Foreign material are plants derived from seed or plants derived outside of Ireland. In contrast to Irish provenance material, foreign provenance stock has evolved over the millennia in differant environmental and climatic regimes and is genetically distinct. Many nurseries registered in the U.K. or Holland, for example, supply foreign provenance trees and shrubs to the Irish market. In Ireland, studies to date indicate that the majority of Hawthorn (Crataegus monogyna) planted under the Rural Environmental Protection Scheme (REPS) and on national road schemes is of foreign provenance, especially of Eastern European stock (Foulkes 2008; Dolan et al., in press).
Genetic differences between populations of native species of local and foreign provenance are evident. This is sometimes due to local adaptation. Locally adapted species usually perform better where they evolved than elsewhere (He & Kraus 2006). In Britain, Jones et al (2001) discovered that hawthorn of local origin is superior to hawthorn of non local origin. This study found that locally sourced hawthorn had more thorns and compact branches, was least affected by mildew and budded later than all other provenances tested (approximately 5 weeks after the emergance of the earliest provenance tested). Late budding is almost certainly due to adaptation to colder springs. It also exhibited better growth performance in adverse conditions. In contrast, hawthorn of Hungarian provenance was most affected by mildew, grew faster and budded earlier (Jones et al. 2001).
Foreign provenance plant material may also disrupt food chain dynamics (Jones et al. 2001). For example, early budding in pedunculate oak is thought to impact the tree-insect-bird (i.e.Oak-Winter Moth-Tit) food chain. It is predicted that the reproduction success of the Winter moth won’t be unduly impacted but will develop faster and earlier. However, the brood size of the tits maybe reduced because there will be less abundance of Winter moths when hatchlings emerge (Buse et al. 1999). The large amount of Hungarian hawthorn planted into hedgerows planted under REPS in Ireland over the past decade or so will almost certainly impact the lifecycles of the wildlife they support. Also, nesting birds won’t be protected as much in a hawthorn shrub with fewer thorns (Jones et al. 2001).
Specifically, the use of foreign provenance plant material can have impacts on species of flora and fauna, especially on the abundance of invertebrates and the availability of food for birds. Studies on the impacts of utilising foreign provenance native stock are ongoing in Ireland (Spillane et al., in draft).
Where there is a shortage of particular Irish provenance native planting stock it is best to substitute with species that are site-suitable, e.g. pedunculate oak (Quercus robur) and/or hazel (Corylus avellana) for ash (Fraxinus excelsior), guelder rose (Viburnum opulus) for spindle (Euonymous europaeus), etc.
It is inadvisable to plant a mixture of Irish and foreign provenance material as the genetic pollution of subsequent generations of trees and shrubs will result.