One of the first plants that screams out ‘spring’ here at the Garden is the Yoshino cherry and its white cloud of blossom, which usually lights up the Main Lawn towards the end of March. However, this year it is flowering earlier and the question being asked is: ‘is climate change causing plants to burst into bloom earlier than usual?’
Is climate change causing plants to burst into bloom earlier than usual?
This year, our Yoshino cherry is in full bloom around 5 days earlier than last year. It, along with several other plants in the Garden, is being closely monitored in a new project to provide us with scientific data which, over time, will demonstrate the impact climate change is having on these plants.
The project is being run by Dr Chantal Helm in our Learning team, along with a small team of students and volunteers. They have been monitoring plants here at CUBG since October 2020. Weekly observations of seasonal events such as bud burst, first flowering, flowering duration, autumn tinting and leaf loss are recorded. Some of this information is then uploaded to Nature’s Calendar – a citizen science project that has been tracking seasonal events for decades. Chantal will also be using these observations to make comparisons of plants over years, so that this information can be shared with our visitors and those who are interested in the timings of seasonal changes here at the Garden and how they differ year to year.
Chantal explains more about this Phenology project and how people can get involved in it, either at home or here at CUBG:
How many plants have you been monitoring in the Garden and for how long?
We started recording about 30 trees across the Garden in October 2020 and this spring added another 50 woody plants to the list for weekly monitoring.
What type of plants are you monitoring and what have you discovered so far?
We are recording some native tree species to contribute to a long-standing UK based phenology project called Nature’s Calendar, run by the Woodland Trust. We are also recording a number of commonly planted Garden plants, as well as some of the Garden’s iconic plants that have seasonal changes such as the Yoshino cherry. We think that these changes will be of particular interest to Cambridge residents who look forward to these seasonal changes.
Some of the plants being monitored:
- Cherry plum (Prunus cerasifera). This is commonly found along the roads in the countryside and is one of the first spring flowering trees to blossom. The tree we are following in the Garden burst its flower buds on 4 February this year – last year this happened by 25 February.
- Yoshino cherry (Prunus x yedoensis). This year its buds had burst on 4 March and it was in full bloom on 21 March. Last year its buds also burst by 4 March and it was in full bloom by 26 March.
- Purple toothwort (Lathraea clandestina) started flowering on 23 February this year – 5 March last year.
- Prunus x incam was recorded flowering by 24 February this year and was flowering by 2 March last year.
How do plants seem to be responding to climate change?
Timing of flowering is controlled by multiple, complex pathways related to temperature at different points in the plant’s life cycle. As the climate warms, spring arrives earlier. Germination, leaf emergence, flowering and fruiting have all advanced in concert with these warming trends for many plants.
Plants flower to attract pollinators. These species are in sync with each other by relying on environmental cues. As temperatures warm, plants flower and trees burst into bud earlier and a mismatch between interdependent species may occur.
Some species, however, are not following the expected pattern. Those bucking the trend seem to be responding to a lack of chilling occurring over the winter period due to warmer winters. The sum of two opposing drivers results in some plants responding differently to the majority.
Deadly nightshade, Atropa belladonna now actually flowers later as a result of the lack of winter chilling, while Sycamore Acer pseudoplatanus flowers at the same time as before, due to the two drivers cancelling each other out.
So climate change is affecting plants in different ways.
Can you conclude anything from the data you’ve collected so far?
It’s really early days for our monitoring project and it’s difficult to draw any conclusions from just two years of data. The frustration with any long term monitoring project is that it needs many years of data to start seeing changes. The differences we have seen over the last two years so far could just be noise and we need long term data to find the signal. However, a recent study comparing native UK plant flowering times today with those recorded in the 1700s, found that plants are, on average, flowering a month earlier today than they did back then. The data that has informed this study was collected by members of the public in their own gardens and surrounding countryside, contributing records over many years to a citizen science project called Nature’s Calendar.
How can people get involved in Nature’s Calendar?
Anyone can get involved in this citizen science project by signing up.
All they need to do is choose a plant they want to record and can check at least once a week and submit information required for that plant. One example might be the Elder plant which is one of the earliest native plants to burst its buds. The first leaves will appear by the end of January and flowering will start mid-April; the first ripe fruit will appear in July, followed swiftly by autumn tinting of the leaves and the start of leaf loss by early September, with bare trees expected from mid-October.
We need you!
In order to continue monitoring the selected plants here at CUBG, we need dedicated volunteers to check the plants twice a week and make a photographic diary of the changes. If you are interested in helping with this, please get in touch with Chantal Helm on cvh25@cam.ac.uk.
Plants and climate change:
Discover more about how plants are responding to climate change and follow our Plants and Climate Change Trail in the Garden.
