The development of a site classification for Irish forestry.

Abstract

Criteria and site classification methods to assist in the identification of land that have potential for afforestation grant aid were evaluated in this study. The study examined the nature, fertility and productivity of unenclosed land to determine if opportunities existed for future afforestation. Local variability in soil nutrient regime and the changing nature of land-use in Ireland may have contributed to some of the observed variability in productivity potential. The results indicated that classifications based on historical enclosures provided limited scope for evaluating the potential suitability of sites for forestry. Therefore, alternative site classification methods, based on productive criteria, were evaluated. Results indicated that the classification of soil nutrient regime, supplemented with indicator plant analysis, showed the greatest potential. A new classification was developed, which was heavily influenced by ecological classifications but with supplementary classes to cover less fertile but still productive site types. The newly-developed classification has seven classes (referred to as site types A to G, in order of decreasing suitability). Sites classed from A to C were typically arable land, improved pasture and “rush-pasture”, and offer the potential to diversify species selection. The D type, typically associated with bracken (Pteridium aquilinium), is considered potentially suitable for more diverse conifers including Douglas fir (Pseudotsuga menziesii (Mirb.) Franco), western red cedar (Thuga plicata D. Don), and western hemlock (Tsuga heterophylla (Raf.). The wetter site types with rush (Juncus spp.) are suitable for Sitka spruce (Picea sitchensis (Bong.) Carr.) assuming a single application of phosphorus. The E site type is typically associated with pure Molinia spp. requiring phosphorous fertilisation to support productive Sitka spruce. The F type was considered unsuitable for pure Sitka spruce without the use of nursing mixtures of lodgepole pine (Pinus contorta Douglas ex Loudon). Site type G, the lowest classification level, was unsuitable for forestry.