Changing climate and changing ecosystems; what’s happening with the start of spring?

1Sedge in Greenland, spring is almost a month earlier than a decade ago. (photograph: Pearl Bucknall/Alamy)

The climate is changing, and hopefully most of you will agree with me when I say that it is human induced change. The changing climate has many different implications and because temperature is rising globally and precipitation patterns are changing, there are various climate impacts. Some are well known, think of rising sea-levels, where others are less known, such as phenological changes. Phenology is the study of seasonal biological events, which includes growing seasons of plants. Studies show that with increasing temperatures the spring comes earlier, which can lead to, for example, false springs and changing agricultural patterns [Menzel 2002]. Maybe you noticed that some flowers started to grow in your garden or neighbourhood, but that they unfortunately did not survive due to low temperatures that followed. This phenomenon is known as false spring, which can affect agriculture and thus possibly negatively affect our food resources [Menzel 2002]. For this reason, it is important to understand what the impact is of climate change on, in this case, growing seasons of vegetation. Additionally, we can use phenological changes to understand how terrestrial ecosystems react to climate change. This could be a promising tool to quantify climate impact all over the globe. So what tool am I talking about here? What exactly is phenology, and how can we see if it changes? And more importantly: why is this so important to track these changes? In this blog I will dig into the relation between phenology and climate change to answer all these questions and more!

First of all, I want to elaborate on the emergence of phenology as a study. Ever since farmers existed, they have been using knowledge of growing seasons to estimate when to plant seeds and when to harvest their crops [Menzel 2002]. Later on, enthusiastic hobbyists started to track the blossoming of certain flowers they kept in their gardens, for example the Dutch brothers Bos observed 29 plants during the period of 1894 to 1932 [van Vliet et al. 2013]. In the 20th century larger frameworks came to existence to gather all observations, such as the Dutch Phenological Society in 1940 (ended in 1968) and the The International Phenological Gadens in the 1957. Ever since the first volunteers started to track their vegetation in their gardens, scientists have been investigating growing seasons and how it changes (www.naturetoday.com contains observations in the Netherlands). Around 1970, satellites started to also track vegetation growth, which allowed larger scale tracking of phenology This tracking happens by looking at changes in the Normalized Difference Vegetation Index (NDVI), which shows the plants activity by looking at the Near Infrared (NIR) and Red spectrum. The figure below shows how the NDVI is calculated and how it works. If you look at the NDVI over an entire year, you can see when the plant’s activity increases (the start of the growing season) and when it decreases (the end of the growing season).

2

Source: https://www.integraldrones.com.au/comparing-ndvi-mapping-systems/ 

Because of the large history of observations and with satellites that observe the entire globe, there is a lot of data on phenological changes, especially on growing seasons. Even though much research has been done, studies around the globe mention different outcomes, some see a small shift in growing seasons with ‘only’ 8 days per decade, where others state the growing season is moving a shocking 26 days per decade. With growing seasons coming earlier, chances of getting a false spring are higher, which is very worrying. So we see that the start of season is changing, but what exactly are the drivers behind these changes?

Temperature is not the only thing that influences the growing season, for example precipitation and day length also play an important role. Ivits et al. [2012] investigated the changing growing seasons in Europe, and showed that temperature only plays a major role in certain climate zones, as can be seen in the figures below.

Screen Shot 2018-03-28 at 20.33.39

The right figure shows the different climate zones, the middle one shows the changes in the Start Of the Season (SOS) per year, and the right figure shows the change in the total Season Length (SL) per year. Apparently the growing season does not change the same in different areas. To make the relation between the phenological changes and climate change even more clear, I want to show you the next two graphs, from Post et al. [2018].

Screen Shot 2018-03-28 at 20.34.19.png

The right figure shows that with increasing latitude global warming also increases (the black line is the mean and the grey lines are the 95% confident limits). When you compare this increase with the rate of seasonal change in the left figure, you can clearly see that higher latitude regions experience more warming. This is of course very alarming, as most of the glaciers can be found in the Arctic, Greenland, and Antarctic. With the growing season starting up to a month earlier, more and more ice will melt. With temperatures still increasing, and no clear sign of climate change coming to an end, the start of the growing seasons may come even earlier in the future.

It is alarming to see the growing seasons change so much, but tracking phenological changes can also give us insight on the scope of climate impacts. By using phenological changes as a proxy for climate impact, we are able to see where the impacts on terrestrial ecosystems are the highest. This will give us insight in the future, but even more important, it allows us to improve our adaptation policies. Using satellite derived phenological data is favourable for tracking phenology on a global scale, as this data is objective and able to cover more vulnerable areas as well (e.g. poor areas or war zones).

Phenology is an old field of study, and has helped farmers for many years now. Recently however, more and more phenological studies have been conducted to examine the relationship between observed changes and climate change, focussing mostly on temperature increase. With satellite data scientists are able to track phenological changes globally. These studies help us understand the climate impact on terrestrial ecosystems worldwide, and aid us in adapting to these changes, especially with regards to food production. So next time you see flowers popping up in your garden when you are still wearing gloves, you can explain to your neighbour the phenomenon of false spring and why it is so worrying…

Interested in this topic?

Check out this or this article on early springs in the Guardian, www.nature.com for all phenological news and data in the Netherlands, or this website on remote sensing of phenology in the USA.

References

Ivits E, Cherlet M, Tóth G, Sommer S, Mehl W,Vogt J, Micale F. May 2012. Combining satellite derived phenology with climate data for climate change impact assessment. Global Planet Change. 88-99: 85-97. Available from: https://doi.org/10.1016/j.gloplacha.2012.03.010

Menzel  A. September 2002. Phenology: its importance to the global change community. Climatic Change. 54(4): 379-385.

Van vliet AJH, Wichertje AB, Mulder S, van der Slikke W, Odé B. July 2013. Observed climate-induced changes in plant phenology in the Netherlands. Reg Environ Change. 14:997-1008. Available from: https://doi.org/10.1007/s10113-013-0493-8

Post E, Steinman BA, Mann ME. March 2018. Acceleration of phenological advance and warming with latitude over the past century. Nature. 8:3927. Available from: https://doi.org/10.1038/s41598-018-22258-0

 

 

4 thoughts on “Changing climate and changing ecosystems; what’s happening with the start of spring?

  1. Like you, I consider these phenology to be very promising for studies into climate change and ecosystem behaviour. Apart from giving a more detailed understanding of the geographical pattern in climate change, they will certainly help to adapt to the shift in the growing season, whether the change is a few or many days per decade.
    However, will people notice or even see it as alarming, considering the general alienation from nature? It becomes an alarming problem for people working in the sectors of agriculture or horticulture as for them it becomes more and more difficult to apply traditional phenological knowledge and predict plants’ growing behaviour. But I doubt that people who’s income doesn’t depend on this knowledge will mind too much, especially since most of the food is available in the supermarkets anyway year in, year out. So at least with regards to food production, producers will need new phenological insights in order to adapt, while consumers won’t necessarily notice any alarming changes.

    Since you mentioned that other alarming climate impacts such as sea level rise or, for instance, the extinction of flagship species are better known, do you think it makes sense to draw people’s attention to phenological changes? In other words, apart from being a promising tool for quantifying climate change impacts and ensure adaption measures, to what extent could it be a tool for increasing the awareness on climate change?
    To illustrate what I mean, I’ll give an example of phenological change that caught many North-Americans’ attention: Monarch butterfly migration from Canada to México has noticeably decreased in number due to changes in temperature and precipitation patterns. People in México, Florida, and South-Canada are so attached to this phenomenon that they have become worried about the impacts climate change has on their cultural and natural heritage. In my opinion, only if such a bond exist people will notice phenological changes and see them as an alarming indication for climate change.

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  2. Thank you for your comments and questions.
    For food production you mention that producers need to adapt, and to some extent they are of course able to do so. However, with the growing season starting earlier, you have higher risk to experience a false spring. This is not something you can adapt to, and will thus increase uncertainty in food security. With more crop failure, food becomes more expensive and that is something that everyone will notice (and probably also mind).

    I agree with you to some extent that not everyone will care about the phenological changes, and may not see it as alarming. However, I do think that everyone is able to notice, as flowers and trees in their surroundings start to blossom earlier in the year. For example, this year we experienced a very cold period (which Judith explained in the previous blogpost) after a warmer period; you could see that flowers died off during this period around Science Park. You then may not necessarily see what happens to agricultural crops, but you do see the effects in your direct surroundings. I thus also believe this is a promising tool for educating about climate change and its impacts, as it is a quite direct effect which is noticeable everywhere around the world. I hope this answers your questions!

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  3. Firstly, @agneeesss @auctamara, I agree with Tamara, I’ve started noticing that flowers (predominadly daffodils) started to grow significantly earlier. About 3 to 4 years ago I was shocked when they were already blooming in DECEMBER! This was before I was as aware of climate change as I am today, and it definitely had an effect on me. So yes, It may be a promising tool to educate people about climate change. However, I never knew there was a term for it. Next year December/January I’ll start complaining about “false spring”.

    Secondly, “Temperature is not the only thing that influences the growing season, for example precipitation and day length also play an important role.“
    Obviously CO2 is indirectly influencing the growing season through the temperature increase etc.. but do you think/know if CO2 also influences the growing season directly (because photosynthesis depends on CO2)?

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  4. @judithnuria; Thanks for your question, it is indeed correct that atmospheric CO2 concentrations are also involved in photosynthesis and thus also on growing seasons. Many papers regarding this topic mention that the growing seasons are influences by different factors, such as temperature, precipitation, day length (light even more specifically), CO2 concentration, fertilisers, vegetation type (!), and more. It is even the case that growing seasons influence the CO2 concentration as well (think of the ‘breathing’ of the earth: https://www.youtube.com/watch?v=YcxS2LoZukQ).
    However, it is not showed that CO2 is significantly influencing the growing seasons. At this moment, the main drivers are day length and light on the short term (think of time scale of hours or 1 day), and precipitation (in dryer areas) and temperature (in wetter areas) on the long term (months to years). I do think there may be some influence on CO2 levels on the long term, when all growing seasons are becoming larger. However, this would require a long global research and as far as I’m concerned this hasn’t been done yet, but maybe your question will be answered in more details in the future!

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