Impacts of grazing abandonment on ecosystem service provision: Coastal grassland as a model system
Highlights
► Even low intensity grassland management involves trade-offs among ecosystem services. ► Extensively grazed grassland favours provisioning, cultural and pollination services. ► Un-grazed grassland favours flood control and pest regulation services.
Introduction
Grassland management for multiple ecosystem services often results in potential conflicts or trade-offs (MacLeod and McIvor, 2006). This is important as many ecosystem services are delivered by semi-natural grasslands (Bullock et al., 2011; Table 1); “supporting services” (primary productivity and nutrient cycling); “provisioning services” (food production, preservation of the genetic diversity of wild species and fresh water supply); “regulating services” (maintenance of an equable climate, water storage, pest regulation and pollination) and “cultural services” (conservation status, environmental appreciation and recreation). In managed grasslands, the basic trade-off is between intensive management to maximise food production and extensive management resulting in lower production, but increased biodiversity and a wider range of cultural services (Power, 2010). Semi-natural, low productivity grasslands, traditionally used for low intensity cattle and sheep farming, have declined by 90% in the UK since 1945, converted to intensive production by drainage and fertilisation (Bullock et al., 2011). In many parts of Europe they now face a further threat, with managed grazing of these habitats being ‘abandoned’ in both the uplands and lowlands due to the removal of European Union (EU) subsidies (Strijker, 2005). Policy makers have signed up to halt biodiversity loss and degradation of ecosystem services within the EU by 2020 and to adopt an integrated approach to land use management (Kleijn et al., 2011). It is therefore vital to assess how abandonment of low productivity grazing land impacts on biodiversity, ecosystem function and potential consequences for ecosystem service provision.
The effects of removing large herbivores (i.e. cattle, sheep or horses) are well understood for grassland biodiversity and ecosystem function, but the implications for wider ecosystem service provision have been poorly quantified, or not quantified at all, especially for multiple services (Power, 2010). Grazing removal decreases plant diversity (Pykälä, 2003), increases invertebrate and small mammal abundance and diversity (Morris, 2000, Schmidt et al., 2005), and can either increase or decrease bird abundance and diversity dependent on feeding and nesting sward requirements (Vickery et al., 2001). Where large grazers are removed smaller grazers, particularly rabbits, may define habitat characteristics, keeping patches of grassland fairly open, preventing declines in plant diversity but allowing soil to become less compact (Isermann et al., 2010), creating a habitat with characteristics of both grazed and un-grazed grassland, with likely mixed effects upon ecosystem services. Voles and other small mammals are usually present, even within ‘un-grazed’ areas and have different effects on vegetation and nutrient cycling characteristics to large herbivores (Bakker, 2003). Cessation of cattle grazing where rabbits are not present leads to the development of a plant community dominated by highly competitive tall grasses or shrubs (Janišová et al., 2011) with reduced soil compaction and possible implications for several variables linked to ecosystem service provision.
Above-ground primary productivity (ANPP), a key supporting service, may increase or decrease with grazing intensity (De Mazancourt et al., 1998, Leriche et al., 2003). Nutrient turnover, another supporting service, also shows variable effects with grazing management (Bakker, 2003, Bardgett et al., 1998, Van Wijnen et al., 1997). Coastal grasslands, particularly those adjacent to crop fields, may potentially provide invertebrates for the twinned regulating services of pest control and pollination (Everard et al., 2010, Losey and Vaughan, 2006). However, effects of grazing intensity on these services are difficult to predict. Invertebrate pest regulators, such as spiders and beetles, are often more abundant on un-grazed grassland (Morris, 2000) but pollinators may be most abundant on grazed grassland due to a likely increase in floral resources (Potts et al., 2003, Sjödin et al., 2008). Soil moisture and temperature changes may also affect the regulating service of equable climate, via impacts upon C storage and greenhouse gas emissions (Luo and Zhou, 2006). The cultural service of aesthetic appreciation is likely to be higher in grazed grasslands due to expected greater plant diversity and abundance and diversity of forbs (Pykälä, 2003).
To date, where links have been drawn between grazing intensity, impact upon ecosystem characteristics, and multiple ecosystem service provision, these have been largely based on literature reviews (Bullock et al., 2011, Kemp and Michalk, 2007). There have been few habitat case studies where these effects have been quantified within an ecosystem services framework. The novelty of this study lies in using a wide range of habitat measurements across different grazing intensities as proxies for specific ecosystem services (Table 1). A managed grazing experiment within a low fertility grazed coastal grassland was used as a model system to examine how grazing affects ecosystem service provision, following the framework of the Millennium Ecosystem Assessment (MA, 2005) and the UK National Ecosystem Assessment (Bullock et al., 2011). The three grazing treatments used were ‘fully grazed’ (i.e. extensively cattle, pony and rabbit grazed), ‘rabbit grazed’ and ‘un-grazed’ (i.e. abandoned). The overarching hypothesis of this study is that ‘changes in grazing will differentially affect individual services, and will alter the balance of supporting, provisioning, regulating and cultural ecosystem service provision of semi-natural grassland.
Section snippets
Study site and experimental design
Fixed sand dune grasslands are low-productivity semi-natural grasslands, and a UK Biodiversity Action Plan (BAP) priority habitat. Newborough Warren is a calcareous coastal sand dune grassland, located in NW Wales (53°8′59″N, 4°21′1″W), noted for its high biodiversity and designated as a National Nature Reserve, Site of Special Scientific Interest and Special Area of Conservation under the EC Habitats and Species Directive 1992. The 389 ha site is managed by Countryside Council for Wales (CCW).
Soil and vegetation characteristics
Soil temperature was significantly higher on the fully grazed than the un-grazed grassland. Vegetation height was significantly different between all treatment pairs with the lowest sward height in the fully grazed, intermediate in the rabbit grazed and highest in the un-grazed grassland (Table 2). Root biomass was significantly greater in the rabbit grazed than the un-grazed grassland. Plant litter was significantly higher in the un-grazed and rabbit grazed compared to the fully grazed
Discussion
Most European semi natural grasslands, including coastal grasslands, have suffered a decline in traditional grazing, with marginal grasslands being ‘abandoned’ or replaced by ‘conservation grazing’ to address conservation priorities such as plant diversity or provision of habitat for breeding birds (GAP, 2012). The relationships between grazing impacts on biophysical measures in this study and probable impacts on ecosystem services are summarised in Fig. 6, supplemented by additional
Acknowledgements
This study was funded as part of a NERC - Centre for Ecology and Hydrology project - NECO3610. Thanks to CCW for access to field site, Rhian Walsh and Aled Roberts for fieldwork assistance, David Cooper for statistical advice and Dick Loxton for invertebrate identification.
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