Spring’s early arrival nothing to celebrate
Shifts in the seasons have potentially dire consequences for finely balanced ecosystems. James Mitchell Crow explains.
For a fleeting few days each year in Japan, Kyoto blushes, turning a perfect shade of pink. Cherry trees burst into blossom right across the city, marking the beginning of spring.
The display will last just a few weeks. Visitors flock to the city’s annual cherry blossom festival both to celebrate Prunus perfection and to contemplate the fleeting nature of life. This ancient custom, and the date each year the blossom peaks, has been documented for more than 1200 years.
From this remarkable data set of spring’s arrival a pattern emerges. After fluctuating around April 15 for a millennia, since 1830 the date of peak blossom has crept forward to April 7.
Spring creep is happening around the globe. The early arrival of Kyoto’s cherry blossom, while conspicuous, is hardly the most profound example. In the Arctic, which is warming more rapidly than other parts of the planet, some plants are awakening 26 days earlier than just a decade ago.
The study of timing patterns in the biological world is known as phenology. It has become a growing, and fast-moving field, as global warming drives climate change. “A lot of physiological events in species’ lifecycles are cued by temperature thresholds,” explains Lesley Hughes, of Macquarie University in Sydney, who studies the impacts of climate change on natural ecosystems. “Plants and animals over the past two decades have been responding very sensitively to warming.”
Where Japan has its blossom festivals to track the seasons, Australia has its vineyards; as climate critically affects the quality of a vintage, wine makers record it carefully, creating some of the nation’s best long-term records of seasonal change.
Vines aren’t just awakening earlier in spring; the whole growing season is speeding up, says Mardi Longbottom from the Australian Wine Research Institute (AWRI) in Adelaide. White grape varieties used to ripen first, neatly followed by the reds; these days they are all ripening at once. Part of Longbottom’s work is to help wineries manage the bottleneck. One option being researched to delay grape ripening is to delay vine pruning, she says. Another is to switch to Mediterranean varieties better suited to warm conditions. As the bushfire season gets longer, AWRI is also researching how to minimise smoke taint flavours in wine.
It’s not just an ecosystem’s plants that are affected by the shifting seasons. With spring arriving earlier and summer lingering longer, the extension of flowering seasons and delay of autumn has consequences for animals bound to the seasonal cycle, says Hughes. Migratory birds, for example, are arriving at their summer feeding grounds earlier and staying longer.
A foreshortened winter may sound like something to celebrate but it can have consequences for natural ecosystems. Neighbouring species can respond to warming in different ways, throwing interdependent species out of sync.
Vertebrates are often the most disadvantaged by these changes, Hughes says. When spring comes early in the Arctic, for example, the peak period of plant growth precedes caribou calving season. In years when spring comes early, there is less for the animals to eat and fewer calves survive.
Even in temperate climes, mismatches are emerging. One of the best studied is the relationship between oak trees, winter moths and great tits. As the climate warms, the oak leaves are coming out earlier, and the moth larvae that eat the young leaves are hatching earlier. But the birds respond mainly to day length rather than temperature. Their fledglings are hatching too late to take advantage of that flush of food available from the winter moth, so their populations are declining.
“We’re all expecting that, as climate changing is a very strong selective pressure, there will be some species that will respond quite quickly,” Hughes says.
“The problem for the bird, which has a relatively long lifecycle compared to an insect, is that their capacity for evolutionary change is going to be a lot less.”