FACTORS AFFECTING THE NATURAL REGENERATION OF QUERCUS IN SCOTTISH OAKWOODS .1. COMPETITION FROM PTERIDIUM-AQUILINUM

1. In upland, semi-natural oakwoods, the natural regeneration of oak Q uercus petraea and Q. robur is frequently lacking. This threatens the long-term persistence of a habitat of considerable conservation import ance. 2. In the absence of excessive grazing pressure, large openings in the woodland canopy can provide suitable sites for regeneration, bu t these are often dominated by dense stands of bracken Pteridium aquil inum, which is thought to restrict woody growth severely. 3. In this p aper we describe experiments carried out in a semi-natural oakwood in north-eastern Scotland, which tested the hypothesis that shading by a Pteridium canopy in summer and smothering by the dying fronds in winte r exert a detrimental effect on the growth of oak seedlings. 4. Two se parate types of Pteridium stand were selected: the first, and more den se, growing in relatively large gaps in the oak canopy, the second and less dense growing in smaller gaps. In the large gaps, three treatmen ts were used: Pteridium cut continuously all year, cut in winter only, and uncut all year; in the small gaps only the first and second treat ments were used. The effects of a Pteridium canopy on photosynthetical ly active radiation (PAR) during the growing season were also measured . 5. The presence of a Pteridium canopy during the growing season redu ced PAR to 5.9% of full sunlight in the larger canopy gaps, and to 11. 4% in the small gaps. Over two growing seasons, significant reductions in accumulated oak seedling biomass were recorded in both large and s mall canopy gaps. Significant increases in specific leaf area, leaf ar ea ratio, and a decrease in root:shoot ratio were also recorded. 6. Sm othering by dying Pteridium fronds in winter significantly reduced see dling biomass, but had no effect on biomass partitioning or seedling m orphology. 7. These results suggest that effective control of dense Pt eridium stands is necessary to promote the successful regeneration of oak. However, this should be done in conjunction with measures to ensu re the continued supply of early successional woodland habitats.