Feature Image: Photo credit: https://pixabay.com/photos/magnolia-trees-springtime-blossoms-556718/
Source Article: Ma, Q., Huang, J.-G., Hänninen, H., Berninger, F. 2018. Reduced geographical variability in spring phenology of temperate trees with recent warming. Agricultural and Forest Meterology, 256/257: pp. 562-533. https://doi.org/10.1016/j.agrformet.2018.04.012
Climate warming and spring events
The signs that our planet is warming are all around us. Whether you have to take a second trip to the water cooler on a scorching hot summer day or make an observation on the early arrival of tulips in the spring, we’ve all noticed the air temperatures rising and the timing of natural events shifting. According to the International Panel on Climate Change, commonly called the IPCC, the past three decades have been the warmest in the Northern Hemisphere in over 1400 years!
Temperature is the primary factor that affects when plants leaf out, flower, and undergo other changes in the spring. The timing of these events—known as the phenology—impacts the success of the plants and the success of other species that depend on the plants. That means that any change in the timing of spring events can have broad consequences.
Many studies have shown that plants are waking up earlier in the spring, leading to earlier leaf unfolding and flowering. These changes in timing have been attributed to warmer spring air temperatures, less cold days during the winter, or a combination of both. How much spring events change depends on the characteristics of the site, which makes it difficult to study changes across large geographical regions.
Has the timing of spring events changed across Europe?
Qianquian Ma and her colleagues set out to determine how the timing of spring events, including leaf unfolding and flowering, have changed due to climate warming across Europe. They selected 16 species of trees to examine, including the European alder (Fig. 1), lilac, chestnut, and Norway spruce. Ma and her team used timing records from a network of observations taken across Europe known as the Pan European Phenology (PEP) network. This network combines observations of scientists with those of citizen scientists, who record the timing of important springtime events. In total, Ma and her colleagues used 510,506 observations from the PEP network to examine changes in spring phenology in these tree species from 1980-2013.
In addition to records on spring phenology, Ma and her colleagues also used other data networks to obtain detailed information about the temperature at each of the sites they examined. In addition to examining the average temperature at sites in relation to the timing of spring events, they also examined how the number of cold days influenced these events.
Ma and her colleagues reported that 22 examined events had advanced from 1980-2013. Events that have advanced ranged from leaf unfolding in European alder, silver birch, and chestnut trees to flowering of lilac (Fig. 2), largeleaf linden, and black locust trees. What made the results of Ma and her colleagues even more shocking, was that they showed that the timing of spring events was becoming similar across the entire geographic region they examined.
Generally leaf unfolding and flowering occur earlier in warmer regions. This is why I can plant my summer garden in Rhode Island weeks earlier than my parents can at their home in central New Hampshire.
What Ma and her colleagues discovered, however, was that the timing of spring events in trees in the colder regions of Europe was advancing faster than the timing of spring events in trees in the warmers regions of Europe. This effectively means that the timing of events in the cooler and warmer regions is becoming chronologically closer to one another.
Why should we be concerned that the timing of events across regions is becoming closer? As Ma and her colleagues point out, many animals depend on the timing of spring events, especially flowering. For example, hummingbirds fly from the south to their breeding grounds in the north in the spring, depending on flowers for feeding as they travel. With the timing of flowering in the south and north becoming closer, it’s possible that there will be a lack of food when they arrive in their breeding grounds, leading to lower reproductive success. There are countless other examples of these time sensitive interactions. With one change in nature, always comes another. For now, scientist will focus on continued monitoring and research to help unravel the changes that have already occurred and predict those that will come in the future.