Trees of Britain and Ireland

Many lists of Trees of Britain and Ireland have been written. There are a number of issues surrounding the inclusion of a species in such a list. As can be seen from the outline of debate below, there is no 'correct' list of trees of Britain and Ireland.
==Issues of Debate==
===Definition of Species===
There are a number of different opinions regarding the validity of some species, notably apomictic microspecies and whether some 'species' may actually be hybrids. In particular, the number and definition of species in the genera Sorbus (rowans, whitebeams etc.), Ulmus (elms) and Salix (willows) are open to debate.
===Definition of Native===
Native (usually synonymous with indigenous) species are considered to be species which are today present in the region in question, and have been continuously present in that region since a certain period of time. When applied to the British Isles, three possible definitions of this time constraint are:
* a species that colonised these islands during the retreat of ice at the end of the last ice age
* a species that was present in these islands when the English Channel was created and the land bridge between Britain and continental Europe was flooded
* a species that has colonised without human assistance; in some cases this is uncertain.
The only endemic tree species in Britain and Ireland (that is, that are native only to this region) are some apomictic whitebeams.
Species that were native in the region in prehistory before the last ice age, but not subsequently, are generally regarded as extinct and no longer native.
Many additional species have been imported by humans; the total list of all introduced trees numbers several thousand. A far smaller number of these have become widely naturalised, spreading by their own accord without recourse to further human assistance.
===Definition of Tree===
A tree can be defined as a large, perennial, woody plant with secondary branches supported by a primary stem (compare with shrub). There is no set definition regarding minimum size, though most authors cite a tree species as being one which regularly reaches 6 m (20 ft) tall (see also tree).
==List of species==
===Native trees===
* Alders
** Alder (Alnus glutinosa)
* Ashes
** Common Ash (Fraxinus excelsior)
* Birches
** Silver Birch (Betula pendula)
** Downy Birch (Betula pubescens)
* Box
** Box (Buxus sempervirens; southern England only)
* Cherries and Plums
** Wild Cherry (Prunus avium)
** Bird Cherry (Prunus padus)
** Blackthorn (Prunus spinosa)
* Elms
** Wych Elm (Ulmus glabra)
** English Elm (Ulmus procera; southern Great Britain only; doubtfully native)
** Smooth-leaved Elm (Ulmus carpinifolia; southern Great Britain only)
* Hawthorns
** Common Hawthorn (Crataegus monogyna)
** Midland Hawthorn (Crataegus laevigata; southern Great Britain only)
* Hazels
** Common Hazel (Corylus avellana)
* Hornbeams
** European Hornbeam (Carpinus betulus; southern Great Britain only)
* Hollies
** European Holly (Ilex aquifolium)
* Junipers
** Common Juniper (Juniperus communis)
* Lindens (Limes)
** Small-leaved Linden/Lime (Tilia cordata; southern Great Britain only)
** Large-leaved Linden/Lime (Tilia platyphyllos; southern Great Britain only)
* Maples
** Field Maple (Acer campestre; southern Great Britain only)
* Oaks
** Pedunculate Oak (Quercus robur)
** Sessile Oak (Quercus petraea)
* Pines
** Scots Pine (Pinus sylvestris)
* Poplars
** Aspen (Populus tremula)
** Black Poplar (Populus nigra; southern Great Britain only)
* Rowans and Whitebeams
** European Rowan (Sorbus aucuparia)
** Common Whitebeam (Sorbus aria) and several related apomictic microspecies
** Service Tree (Sorbus domestica; recently discovered growing wild on a cliff in south Wales)
** Wild Service Tree (Sorbus torminalis)
* Strawberry Tree
** Strawberry Tree (Arbutus unedo; Ireland only)
* Willows (Salix spp.; several species)
* Yews
** European Yew (Taxus baccata)
===Native large shrubs===
These larger shrubs occasionally reach tree size:
** Alder Buckthorn (Rhamnus frangula)
** Purging Buckthorn (Rhamnus cathartica)
** Elder (Sambucus nigra)
** Common Dogwood (Cornus sanguinea)
** Sea-buckthorn (Hippophae rhamnoides)
** Spindle (Euonymus europaeus)
===Naturalised trees===
* From Europe
** European Larch (Larix decidua)
** Crab Apple (Malus sylvestris; often regarded as native)
** European Pear (Pyrus communis; sometimes regarded as native)
** Cherry Plum (Prunus cerasifera)
** European Beech (Fagus sylvatica; widely considered native, but probably a stone-age human introduction)
** Sycamore (Acer pseudoplatanus)
** Norway Maple (Acer platanoides)
** Sweet Chestnut (Castanea sativa; a Roman introduction)
** Turkey Oak (Quercus cerris)
* From Asia
** Japanese Larch (Larix kaempferi)
* From North America
** Lodgepole Pine (Pinus contorta)
** Sitka Spruce (Picea sitchensis)
** Grand Fir (Abies grandis)
** Western Hemlock (Tsuga heterophylla)
** Western Redcedar (Thuja plicata)
** Lawson's Cypress (Chamaecyparis lawsoniana)
==See also==
* Trees of the world
* Woodland management
* Coppicing
* Pollarding
* NVC National Vegetation Classification, of the above data
==External links==
*The Woodland Trust (UK conservation charity promoting woodland restoration and expansion.)
*Tree For All (Tree For All is the most ambitious children's tree-planting project ever launched in the United Kingdom, with plans to help plant 12 million trees over the next five years.)
Category:Trees