Factors affecting the improvement of hill land dominated by bracken (Pteridium aquilinum (L.) Kuhn)

The work described was carried out between 1978 and 1981, and continues the extensive studies of The West of Scotland Agricultural College into methods of controlling bracken (Pteridium aquilinum (L.) Kuhn) and subsequent sward improvement. Bracken frond growth is readily controlled with the herbicides asulam (Asulox) and glyphosate (Roundup) but the quality of the resulting sward is frequently poor as a large area of ground is covered with frond litter. The recolonisation of this litter by indigenous species can be slow and may result in a high proportion of plants of little grazing value, but conventional re-seeding methods involving ploughing are not usually possible because the ground is too steep or too rocky. The main aim of this study has therefore been to examine some of the factors affecting sward development from either indigenous or introduced species, following frond clearance, in order to assess other methods by which swards may be improved. Field surveys of a large number of bracken-infested hill sites in the West of Scotland showed that the main species in the sward were Aqrostis tenuis, A. stolonifera, A. canina, Anthoxanthum odoratum, Festuca rubra, Holcus mollis, Poa pratensis, P. trivlalis and Galium saxatile, and to a lesser extent. Digitalis purpurea, Viola palustris, Luzula campestris and Potentilla erecta. The amount of uncolonised ground covered with bracken litter varied greatly from site to site. The main species found as viable seed in the soil were Erica cinerea, Calluna vulgaris. Digitalis purpurea, Juncus bufonius, J. effusus and Agrostis spp. Large numbers of viable seeds were found at some sites but there was much variation (approximately 3,000- 30000 2 seeds/m ). Sampling to a depth of 3 cm was considered to account for 74?o of the seeds present. Species which were well represented in the buried seed population frequently had very small seeds and there were far fewer seeds of grasses than of non-grasses. The composition of the soil seed bank and of the sward above frequently did not correspond. Two sites were examined where frond clearance with herbicides had taken place and where there had been subsequent soil disturbance from the winter feeding of cattle. The composition of the sward and the seed bank at these sites differed from that of untreated sites and probably reflected the introduction of species from the feed. Data from a variety of experiments produced evidence of changes in the buried viable seed population. Both short-term (month to month) and long-term (year to year) changes in the population as a whole and in the individual species were noted. The results of these studies on soil seed populations have been related to those of other workers who have examined the survival of seeds in soil. They found that several factors affected the period of survival including the depth of burial, the soil type and its moisture content, the dormancy characteristics of the individual species and the extent to which the soil was disturbed. The problems associated with the estimation of buried viable seed populations have been discussed. Many of the seeds found during the surveys were not described in standard reference works and had to be germinated and grown on before they could be identified. Photographs and descriptions of these seeds have been included. A trial was set up to examine the changes in the composition of the sward following frond control with either asulam or glyphosate, and the role of the buried viable seed population. Whilst asulam adversely affected only Aqrostis spp., many more species were affected by glyphosate. The only species present in the seed bank in any quantity were Agrostis spp. and, to a lesser extent, Galium saxatile. There was little evidence that the buried viable seed population was playing a significant role in the recovery of the swards, particularly on the 9 glyphosate-treated plots. Sward development following frond control was therefore dependent upon the existing species and their ability to tolerate or recover from the effects of the herbicides. (Abstract shortened by ProQuest.)