Hedgerow equations

Large parts of the North York Moors have either no field boundaries (open moorland) or have drystone walls as boundaries (upland tops and slopes), but round the edges of the area and in the farmland dales there are often hedgerows. A large number of these hedges will have existed for years, but they’re not considered ‘ancient’ unless they’re older than 1700, just like Ancient Woodland.

Hedgerows of course are made out of trees and shrubs just like woodland but are otherwise culturally and ecologically distinctive. Hedgerows have long been a man-made feature of landscapes – boundaries to keep things in as well as out. In other parts of England there are hedgerows that are thought to date back over a millennium. This is not so likely in the North York Moors. Many hedgerows here probably just date back to the 18th and 19th centuries when there was a lot of enclosure and land ‘improvement’ going on, here as elsewhere in the country.

Old roadside hedgerow, Bilsdale. Copyright Ami Hudson, NYMNPA.

Hedgerows have been created through one or more of these three methods – original planting/transplanting, allowing uncultivated field edges to grow up, or by leaving a ‘ghost’/edge of a removed woodland. A curved hedge suggests a ghost hedge because natural woodlands are more likely to have had curved not straight edges, whereas constructed boundaries are often as straight as possible.

Ancient hedges share Ancient Woodland herbaceous ground flora such as Wood anemone, Sweet woodruff and Golden saxifrage. There is also a well-known ‘rule’ (Hooper’s Law) sometimes used to estimate the age of a hedge by counting the number of established woody species over a 30 yard/30 metres stretch or preferably an average over a series of stretches. The equation is then Age = no of species in a 30 yard stretch (or average number) x 110 + 30 years.

Whereas an enclosure hedge (18th/19th century) will have one or two species, a pre Norman Conquest hedge might have more than ten species. However such ancient hedges would have been an unlikely feature in the ‘wastes’ of the North York Moors recorded in the Domesday Book at the end of the 11th century.

Managed hedgerow, Glaisdale. Copyright NYMNPA.

Like all rules there is bound to be exceptions. Hooper’s Law relies on the hedgerow being mainly naturally colonised, not planted 30 years ago by a biodiversity enthusiast. Also any hedgerow adjoined to or close-by woodlands are more likely to be colonised at different rate than another hedge. In the end it’s probably best to use other evidence of dating, such as maps and records, as well.

Although original hedgerows may have been planted and laid to incorporate existing older trees it would be difficult to keep such trees alive, and therefore much more likely that in-boundary trees were planted at the same time as a hedge or added later. The first edition Ordnance Survey 25 inch mapping includes individual in-field and in-boundary trees. For the North York Moors area these maps are usually from the 1890s. The presence of a mapped in-boundary tree suggests that boundary was a hedge rather than wall or fence at that time.

Since the middle of the 20th century the amount of hedgerow in the country as well as the number of boundary trees has been reduced. Machinery meant it became easy enough to remove a hedgerow, and to maximise the cutting of hedgerows. At the moment the cultural and ecological importance of hedgerows is valued and lately there have been efforts to use agri-environment schemes to encourage good practice management and to use the 1997 Hedgerow Regulations to control removal.

Briar rose in an old hedgerow. Copyright NYMNPA.

* This is the list of species which count towards Hooper’s Law. The species listed grow in a wide variety of habitats across the country, only some of these would ever have been used in and around the North York Moors. As it is currently winter, identifying different species is particularly difficult and therefore maybe more fun.

Alder Cherry-plum Hornbeam Sallow
Apple incl crab apple Dogwood Lime – ordinary, pry Service
Ash Elder Maple Spindle
Beech Elm – Wych, English, East Anglian, Cornish, Dutch/Huntingdon etc Oak – pedunculated, sessile Sycamore
Blackthorn Furze Pine Wayfaring-tree
Briar (three named species) Guelder-rose Plum incl bulace Whitebeam
Broom Hawthorn – ordinary, woodland Poplar – aspen, blackwhite, grey Willow – crack, white
Buckthorn Hazel Privet (wild) Yew
Cherry Holly Rowan

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