Sitka spruce (Picea sitchensisi is one of the most widely planted forest trees in the UK and and its high timber yields make it a commercially important species. The green spruce aphid Elatobium abietinum is a serious defoliating pest of Sitka spruce, and has been shown to have a significant impact on productivity. Little is known about how future changes in forest management will affect the abundnace, and hence impact, of this pest. This study set out to compare aphid performance and populations on trees of different ages, in stands under varying forms of forest management, and to try to identify the most important factors responsible for variation in aphid abundance. The results of this research highlighted key differences in aphid abundance with respect to variations in tree age and forest stand structure. These patters appeared to be linked with a number of biotic and abiotic factors, including foliage suitability, the level of shade within forest plots, canopy temperature and the abundance of certain natural enemies. Population densities of E. abietinum in the field were significantly higher on young regenerating trees growing in shaded environments compared with light environments. In addition, aphids reared on potted plants achieved a significantly higher growth rate when reared on trees grown under high levels of shade compared with lower levels of shade, a trend which was not explained by differences in the percentage dry weight of nitrogen in needles. Exposure to high temperatures (above 25°C) was detrimental to the individual performance (in terms of growth rate and survival) of E. abietinum. A significant negative relationship was detected between populations of aphidophagous syrphids and peak populations of E. abietinum implying that these predators may play an important role in suppressing aphid densities. Alternatives to the traditional "clearfell and replant" approach to forest management can influence the abundance, and hence impact, of E. abietinum. Forests managed under the uniform shelterwood system supported large aphid populations, whereas the group selection system of forest management, which gives rise to a highly structurally diverse forest, with a high frequency of canopy gaps (increasing light penetration), and high level of ground flora (enhancing certain natural enemy groups including hoverflies), my offer benefits in terms of reduced aphid populations. The findings of this study will have important applications in the future management of commercial Sitka spruce forests in the UK, and will enable more accurate predications to be made of the threat posed by this damaging pest in the future.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:554264 |
| Date | January 2010 |
| Creators | Bladon, Freia May |
| Publisher | University of Ulster |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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