Rotational vegetation burning effects on peatland stream ecosystems

Burning increases post-fire carbon emissions in a heathland and a raised bog, but experimental manipulation of fire severity has no effect

Large amounts of carbon are stored in northern peatlands. There is concern that greater wildfire severity following projected increases in summer drought will lead to higher post-fire carbon losses. We measured soil carbon dynamics in a Calluna heathland and a raised peat bog after experimentally manipulating fire severity. A gradient of fire severity was achieved by simulating drought in 2 × 2 m plots. Ecosystem respiration (ER), net ecosystem exchange (NEE), methane (CH₄) flux and concentration of dissolved organic carbon ([DOC], measured at the raised bog only) were measured for up to two years after burning. The response of these carbon fluxes to increased fire severity in drought plots was similar to plots burnt under ambient conditions associated with traditional managed burning. Averaged across all burnt plots, burning altered mean NEE from a net carbon sink at the heathland (-0.33 μmol CO₂ m^-2 s^-1 in unburnt plots) to a carbon source (0.50 μmol m^-2 s^-1 in burnt plots) and at the raised bog (-0.38 and 0.16 μmol m^-2 s^-1, respectively). Burning also increased CH₄ flux at the raised bog (from 1.16 to 25.3 nmol m^-2 s^-1 in the summer, when it accounted for 79% of the CO₂-equivalent emission). Burning had no significant effect on soil water [DOC].

Seasonal time-series reveal the impact and rapid recovery in richness, abundance and community structure of benthic macroinvertebrates following catchment wildfire

Catchment wildfire can decimate freshwater benthos when burnt material washes through river channels. We conducted detailed seasonal surveys over the course of one-year at N = 9 sites following summer-time wildfire in 2009 and N = 3 sites following summer-time wildfire in 2010 (constituting one-year time-series of 9 ∗ 5 and 3 ∗ 5 samples, respectively). Basic one-year-on surveys were conducted at an additional 12 sites following 2009 wildfires (Sum_postfire:Sum_+one.yr; N = 12 ∗ 2). Burnt sites were compared with 6 reference sites surveyed seasonally between autumn and summer, 2009-2010 (N = 6 ∗ 4), supplemented by 6 additional sites surveyed in summer 2004 (total reference samples: N = 6 ∗ 5). While benthic macroinvertebrates were largely unaffected by the fire event, richness and abundance were decimated during the winter, yet recovered to initial survey levels by the following summer. The differential response of assemblages in the exceptionally wet winter of 2009-10 versus 2010-11 highlighted the catalytic role of rainfall as a driver of benthic disturbance. Ecological disturbance was proportionally greater for less abundant taxa with community evenness peaking at the time of maximum disturbance. Seasonal dynamics in fire-impacted and reference sites followed a similar pattern, implying that despite the major reduction in macroinvertebrate standing crop the general character of benthic processes was sustained. One year after the wildfire event community structure was similar to the immediate post-fire assemblages and generally indistinguishable from reference samples. The statistical importance of habitat parameters at the landscape and local scale (catchment size, landuse, slope, bank management and benthic substrate) were indicative of mechanistic processes underlying wildfire disturbance-recovery and define the scope for mitigation management. The remarkable resilience of community structure in these Mediterranean streams marks an emphatic contrast to the response of benthic macroinvertebrates to comparable disturbance processes in temperate regions. Given the increasing geographic scale and frequency of fires accompanying global warming wildfire-risk may become a leading issue for river management.

Sediment deposition from eroding peatlands alters headwater invertebrate biodiversity

Land use and climate change are driving widespread modifications to the biodiverse and functionally unique headwaters of rivers. In temperate and boreal regions, many headwaters drain peatlands where land management and climate change can cause significant soil erosion and peat deposition in rivers. However, effects of peat deposition in river ecosystems remain poorly understood. We provide two lines of evidence-derived from sediment deposition gradients in experimental mesocosms (0-7.5 g/m² ) and headwaters (0.82-9.67 g/m² )-for the adverse impact of peat deposition on invertebrate community biodiversity. We found a consistent negative effect of sediment deposition across both the experiment and survey; at the community level, decreases in density (1956 to 56 individuals per m² in headwaters; mean 823 ± 129 (SE) to 288 ± 115 individuals per m² in mesocosms) and richness (mean 12 ± 1 to 6 ± 2 taxa in mesocosms) were observed. Sedimentation increased beta diversity amongst experimental replicates and headwaters, reflecting increasing stochasticity amongst tolerant groups in sedimented habitats. With increasing sedimentation, the density of the most common species, Leuctra inermis, declined from 290 ± 60 to 70 ± 30 individuals/m² on average in mesocosms and >800 individuals/m² to 0 in the field survey. Traits analysis of mesocosm assemblages suggested biodiversity loss was driven by decreasing abundance of invertebrates with trait combinations sensitive to sedimentation (longer life cycles, active aquatic dispersal of larvae, fixed aquatic eggs, shredding feeding habit). Functional diversity metrics reinforced the idea of more stochastic community assembly under higher sedimentation rates. While mesocosm assemblages showed some compositional differences to surveyed headwaters, ecological responses were consistent across these spatial scales. Our results suggest short-term, small-scale stressor experiments can inform understanding of "real-world" peatland river ecosystems. As climate change and land-use change are expected to enhance peatland erosion, significant alterations to invertebrate biodiversity can be expected where these eroded soils are deposited in rivers.

Prescribed fire and its impacts on ecosystem services in the UK

The impacts of vegetation fires on ecosystems are complex and varied affecting a range of important ecosystem services. Fire has the potential to affect the physicochemical and ecological status of water systems, alter several aspects of the carbon cycle (e.g. above- and below-ground carbon storage) and trigger changes in vegetation type and structure. Globally, fire is an essential part of land management in fire-prone regions in, e.g. Australia, the USA and some Mediterranean countries to mitigate the likelihood of catastrophic wildfires and sustain healthy ecosystems. In the less-fire prone UK, fire has a long history of usage in management for enhancing the productivity of heather, red grouse and sheep. This distinctly different socioeconomic tradition of burning underlies some of the controversy in recent decades in the UK around the use of fire. Negative public opinion and opposition from popular media have highlighted concerns around the detrimental impacts burning can have on the health and diversity of upland habitats. It is evident there are many gaps in the current knowledge around the environmental impacts of prescribed burning in less fire-prone regions (e.g. UK). Land owners and managers require a greater level of certainty on the advantages and disadvantages of prescribed burning in comparison to other techniques to better inform management practices. This paper addresses this gap by providing a critical review of published work and future research directions related to the impacts of prescribed fire on three key aspects of ecosystem services: (i) water quality, (ii) carbon dynamics and (iii) habitat composition and structure (biodiversity). Its overall aims are to provide guidance based on the current state-of-the-art for researchers, land owners, managers and policy makers on the potential effects of the use of burning and to inform the wider debate about the place of fire in modern conservation and land management in humid temperate ecosystems.

Leaving moss and litter layers undisturbed reduces the short-term environmental consequences of heathland managed burns

Variation in the structure of ground fuels, i.e. the moss and litter (M/L) layer, may be an important control on fire severity in heather moorlands and thus influence vegetation regeneration and soil carbon dynamics. We completed experimental fires in a Calluna vulgaris-dominated heathland to study the role of the M/L layer in determining (i) fire-induced temperature pulses into the soil and (ii) post-fire soil thermal dynamics. Manually removing the M/L layer before burning increased fire-induced soil heating, both at the soil surface and 2 cm below. Burnt plots where the M/L layer was removed simulated the fuel structure after high severity fires where ground fuels are consumed but the soil does not ignite. Where the M/L layer was manually removed, either before or after the fire, post-fire soil thermal dynamics showed larger diurnal and seasonal variation, as well as similar patterns to those observed after wildfires, compared to burnt plots where the M/L layer was not manipulated. We used soil temperatures to explore potential changes in post-fire soil respiration. Simulated high fire severity (where the M/L layer was manually removed) increased estimates of soil respiration in warm months. With projected fire regimes shifting towards higher severity fires, our results can help land managers develop strategies to balance ecosystem services in Calluna-dominated habitats.

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’.

Forest clearfelling effects on dissolved oxygen and metabolism in peatland streams

Peatlands cover ∼3% of the world's landmass and large expanses have been altered significantly as a consequence of land use change. Forestry activities are a key pressure on these catchments increasing suspended sediment and nutrient export to receiving waters. The aim of this study was to investigate stream dissolved oxygen (DO) and metabolic activity response following clearfelling of a 39-year-old lodgepole pine and Sitka spruce forestry in an upland peat catchment. Significant effects of clearfelling on water temperature, flows, DO and stream metabolic (photosynthesis, respiration) rates were revealed. Stream temperature and discharge significantly increased in the study stream following clearfelling. Instream ecosystem respiration increased significantly following clearfelling, indicating an increase in the net consumption of organic carbon.

Vegetation management with fire modifies peatland soil thermal regime

Vegetation removal with fire can alter the thermal regime of the land surface, leading to significant changes in biogeochemistry (e.g. carbon cycling) and soil hydrology. In the UK, large expanses of carbon-rich upland environments are managed to encourage increased abundance of red grouse (Lagopus lagopus scotica) by rotational burning of shrub vegetation. To date, though, there has not been any consideration of whether prescribed vegetation burning on peatlands modifies the thermal regime of the soil mass in the years after fire. In this study thermal regime was monitored across 12 burned peatland soil plots over an 18-month period, with the aim of (i) quantifying thermal dynamics between burned plots of different ages (from <2 to 15 + years post burning), and (ii) developing statistical models to determine the magnitude of thermal change caused by vegetation management. Compared to plots burned 15 + years previously, plots recently burned (<2-4 years) showed higher mean, maximum and range of soil temperatures, and lower minima. Statistical models (generalised least square regression) were developed to predict daily mean and maximum soil temperature in plots burned 15 + years prior to the study. These models were then applied to predict temperatures of plots burned 2, 4 and 7 years previously, with significant deviations from predicted temperatures illustrating the magnitude of burn management effects. Temperatures measured in soil plots burned <2 years previously showed significant statistical disturbances from model predictions, reaching +6.2 °C for daily mean temperatures and +19.6 °C for daily maxima. Soil temperatures in plots burnt 7 years previously were most similar to plots burned 15 + years ago indicating the potential for soil temperatures to recover as vegetation regrows. Our findings that prescribed peatland vegetation burning alters soil thermal regime should provide an impetus for further research to understand the consequences of thermal regime change for carbon processing and release, and hydrological processes, in these peatlands.

Restoration of blanket peatlands

There is concern that ecosystem services provided by blanket peatlands have come under threat due to increasing degradation. Blanket peatlands are subject to a wide range of drivers of degradation and are topographically variable. As a result, many degradation forms can develop, including those resulting from eroding artificial drainage, incising gullies and areas of bare peat. Many degraded blanket peatlands have undergone restoration measures since the turn of the century. However, there has been little formal communication of the techniques used and their success. Using practitioner knowledge and a review of the available literature, this paper discusses the methodologies used for restoring sloping blanket peatlands. It then considers current understanding of the impact of restoration on blanket peatland ecosystem services. There is a paucity of research investigating impacts of several common restoration techniques and much more is needed if informed management decisions are to be made and funding is to be appropriately spent. Where data are available we find that restoration is largely beneficial to many ecosystem services, with improvements being observed in water quality and ecology. However, the same restoration technique does not always result in the same outcomes in all locations. The difference in response is predominantly due to the spatial and temporal heterogeneity inherent in all blanket peatlands. Peatland practitioners must take this variability into account when designing restoration strategies and monitoring impact.

River ecosystem response to prescribed vegetation burning on Blanket Peatland

Catchment-scale land-use change is recognised as a major threat to aquatic biodiversity and ecosystem functioning globally. In the UK uplands rotational vegetation burning is practised widely to boost production of recreational game birds, and while some recent studies have suggested burning can alter river water quality there has been minimal attention paid to effects on aquatic biota. We studied ten rivers across the north of England between March 2010 and October 2011, five of which drained burned catchments and five from unburned catchments. There were significant effects of burning, season and their interaction on river macroinvertebrate communities, with rivers draining burned catchments having significantly lower taxonomic richness and Simpson’s diversity. ANOSIM revealed a significant effect of burning on macroinvertebrate community composition, with typically reduced Ephemeroptera abundance and diversity and greater abundance of Chironomidae and Nemouridae. Grazer and collector-gatherer feeding groups were also significantly less abundant in rivers draining burned catchments. These biotic changes were associated with lower pH and higher Si, Mn, Fe and Al in burned systems. Vegetation burning on peatland therefore has effects beyond the terrestrial part of the system where the management intervention is being practiced. Similar responses of river macroinvertebrate communities have been observed in peatlands disturbed by forestry activity across northern Europe. Finally we found river ecosystem changes similar to those observed in studies of wild and prescribed forest fires across North America and South Africa, illustrating some potentially generic effects of fire on aquatic ecosystems.