“Save the centenary tree” is named after an American film, but it is an alert that is increasingly heard among requests from environmentalist and not-so-environmental organizations on World Forestry Day. Nietzsche pointed out in his poem ‘A Tree’ that these ‘remind us that to grow upwards, towards the spiritual, the abstract, it is necessary to be well rooted in the earth’. In fact, these are the oldest living beings that inhabit planet Earth and “we must be concerned about the state of the forests if we don’t want them to collapse in a general way in a few years”, says Francisco Lloret, professor of Ecology at the Universitat Autònoma de Barcelona (UAB), researcher at Creaf and author of the book ‘The death of the forests’ (Ed. Arpa).

Italy recently passed a law granting legal protection to 20,000 trees as natural monuments. “In the UK we are exploring how we can provide tree shelters similar to historic buildings,” says The Woodland Trust. «Our oldest tree, the Fortingall Yew (Scotland), is between 3,000 and 5,000 years old; it is the oldest living entity in Europe, but it does not have the same level of protection as St Paul’s Cathedral,” an association spokesperson told The Guardian.

On the other side of the Atlantic and thousands of meters above the Nevada desert, stand mighty millenary trees. “In Spain it is difficult to find this type of being”, adds Lloret. Its imposing trunks tell a story inside in the form of rings that reveal past fires, plagues, wet times and, now more frequently, droughts. Dendrochronology is the science that observes the interior of trees and writes their particular ‘civil record’.

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Dendrochronology reveals the secret history of trees through their rings

two The center is the birth of the tree

3 At first, they are not usually elliptical rings because the tree can grow inclined.

4 Wide and clear zone: corresponds to spring/early summer growth, when rainfall and nutrient inputs are greater and the tree develops more.

5 Narrow dark zone: It is formed with late summer growth and the end of growth for that year. Its dark color and thinness are a consequence of the lower availability of water and nutrients by the tree.

6 Also, the size of the rings varies from one year to the next:

wide rings if they were rainy and hot years

narrow rings if there were droughts and cold

7 scar from a fire

Dendrochronology reveals the secret history of trees through their rings

two The center is the birth of the tree

3 At first, they are not usually elliptical rings because the tree can grow inclined.

4 Wide and clear zone: corresponds to spring/early summer growth, when rainfall and nutrient inputs are greater and the tree develops more.

5 Narrow dark zone: It is formed with late summer growth and the end of growth for that year. Its dark color and thinness are a consequence of the lower availability of water and nutrients by the tree.

6 Also, the size of the rings varies from one year to the next:

wide rings if they were rainy and hot years

narrow rings if there were droughts and cold

7 scar from a fire

As if it were an accounting book, the tree rings record the day to day of each year of these plants. An annotation that is getting narrower and the concentric ellipses are overlapping more and more. “In the forests there are red lights on that can lead to the collapse of the forests”, responds Lloret. Alerts that are already known: heat waves, rising temperatures and droughts. “In Catalonia, for example, we have seen that holm oaks reduce their growth by 90%, while the Aleppo pine, which adapts well to drought, does so by 60%”, says Rafael Poyatos, a scientist at Creaf.

This lack of water resources is killing many trees thirst and, in addition, is limiting their ability to absorb carbon. In drought conditions, plants are forced to close their stomata, some pores in the leaves through which CO2 used to carry out photosynthesis enters. Trees use 99% of their water to keep their stomata open and, by closing them, plants avoid losing a large amount of water through transpiration, explains Lloret in one of the chapters of his book.

«In Catalonia, for example, we have seen that holm oaks reduce their growth by 90%, while the Aleppo pine, which adapts well to drought, does so by 60%»

Rafael Poyatos

creaf scientist

A blockage that prevents photosynthesis and that “run out of reserves and starve,” says University of Oklahoma professor Henry D. Adams. “We saw that around 50% of the trees run out of carbon stocks at the time of death,” he adds.

“We have to act against this collapse,” says Lloret. “To protect forests from drought, you first need to understand them,” he adds. A preliminary study that involves investigating which trees best adapt to climate change, how many there are, what size they are and, above all, previous experiences. “We are now confident that the old trees are responding to future levels of carbon dioxide,” says Rob MacKenzie, founder of the Forestry Research Institute in Birmingham.

A study led by this researcher found that mature trees react better to high levels of CO2 in the air. British scientists carried out this project in rural areas of England and spotted oak trees that were around 175 years old. “They clearly responded to carbon dioxide by steadily increasing their rate of photosynthesis,” they note in the study.

“Now we are sure that the old trees are responding to future levels of carbon dioxide”

rob mackenzie

founder of the Birmingham Forestry Research Institute

During the first three exercises out of a total of 10, these trees were exposed to 37% more CO₂ (relative to normal), with the aim of mimicking the levels of this greenhouse gas (GHG) predicted for the air by 2050. Through some towers, the researchers released CO2 emissions into the air to calculate how many of them were captured by the surrounding trees. Now they are in a second step measuring leaves, wood, roots and soil to find out where the extra carbon captured goes and how long it is trapped in the forest.

An important step to see what happens to this carbon stored for years, decades in some and centuries in others, since when “an old forest contains a stock of carbon and if it dies it returns to the atmosphere”, points out Lloret. “Although -he assures- we must understand forest dynamics and the multiple functions of forests. We have to accompany them to make them more resilient to these changes that we are causing and that are too fast for them”.

Increase in forest mass

Although climatic and water conditions make it difficult for many species to survive, the forest mass in Spain, in recent years, has not retreated, but has advanced due to “abandonment of agricultural or forest areas, if you do nothing the vegetation grows”, explains Lloret .

28.4
million hectares

of wooded forest area in Spain

In the latest Environmental Profile of Spain 2021, published at the end of 2022, the Ministry of Ecological Transition and Demographic Challenge raises up to 28.4 million hectares of wooded forest area in Spain. “The total forest area is also increasing, but in a smaller proportion than the forested area”, points out the text.

In addition, the 2021 global results show a slight recovery in tree condition compared to the average of the last five years. “The slow recovery may be related to the fact that the drought periods are more extreme, recurrent and prolonged, a fact that affects the recovery capacity of forest masses after these events”, point out Miteco specialists.

Despite the growth of the forest mass, “the formations that occupy the largest area comprise two to three dominant species”, reveals the Environmental Profile of Spain. The holm oak is the most abundant species in Spain, while the pine forests occupy 28% of the total area, the most abundant being the Aleppo pine with more than two million hectares. Although the data show insignificant variations, “one can observe a reduction in the area occupied by repopulations of fast-growing species”, highlights the report.