Sphagnum production and decomposition in a restored cutover peatland

Natural peatlands represent a long-termsink of atmospheric carbon dioxide(CO₂), however, drained and extractedpeatlands can represent a source ofatmospheric CO₂. The restoration ofSphagnum mosses on abandoned milledpeatlands has the potential to sequesteratmospheric CO₂ thereby returning thepeatland to a peat accumulating system.Micrometeorological and chambermeasurements of net ecosystem CO₂exchange are proven methods forinvestigating production and decompositionprocesses in both natural, extracted, andrestored peatlands. However, this approachis relatively expensive because ofinfrastructure and human resources that notonly limits potential use for ecologicalmanagers but it limits the number of sitesthat can be monitored due to high spatialvariability. Here we present crank wire anddestructive sampling productionmeasurements, litter bag decompositionmeasurements and measurements of netecosystem CO₂ exchange made in arestored peatland and natural peatlandsites nearby. The objectives were to assessproduction and decomposition rates in thetwo systems as well as to compare thedifferent measurements techniques.Estimates of Sphagnum fuscumproduction at a restored peatland, usingthe different methods, followed the trend:crank wire < destructive sampling < gasexchange, with the two last methodsproviding comparable estimates. Productionestimates using crank wires in cutover peatsurfaces with a thin newly formed Sphagnum mat were shown unreliable due topeat subsidence. Results using thedestructive sampling method suggest thatSphagnum production varies betweenspecies (S. fuscum > S.capillifolium) according to their abilityto withstand harsh conditions on restoredpeat surfaces. Decomposition rate was alsosignificantly greater (p<0.05) for S. capillifolium than S. fuscum,resulting in an overall plant accumulationgreater for S. fuscum. Although therestored surfaces were fairly young,production rates estimated on cutoversurfaces that were fully covered with athin Sphagnum mat compared withproduction rates observed in natural sitesnearby.     

Organic matter accumulation following fires in a moorland soil chronosequence

Severe fires in 1957 and 1976 removed the vegetation and soil organic matter from the litter layers and organic horizons of soils at two adjacent moorland sites leaving exposed the uppermost mineral horizon of the soil. In the period since, plant recolonization and soil organic matter reaccumulation have occurred to give a chronosequence. Assuming no major changes in the carbon and nitrogen content of the unburned soil since 1957, the rates of accumulation of soil C and N were estimated to be 0.035 kg C m^–2 y^–1 and 0.001 kg N m^–2 y^–1 over the first 19 years, and 0.50 kg C m^–2 y^–1 and 0.023 kg N m^–2 y^–1 over the period from 19 to 38 years after burning. Solid-state ¹³C NMR (cross-polarization, magic angle spinning ¹³C nuclear magnetic resonance spectroscopy) showed that the ratio of alkyl- and methyl-C-to-O-alkyl-C increased with stage of decomposition and in the unburned soil with decreasing particle-size. For the organic matter that had reaccumulated in the 1957-burned soil, the alkyl-C-to-O-alkyl-C ratio of the > 2000 μm and 2000–250 μm particle-size fractions were greater than those of the corresponding size fractions from the unburned soil, indicating that the reaccumulated soil organic matter was subject to decomposition but limited fragmentation or comminution.     

Transplanting success of two alpine plant species in combination with mulching during restoration of a high-elevation peatland

Wetlands Ecology and Management - Many high-elevation wetlands have been degraded by activities related to the skiing industry. However, few studies exist on their restoration in this harsh...     

Methane dynamics of a restored cut‐away peatland

We measured a cut‐away peatland's CH₄ dynamics using the static chamber technique one year before and two years after restoration (rewetting). The CH₄ emissions were related to variation in vegetation and abiotic factors using multiple linear regression. A statistical model for CH₄ flux with cottongrass cover (Eriophorum vaginatum L.), soil temperature, water level, and effective temperature sum index as driving variables explained most (r² = 0.81) of the temporal and spatial variability in the fluxes. In addition to the direct increasing effect of raised water level on CH₄ emissions, rewetting also promoted an increase of cottongrass cover which consequently increased carbon flux (substrate availability) into the system. The seasonal CH₄ dynamics in tussocks followed seasonal CO₂ dynamics till mid August but in late autumn CH₄ emissions increased while CO₂ influxes decreased. The reconstructed seasonal CH₄ exchange was clearly higher following the rewetting, although it was still lower than emissions from pristine mires in the same area. However, our simulation for closed cottongrass vegetation showed that CH₄ emissions from restored peatlands may remain at a lower level for a longer period of time even after sites have become fully vegetated and colonized by mire plants.     

Ecosystem-scale flux of CO2 from a restored vacuum harvested peatland

At the ecosystem scale, the water and gasexchange processes are strongly coupled.Drainage and removal of a peatland'ssurface vegetation cover for peatharvesting alters its hydrology, and as adirect consequence the carbon budget.Previous studies have measuredpeatland-atmosphere carbon exchange usingthe chamber methodology. These studies haveindicated that the spatial and temporalvariability is large, suggesting the needfor continuous ecosystem-scalemeasurements. This paper presents ecosystemscale measurements of the atmosphericexchange of water and carbon dioxide(CO₂) from a restored vacuum-harvestedpeatland in eastern Québec, Canada,using the eddy correlation measurementapproach.Results indicate that the adoptedrestoration practices reduce the loss ofwater from the peat. Evapotranspirationfrom the restored site was 20 and 25% lessthan that from an adjacent abandonedcomparison site in 2000 and 2001respectively. However, CO₂ emissionsremain large during non-snow periods (478and 468 g C m^-2 in 2000 and 2001,respectively). The blockage of drainageditches and the existence of a mulch coverat the site keep the moisture and thermalconditions more or less constant.Consequently, the CO₂ flux, which ispredominantly soil respiration, is stronglycontrolled by peat temperaturefluctuations.     

Comparing survey methods for monitoring vegetation change through time in a restored peatland

Monitoring is an essential step to assess vegetation trajectories post-restoration and ultimately evaluate success. In this paper, we compare two monitoring methods, the line-point intercept (LPI) and the permanent plot (PP) methods, for evaluating plant recovery of a restored cut-over peatland (8.5 ha), following a “moss layer transfer technique”. We used the LPI method to estimate covers (from frequency measures) for each plant species using a systematic grid of approximately 5,700 points (every 3 m × 5 m). In parallel, 43 PP (3 m × 8 m) were established and used to evaluate plant covers. The post-restoration recovery of vegetation was assessed against a reference ecosystem encompassing the variation in species cover from natural undisturbed peatlands in the same region. For all plant groups considered, the LPI consistently showed higher cover estimates than the PP method. Discrepancy between the two methods was particularly evident for the Ericaceae group. A complementary sampling method, the line-intercept (LI), showed strong correlations with the visual estimations of Ericaceae covers (akin to PP), suggesting an overestimation from the LPI method. Most life form groups of the restored peatlands are developing a structure similar to the regional reference ecosystem 8 years post-restoration with the herb group being still most dissimilar. Indeed, when analyzing the temporal evolution of the different key peatland plant components, several are within the range of regional abundance values or moving positively towards range of cover abundance of the reference system such as Sphagnum cover, a key peat-accumulating plant group.     

Ecological restoration success: a policy analysis understanding

This article discusses how ecological restoration success can be understood and evaluated using a policy analysis lens. First, this article details a conceptual tool that helps to develop a more encompassing set of criteria to assess restoration activities that provide socioeconomic benefits. Second, by broadening the understanding of restoration success and how it can be evaluated, it allows a more critical view of evaluation itself and its uses as a policy tool. A table is presented that can help practitioners reveal preferences and clarify the aims and objectives of particular initiatives. The table also sensitizes practitioners to the complexity of the links between restoration rationales and evaluation criteria, which in turn may open up much needed discussion and dialogue between restoration participants about the underlying values an actor may wish to promote. It heightens awareness of the fact that evaluation methods need to recognize that restoration is driven by multiple rationales often in the same project, both process driven and output oriented, which in turn can change over time. Adding process and output criteria together may also raise issues of priority. Evaluation criteria thus need to be assigned in ways that reflect these multiplicities, while at the same time recognizing that some restoration values might be conflictual and that there may be winners and losers. Furthermore, judgement about “failure” of a project can change as new goals emerge in delivery and implementation. Ecological restoration evaluation should therefore be ongoing, contextual, and not a one‐off event.     

Peat CO2 production in a natural and cutover peatland: Implications for restoration

Although studies have shown that peatland drainage andharvesting alter local hydrology, microclimate, and peatcharacteristics, little is known about the effects of these changes onCO₂ production rates. This study examines the differentfactors affecting CO₂ production from natural and cutoverpeatlands. Laboratory peat incubations were performed under aerobic andanaerobic conditions to determine the influence of temperature, soilmoisture, and peat depth on CO₂ production rates from peatsamples taken from: (1) a natural peatland; (2) a 2-yearpost-cutover peatland and; (3) a 7-year post-cutover peatland.CO₂ production rates ranged from 0.21 to 4.87 µmolg^–1 d^–1 under anaerobic conditions,and from 0.37 to 15.69 µmol g^–1d^–1 in the aerobic trials. While no significantdifferences were found between the CO₂ production rates ofthe two cutover sites, the natural site consistently displayed higherproduction values. The natural site was also the only site to exhibitstrong depth dependent trends, thus indicating the importance of theupper peat layer with respect to substrate quality. Higher productionrates were found under aerobic than anaerobic conditions, with thegreatest response to oxygen observed at the natural site. Productionrates increased with both temperature and soil moisture, with maximumproduction rates found at 20 °C and 92% moisture content.Temperature responses were generally greater at the cutover sites, whilesoil moisture had greater effects on the natural site peat.Results of this work agree with previous studies that suggest that itis essential to begin restoration once a cutover peatland is abandoned.Re-wetting a cutover peatland (through restoration practices) isnecessary to prevent an increase in peat temperature and CO₂production since cutover peat has higher Q₁₀ values thannatural peat. A decrease in overall peatland oxidation should reduce thepersistent source of atmospheric CO₂ from cutover peatlandsand the irreversible changes in peat structure that impedeSphagnum re-establishment.     

Internal eutrophication of restored peatland stream: The role of bed sediments

The improvement of site hydrology is a major determinant of the success or failure of wetland restoration. Unfortunately, the influence of new hydrological conditions on wetland chemistry and nutrient cycling is often ignored or simply not monitored. This study assessed how changes in the composition of stream sediments that occurred after peatland stream restoration affected the pool and bioavailability of phosphorus (P) stored on the stream floor. The studied watercourses were located in the Narew River valley, NE Poland. They were restored in 2002 by excavating channels about 4-6 m wide and 1-1.5 m deep. Channels were cut through a peat layer to basal sands that underlay the organic deposits. Due to fallacious assumption about the high stability of peat stream banks, the banks were not modelled or protected by any technical measures to eliminate potential slump and erosion.Within a few years of the completion of the restoration project, peat bank failures led to the substantial deposition of organic material onto the floor of the newly created water-bodies. This resulted in an increase in the mean total phosphorus (TP) concentration in the sediment from 19 μmol g⁻¹ to more than 35 μmol g⁻¹ as well as an increase in both the concentration and pool of potentially mobile P fractions. A potential for the release of P was confirmed by the change in the concentration of P fractions that has been recorded over the summer period. Between June and October 2008 their content in the top 1-cm layer diminished from 134.1 mmol m⁻² to 100.6 mmol m⁻², implying an average net release of P of about 0.3 mmol m⁻² day⁻¹.This suggests that examined sediments primarily act as a highly dynamic transformer system, being the sink for particulate organic and mineral forms of P and serving as the net source of bioavailable (soluble reactive phosphorus) SRP.     

Evaluating the use of dominant microbial consumers (testate amoebae) as indicators of blanket peatland restoration

Peatlands represent globally-important ecosystems and carbon stores. However, large areas of peatland have been drained for agriculture, or peat has been harvested for use as fuel or in horticulture. Increasingly, these landscapes are being restored through ditch blocking and rewetting primarily to improve biodiversity and promote peat accumulation. To date we have little knowledge of how these interventions influence the microbial communities in peatlands. We compared the responses of dominant microbial consumers (testate amoebae) to drainage ditch restoration relative to unblocked ditches in a UK upland blanket peatland (Migneint, North Wales). Two techniques were used for restoration: (i) dammed ditches with re-profiling; and (ii) dammed ditches with pools of open water behind each dam. Testate communities in the inter-ditch areas changed markedly over time and between treatments illustrating the potential of this group of organisms as indicators of blanket peatland restoration status. However, the responses of testate amoebae to peat rewetting associated with restoration were partially obscured by inter-annual variability in weather conditions through the course of the experiment. Although there was considerable variability in the response of testate amoebae communities to peatland drain blocking, there were clearly more pronounced changes in samples from the dammed and reprofiled treatments including an increase in diversity, and the appearance of unambiguous wet-indicator species in relatively high abundances (including Amphitrema stenostoma, Archerella flavum, Arcella discoides type, Difflugia bacillifera and Difflugia bacillarium). This reflects a shift towards overall wetter conditions across the site and the creation of new habitats. However, water-table was not a significant control on testate amoebae in this case, suggesting a poor relationship between water table and surface moisture in this sloping blanket peatland. Our findings highlight the potential of testate amoebae as bioindicators of peatland restoration success; however, there is a need for caution as mechanisms driving change in the microbial communities may be more complex than first assumed. Several factors need to be taken into account when implementing biomonitoring studies in peatlands including: (i) the natural variability of the peatland ecosystem under changing weather conditions; (ii) any disturbance connected with the restoration procedures; and (iii) the timescales over which the ecosystem responds to the management intervention. Our results also suggest an indicator species approach based on population dynamics may be more appropriate for biomonitoring peatland restoration than examining changes at the community level.     

Detecting restoration impacts in inter-connected habitats: Spring invertebrate communities in a restored wetland

Habitat restoration that improves the ecological status of a target ecosystem may have undesired effects in adjoining ecosystems. We assessed how restoration of a mire influenced benthic macroinvertebrates in associated freshwater springs. We included springs affected by restoration and compared these to remote control springs. We collected pre-restoration samples in May 2001 and post-restoration samples in May 2003, 2005 and 2010. Following restoration, water table rose in the whole mire. Restoration also caused profound changes to groundwater quality but, for the most part, water quality returned close to pre-restoration conditions within two years. Reflecting these chemical and hydrological changes, restoration altered spring invertebrate communities, especially the relative abundances of species, but had only weak effect on species richness. The proportional abundance of spring-dependent macroinvertebrates decreased in the restoration area, whereas their proportion remained stable in the remote control sites. Macroinvertebrate community structure at the remote control sites remained almost unchanged throughout the study, whereas communities in the restoration-area springs showed profound changes after restoration, followed by a slow recovery toward the initial conditions. Our results suggest that restoration planning and monitoring should be extended to adjoining ecosystems, and not only species richness but more complete compositional analysis of communities and species abundances should be used to indicate restoration impacts.     

Methane dynamics of recolonized cutover minerotrophic peatland: Implications for restoration

In North America, mulching of vacuum-harvested sites combined with blocking of the drainage system is widely used for peatland restoration to accelerate Sphagnum establishment. However, peat extraction in fen peatlands or exposure of deeper minerotrophic peat layers results in soil chemistry that is less suitable for re-establishment of Sphagnum moss. In this situation, restoration of plant species characteristic of minerotrophic peatlands is desirable to return the site to a carbon accumulating system. In these cases, it may be worthwhile to maintain spontaneously revegetating species as part of restoration if they provide desirable ecosystem functions. We studied the role of six spontaneously recolonizing vegetation communities for methane (CH₄) emissions and pore water CH₄ concentration for two growing seasons (2008 and 2009) at an abandoned minerotrophic peatland in southeastern Quebec. We then compared the results with bare peat and adjacent natural fen vegetation. Communities dominated by Eriophorum vaginatum, Carex aquatilis and Typha latifolia had CH₄ flux an order of magnitude greater than other cutover vegetation types and natural sites. In contrast, Scirpus atrocinctus and Equisetum arvense had CH₄ emission rates lower than natural hollow vegetation. We found seasonal average water table and vegetation volume had significant correlation with CH₄ flux. Water table and soil temperature were significantly correlated with CH₄ flux at plots where the water table was near or above the surface. Pore water CH₄ concentration suggests that CH₄ is being produced at the cutover peatland and that low measured fluxes likely result from substantial oxidation of CH₄ in the unsaturated zone. Understanding ecosystem functions of spontaneously recolonizing species on cutover fens can be used to help make decisions about the inclusion of these communities for future restoration measures.     

Evaluating future success of whitebark pine ecosystem restoration under climate change using simulation modeling

Major declines of whitebark pine forests throughout western North America from the combined effects of mountain pine beetle (Dendroctonus ponderosae) outbreaks, fire exclusion policies, and the exotic disease white pine blister rust (WPBR) have spurred many restoration actions. However, projected future warming and drying may further exacerbate the species' decline and possibly compromise long‐term success of today's restoration activities. We evaluated successes of restoration treatments under future climate using a comprehensive landscape simulation experiment. The spatially explicit, ecological process model FireBGCv2 was used to simulate whitebark pine populations on two U.S. Northern Rocky Mountain landscapes over 95 years under two climate, three restoration, and two fire management scenarios. Major findings were that (1) whitebark pine can remain on some high mountain landscapes in a future climate albeit at lower basal areas (50% decrease), (2) restoration efforts, such as thinning and prescribed burning, are vital to ensure future whitebark pine forests, and (3) climate change impacts on whitebark pine vary by local setting. Whitebark pine restoration efforts will mostly be successful in the future but only if future populations are somewhat resistant to WPBR. Results were used to develop general guidelines that address climate change impacts for planning, designing, implementing, and evaluating fine‐scale restoration activities.     

Ecohydrological characterisation of a degenerated valley peatland in Northern Germany for use in restoration

Present environmental policy aims to restore wetlands for multifunctional purposes and requires quantitative information on the spatially interrelated biohydrochemical processes which allow wetlands to regulate water- and nutrient flow on different scales. For this purpose, this study presents an ecohydrological system analysis as a basis for a future management concept of the Eider valley peatland. This study combines field data with existing knowledge to set up different modelling techniques to study hydrological processes and nitrogen transformations. The Eider valley of northern Germany is a riverine freshwater wetland of 150 ha. Mire genesis was dominated first by river water inflow from the upstream catchment area, and in a later successional stage by groundwater inflow at the mire margins. Drainage, land use intensification and river regulation have resulted in severe degeneration of the peatland. Altering of the water flow patterns led to the mobilisation of nutrients and resulted in eutrophication of the sites. Abandonment of the mown or grazed sites led to the establishment of species poor Urtica dioica stands. The scenario calculations of the nitrogen budget of the peatland with a process oriented nitrogen model indicate that a water level increase of 30 cm is not sufficient to reduce peat loss due to oxidation. On the basis of the system analysis, restoration prospects for the Eider valley peatland are discussed where the historical subsurface flow pattern can be a long term restoration goal. Due to irreversible changes in peat hydraulic conductivities combined with subsidence, it is only possible to restore surface flow on top of the peat. Raising river water level will result in a shallow lake system. The limnic stage is a draw-back in the genesis of the valley, but necessary for the restoration of wetlands as self-evolving landscape entities.     

Contemporary carbon balance and late Holocene carbon accumulation in a northern peatland

Northern peatlands contain up to 25% of the world's soil carbon (C) and have an estimated annual exchange of CO₂‐C with the atmosphere of 0.1–0.5 Pg yr⁻¹ and of CH₄‐C of 10–25 Tg yr⁻¹. Despite this overall importance to the global C cycle, there have been few, if any, complete multiyear annual C balances for these ecosystems. We report a 6‐year balance computed from continuous net ecosystem CO₂ exchange (NEE), regular instantaneous measurements of methane (CH₄) emissions, and export of dissolved organic C (DOC) from a northern ombrotrophic bog. From these observations, we have constructed complete seasonal and annual C balances, examined their seasonal and interannual variability, and compared the mean 6‐year contemporary C exchange with the apparent C accumulation for the last 3000 years obtained from C density and age‐depth profiles from two peat cores. The 6‐year mean NEE‐C and CH₄‐C exchange, and net DOC loss are −40.2±40.5 (±1 SD), 3.7±0.5, and 14.9±3.1 g m⁻² yr⁻¹, giving a 6‐year mean balance of −21.5±39.0 g m⁻² yr⁻¹ (where positive exchange is a loss of C from the ecosystem). NEE had the largest magnitude and variability of the components of the C balance, but DOC and CH₄ had similar proportional variabilities and their inclusion is essential to resolve the C balance. There are large interseasonal and interannual ranges to the exchanges due to variations in climatic conditions. We estimate from the largest and smallest seasonal exchanges, quasi‐maximum limits of the annual C balance between 50 and −105 g m⁻² yr⁻¹. The net C accumulation rate obtained from the two peatland cores for the interval 400–3000 bp (samples from the anoxic layer only) were 21.9±2.8 and 14.0±37.6 g m⁻² yr⁻¹, which are not significantly different from the 6‐year mean contemporary exchange.     

Drivers of post-fire resprouting success in restored Banksia woodlands

Disturbances can alter persistence trajectories of restored ecosystems. Resprouting is a common response of plants to disturbances such as fire or herbivory. Therefore, understanding a plant's resprouting response can inform successful restoration. We investigated patterns and drivers of resprouting following fire in fire-prone Banksia woodlands restored after sand mining in the Mediterranean-climate region of Western Australia. We applied experimental fire to samples of nine species with different resprouting types (rhizome, root crown, root sucker and lignotuber) across a 4- to 27-year-old restoration chronosequence. We investigated the influence of pre-fire plant size, restoration age and soil conditions on resprouting success, defined by: (i) the probability of resprouting (measured ~5 months after fire), (ii) the probability of surviving the first summer and, (iii) vigour (both measured ~12 months post-fire). We found that the probability of initial resprouting was high across most species, but summer survival was lower but comparable to that in other post-mining restored ecosystems following fire. Generally, pre-fire plant size did not influence probability of resprouting, while size and soil conditions were important for two species survival. Pre-fire plant size was a significant predictor of vigour for all species with soil conditions influencing four species. Restoration age significantly influenced survival of three species. However, as our models explained low amounts of variation in probabilities of resprouting and survival (R² = <0.11), other factors influencing resprouting success remain unidentified. Resprouting response to fire disturbance in restored Banksia woodlands are species and resprouter type specific, with plant size and soil conditions potentially more informative for understanding responses to disturbances than restoration age alone.     

Organic matter accumulation in western boreal saline wetlands: A comparison of undisturbed and oil sands wetlands

Reconstructing landscapes after open pit mining of the Canadian oil sands presents enormous challenges. Freshwater peatlands dominate the pre-disturbance landscape; however, elevated salinity in the post-disturbance landscape will exclude the use of many freshwater vegetation species for reclamation. Successful reclamation will require plants to grow and accumulate peat despite elevated salinity. We evaluated the potential of salt-tolerant plants to accumulate peat by integrating plant production and decomposition rates in natural and oil sands wetlands across a salinity gradient. These wetlands were dominated by marsh-like vegetation with relatively rapid decomposition, especially of the belowground plant material. Aboveground production was high enough to compensate for rapid decomposition, resulting in mean annual organic matter accumulation of 307 g m^?2. Thus, both natural wetlands (which despite the elevated salinity had peat deposits >35 cm) and the oil sands wetlands accumulated organic matter during the study. There is potential for peat to accumulate in future oil sands wetlands, although long-term accumulation rates may be slower than in undisturbed freshwater fens and bogs. A reliable water supply and a host of other factors will be required for wetlands to accumulate organic matter, and eventually peat, in the post-mining landscape.     

Organic matter and nitrogen accumulation and nitrogen fixation during early ecosystem development in Hawaii

We used a chronosequence comprised of 10 y, 52 y and 142 yold `a'a lava flows on Mauna Loa, Hawaii, to determine theaccumulation of organic matter and nitrogen and rates of nitrogenfixation through time. The mass of organic matter (live and deadbiomass and soil organic matter) on the 1984, 1942 and 1852 lavaflows was 0.6, 2.2 and 7.6 kg m^{– 2}, respectively, while total N was 4.8, 10.9 and 85.7 g m^{– 2}.We estimated the total rates of nitrogen fixation for thethree different aged ecosystems using an acetylene reduction assaycalibrated with ¹⁵N incubations. While mean rates of total N fixation remained largely constant across the three sites – between2.0 and 3.1 kg ha^{– 1} y^{– 1} – the most important sources of N fixation changed. On the 10 y flow, the most important fixer was the pioneering cyanolichen, Stereocaulon vulcani. After 52 years ofecosystem development, the most important N fixer was a cyanoalga,while after 142 years, the predominant N fixers were heterotrophicbacteria associated with leaf litter, twigs and detritus. The totalamount of N accumulated after 52 years of ecosystem development wasequivalent to cumulative inputs through biological N fixation. After 142 years, however, cumulative inputs from N fixation couldonly account for between 27–59% of the total nitrogen accrued.We used fertilizer additions of all essential nutrients otherthan N to test whether the availability of lithophilic nutrientsregulated rates of N fixation in early ecosystem development. Ratesof nitrogen fixation by the lichen, S. vulcani, approximately doubled when fertilized on the 1984 and 1942 flows. Rates of N-fixation by heterotrophic nitrogen fixing bacteria on leaf litter ofMetrosideros polymorpha also increased significantly when fertilized with lithophilic nutrients. These findings suggest that weathering rates of lava in part regulate rates of nitrogen fixation in these young ecosystems.     

Evaluating the use of spawning success to estimate reproductive success in a Caribbean reef fish

Observations on egg batch production by known female Stegastes partitus and the fates of those egg batches within the nests of known males revealed that spawning success was not a reliable predictor of hatching success and, hence, reproductive success because of high egg batch mortality. Moreover, while numbers of eggs per batch increased with increasing female length, both inter- and intra-individual variation in batch size was considerable, demonstrating that spawning events cannot be considered equivalent. These two findings indicate that spawning success cannot be assumed to provide a direct quantitative substitute for a measure of reproductive success in this benthic spawning reef fish.