Trophic layers are re-shuffled as nature’s calendar shifts across a continent

With climate warming, nature’s springtime events are becoming earlier and autumn events later. By bringing together data across the massive region of Russia and its neighbors, a new study shows that how much events advance, or delay, depends on when and where they occur, and what type of species they concern. Overall, these differential shifts make food chains wobble in the changing climate.

Climate is shifting and so is the timing of nature. Over the last decades, research has shown how springtime events become earlier and autumn events later. A new international study shows just how much this rule of thumb differs between regions.

The research makes use of a recently assembled unique archive of nature’s calendar. For many decades – in some cases a full century – scientists have been recording the timing of ecological events (i.e. phenology) in more than 150 protected areas across the former Soviet Union. Now all these data have been compiled through a collaboration of more than 300 colleagues in over 80 organizations from Russia, Ukraine, Belarus, Kyrgyzstan, Uzbekistan, Finland and Sweden.

“Bringing together data across the massive region of the former Soviet Union, it turns out that how much events advance, or delay, depends on when and where they occur, and what type of species they concern”, says professor Tomas Roslin from the Swedish University of Agricultural Sciences, Sweden, who led the study together with professor Otso Ovaskainen from the University of Helsinki, Finland.

A tapestry of changes

The key result brought out by the new study is variation – but indeed variation along some general patterns. In a warmer climate, spring events tend to occur earlier and autumn events later at warmer sites, i.e. typically at lower latitude or elevation. This results in longer growing seasons for plants and longer activity periods for animals.

Spring events showed the strongest shift towards earlier dates, whereas autumn events showed the strongest shifts towards later dates. This was particularly evident for plants, which advanced early or delayed late events faster than did higher trophic levels. Fastest of all changed the abiotic (non-living) events such as the melting of snow cover, or the breakup of ice. This shows that overall, organisms are failing to keep pace with the variable climate.

Tomas Roslin uses an unexpected metaphor to explain why these results are so worrying: “Did you ever play Jenga – the game where you create a high tower of wooden blocks piled on each other? Then you will be well posed to see the perils of what is happening, Consider what will happen if – once you have built your Jenga tower high and mighty – you try to move it across the table by pushing on the lowest layer of blocks. With the different layers waggling at slightly different speed, your tower will first sway perilously, then fall apart. Now it does not take much imagination to replace your bricks with species piled on top of each other into tropic layers; that is, species feeding on the layers below them. And what we do not want to happen is that whole construct coming tumbling down.”

Complicating things even further, some shifts occurred in opposite directions between cold and warm sites. For instance, the first spring rain, the onset of blooming in Scots pine and marsh Labrador tea, and the first song of the skylark have all shifted towards later at cold sites, but earlier at warm sites. In the opposite direction, the arrival of the rook and the ripening of blueberry and lingonberry actually shifted earlier at cold sites, but later at warm sites. Surprisingly, the timing of events within a site seemed linked together by some factor beyond just year-to-year changes. A large majority of the studied events within a given site in a given year tended to be consistently ‘early’ or ‘late’. “This coordinating factor might be interactions between species”, says Otso Ovaskainen and continues “It looks like local ecological communities tend to respond as a whole, which may make them robust to the Jenga-effect at the local level.”

Original article:

Roslin, T., [+203 authors] & Ovaskainen, O. 2020. Phenological shifts of abiotic events, producers and consumers across a continent. https://www.nature.com/articles/s41558-020-00967-7

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