Forest protection

Francisco Lloret: “We must accompany forests in their transition to a new climate environment”

Professor of Ecology at the Autonomous University of Barcelona (UAB) and researcher at the Center for Ecological Research and Forestry Applications (CREAF), Francisco Lloret has just published The Death of the Forests, in the Arpa publishing house. We interviewed him precisely to talk about the intensification of the death of forests, a phenomenon that has climate change as its common thread and that happens all over the world, both in Mediterranean forest masses and in tropical forests. In addition to focusing particularly on the situation in Catalonia, during the conversation Lloret explains the multiple functions that forests have for human societies and the processes that will take place in the coming decades, marked by an increase in temperatures and changes in the rainfall. Situations that will impact them strongly.

Surely, the main thesis of the book is that the death of forests is a phenomenon that is intensifying and that it occurs in areas all over the planet. First of all, why does a forest die?

What I am explaining is that we are seeing a series of situations that have a common link, which are episodes of drought, which are accompanied by high temperatures. A little what the book tries to highlight is not that all the forests are dying of drought, but that we found a warning signal. We already know that we are in a context of climate change and these temperature conditions are increasing. It is a warning sign of the situation in which many forests will find themselves. The book talks about many extreme situations that make trees and forests disappear.

Climate change is an intensifier of this phenomenon. So, are we waiting for a few decades in which the death of the forests will be more and more frequent?

Probably yes. We still do not have long enough series to see this increase, but we do appreciate that in relation to the data we had, the phenomenon is intensifying. We don’t have the long-term correlation, but we can expect this to be the case with higher temperatures if they are not accompanied by more precipitation.

Is a logical deduction that in the areas most affected by climate change, such as the Mediterranean basin, the forests are in a more vulnerable situation?

It is difficult to say that one region is particularly more vulnerable than another, because we are seeing the phenomenon in all types of forests, even in tropical forests. This has to be taken into account. The Mediterranean ecosystems are especially vulnerable because they are in a transition zone and will have more and more periods of continuous drought, but it is important to say that we are also seeing the phenomenon in tropical forests, which do not expect less water, but expect more rain. It is necessary to understand that climate change does not only imply higher temperatures, but also greater variability. In tropical forests, trees are used to receiving regular rainfall and when one of these extreme periods is dryness, without rainfall, the trees are not acclimatized to the situation and become vulnerable. If there is human pressure in this tropical area to use the space occupied by the forest in another way and fires are favored, especially during the dry period, then the phenomenon increases. Because it is very difficult for tropical forests to return to the structure they had before, they need a long time to recover it. This variability makes a tropical forest also vulnerable.

In the book he talks about the disturbances that affect the forests, among which he cites extreme droughts, very intense fires or a greater incidence of plagues, since with the increase in temperature they reach where they did not before.

Climate change is the common thread, but the fact that we have very different situations is already giving you indications that there are multiple factors that interact with drought episodes. The increase in temperatures, for example, also favors insects being able to have more than one generation throughout a year, which causes them to generate more pressure on the trees. If the tree is already in a situation of vulnerability, because it is experiencing a period of drought and its reserves have been diminishing, it will be less able to defend itself against these insects. The characteristics of the soil also influences, in rockier areas there is also higher mortality, because the soil is less developed and there is less water available for the roots to take. And there is an effect of the history of use that humans have made of the forests, because it leaves an imprint that causes there to be a certain structure, with larger or smaller trees and that there are fewer or more, and this can lead to the trees are more vulnerable. If you have a very high density of trees, then they are competing with each other and, therefore, you have to distribute the little water that there is, while in a forest where there are not so many, each tree gets more water.

Why should we worry about the disappearance of forests?

It is particularly serious because of the role that forests play for people. From the point of view of human society, forests serve many functions. Some are very obvious, such as the extraction of wood or the obtaining of other consumer goods, such as food. Forests also have the function of retaining soil and preventing erosion from carrying it away. If one day you want to cut it, you will need this soil to cultivate and, in addition, it makes the forest continue to grow and the wood can grow again once cut. The soils and the vegetation of the forests regulate the water, if they were not there the water that falls would go directly to the sea and before arriving you would have it in the avenues, next to the houses. In addition, forests play the role of maintaining biodiversity. And more recently we have found that they have another function, which is the ability to regulate the climate, due to their ability to capture and retain CO2. And on top of that we find a certain gratification when we walk through the woods. See if the forest gives us ecosystem services. And why does a forest provide so many different services? Well, because it is a complex system and that leads us to something we have learned: if you focus too much on one of these services without worrying about the others, you will end up having problems.

Forest management, therefore, must be complex and not be limited to a single aspect?

Effectively. I think there is an overly simple use of the term forest management, because sometimes it can be understood only as the use of wood, when basically it is to analyze what objectives you have for the forest and implement actions to achieve them. And we are seeing how the objectives are multiple and, therefore, the actions can be multiple. Forest management is not the same as forest exploitation.


Should part of this forest management be aimed at preparing the forests for the conditions that the coming decades will have?

A tree grows slowly, it is an ecosystem that is structured over decades or centuries, a long time. Therefore, if we know that conditions change, it means that forest management must be thinking about how they will be decades from now. This is important and in theory forest management takes it into account and that is why there is the concept of sustainable management. Which means that you use the forests thinking that the forest and its services will be maintained over time. Forest management must be sustainable and multifunctional.

In which areas of Catalonia is there currently a greater mortality of forests?

The greatest should be quantified and it is not easy, what I can tell you are some areas where we detect the phenomenon. For example, in the Muntanyes de Prades or Montserrat; we have also seen it in the Maresme area, especially with the Scots pine; in the Pyrenees, from Cerdanya -where it seems that it is also related to ozone pollution-, in Pallars, with black mountain pine groves; also in some oaks in the area of ​​Central Catalonia; Scots pine populations from Prades or the Pre-Pyrenees, from Pallars Jussà and Pallars Sobirà to Ripollès. It does not mean that it occurs everywhere, but we see the phenomenon in many areas.

Will we see a process of substitution of tree species, in the sense that those most adapted to the new climatic conditions will increase?

Yes, we are also studying this with significant uncertainty, because until 20 or 30 years have passed we will not know. We have seen that the forest changes slowly, but we try to see the signs with the species that grow under the dying trees. We have done this with forests around the world. The most resilient possibility is that trees of the same species of those that have died come out again and that happens, but it is not the majority situation. The majority is that other different species appear and there is a tendency for them to live naturally in more arid areas. In some cases, although they are not the majority, we do not see any trees and, sometimes, no bushes. There is no recovery of the forest, we go to meadows in these cases. This is the most critical situation, because when we talk about ecosystem services, many are associated with plant cover and without trees it costs much more to recover the vegetation and in the meantime you have the water that runs away. This would be an alert situation.

Is the first step to address the current situation to intensify and improve the warning systems to detect the death of the forests and to be able to act?

I would say that the first step is to know the forests, to take advantage of the knowledge that we already have. Having warning signs is important to act if necessary when you have certain episodes. What we must have is an attitude of accompanying trees and forests in their transition to a new climatic environment. We must accompany them based on knowledge and empathy, taking advantage of the same natural processes that we have in the forests. We have learned that intervening in ecosystems in an intense way causes problems, because then it means that you focus only on one thing and the criterion of multifunctionality must be applied.

It also focuses on the importance of biodiversity and the variety of species in a forest because, among other issues, it makes it less vulnerable.

We must understand that nature is diverse and that it plays with abundance, that is, the predominance of some species, and the rarity of others, and it is the combination of both that gives it strength. If everything were different at all times, we would optimize things very little. If you have a species that lives well in one place, it is logical that it is dominant, but if it only exists it is not prepared for when the environment changes. Therefore, biodiversity is this, the combination of few very abundant species with many less abundant species. And it is in that combination on certain time scales that ecosystem functions are optimized.

In the forest support processes, should this biodiversity also be favored?

Yes, but you must favor biodiversity without losing sight of the other functions [of the forest]. In general, biodiversity provides many advantages, especially in highly variable environments, in which some years are colder than others or rainier. Biodiversity is not only from trees, but also from microbes or insects. And when you have that intertwined biodiversity, the trophic chains, this regulates, it makes sure that no one goes overboard.

How do you imagine the Catalan forests in about 30 years?

If I do an exercise of imagination, the forests of the Pyrenees in a few decades would be similar to those of the Ports of Tortosa, coniferous forests, much larger and with a few levels of trees higher. And the forests of southern Catalonia, rather on the coast, with the landscape that we have right now in Alicante, that is, very deforested. Closer to Barcelona, I could say that there will be more Aleppo pine and less holm oak, but the holm oak is very hard to peel, but I would say clearer forests, if they have not been burned and have not been recovered. One of the doubts we have is to what extent the fires will be the triggers for these changes, but what we do know is that the forests, which will have to adapt to the new environment, will have less wood, that is, they will be more scattered, and the species will also suffer. What we should try is that when there are fires there is a certain recovery capacity of the vegetation. Many forests will become bushes and we must also be aware of this and as a society we will have to learn to value bushes.