Hydrogeological classification of superficial clays: apparent resistivity measurements from the Garboldisham, Norfolk pilot study area

[摘要] In order to re-establish mobile sand and typical dune zonation in the frontal dune area of parts of Newborough Forest, small scale felling was carried out in two zones. The West zone is just west of the rock ridge, the East zone lies between the main visitor car park and the Warren area.Within these zones, four treatments were established to examine restoration success in different areas and with different techniques, with at least 6 replicate monitoring locations per treatment per zone. The 鈥榯reatments鈥?were as follows:鈥?Dune vegetation understory with sparse or stunted tree cover (T). Trees only removed, with relict dune understory left undisturbed.鈥?Felling and Scraping (FS). Trees, stumps and organic soil removed, stumps removed by grinding or de-stumping, litter layer and surface organic soil layer scraped and removed, to approximately 5 cm depth.鈥?Felling only (F). Trees only removed, but soils and litter layer remain undisturbed. These are 10 x 10 m experimental plots located within treatment zone 鈥楩S鈥?鈥?Unfelled control areas (UF). Locations behind or adjacent to felling zones, on similar substrate, and with similar tree canopy structure where possible.Experimental plots were felled in February-March 2014 with stumps, brash and litter removal ongoing until 2015. Two plots remained unfelled by the time of the second year resurvey. Plots were relocated and resurveyed in August 2015, and again in August 2016 and 2017. This report focuses on vegetation monitoring, with analysis of 2017 (Year 3) data, and comparison with 2014 baseline and 2015 and 2016 data.Changes in speciesChanges in species occurrence in 2017 broadly follow the direction of changes in 2015 and 2016 though the magnitude of many of the changes are smaller. Overall theshift to species of open sandy habitats, and a decline in species typical of woodland understorey has continued. Many species briefly colonising at low cover and frequency in 2015 were not able to establish and have disappeared; a few disappeared only to recolonise in 2017. Changes in NVC communityThe net movement in all treatment plots except the UF controls is towards National Vegetation Classification (NVC) types which are characteristic of early successional sand dune communities. The FS treatment initially produced the most mobile conditions, with vegetation more akin to the mobile Ammophila arenaria (SD6) community in 2015 and 2016, while the F and T plots are more closely aligned to the Ammophila arenaria-Festuca rubra (SD7) semi-fixed sand dune community. In 2017 the FS treatment has become more stable; and is now a better fit to theSD7c subcommunity than the mobile SD6 community. The other treatments remain closer to the SD7c unit thoughhaveall shown modest declines in their goodness of fit. In general the plots in the west remain better expressions of the SD7 community than in the east.Changes in physical and vegetation parametersBare soil has remained at a significantly higher cover in the FS treatment compared to all other treatments. There was no significant change in the cover of bare soil between 2015 and 2016 but a decline in 2017. Species richness increased between 2015 and 2016 following the initial decline from 2014, but the increases appear to be uniform across the treatments. The increase is caused by new species colonising areas of largely bare sand following the removal of tree cover. Ellenberg R (pH) and L (Light) values remain highest in the FS treatment, whilst Ellenberg N (fertility) has shown a steady increase across all the treatments.Changes in matched quadratsThe matched quadrats allow more focused analysis of change at individual locations. Patterns of species richness match those of the wider analysis, with a strong decline in species richness after 2014, a slight recovery between 2015 鈥?2016 but little change between 2016 and 2017. This pattern is reflected in the DCA ordination analysis which shows a large shift in species composition from 2014, followed by a slight reversal of that change in 2016 and 2017. When interpreted separately, the FS plots show the greatest change in composition. Composition of all treatments shows a general trend towards species with higher Ellenberg L scores, signifying higher light levels and more open conditions since 2014. In summary, all treatments except the UF control show a clear affinity to vegetation and conditions of open dune habitats,the FS treatment which initially showed the most open character, similar to mobile dunes, now have a composition closer to the semi-fixed SD7 community despite the overalllow vegetation cover in these plots. In these first few years following the restoration work, the extent of bare soil remains high and cover of Ammophila arenaria and Festuca rubra relatively low. Coupled with the decline in generic woodland species and the persistence or increase of many typical dune species this means that one of the primary objectives of the study, which was to create early successional mobile dune habitat, has been successful. Early colonisation by typical species of open dunes, and the relatively close match of the developing vegetation to mobile and semi-fixed dune communities of SD6 and SD7 suggest that the trajectory is heading towards that of a typical dune succession. However, further monitoring will be required to show whether these early trajectories of change result in a typical successional sequence for dry dune vegetation types.

[发布日期] 2018-01-01 [发布机构] NERC/Centre for Ecology & Hydrology