Citizen Science - What makes oak buds burst in spring?

When my daughters were younger than they are now*, and before boys became more interesting than natural history, I tried to interest them in recording what was happening in the natural world around them. We recorded all sorts of things - the date of the first bluebell, the arrival of the house martins, weekly rainfall and temperatures, and many others. We also tried to see if any of these things were linked in any way. For instance, did excessive rain and low temperatures delay the bluebells? One of the things that we did find apparently linked was ground temperature and oak bud burst.

Now, is our tree alone in finding 10°C the signal to get its act together? Tree leaves are unfurled by water entering them from the tree and its roots and it is accepted wisdom that it is the air temperature that starts this happening. But is it actually the warming of the water in the ground that starts things moving with 10°C the critical level? The ground temperature rises at a much steadier rate than the air temperature that usually varies wildly in Spring. Some mass recording might throw light on the subject.

oak leaves

We have an oak tree in our garden and the pipe from the water main in the road runs through its roots. We reasoned that water standing in the pipe overnight would attain the same temperature as the ground around it. So every Sunday morning we ran the cold tap arid held my brewing thermometer under it. (I did say this was 'citizen' science!). Over several years we found that - regardless of air temperature or day length or anything else - when the cold tap read 10°C the oak buds burst! Bud burst is very quick - sometimes only a matter of a few hours - and it is easy to put a date to it.

As I said, boys eventually became more interesting than buds, but some years later I started to watch the water temperature and bud burst again. Sure enough at 10°C the oak buds burst.

The experiment
If you have a free-standing oak tree hand - in your garden, in a hedge, in a park - but not in a wood, would you care to record the cold tap water temperature first thing in the morning for two or three weeks in April - May and keep an eye on your oak to spot bud burst? If we could find enough like- minded people spread over a variety of terrains we might be able to take the hypothesis a stage further. Perhaps even far enough to get the professionals interested, because to date my family's findings have been met with total lack of interest!

Things start to happen in a warm spring about the second week in April. If you like the idea in please contact me by email .

*I could not possibly say how long ago that was

Dick Greenaway

Earley Trees

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