The importance of plantation forests for biodiversity conservation is greatest in landscapes that have experienced significant loss of natural forest ecosystems and the plantation forest estate continues to expand, as is the case in Ireland. We investigated the role of plantation forests in supporting forest plants, invertebrates and birds of conservation concern in comparison to semi-natural woodlands in Ireland. Of the 169 vascular plant species, 97 bryophyte species, 162 spider species, 159 beetle species and 36 bird species recorded 5, 3, 9, 1 and 5 species of conservation concern, respectively, were recorded. Many of these were found in semi-natural woodlands, highlighting the importance of the retention or restoration of these habitats for forest biodiversity. A number of species of conservation importance were also recorded in plantation forests demonstrating that the role of these forests in the provision of habitat for biodiversity conservation should not be overlooked.