MEASURING TREES
The measurements given in this book are only approximate. Girth, or circumference, is given in feet and inches (veteran pre-metric tape measure!) One foot is twelve inches and converts to 30 centimetres, three feet make a yard which is approximately one metre.
Girth should be measured at chest height, 5 feet or 1.3 metres. This is easier said than done with trees which are leaning, surrounded by undergrowth, with low side branches, or growing against a wall. A few inches up or down can make a considerable difference in the circumference measurement. The tape measure must be kept level.
Height may be estimated by triangulation – in an isosceles triangle with a right angle (90 degrees) the two sides are of equal length. A stick is held with outstretched arm at eye level to form this right angle. The length of the stick must be equal to the distance between the eye and outstretched fingers i.e. are specific to each person.
The tree surveyor walks back until top and bottom of the stick coincide with tip and base of tree. The distance between that position and the tree then equals the height of the tree: this may be measured or paced out.
BIG TREES
Height and girth do not tell the whole story. The overall size of the tree and the effect it makes on the observer is also due to the shape of the crown and spread of the branches. Some of the largest oak and beech trees have massive canopies springing from trunks of relatively modest girth. The greatest trunks may belong to over-mature trees with reduced foliage.
A rough guide is that trees over 10’ in girth are substantial specimens for smaller trees – holly, rowan, birch, cherry, even Scots Pine.
Alder, willows, poplars may exceed 12’. Over 15’ and the tree may be considered big for most broad-leaved species – beech, horse chestnut, lime, sycamore, oak and sweet chestnut. Long-lived specimens often reach 18’.
Once over 20’ the tree is exceptional; over 25’ and it is a real giant – to be expected from exotic conifers like Wellingtonia but very rare for others.
TREES AND SEEDS
Trees propagate naturally from seed. Almost every tree – female trees for those species which are single sex – will produce seed each year. The quantity of seed varies from year to year, and how much of it is fertile/viable : this is related to the weather at flowering times and success of pollination.
The exceptions are hybrid trees some of which are infertile and have to be propagated by cuttings, such as the hybrid Cupressus varieties common in gardens. Cuttings are also used for willows and some poplars.
Once seeds are produced by the tree, many, like acorns, hazel nuts, are eaten even before they fall and more go once they reach the ground. Squirrels, mice, birds all rely on the seasonal feast. They also have a more positive role because they help to spread seeds, by eating indigestible hard seeds which are then evacuated in droppings, and also by burying seeds for storage – squirrels and jays are best at this.
Seeds often remain dormant over winter, and need a cold weather spell before they develop. They need warmth and moisture to germinate, light to grow further. Woodland glades and edges, so long as the grassy vegetation is not too thick, are good. A fallen tree creates space, light, and disturbed ground which is ideal for new young seedlings to grow and so eventually take its place.
ACKNOWLEDGEMENTS
Thanks for the production of this book are due to John McClean, Chairman, and to all members of the ‘Seeds of Place & Time’ Group:
Dinah Browne
Neville McKee
Fiona Holdsworth – Belfast City Council
Stuart Morwood – DANI, Forest Service
Dermot Hughes – Ulster Wildlife Trust
Mike Meharg, Ian Irvine – Northern Ireland Environment Agency
Jo Whatmough – The National Trust
Jane Picton – Greenmount Agricultural College
Maia Taylor – The Woodland Trust
John Witchell – Clandeboye Estate
Ben Simon – Forest of Belfast
Pascal McCaughan and Frances Claxton, Conservation Volunteers Northern Ireland
Help was received from many individuals and Government departments and their advisory bodies.
Every owner of every tree deserves thanks, not only for providing access to the specimens and information about them, but for looking after them in the first place. So many trees have been lost – more would have gone but for the protection offered by such concerned owners and guardians.
Previous tree records were sourced from TROBI (Tree Register of the British Isles).
Most of the photographs were taken by Mike Hartwell of Northern Ireland Environment Agency, who dedicated much of his spare time in the inclement summer of 1998 to capture the true spirit of our trees. Others are from Dinah Browne, Ian Jackson of Ballynahinch and Ben Simon of Forest of Belfast; the line drawings of the Wesley trees are by Niall Timmins.