Oak and ash
Oak before ash, in for a splash
Ash before oak, in for a soak
If the old rhyme is to be believed the sightings submitted to the Nature’s Calendar survey so far this spring indicate we could be in for a pretty dry summer. According to the rhyme if Oak comes into leaf before Ash we’ll have a good summer, if Ash leafs first summer will be pretty wet.
Disappointingly, there's no evidence linking the relative timings of oak and ash and subsequent rainfall. Rather the relative timings are influenced by temperature with oak being more responsive than ash. This has been determined by the data being collected within the Nature’s Calendar project.
In 2011 Oak is in the lead again, with the first observation of leafing recorded at the Nature’s Calendar survey on March 21st 2011 in Essex. Ash leafing wasn’t recorded until April 4th 2011 in Cardiff. So if you were still seeing dead-looking trees in May in your local wood or in fields they might not actually have been be dead – just ash.
Using historical data from Norfolk (1750-1958) we have 158 years when both ash and oak were recorded. On 46 occasions (30%) ash was earlier.
More recently data from Surrey suggest ash earlier on only 3 occasions in 39 years, and in Northumberland only 3 occasions in 28 years.
In all instances oak gets more advantage over ash in warmer springs as shown in the following graph.
Usually Oak leafs late March-May which is about 2 weeks earlier than 30 years ago. Ash usually leafs during April and May which is about 7-10 days earlier than 30 years ago. It may come as a surprise but on average spring now arrives 8 days earlier than 30 years ago.
These patterns all point to the fact that it will become increasingly unlikely for ash to precede oak as the climate warms.
Woodland consists of communities of plants and animals that live in support of or in competition with one another. That oak is taking greater advantage of a warming climate suggests that there may be a change in the competitive balance in woodland in the years to come.
Interestingly there are similar rhymes about oak and ash in, at least, German and Norwegian:
UK
Oak before Ash, in for a splash
Ash before Oak, in for a soak
Germany
Grünt die Eiche vor der Esche
hält der Sommer große Wäsche
Grünt die Esche vor der Eiche
hält der Sommer große Bleiche.
Norway
Ask før eik blir steik
og eik før ask blir plask
But stranger still, these suggest the opposite relationship to the English rhyme.