Climate change: How biologists want to save the beech from the climate crisis – knowledge

If you were looking for the oldest beech in Germany, you would almost certainly pass it by. If you think of the Methuselah tree as meter-wide trunks and gigantic branches, you are wrong. Bhaga is a small, hunchbacked figure. The common beech is located in Northern Hesse in the Kellerwald-Edersee National Park and is overgrown with mosses and mushrooms. Purple shimmering thimble surrounds her foot. Bhaga has been clinging to a rugged rocky promontory above the Edersee for around 350 years, perhaps for a longer time.

What special properties made this tree so resilient? To find out, the biologists Marco Thines and Stefan Wötzel deciphered Bhaga’s DNA. The old lady is supposed to help secure the future of the European forest – especially with a view to global warming. With the knowledge of the peculiarities of their genome, climate-proof beech forests could be reforested in the future and foresters could plant trees that are particularly well armed against heat and drought due to their genetic requirements.

Thines wears ankle-high hiking boots and tucked the legs of his jeans into his socks. The walk from the parking lot at the lake to the beech takes just under half an hour. A reflex camera with a telephoto lens hangs around Wötzel’s neck, the strap of the rucksack is strapped tightly around his chest. The two researchers work at the Biodiversity and Climate Research Center of the Senckenberg Society for Nature Research in Frankfurt.

Thines drove to northern Hesse four times and hiked to the beech. The scientists collected more than a hundred buds, placed them in a cool box with ice flakes and took them with them for analysis. Up until now it was common practice to examine leaves for DNA analysis. But the two biologists opted for buds because, unlike leaves, they are not a small ecosystem of their own and because their interior is protected by scales. Without the microorganisms living on the leaves, the DNA of the beech trees examined is purer.

So far, Bhaga has been spared human interference

Bhaga’s genome serves as the basis for all research Fagus sylvatica, the European beech. Everything that is researched on this species from now on relates to the genes of this individual. Thines and his team are the first to determine the beech’s genome. The name that the researchers gave the old beech is the reconstructed Indo-European word “Bhaga”, the primordial mother of the beeches.

As a reference, their genome enables various research projects. The team around Wötzel compares old and young beeches in order to investigate possible changes due to climate change. The biologists are also looking for variations in trees from different regions: from Breisgau, where the summers are hot, from the temperate north of Poland or the south-east of Poland, where the winters are severe and the summers are dry. The researchers compare the new data with Bhaga’s genome to determine which genotypes caught on and when.

“A beautiful tree, a strange tree,” says Thines, arriving at Bhaga. Gnarled branches grow in all directions. The trunk is hollow, with furrows and cracks in it. Old beeches can be recognized by the fact that their bark is often torn and leathery, explains Thines. There are many such trees in that part of the basement forest, and the beech forest has been a Unesco World Heritage Site since 2011. Very rare beetles also live here, such as the violet-blue root neck beetle, which only occur when there is a high proportion of dead wood. Relics of old primeval forests that are rarely found in Germany.

Open detailed view

It took a little more than a year from the first sampling of the tree to the first analysis results. In total, the scientists discovered more than 63,000 genes on twelve chromosomes, 87 percent of which could be assigned to a function. That is a comparatively large amount. Biologists often find the sequence of a gene but do not know what specific role it plays in the organism.

The researchers opted for Bhaga on the one hand because of her age. They estimate that Bhaga is at least 300 years old, probably more like 350. On the other hand, scientists rule out human interference such as afforestation or deforestation in this part of the forest. The terrain is too steep and inaccessible to remove the trunks with forest machines or, as in the past, with horses. The trees there date from a pre-industrial era.

Over the years, the beech has had to master one or two challenges. At Bhaga’s rocky promontory, the ground can hardly absorb rainwater, it immediately flows down into the valley. It takes the tree around 20 years for a branch to grow ten centimeters, says Thines. Bhaga’s roots have clung to the stone. Thines even suspects that only the tree still holds the rock together. The robustness of the beech can also be seen in the green of its leaves – it is the most saturated of the surrounding trees.

“There’s a cut in front,” calls Wötzel, pointing to a young branch that is missing a twig. Two years later you can still see the four places at which the researchers cut off thin branches. Wötzel boots around the beech and photographs it from all angles. In doing so, he does not once hold onto Bhaga’s trunk, does not touch a branch so that the tree can grow as unaffected as possible.

“What the trees have been through in recent years is nothing compared to what to expect.”

When the biologists examined the DNA in the second step at the chromosome level, they came across a large amount of genetic material from mitochondria, the power plants of cells, and chloroplasts, which harness solar energy. These cell organelles have their own, usually separate, DNA. If the organelles perish, their DNA can get into the cell nucleus. Thines considers the fact that this is evidently happening to a large extent with Bhaga to be “evolutionarily exciting”. He searched further and came across a statistical correlation between certain mutations and the drought resistance of individual beeches.

According to a study in the trade journal eLife, in which Thines was involved, it is possible to predict whether a tree will be damaged by persistent drought or not after examining almost 100 locations in the genome. And that with a probability of 99 percent. These gene segments are therefore likely to be a reason for Bhaga’s extraordinarily long life.

The fact that the beech survived for more than three centuries despite the adverse conditions should now benefit its entire species. Bookings are considered adaptable, but only to a limited extent. The climate crisis is already causing widespread beech deaths. And Thines is certain: “What the trees have been through in recent years is nothing compared to what to expect.”

But how do you bring the fight against climate change from the laboratory to the forest? A new rapid test will in future be used to compare the extent to which the DNA of beech trees contains mutations that can provide information about drought resistance. The aim of the Senckenberg researchers is a handy device to examine tree samples. The results could then be compared with a database in a built-in chip in a few minutes. Then you know whether a tree has a good chance of surviving future years of drought – or not.

That costs about five euros per tree, says Thines. An affordable price. Especially when you consider that forestry sales with beech trees in 2017, according to the Thünen Institute, the Federal Research Institute for Rural Areas, Forests and Fisheries, amounted to over one billion euros. The devices are now to be tested in a pilot project in Hesse. A comparable process does not yet exist in forestry; in principle, it can also be applied to other tree species.

Bhaga’s heartwood is rotten. A tinder fungus grows on the trunk below. A sign that parts of the tree are dilapidated – but this does not necessarily have to be problematic. Over the years, trunks have died and broken off again and again, and new ones have grown out of them. So the beech is self-rejuvenating, and Bhaga is doing surprisingly well considering its old age. Last year, despite the hot summer, it even carried beechnuts: The fruits distribute the beneficial genes of this ancient tree, even without humans.