Description of Atlantic Hazel

Note: For more information and illustrations, take a look at chapter 2    of the free Scottish Natural Heritage publication 'Atlantic Hazel'.

Hazel is a multi-stemmed shrub, i.e. there is more than one stem arising from the rootstock in the healthy plant. It is a pioneering, light-demanding shrub, so one of the requirements for successful germination and establishment is that there is no closed canopy above to shade out the emerging seedling. Seedlings germinate from the previous autumn's nuts. Initially a single stem will arise, soon to be joined by other stems, and in 5-10 years, a characteristic, small, multi-stemmed and branching hazel shrub will develop. Seedlings are palatable to most herbivores, from field voles through to sheep, cattle, ponies or deer. However, once established, and depending on the situation, a typical multi-stemmed hazel stool can reach in excess of 10m in height, although most hazel bushes tend to be between 3-5m high. There are also examples of very exposed, wind-pruned hazel, which forms dwarf stands.

Bark

Young stems of hazel have smooth bark. In Atlantic hazelwoods, this is colonized by a range of crustose lichens (including some species given priority for conservation action under the UK Biodiversity Action Plan), which form pale-coloured, closed mosaics over the surface of the bark.

Old hazel stems (where the bark has become roughened and fissured, trapping moisture) support mosses, liverworts and a profusion of larger leafy lichens such as the tree lungwort  .

Catkins

In the early spring, before the leaves appear, male catkins ("lambs-tails") develop. The catkins produce conspicuous pale yellow pollen that is wind-dispersed, and dancing hazel catkins are a characteristic sight early in the year, shedding pollen into the spring air.

The female flowers  are mostly overlooked because of the showy male catkins; they occur on the same branch as the male catkins, and are small squat reddish buds ("the dwarfy females"). They have neat tufts of twelve crimson styles, which catch pollen.

Leaves and nuts

Hazel leaves are fairly large (up to 10 x 10 cm), oval with serrated edges and a pointed tip. There is a rough feel to the upper side of the leaf (short hairs); the underside is paler with soft, whitish hairs on the veins. Hazel stems bear alternate buds, giving the twig a slightly angular look.

Nuts develop, encased in strong, papery sheaths (bracts, or bracteoles). Young nuts are pale green, changing in colour to ivory and eventually to brown, a strong, wooden nutshell enclosing a single seed (or kernel). Nuts are not produced every year; it depends on several factors, such as the spring weather (incidence of late frosts). Nuts are most often found on well-lit bushes in relatively warm, sheltered situations. Hazel occurring under the canopy of tall trees very rarely flowers or sets seed. Hazelnuts are an important food source for a whole range of animals and birds e.g. in western Scotland field voles, wood mice, great spotted woodpeckers and great tits.

The Celtic rainforest!

Atlantic hazel is part of the Atlantic rainforest. In global terms, coastal temperate rainforest is extremely rare (map  ), confined to just seven regions in the world: the Pacific Northwest; the Valdivian forests of south-western South America; New Zealand; Tasmania (and a strip along New South Wales of SE Australia); the north-eastern Atlantic (including the Pyrenees, West Highlands of Scotland, Ireland, Norway and Iceland); south-western Japan, and the eastern Black Sea. Total world area of coastal temperate rainforests is estimated to be only 302,227km².

Temperate rainforest experiences high rainfall (with over 1500mm of annual rainfall), but some parts are effectively even wetter through having large number of 'wet days' (a day with at least 1mm of precipitation). The regularity of 'wetting' throughout the year keeps some areas constantly damp and humid. Added to this can be 'occult' precipitation, or sea-mists, which condense as water droplets on coastal vegetation. Temperatures are generally mild and do not vary greatly between summer and winter (equable). North-western Scotland and western Ireland have the most oceanic climate in Europe, and this is why these areas are of international importance for 'oceanic' bryophytes, lichens and ferns.

In north-western Scotland, temperate rainforest is estimated to amount to 6,895.8 km² and broadly includes woodlands dominated by oak, birch and hazel, where trees and rocks are often thickly clothed with bryophytes, lichens, ferns and fungi, leading to these woods being termed the 'Celtic rainforest'.

Scrub or Woodland?

'Scrub' used to be a dismissive, derogatory term, often indicating a secondary habitat of low value, but recently, the biodiversity value of scrub has been recognised, resulting in it being reassessed as an important habitat in its own right. 'Scrub' is also often taken to be a seral stage, being a transition from open, herbaceous vegetation to woodland.

However, there are exceptions: there are natural types of scrub, but they are very rare. Hazel stands occurring in some parts along the west coast of Scotland and Ireland form climax scrub; this is scrub that has, and will continue to, persist indefinitely under the current climate, and not become infiltrated by taller trees and develop into "woodland". Hazel-dominated landscapes appear to have persisted in these localities from as long as 10,000 years ago, mostly along the coastal fringes where exposure, thin soils over rocky or steep slopes have inhibited other woody species becoming established.

Hazel 'scrub' today usually forms dense, compact stands, the twigs forming a closed canopy, so that within the stand it is relatively sheltered, yet in summer, when in full leaf, it is shaded and dark. Under these conditions, it is almost impossible for other trees to establish.

Can hazel scrub can persist indefinitely?

Hazel possesses a unique advantage over other forms of scrub, such as hawthorn and blackthorn. Hazel stools (being multi-stemmed shrubs) can be constantly replenished, not reliant on the life-span of the single trunk, so the stand can be a structural continuum.

Is hazel a tree or shrub?

The term 'tree' has been used for hazel, although strictly speaking it is a 'shrub'. Hazel 'trees' are known to exist, but these are almost always created as a result of the long exposure of the hazel to constant grazing whereby the natural growth form of many stems arising from the rootstock has been thwarted. They are found in upland wood pasture as well as in grazed woodlands.