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Why do forest trees sometimes produce such masses of fruit? Volunteers help with the research

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Last autumn the beech trees on Switzerland’s Central Plateau were filled with immense quantities of tiny beech-nuts. Regular forest visitors know that this does not happen every year. Thomas Wohlgemuth, a biologist at WSL, says: “This phenomenon occurs with beech about once every three years, and with spruce every six years. We call it mast seeding or masting. So far we know little about why this happens, what roles climate and weather play or what it means for other plants and animals in the forest.” It could be evolutionarily advantageous for the trees to produce massive quantities of seed once every few years instead of each year, perhaps because pollination then works better or more seedlings survive. For researchers to understand forest regeneration, they need to study the mast phenomenon as well because seed or fruit production is the first step in the process.


For this they need data. Records are available for some tree species from practical forestry. Anton Burkart, head of WSL’s experimental garden, has, since 1991, kept annual records of where particular tree species bear fruit in Switzerland and how much they produce. These records provide the core dataset for Thomas Wohlgemuth. But he needs much more information. “Here we rely on Citizen Science. This means that anyone interested can help us,” explains Tom. He and his colleagues have constructed the online portal where experts and laypeople can enter how full of seeds or fruit forest trees are. To begin with, the focus is on six tree species. But it is planned to expand this to about twenty species, including some of those typical for the Southern slopes of the Alps, such as the chestnut. Observations of years with no or almost no seed production over a large area are also valuable.

Tom thinks the growing dataset has a lot of potential. Even the records his colleague Anton Burkart provided have, on evaluation, already revealed interesting interconnections. He noticed, for example, that during a winter after an oak mast hunters in Canton Zurich killed significantly more boars.  The rich food supply seems to increase the natural survival rate of the boars, even though only 5% of the trees in the canton are oaks. Such studies might seem, at first sight to be researchers just playing around. If, however, mast years become more frequent – or perhaps less frequent – due to changes in the climate, the ecosystem could markedly change with unknown consequences. And the volunteer reporters? They can follow via the Internet how the maps showing the mast intensity of different tree species are produced using the many reports sent in. (Birgit Ottmer, Diagonal 1/17) (in German)