Scots pine growing on forested mires in Abernethy Forest,Strathspey, Scotland

Summary

A substantial proportion of the Abernethy Forest Reserve has Scots pine (Pinus sylvestris) growing on the surfaces of a variety of mires. The hydrology of the mires has been affected by drainage and peat cutting but this area is unusual in having had a long period of protection from grazing by domestic stock. There are three main types of pine populations found on these mires. Woodland bog comprises predominantly bog vegetation with abundant pine seedlings due to the heavy seed rain from the surrounding woodland. Only a few very small trees survive, which are stunted, heavily diseased and have very low seed production. Wooded bog also comprises predominately bog vegetation but there are scattered mature trees of a moderate height with an open canopy. The trees are fertile and can form uneven aged stands with regeneration. Bog woodland is a predominantly woodland vegetation with tall, dense tree cover on deep peat. The trees are well grown with a dense canopy. A few remnants of bog vegetation remain in the ground flora although most have been replaced by woodland bryophytes and shrubs. Each of these three types is described and their development is discussed.     

Terrestrial export of highly bioavailable carbon from small boreal catchments in spring floods

1. We assessed the terrestrial export of organic carbon, which effectively supported aquatic bacterial production (BP), from small boreal catchments during spring flood. We analysed stream runoff from nine small catchments with different proportions of peat mires and coniferous forests by monitoring the dissolved organic carbon (DOC) flux in combination with conducting bacterial bioassays.
2. Multiple linear regression analysis showed that BP during 7-day-dark bioassays (BP₇; μg C L⁻¹day⁻¹) was explained by both the quantity and quality (low-molecular weight fractions) of the DOC. BP₇ can be used as a measure of export of terrestrial organic carbon that is highly bioavailable.
3. Total export of DOC during spring flood from the different catchments ranged from 20 to 27 kg ha⁻¹ and was negatively correlated to forest cover (%). However, the export of BP₇ carbon was positively correlated to forest cover and varied from about 0.1 kg ha⁻¹ in mire-dominated streams to about 0.2 kg ha⁻¹ in forest-dominated streams.
4. The high bioavailability of forest carbon suggests that forests are the main contributors of BP-supporting carbon in boreal streams although mires have higher area-specific export of DOC.     

Effect of experimental nitrogen load on methane and nitrous oxide fluxes on ombrotrophic boreal peatland

Methane (CH₄) and nitrous oxide (N₂O) dynamics were studied in a boreal Sphagnum fuscum pine bog receiving annually (from 1991 to 1996) 30 or 100 kg NH₄NO₃-N ha^–1. The gas emissions were measured during the last three growing seasons of the experiment. Nitrogen treatment did not affect the CH₄ fluxes in the microsites where S. fuscum and S. angustifolium dominated. However, addition of 100 kg NH₄NO₃-N ha^–1 yr^–1 increased the CH₄ emission from those microsites dominated by S. fuscum. This increase was associated with the increase in coverage of cotton grass (Eriophorum vaginatum) induced by the nitrogen treatment. The differences in the CH₄ emissions were not related to the CH₄ oxidation and production potentials in the peat profiles. The N₂O fluxes were negligible from all microsites. Only minor short-term increases occurred after the nitrogen addition.     

Nitrous oxide and methane fluxes of a pristine slope mire in the German National Park Harz Mountains

Pristine peatlands covered by Histosols (bogs and fens) with high water table and a restricted oxygen (O₂) availability are known to have low emissions of nitrous oxide (N₂O) but may be a significant source for atmospheric methane (CH₄) which are both important greenhouse gases. For the first time N₂O and CH₄ fluxes of a pristine slope mire in the German Harz Mountains have been monitored. Previously reported peatlands are characterised by anaerobic conditions due to high water table levels. Slope mires monitored here receive O₂ through slope water inflow. Gas fluxes have been monitored deploying closed chamber method on a central non-forested area and a forested area at the periphery of the slope mire. By means of groundwater piezometers water table levels, ammonium and nitrate contents as well as hydro-chemical variables like oxygen content and redox potential of the mire pore water have been concurrently measured with trace gas fluxes at both monitoring sites of the slope mire. The slope mire took up small amounts of atmospheric methane at a rate of −0.02 ± 0.01 kg C ha⁻¹ year⁻¹ revealing no significant difference between the forested and non-forested site. Higher uptake rates were observed during low water table level. In contrast to pristine peatlands influx of oxygen containing pore water into slope mire does limit reduction processes and resultant CH₄ emission. N₂O fluxes of the forested and non-forested sites of the slope mire did not differ and amounted to 0.25 ± 0.44 kg N ha⁻¹ year⁻¹. Higher emissions were observed at low water table levels and during thawing periods. In spite of favourable conditions N₂O fluxes of the slope mire have been comparable to those of pristine peatlands.     

The biogeochemistry of nitrogen in freshwater wetlands

The biogeochemistry of N in freshwater wetlands is complicated by vegetation characteristics that range from annual herbs to perennial woodlands; by hydrologic characteristics that range from closed, precipitation-driven to tidal, riverine wetlands; and by the diversity of the nitrogen cycle itself. It is clear that sediments are the single largest pool of nitrogen in wetland ecosystems (100's to 1000's g N m^-2) followed in rough order-of-magnitude decreases by plants and available inorganic nitrogen. Precipitation inputs (< 1–2 g N m^-2 yr^-1) are well known but other atmospheric inputs, e.g. dry deposition, are essentially unknown and could be as large or larger than wet deposition. Nitrogen fixation (acetylene reduction) is an important supplementary input in some wetlands (< < 1–3 g N m^-2 yr^-1) but is probably limited by the excess of fixed nitrogen usually present in wetland sediments.Plant uptake normally ranges from a few g N m^-2 yr^-1 to 35 g N m^-2 yr^-1 with extreme values of up to 100g N m^-2 yr^-1 Results of translocation experiments done to date may be misleading and may call for a reassessment of the magnitude of both plant uptake and leaching rates. Interactions between plant litter and decomposer microorganisms tend, over the short-term, to conserve nitrogen within the system in immobile forms. Later, decomposers release this nitrogen in forms and at rates that plants can efficiently reassimilate.The NO₃ formed by nitrification (< 0.1 to 10 g N m^-2 yr^-1 has several fates which may tend to either conserve nitrogen (uptake and dissimilatory reduction to ammonium) or lead to its loss (denitrification). Both nitrification and denitrification operate at rates far below their potential and under proper conditions (e.g. draining or fluctuating water levels) may accelerate. However, virtually all estimates of denitrification rates in freshwater wetlands are based on measurements of potential denitrification, not actual denitrification and, as a consequence, the importance of denitrification in these ecosystems may have been greatly over estimated.In general, larger amounts of nitrogen cycle within freshwater wetlands than flow in or out. Except for closed, ombrotrophic systems this might seem an unusual characteristic for ecosystems that are dominated by the flux of water, however, two factors limit the opportunity for N loss. At any given time the fraction of nitrogen in wetlands that could be lost by hydrologic export is probably a small fraction of the potentially mineralizable nitrogen and is certainly a negligible fraction of the total nitrogen in the system. Second, in some cases freshwater wetlands may be hydrologically isolated so that the bulk of upland water flow may pass under (in the case of floating mats) or by (in the case of riparian systems) the biotically active components of the wetland. This may explain the rather limited range of N loading rates real wetlands can accept in comparison to, for example, percolation columns or engineered marshes.     

A rapid and cost-effective tool for managing habitats of the European Natura 2000 network: a case study in the Italian Alps

“Habitats” Directive 92/43/EEC is the pivotal European law for building a continental network of sites of community importance (SCIs) for nature conservation. Article 6 of such directive underlines the importance of biodiversity conservation through the realization of proper management plans. As a result, such plans are increasingly common. A management plan based on intensive field studies and monitoring activities requires time and financial resources, which are generally limited. The aim of this paper is to offer a rapid, cost-effective and scientifically based decision tool aimed to achieve GIS-based conservation strategies for habitats of EU interest within SCIs and, in general, within protected areas. As a case study, we considered species-rich Nardus grasslands (threatened by natural reconversion and intensive cattle grazing), and transition mires (threatened by pasturing and human disturbance) in a SCI in the Alps. Through a multi-criteria evaluation, we selected indicators and weights based upon our knowledge of the study area. As a result, we were able to: (a) quantify the level of existing threats, (b) suggest urgent conservation strategies, and (c) suggest future monitoring activities. Since the study area is representative of many protected areas in the Alps and the conservation topics under evaluation are frequent threats impacting habitats of EU interest, our decision model might be transferable to further areas given proper adaptation of weights to the intensity and the frequency of current threats.     

The value of open power line habitat in conservation of ground beetles (Coleoptera: Carabidae) associated with mires

The draining of mires for silvicultural purposes has caused one of the most dramatic changes in the landscape during the last century in Finland. To study the effects of mire drainage, carabid beetle assemblages were sampled using pitfall trapping in three different mire habitat types. Carabids were sampled from mires in their natural state, drained mires and drained mires with an open power line to see whether the cleared power line can serve as an alternative habitat for mire dependent carabids. The draining of mires greatly increases the species richness of the carabid assemblages. Yet, the conservation value of the environment has dropped following the draining, since only common and abundant forest carabids have benefited from human impact. The role of the open power line as an alternative habitat for mire specialists remains questionable. A few carabid species have, however, benefited from the open habitat of the power line. The vegetation structure had a significant effect in determining the compositions of the carabid assemblages on the studied habitat types. It seems that mire dwelling carabids cannot survive on the drained mires, unless at least some characteristics, other than the mere openness of the cleared power lines, of natural mires remain.     

Community and species responses to water level fluctuations with reference to soil layers in different habitats of mid-boreal mire complexes

The present paper discusses water level fluctuations in different parts of boreal mire complexes (eleven localities), mainly aapa mire complexes, on the basis of measurements performed by means of shallow observation wells and a few deeper observation tubes (piezometers) in the coastal half of the southern aapa mire zone in Finland. The sites represented intact vegetation from 12 different habitat types (communities), which were divided a priori into habitats with a stable surface moisture status (stable habitats) and into habitats with an unstable surface moisture status (unstable habitats). In stable habitats water level fluctuations took place according to the acrotelm–catotelm model, but the unstable habitats clearly deviated from the general pattern: water level fluctuations in them were not at all concentrated to the surficial, porous peat layer. Direct gradient analysis was used for arranging the communities along the water level fluctuation gradient. Variability of the water table, using 80% amplitude of water table residence, was used for the arrangement. The gradient was split into three groups: (1) habitats with a slightly fluctuating water table, (2) habitats with a considerably fluctuating water table and (3) habitats with an extremely fluctuating water table. The last group nearly corresponded to aro wetlands, and represented a very special habitat type. Indirect gradient analysis (NMDS ordination) also revealed the water level fluctuation gradient along with the gradient of traditional water level categories. According to the results of direct and indirect gradient analysis, the water level fluctuation seems to be an independent and important vegetation gradient. In peatlands, it occurs alongside with the traditional gradient of water level categories reflecting the mean water table. The responses of species to the range of water level fluctuations seem to reflect their tolerance to disturbances and evidently to seasonal drought. Most Sphagnum species are absent or in poor condition in habitats with extremely fluctuating water table. Vascular plant species that experienced most extreme water level fluctuations (Carex nigra, Juncus filiformis) have earlier been regarded as disturbance indicators. In addition, the difference between the piezometric water level and simultaneously measured water table depth reached the highest values within the habitats of those species (i.e., within Polytrichum commune aro wetlands) showing the downward direction of water movement in sandy mineral soil.     

Elevated ozone reduces methane emissions from peatland mesocosms

Although the effects of elevated ozone on aboveground carbon (C) assimilation are well understood, its effects on soil C fluxes are less certain. Mesocosms taken from a lowland raised bog in northern England were exposed in open‐top chambers for 2 years to ambient air or ambient air plus ozone elevated for 8 h day^?1 by an average of 49 ppb in summer and 10 ppb in winter. The effects of elevated ozone on methane emission and ecosystem dark respiration were measured throughout this period, along with soil and plant variables. Methane emissions were significantly reduced, by about 25%, by elevated ozone during midsummer periods of both years, but no significant effect of ozone was found during the winter periods. Dark ecosystem respiration was not significantly affected by elevated ozone. There was no evidence that effects of elevated ozone on methane emissions were mediated through changes in aboveground plant biomass or soil water dissolved organic C concentrations. Our results imply that the increased northern hemisphere background ozone concentrations over the 21st century that are predicted by most models may reduce the rate of increase in methane emissions as the region warms.