Trees of Ecological Importance
Native species and Introduced Species from other places
“Perfection is everything in its proper place”
Chinese Proverb
Much emphasis is put by conservationists on the use of “native species” as opposed to the use of species from other countries in the management of the countryside for wildlife. Why bother with the distinction? Does it really matter what we plant? To understand the question and to be able to formulate an answer we need to look back in history for a moment…. to understand what is meant by a native species and why from a conservation point of view this is something important to understand.
It is an implicit belief of the Living Tree Campaign as well as of the “Seeds of Time and Place” project that every tree, whether native or from another country, has value in itself and that the important distinction is where the tree is planted and grows. There are definitely important issues of “appropriateness of place” for a individual tree species but we believe that every tree is valuable, if, “in its proper place”.
NATIVES
Natives are generally seen to be those species that managed to arrive in a location naturally, without the help of man, whilst those that he has introduced are seen as distinct from the natural vegetation. In the British Isles our native vegetation is comparatively young, for 15,000 years ago most of the land surface had just been released from the grip of the last ice age and was beginning to recover as the temperatures warmed up. If we could have stood anywhere in Ireland for the next 2000 years we would have seen an ever changing scene, with advancing waves of plants and animals migrating back into Ireland from the warmer parts of Europe over the land which later became drowned under the English Channel and Irish Sea. The first woody plants to appear, hardly big enough to be called trees, colonized the grasslands and lake edges which had developed over the poorly developed soils and gravels left behind by the ice.
Today these first plants, dwarf willows and junipers, now hang on only in places where the environment makes it difficult for other taller trees to grow, or on mountain cliffs. Over much of the country they were rapidly crowded out by taller birches, willows, aspens and bird cherry when woodland as we know it started to establish itself. This in its turn was swamped on the drier ground by a great wave of hazel which by 9,000 years ago covered Ireland from end to end. These rapidly spreading trees relied on the production of vast quantities of seed dispersed by wind as is the case of willows and birch, or animals as in the case of hazel. They could also produce the seed when they were relatively young, unlike the big forest trees such as oak. However the longer lived high forest trees eventually arrived, so that by 8,000 years ago pine grew on the western sea board, oak on the drier more acid soils and Wych elm flourished where the soil was more alkaline over the major central parts of Ireland. Apart from the wetlands, woodland covered most of Ireland.
The land bridges which allowed the re-colonisation of plants and animals into Ireland disappeared in the next 1,000 years. This meant that those which had not yet spread as far as Ireland were cut off, so that some species regarded as native to England can not be considered to be native to Ireland. Beech is one, limes, field maples and hornbeams are others. This could be because the most appropriate habitat for these species does not occur in Ireland, eg chalk downs in the case of beech, or the climate is not normally warm enough to produce viable seed, as in the case of lime.
During the re-colonisation of the land by woodland, all the other components of what makes a woodland a very complex community of plants and animals spread with them. Each species of tree carried with it a baggage of snails, insects, lichens, birds and fungi as well as herbs and plants which grew in its shade and in the soil it created. Insects, in particular, form very complex webs of life, with things that eat leaves, buds, flowers, roots, then things that eat those, or parasitise them etc, etc. All these make good food in their turn for birds, mice and other mammals. It is not surprising then to realise that trees such as oak and willows have developed a large number of insects which feed only on them, over 450 species. Birches support over 300, and alder, elm and hazel over 100 each. They are therefore supporting a wide range of wildlife in their own right.
SPECIES FROM OTHER PLACES
Beech does well supporting 98 species, but sycamore has only 43. The problem is that neither of these arrived in Ireland under their own Steam, but were brought in by man, and have mostly only been here for the last 200 years. They are both beautiful trees but the chances are that only a small amount of the associated baggage arrived with them. So generally speaking species from other places definitely do not support such a diversity of other wildlife as do native species. In addition both of the species mentioned above cast very dense shade and are in leaf for a much longer season than the native species.
in addition both of the species mentioned above cast very dense shade and are in leaf for a much longer season than the native species, which kills off most of the Irish woodland flowers with the exception of bluebells.
“NATIVE NATIVES” OR NATIVES FROM OTHER PLACES
In modern day times a further complication arises, the arrival of native species of trees, but from a non native stock. Does it matter if the hawthorn or oak we plant are derived from Irish sources or from seed collected in Central Europe? I believe yes is the answer. One could even be really pedantic and say that it matters that you should plant an Antrim hawthorn in Antrim, and a Fermanagh bird cherry in Fermanagh. The reason is really simple and obvious. The two places are different, especially their climate and soil. The plants from the two counties of Ireland will have evolved over the last 9,000 years to produce slightly different genetic make up which allows each in its own place to be good at surviving that is growing and reproducing by flower and seed. At the same time, the associated baggage has evolved with each species, utilising each specific nuance of adaptation. e.g. insects have evolved to emerge at the appropriate time when the tree is in flower, lichens have adapted for the climate.
Thinking back to the comparison of the Central European and Irish sources, the differences in climate, soils, day length and many more environmental characters are going to be even greater. Also the plants from the European nurseries may be derived from cultivation methods which produce plants of identical genetic make up. The imported plants are thus very likely to be different in their behaviour or growth forms and not so well suited to the Irish environment and not suitable for Irish wildlife. Significant differences have been noted with hawthorns for example in their flowering periods, as well as their response to cutting back and growth forms. Therefore, whenever possible, if nature conservation is your aim, it is best to use not just native species but native species grown from locally collected seed sources.
No doubt about it but when it comes to conserving wildlife and the natural environment then native is definitely best! So if this is your aim then this guide is for you. Of course native trees are also beautiful in their own right but have the added benefit of supporting our native wildlife. Species from other countries have different and important roles to play in our tree heritage but if your main reason for planting trees is wildlife conservation then choose native.
Jo Whatmough
The National Trust
