The first question was, obviously, what was the rate of destruction? This was easy to answer-and I could do it indoors, sitting down. You see the RAF trained its photo-reconnaissance people by telling them to fly over, and photograph, England and every few years had to train some more. So there were photos taken in 1946-7, 1953, 1963 etc for most of the country ( a few places were obscured by cloud). And then the Ministry of Housing & Local Government (MHLG) kept all these photos for their own, planning, purposes. I took a table of random numbers, read them as Ordnance survey grid co-ordinates and borrowed the photos from the MHLG. I found that we were losing 10,000 miles a year in the 60s, which was the peak rate.

This figure of 10,000 caused a tremendous fuss with MAFF who said only 1,000 miles of hedge were removed with grant aid. From the Nature Conservancy side whether MAFF financed it or the farmers just let a little straw burning get out of hand and into the hedge was neither here nor there. Hedges were going fast.

We next needed to know what did hedgerow removal (1,000 or 10,000 miles) mean for wildlife? For example how many birds nest in a mile's length of hedge? To find out we went birds' nesting like small boys, It wasn't just me, or even mainly me, looking for nests and counting them: Norman Moore, Brian Davis, John Parslow, & Ernie Pollard-the zoologists in the team, did most.

The results showed that pure hedges, only of Elm or Beech, were not very good and might have very few nests in them. Pure Hawthorn was better but best of all was a big mixed hedge ---that is a hedge with a mixture of trees and shrubs in it.

Of course there was considerable variation, in particular it seemed that there were more nests if you counted them in a hedge with no other hedges nearby, and fewer in hedges surrounded by other hedges. It looked as if birds might be able to nest closer and closer together as the hedges were removed. Or to put it in more ecological terms is the limiting factor the food available in the adjacent field or overcrowding in the hedge? And does it change as hedges are removed? To cut this part short the answer is yes it does. If you start off with, say, 15 miles of hedge on a square mile of land and remove 5 miles of hedge the bird population will not change (unless you happen to remove the only mixed hedges and leave only pure Elm ones) but then remove another 2, 3 or 4 miles: somewhere about 8 miles per square mile the bird population begins to fall - competition for nesting sites begins to have an effect.

Another point to bear in mind is Parslow's observations of Blackbirds' nests at Sacrewell Farm - he found they produced insufficient young to make good adult mortality --- therefore the population of Blackbirds on this farm through time was dependent on immigration of the excess production of young birds from nearby woods -- and this was one of the triggers that led me into the Size and Surroundings ideas.

Back to the botany. Remember some hedges are better than others and these are the ones with a mixture of trees and shrubs in them. And you also need to know that in the hedgerow removal studies we found that even in the areas where most hedges went there were still some left. You might start with 15 miles of hedge on the farm and finish with only 2 or 3 miles, probably the farm boundary hedges which did not interfere with the operation of machinery in the fields. Farmers were willing to leave some hedges-how could the Nature Conservancy ensure they were good i.e. mixed hedges ?

Why are some hedges mixed, others pure? Does the answer lie in the soil? Remember many of our shrubs do like a high base status (Wayfaring tree, Spindle, Field maple and Privet for example). Or could it be management? Farmers assured us they always cut out some species like Elder.

We rushed around the country counting trees and shrubs in 30 yard samples, on chalk soils, on clay soils, sandy soils, managed by clipping with reciprocating cutters, flails or cut and layed. But there were mixed hedges on chalk, clay and sand, managed by flails, cutter bars or cut and laid. The mixtures might differ-Birch and Gorse turned up on the sands but Spindle and Dogwood were only on calcareous soils.

Then Terrry Wells drew my attention to Grose's Flora of Wiltshire which has in it some Habitat Studies. In particular Grose was interested in the difference between the chalk and clay soils so he lists the species in two hedges on chalk and two hedges on clay. He also said that one of each pair was ancient, going back to Saxon times and the other was more recent going back to the Enclosure period.

His lists are full ones, he puts in trees, shrubs, climbers, herbs, grasses. I was interested in only the first two. I went through his lists crossing the rest out and there it was. In the old hedges I was left with 10 or 12 species and in the younger ones with only a couple! The 1 to 100, Hoopers law, came in a flash, in that moment. But only four hedges isn't enough evidence to convince everyone.

I had to get out in the field, into the wind and rain again, and interview dated hedges. But how do you date a Hedge?

The foremost Landscape Historian at that time was the late W.G.Hoskins. He had just retired to Devon. He promised to date some hedges for me so my wife and I, and Johnny Lovell, my assistant, had a field trip to Devon to count shrubs in these 20 or 30 hedges he had dated. Two I remember well were Saxon boundaries not too far from here at Chelfam and Chumhill and they had the requsite dozen species in them, while hedges from the 1840s at Bratton Fleming had only one or two. I felt we could go into print and the first paper on Hooper's law was in the Devon Naturalists Trust Journal in December 1965.

We did more field work on dated hedges and by the time I wrote the first 8 chapters of the Hedges book we had 227 dated hedges. Enough to be sure that 70% of the variation in tree & shrub content of a hedge was explained by its age! Or Hooper's Law, one species for every hundred years, was at least a good rule of thumb. And I've been dining out on it ever since!

Dr. Max Hooper was working for the then Nature Conservancy at Monks Wood Research Station when he did the work on hedges. The New Naturalist volume "Hedges" was published just after the old Nature Conservancy was split into the Nature Conservancy Council and the Institute of Terrestrial Ecology. He subsequently became Head of Station at Monks Wood for the Institute of Terrestrial Ecology. Dr. M. Hooper delivering his lecture.

Photo © Tom Thomas