
Gases being the main threat, the damage caused by the ashes is not negligible. On the one hand, by transforming into small aerosols, they cover the atmosphere, making it more opaque. Although it is a very local effect, this circumstance prevents the pines from being able to adequately capture sunlight in order to start their photosynthesis. But the fall and accumulation of pyroclasts of different sizes have other consequences for the survival of the pine forest. “They are also deposited on the branches until they precipitate that they break and fall”, narrates Nogales. In fact, as he explains, there have been several occasions in which they have had to pick up large branches from the ground that prevented them from passing through the path that they usually use to reach the study area.
Experts hope that, as has been demonstrated in the great fires that the Canary Islands have suffered, the pines will once again demonstrate their resilience
In the last days, the already characteristic yellow color that has been installed throughout the pine forest, has been joined by an intense reddish tone that impregnates part of the needles of the specimens that make up the pine forest. Although chemical studies have not yet been carried out, some of the scientists consider that the leaves have acquired this color due to a punctual acid rain. However, rather than being generated as a result of an episode of rainfall –which has not happened too much on La Palma so far and has almost always been associated with low clouds–, the researchers believe that it may be related to the humidity in the area. zone. It should be remembered that for acid rain to occur, as explained by the atmospheric physics of the Izaña Atmospheric Research Center, Omaira Garcia, it is necessary that several conditions are met. Among them, that there is water vapor and sulfur dioxide in the environment, that the latter is in very great conditions and that there is atmospheric stability, that is, there is hardly any wind. Although the condition in the pine forest is important –80% have lost their usual color-, the distribution of this destruction is not being homogeneous. “It is having repercussions especially in high areas – close to the maximum height of the volcanic plume – and to the south of the island,” insists Nogales. And it is that the usual wind regime of La Palma blows against the development of this ecosystem. “The prevailing winds are the trade winds that blow in a northeast direction, that is, they enter through San Andrés y Sauces and travel the island to the southwest, which is where this pine forest is located,” he concludes. This means, in turn, that the lower areas of the island hardly have problems related to the toxic environment generated by the volcano.
Despite the ecological disaster that the eruption is causing indirectly, experts hope that, as has been shown in the large fires that the Canary Islands have suffered, the pines are resilient. The characteristic that makes these pines special compared to others is their ability to re-sprout from a burned trunk, a stump or a stump. In fact, it is considered to be the tree best adapted to live in a volcanic ecosystem or to sprout after a fire of the kind that we have in the national geography. And even with the desolation, much of the pine trees are still alive in the interior. “If you scratch the bark a little, you can see that there are green parts inside,” says the researcher, who has been visiting this part of the exclusion zone for 64 days and has been able to see its evolution day by day. There are also some leaves that remain green at their base, which means that they have not yet been affected. That this color can still be seen in the pine forest is a ray of hope regarding its later recovery. «I am confident in the recovery of our pine tree», insists Nogales, who does not hide that, nevertheless «it is shocking to see it like this».