Botanical benchmarks: application of single assessment site-based vegetation survey data in habitats regulations assessment for regulatory decision-making

Jones, L.; Banin, L.F.; Bealey, B.; Field, C.; Caporn, S.J.M.; Payne, R.; Stevens, C.; Rowe, E.; Britton, A.J.; Mitchell, R.J.; Pakeman, R.J; Dise, N.; Robinson, E.; Tomlinson, S.. 2018 Botanical benchmarks: application of single assessment site-based vegetation survey data in habitats regulations assessment for regulatory decision-making. Stirling, Scottish Environment Protection Agency (SEPA), 65pp. (SEPA Commissioned Report no. DK1605, CEH Project no. C06198) (Unpublished)

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Nitrogen has caused, and is continuing to cause, extensive changes in ecosystem functions and the ecological communities these ecosystems support in nutrient-poor habitats in the UK. This project aimed to develop indicators which could be calculated from readily-collected field survey data, and to benchmark those indicators against national datasets, to show the expected impact of additional N deposition from new point or diffuse sources of N. In this study, we considered a wide range of metrics all of which could be derived from botanical survey in the field. To avoid correlation among similar indicators, a subset was selected which were largely uncorrelated with each other, and required varying levels of botanical expertise and investment of time to collect the field data. The selected indicators were: - Graminoid cover as a proportion of total cover - Nitrophile-nitrophobe indicator - Species richness - Mean Ellenberg N Multiple vegetation survey datasets across the UK were collated and analysed in order to assess the response of each indicator against N deposition. The final datasets selected for use included broad (non-targeted) surveys such as Countryside Survey, the Scottish Birse & Robertson re-survey, the Scottish coastal resurvey; and targeted surveys which were primarily designed to detect impacts of N deposition, and which tried to minimise covarying factors such as climate. These included N gradient studies from the Defra-funded Terrestrial Umbrella (TU) consortium, wider acid grassland datasets, and CEH sand dune datasets. Multi-year average N deposition spanning the timeframe of the survey data (2002-2014) and historical S deposition data (1986-1988 average), both derived from the CBED model, and 30-year mean annual temperature and precipitation data (1981-2010) were also collated. 2 Four habitats were selected where surveys provided sufficient data for derivation of indicators. These were: - Acid grassland - Dry heaths - Wet heaths and bogs - Acidic dune grasslands Regression models were produced to explore relationships between the indicators and pollution (N and S) and climate variables. Equations were developed for roughly two thirds of the indicators; equations for the other indicators were not reported due to ambiguous relationships with N deposition. Not all indicators showed significant responses with N deposition in all habitats. In many cases, S deposition was highly correlated with N deposition, meaning that it was not possible to attribute the impacts to one pollutant over another. Statistical uncertainty is high in the parameters of the resulting equations due to variability in the source data unaccounted for in the regression model, which may encompass other drivers of vegetation change. Potential application of the equations was demonstrated using independent data from SEPA biomonitoring programmes, using multiple sites for each habitat. The equations are useful for three main purposes: - They provide an estimate for the effect size, direction and form (e.g. linear) of the relationship between each indicator and N deposition, from which an estimate (prediction) of the indicator can be derived for a typical site at the current level of N deposition, and at given values of temperature, rainfall and historical sulphur deposition. This prediction is benchmarked against the UK-wide dataset used to generate the relationships. - Plotting current values of the indicators using measured data from the field allows comparison of the current status of the site against this UK benchmarked relationship. - The multiple indicators can be used to build up a ‘weight of evidence’ of the eutrophication status of the site. When applying the equations, it should be borne in mind that many factors determine the vegetation of an individual site and not all of these can realistically be included in models of this nature. There is inevitably a high level of uncertainty associated with these predictions. Suggested work to take these findings further includes: - Consideration of additional variables likely to be contributing to within-habitat variation in responses to N, such as soil parameters, current or historical management including grazing by managed livestock and wild grazers such as deer, where appropriate data is available - Benchmarking of additional indicators which include bryophytes and lichens - Application to other habitats not considered in this study, such as woodlands, calcareous grasslands, alpine communities, and additional dune habitats 3 (fixed dune grasslands, semi-fixed and disturbance communities, dune slack wetlands). - Integrating multiple lines of evidence, for example results from experimental manipulation sites - Incorporation of more of these indicators into dynamic process models, to predict the timescales over which change might be expected in response to additional N deposition, and impacts at individual sites. - Evaluation of the number of quadrats at a site required to adequately characterise indicator metrics, for different habitats

Item Type: Publication - Report
UKCEH and CEH Sections/Science Areas: Atmospheric Chemistry and Effects (Science Area 2017-)
Soils and Land Use (Science Area 2017-)
Water Resources (Science Area 2017-)
Funders/Sponsors: Scottish Environment Protection Agency
Additional Information. Not used in RCUK Gateway to Research.: For further information on this report please contact Claire Campbell SEPA Corporate Office, Stirling. Telephone 01786452448. E-mail
NORA Subject Terms: Ecology and Environment
Atmospheric Sciences
Date made live: 11 Jul 2019 14:31 +0 (UTC)

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