Optimising oak woodland establishment into UK upland pastures in the context of climate change; and the role of oak woodland in soil hydrological recovery for natural flood management
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Increases in the magnitude and extremity of upland (>250-300m a.s.l.) precipitation associated with anthropogenic climate change (ACC) and coinciding with soil compaction leave downstream communities at elevated flood risk. The study examines changes in upland precipitation and the impact of upland ‘Atlantic’ oak (Quercus robur, Quercus petraea) woodland establishment on the recovery of soils for natural flood management (NFM). The soil moisture, livestock grazing and dispersal constraints for potential oak woodland expansion in upland pastures are assessed. The study is located within Dartmoor National Park (DNP) and finds greater increases in precipitation in upland areas than the lowland site, with long term (1879 - 2012) significant increases in spring, autumn, winter and annual total precipitation. Deviation between observed and latest projected changes (UKCP18) (%) in precipitation are greatest (higher observed precipitation trends) in upland areas. Upland oak woodland establishment offers a rapid (< 12 years) mechanism to improve the hydrological functioning of soils for the mitigation of flood risk associated with ACC and soil compaction. The development of oak seedlings and response of saplings in organic upland soils suggest there is a high degree of diversity within UK native oak to varying soil saturation expected with changes in upland precipitation. Natural colonisation of oak saplings is most frequent on west-facing, freely-draining acid grassland pastures, establishment is constrained by dispersal outside the woodland edge (13m average), and the character of livestock grazing. There is growing interest in woodland establishment for the provision of multiple climate mitigation and ecosystem services (ESS), the thesis discusses the role of upland afforestation and its application in land–use management based natural climate mitigation. Research findings suggest effective and rapid establishment of upland oak woodland for NFM will require the planting and protection of native oak trees from livestock, strategically placed in valley pasture slopes within catchment headwaters.