Ground flora communities in temperate oceanic plantation forests and the influence of silvicultural, geographic and edaphic factors

Baseline information on the biodiversity of plantation forests, including how it varies with silvicultural methods and along geographic and edaphic gradients, is fundamental when designing conservation and enhancement programmes. Ground flora communities in Sitka spruce (Picea sitchensis), ash (Fraxinus excelsior) and Japanese larch (Larix kaempferi) forests at the main stages of stand structural development, and located across the Republic of Ireland on a range of varied site types, are examined. Using flexible beta clustering and indicator species analysis, eight distinct ground flora community types are identified, varying in composition, structure and/or diversity: (i) grassland, (ii) heath, (iii) basophilic forest, (iv) closed-canopy conifer forest: first stage, (v) closed-canopy conifer forest: second stage, (vi) acidophilic forest: bryophyte-dominated, (vii) acidophilic forest: grass-dominated, and (viii) bramble-dominated. Canonical correspondence analysis (CCA) and variance partitioning are used to assess the relative influence of silvicultural, geographic and edaphic factors on ground flora composition. While geographic (e.g. previous land-use, underlying geology, proximity to old woodland and elevation) and edaphic (e.g. soil pH, organic matter content and extractable Mg and P) factors are important influences, our results demonstrate considerable scope for manipulating ground flora communities through silvicultural operations. We show, in particular, the opportunity for managing stand structure as a means of enhancing ground flora diversity and composition at the plantation scale.