The field of phenology involves the study of recurrent natural events in relation to seasonal changes. The phenological calendar divides the year into 10 seasons, each of them beginning with a biological state of a specific plant. The calendar starts with hazelnut blossoms and ends with larch trees shedding their needles.
But there's been a shift in the phenological seasons — as is evident from a comparison of data from today and the period 1961 through 1991. Instead of on March 3, spring now dawns more than two weeks earlier, on February 14, which at the same time makes winters shorter.
And that shift is a consequence of climate change. Apple-trees starting to blossom — another typical indicator of spring — has moved forward in Germany by 10 days over the last 50 years. And there have been similar changes in the animal world too.
Short-distance migratory birds and those that hibernate, such as tits, now start reproducing about two weeks earlier. And at this point, potential breeding site rivals — long-distance migrants like pied flycatchers and red-starts — have yet to return from Africa. The timing of their migration is genetically programmed and based on the length of days.
The winners and losers of 'season creep'
There are winners and losers. The earlier arrival of spring is called "season creep" and has an effect on reproductive cycles, feeding relationships and competitive systems. Less exposure to light is bad news for plants.
Ecosystems are sensitive by nature, and interactions between plants and animals are finely tuned affairs. Their life cycles are like interlocking gears, where one partner engaging too late or too soon can disrupt these fragile systems.
The advent of spring sees flowering plants pollinated by insects and then blossoming. Insects become more active as temperatures rise. Plants, on the other hand, take their cues to sprout from other signals, such as soil humidity and longer days.
Sometimes, insects might not be out and about while the plants are in blossom. And as they miss each other, the former are denied food and the latter their pollinators.
The phenomenon has yet to be thoroughly researched. But what is already clear is that extreme weather conditions in the wake of climate change increase the likelihood of a plant-pollinator mismatch.
Butterflies and other species at risk
Among the species at acute risk are specialists like the scarce large blue butterfly (Phengaris teleius). To produce young, it's dependent on its sole host plant — the "great burnet" — blossoming at the same time that it lays its eggs.
The butterfly is one of around one million species under threat from climate change, roughly one in three species of plants and animals. And those reliant on their own little niche are especially vulnerable.
And the disappearance of species means that ecosystems start to break down. They come under increasing pressure and face a growing struggle to recover from extreme weather events. And that in turn fuels the extinction of further species.
Their demise also means the loss of functions that are crucial for humans. Many of the crops we grow, eat or feed to livestock need animals to help generate seeds and fruit. So, while earlier springs at first sight seem like something to welcome, they mean excessive stress for nature and, for a lot of ecosystems, a major threat.