Monitoring vegetation change on upland raised and blanket bogs in the north of England

Abstract

Peat bogs are increasingly recognised for their importance in carbon capture, flood management, water quality and biodiversity. The damage to peat bogs for the increase of farming, grouse and timber productivity is widespread, e.g. through drainage, overgrazing, over burning and afforestation. There has been much investment in restoration projects to reverse the process of peatland degradation to ensure it continues to provide ecosystem services and to be resilient to environmental change, but less investment in monitoring the success of the restoration projects. There is a need, therefore, to understand the drivers of bog quality and to develop long-term, cost-effective, reliable monitoring and analysis techniques for assessing changes in bog condition. This study aims to: 1. investigate long-term vegetation changes and their drivers on a raised bog 2. test a vegetation index and associated field technique for monitoring changes in bog quality 3. use this bog quality index to determine the effects of drain blocking on the quality of a blanket bog 4. develop remote sensing techniques to monitor indicators of bog quality Two study areas were used in the uplands of the northeast of England, which has significant areas of raised and blanket bog. First, on Coom Rigg raised bog in Kielder SSSI, vegetation was monitored in 2014, repeating surveys conducted in 1958 and 1986, using a modified existing ecological index, the Wet Bog Quality Index (WBQI), which was tested across these years. There was a rapid deterioration in quality between 1958 and 1986 which did not recover, despite some deforestation of the surrounding land and some drain blocking. Moisture was identified as the primary driver of change, suggesting a need to re-wet the land to prevent further decline and to provide resilience against under grazing, nutrient deposition and possibly climate change. The research provides evidence that WBQI can be used to detect spatial and temporal change in a robust, single measure incorporating drivers such as moisture, nutrients and species richness. Second, in the North Pennines AONB, the effect of drain blocking on surrounding vegetation was carried out between 2010, 2015 and 2019. Here, ecological indices, including a modified WBQI, the Blanket Bog Quality Index (BBQI) and functional groups, were used to detect change in distance from the drain and temporal changes. Bare peat and standing water decreased and vegetation cover increased. Sphagnum cover was highest near the drains while Calluna cover was lowest here. The BBQI detected differences between blanket bogs of different quality, but did not detect change in quality with distance from the drain. A more sensitive index is suggested, which may be suitable for use across UK blanket bog. The overall indication is that, in the short term, drain blocking is effective in increasing vegetation cover and species responsible for carbon capture. Finally, a linear mixed effects regression model linking WBQI to freely available Sentinel-2 Multi Spectral Image satellite data was developed using 1598 vegetation quadrats over 27 bogs from across Kielder Mires SSSI. Five potential models were proposed with R2 around 0.65 and RMSE of 0.28, with independent ground validation of the five models resulting in R2 between 0.27 and 0.61. The models appear to be effective at detecting spatial differences in bog quality, and shows potential for detecting temporal changes. Suggestions for improvement include adding Sentinel-1 Synthetic Aperture Radar data and Principal Components Analysis or Tasseled Cap Transformations of the Sentinel-2 spectral bands, as predictors in the model. The Wet Bog Quality Index is a useful tool to monitor change, but linking this to remote sensing data would increase the cost-effectiveness and efficiency of monitoring, which may be of particular relevance to monitoring restoration trajectories in the context of ecosystem markets and net-zero targets. Monitoring change over the long-term and in response to management is crucial in order to understand processes and to inform future management for biodiversity, flood prevention and GHG emissions from peatlands.