Which is the best provenance to use?
The first step in any tree improvement programme is to determine the best provenance or seed source to use. This work has been completed for most tree species in Ireland, especially the conifers. The FORGEN programme is now addressing the best provenances for some of the broadleaf species used in Irish forestry. One of the most relaible ways to determine the best provenace of a species to use is to establish provenance trials, in which trees from each provenance of interest are planted in a statitstically designed trial at different sites in the country. Provenance trials have been established in most cases, many of which were laid down in the last 15-20 years.
The best provenances for use in Ireland have been determined for most conifers, including Sitka spruce. Sitka spruce of Washington origin performs best in most parts of Ireland, so the breeding programme is based on this material. However, there is some evidence that Oregon origin Sitka spruce material may perform well in the milder southern parts of Ireland, with the possibility also of supplying biomass for energy use. In addition to this geoclimatic issue, a study of the potential for extending the use of Oregon material in Ireland is also warranted in the context of the likely effect of climate change on tree growth responses.
The broadleaf work focuses on measuring tree growth responses (mainly height, diameter and stem quality) in field trials with a view to determining the most suitable provenances for use in Ireland. Some progeny performance data will be collected, but this is being used solely to assess genetic variation at family compared to provenance level. The work on Sitka spruce focuses on examining growth data from Sitka spruce provenance trials and stands in Ireland to determine the relative importance of provenance and site on the yield from Oregon material compared with Washington material.