Can plantation forests support plant species and communities of semi-natural woodland?

Abstract

The potential contribution of plantation forests to the conservation of woodland plant diversity needs to be assessed in order for commitments to Sustainable Forest Management (SFM) to be fulfilled. To this end, the plant communities of mature Sitka spruce, Norway spruce, Japanese larch and ash plantations were compared with those of semi-natural oak and ash woodlands at 75 sites across the island of Ireland. A number of different plant communities were recognized in plantations, with only one resembling either of the semi-natural woodland types studied. The exception was a community of ash plantations on base-rich soils, on or adjacent to historic woodland, which was similar to the semi-natural ash woodland community. Despite supporting a plant community similar to semi-natural ash woodlands, the ash plantations supported significantly fewer woodland species. While none of the other plantation communities strongly resembled either the semi-natural oak or ash communities, they had the potential to support high numbers of woodland species. A range of forestry (forest type, canopy cover, grazing), geographic (elevation, historic woodland) and edaphic variables (soil pH, drainage) were found to be important in determining the types of plant communities and numbers of woodland species supported. While geographic and edaphic factors are either impossible or difficult to control, considerable scope exists for enhancing the plant diversity of plantation forests through changes in forest planning and management.