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Thursday 13 December 2018

Acorns a great source of nutrients for wild animals

Acorns are objects of great natural beauty
Acorns are objects of great natural beauty

Jim Hurley - Nature Trail

Acorns are objects of great natural beauty. They are, of course, the nuts or fruits of oak trees. Each nut sits in its own little cup somewhat like an overgrown hen egg in a tiny, misfit egg-cup. Shiny and smoothly rounded, each nut is tipped with a little point, the remains of the style of the female flower that gave rise to it.

Acorns are such attractive objects that they feature as motifs in architecture and art, as ornaments on furniture, cutlery, and jewellery, as emblems in heraldry, and as symbols for woodland walks.

Acorns are rich in nutrients, so they are an important source of food for birds like Jays and Woodpigeons, rodents like squirrels and mice, and larger mammals like deer.

The benefit that oak trees gain from unwittingly feeding all these creatures is the dispersal of their offspring. The natural process of evolution over a long number of years ensures that while many creatures feast on the autumn mast, enough fruit survives to perpetuate the species.

We have only two native oaks in Ireland: the Pedunculate Oak and the Sessile Oak. On the face of it, it is not a big job to identify an oak tree to species level; the clue is in the names.

A peduncle is the technical term for a stalk. Note that in the image above the acorn sitting in its cup is supported on a stalk almost as long as the acorn itself. Since the acorn is supported on a stalk or peduncle it is said to be pedunculate hence the tree's common English name Pedunculate Oak.

'Sessile' means having no stalk, so the Sessile Oak is the tree with acorns sitting directly on twigs without any supporting stalks.

But how do you tell the two species apart when the trees are not in fruit? Again, note that in the image above the leaf to the right of the acorn has two little extensions at its base like the lobes at the ends of our ears. The leaves of the Pedunculate Oak have these little ear-like extensions whereas the leaves of the Sessile Oak do not.

However, like most things in nature, it is not that simple. Our two native oaks breed with each other producing hybrids that display intermediate characteristics. Hybrids are frequent and since they are fertile, they can, and do, breed with their parents producing further variation.

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