Orchards are biodiversity hotspots, home to a wide range of organisms including epiphytic bryophytes and lichens. However, the area of the UK given over to orchards has become considerably reduced; these habitats are under threat. In response to this, Traditional Orchards are now included as a priority habitat in the UK Biodiversity Action Plan. Local Habitat Action Plans have been produced. It is important that the factors which cause orchards to be such biodiverse habitats are understood in order to facilitate the management of newly planted and restored orchards. Surveys across 7 orchards were carried out, six in Hertfordshire and one in Cambridgeshire. A total of 141 apple trees were surveyed. Epiphytic bryophyte species were recorded, and in 7 of the surveys the cover of individual species was also included. 26 species of epiphytic bryophyte were recorded. There was a high level of similarity in species composition between the orchards, however this was much reduced when relative species cover was taken into account. In order to assess the overall diversity in order to compare orchards, the optimal number of trees to sample was found to be 10. Within the same orchard, significant differences in number of bryophyte species per tree and bryophyte cover were found between two varieties of apple tree, Ashmead's Kernal and Newton Like. This was accompanied by significantly different bark pH and nitrogen concentrations. However, pH was found to be of low importance in explaining the distribution of epiphytic bryophytes on Bramley trees across orchards. In vitro experiments found that low pH inhibited spore germination and growth in the species Brachythecium ve!utinum, Rhynchostegium confertum, Orthotrichum affine and Bryum capillare. High concentrations of nitrogen inhibited spore growth but not germination in the species Orthotrichum affine. The in-depth surveys of Bramley trees showed that across orchards, tree structure, as determined by management, explained about 10% of the observed variation in bryophyte cover. Within that, trunk girth and distance to nearest neighbouring orchard trees were the most important factors. Site was found to be the strongest influence on epiphytic bryophyte distribution in the orchards.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:629457 |
| Date | January 2012 |
| Creators | Whitelaw, Mari |
| Publisher | University of Hertfordshire |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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