Climate change: trees bloom earlier and earlier

Globally, trees and shrubs germinate early and flower early as a result of climate change. This is evidenced by an assessment published in the specialized journal “Nature”. Of the five longest known spring bud time series of these plants. Since the mid-1980s, all data series have shown an earlier onset of leaf budding and flowering—in parallel with the observed warming in the Northern Hemisphere.

Annually repeated biological processes such as the beginning of flowering of plants or the beginning of the migration of birds are examined under the technical term phenology. He divides the year not into four but into ten seasons – spring, for example, into early spring, first spring and full spring. Data at the onset of characteristic events, some of which have been available for decades or even centuries, allow us to draw conclusions today about the impact of climate change on nature.

Cherry blossoms have been recorded in Kyoto since 812

The beginning of the cherry blossom season in Kyoto, Japan, can be traced back to 812 in ancient diaries and records – this is the longest phenological time series ever, writes scientists led by Jan Vitas of the Swiss Federal Institute for Forestry, Snow and Landscape Research (WSL) in Birmensdorf (Switzerland) ). This data collection is one of the five analyzed time series.

According to the researchers, records of the Marsham family from southeastern Great Britain represent the longest data set in Europe: its members observed leaves budding in different types of trees from 1736 to 1958, the researchers wrote. On the other hand, since 1950, a British woman has observed the beginning of the bursting of buds of the English oak (Quercus robur), so that the data series extends from Great Britain to the present. In Switzerland, the bud burst of horse chestnut (Aesculus hippocastanum) has been recorded since 1808, and the beginning of flowering of wild cherry (Prunus avium) since 1894. Finally, data from notes on three trees in China since 1834 were available.

An important biological indicator of global warming

Time series analysis showed that the timing of leaf budding and flowering was quite stable over the course of the 19th century. Since the mid-1980s, timing has moved forward: in China, spring buds started an average of six days earlier, six days earlier in the last 36 years, in Switzerland up to 30 days before 1950. It started earlier than ever before in 1200 years.

Given the relationship between temperature and spring buds, it can be assumed that the observed phenological shift in plants is an important bioindicator of global warming. The researchers point out that the time series they analyzed do not come from regions where warming has been strongest, such as Central Asia. “It is expected there that the temporal displacement of events in the life cycle of organisms will be more extreme,” Vitas explained.

Pollen counting also begins earlier and earlier

In contrast to the increase in carbon dioxide in the atmosphere, the beginning of leaf growth and flowering is visible to everyone, and therefore it is concrete evidence that climate change is affecting the ecosystems around us.

In Germany, the German Weather Service (DWD), among others, collects phenological data. According to DWD, hundreds of volunteers observe selected plants and report when trees have budded, started flowering, or changed leaf color. According to the Department for Social Development, the data will primarily be used for studies on climate change. But it’s also important for pollen prediction. Here, too, the phenological data of hazelnut flowers, for example, showed that the number of pollen grains begins earlier and persists longer.