ReviewThe UK Environmental Change Network: Emerging trends in the composition of plant and animal communities and the physical environment
Introduction
Scientifically robust monitoring of the natural environment is necessary for the detection and attribution of the effects of environmental change on biodiversity. It is, therefore, essential for the development of effective conservation strategies in the face of an unprecedented array of anthropogenic pressures on ecosystems. Awareness of the need for long-term monitoring has grown as the nature of environmental change has become clearer (Goldsmith, 1991, Risser, 1991, Burt, 1994). Many monitoring programmes have been developed, but most focus on specific organisms (such as birds or butterflies) or specific threats (such as acidification). Whilst these are undoubtedly valuable, it can be difficult to attribute effects to the appropriate cause without site specific-information about potential drivers of change. The UK Environmental Change Network (ECN) is unusual in monitoring a wide range of biota together with key aspects of climate, pollution and land management at a series of terrestrial sites across Great Britain and Northern Ireland. It aims to identify links between environmental drivers and biological responses across a range of trophic levels and also provides a good basis for comparing trends in contrasting taxa.
The ECN was established in 1992 and currently comprises 12 terrestrial and 45 river and lake sites across the UK (Sykes and Lane, 1996). Eight of the terrestrial sites have been monitored since the start of the network in 1992, the remaining four joining in the following six years. The terrestrial ECN sites include many major research sites and ECN data have been used in a wide range of investigations of ecological patterns and processes at individual sites (Adamson et al., 2001, Morecroft et al., 2001, Benham, 2008, Morecroft et al., 2008, Worrall and Adamson, 2008, Taylor and Morecroft, 2009). However, the ECN data also provide a unique opportunity to compare trends in different aspects of environmental change across a wide geographical area using common methodology. All sites use common protocols and there is central collation, management and quality control of data. A number of specific comparisons of this sort have been carried out on, for example, the effects of drought on contrasting plant and insect species (Morecroft et al., 2002); trends and patterns in carabid beetle communities (Scott and Anderson, 2003), frog breeding phenology (Scott et al., 2008) and aspects of stream water chemistry (Miller et al., 2001). To date, however, there has been no overview of the trends emerging across the network and no review of the effectiveness of the network as a whole. With 15 years data available for many terrestrial sites, such a synthesis and review is timely.
Taking a global perspective, the Millennium Ecosystem Assessment identified habitat change, climate change, over-exploitation (particularly agricultural land, forestry and fisheries), invasive alien species and pollution as the main drivers of ecosystem change (Millennium Ecosystem Assessment, 2005). Within a UK terrestrial context, climate change, air pollution, and land management change are arguably the three most significant threats to biodiversity. Invasive alien species have locally important impacts on ecosystems and these might become a more general threat in future, particularly as the climate changes (Sutherland et al., 2008). From a conservation perspective, it is important to ensure that it is possible to discriminate between effects of different causes of change so that management responses are directed in ways that are most likely to be effective. Long-term monitoring provides the necessary basis for this. In addition it provides a baseline against which future novel threats to species and ecosystems, such as pathogens, extreme weather events and increased fire risk (Sutherland et al., 2008), can be judged.
The evidence that the climate is changing, both globally (IPCC, 2007) and regionally (Jenkins et al., 2007) is well-documented. It is also becoming clear that ecological impacts are starting to emerge (Rosenzweig et al., 2007, Hickling et al., 2006). To date, changes in climate are modest relative to short term variability, but the increase in air temperatures and changes in precipitation patterns projected for the 21st Century (Hulme et al., 2002) are likely to have profound consequences for community composition and structure, and ecosystem processes across the UK (Walmsley et al., 2007). Likely effects of climate change will be complicated by the additional stresses imposed by air pollution loads and pollutant levels within soils, and changes in land management practices. The development of effective adaptive measures for biodiversity conservation will require an integrated assessment of these effects.
Air pollution and its effects, particularly acidification and eutrophication, as a result of S and N deposition, have been extensively monitored in some ecosystems, for example, through the ICP Forests Level 2 Programme (Vanguelova et al., 2007) and the UK Acid Waters Monitoring Network (Monteith and Evans, 2005). Changes in inputs of S and N species affect soil biogeochemistry in two ecologically important ways. Both S and N represent acidifying inputs: non-marine sulphate and nitrate are directly associated with increased hydrogen ion inputs, but ammonia (NH3) and ammonium may also have an acidifying effect, depending on the balance between nitrification, plant uptake and leaching (National Expert Group on Transboundary Air Pollution, 2001). N is also a nutrient that is often limiting in semi-natural habitats in the UK. There is evidence that N is accumulating in soils in many areas, leading to changes in nutrient cycling and N deposition is likely to be a major cause of recent change in British vegetation (Smart et al., 2003, Smart et al., 2005, Stevens et al., 2004).
Internationally agreed controls on emissions of S and N have resulted in substantial reductions in acid deposition across the UK and much of western Europe (Fowler et al., 2005). However, this results largely from reductions in S deposition. Atmospheric nitrogen dioxide (NO2) concentrations in the UK have decreased but total N deposition remains high in many places, particularly where there are local NH3 emissions, for example from intensive livestock rearing units (Sutton et al., 1998). In addition, N is often tightly cycled and retained within the soil ecosystem, unlike S, which may be quickly leached in oxic soils. Recent trends in N deposition may, therefore, be less important in changing soil N status given the history of N accumulation in soils.
For much of the 20th century there was a loss of habitats and biodiversity as a result of agricultural intensification in the UK. However, in recent decades this trend has slowed and in some cases reversed (Haines-Young et al., 2000), with more emphasis on agri-environment schemes and habitat restoration. Land-use and management changes are likely to remain important drivers of ecosystem change as markets and policy priorities change. Many of the key questions for ecologists identified by Sutherland et al. (2006) relate to changes in management practices in agricultural and forestry systems as well as, for example, climate change.
In this paper, we present an integrated assessment of changes in a range of communities and species, together with trends in environmental pressures. Our aims were to:
- (1)
Characterise the major trends in physical drivers of change and soil chemistry at ECN sites over the past 15 years.
- (2)
Identify major trends in plant communities and selected animal populations (butterflies, moths, carabid beetles, bats).
- (3)
Assess the effectiveness of the terrestrial ECN in detecting environmental change impacts and informing the development of science and policy.
Section snippets
Site descriptions
The 12 terrestrial ECN sites (Fig. 1, Table 1) represent a wide variety of habitats, climates, levels of air pollution, and management regimes. All have a history of research on the site and stability of management and ownership. The sites can be broadly categorised as upland or lowland. The upland sites are Snowdon, Cairngorm, Glensaugh, Sourhope and Moor House-Upper Teesdale. They have steep or rolling hillsides and soils comprised mostly of acidic podsols or peats. Vegetation includes acid
Climate
The sites represent a wide range of UK climatic conditions and differed consistently in mean temperature and precipitation (Table 1). The differences in annual precipitation are particularly pronounced, ranging from 598 mm at Drayton to 3393 mm at Snowdon.
Across all sites there was a significant warming trend (Fig. 2a) of 0.9 °C (lower bound 0.6 °C, upper bound 1.1 °C) over 15 years (p < 0.001). Trends differed between upland and lowland groups of sites (p < 0.05), although not between individual sites.
Discussion
The range of high-frequency, co-located measurements at ECN sites provides a unique comparative account of recent change in the major climate and air pollution drivers of environmental change and a robust dataset with which to examine evidence for ecological responses.
Conclusions
Three trends in the physical environment stood out across the network: recovery from acidification in response to falling levels of S deposition, rising temperatures and increasing precipitation. Rising temperatures and recovery from acidification are consistent with longer-term trends identified from other data sources. Nitrogen deposition trends were more localised, but nevertheless significant.
Despite clear changes in soil water pH, at least at depth, there has, however, been little obvious
Acknowledgements
We thank the many people who have contributed to the collection and management of ECN data both at sites and the Central Coordination Unit. ECN is funded by: Agri-Food and Biosciences Institute (Northern Ireland), Biotechnology and Biological Sciences Research Council, Countryside Council for Wales, Welsh Assembly Government, Defence Science and Technology Laboratory, Department for Environment, Food and Rural Affairs, Environment Agency, Forestry Commission, Natural England, Natural
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2020, Science of the Total EnvironmentCitation Excerpt :Wet deposition of NH4 and NO3, sulphate (SO4), chloride (Cl), BC and P during 1962–1991 were derived from e-RA (the electronic Rothamsted Archive, providing a permanent managed database for secure storage of data from Rothamsted's Long-term Experiments; http://www.era.rothamsted.ac.uk/). From 1992 onwards, estimations of wet deposition of those elements were derived from (i) precipitation chemistry data reported by Rennie et al. (2017) for the UK Environmental Change Network (ECN), a long-term environmental monitoring and research program (Morecroft et al., 2009) and (ii) daily rainfall extracted from Rothamsted daily meteorological data from e-RA. Total deposition of all elements, shown in Fig. S1, was calculated based on the wet deposition, derived from e-RA and a total:wet ratio (total deposition of NO3 between 1994 and 2012 was available in e-RA).
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