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Flowering patterns across Europe

We can now see how the timing of flowering is changing both across Europe and between different tree species. I have taken four species (birch, horse chestnut, oak and rowan) which are well represented in the Beagle records. For each species I have noted the first four flowering observations and used the average date of the second, third and fourth flowering occurrences. If there are three or fewer records in total then I have used all the data. There is no fixed way to do this but we need to produce a measure of the average earliest record, avoiding any very early records which may be due to unusual factors. The date is set as 1 for 1st March so a date such as 4th April would be 4+31 = 35.

The data from some countries can be combined as their overall averages are very similar. This is also convenient where there are less than three records from a particular country. I have chosen to combine Hungary with Slovakia, Germany with the United Kingdom and Sweden with Norway (Table 1). The records for Romania, Czech Republic and Russia are fewer (generally taken from less than three observations) but are useful comparisons and are shown in brackets.

Table 1. Average earliest flowering record for four tree species in 2010. Values based on less than three records are italicized. Dates are based on 1st March as day 1.


Hungary and Slovakia (Romania, Czech Republic)


Germany and U.K.

Sweden and Norway (Russia)

difference between first and last date


29.5 (19.0, 39.0)



74.5 (71.0)


Horse Chestnut

50.8 (59.0, 65.0)












58.5 (72.5)



94.0 (73.0)


overall average for country group







There are some striking patterns emerging from these data. Look at the final column which shows the difference between the first and last observation date. Birch and rowan are consistent in differing by about 1.5 months, with the horse chestnut difference close to two months. This is in strong contrast to oak which differs by only three weeks. We need to be cautious as the data for oak and rowan for Sweden and Norway are based on a single record from Sweden. However, the data do point to some important differences between species, which have considerable implications for the animals which depend on them and the value of the trees as climate indicators.

The overall average for each country group also shows an interesting pattern. Hungary-Slovakia, Germany-U.K. and Sweden-Norway show increasing values from south-east to north-west, differing by 12.9 and 22.5 days respectively. Poland is different in that it is the earliest overall. Poland is a large country and the differences may be due to variation within the country. We will need to look more closely at differences within countries, for example due to altitude or the effects of urban areas.

Later in the year we will be able to look at whether other phenophase observations agree with those from the flowering records. In the meantime we can reflect on the valuable results emerging from the Beagle project and enjoy our summer break.

Best wishes

Dr Michael Gillman
Department of Life Sciences
Open University

Published 16.07.2010.