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Anyone who found the first blooming violet in medieval Vienna could rejoice. "Immediately, according to old custom, the Duke called together the festive procession to pick the first violet and, accompanied by music in the company of cheerful gentlemen and women and followed by a large crowd of curious townspeople, marched to the site of the discovery to start the violet festival," says an old Viennese legend. With this spring tradition we are in the 14th century, with Duke Otto III the Merry. Since ancient times, the end of winter and the first blooming flowers have been a welcome reason to celebrate. One of the largest violet festivals in recent memory took place on May 20th and 21st, 1905 in the Dreherpark, a former entertainment establishment in Vienna Meidling (Schönbrunner Straße 307). The late date, long after the first violets had bloomed, was chosen because they were hoping for nice weather. Not at all, the first day was rainy. Nevertheless, more than 5,000 people came to witness the historic spectacle with mounted fanfarers and more than 200 people in costumes. While the Old Viennese Spring Festival was forgotten, today – to name another spring custom – the Japanese Cherry Blossom Festival in distant Nippon is on everyone's lips.
Naturally, the onset of flowers depends on the location, temperature, snow conditions, to name just a few parameters. During the course of the year, the distinctive fixed points of the vegetation have been of great importance for centuries. Looking back, the change in the climate can be reconstructed.
The beginning of the scientific discipline of systematic plant observation, phenology, in the k. k. Monarchy leads to Prague in the Biedermeier period. Karl Fritsch was born there on August 16, 1812. Even as a child he was very interested in nature. "Every day after school I ran to the river (the Vltava) and feasted my eyes on the play of waves associated with their rise and fall. (…) I chased butterflies and caught beetles." But the young Karl neither became a hydrologist nor an entomologist; rather, he was appointed as a meteorologist together with Karl Kreil (1798 to 1862) in the summer of 1851 to head the Central Institute for Meteorological and Magnetic Observations (today: Geosphere Austria).
By the time it was founded, Fritsch had already kept meticulous records of the plant world over the course of the year for over 15 years and published it in 1847. The reason for his notes was the mild winter of 1834 ("unheard of temperature of + 11°" on January 24, 1834) in Prague. This is how he came up with "the idea of writing down in a diary every year the days on which certain plants began to bloom." 190 years later, Fritsch, who died in Salzburg on December 26, 1879, would have experienced the first February in Vienna without any frosty days.
In the 1830s, the young Fritsch only described the beginning of flowering of more than 80 plant species, from early violets to maples to meadow bellflowers, which bloom from March to mid-June. From 1840 onwards, he expanded his records to include the entire annual cycle of plants. Fritsch says in the original wording: "These are the stages of leaf bud, leaf, flower bud, flower and fruit development. Furthermore, the stages of fruit ripening, color change and leaf fall." That was groundbreaking. "Fritsch included important phases of vegetation in his observations that we still record today," emphasize Helfried Scheifinger and Thomas Hübner, phenologists at Geosphere Austria.
Based on his individual observations, Fritsch knew how to win over a network of observers in the monarchy for his observations. He took the circumnavigation of the world on the frigate Novara (1857 to 1859), which was accompanied by a dense scientific research program, as an opportunity to recommend a phenological observation program. He not only asked to note the day of the "first fully developed flowers" and the "first fully ripe fruits" of all (!) plant species. He also wanted to know the day of first appearance and complete departure of "animals that periodically arrive at a certain place every year." This gave Fritsch his foot in the door not only in botany but also in fauna. He saw potential for development. "There is perhaps no field of scientific activity in which, given the current great development of most branches of it, a greater yield can be hoped for."
Fritsch's ambitious research, which he carried out with great enthusiasm until the end of his life in 1879, experienced a new upswing after the end of the Second World War. In 1946, systematic phenological observations and recordings began at the Central Institute for Meteorology and Geodynamics (ZAMG). Dedicated observers recorded their “observations of plants” on pre-printed observation sheets throughout the year.
Starting with early, first and full spring (wine blooms) through early, mid and late summer (crocus blooms) to early and full fall (horse chestnut ripe, fruits burst). In total, over 70 stages of vegetation were surveyed. The spectrum of plants ranged from flowers to bushes, trees and grains to wine. The first mowing and the grape harvest were also an issue. Since 2006, in addition to the observation forms, phenological observations can be entered via the phenology portal "phenowatch" and since 2018 via the nature calendar app. The observations are collected in the Geosphere Austria phenological database and evaluated in real time. The most important phenological indicator plants are planted in a specially created phenological garden on the Hohe Warte in Vienna Döbling, the headquarters of Geosphere Austria.
"In order to be able to make statements about the climate, we need data over a normal climate period, which corresponds to an observation period of 30 years," says Helfried Scheifinger. In this context, it is worth taking a look at the phenology mirror available on the web. In particular, the current overview in the calendar year section shows the changes in vegetation starting with observations from 1946 to the present day. The observations from the start of snowdrop flowering to the leaf discoloration of the apple, each in comparison with the normal climate period from 1991 to 2020, impressively show the increasingly earlier start of the growing season.
For a current example, a look at the still young year 2024, with one of the warmest winters in measurement history. The dark red color of the bar at "Apricot flowering start" means: "extremely early entry date"; light red (earlier entry date) and medium red (significantly later entry date) clearly signal: the plants are early. In the case of snowdrops and hazel, most observations have already been received and this year's flowering times will hardly change. In the case of the apricot blossom, most observations are still pending, which means that the Austrian average shown in the phenology mirror will shift significantly backwards. A look back to 1964, the year the author was born, shows a different picture: the blue colors stand for a later or significantly later entry date.
"The phenological evaluations prove the effect of climate change on the annual cycle of plants. Activities in nature start earlier and stop later," said Hübner and Scheifinger. If you compare the elderflower with the measured values of the temperature curve, you can see that the flowering date is clearly dependent on the temperature. In general, flowering in medium and higher latitudes correlates very well with temperature values.
The coupling of vegetation with temperature allows - based on vegetation observations - retrospective conclusions to be drawn about temperature when there were no recorded measurements. Proxy data would be the correct technical term for the records of vegetation parameters in ancient chronicles that contain information about harvest dates or grain prices.
In other words: The data collected by volunteers over many years proves climate change independently of instrumental measurement data. Once again we would like to thank the many observers, including you, dear reader. Entry into the world of phenological observation is low-threshold and uncomplicated using the Nature Calendar app. (Thomas Hofmann, March 4, 2024)