Spring 2021: How It Happened

This spring has been an unexpected, unpredictable and turbulent season, that has taken its time to unfurl. Traditionally spring is a season that is characterised as calm and dry, with days getting longer and warmer, and the potential for cooler nights. As lighter evenings returned this year though, spring was far from traditional, with a stormy then hot March, cold and frosty April, and a wash out of a May.

Since 2017, I have recorded the dates of the events of spring every year, and with the start of my blog, every year since I have analysed and compared spring events to see how the season took form. Last year I showed that the timing of spring events is heavily linked to spring weather, resulting in either earlier or later occurrence accordingly. Over the last couple of years this has varied alot, so it will be interesting to see what has gone on this year.

This spring a lot has been going on for me, but I have still found time to be out in nature as much as possible and to enjoy the time when one season slips into another. It has felt that spring has dragged on longer this year, with the potential effects of spring starting warm and progressing to cold, then wet. So as this spring comes to a gradual close and the heat sets in, it is time to find out what actually went on during spring 2021.

Trees

This year there was a general trend for trees being later in their bud burst, leaves unfurling, and flowering compared to 2020. Even before the frosty nights of April, silver birch (Betula pendula) buds burst 14 days later on 26th March, Norway maple (Acer platanoides) first flowered 5 days later on 26th March, and beech (Fagus sylvatica) buds burst 14 days later on 27th March.

As we moved through April and into May, spring events began to stretch even further in their lateness. For example, wild cherry (Prunus avium) buds burst 35 days later on 8th April, horse chestnut (Aesculus hippocastanum) first flowered 18 days later on 20th April, alder (Alnus glutinosa) buds burst 15 days later on 21st April, the first lime (Tilia x europaea) leaves unfurled 23 days later on 26th April, pedunculate/english oak (Quercus robur) leaves first unfurled 31 days later on 5th May, and ash (Fraxinus excelsior) flowered 37 days later on 9th May.

Field maple (Acer campestre) did not follow this trend though, with bud burst being 10 days earlier on 26th March, and first leaves unfurling 5 days earlier on 1st April. This may be as these trees missed the worst of the spring weather, but for the other trees spring events ranged from being 1 to 37 days late!

Shrubs

For a lot of the shrub species I monitored a similar trend was shown as with tree species, being later compared to 2020. For example, elder (Sambucus nigra) leaves first unfurled 34 days later on 18th March, blackthorn (Prunus spinosa) first flowered 17 days later on 23rd March, and hawthorn (Crataegus monogyna) first flowered 23 days later on 11th May.

Though half of the shrubs I monitored were later in their spring events, ranging anywhere from 2-34 days later, two species did not completely fit this trend. For lilac (Syringa vulgaris) bud burst occurred 12 days earlier on 24th February, but flowered 17 days later on 2nd May. This was the same for dog rose (Rosa canina), where buds burst 12 days earlier on 22nd February, but first flowered 22 days later on 8th June. For both of these species though, it is the spring events occurring before April that are earlier, as the ones occurring in April and May were not immune to the frosts and heavy rainfall like the other shrubs.

Flowers

For many of our commonly associated spring flower species, there was a little more of a split between appearing earlier or later, but on average they flowered later compared to 2020. Snowdrops (Galanthus spp.) first flowered 15 days later on 18th January, wood anemones (Anemone nemorosa) 8 days later on 30th March, bluebells (Hyacinthoides non-scripta) and greater stitchwort (Stellaria holostea) both 4 days later on 1st April, cowslips (Primula veris) 12 days later on 2nd April, early purple orchid (Orchis mascula) 12 days later on 18th April, wild garlic (Allium ursinum) 14 days later on 20th April, and oxeye daisy (Leucanthemum vulgare) 16 days later on 3rd June.

The exceptions were a section of earlier flowering species, including primrose (Primula vulgaris) first flowering 27 days earlier on 31st December, lesser celandine (Ficaria verna) 3 days earlier on 15th January, daffodil (Narcissus spp.) 22 days earlier on 19th January, and cuckooflower (Cardamine pratensis) 10 days earlier on 8th April. These flowers would have been influenced by a warmer winter and start to spring, generally flowering before the cold spell in April.

Birds

On average, bird species spring events have also become later this year compared to 2020. I heard my first song thrush (Turdus philomelos) singing 17 days later on 1st January, I saw my first rook (Corvus frugilegus) nests being built 10 days later on 25th February, and I heard my first chiffchaff (Phylloscopus collybita) on 16th March. April and May events were again influenced, for example I saw my first swallow (Hirundo rustica) 5 days later on 10th April, saw my first house martin (Delichon urbicum) 9 days later on 21st April, heard my first cuckoo (Cuculus canorus) 3 days later on 1st May, and saw my first swift (Apus apus) 10 days later on 16th May.

There were two exceptions though, where I recorded hearing my first blackbird (Turdus merula) singing 13 days earlier on 10th February, and saw my first blackcap (Sylvia atricapilla) 8 days earlier on 14th April. These would most likely relate to other influencing factors, such as overwintering in the UK or habitat requirements.

Insects

Compared to previous years, I have still yet to see some species of butterfly that would typically be on the wing by now, such as gatekeeper butterflies (Pyronia tithonus). For the insects I have seen though, again there was a split in event occurrence compared to 2020. For example, I saw my first small tortoiseshell butterfly (Aglais urticae) 2 days later on 7th April, red admiral butterfly (Vanessa atalanta) 26 days later on 7th April, brimstone butterfly (Gonepteryx rhamni) 26 days later on 18th April, and speckled wood butterfly (Pararge aegeria) 52 days later on 13th June.

The early emergers came in the form of my first buff-tailed bumblebee (Bombus terrestris) 14 days earlier on 27th February, peacock butterfly (Aglais io) 5 days earlier on 30th March, orange-tip butterfly (Anthocharis cardamines) 13 days earlier on 31st March, and red-tailed bumblebee (Bombus lapidarius) 12 days earlier on 19th April. Despite these species appearing earlier in spring, later flowering plants will have had a knock-on effect for them due to a mismatch in timing for food. Only further down the line will we be able to see the extent of this impact.

Summary

This year I have recorded more spring dates than I have done so before, such as alder trees flowering, first yellowhammer singing, and first green-veined white butterfly, which will be useful information during the years to come. This reflects how I have felt more in touch with nature this year even with the unusual weather patterns, such as alot of rain! It became clear as we went through May though, that there was a trend for events happening later and later. This is why I was so interested to see how far this trend actually extended amongst species.

Last year I wrote that spring events are ‘in fact getting later, which will be related to… weather and environmental factors here and further afield’. This year this has turned out to be the case, which shows how climate change is having more of an impact through changes in weather patterns rather than just warmer temperatures. Earlier spring events have been getting earlier with warmer winters, but heavy rainfall and colder starts to spring have been affecting late March to May events most. I wonder now what impact this might have as we move forward, for example greater mismatches in ecological timings.

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