The hedge is not a wall.
It is a corridor.

A hedge looks like a full stop. Standing in the middle of a field in February, with the wind coming off the ridge and nothing green in sight, the line of blackthorn at the far end reads as the edge of things: the place where this field stops and the next one starts. That is certainly what it was planted for. Most of the hedges in this country went in to keep something out, or more often to keep something in, and the older ones went in to say whose field was whose.1

The great wave of enclosure ran from roughly 1750 to 1850 and added an estimated 200,000 miles of hedge. But a substantial minority are far older: a hedge on a parish boundary is often the boundary itself, predating the fields on both sides of it.

Walk along it rather than across it, though, and it stops being a full stop. It becomes a sentence. Over eleven days last spring we followed a single hedge line for thirty-one miles, from a lane end outside Ockley to the point where it gives out at the edge of an industrial estate. We were not counting species, though we counted some. We wanted to know what the hedge was doing that a wall could not.

What a wall cannot do

The short answer is that a wall stops everything, and a hedge sorts. It is permeable in a way that is highly specific about what gets through. A badger goes under it, using the same gap its predecessors used, and the gap becomes a run, and the run appears on maps drawn a century apart. A wren goes into it and effectively never leaves; a wren will spend most of its life within a few hundred metres of where it hatched, and a hedge is the whole world for that bird.

A dormouse will not cross eight metres of open ground. That number is the reason hedgerows matter more than their area suggests. Eight metres is nothing at all, and yet it is enough that a dormouse population on one side of a gap and a population on the other side are two populations rather than one, with everything that implies for how long either of them lasts.2 Restore the hedge across that gap and they become one population again. Nothing else about the landscape has to change.

Hazel dormice are the standard example because they are so reluctant to descend to ground level, but the principle holds for a long list of woodland invertebrates that simply do not disperse across bare arable soil.

A hedge is not a boundary between two habitats. It is a habitat that happens to be three metres wide and thirty miles long. Dr Marian Ellis, Ockley Hedgerow Survey

Eleven days, thirty-one miles

The walk was not picturesque. A hedge line does not follow the route you would choose, and for two of the eleven days it followed the verge of a B road with lorries a metre from our shoulders. The hedge was still there, still doing its work, still carrying a continuous ribbon of bramble and hawthorn through a stretch of countryside that had otherwise been reduced to surfaces.

The gappy middle

Between miles fourteen and twenty-two the hedge is in poor condition, and it is worth being precise about what poor means. It is not absent. It is present as a row of individual hawthorns with two to four metres of nothing between them, which from a car at fifty is indistinguishable from a hedge, and from the point of view of a dormouse is a series of islands.

This is the commonest condition of hedgerow in lowland England and it comes from a specific practice: flailing the same line every year, at the same height, in the autumn. The plant responds the way any plant responds to being cut in the same place repeatedly. It thickens at that height and thins everywhere else, and then it starts to die back from the base, and then there is a gap.3

Cutting on a two or three year rotation, and raising the blade by four inches each time, largely prevents this. It also leaves the berries on through the winter, which is when they are worth something.

What we are actually counting

There is a temptation, in writing about this, to reach for the ecosystem-services argument: hedges store carbon, hedges slow runoff, hedges shelter stock and reduce lamb mortality, hedges support the pollinators that the crop in the field is relying on. All of that is true and all of it is measurable, and none of it is quite the reason people plant them.

Every farmer we spoke to on the walk gave us a services answer first and something else second. The something else was usually about time. A hedge you lay this winter is a hedge that will be doing its job in eighty years and will still be recognisably the thing you made. There are not many jobs on a modern farm with that shape.

You are not planting it for you. That is the whole trick of it, and it is why the ones that get planted get planted at all. Tom Reyner, Ockley

Ockley, in the end

The hedge gives out four hundred metres short of the estate boundary, at a point where a access road was cut through it in the nineteen eighties. Standing at the cut, you can see the line continue on the far side of the tarmac, thinner but unmistakable, and then stop against a fence.

The parish has planning permission to reconnect it. Two hundred whips, a gap of eleven metres, and a culvert that already exists. It will cost less than the survey that recommended it. If it goes in this winter, the two halves of a thirty-one mile hedge will be one hedge again for the first time since 1987, and the dormice at the northern end will have somewhere to go.