News November 2023

Not a fruitful year for pedunculate oak, but lots of beechnuts

While it rained acorns in many forests last autumn, it remains remarkably quiet this year. In INBO's crown condition survey (Level I), pedunculate oaks produced few seeds this year. We more often see beeches with beechnuts.

We  assess seed production in summer only qualitatively. In doing so, we look at the tree crown with binoculars, searching for fruits. The score a tree receives ranges from 'no' or 'little' seed production, to 'moderate'  or ' ‘strong’ seed production.

In 2023, we surveyed 397 oaks. On only 1% of the pedunculate oaks we saw moderate to strong fructification. Last year, this was at 16.8% of the oak trees. Among 147 beeches surveyed in 2023, one tree in five (19.8%) showed moderate to strong seed production. In 2022, we saw this in one in three (33.6%) beeches.

Research on flowering and seed production is important in order to assess the effects of climate change on trees. It used to be assumed that beech trees have a so-called ' mast year' only every 5 to 12 years. During mast years, there are remarkably many trees with seed production, while in the intermediate years few or no seeds are formed. This pattern increases the chances of seed survival: in lean years, many animals that feed on the seeds starve and thus their numbers drop. In a mast year, the animals are then not numerous enough to eat all the seeds.

However, under the influence of global warming, beech appears to be producing seeds more and more frequently. A mast year every 2-3 years is no longer exceptional. In some  forest plots in Flanders and the UK, even successive mast years have been observed.

Research on forest  condition is carried out under the international umbrella of ICP Forests.

Geert Sioen, Arne Verstraeten

Image above: beechnuts (photo INBO)


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