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Autumn colouring in the Netherlands is late; European autumn campaign with students

De Natuurkalender, GLOBE, Wageningen University

11-OCT-2021 - Autumn colours are now gradually appearing in nature. Years of time-lapse videos from the GrowApp show that leaf colouring starts relatively late this year in The Netherlands. Cause: the warm September and the absence of night frost. Students from all over Europe are closely examining the process of autumn colouring as part of GLOBE. Secondary schools, but also volunteers can still join.

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The moment of leaf colouring and leaf fall is an important moment for plants, but also for the composition of the atmosphere. With the disappearance of chlorophyll, photosynthesis, and thus energy production in the plant stops. At the same time, the absorption of CO₂ by the plants stops. Because photosynthesis stops in countless plants in the northern hemisphere in autumn, the CO₂ concentration in the atmosphere starts to rise by the end of September. See the course of the CO₂ concentration in Hawaii over the past two years in the graph below. Mr. Keeling started measuring the CO₂ concentration every hour as early as 1958. The result is the famous Keeling curve.

Course of daily (small dots), weekly (thick black dots) and monthly (open circles) CO2 concentration in Hawaii from October 6, 2019 to October 6, 2021 in parts per million, the number of parts of CO2 per million parts of air

The Keeling curve has also been incorporated into a beautiful animation showing the course of the CO₂ concentration on earth over the past 800 thousand years. In addition to the CO₂ measurements on Hawaii, measurements from many other stations on Earth have been processed. By determining the CO₂ concentration in air bubbles in old ice layers, it is possible to go back 800,000 years in time.

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Course of CO₂ concentration in the atmosphere on earth from 800,000 years ago till January 2019 (Source: NOAA)

Influence of climate change on the start of autumn colouring

The time at which the leaves change colour varies from year to year. Due to an increase in temperature, we expect autumn to start later and later. Does that happen indeed and do all plants react in the same way or are there differences? And what is the effect of drought or a lot of precipitation on leaf colouring? What are the effects of night frost and storms? Many questions to answer still.

One way to find answers is to monitor the course of leaf colouring and leaf fall. A tool for this is the GrowApp. Since spring 2017, this App has been available to the public to create time-lapse videos of changes in nature. The GrowApp was created in the context of the Dutch department of the worldwide GLOBE program together with Geodan and the Dutch phenological network De Natuurkalender of Wageningen University.

European autumn campaign

The European autumn campaign has recently started. School students from all over Europe record the development of autumn. They make GrowApp timelapse videos of various tree species. Of the tree as a whole, but also of specially marked leaves. They determine the colour of these leaves every few days with a special leaf colouration chart. Schools can still join in. A great subject for the biology or science class or the research skills course. Schools in The Netherlands can get help from Wageningen Pre-University in starting up and completing the programme. Also view the teaching materials on the European campaign page.

The course of the leaf colouration of a Birch in 2018 and 2020 recorded with the GrowApp by students from OSBanija in Karlovac, Croatia
Watch the entire timelapse video on GrowApp.today.

Late start of autumn

From the analysis of many historical observations of leaf colouration, we already know that the temperature in September has a strong influence on the rate of leaf colouration. The average temperature in September in the Netherlands in 2021 of 15.9°C comes in the top ten warmest September months since 1901. Also, there has been no night frost yet. Various GrowApp series below show that autumn colouring starts late in 2021.

The temperature on the ground dropped below freezing last weekend. It is still unclear whether frost on the ground is enough to accelerate the process of leaf colouration.

Do you also find it interesting to record the development of autumn colouring in nature in beautiful time-lapse videos and participate in scientific research at the same time? Then install the GrowApp (Android, en iOS).

Difference in the degree of leaf colouring of two white Horse chestnuts on the Wageningen University campus around the beginning of October in the years 2016 to 2021. For these two trees, an estimate has also been made of the percentage of coloured leaves. The first percentage after the date is for the left tree and the second percentage is for the right tree
Watch the entire timelapse video on GrowApp.today.

Difference in degree of leaf colouration of an Austrian oak on the campus of Wageningen University around the beginning of October in the years 2016 to 2021