Shrub-Layer: woody shrubs and small trees

Above: hawthorn (Crataegus). The shrub layer of a woodland consists of shade-tolerant shrubs and small trees that can photosynthesise using the dim light that filters through the tree canopy. This small tree is a hawthorn. Hawthorns typically produce a considerable tangle of branches and when grown in hedges and regularly pruned they respond by producing more modified, stunted and pointed branches - the thorns that make this plant such an effective barrier to contain livestock.


Hawthorn

In these woods the shrub-layer is predominantly small trees like hawthorn, shown above, hazel (Corylus avellana), some rowan (Sorbus) and holly (Ilex). Saplings of larger trees, the oaks, beeches, maples, sycamores, chestnut trees and ash trees also add to the shrub-layer.Shrubs like bramble (Blackberry, Rubus fruticosus)

Hawthorn leaf

Above:The characteristic small, lobed leaf of Hawthorn; below: underside of a Holly leaf.

Holly leaf

Hawthorn

Hawthorn

The hawthorn is famous and much-loved for its May-blossom (above) - an ancient fertility symbol. It flowers more-or-less around May-time, producing a spectacular display of small white (sometimes pink) flowers - the May blossom. In late summer and early winter it is well known for its bright red berries (haws), below, which provide birds with valuable food well into the winter. The leaves are said to be very nutritious and to stave-off hunger (could this be a defense against being eaten?) and the berries apparently make good wine. In summer the hawthorn has neither its pretty white garment nor its red berries but the strange twisted and tangled form of hawthorn trees is striking beneath the darkness of the late summer canopy.

Hawthorn

Hawthorns are very slow growing trees and typically live for 100 years, though quite a few make it to about 400. Its tangled and twisted growth habit always makes hawthorn trees look ancient. Being slow growing their wood is extremely hard and dense (fine grained) but has few uses, perhaps because of the smallness of the trees, sometimes being used for tool handles and walking sticks.

Holly

Holly

Above: holly, Ilex aquifolia. The holly typically has spiny leaves with thick waxy cuticles, especially on the upper surface. The tough leaves are well-adapted to survive the winter and the holly is evergreen. In winter the holly is one of the main sources of colour in the woodland, with its lush green leaves and red berries, famous as a Christmas decoration. Tradition has it that in late Autumn the oak hands-over his crown for the holly to bear until the following Spring.

Holly

Holly

Holly

Folklore has it that both the hawthorn and holly make safe shelter during an electrical storm:

Beware of an oak,
it draws the stroke,
Avoid an ash, It courts the flash,
Creep under a thorn,
It will save you from harm.

Elder

Elder

Elder fruit

Above: elder, Sambucus nigra. Elder forms shrubs or small trees up to 10 m tall. It prefers nitrogen and phosphorus rich soils and is often associated with rabbit warrens (although rabbits do not eat it) and eutrophic soils (soils polluted by excess fertiliser). It is pollution resistant and colonises open spaces rapidly. It grows rapidly and has a light-weight construction, with white porous spongy pith in the younger branches. The leaves and bark are toxic. The leaves contain cyanogenic glycosides (e.g. sambunigrin) which react with enzymes, when eaten, to produce toxic hydrogen cyanide (HCN) gas! However, cases of poisoning are isolated and deer will graze elder, but the toxicity undoubtedly makes it harder for animals to graze too heavily on elder. The bark contains ribosome-inactivating proteins (RIPs) (constitute about 80% of bark protein). The RIP forms a complex with lectin; the lectin molecule binds the target cell-surface membrane and then the RIP enters the cytoplasm and kills the cells by inhibiting the ribosomes, which make proteins. RIPs are also found in the fruit, and yet, the fruit and flowers make excellent wine! Elder is pollution resistant and resistant to high levels of alkali, salt, ozone, sulphur dioxide emissions, and certain metals like copper and lead. Being a fast-growing coloniser, elder is short-lived, with a lifespane of about 25-30 years, occasionally over 40 years. Younger plants are shrubby with many stems branching from a single base, but by 20-30 years of age a single trunk becomes dominant.

The leaves emerge in Feb?March, the flowers in May/June and the fruits in July, ripening by early September. The flowers are nectarless and have five-fold radial symmetry, but are visited by beetles (especially the longhorn beetle), flies and honeybees. The seeds are small (about 2-3 mg) and the fraction that germinate is quite low, but increases when the seeds have been defecated by birds. The flowers develop by the third or fourth year and each plant produces up to 100 000 seeds or more.

The wood of elder is diffuse-porous with small-diameter vessels (about 40 micrometres diameter in the stem, but 2-3l times larger in the roots). Heartwood forms after 6-10 years. the bark is brownish-grey.

Rowan

Rowan

Rowan (Mountain Ash)

Rowan bark

Bramble

Below: Blackberry or Bramble (Rubus fruticosus) forms part of the shrub-layer of many woods, and when ripe the berries taste delicious! Bramble also puts out branches that stretch across the woodland floor, snaking from side-to-side in slow motion, searching for something to grab hold off for support: Bramble is a scrambling plant. Many Bramble flowers can produce seeds without the need for fertilization from pollen (apomixis) giving rise to over 400 microspecies, although pollination is still needed to trigger seed production.

Rowan bark

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