Backstone Bank and Baal Hill Woods one side valley, there is a small population of small-leaved lime, "Tilia cordata", which occurs here close to its northern limit and at an unusually high altitude. On base-rich soils, the woodland typically consists of ash, "Fraxinus excelsior", and wych elm, "Ulmus glabra", over an understorey of hazel, "Corylus avellana", and bird cherry, "Prunus padus", and a rich ground flora that includes lady-fern, "Athyrium filix-femina", male fern, "Dryopteris filix-mas", and hard shield-fern, "Polystichum aculeatum". On more acid soils, sessile oak, "Quercus petraea", and birch, "Betula sp.", are dominant. The under-storey, of hazel, holly, "Ilex aquifolium", rowan, "Sorbus aucuparia", and hawthorn,
Sorbus aucuparia The tallest "S. aucuparia" in the United Kingdom stands in the Chiltern Hills in South East England. This exceptional specimen is 28 m tall and has a trunk diameter of 56 cm. In Germany, an unusually large specimen is located near Wendisch Waren, a village in Mecklenburg-Vorpommern. This tree stands at more than 15 m tall, is around 100 years old, and has a diameter of 70 cm. The tallest known "S. aucuparia" in Ireland is an 18 m tall specimen at Glenstal Abbey, County Limerick. "Sorbus aucuparia" is pollinated by bees and flies. Its seeds are not digested by