Quercus petraea × Q. robur (Q. × rosacea Bechst.), Hybrid Oak
Account Summary
Native, occasional, but possibly under-recorded. European temperate.
8 January 1986; Leach, S.J., Corbett, P. & Dunlop, D.; wood on Gorminish Island, Lough Melvin.
Throughout the year.
There are 60 records from 51 Fermanagh tetrads referring to deciduous oak specimens in woodland which field recorders regarded as intermediate and which could not easily be referred to either parent species. As such they represent just over 10% of the oak records in the Fermanagh Flora Database – quite a significant proportion. They appear quite widely scattered, but lie chiefly in the northern half of the county. Leaf samples examined by Rushton (1983) found that oaks in woods at both the Marble Arch Glen (or Cladagh River Glen) and nearby Rossaa Td (between Mullaghbane and Gortatole) had mixed populations of both parents with a high proportion of the hybrid: indeed at Marble Arch almost 50% of the trees sampled were hybrids. However several woods also had low proportions of hybrids or none, including Killesher Forest NR, also near Marble Arch Glen, where the samples were exclusively Q. robur. In the Marble Arch wood, ash is the dominant tree on the damp valley floor and the oaks are confined to the higher slopes, where the spacing and even-age of the population suggest a managed plantation origin. The pattern of extensive removal of natural woodland and its replacement by plantations, especially on landed estates, is an all too common one across NI. It reflects a longstanding shortage of timber, major social change and land ownership both ancient and modern (McCracken 1971; Tomlinson 1982).
The limited number of oak populations so far studied in Ireland, and the high levels of introgression found in them tend to suggest that the frequent mixed populations of Q. robur, Q. petraea and their hybrid that occur have most probably (and most often) arisen naturally in ancient times, or through plantation of mixed stock, rather than by recent horizontal spread of one or other of the oak species (Cousens 1963; Rushton 1983).
Threats
Grazing pressure is preventing regeneration and many oaks are reaching a stage of over-maturity when boughs begin to drop off. As trees die, active management of existing woods, plus a programme of replanting using local acorns is urgently needed to maintain the species and its genome at anything approaching present levels.