Fen-meadow, rush pasture, mire and swamp communities: A review of knowledge gaps, restoration issues and their potential to deliver Ecosystem Services CTE1021 Contents Executive Summary Introduction and aims of review Section 1. Fen-meadow, rush pasture and associated mire communities Section 2. Swamp communities Section 3. Mire communities Section 4. Effects of ammonium and nitrate deposition on fen bryophytes Section 5. Gaps in ecology knowledge - research needs Section 6. Field-based programme to characterise the state/condition of a range of restoration sites Section 7. Decision support system 1 Executive Summary The aims of this review were to identify gaps in knowledge and areas requiring research on the abiotic and biotic conditions required for the restoration or re-creation of fens, ‘purple moor-grass and rush pastures’ (PMGRP) and swamp communities. Past and present land management practices on existing and restored habitats; restoration/re-creation methods including seed introduction, soil/hydrological management and vegetation management were reviewed. Information on the Ecosystem Services provided by these wetland communities was also reviewed. The quantity, quality and distribution of wetland community types in the UK Data on the extent and quality of existing wetland communities in the UK and across Europe needs to be collated. Within the UK, our database on wetland communities appears to be deficient for the upland fringe zone for which a comprehensive inventory is needed. Abiotic constraints on wetland community restoration Enhanced site fertility and soil drainage are the two key constraints to the restoration or creation of high nature value wetlands in the UK. Remediation techniques to reduce fertility, such as topsoil removal, although of proven value can produce disappointing results despite careful targeting based on soil chemical analysis. Further detailed studies of ecological and environmental constraints to targeted wetland restoration/creation via soil ameliorative strategies including topsoil removal, soil organic matter manipulation and rewetting are needed. The extent to which acidification is a factor impeding the restoration/creation and maintenance of more basophilic PMGRP and other wetland communities in the UK is uncertain due to a paucity of systematic monitoring of soil and hydrochemistry of sites. High ammonium concentrations have been found to reduce germination and seedling survival of some characteristic PMGRP species. However, insufficient is known about the effects of elevated ammonium levels on the recruitment of PMGRP species in the UK. The hydrological processes that underpin the existence of PMGRP in the UK are poorly understood. Lateral water movement in the root zone appears to be a typical characteristic of these vegetation types, but knowledge of the soil-water regime of different communities and their tolerance to hydrological variation is deficient. This information will provide a basis for successful restoration/creation of these communities. Biotic drivers of unsustainable changes in wetland communities There are severe gaps in knowledge on the scale of genetic erosion and the consequences for regeneration and resilience to environmental change in fragmented, isolated small populations of wetland species. There is a need for long-term manipulative experiments to examine interactions between habitat management, dispersal processes and population dynamics. There is an urgent need for evidence to support or otherwise, genetic reinforcement through the periodic introduction of seed of rare/declining species from a wide range of sites to prevent continued genetic erosion. 2 Gaps in knowledge on the autecology of several wetland species were identified, notably those that dominate swamp communites with the exceptions of Phragmites australis and Typha species. It is suggested that the research needs that exist for wetland species can be addressed to some extent through targeted effort in the Biological Flora of the British Isles. There is a paucity of information on mycorrhization of species in wetland communities. It is considered important that this knowledge gap be addressed, not least to identify the potential role of mycorrhiza in the restoration/creation of these communities. There is a need for a comprehensive study/quantification of the risks posed by alien species to the different wetland community types in the UK. Management and climate change effects on wetlands Management information on fens, fen-meadows, mires were generally extensive and detailed, with the exception that for many swamp communities the information was anecdotal at best. However, the extent to which environmental changes such as atmospheric nutrient deposition, increased temperatures, shifts in rainfall and droughting patterns are likely to affect wetland community structure and interact with management practices, such as timing of mowing or grazing, is largely unknown. Research to examine long-term effects of manipulated changes in the above environmental drivers and their interaction with management practices is considered to be a priority. A 50-year projection by the Wetland Vision project suggested that the viability of wetlands in the UK will be highly dependent on geographic location and water source with sites that are either rain-fed or groundwater-fed in SE England being particularly vulnerable to climate change. Wetland species with a more southern distribution are likely to disperse northwards providing that appropriate hydrological and edaphic conditions are available and that active conservation measures to aid dispersal, such as seed sowing and green “hay” /litter strewing are implemented. In order to ensure resilience to climate change close attention will need to be paid to understanding and maintaining good hydrological conditions in existing and restored/created wetland sites, which may mean removing pressures such as reducing or stopping water abstraction and blocking drainage ditches. Ecosystem-service value knowledge gaps It is suggested that restoration/creation of high ecological value wetlands should, where possible, be closely linked to future landscape scenarios in the UK to optimise their Ecosystem Service values. However, information on the regulatory services, such as water quality and storage, GHG emissions and carbon storage provided by many of the reviewed wetlands was found to be patchy. Gaps in information on methane emissions particularly where wetland communities are established on stagnogley and stagnogley humic soils, on the role played by the plants themselves in facilitating methane release and on carbon–storage potential of many wetland communites were identified as priority areas needing further research. 3 Introduction and the aims of Project CTE1021 The majority of fens, purple moor-grass and rush pastures (PMGRP) in lowland Europe have disappeared or been degraded particularly during the 20th Century by drainage and land use intensification (Bragg and Lindsay, 2003; Vasander et al., 2003; Montanarella et al., 2006). Designation as priority habitats within the UK Biodiversity Action Plan recognizes the parlous state of existence for these habitats in a geographic region that should be their stronghold. In addition to the loss of biodiversity and their cultural service, the degradation of fen and PMGRP systems also diminishes their regulatory and supporting ecosystem functions and services (Millennium Ecosystem Assessment 2005). Fens and PMGRP play a critically important role in regulating GHGs and water, -2 for example drained peat soils can lose 700 g CO2-C m per year, mostly as a direct contribution to the atmosphere (Kluge et al., 2008). The maintenance of existing fen and PMGRP systems is therefore extremely important, but also important is to achieve successful restoration of degraded sites and re-creation of these habitats where possible and appropriate (English Nature et al., 2006; Klimkowska et al., 2007; Hume, 2007; Holliday, 2008). Most ecological and floristic variation within north-west European mire vegetation is accounted for by three ecological gradients: the acid base-poor vs. neutral, base- and bicarbonate-rich gradient; the gradient in fertility related to availability of the limiting nutrient elements N and P; and the water level gradient (Wheeler and Proctor, 2000). An important characteristic of most lowland fen and PMGRP habitats is their complexity; many existing sites show continuous variation in floristic composition among the principal types of wetland vegetation (Van Diggelen et al., 1996; Blackstock et al., 1998). The complexity of existing fen and PMGRP systems therefore provides considerable challenges for their conservation and potential constraints on the scope of their restoration or re- creation within contemporary highly modified and multifunctional European landscapes (Van Diggelen et al., 2006). Use of existing fen and PMGRP systems as ‘reference’ sites for restoration objectives may also mislead where the ‘reference’ site is itself in the process of degrading. It is therefore important to understand the criteria for quantifying the condition of these habitats. Restoration goals may vary depending on whether the focus is on target species or system function, on the spatial and temporal scale from species to landscape, years to centuries and whether the overall objective is to restore the original system or simply improve the condition (Ehrenfeld, 2000; Hobbs and Harris, 2001). Restoration of fen and PMGRP systems