Pollination of hazel is by wind, and only takes place between different trees (a tree cannot pollinate itself). The catkins appear in February, but the leaves do not grow until April; they turn yellow before falling in October (3). The nuts are an important source of food for many animals, including red squirrels (Sciurus vulgaris), woodpeckers, dormice (Muscardinus avellanarius) and wood mice (Apodemus sylvaticus). Some nuts that are hoarded may germinate, and so these animals aid in the dispersal of the hazel (3).  Hazel lives for 50-70 years, but the ancient technique of coppicing can dramatically extend the life-span (3). This species has been employed by humans for a variety of uses during the past 6000 years (5). Hazel poles, which result from coppicing, can be split lengthways, and can be twisted without breaking. They were used during the Neolithic to make wattle (hazel strips woven into a lattice), for the construction of wattle and daub houses. Wattle fencing has been used in more recent times as sound screens beside motorways (5). Hazel wood was (and still is) used to make staffs, crooks, walking sticks, and baskets. It is also the wood of choice for divining rods. Hazel leaves were used to feed cattle, and hazelnuts were an essential part of the diet of prehistoric humans. In Celtic mythology, hazel nuts were believed to represent concentrated wisdom (5).

Hazel belongs to the same family of trees as the birch (family Betulaceae), however it is often described as a bush rather than a tree, as it tends to produce several 'trunks' or shoots rather than just one (3). The brown bark is shiny, and tends to peel away in horizontal strips. The twigs are covered in short hairs (2); the roundish leaves have serrated edges, reach 10 cm in length, and are also hairy (4). The male flowers are in the form of pendulous pale yellow catkins, which are known as 'lamb's-tails' (5); they open in February, a time when most other trees are leafless, and are one of the first harbingers of spring (3). The female flowers appear on the same branches as catkins, they are small red tufts on swollen bud-like structures, and it is these that develop into hazel nuts after fertilisation. The edible nuts grow in groups of up to four; they reach 2cm in size and are sheathed by papery modified leaves (3). The English name for this tree derives from the Anglo-Saxon 'haesel knut'; haesel means cap or hat, and refers to the papery cap of leaves on the nuts (6).

Widespread in Europe, Russia, the Caucasus, and Central Asia. The list of countries of occurrence is incomplete.

Corylus avellana L.:
Canada (North America)

Canada

Origin: Exotic

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

United States

Origin: Exotic

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

Hazel has a wide distribution throughout Europe, reaching as far east as the Ural Mountains in Russia, and from Scandinavia in the north to Spain, Italy and Greece in the south. It is also found in North Africa, Turkey, Iran and the Caucasus region of south west Russia (3).

Corylus avellana is widely grown as an ornamental shrub in temperate North America, and it sometimes persists following cultivation, although it seldom becomes established. 

 Corylus avellana is similar to C . americana in habit, leaves, and fruit characteristics, although it becomes much larger. If fruits are present, the two species can be distinguished by the involucre, which is shorter than the nut in C . avellana . The best technical character for separating these species in the absence of fruits is the length of the peduncles of the staminate catkins (which are formed during the summer prior to the season of blooming).

Shrubs , broadly spreading, to 5(--8) m. Bark coppery brown, smooth, sometimes exfoliating in thin papery strips. Branches ascending; twigs pubescent, covered with bristly glandular hairs. Winter buds containing inflorescences ovoid, 5--6 × 3--4 mm, apex obtuse. Leaves: petiole pubescent, covered with bristly glandular hairs. Leaf blade broadly ovate to broadly elliptic, often nearly angled to lobulate near apex, 5--12 × 4--12 cm, moderately thin, base narrowly cordate to narrowly rounded, margins coarsely and doubly serrate, apex abruptly acuminate, abaxially sparsely to moderately pubescent, velutinous to tomentose along major veins and in vein axils. Inflorescences: staminate catkins lateral along branchlets on relatively long short shoots, usually in clusters of 2--4, 3--8 × 0.7--1 cm; peduncles mostly 5--12 mm. Nuts in clusters of 2--4; bracts much enlarged, distinct nearly to base, expanded, shorter than to only slightly longer than nuts, apex deeply lobed; bract surfaces pubescent. 2 n = 22, 28.

Systems

• Terrestrial

Throughout its range, hazel tends to occur as an understory species in deciduous woods, particularly oak woodlands (3). In Britain it is a common feature of hedgerows, where it is coppiced (2).

Flowering very early spring. Abandoned plantings, roadsides, thickets, waste places; 0--700 m; introduced; B.C.

Foodplant / internal feeder
larva of Agrilus angustulus feeds within wood of Corylus avellana

Foodplant / internal feeder
larva of Agrilus laticornis feeds within wood of Corylus avellana

Plant / hibernates / within
naked prepupa of Allantus coryli hibernates inside rotten wood of Corylus avellana
Remarks: Other: uncertain

Foodplant / open feeder
larva of Altica brevicollis grazes on leaf of Corylus avellana

Foodplant / roller
larva of Apoderus coryli rolls leaf of Corylus avellana

In Great Britain and/or Ireland:
Foodplant / pathogen
Armillaria mellea s.l. infects and damages Corylus avellana

Foodplant / spot causer
hypophyllous, subcuticular, often in large irregular groups acervulus of Asteroma coelomycetous anamorph of Asteroma coryli causes spots on fading leaf of Corylus avellana
Remarks: season: 9-11

Foodplant / roller
larva of Byctiscus betulae rolls leaf (several leaves) of Corylus avellana
Other: major host/prey

Plant / associate
adult of Campyloneura virgula is associated with Corylus avellana
Remarks: season: 7-10
Other: major host/prey

Foodplant / sap sucker
adult of Compsidolon salicellus sucks sap of Corylus avellana
Remarks: season: 7-10

Foodplant / mobile cased feeder
larva of Cryptocephalus coryli grazes in mobile case on fallen catkin of Corylus avellana
Remarks: captive: in captivity, culture, or experimentally induced

Foodplant / mobile cased feeder
larva of Cryptocephalus labiatus grazes in mobile case on leaf of Corylus avellana

Foodplant / open feeder
adult of Cryptocephalus nitidulus grazes on live leaf of sapling of Corylus avellana
Remarks: season: early 5-9

Foodplant / open feeder
adult of Cryptocephalus primarius grazes on live petal of Corylus avellana
Remarks: season: 5-6
captive: in captivity, culture, or experimentally induced

Foodplant / open feeder
adult of Cryptocephalus sexpunctatus grazes on pollen of Corylus avellana
Remarks: season: 5-7
Other: uncertain

Foodplant / internal feeder
larva of Curculio nucum feeds within live nut (kernel) of Corylus avellana

Foodplant / roller
larva of Deporaus betulae rolls leaf of Corylus avellana

Foodplant / saprobe
perithecium of Diaporthe conjuncta is saprobic on dead Corylus avellana

Foodplant / saprobe
erumpent conidioma of Phomopsis coelomycetous anamorph of Diaporthe revellens is saprobic on dead nut of Corylus avellana
Remarks: season: 2-5
Other: minor host/prey

Foodplant / saprobe
fruitbody of Dichomitus campestris is saprobic on dead, white-rotten, attached branch of Corylus avellana
Other: major host/prey

Foodplant / saprobe
fruitbody of Dichomitus efibulatus is saprobic on dead, white-rotten wood of Corylus avellana

Foodplant / saprobe
effuse colony of Diplococcium dematiaceous anamorph of Diplococcium lawrencei is saprobic on rotten wood of Corylus avellana

Foodplant / internal feeder
larva of Dryocoetinus alni feeds within cambium of Corylus avellana

Foodplant / sap sucker
adult of Elasmostethus interstinctus sucks sap of Corylus avellana
Other: minor host/prey

Foodplant / gall
Eriophyes avellanae causes gall of live bud of Corylus avellana

Foodplant / feeds on
Gonioctena pallida feeds on Corylus avellana

Foodplant / open feeder
gregarious larva of Hemichroa crocea grazes on leaf of Corylus avellana

Plant / associate
fruitbody of Hypocreopsis rhododendri is associated with dead, fallen branch of Corylus avellana

Plant / associate
larva of Hypulus quercinus is associated with red rotten wood of Corylus avellana

Foodplant / open feeder
larva of Luperus flavipes grazes on leaf of Corylus avellana

Foodplant / feeds on
Malacocoris chlorizans feeds on Corylus avellana
Other: minor host/prey

Foodplant / hemiparasite
Melampyrum sylvaticum is hemiparasitic on root of Corylus avellana

Foodplant / saprobe
sessile, densely clustered, erumpent apothecium of Mollisia caespiticia is saprobic on dead, corticate branch of Corylus avellana

Foodplant / pathogen
Monilinia fructigena infects and damages live nut of Corylus avellana

Plant / associate
mycelial muff of tree of Morchella esculenta is associated with live root of Corylus avellana
Other: major host/prey

Foodplant / saprobe
fruitbody of Mycoacia uda is saprobic on dead, fallen, decayed, white rotted wood of Corylus avellana

Foodplant / open feeder
larva of Nematinus acuminatus grazes on leaf of Corylus avellana
Other: unusual host/prey

Plant / associate
Orthotylus prasinus is associated with Corylus avellana
Other: minor host/prey

Foodplant / feeds on
nymph of Orthotylus tenellus feeds on catkin of Corylus avellana

Foodplant / sap sucker
Palomena prasina sucks sap of Corylus avellana

Foodplant / roller
larva of Pamphilius fumipennis rolls leaf of Corylus avellana
Other: sole host/prey

Foodplant / sap sucker
Pentatoma rufipes sucks sap of Corylus avellana
Other: minor host/prey

Foodplant / saprobe
fruitbody of Phellinus lundellii is saprobic on dead, decayed wood of Corylus avellana
Remarks: Other: uncertain

Foodplant / parasite
hypophyllous Phyllactinia guttata parasitises live flower of Corylus avellana

Foodplant / spot causer
pycnidium of Phyllosticta coelomycetous anamorph of Phyllosticta coryli causes spots on live leaf of Corylus avellana
Remarks: season: 7

Plant / associate
nymph of Phylus coryli is associated with Corylus avellana
Remarks: season: late 5-end 6

Foodplant / spot causer
subcuticular acervulus of Piggotia coelomycetous anamorph of Piggotia coryli causes spots on live leaf of Corylus avellana
Remarks: season: 7-11

Foodplant / feeds on
larva of Rhynchaenus avellanae feeds on Corylus avellana

Fungus / feeder
Sciurus carolinensis feeds on fruit of Corylus avellana

Foodplant / feeds on
Sciurus vulgaris feeds on fruit of Corylus avellana

Foodplant / open feeder
adult of Smaragdina affinis grazes on leaf? of Corylus avellana
Remarks: season: 5-6
Other: major host/prey

Plant / associate
Strophosoma melanogrammum is associated with Corylus avellana

Foodplant / feeds on
Tachyerges stigma feeds on Corylus avellana

Foodplant / open feeder
nocturnal larva of Tenthredo fagi grazes on leaf of Corylus avellana

Foodplant / internal feeder
larva of Trachys minuta feeds within wood of Corylus avellana

Foodplant / internal feeder
larva of Triotemnus coryli feeds within cambium of Corylus avellana

Foodplant / saprobe
erumpent stroma of Cytospora coelomycetous anamorph of Valsa ceratosperma is saprobic on branch of Corylus avellana
Remarks: season: 11-3

Foodplant / saprobe
effuse colony of Veronaea dematiaceous anamorph of Veronaea botryosa is saprobic on wood of Corylus avellana

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 20
Species: 52
Species With Barcodes: 1

Canada

Rounded National Status Rank: NNA - Not Applicable

United States

Rounded National Status Rank: NNA - Not Applicable

Rounded Global Status Rank: GNR - Not Yet Ranked

Widespread and common (3).

Throughout Britain, there has been a prolonged decline of traditional forms of woodland management, particularly coppicing. At present, however, this ancient woodland skill is undergoing a revival in many areas.

Conservation Actions

This species has been rather neglected in terms of conservation when compared to other native trees. However, its importance has now been recognised, and steps are underway to conserve this species (3).