When a large fifth-generation fire burns thousands and thousands of hectares of forest uncontrollably for days, the losses are palpable and visual. And yet, another danger, more widespread and more continuous, also deteriorates Spanish forests year after year. The intense thirst imposed by the advance of climate change causes lasting damage that goes unnoticed.
The results of the latest National Inventory of Forest Damage from the Ministry of Ecological Transition show in 2023 a general defoliation – loss of leaves – of 23%, among the high values of the last decade. The analysis explains that the most serious levels “are associated with the intense episode of water deficit suffered by vegetation”.
Drought, the technicians explain, is the main cause of rot in the trees examined, followed by insects and fungi, before reaching the damage caused by fire. An order that has been repeated in the different editions of the inventory. In addition, water stress makes plants more vulnerable to attacks by certain insects, which in turn defoliate them.
“Trees need light, roots and water, and the latter is becoming increasingly scarce,” explains Mireia Banque, a researcher at CREAF (Centre for Ecological Research and Forestry Applications). “And the situation is generally getting worse because, in addition, the hotter it is, the trees need more water to carry out the same photosynthesis.”
Even if we had the same amount of water as 50 years ago, the trees would need more, but we have less!
Mireia Bank
— CREAF researcher
Exactly the opposite of the panorama that climate change brings to Spain: increasingly hot periods (higher temperatures) crossed by more frequent and more acute periods of drought (less water available). The year 2023 was extremely hot with a very dry spring. And this came after a 2022 that was also very hot and dry.
“When the heat hits, plants evaporate water faster through their stomata, so with hotter summers like the ones we are already experiencing, the demand for water in forests increases,” continues the ecologist. “Even if we had the same amount of water as 50 years ago, trees would need more, but we have less!”, the scientist emphasizes.
The climate crisis impacts forests in multiple ways to the point of “changing their functioning”, as described in the analysis carried out by the Ministry of Ecological Transition in 2020. “Changes have been detected in the phenology of foliation, leaf fall, flowering and fruiting”. They also have an impact on the growth and survival of species.
Looking at the Spanish forest massifs during the year 2023, the impact generated by the lack of precipitation recorded in winter and summer is visible in the areas of Castilla-La Mancha, Extremadura, Sierra Morena (Andalusia) and especially in Catalonia.
In this autonomous community, the CREAF Deboscat program has recorded “by far” the record of forests affected by drought. They have detected more than 66,000 hectares of forests with a loss of leaves. The previous maximum was measured in 2012 with 40,000 hectares. In Deboscat, they respond that in ten years, forest fires have destroyed 22,500 hectares in Catalonia.
Thus Banqué considers that “we worry a lot about whether the forests are burning, but we should also worry because they are dying of thirst.”
Recovery possible?
In 2024, July was very dry and very hot. And August extended the intense heat to become the hottest August on record. On the other hand, spring was normal in terms of precipitation followed by a very wet June (150% above average). Is this enough for the forests to recover?
“It depends on the species,” says Mireia Banqué. Conifers – such as pines or firs – are generally very resistant to water stress. “They last longer and are able to isolate their roots from dry soil,” explains the scientist. In this way, they can last for months or even a year. However, if their resistance limit is exceeded, they die irreparably. “We have seen pines whose tops turned brown when it was already raining. Why? Because they had already broken their maximum resistance and had not grown back, the water arrived late and they were doomed,” he describes.
On the other hand, planifolias (like oaks, cork oaks or holm oaks) develop another strategy: as soon as they arrive badly, they get rid of their leaves and we detect the oaks that are flaking in July. “They wait for it to rain to grow new shoots, they do not die”, underlines the researcher.
Beyond any specific evolution, the advance of climate change draws a horizon in which Spanish forests, in a more abrupt or progressive way, will be transformed. The new climatic conditions of heat and drought “can result in less dense forests or even areas where only scrubland returns after a fire,” describes Creaf’s technique.
From his point of view, “we will have to support the forests to adapt to the new conditions. Favor the most resistant species and assume that certain varieties will not be able to persist in certain areas.
