It is not only the dry leaves of the beech trees that fell prematurely during the hot and dry summer of 2018, but also their fruits, the bees. This reaction had never been documented before, reports WSL Institute in study.
As far as we know, 2018 should have been a year rich in beech trees, a year known as “of great big one”. In the spring, pollen was abundant, and the beech trees formed a lot of fruit. But in the middle of summer, many trees simply dropped the fruits that were not yet fully developed.
A beech in a period of massive fruiting. (Ulrich Wasem, WSL)
Numerous bees have been collected from plots of the Long-term Research Program on Forest Ecosystems (LWF), implemented by the Federal Institute for Forest, Snow and Landscape Research (WSL) at 19 sites in Swiss. This is how scientists saw the early and unexpected fall of the beetles.
For three of the LWF plots, studied for 15 to 19 years, the scientists first examined the pollen measurements and the data from the litter collectors to see if such a phenomenon had already occurred since the start of the observations, said WSL said in a statement on Thursday.
Also in 2003
For the summers of the years when it was observed, analysis of the climate data showed that precipitation was 45% below the long-term average, while the average temperature was 1.5 ° C above. Also in the heat wave of 2003, fruit formation stopped prematurely.
Scientists conclude that in the heat and summer drought, there is an “environmental veto, a sort of emergency stop for fruit development, as they report in the specialized journal Scientific Reports.
“Beech trees stop this development before they have invested too many resources,” said first author Anita Nussbaumer of the WSL. In a difficult climatic climate, fruits are a luxury for trees, so to speak, which must direct their resources mainly towards vital structures such as leaves, wood and roots. “Fruits have a very low priority level,” says Anita Nussbaumer.
The oaks do the same
The phenomenon of fruit drop during unfavorable environmental conditions or outbreaks of pests had previously been observed in Europe in cultivated trees, but not in forest trees.
Freezing or very humid conditions during pollination can also prevent beech trees from fruiting, but the fact that they lose fruit that is already well advanced has never been described before. However, we know that oaks are able to sacrifice their acorns in the development phase during late frosts.
In autumn, the cups burst and the bees fall.(Ulrich Wasem, WSL)
The premature fall of the fruits is another indication that beech trees are not necessarily adapted to the increasingly hot and dry summers that we can expect in Switzerland with climate change.
“Such conclusions are important for forest services because they have to decide today which species they want to focus on for the next 50 to 100 years,” concludes Anita Nussbaumer. Beech, currently the most common hardwood in Switzerland, may not be one of them.