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Species Diversity

Ireland positioned at mid latitudes and washed by the warm Gulf Stream, experiences a climate that is very favourable for tree growth.  Moderate temperatures, moist conditions created by all year round rainfall and the absence of extreme weather conditions create an ideal environment for the growth of a wide range of tree species. The effects of this benign climate can be seen in Ireland’s many gardens and arboreta which contain a wide range of exotic tree species that come from many parts of the globe.

Early introductions by Victorian plant hunters during the mid 19th century showed that tree species from Northwest America were particularly suited to the Irish climate. By the time the afforestation programme began in the early 1920s these species had proven their adaptability to their new location and also their potential for timber production.

Through research and demonstration trials as well as production plantations conifer species such as Sitka spruce, Douglas fir, lodgepole pine, western hemlock, western red cedar, grand fir, noble fir were shown to be able to out perform native species in terms of survival and timber volume production, particularly on the site types that were available for afforestation at the time.

As timber production was the main objective of forestry following the almost complete deforestation of the country, these North American species were seen as a solution to creating a productive forest resource in a short period. These species came to dominate plantations to such an extent that by the 1980s the state forests were approaching a conifer monoculture.  Sitka spruce was a particularly successful species having a fast growth rate, resistance to exposure, an ability to thrive on the wet soils and timber suited to many end uses. The species was so successful that by the late 1980s it formed approximately 85% of all trees planted annually.

Concern, however, was expressed about the dangers of relying too heavily on one species, particularly a non-native species that could be vulnerable to an introduced insect pest or disease for which it may not have resistance. Also, concerns were raised about the extremely low planting levels of native broadleaf species and our consequent reliance on imports of hardwood timber from tropical countries.

These concerns together with a number of other factors such as:

  • the introduction of a species diversification policy for all new plantations in 1996 by the Forest Service;
  • the availability of better quality  land for afforestation due to CAP reform and the provision of attractive planting grants and premiums; and
  • FSC certification of Coillte forests which required specific species proportions for all forest management units including the increased planting of broadleaves.

resulted in a general shift towards the planting of more diverse species.

Over time these factors will have a considerable impact on the composition of the national forest estate, changing it from being conifer dominated to a more mixed species situation. This, however, will take time to become apparent, particularly in existing forests, as species change can only occur when the current crops are felled and replanted.

Diversity - M. Keane

Planting a mix of species will create more diverse forests in the future (photo M. Keane)

Today, while the same species are being planted in our forests as in past decades, the proportions have changed significantly. More native broadleaves are being planted  such as oak, ash, alder and birch,  as well as some of the minor conifer species – Scots pine, Norway spruce and European and hybrid larch. Sitka spruce and lodgepole pine still remain the main species but are planted to a lesser extent than heretofore.

Creating greater species diversity in our forests will have many benefits some of which include: enhancing the appearance of the landscape, creating wildlife habitats, protecting forest health and providing a range of timbers that can be used in a wide range of end uses, from rough construction up to high quality joinery.

Comprehensive data on the current species composition of Irish forests are available in the results of the 2007  National Forest Inventory.