(Production: Pablo Cantudo)
For several decades now, thousands of holm oaks throughout the Iberian Peninsula have been affected by an evil that causes their decay and death. The symptoms of this lethal process are very similar to those of drought, which is why this problem began to be referred to as ‘the dry one’.
“In reality, forest decline is not something exclusive to dehesas, we are talking about massive tree mortality processes that are being observed worldwide and that are related to many different factors,” explains José Luis Quero, professor and researcher at the Department of Forest Engineering of the University of Córdoba. For example, already in the 70s of the last century, people began to speak of decay in different highly populated areas with intense industrial activity in central Europe and North America, in which a series of pathological processes that caused aging were described. premature and the death of different species of trees.
In the case of holm oak forests in Spain and Portugal, it is known that the dry phenomenon is associated with an infection by an invasive oomycete called phytoptora (the most common species in the meadows is Phytophthora cinnamomi ) that acts by rotting the roots of the tree. However, it seems that there are other factors that intervene in the decline of the trees: drought, pollution, bad management practices … For example, due to phenomena such as climate change it can happen that organisms that were in equilibrium in that ecosystem become pests. ” The dry season, in reality, is a multistress process, we cannot even speak of disease because it is determined by a set of interacting variables and, together, they end up compromising the future of the pasture “, the researcher explains.
How do you combat the decay of the holm oak?
Since, as we have said, there is no single determining factor in the outbreak of a focus of decay, the problem must be approached from different fronts. ” There is no single and miraculous solution, but rather that each specialist or manager approaches it from a different perspective and in the end a comprehensive management plan for the pasture is achieved “. For example, in the case of phytoptora, it is not enough to apply a phytosanitary, since, in fact, it is known that it is impossible to completely eradicate the fungus. Rather, it is about making a management focused on providing vigor to the tree and suppressing, as far as possible, the activity of the pathogen.
“There are many management measures that help to combat decay: for example, avoiding excessive livestock loads that compact the soil, or disinfecting farm implements between some areas and others,” explains Quero. “Another thing to keep in mind is that many times we focus on adult trees, which is where decay is observed, but we must think about the pasture from a demographic point of view and promote regeneration .” And is that many of the Iberian pastures are very old. If we look closely, they are made up of adult trees of the same size, and there are hardly any young holm oaks. If there is a focus of decay or any event of massive mortality that destroys the old and weakened trees, those pastures would become a wasteland, there would be no young trees to replace the old ones.
Objective: detect decay in time
The team from the University of Córdoba is currently working on a project that aims to perceive symptoms of decay early. “This is essential, because when an adult oak shows visual symptoms of decay, it may be too late to cure it, ” Quero explains.
The idea is to find early warning or pre-visual symptoms, which are not appreciated with the naked eye but which would already be indicating the beginning of a process of decay. These symptoms can be detected by measuring different physiological variables in the trees, such as the rate of photosynthesis or the flow of sap, whose variations already warn that the tree is beginning to suffer.
On the other hand, as at the management level it is impossible to monitor each tree individually, the researchers intend to find a correspondence between this physiological information, measured at the top of the canopy, and that obtained by remote sensing. “Remote sensing uses a type of image called hyperspectral aerial photography to detect things that the human eye cannot see, and in them we can find the trace of those same physiological phenomena that we have measured, for example with a color change in the images. cups ”, explains the expert. “If we can accurately extract all this physiological information in an aerial photo, we will be able to monitor very large areas of forest in order to locate the sources of decline and go to them for treatment before it is too late. It is a very interesting tool for management ”.
The rural environment is valuable
At a time when there is much discussion about the economic and social model with which we want to get out of this new crisis, Quero reminds us of the importance of the rural environment. “Many times I get the idea that ‘going back to town’ is a failure, and that thought needs to be changed. Rural environments are a source of services, both economically and environmentally. Some of these services are very tangible: Iberian pig, cork, mushrooms, beekeeping, wood … but there are also more intangible services such as carbon dioxide capture that mitigates climate change or soil conservation that prevents floods. . All of this is very important both for those who live in the countryside and for those who live in the city ”, reflects the researcher.
“In these times that we live now in which it seems that nature urges us, it is important to promote the rural world. And we should all be much more aware that what is produced in the field and with sustainable management, as well as local and short-distance trade, all of this has a lot of value . “
