Unpredictable spring disturbs species seasonal cycles | Polarjournal
Zackenberg, a mountain in northeast Greenland offers a habitat for Arctic organisms while the nearby research station ZERO (Zackenberg Ecological Research Station) offers a habitat for research teams since 1996. (Photo: NTNU Vitenskapsmuseet, CC BY 2.0)

Initially, Arctic spring was thought to arrive ever earlier, prompting species to adapt as best they could, even emerging from hibernation sooner. A new study shows that this scheme is outdated, and that plants and animals must now adapt year on year to an increasingly unpredictable and chaotic spring.

Between 1996 and 2005, scientists at Zackenberg documented that the timing of spring had advanced faster than observed anywhere else in the world. For example, arthropods (spiders and millipedes) emerged from hibernation up to four weeks earlier with the arrival of an early spring.

In 2020, scientists investigated what the Zackenberg ecosystem would look like with a further 15 years of data, and whether spring would continue to arrive more quickly. “We looked at the extreme rates of phenological advance previously reported in the Arctic and found that directional advance is no longer the dominant pattern,” observes Niels Martin Schmidt, professor at the University of Aarhus in Denmark. “In fact, the previously observed trend has completely disappeared and been replaced by extreme variation from one year to the next in early spring,” he notes in an article recently published in Current Biology.

Arctic Bell Heather (Cassiope tetragona) is one of the species observed at Zackenberg for 25 years. In addition to the basics of the Arctic climate, it now also has to deal with the consequences of global warming. (Photo: Jacob W. Frank)

This means that, instead of arriving earlier, Arctic spring is now determined by great climatic variability, with significant year-to-year differences. 

For the first fifteen years of data, temperatures were rising steadily, while snow cover was decreasing. The latest data analyzed by Professor Schmidt and his team show a stagnation in temperature increase and considerable fluctuation in snow cover. “Some years there is almost no snow in spring, while others have snow on the ground during the summer season,” Schmidt tells Science Daily. “This leaves us with a generally warmer but much more unpredictable spring climate”. Difficult then for plants and animals to adapt under these conditions: “Some species seem unable to take advantage of the warmer conditions in spring and appear to have reached the limits of their phenological plasticity.”

Phenology studies the appearance of periodic events in animal and plant species, linked to seasonal variations such as flowering, insect larvae hatching and the arrival of migratory birds such as the Dunlin (Calidris alpina), which returns to Greenland each year to nest. (Photo: Jevgenijs Slihto from Riga, Latvia, CC BY 2.0).

Arctic plants and animals are known to be quite resilient and flexible to the conditions in which they evolve. But when pushed to their limits year after year, more and more species will become out of synchronisation, creating “a less predictable Arctic community”.

Although the paper’s findings are limited to a delineated region, Zackenberg, such studies highlight the importance of meticulous long-term monitoring and data collection in understanding ecosystems and the response of species to changes imposed by global warming.

Featured image : Irene Quaile-Kersken

Mirjana Binggeli, PolarJournal

Link to the study : Schmidt et al., Little directional change in the timing of Arctic spring phenology over the past 25 years, Current Biology (2023), https://doi.org/10.1016/j.cub.2023.06.038

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