Vegetation and ecology of four western oakwoods (Blechno-Quercetum petraeae Br.-Bl. et Tx. 1952) in North Wales
Edwards, Mary E.; Birks, H. J. B.
This paper is part of an investigation of four deciduous woods in North Wales that attempts to relate their present structure and vegetational composition to woodland history. In this paper the modern vegetation is described and related to environmental factors within each wood, based on TWINSPAN analysis of a total of 130 quadrats from the four woods. Quercus petraea dominates the canopy layer, except in Coed-y-Rhygen, where it is co-dominant with Betula pubescens. Moisture, soil pH, rockiness of substrate, and sheep grazing are the main directions of ecological variation that influence species composition of the ground and field layers. Species composition is related to the following habitat types: mires and flushes, rocky areas, acidic soils (pH 4.0). Saxicolous bryophytes dominate the rockiest areas. In extremely humid and shaded locations in Coed Ganllwyd and Coed-y-Rhygen these bryophyte communities are particularly rich in Atlantic species. If grazed, richer soils in less rocky areas are characterized by a grassy field layer, but if ungrazed they support ferns, such as Dryopteris dilatata and D. filix-mas, and forbs such as Circaea lutetiana and Geranium robertianum. Thin, acidic soils in rocky areas are covered by pleurocarpous bryophytes when heavily grazed. Where grazing has been stopped vascular plants are prominent. Festuca ovina, Melampyrum pratense, and Molinia caerulea are characteristic in less steep areas that have an accumulation of leaf litter, but other areas, especially litter-free slopes, are usually covered by a dense mat of Deschampsia flexuosa, often in association with Vaccinium myrtillus. Pteridium aquilinum commonly occurs in dense stands on deeper soils in clearings and at woodland edges. Within woods it may indicate previously cleared areas.