A century of woodland phenology

Christine Tansey's picture

Well, as predicted, things have been quiet on the Track a Tree blog front over the last month. I’m afraid I have been very much occupied with writing up my thesis, including the work based on your Track a Tree records. It can be frustrating writing about the progress of spring during spring, in fact, rather like this Stephen Collins cartoon

Thankfully, I’ve been able to keep making a weekly visit to Roslin, my own Track a Tree recording site, and being in the woods has helped keep me sane in the midst of writing! I’ve been posting shorter updates about this recording season on Facebook and Twitter, so please check our social media sites for the latest news.

I will be writing another post about the first research results based on Track a Tree in due course, but today I want to mention some of the fascinating literature I’ve read as part of my recent work. Historic papers on woodland ecology and phenology have proved especially interesting, in particular those by E J Salisbury from early last century. In 1916 Salisbury published the first part of a large woodland study called ‘The Oak-Hornbeam Woods of Hertfordshire Parts I and II’1. He followed this with Parts III and IV in 19182, and ‘Phenology and habitat with special reference to the phenology of woodlands’ in 19213.

Much has been published in the 100 years since Salisbury’s first paper on Hertfordshire’s woods, but that study helped establish many principles of woodland ecology and phenology. In the 1921 paper he notes that ‘woodland plants are early bloomers as compared with plants of other habitats, or even with the flora as a whole.’ In the 1916 paper, Salisbury demonstrates this by plotting the distribution of flowering times in woodland and non-woodland species in the UK flora, which you can see below. The figure shows that the greatest percentage of common woodland species are flowering in May, while the greatest percentage of the non-woodland species are in flower during July.


Salisbury also discusses an important principle about phenology in the 1921 paper and says that there are '...data which indicate that it is not merely the conditions immediately antecedent to an observation which are important, but also the conditions of the seasons previous.’ We now know much more about how the environmental conditions of previous seasons and of spring itself help cue phenological events in different plant species. For example, it is now known that a period of cold temperatures during winter can be an important cue for some species, particularly trees.

Every spring people comment on whether it is ‘too cold’ or ‘too warm’ for the time of year, and recently I have heard a few mentions of April being very cold. Since Salisbury’s 1916 paper provides an insight into the temperature of spring in Hertfordshire, I thought it might be interesting to see how recent springs compare, and whether this year has been colder or warmer.

The 1916 paper uses mean monthly temperatures for Hertfordshire from a 25 year record, which I converted from Fahrenheit to Celsius. I then used the Central England Temperature (CET) record from the Met Office to calculate mean monthly temperatures for the last 25 years (1991-2015). If you look at the table below you can see that the mean temperatures from Hertfordshire in Salisbury’s 1916 paper are cooler than those obtained from the last 25 years of the CET record. So, while some of you may have noticed that April 2016 felt cool (mean CET 7.5°C), it was much closer to Hertfordshire's mean April temperature a century ago than that of recent years.


Mean montly temperatures (º Celsius) for January-June for two 25 year periods
Temperature record Jan Feb Mar Apr May Jun
Hertfordshire from Salisbury (1916) 2.9 3.4 5.1 7.8 10.6 14.4
CET (1991-2015) 4.6 4.8 6.7 8.9 11.8 14.6


Below you can see another figure from Salisbury's 1916 paper that depicts the timing of vegetative growth and flowering in several woodland ground flora species throughout spring. The use of some of the Latin names of these species have changed in the intervening century, so you may be more familiar with the following names. The species mentioned from top to bottom in the figure are; wood anemone (Anemone nemorosa), dog’s mercury (Mercurialis perennis), lesser celandine (Ranunculus ficaria), bluebell (Hyacinthoides non-scripta) and pignut (Conopodium majus). This figure shows that growth of leaves starts before flowering in each species, and that dog's mercury starts to flower first, peaking at the end of March/start of April. It is followed by wood anemone and lesser celandine, which both peak in April before bluebells, which reach their peak in May.


One of the noticeable things about reading this paper, and others of the period, is the emphasis on the role of woodland management such as coppicing on the ground flora distribution and flowering. The active management of woodlands at the time strongly influenced the light patterns and growth of such species. As traditional coppice management has changed over the last century, this is likely to have affected the ground flora species.

These historic studies have given me lots to think about as I write and provide an important context to the observations that Track a Tree recorders make.  I hope they have also given you an interesting insight into the history of studying woodland phenology.

Now it must be nearly time to head back out to the woods....



1. Salisbury, E.J. (1916). The Oak-Hornbeam Woods of Hertfordshire Parts I and II. J. Ecol., 4, 83–117.
2. Salisbury, E.J. (1918). The Oak-Hornbeam Woods of Hertfordshire Parts III and IV. J. Ecol., 6, 14–52.
3. Salisbury, E.J. (1921). Phenology and habitat with special reference to the phenology of woodlands. Q. J. R. Meteorol. Soc., 47, 251–260.


Thanks for taking the time to share that bit of history, very interesting temperature pattern for the 25 year record used in 1916: a proper winter may have been the norm?   Now that I can look back over a period long enough to be called climate (well into my 60s) I do wish I had a better momory of what it was really like - you can't trust your memory for weather, only for some key memorable events.

I also saw the Guardian cartoon and empathised: I am doing a course just now and should be writing up a project even as I am writing this. So I'll close this and get back to some work... in spite of mild/warm sunny-ish weather in Glasgow.




Christine Tansey's picture

Hi Mags49,

Glad you enjoyed the history in that post. If you are interested in the Central England Temperature record, it is available online and you can have a look at its records.

Good luck with your own project, it's been a difficult week to concentrate with all the sun outside!

Brilliant - thanks so much for sharing your sources. Hope the writing goes well and you get the occasional time to pop into the woods!. Also thanks for sharing Alli Phillimore et al paper on passerines from the tweets. I don't do tweeting but can read them on this website.

Christine Tansey's picture

Thanks Sue. Glad you enjoyed the blog post and that you got to see the info about Ally's paper via the website.

Happily, I'm still managing a weekly visit to the woods, hope your season is going well!