Species Focus- Oak (Quercus spp.)

Species Focus- Oak (Quercus spp.)

Blog by Ciara Laverty

There is an old saying that “an Oak tree spends 300 years growing, 300 years resting and 300 years dying”. These iconic trees are easily recognisable by their lobed leaves and fruiting acorns. Historically there is evidence of Oak woodland around Lough Neagh’s shores, which we can see through local place-names derived from the Irish word Daire (Oak woodland/plantation):

  • Derryloughan Co.Tyrone:   Doire Lochain   “Oakwood of the Little Lough”
  • Derrylileagh Co. Armagh:   Doire Loilíoch    “Oakwood of the Milch Cows”
  • Derrymore Co. Antrim:       Doire Mór           “Great Oak Grove”

There are two native species of Oak found on the island of Ireland. Sessile Oak (Quercus petraea) which is the national tree of Ireland and Pedunculate Oak (Quercus robur) which is often referred to as English Oak. The two species can be told apart by looking closely at their acorns- Pedunculate Oak acorns hang on long stalks while those of the Sessile Oak appear stalkless.

Oak 1

Oak woodlands with mature trees are an important habitat, supporting a wealth of wildlife species. Hundreds of invertebrate species are at home here which in turn are a vital food source for breeding birds. Crevices and holes in the bark of these ancient giants provide places for birds like the Treecreeper to nest and for bats to roost in.

As we are now on the cusp of Autumn, our Oak trees are now laden with their crop of acorns. Squirrels, deer and badgers readily feed on this autumnal harvest. This time of year is also an excellent opportunity to spot the most colourful member of the crow family- the Eurasian Jay.

Despite their vibrant appearance this shy corvid can be tricky to spot amongst the foliage, their presence is usually announced by their harsh, screaming call. Throughout autumn Jays are busy collecting and caching acorns, a food source that will help see them through the cold winter months ahead. Not all of these acorns will be consumed, and those that are left will have the chance to germinate.

When out on your woodland wander keep your eyes peeled for abnormal growths on the twigs and leaves of Oak trees. These are known as galls and are caused by a parasitic relationship between Oaks and Oak Gall Wasps. Sessile and Pedunculate Oak are the host plant for around 70 species of Gall Wasp.  Two commonly seen galls on Oak are the Oak Knopper Gall and the Silk Button Gall:

Oak Knopper Gall

This gall is the result of a tiny parasitic wasp (Andricus quercuscalicis) laying an egg on pollinated Pedunculate Oak flowers. The larvae secrete a chemical that alters the development of the acorn, causing it to grow in a knobbly, distorted shape. The wasp larvae develops inside this gall, which will turn a woody brown colour and fall to the ground in Autumn. The adult wasp emerges in Spring.

Silk Button Gall

This gall is present on the underside of Oak leaves and is caused by the parasitic wasp (Neuroterus numismalis). They look like a small golden coloured disk with a sunken centre. A single gall holds one wasp larvae. Like the Knopper Gall, these will also fall to the ground and the adult wasp will emerge in Spring.

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