Controls upon biomass losses and char production from prescribed burning on UK moorland.

Prescribed burning is a common management technique used across many areas of the UK uplands. However, there are few data sets that assess the loss of biomass during burning and even fewer data on the effect of burning on above-ground carbon stocks and production of char. During fire the production of char occurs which represents a transfer of carbon from the short term bio-atmospheric cycle to the longer term geological cycle. However, biomass is consumed leading to the reduction in litter formation which is the principal mechanism for peat formation. This study aims to solve the problem of whether loss of biomass during a fire is ever outweighed by the production of refractory forms of carbon during the fire. This study combines both a laboratory study of char production with an assessment of biomass loss from a series of field burns from moorland in the Peak District, UK. The laboratory results show that there are significant effects due to ambient temperature but the most important control on dry mass loss is the maximum burn temperature. Burn temperature was also found to be linearly related to the production of char in the burn products. Optimisation of dry mass loss, char production and carbon content shows that the production of char from certain fires could store more carbon in the ecosystem than if there had been no fire. Field results show that approximately 75% of the biomass and carbon were lost through combustion, a figure comparable to other studies of prescribed fire in other settings. Char-C production was approximately 2.6% of the carbon consumed during the fire. This study has shown that there are conditions (fast burns at high temperatures) under which prescribed fire may increase C sequestration through char production and that these conditions are within existing management options available to practitioners.

Accuracy of tropical peat and non-peat fire forecasts enhanced by simulating hydrology.

Soil moisture deficits and water table dynamics are major biophysical controls on peat and non-peat fires in Indonesia. Development of modern fire forecasting models in Indonesia is hampered by the lack of scalable hydrologic datasets or scalable hydrology models that can inform the fire forecasting models on soil hydrologic behaviour. Existing fire forecasting models in Indonesia use weather data-derived fire probability indices, which often do not adequately proxy the sub-surface hydrologic dynamics. Here we demonstrate that soil moisture and water table dynamics can be simulated successfully across tropical peatlands and non-peatland areas by using a process-based eco-hydrology model (ecosys) and publicly available data for weather, soil, and management. Inclusion of these modelled water table depth and soil moisture contents significantly improves the accuracy of a neural network model in predicting active fires at two-weekly time scale. This constitutes an important step towards devising an operational fire early warning system for Indonesia.

Charcoal production in a UK moorland wildfire--how important is it?

Wildfires are a common feature of peatland environments, but the carbon balance of these wildfires is often not considered and the production of refractory black carbon in these wildfires could be an important addition to carbon accumulation and mitigate losses of biomass during the fire. This study investigates the biomass and carbon losses during a moorland wildfire. Changes in above-ground carbon stocks were calculated using a combination of field data, laboratory measurements and literature values. The results show that approximately 14% of the carbon in the original above-ground biomass remained on the site after the burn. Black carbon production was approximately 6 gC m(-2) which constituted 4.3% of the biomass lost. The survival of biomass and black carbon may help to mitigate the loss of carbon during the fire.

Towards a microbial process-based understanding of the resilience of peatland ecosystem service provisioning - A research agenda.

Peatlands are wetland ecosystems with great significance as natural habitats and as major global carbon stores. They have been subject to widespread exploitation and degradation with resulting losses in characteristic biota and ecosystem functions such as climate regulation. More recently, large-scale programmes have been established to restore peatland ecosystems and the various services they provide to society. Despite significant progress in peatland science and restoration practice, we lack a process-based understanding of how soil microbiota influence peatland functioning and mediate the resilience and recovery of ecosystem services, to perturbations associated with land use and climate change. We argue that there is a need to: in the short-term, characterise peatland microbial communities across a range of spatial and temporal scales and develop an improved understanding of the links between peatland habitat, ecological functions and microbial processes; in the medium term, define what a successfully restored 'target' peatland microbiome looks like for key carbon cycle related ecosystem services and develop microbial-based monitoring tools for assessing restoration needs; and in the longer term, to use this knowledge to influence restoration practices and assess progress on the trajectory towards 'intact' peatland status. Rapid advances in genetic characterisation of the structure and functions of microbial communities offer the potential for transformative progress in these areas, but the scale and speed of methodological and conceptual advances in studying ecosystem functions is a challenge for peatland scientists. Advances in this area require multidisciplinary collaborations between peatland scientists, data scientists and microbiologists and ultimately, collaboration with the modelling community. Developing a process-based understanding of the resilience and recovery of peatlands to perturbations, such as climate extremes, fires, and drainage, will be key to meeting climate targets and delivering ecosystem services cost effectively.

Organic matter properties of Fennoscandian ecosystems: Potential oxidation of northern environments under future change?

The oxidative ratio (OR) of an ecosystem, which reflects the ratio of O2:CO2 associated with ecosystem gas exchanges, is an important parameter in understanding the sink of CO2 represented by the terrestrial biosphere. There is a growing body of ecosystem-based approaches to understand OR; however, there are still a number of unknowns. This study addressed two gaps in our understanding of the oxidation of the terrestrial biosphere: (1) What is the oxidation state of Arctic ecosystems, and in particular permafrost soils? (2) Will coupled climate and land use change cause the terrestrial organic matter oxidation state to change? The study considered eight locations along a transect from southern Sweden to northern Norway and sampled different organic matter types (soil, litter, trees, and herbaceous vegetation) as well as different soil orders (Inceptisols, Spodosols, Histosols, and Gelisols). The study showed that although there was no difference between soil orders, there was a significant effect due to location with OR increasing from 1.03 at the southernmost location to 1.09 in the northernmost location; this increase is independent of soil order or type of organic matter. The pattern of post hoc differences in the OR with latitude suggests that the increase in OR is correlated with the northern limit of arable agriculture. The study suggests that the combined effects of climate and land use change could lead to a decrease in terrestrial organic matter OR and an increase in its oxidation state.

The role of fire in UK peatland and moorland management: the need for informed, unbiased debate.

Fire has been used for centuries to generate and manage some of the UK's cultural landscapes. Despite its complex role in the ecology of UK peatlands and moorlands, there has been a trend of simplifying the narrative around burning to present it as an only ecologically damaging practice. That fire modifies peatland characteristics at a range of scales is clearly understood. Whether these changes are perceived as positive or negative depends upon how trade-offs are made between ecosystem services and the spatial and temporal scales of concern. Here we explore the complex interactions and trade-offs in peatland fire management, evaluating the benefits and costs of managed fire as they are currently understood. We highlight the need for (i) distinguishing between the impacts of fires occurring with differing severity and frequency, and (ii) improved characterization of ecosystem health that incorporates the response and recovery of peatlands to fire. We also explore how recent research has been contextualized within both scientific publications and the wider media and how this can influence non-specialist perceptions. We emphasize the need for an informed, unbiased debate on fire as an ecological management tool that is separated from other aspects of moorland management and from political and economic opinions.This article is part of the themed issue 'The interaction of fire and mankind'.

The impact of sheep grazing on the carbon balance of a peatland.

Estimates of the greenhouse gas (GHG) fluxes resulting from sheep grazing upon upland peat soils have never been fully quantified. Previous studies have been limited to individual flux pathways or to comparing the presence to the absence of sheep grazing. Therefore, this study combines a model of the physical impact of grazing with models of: biomass production; energy usage in sheep; and peat accumulation. These combined modelling approaches enabled this study to consider the indirect and direct impacts of sheep upon the carbon and greenhouse gas balance of a peatland at different grazing intensities as well as the changes between grazing intensities. The study considered four vegetation scenarios (Calluna sp., Molinia sp.; reseeded grasses, and Agrostis-Festuca grassland) and a mixed vegetation scenario based upon the vegetation typical of upland peat ecosystems in northern England. Each scenario was considered for altitudes between 350 and 900 m above sea level and for grazing intensities between 0.1 and 2 ewes/ha. The study can show that the total GHG flux at the vegetative carrying capacity tended to decline with increasing altitude for all vegetation scenarios considered except for Molinia sp. The average total GHG flux for all scenarios was 1505 kg CO(2)eq/ha/yr/(ewe/ha), and on average 89% of the fluxes were directly from the sheep and not from the soil, and are therefore not unique to a peat soil environment. The study suggests that emission factors for upland sheep have been greatly underestimated. By comparing the total flux due to grazers to the flux to or from the soil that allows the study to define a GHG carry capacity, i.e. the grazing intensity at which the flux due to grazing is equal to the sink represented by the peat soils, this GHG carrying capacity varies between 0.2 and 1.7 ewes/ha with this capacity declining with increasing altitude for all model scenarios.

The multi-annual nitrogen budget of a peat-covered catchment--changing from sink to source?

Only a few studies have considered the N budget of peat soils and this in turn has limited the ability of studies to consider the impact of changes in climate and atmospheric deposition upon the N budget of a peat soil. This study considered the total N budget of an upland peat-covered catchment over the period 1993 to 2009. The study has shown: i) Over the period of study the total N atmospheric deposition declined from 3.5 to 0.7 tonnes N/km2/yr. ii) The total fluvial export of N at soil source varied from 0.41 to 1.85 tonnes N/km2/yr with the fluvial flux being greater than the atmospheric input in 3 years of the study, implying significant internal processing. iii) Measuring the C:N ratio of organic matter pools in the ecosystem shows that gross primary productivity and litter decomposition represent outputs of N from the soil while DOC production and humification represent inputs of N. iv) Overall, the total N budget of the peat ecosystem varies from − 1.0 to + 2.5 tonnes N/km2/yr, i.e. in some years the ecosystem is a net source of N. The time series of the total N budget suggests that the ecosystem is responding to the occurrence of severe droughts with a long-term decline in N storage that could be interpreted as a response to long-term high N deposition rates, even if those rates have now diminished.