For the first time in a very long time I thought about Hooper’s Rule, a sort of rule of thumb worked out by the ecologist Max Hooper, as a way to estimate the age of hedges in England and Wales.

It is simply a rule of thumb based on observation, and of course does not work everywhere.

For example it doesn’t work in Cornwall, where many of the hedges are essentially overgrown stone and earth banks, and I suspect it may not work in Scotland where the flora is less diverse.

Equally, applying it to northern France where the species mix is more diverse may not work either.

So what is Hooper’s rule?

In a 30m section of hedge, count the number of woody plants. Multiply the number of woody plants by 100. If possible, repeat the exercise at a couple of sample points on the same hedge.

This should give you a rough estimate of the age of the hedge.

Like all good rules Hooper made this up – he looked at old maps where there were hedges marked and realised that nineteenth century enclosure hedges were less diverse than late medieval hedges or hedges dating from the Tudor or Stuart period.

How does it work?

Traditionally, when a hedge is planted as a field boundary only one species of plant is used, traditionally something thorny like hawthorn. Over time, other plants self sow themselves and establish themselves in the hedge, so a hedge that is relatively non diverse is more recent than one that is quite species diverse.

The rule breaks down with older hedges as there’s more chance of other plants installing themselves, so that by the middle medieval period the results are quite ambiguous as an estimate of age, other than being able to say it’s old.

The rule is basically an estimate based on a range of hedges in the southern half of England, as I’ve said it doesn’t work everywhere.

Equally, it might work in surprising locations.

In upland Sri Lanka the tea plantations are surrounded by hedges planted by the British colonists in the late 1800s.

Unsurprisingly they are pretty non diverse – except in some place there a coffee shrubs in the hedges.

Some of the older tea plantations started life as coffee plantations until blight struck in the 1870s. The coffee plants were grubbed out and tea planted. But in the older hedges some coffee shrubs survived, and Hooper’s rule probably just about works to let you separate earlier plantings from later plantings…