Review of the effectiveness of on-site habitat management to reduce atmospheric nitrogen deposition impacts on terrestrial habitats

1. Given the widespread impacts on habitats in the UK it is essential to understand how habitat management measures could mitigate N deposition impacts and promote recovery. This project reviews the effectiveness of ‘on-site’ land management methods to mitigate nitrogen deposition impacts on sensitive habitats; assesses what effect current management practice has on habitat response to nitrogen deposition; considers how measures may be affected by climate change; and recommends realistic and practical management measures for different habitat types which could be used to mitigate nitrogen impacts or speed recovery. 2. The potential for management to mitigate N deposition impacts was considered across the following broad habitats: broadleaved, mixed and yew woodland & (natural) coniferous woodland; neutral grassland; calcareous grassland; acid grassland; dwarf shrub heath; bog; coastal dunes and slacks; other coastal habitats. For all habitats we were able to identify management techniques with some potential to mitigate N deposition impacts. 3. Management techniques may improve habitat suitability (e.g. control dominant species), remove nitrogen from the system, or both. 4. However, all management techniques also have unintended consequences meaning that their implementation might conflict with other conservation priorities. 5. There are a range of schemes and handbooks providing habitat management advice in the UK. The following techniques were reviewed in detail: grazing; cutting; burning; fertilisation; liming; hydrological management; scrub and tree management; disturbance. 6. Current management may already be partially offsetting the impact of N deposition. 7. Management for N is unlikely to make habitats more vulnerable to climate change. There is complementarity in the management options required to tackle N deposition and climate change. The frequency or intensity of measures such as grazing, cutting or burning will all need to increase. Regional variation in climate change may lead to different emphasis of management options in the wetter north west and the drier south east. 8. Climate change will alter habitat sensitivity to N deposition, via changes in ecosystem processes. Overall, climate change will make woodlands less sensitive to N deposition, but will make heathlands more sensitive to N deposition. Effects on other habitats have not yet been evaluated. 9. There is some potential for mitigating the impacts of N deposition through on-site management although this varies greatly between habitat and management practice. It is likely that small changes in management and adherence to appropriate guidelines could partially improve habitat suitability and/or increase N removal. 10. The majority of management practices do not remove significant quantities of N (with the exception of removing biomass or topsoil). Furthermore, management of a suitable intensity to remove sufficient N to fully offset N added by atmospheric deposition is likely to damage the habitat and result in a number of unintended consequences. 11. Further research is needed to determine the impacts of individual management practices on the N budget in different habitats. Further research is also needed to explore the potential for novel management techniques to remove N from sites. 12. For an individual site where N is identified as a pressure, a manager can look at current management and compare this with the management recommendations in the report to make changes where appropriate. 13. All management recommendations that remove N from the site move it elsewhere and have the potential for unintended consequences. Consequently there is no substitute for reducing the amount of N deposited onto a site which can only be achieved through emission controls

A novel technique for reducing soil fertility in ecological restoration projects

Surface soil eutrophication hinders ecological restoration projects by favouring communities of low biodiversity. This study assesses the effectiveness of a novel technique known as topsoil inversion that may promote recovery from eutrophication. Topsoil inversion is undertaken by a deep plough, which buries 30 cm of topsoil under approximately 40 cm of subsoil. The main study site is within new community woodland on former agricultural land. It comprises deep ploughed and conventionally ploughed plots, to compare two planting types: wildflowers only, and wildflowers with trees. This presentation will discuss some preliminary findings of the effect of topsoil inversion on soil properties and plant tissue nutrient content. Surface soil fertility is lowered following inversion treatment, and this appears to affect plant nutrient sequestration. These results suggest that topsoil inversion has the potential to facilitate ecological restoration on eutrophic soil. This technique may have benefits for restoration projects taking place in a variety of habitats affected by air pollution, including former agricultural land and lowland heaths

Highest densities of mountain hares ( Lepus timidus ) associated with ecologically restored bog but not grouse moorland management

Over the last 20 years, ecological restoration of degraded habitats has become common in conservation practice. Mountain hares (Lepus timidus scoticus) were surveyed during 2017–2021 using 830 km of line transects in the Peak District National Park, England. Historically degraded bog areas were previously reported having low hare numbers. Following bog restoration, we found hare densities of 32.6 individuals km−2, notably higher than neighboring degraded (unrestored) bog with 24.4 hares km−2. Hare density on restored peatland was 2.7 times higher than on bogs managed for grouse shooting at 12.2 hares km−2 and 3.3 times higher than on heather moorland managed for grouse shooting at 10.0 hares km−2. Yearly estimates varied most on habitats managed for grouse, perhaps indicative of the impact of habitat management, for example, heather burning and/or possible hare culling to control potential tick-borne louping ill virus in gamebirds. Acid grassland used for sheep farming had a similar density to grouse moorland at 11.8 hares km−2. Unmanaged dwarf shrub heath had the lowest density at 4.8 hares km−2. Hare populations are characterized by significant yearly fluctuations, those in the study area increasing by 60% between 2017 and 2018 before declining by ca. 15% by 2020 and remaining stable to 2021. During an earlier survey in 2002, total abundance throughout the Peak District National Park was estimated at 3361 (95% CI: 2431–4612) hares. The present study estimated 3562 (2291–5624) hares suggesting a stable population over the last two decades despite fluctuations likely influenced by weather and anthropogenic factors. Mountain hares in the Peak District favored bog habitats and were associated with restored peatland habitat. Wildlife management should be cognizant of hare density variation between habitats, which may have implications for local extinction risk

An overview of the progress and challenges of peatland restoration in Western Europe

Peatlands are the most efficient terrestrial carbon store on Earth, and deliver multiple other ecosystem services including climate regulation, water purification, preservation of ecological and archaeological records, etc. Disturbed and degraded peatlands do not provide the same ecological services and thus bear a significant cost to society. Because this cost may be alleviated by appropriate restoration measures, money is being invested in peatland restoration projects around the world. Here, we review over 25 years of restoration in Western Europe. First, we provide an overview of techniques used in different contexts and evaluate the status of the evidence base for restoration outcomes. Between 1993 and 2015, the EU-LIFE nature programme alone invested 167.6M € in 80 projects, which aim to restore over 913 km2 of peatland habitats in Western European countries, mostly in protected sites part of the Natura 2000 EU network. This represents less than 2% of the total remaining area of peatlands in these countries, most of which have been impacted to some degree by anthropogenic disturbances. Potential for restoration should be considered in nondesignated sites. We reviewed a number of case studies covering a range of restoration approaches used in different parts of Western Europe. We found that published evidence of restoration progress was limited to specific sites/areas, and in many cases lacked baseline measurements and clear goals, that is, measurable target or contemporary reference(s). We discuss barriers and opportunities to turn the tide for peatland restoration in Western Europe and promote the establishment of robust, standardized monitoring schemes

Managing for nitrogen, the lesser of two evils. A response to Maes et al.

Letter to the Editor

What is the most ecologically-meaningful metric of nitrogen deposition?

Nitrogen (N) deposition poses a severe risk to global terrestrial ecosystems, and managing this threat is an important focus for air pollution science and policy. To understand and manage the impacts of N deposition, we need metrics which accurately reflect N deposition pressure on the environment, and are responsive to changes in both N deposition and its impacts over time. In the UK, the metric typically used is a measure of total N deposition over 1–3 years, despite evidence that N accumulates in many ecosystems and impacts from low-level exposure can take considerable time to develop. Improvements in N deposition modelling now allow the development of metrics which incorporate the long-term history of pollution, as well as current exposure. Here we test the potential of alternative N deposition metrics to explain vegetation compositional variability in British semi-natural habitats. We assembled 36 individual datasets representing 48,332 occurrence records in 5479 quadrats from 1683 sites, and used redundancy analyses to test the explanatory power of 33 alternative N metrics based on national pollutant deposition models. We find convincing evidence for N deposition impacts across datasets and habitats, even when accounting for other large-scale drivers of vegetation change. Metrics that incorporate long-term N deposition trajectories consistently explain greater compositional variance than 1–3 year N deposition. There is considerable variability in results across habitats and between similar metrics, but overall we propose that a thirty-year moving window of cumulative deposition is optimal to represent impacts on plant communities for application in science, policy and management

Sphagnum farming from species selection to the production of growing media : a review

Sphagnum farming - the production of Sphagnum biomass on rewetted bogs - helps towards achieving global climate goals by halting greenhouse gas emissions from drained peat and by replacing peat with a renewable biomass alternative. Large-scale implementation of Sphagnum farming requires a wide range of know-how, from initial species selection up to the final production and use of Sphagnum biomass based growing media in horticulture. This article provides an overview of relevant knowledge accumulated over the last 15 years and identifies open questions.Peer reviewe

Genetic analysis of the naked trait in panicles of hexaploid oat

The aim of this study was to estimate the number of genes that control the naked (hull-less) trait and the mode of expression of this characteristic in panicles of hexaploid white oat. Parents and the segregating population (in the F2 and F3 generations) were evaluated in regard to the presence and distribution of naked grains in panicles of individual oat plants. For each plant, a drawing of the main panicle was developed. From the drawings obtained in the progenies of the F2 population, six distinct phenotypic classes were produced. The expected phenotypic proportion of 3:9:4 (naked:segregating:hulled) was that which best fit by the Chi-square test. In the F3 generation, the results showed agreement with the hypothesis observed in the F2 generation. The naked trait in oat is passed on by two genes and the greatest expression of this trait occurs in the upper third of the panicles. Expression of this trait in oats is not complete, even in homozygous genotypes

Disparities between plant community responses to nitrogen deposition and critical loads in UK semi-natural habitats

Empirical critical loads are widely used to quantify and manage the ecological impacts of reactive nitrogen (N) deposition. Critical load values aim to identify a level of N deposition below which significant harmful effects do not occur according to present knowledge. Critical loads have been primarily based on experiments, but these are few in number and have well-known limitations, so there is a strong imperative to test and validate values with other forms of evidence. We assembled data on the spatial variability in vegetation communities in the United Kingdom and used Threshold Indicator Taxa Analyses (TITAN) to investigate linkages between species changes and modelled current and cumulative N deposition. Our analyses focused on five datasets: acid grasslands, alpine habitats, coastal fixed dunes, dune slacks and wet grasslands. In four of these habitats there was evidence for a significant decline in the cover of at least one species (a ‘species-loss change-point’) occurring below the critical load, and often at very low levels of N deposition. In all of the habitats there was evidence for clustering of many individual species-loss change-points, implying a community change-point analogous to an ecological threshold. Three of these community change-points occurred below the critical load and the remaining two overlapped with the critical load range. Studies using similar approaches are now increasingly common, with similar results. Across 19 similar analyses there has been evidence for plant species loss change-points below the critical load in 18 analyses, and community-level species loss change-points below the critical load in 13 analyses. None of these analyses has shown community change-points above the critical load. Field data increasingly suggest that many European critical loads are too high to confidently prevent loss of sensitive species