Dear Readers, every gardener or natural history enthusiast that I bump into has something to say about the way that plants are changing their habits. So often, though, the information is anecdotal, because we don’t tend to actually record things when they happen. So, it was wonderful to attend this talk by Alastair Fitter, son of Richard Fitter, who wrote the first book about London’s wildlife in the New Naturalist series back in the 1940s and who was, among many other things, president of the London Natural History Society. From 1954 to 2000, Richard Fitter recorded the first flowering dates of various wildflowers growing in his garden and this produced a data set that turned into the first major study of the impact of climate change on the flora of the UK. That document was published in 2002, a collaboration between Richard and Alastair Fitter, when Fitter Senior was nearly 90 years old. The Fitters were interviewed on Radio Four’s Today programme, and when Richard was asked why he’d done all that recording, he replied that as a boy he’d been told that it was always good to write things down. As Alastair Fitter remarked, thank goodness he did!
Another very useful resource is the Woodland Trust’s ‘Nature’s Calendar’, which recorded ‘First Flowering Days’ for a selection of different plants between 2001 and 2016.
What is very clear is that plants are coming into flower earlier, and that this process has speeded up over the past 25 years. From the Woodland Trust data, we see that:
Hazel (Corylus avellana) produced its catkins 31 days earlier in 2016 compared to 2000.
Lesser celandine (Ficaria verna) has advanced its flowering date by 27 days between 2001 – 2016, but Richard Fitter recorded the flowering had already come forward by 20 days between 1954 and 2000, making a total advance of an astonishing 47 days between 1954 and 2016.
English bluebells have advanced their flowering date by three weeks since 2001.
From Fitter’s data, if you took all the different species in the sample, there had been a general movement towards earlier flowering of about 6 days by 2000, but this hid some major movements by individual plants. For example, white deadnettle (Lamium album) flowered 55 days earlier in the 1990s than it had in the 1950s (and indeed now flowers all year round).
There are some very strange anomalies, however: our old friend Buddleia flowered a whole 36 days later in the 1990s compared to the 1950s, and it’s still unclear why. All theories duly considered!
And while we’re on the subject of garden plants, Fitter describes how Fred Last studied his garden and recorded first flowering dates from 1978 to 2007. Mahonia advanced its flowering time during this period by an extraordinary 3 months (which now makes it one of the handiest garden plants for early bumblebees).
More recent data comparisons by Alastair Fitter show that over 50% of plants are coming into flower by the end of April, an advance of about 5 weeks. But the question is, why?
Fitter explained that flowering times are determined by a number of factors. Firstly, there’s the question of when the flower buds form. For spring bulbs, next year’s flowers are formed during the previous summer, but the actual flowering time is determined by the temperature in the spring. Fitter used the example of the Tulip Society shows to illustrate this. The date of the Wakefield and North of England Tulip Society’s annual show is determined by when the ‘English florist tulips’ are thought to be coming into their best. The Society was founded in 1836, and Fitter showed a lovely slide, where the date of the show has been coming forward on a smooth curve that exactly matches the average mean temperature in March: for every degree increase, the show comes forward by three days. The show is now commonly held in the second week of May, compared with the very end of May in the mid 1800s.
Another factor that determines flowering time is day-length, with some plants coming into flower as the days lengthen, and others as the days get shorter. Fitter points out that for the majority of plants, we simply don’t know how day-length affects them but for a few, such as red campion (which responds to lengthening days) and hops (which react to shortening days) we can see a correlation.
Temperature is, however, critical. Fitter showed how the flowering time of Coltsfoot was dependent on the mean temperature in February but, more generally, an increase in temperature of 1 degree in the four months before flowering could advance the flowering date by about three days. However, a warm summer and autumn could act to delay flowering by about the same amount. Go figure! I wondered if a warm summer and autumn might mean lower rainfall, which could delay bud formation. What is clear is that a lot more research is needed, and there is still a lot that we don’t know. The pattern is clear, however: most plants are flowering earlier, and flowering patterns are becoming a lot less predictable.
Fitter’s final point was, do these earlier flowering times matter? And of course, there are a number of problems not just with earlier flowering, but also with the increased unpredictability of flowering times. Some pollinators, for example, will take advantage of earlier flowering, but where there is a very specific relationship, such as that which occurs with orchids, the plant may come into flower but the pollinator will not yet have emerged. Sometimes, as in the case of the orange-tip butterfly, the insect is responding to earlier flowering times of cuckooflower, so that its caterpillars, which feed on the seedpods of the plant, are still ‘in sync’.
However, something that had never occurred to me was that, as flowering times change, some plants will be more or less likely to hybridise because their flowering times will move further apart, or begin to overlap. Sweet violets (Viola odorata) will be less likely to crossbreed with hairy violets (Viola hirsuta) because their flowering times are now 15 days further apart. Red campion (Silene dioica) and white campion (Silene latifolia) are, however, coming closer together, and so hybridisation is more likely. As Fitter points out, hybridisation is a major driver of evolutionary change, and so some groups may become less able to adapt over time as their flowering times grow further apart.
And so, Fitter ended by saying that earlier flowering times are a clear harbinger of climate change, and an indicator that things were changing rapidly in the natural world. We owe a debt of gratitude to Richard Fitter for ‘writing things down’, and it seems to me that this illustrates yet again the importance of citizen science, of recording these extraordinary times that we live in. And Fitter finished as he’d started, with a quote from Shakespeare, in which Titania blames Oberon for the strange changes in the climate. I think we need to look a little closer to home.
‘And thorough this distemperature we see
The seasons alter: hoary-headed frosts
Far in the fresh lap of the crimson rose,
And on old Hiems’ thin and icy crown
An odorous chaplet of sweet summer buds
Is, as in mockery, set: the spring, the summer,
The childing autumn, angry winter, change
Their wonted liveries, and the mazed world,
By their increase, now knows not which is which.’
I cannot recommend this talk highly enough, and you can watch the whole thing here.
Photo One by Agnes Monkelbaan, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Photo Two by By Michal Osmenda from Brussels, Belgium – https://www.flickr.com/photos/michalo/2425723494/, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=46945738
Photo Three by MichaelMaggs, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons
Photo Four by Rosser1954, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Photo Five by Agnieszka Kwiecień, Nova, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Photo Six by Photo by David J. Stang, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Photo Eight by Andreas Trepte, CC BY-SA 2.5 <https://creativecommons.org/licenses/by-sa/2.5>, via Wikimedia Commons
Photo Nine by Jessica Towne, CC0, via Wikimedia Commons
Photo Ten by The original uploader was Sannse at English Wikipedia., CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/>, via Wikimedia Commons