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The impacts of species invasions can subside over time as ecosystems 'adapt' and invaders decline or increase over time as additional species invade. The character and timescales of invasion impacts provide important insights into ecosystem dynamics and management. Yet long-term studies of invasion impacts remain rare and often confound invasive species impacts with coincident environmental change. One way to address this challenge is to ask: what ecological changes over time since invasion are recapitulated in ecosystems that span a range of conditions, are located in different regions, and were invaded in different decades? We synthesize many-decade time series across seven ecosystems to resolve shared changes in seven key ecosystem features following invasion by zebra mussels and subsequent invasion by quagga mussels. These two congeners are among the most widespread invasive species that re-engineer and increasingly co-invade freshwater ecosystems. Seven polymictic shallow lakes with long-term data sets reveal remarkably similar trends, with the strongest ecosystem impacts occurring within 5–10 years of zebra mussel invasion. Surprisingly, plankton communities then exhibited a partial, significant recovery. This recovery was absent, and impacts of initial invasion amplified, in four lakes where quagga mussels outcompeted zebra mussels and more completely depleted phytoplankton. Thus, we show that the ecosystem impacts of invasive species can subside over time but amplify with serial introductions of competing, even closely similar, taxa. [ABSTRACT FROM AUTHOR]

Carrion production is one of the most crucial yet neglected and understudied processes in food webs and ecosystems. In this study, we performed a large-scale estimation of the maximum potential production and spatial distribution of ungulate carrion biomass from five major sources in peninsular Spain, both anthropogenic (livestock, big game hunting, roadkills) and natural (predation, natural mortality). Using standardized ungulate carrion biomass (kg/year/100km2) estimates, we evaluated the relationship between ungulate carrion production and two ecosystem-level factors: global human modification (GHM) and primary productivity (NDVI). We found that anthropogenic carrion sources supplied about 60 times more ungulate carrion biomass than natural sources (mean = 90,172 vs. 1533 kg/year/100km2, respectively). Within anthropogenic carrion sources, livestock was by far the major carrion provider (91.1% of the annual production), followed by big game hunting (7.86%) and roadkills (0.05%). Within natural carrion sources, predation of ungulates provided more carrion (0.81%) than natural mortality (0.13%). Likewise, we found that the spatial distribution of carrion differed among carrion sources, with anthropogenic carrion being more aggregated in space than natural carrion. Our models showed that GHM was positively related to carrion production from livestock and roadkills, and that wild ungulate carrion supplied by natural sources and big game hunting was more frequently generated in more productive areas (higher NDVI). These findings indicate a disconnection between the main ungulate carrion source (livestock) and primary productivity. Ongoing socio-economic changes in developed countries (for example increase of intensive livestock husbandry and rewilding processes) could lead to additional alteration of carrion production processes, with potential negative impacts at the community and ecosystem levels. Overall, we highlight that carrion biomass quantification should be considered a crucial tool in evaluating ecosystem health and delineating efficient ecosystem management guidelines in the Anthropocene. [ABSTRACT FROM AUTHOR]

Mapping ecosystem functions and services has gained considerable importance, particularly for its applications in ecosystem management and conservation. While practices for terrestrial ecosystems are well established and mainly rely on land cover, marine ecosystems face challenges that hinder our ability to quantify and understand the distribution of ecosystem services. In particular, soft-sediment marine habitats are complex and heterogeneous but data on the distribution of communities and habitats in these systems in scarce. Mapping relies primarily on the sampling of abiotic variables and physical attributes, easier to obtain at broad scale, and therefore underestimates the role of the underlying biodiversity. In our study, we develop a mapping procedure that can handle situations where only a limited amount of data can be collected. We combined field measurements of species abundance and benthic fluxes to create models and then used data from a drone survey of the distribution of selected sediment microtopographic features linked to specific species to extrapolate these measures. This method quantifies ecosystem functions at broad spatial scales and with high resolution leading to the creation of ecologically nuanced maps that target the underlying mechanisms of ecosystem functioning, necessary to close the mismatch between physical and biological methods and accurately assess ecosystem services. [ABSTRACT FROM AUTHOR]

Shifts between the alternative stable states have been a popular topic of ecological studies for over 50 years. However, identifying the mechanisms that drive these regime shifts remains a challenging task in the field of applied ecology and ecosystem management. Herein, we applied a Bayesian latent variable regression (BLR) to the dataset obtained for a shallow lake experiencing a shift from the dominance of submerged plants to the dominance of floating plants to classify the observed lake states, determine total phosphorus (TP) thresholds, and establish a steady-state relationship between the phosphorus content and the size of an aphotic zone. In addition, a structural equation model was utilized to elucidate the mechanisms driving this shift and their effects on the trophic web of the ecosystem. The BLR model exhibited high state classification rates (median/mean accuracy > 97.5%) and accurately determined the steady-state relationships between the TP thresholds and the aphotic zone size. We also found that the top-down control via piscivorous fish was stronger in the state dominated by submerged macrophytes, while the bottom-up control via TP was stronger in the state dominated by floating macrophytes. Additionally, the dominance of floating macrophytes was related to the low degree of biodiversity and simplification of the trophic web. Our results show that top predators can be used to control nutrient levels and ensure the dominance of submerged macrophytes. It also provides a new perspective on the theory of alternative states and potential tools for the management of ecosystems experiencing regime shifts. [ABSTRACT FROM AUTHOR]

Forested peatlands are widespread in the boreal landscape, but their role as carbon (C) pools remains poorly documented. In this study, we investigated the long-term C sequestration function of boreal forested bogs in relation to fires in eastern Canada. Results show that the forested peatlands comprise substantial peat C mass reaching values similar to open peatlands. At the six studied peatland sites, the amount of C stored in peat (62–172 kg C m−2) exceeds substantially the aboveground tree biomass C (1.5–5.3 kg C m−2). The C locked up in live conifers on the peatlands corresponds only to a small fraction of the C stored in peat (1–6%). In comparison, the shallow organic layer (≤ 30 cm) in the adjacent paludifying stands store 10.8 kg C m−2 on average, which is about twice as much C as the live conifers. Long-term apparent C accumulation rates are relatively low in the studied forested bogs (mean: 15.9 g C m−2 y−1), suggesting that these ecosystems have lower C sequestration potential than non-forested bogs over millennia. The charcoal data suggest that past local fires reduced C sequestration rates, but these peatlands burn much less frequently than upland forests and are thus more efficient long-term C stores. This study highlights the importance of boreal forested peatlands as C reservoirs and helps understanding how fires, logging and climate change can affect their C sequestration function. These findings have important implications for ecosystem management that aims at maximizing C sequestration at the landscape level to mitigate climate change. [ABSTRACT FROM AUTHOR]

Nutrient reduction in impacted lowland freshwater systems is ecologically and culturally important. Gaining a greater insight into how lakes respond to lowering nutrient loads and how climate-driven physical limnology affects present and future cycling of available nutrients is important for ecosystem resource management. This study examines the nutrient decline in a hypereutrophic freshwater lake (Rostherne Mere, Cheshire, UK) 25 years after sewage effluent diversion, a uniquely long-term analysis of a recovering nutrient-rich deep lake. Using nutrient, phytoplankton, climate and catchment hydrological monitoring, the contemporary lake system is compared to previous studies from 1990 to 2002. Nutrient change since point source load diversion showed annual average and maximum phosphorus (P) concentrations decreased significantly for the first 10 years (1992: ~ 600 µg P L−1; 2002: ~ 200 µg P L−1), but have since stabilised due to a substantial legacy sediment P internal load. Dissolved inorganic nitrogen (DIN) concentrations have not substantially changed since diversion, resulting in the alteration of the DIN/SRP ratio from a system characterised by N limitation (N:P ~ 5), to one predominantly P limited (N:P > 20). Nutrient changes over this time are shown to drive ecological change, especially in the cyanobacterial and algal communities. Furthermore, very high-resolution monitoring of lake inflow and outflow (every 5 min during 2016) shows that water residence time at this lake is significantly shorter than previously estimated (~ 0.8 years compared to previous estimates of ~ 1.6–2.4 years). Together with long-term data demonstrating that the stratification period at Rostherne Mere has increased by 40 days over the last ~ 50 years (due to later autumnal mixing), we show that a rapid rate of epilimnetic flushing together with a long stratification period substantially reduces the available epilimnetic P during the summer cyanobacterial bloom. This is of growing importance for many such lakes, given widespread climate-driven lengthening of stratification and a national trend of decreasing summer rainfall (decreasing seasonal flushing) but more intense summer storm events (resulting in short-term flushing events). [ABSTRACT FROM AUTHOR]

Foundation species often interact with each other and co-create habitat upon which other species depend. Whether the presence of these facilitated species feeds back to mediate the growth and resilience of the foundation species themselves, and influence the strength of their interactions, remains poorly understood. In a 16-month field experiment in a southeastern US salt marsh, we tested how the overlapping presence of two foundation species, cordgrass (Spartina alterniflora) and ribbed mussels (Geukensia demissa), influences the abundance of facilitated species, specifically burrowing crabs (mainly Uca pugnax), and how crabs, in turn, affect each foundation species and their mutualistic interaction. Mussel aggregations enhanced crab abundance 3.9-fold, which in turn reduced both mussel and cordgrass growth and stifled cordgrass recovery after a simulated disturbance. Porewater and plant tissue analyses suggest crabs reduced cordgrass growth by reducing nitrogen availability, damaging roots, and potentially interfering with mussel deposition of nutrient-rich pseudofeces. A five-site field survey along 700 km southeastern US coastline revealed that cordgrass biomass and crab abundance are consistently higher in mussel aggregations. Furthermore, cordgrass biomass correlated negatively with crab abundance, supporting our experimental findings and the hypothesis that facilitated biota can negatively impact the foundation species upon which they depend. We anticipate that such negative, but non-lethal, feedbacks between foundation species and the biota they facilitate may be a common but overlooked phenomenon controlling foundation species growth and interactions in a wide range of ecosystems. [ABSTRACT FROM AUTHOR]

Dryland (semiarid and arid) ecosystems are responsible for most of the interannual variation in atmospheric CO2 concentrations and contain a considerable fraction of the globe's soil carbon (C) stock. Despite their important contribution to the global land C sink, we have a poor mechanistic understanding of the processes that drive C cycling patterns in drylands. In this study in eastern Utah, we examined the natural variation of soil C pools and fluxes along semiorthogonal gradients of climate and soil texture in order to determine the pertinent environmental controls on soil C cycling dynamics. Our study revealed a high degree of collinearity among C stocks and fluxes, which were related to climate, vegetation, and soil clay content. Soil C pools were positively correlated with both soil clay content and precipitation, which in turn was linked to aboveground plant biomass. By contrast, enzyme activities were negatively associated with temperature. We observed a strong decoupling of C pools and fluxes (for example, total C, DOC, microbial biomass C, and respiration) from the enzyme activities involved in organic matter decomposition. Overall, our findings indicate that the within- and between-site variation of soil C pools across diverse dryland ecosystems was strongly linked to both climate and edaphic characteristics, but the high degree of local variability within sites could challenge interpretations of environmental controls at broader scales. [ABSTRACT FROM AUTHOR]

Forest ecosystems worldwide are subjected to human-induced stressors, including eutrophication and acidification, and to natural disturbances (for example, insect infestation, windstorms, fires). The occurrence of the later is expected to increase due to the ongoing climate change. These multi-stressor forcings modify ecosystem biogeochemistry, including the retention of limiting nutrients, with implications for terrestrial and aquatic biodiversity. Here we present whole ecosystem nutrient (N, Ca, Mg, K) mass balances in the forested catchment of Plešné Lake, CZ, which has undergone transient changes linked to the recovery from anthropogenic acidification and to the forest disturbances caused by severe infestations by the bark beetle (Ips typographus). Measured fluxes and storage of nutrients in the lake-catchment ecosystem were used to constrain the process-oriented biogeochemical model MAGIC (Model of Acidification of Groundwater In Catchments). Simulated lake water chemistry and changes in soil nutrient pools fitted observed data and revealed that (1) the ecosystem N retention declined, thus nitrate leaching increased for 10 years following the bark beetle disturbance, with transient adverse effects on the acid–base status of lake water, (2) the kinetics of nutrient mineralisation from decaying biomass coupled with nutrient immobilisation in regrowing vegetation constrained the magnitude and duration of ecosystem losses of N, Ca and Mg, (3) the excess of mineralised base cations from decomposing biomass replenished the soil cation exchange matrix, which led to increased soil base saturation, and (4) the improvement of the catchment soil acid–base status led to an increase of lake water pH and acid neutralising capacity. Forested ecosystems underlain by nutrient-poor soils and bedrock are prone to human-induced damages caused by acidification and eutrophication, and any natural disturbance may further lead to nutrient imbalances. We demonstrated that in this natural forest ecosystem protected from human intervention, disturbances together with natural post-disturbance vegetation recovery have temporally positive effects on the nutrient stores in the soil. [ABSTRACT FROM AUTHOR]

The sensitivity of plant production to precipitation underlies the functioning of ecosystems. Studies that relate long-term mean annual precipitation and production across multiple sites (spatial relationship) or examine interannual linkages within a site (temporal relationship) can reveal biophysical controls over ecosystem function but have limited ability to infer responses to extreme changes in precipitation that may become more common under climate change. To overcome limitations of using a single approach, we integrated satellite- and ground-based estimates of production with a standardized, multi-site precipitation manipulation experiment across a grassland elevation gradient in the southwestern USA. The responsiveness of production to changes in precipitation followed the order: temporal (0.06–0.13 g m−2 mm−1) < spatial (0.21 g m−2 mm−1) < experimental relationship (0.25–0.42 g m−2 mm−1), suggesting that spatial and temporal relationships determined with satellite- and ground-based estimates cannot be extrapolated to determine the effect of extreme events. A strong production response to differences in mean annual precipitation across sites reinforces a regional control of water availability. Interannual sensitivity to precipitation was strongest at the low elevation grasslands, and the high elevation mixed conifer meadow had a large reduction in production in a drought year. Extreme experimental drought strongly reduced production in low elevation grasslands, but water addition had mixed effects. High elevation meadows were insensitive to both extreme drought and water addition. Our results highlight the importance of accounting for extreme climate regimes and site-level factors when scaling climate change effects up to regional and global scales. [ABSTRACT FROM AUTHOR]

Termites are ecosystem engineers in tropical systems, constructing visible biogenic structures (mounds) that influence soil characteristics, decomposition, nutrient cycling, vegetative growth, and biodiversity. Subterranean termites (Reticulitermes spp.) likely influence nutrient cycling within their endemic range in the temperate Holarctic through the translocation of elements from wood to soil by lining their below-ground biogenic structures with frass (feces). We designed a study to 'follow the frass' by comparing concentrations of 18 elements (Al, B, Ba, C, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, N, Na, P, Si, Sr, and Zn) in substrates—food before and after digestion (wood and frass), as well as soil with and without direct termite manipulation (shelter tubes and soil core samples)—associated with 18 subterranean termite colonies. Fourteen elements were more concentrated in frass than wood, and only Cr and Fe were lower in frass. The shelter tube-to-soil contrasts indicate that termites decrease levels of Al, Ba, Co, and Cr while increasing C and Ca in soil. Therefore, Reticulitermes likely modulate element flows by returning organic C and base cations to weathered, acidic Ultisols of southeastern US forests. Research on the ecological role of subterranean termites outside of the built environment is showing the scale of impact these cryptic superorganism ecosystem engineers can have on temperate forest functions. [ABSTRACT FROM AUTHOR]

In terrestrial ecosystem studies, water drainage and nutrient leaching in the soil profile are estimated with hydrological models. Comparing modeled results to empirical data or comparing data from different models is, however, difficult because the uncertainty of input–output budget predictions is often unknown. In this study, we developed a procedure combining a Generalized Likelihood Uncertainty Estimation and a Monte-Carlo modeling approach to estimate uncertainty in model parameter estimates and model outputs water drainage and nutrient leaching fluxes for the WatFor water balance model. This procedure was then applied to compare different model optimization strategies (daily soil moisture measurements, monthly measurements of chloride concentrations in soil solution, and the elution of a concentrated chloride) at the same experimental site in a 90-year-old European beech (Fagus sylvatica L.) forest in Brittany (France). We show that the monitoring data of natural variations of chloride concentrations in soil solution were the most efficient dataset to calibrate the WatFor model compared to the soil moisture and chloride tracing experimental data. We also show that water tracing experimental data are the most efficient data to estimate the preferential flow generation model parameters. The optimization strategy had little influence on the predicted water drainage flux and nutrient leaching flux at the root zone boundary on a yearly time scale but influenced water and nutrient fluxes in the topsoil layers. [ABSTRACT FROM AUTHOR]

Ecosystems are increasingly disturbed by natural disturbances and human stressors. Understanding how a disturbance can propagate through an entire ecosystem and how induced changes can last after apparent recovery is key to guide management and ecosystem restoration strategies. Monitoring programs and impact assessment studies rely mostly on indicators based only on species relative abundance and biomass, potentially misinforming management efforts. Impacts on ecosystem structure and functioning, and subsequent delivery of ecosystem services, are too often overlooked. Here we use an ecosystem network approach to assess the recovery pathway and potential recovery debts of a coral reef ecosystem, following a pulse disturbance. We show that although species abundance and biomass indicators recovered in a decade after the perturbation, the ecosystem as a whole presented a recovery debt. The ecosystem structure lost complexity (became "food chain like") and lost about 29% of its overall cycling efficiency and 9% of its transfer efficiency. Although the ecosystem trophic network in the fore reef may have maintained its general functioning, the ecosystem network in the lagoon, not directly exposed to the disturbance, presented a stronger recovery debt. Our results give new insights on how ecosystem network approaches can help identify ecosystem impacts and recovery pathways. [ABSTRACT FROM AUTHOR]

Nitrate pollution is a global issue threatening the health and function of many lowland freshwater ecosystems. Quantifying nitrate loads and instream attenuation associated with land use is a critical requirement for improving freshwater management. One often overlooked nitrate source in catchments is invasive N-fixing trees such as Ulex europaeus (European gorse). This study compared nitrate concentrations in conjunction with stable isotope analyses (nitrate δ15N and δ18O) to investigate the effects of catchment gorse cover on stream nitrate export relative to three other land uses. These were regenerating native forest, low-intensity (dry-stock) and high-intensity (dairying) agriculture. We tested two hypotheses: (1) gorse is a regionally significant nitrate source; (2) instream nitrate attenuation is land-use dependent. The study was conducted in 24 reaches across six small, mixed land-use coastal catchments located on Banks Peninsula, New Zealand. Our results demonstrated that gorse-dominated stream reaches had significantly higher nitrate concentrations than all other land uses. Within the gorse-dominated reaches, nitrate concentration was significantly correlated with upstream catchment gorse cover. Furthermore, nitrate oxygen and nitrogen stable isotope compositions demonstrated that elevated nitrate concentrations in gorse streams were associated with decomposition of dead gorse foliage. The isotope data revealed sub-catchment-scale land-use-specific patterns of nitrate attenuation within streams. All three anthropogenic land uses (gorse, dry stock and dairy) showed distinctly different N-cycling from native-forested reaches where nitrate was efficiently cycled with evidence for highly localised nitrification. Stable isotope data demonstrated that overall nitrate attenuation became less efficient with higher nitrate loads. Our research demonstrates the significant impact N-fixing plants have on nitrate concentrations and instream attenuation. Quantifying the effects of N-fixing plants on water quality is an important step in achieving globally significant goals of sustaining ecosystem health and (sub)catchment-scale nutrient management. [ABSTRACT FROM AUTHOR]

Understanding drivers of ecosystem structure and function is a pervasive goal in academic and applied research. We used 24 synthetic ecosystem-level indices derived from trophic models, and independently derived data for Net Primary Productivity, to investigate drivers of ecosystem structure and function for 43 marine ecosystems distributed in all oceans of the world and including coastal, estuaries, mid-ocean islands, open-ocean, coral reef, continental shelf, and upwelling ecosystems. Of these indices, ecosystem Biomass, Primary Production, Respiration, the ratio of Biomass to Total System Throughput (sum of total energy flow into and out of an ecosystem as well as between ecosystem components), the ratio of Production to Biomass, Residence Time (mean time that a unit of energy remains in the ecosystem), Average Trophic Level, and Relative Ascendency (index of organization and complexity of a food web) displayed relationships with measures of Net Primary Productivity (NPP). Across all ecosystems, relationships were stronger with seasonal and interannual variability of NPP as compared to mean NPP. Both measures of temporal variability were combined into multivariate predictive relationships for each ecosystem index, with r2 values ranging from 0.14 to 0.49 and Akaike's information criteria values from − 8.44 to 3.26. Our results indicate that despite large geographic and environmental differences, temporal variability of NPP is strongly linked to the structure and function of marine ecosystems. [ABSTRACT FROM AUTHOR]

The integration of lakes into watershed-scale energy budgets remains a major goal of aquatic ecosystem ecology. However, this enterprise has focused almost exclusively on temperate and boreal systems and on zooplankton as representatives of system-wide energy flow. We investigated the proportion of consumer biomass derived from terrestrial sources, allochthony, in three classes of high-elevation lakes—alpine, large and small montane—of varying geometry and watershed ecosystem development, and across five taxa, including macrobenthic invertebrates and fish. We used stable isotopes of carbon (13C:12C), nitrogen (15N:14N), and hydrogen (2H:1H) to fit a modular Bayesian mixing model, which estimated proportional assimilation of phytoplankton, algal periphyton, and terrestrial organic matter by each consumer. The stable isotope analysis was supplemented with a comparison of fatty acid profiles between consumers and producers, and with a Daphnia magna rearing study involving aquatic and terrestrial nutrient sources. The most probable estimate of allochthony across consumer taxa was 41% in small montane lakes (< 0.1 ha) with high terrestrial C loading. For large montane (3-11 ha) and alpine lakes (0.8-3 ha), with substantially less terrestrial influence, allochthony was just 4 and 3%, respectively. Allochthony was also lower on average for benthic grazers than for pelagic consumers. Our results corroborate previous findings that lake size, depth, and light penetration are dominant physical controls on allochthony, but add that it sharply declines at high elevation due to changes in terrestrial primary production near or above tree line. [ABSTRACT FROM AUTHOR]

Burial of aboveground plant litter by animals reduces the amount available for surface transport and places it into a different environment, affecting decomposition rates and fluxes of organic matter to adjacent ecosystems. Here we show that in a Southwestern Atlantic salt marsh the burrowing crab Neohelice granulata buries aboveground plant litter at rates (0.5-8 g m−2 day−1) comparable to those of litter production (3 g m−2 day−1). Buried litter has a low probability (0.6%) of returning to the marsh surface. The formation of burrow excavation mounds on the marsh surface is responsible for most litter burial, whereas litter trapped in burrows was an order of magnitude lower than rates of burial under excavation mounds. Crab exclusion markedly increased surface litter accumulation (3.5-fold in just 21 days). Tides with the potential to transport significant amounts of surface litter are infrequent; hence, most litter is buried before it can be transported elsewhere or decomposes on the surface. Crab litter burial can account for the observed low levels of surface litter accumulation in this ecosystem and likely drives organic matter transformation and export. The impacts of ecosystem engineering by this crab species are therefore substantial and comparable in magnitude to the large effects found for tropical crabs and other litter-burying organisms, such as anecic earthworms. [ABSTRACT FROM AUTHOR]

Decades of research have revealed the crucial roles of cross-system energy flows (spatial subsidies) in mediating trophic interactions in recipient systems. Food web theory predicts that the responses of subsidized consumers are a key to understanding the net impacts of spatial subsidies on in situ prey/resources of recipient systems. However, less is known about the factors triggering the cascading biotic interactions across coupled ecosystems. Here, we quantify how riverine productivity (donor system) mediates terrestrial food web interactions through spatial subsidies to simplified gravel bar communities. Our comparative study in Japan indicated that higher algal biomass in aquatic systems led to increased supplies of emerging aquatic insects, which were associated with greater densities of terrestrial consumers (Carabid beetles) and enhanced consumption rates of supplemental in situ prey on gravel bars. Our results highlight the potential of donor productivity to drive cascading biotic interactions across coupled ecosystems. Because cross-system energy flows should originate, at least in part, from primary producers of donor systems, our fundamental finding may form the basis of future studies exploring the driving factors of cross-system trophic interactions. [ABSTRACT FROM AUTHOR]

Subsidies of detritus from donor habitats are important energy sources for many ecosystems, but understanding their role in structuring recipient food webs requires comparative experimental studies along the full spectrum of detrital fluxes. Here we report results from an experimental addition of maize (Zea mays L.) litter to a detritus-poor cave stream ecosystem, which we then compare with analogous, past experiments using detritus-rich surface stream ecosystems that similarly have detritus-based food webs and extremely low in situ primary production. Bulk-tissue and compound-specific stable isotope analyses showed that maize litter carbon (C) was rapidly assimilated by microbes and transferred via successive trophic levels to the top of the cave stream food web (omnivorous crayfishes and predatory salamanders). All trophic levels increased in abundance and biomass, but only facultative cave taxa, that is those also found in surface streams, contributed to this numerical response. The lack of response by obligate cave species presumably occurred because evolutionary trade-offs associated with adaptations to low-C environments constrained their population-level responses during the one-year period of the litter addition. Comparison of the responses of the cave community with the analogous litter manipulation experiments in surface streams showed strong convergence in the functional relationship between invertebrate and detritus biomass (R2 = 0.72, P < 0.0001). Our results suggest that these seemingly disparate stream food webs lie along a single, common gradient of detritus supply, occupied at its extreme minimum by communities of obligate cave taxa adapted to low-energy environments. [ABSTRACT FROM AUTHOR]

A range of indicators have been proposed for identifying the elevated risk of critical transitions in ecosystems. Most indicators are based on the idea that critical slowing down can be inferred from changes in statistical properties of natural fluctuations and spatial patterns. However, identifying these signals in nature has remained challenging. An alternative approach is to infer changes in resilience from differences in standardized experimental perturbations. However, system-wide experimental perturbations are rarely feasible. Here we evaluate the potential to infer the risk of large-scale systemic transitions from local experimental or natural perturbations. We use models of spatially explicit landscapes to illustrate how recovery rates upon small-scale perturbations decrease as an ecosystem approaches a tipping point for a large-scale collapse. We show that the recovery trajectory depends on: (1) the resilience of the ecosystem at large scale, (2) the dispersal rate of organisms, and (3) the scale of the perturbation. In addition, we show that recovery of natural disturbances in a heterogeneous environment can potentially function as an indicator of resilience of a large-scale ecosystem. Our analyses reveal fundamental differences between large-scale weak and local-scale strong perturbations, leading to an overview of opportunities and limitations of the use of local disturbance-recovery experiments. [ABSTRACT FROM AUTHOR]

The extent to which ecosystems are regulated by top-down relative to bottom-up control has been a dominant paradigm in ecology for many decades. For lakes, it has been shown that predation by fish is an important determinant of variation in zooplankton and phytoplankton community characteristics. Effects of fish are expected to not only be a function of total fish biomass, but also of functional composition of the fish community. Previous research on the importance of trophic cascades in lakes has largely focused on the role of zooplanktivorous and piscivorous fish. We conducted a large-scale multiple-lake fish community manipulation experiment to test for the effect of differences in fish functional community composition on the trophic structure of lakes. We examine the effect of top-down and bottom-up factors on phytoplankton and zooplankton biomass as well as on their community composition. We put our data in a broader perspective by comparing our results to data of a survey that also included ponds with low fish densities as well as ponds with very high densities of fish. Our results indicate that the overall food web structure under relative high fish densities is primarily structured by bottom-up factors, whereas community characteristics seem to be primarily regulated by top-down factors. Our results suggest a subtle interplay between bottom-up and top-down factors, in which bottom-up factors dominate in determining quantities while top-down effects are important in determining identities of the communities. [ABSTRACT FROM AUTHOR]

Determining the fate of deposited nitrogen (N) in natural ecosystems remains a challenge. Heterogeneity of vegetation types and resulting plant-soil feedbacks interact with topo-hydrologic gradients to mediate spatial patterns of N availability and loss, yet net effects of variation in these two factors together across complex terrain remain unclear. Here we measured a suite of N-cycle pools and fluxes in sites that differed factorially in vegetation type (mixed forest vs. herbaceous) and topographic position (upslope vs. downslope) in a protected montane watershed near Salt Lake City, UT. Vegetation type was associated with large variation in N availability-herbaceous sites had larger NO pools, higher NO :NH ratios, higher nitrification potentials, lower soil C:N values, enriched δN values, and lower microbial biomass compared to forests, especially those upslope. Downslope sites tended to exhibit higher N availability and indicators of N-cycle openness, but patterns were moderated by vegetation type. In downslope forest, soil NO depth profiles and higher foliar N content suggested trees were accessing deep soil N and transferring it to the surface via litterfall, while more deep soil NO but no change in surface or foliar N suggested herbaceous cover was not N limited or deeper N pools were not accessible. Soil NO leaching from below the rooting zone closely tracked N availability, revealing a link between N status and hydrologic loss as well as an important role for roots in N retention. NO isotopes did not reveal a similar link for gaseous losses (that is, denitrification), instead reflecting nitrification and/or transport dynamics. Together, these results suggest a coupled ecological, topo-hydrologic perspective can help assess the fate of N in complex landscapes. [ABSTRACT FROM AUTHOR]

Savanna ecosystems are increasingly pressured by climate and land-use changes, especially around populous areas such as the Mt. Kilimanjaro region. Savanna vegetation consists of grassland with isolated trees or tree groups and is therefore characterized by high spatial variation and patchiness of canopy cover and aboveground biomass. Both are major regulators for soil ecological properties and soil-atmospheric trace gas exchange (CO, NO, CH), especially in water-limited environments. Our objectives were to determine spatial trends in soil properties and trace gas fluxes during the dry season and to relate above- and belowground processes and attributes. We selected a Savanna plain with vertic soil properties, south east of Mt. Kilimanjaro. Three trees were chosen from each of the two most dominant species: the legume Acacia nilotica and the non-legume Balanites aegyptiaca. For each tree, we selected one transect with nine sampling points, up to a distance of 4 times the crown radius from the stem. At each sampling point, we measured carbon (C) and nitrogen (N) content, δC of soil (0-10, 10-30 cm depth) and in plant biomass, soil C and N pools, water content, available nutrients, cation exchange capacity (CEC), temperature, pH, as well as root biomass and greenhouse-gas exchange. Tree species had no effect on soil parameters and gas fluxes under the crown. CEC, C, and N pools decreased up to 50% outside the crown-covered area. Tree leaf litter had a far lower C:N ratio than litter of the C grasses. δC in soil under the crown shifted about 15% in the direction of tree leaf litter δC compared to soil in open area reflecting the tree litter contribution to soil organic matter. The microbial C:N ratio and CO efflux were about 30% higher in the open area and strongly dependent on mineral N availability. This indicates N limitation and low microbial C use efficiency in the soil of open grassland areas. We conclude that the spatial structure of aboveground biomass in savanna ecosystems leads to a spatial redistribution of nutrients and thus C mineralization and sequestration. Therefore, the capability of savanna ecosystems to act as C sinks is both directly and indirectly dependent on the abundance of trees, regardless of their N-fixing status. [ABSTRACT FROM AUTHOR]

The phrase 'hot spots and hot moments' first entered the lexicon in 2003, following the publication of the paper 'Biogeochemical hot spots and hot moments at the interface of terrestrial and aquatic ecosystems' by McClain and others (Ecosystems 6:301-312, 2003). This paper described the potential for rare places and rare events to exert a disproportionate influence on the movement of elements at the scale of landscapes and ecosystems. Here, we examine how the cleverly named hot spot and hot moment concept (hereafter HSHM) has influenced biogeochemistry and ecosystem science over the last 13 years. We specifically examined the extent to which the HSHM concept has: (1) motivated research aimed at understanding how and why biogeochemical behavior varies across spatiotemporal scales; (2) improved our ability to detect HSHM phenomena; and (3) influenced our approaches to restoration and ecosystem management practices. We found that the HSHM concept has provided a highly fertile framework for a substantial volume of research on the spatial and temporal dynamics of nutrient cycling, and in doing so, has improved our understanding of when and where biogeochemical rates are maximized. Despite the high usage of the term, we found limited examples of rigorous statistical or modeling approaches that would allow ecosystem scientists to not only identify, but scale the aggregate impact of HSHM on ecosystem processes. We propose that the phrase 'hot spots and hot moments' includes two implicit assumptions that may actually be limiting progress in applying the concept. First, by differentiating 'hot spots' from 'hot moments,' the phrase separates the spatial and temporal components of biogeochemical behavior. Instead, we argue that the temporal dynamics of a putative hot spot are a fundamental trait that should be used in their description. Second, the adjective 'hot' implicitly suggests that a place or a time must be dichotomously classified as 'hot or not.' We suggest instead that each landscape of interest contains a wide range of biogeochemical process rates that respond to critical drivers, and the gradations of this biogeochemical topography are of greater interest than the maximum peaks. For these reasons, we recommend replacing the HSHM terminology with the more nuanced term ecosystem control points. 'Ecosystem control' suggests that the rate must be of sufficient magnitude or ubiquity to affect dynamics of the ecosystem, while 'points' allows for descriptions that simultaneously incorporate both spatial and temporal dynamics. We further suggest that there are at least four distinct types of ecosystem control points whose influence arises through distinct hydrologic and biogeochemical mechanisms. Our goal is to provide the tools with which researchers can develop testable hypotheses regarding the spatiotemporal dynamics of biogeochemistry that will stimulate advances in more accurately identifying, modeling and scaling biogeochemical heterogeneity to better understand ecosystem processes. [ABSTRACT FROM AUTHOR]

The rewilding of abandoned agricultural lands opens up opportunities for the recovery of forest ecosystem extent. Frugivorous animals not only take part in the regeneration of unaltered forests, but leave a visible footprint in restoring areas in the form of the number and spatial distribution of new trees recruited from dispersed seeds. Nevertheless, their contribution is conditioned by how environmental factors affect both the patterns of seed dispersal and the fate of post-dispersal regeneration stages throughout the whole ecosystem. Here, we evaluated the role of avian seed dispersers in tree regeneration in woodland pastures resulting from anthropic deforestation. Using an integrative approach, considering the different tree regeneration stages, we dissected the ways in which forest loss conditioned the contribution of frugivores. Habitat structure influenced bird activity, mainly restricting seed dispersal to forested areas. Tree recruitment was severely reduced during early regeneration stages, but maintained the initial forest-biased spatial distribution. However, the presence of scrub in deforested areas, which protect against grazing at late regeneration stages, drastically increased the relevance of tree recruitment outside the forest. Frugivorous birds made a significant contribution to tree regeneration in the woodland pastures under study. The interplay between seed dispersal by birds and the protective role of scrub was fundamental in facilitating the recolonization of deforested areas. If we wish to encourage this natural reforestation, we will need to preserve populations of frugivorous birds while favoring landscape configurations that encourage seed dispersal outside the forest and species that promote tree establishment (like nurse scrubs). [ABSTRACT FROM AUTHOR]

The North Pacific Subtropical Gyre (NPSG) is one of the largest biomes on Earth. It has a semi-enclosed surface area of about 2 × 10 km and mean depth of nearly 5 km and includes a broad range of habitats from warm, light-saturated, nutrient-starved surface waters to the cold, nutrient-rich abyss. Microorganisms are found throughout the water column and are vertically stratified by their genetically determined metabolic capabilities that establish physiological tolerances to temperature, light, pressure, as well as organic and inorganic growth substrates. Despite the global significance of the NPSG for energy and matter transformations and its role in the oceanic carbon cycle, it is grossly undersampled and not well characterized with respect to ecosystem structure and dynamics. Since October 1988, interdisciplinary teams of scientists from the University of Hawaii and around the world have been investigating the NPSG ecosystem at Station ALOHA (A Long-term Oligotrophic Habitat Assessment), a site chosen to be representative of this expansive oligotrophic habitat, with a focus on microbial processes and biogeochemistry. At the start of this comprehensive field study, the NPSG was thought to be a 'Climax' community with a relatively stable plankton community structure and relatively low variability in key microbiological rates and processes. Now, after nearly three decades of observations and experimentation we present a new view of this old ocean, one that highlights temporal variability in ecosystem processes across a broad range of scales from diel to decadal and beyond. Our revised paradigm is built on the strength of high-quality time-series observations, on insights from the application of state-of-the-art -omics techniques (genomics, transcriptomics, proteomics and metabolomics) and, more recently, the discoveries of novel microorganisms and metabolic processes. Collectively, these efforts have led to a new understanding of trophic dynamics and population interactions in the NPSG. A comprehensive understanding of the environmental controls on microbial rates and processes, from genomes to biomes, will be required to inform the scientific community and the public at large about the potential impacts of human-induced climate change. The pace of new discovery, and the importance of integrating this new knowledge into conceptual paradigms and predictive models, is an enormous contemporary challenge with great scientific and societal relevance. [ABSTRACT FROM AUTHOR]

Despite the importance of future carbon (C) pools for policy and land management decisions under various climate change scenarios, predictions of these pools under altered climate vary considerably. Chronic warming will likely impact both ecosystem C fluxes and the abundance and distribution of plant functional types (PFTs) within systems, potentially interacting to create novel patterns of C exchange. Here, we report results from a 3-year warming experiment using open top chambers (OTC) on the Tibetan Plateau meadow grassland. Warming significantly increased C uptake through gross primary productivity (GPP) but not ecosystem respiration (ER), resulting in a 31.0% reduction in net ecosystem exchange (NEE) in warmed plots. The OTC-induced changes in ecosystem C fluxes were not fully explained by the corresponding changes in soil temperature and moisture. Warming treatments significantly increased the biomass of graminoids and legumes by 12.9 and 27.6%. These functional shifts were correlated with enhanced local GPP, but not ER, resulting in more negative NEE in plots with larger increases in graminoid and legume biomass. This may be due to a link between greater legume abundance and higher levels of total inorganic nitrogen, which can potentially drive higher GPP, but not higher ER. Overall, our results indicate that C-climate feedbacks might be closely mediated by climate-induced changes in PFTs. This highlights the need to consider the impacts of changes in PFTs when predicting future responses of C pools under altered climate scenarios. [ABSTRACT FROM AUTHOR]

Flow regimes are fundamental to sustaining ecological characteristics of rivers worldwide, including their associated floodplains. Recent advances in understanding tropical river-floodplain ecosystems suggest that a small set of basic ecological concepts underpins their biophysical characteristics, especially the high levels of productivity, biodiversity and natural resilience. The concepts relate to (1) river-specific flow patterns, (2) processes 'fuelled' by a complex of locally generated carbon and nutrients seasonally mixed with carbon and nutrients from floodplains and catchments, (3) seasonal movements of biota facilitated by flood regimes, (4) food webs and overall productivity sustained by hydrological connectivity, (5) fires in the wet/dry tropical floodplains and riparian zones being major consumers of carbon and a key factor in the subsequent redistribution of nutrients, and (6) river-floodplains having inherent resilience to natural variability but only limited resilience to artificial modifications. Understanding these concepts is particularly timely in anticipating the effects of impending development that may affect tropical river-floodplains at the global scale. Australia, a region encompassing some of the last relatively undisturbed tropical riverine landscapes in the world, provides a valuable case study for understanding the productivity, diversity and resilience of tropical river-floodplain systems. However, significant knowledge gaps remain. Despite substantial recent advances in understanding, present knowledge of these highly complex tropical rivers is insufficient to predict many ecological responses to either human-generated or climate-related changes. The major research challenges identified herein (for example, those related to food web structure, nutrient transfers, productivity, connectivity and resilience), if accomplished in the next decade, will offer substantial insights toward assessing and managing ecological changes associated with human alterations to rivers and their catchments. [ABSTRACT FROM AUTHOR]

Ecosystem metabolism is an important determinant of trophic structure, nutrient cycling, and other critical ecosystem processes in streams. Whereas watershed- and local-scale controls on stream metabolism have been independently investigated, little is known about how controls exerted at different scales interact to determine stream metabolic rates, particularly in urban streams and across seasons. To address this knowledge gap, we measured ecosystem metabolism in four urban and four reference streams in northern Kentucky, USA, with paired closed and open riparian canopies, during each of the four seasons. Gross primary production (GPP), ecosystem respiration, and net ecosystem production (NEP) were all best predicted by models with season as a main effect, but interactions between season, canopy, and watershed varied for each response. Urban streams exhibited higher GPP during most seasons, likely due to elevated nutrient loads. Open canopy reaches in both urban and forested streams, supported higher rates of GPP than the closed canopy which reaches during the summer and fall, when the overhead vegetation shaded the closed reaches. The effect of canopy cover on GPP was similar among urban and forested streams. The combination of watershed and local-scale controls resulted in urban streams that alternated between net heterotrophy (NEP <0) and net autotrophy (NEP >0) at the reach-scale during seasons with dense canopy cover. This finding has management relevance because net production can lead to accumulation of algal biomass and associated issues like nighttime hypoxia. Our study suggests that although watershed urbanization fundamentally alters ecosystem function, the preservation and restoration of canopied riparian zones can provide an important management tool at the local scale, with the strongest impacts on stream metabolism during summer. [ABSTRACT FROM AUTHOR]

Ecological engineers have important effects on biodiversity because they often increase habitat complexity and moderate environmental conditions, implying that their influence on associated fauna will vary across gradients of environmental stress. To test this, we quantified the positive effects of mussel beds on associated benthic communities around the entire South African coastline (~3500 km). We hypothesised that molluscan assemblages would show stronger affinities to the presence of mussel beds with increasing levels of heat-stress. Biomimetic loggers used to characterise thermal properties within and outside mussel beds found that solitary mussels experienced significantly greater daily maximum temperatures than mussels within beds across all locations. However, the magnitude of such differences did not appear to vary with latitude or time of year but rather was strongly influenced by biogeographic region. Differences in the abundance, diversity and community structure of molluscs within and outside mussel beds showed similar biogeographic variability, with differences in total molluscan abundances being most pronounced along the cool temperate west coast during summer and least pronounced along the warm temperate south coast during winter. Greater affinity of molluscan assemblages for mussel beds within cooler biogeographic regions suggests that evolutionary history and/or other abiotic factors may be the primary cause for the stronger influence of mussel beds on the west coast. This highlights the complex, context-dependant nature of ecosystem engineering and the varying degrees to which associated organisms affiliate with these biogenic structures. Such findings have important implications for the use of ecosystem engineers as umbrella species in ecological conservation. [ABSTRACT FROM AUTHOR]

Globally, ecosystem services are threatened by increasing urbanization and more variable precipitation patterns driven by climate change. However, how these drivers interact over long-time scales to affect underlying processes remains poorly understood, hindering our ability to predict their long-term consequences. Here, we use long-term data spanning nearly a century to investigate changes in hydrologic attributes for two lakes in the Upper Midwest with urbanizing watersheds. We quantified flashiness-the variability of runoff rate, volume, or stage-level of waterways-to investigate the concurrent impacts of urbanization and climate change on flashiness and flooding potential. Our results indicate that flashiness generally increased for both lakes over the period of 1916-2013, although this overall trend consists of sub-periods of increase and decrease. Increasing impervious surface area has been the stronger driver of flashiness historically; however, our results suggest that the impact of urbanization may reach a threshold, such that saturation effects would cause large magnitude precipitation events to become a relatively stronger driver of flashiness. Increasing flashiness indicates an increase in flooding potential, documented by increases in the 10- and 100-year flood threshold levels as large as 30 cm. Since flashiness is strongly related to the provisioning of multiple ecosystem services, the methodology and results presented here provide a unique approach to gain insight into how non-linear interactions between global change drivers, at multiple time scales, impact the simultaneous provision of multiple services. [ABSTRACT FROM AUTHOR]

Ecosystem and community ecology have evolved along different pathways, with little overlap. However, to meet societal demands for predicting changes in ecosystem services, the functional and structural view dominating these two branches of ecology, respectively, must be integrated. Biodiversity-ecosystem function research has addressed this integration for two decades, but full integration that makes predictions relevant to practical problems is still lacking. We argue that full integration requires going, in both branches, deeper by taking into account individual organisms and the evolutionary and physico-chemical principles that drive their behavior. Individual-based models are a major tool for this integration. They have matured by using individual-level mechanism to replace the demographic thinking which dominates classical theoretical ecology. Existing individual-based ecosystem models already have proven useful both for theory and application. Still, next-generation individual-based models will increasingly use standardized and re-usable submodels to represent behaviors and mechanisms such as growth, uptake of nutrients, foraging, and home range behavior. The strategy of pattern-oriented modeling then helps make such ecosystem models structurally realistic by developing theory for individual behaviors just detailed enough to reproduce and explain patterns observed at the system level. Next-generation ecosystem scientists should include the individual-based approach in their toolkit and focus on addressing real systems because theory development and solving applied problems go hand-in-hand in individual-based ecology. [ABSTRACT FROM AUTHOR]

In our study at Mt. Kilimanjaro, East Africa, we quantified gross rates of ammonification, nitrification, nitrogen immobilization, and dissimilatory nitrate reduction to ammonium in soils across different land uses, climate zones (savanna, montane forest ecosystems, extensive agroforest homegarden, and intensively managed coffee plantation), and seasons (dry, wet, and transition from dry to wet season) to identify if and to what extent conversion of natural ecosystems to cultivated land has affected key soil microbial nitrogen turnover processes. Overall variation of gross soil nitrogen turnover rates across different ecosystems was more pronounced than seasonal variations, with the highest turnover rates occurring at the transition between dry and wet seasons. Nitrogen production and immobilization rates positively correlated with soil organic carbon and total nitrogen concentrations as well as substrate availability of dissolved organic carbon and nitrogen r > 0.67, P < 0.05), but did not correlate with soil ammonium and nitrate concentrations. Soil nitrogen turnover rates were highest in the montane Ocotea forest (ammonification 29.84, nitrification 12.67, NH immobilization 38.92, NO immobilization 10.74, and DNRA 1.54 µg N g SDW d) and progressively decreased with decreasing annual rainfall and increasing land-use intensity. Using indicators of N retention and characteristics of soil nutrient status, we observed a grouping of faster, but tighter N cycling in the (semi-) natural savanna and Ocotea forest. This contrasted with a more open N cycle in managed systems (the homegarden and coffee plantation) where N was more prone to leaching or gaseous losses due to high nitrate production rates. The partly disturbed (selected logging) lower montane forest ranged between these two groups. [ABSTRACT FROM AUTHOR]

Human behavior has rapidly evolved from fire-promoting to aggressively attempting to minimize its magnitude and variability. This global shift in human behavior has contributed to the adoption of strict policies that govern the purposeful and planned use of fire in ecosystem science and management. However, it remains unclear the extent to which modern-day prescribed fire policies are altering the potential magnitude and variation of fire behavior in scientific investigations and ecosystem management. Here, we modeled the theoretical historical range of variability (ROV) in fire behavior for the tallgrass prairie ecosystem of North America. We then compared sensitivities in the magnitude and variation in the historical ROV in fire behavior as a result of (1) policies governing prescribed fire and (2) woody and herbaceous plant invasions. Although considerably more attention has focused on changes in fire behavior as a result of biological invasions, our model demonstrates that contemporary fire management policies can meet or surpass these effects. Policies governing prescribed fire management in tallgrass prairie reduced the magnitude and variability of surface fire behavior more than tall fescue invasion and rivaled reductions in fire behavior from decades of Juniperus encroachment. Consequently, fire and its potential as a driver of ecosystem dynamics has been simplified in the study and management of this system, which may be contributing to misleading conclusions on the potential responses of many highly researched environmental priorities. We emphasize the need to study changes in fire dynamics as a function of both social and ecological drivers, in an effort to advance our basic understanding of the role of fire in nature and its potential usefulness in ecosystem management. [ABSTRACT FROM AUTHOR]

Understanding social perceptions of rural communities is essential to construct public policy and management alternatives, not only to maintain natural ecosystems but also to deal with a changing environment due to climatic change. Because climate variability in Mexico has important socio-economic and environmental impacts, it is necessary to build capacities for adaptation. We describe social perceptions of three main local stakeholders (that is, farmers, elders, and local authorities), regarding their relationships with rainforest and local adaptation to climate change in eleven rural communities in Marqués de Comillas municipality, Chiapas, Southern Mexico. We based in a qualitative approach and used participant observation and semi-structured interviews. Even certain subtly variation among stakeholders, we recognized some underlying ideas behind perceptions. Rainforest is considered crucial to maintain human livelihoods and to mitigate climatic changes. They perceived changes in climate occurring in the region, such as raising temperature, unpredictable rainfall, and streams becoming dry. Local organization and government involved in managing rainforest or dealing with climatic changes are practically absent. This emphasizes the needs bring proper and reliable information to make decisions regarding rainforest use and management, but also to adapt to a changing climate. The loss of the collective character of the communities and, certain conflicts in public policies that mirrored in the coexistence of initiatives with contrasting objectives are proposed as particularly important for understanding the emergence of these perceptions. We proposed some recommendations to bolster regional capacities addressing climate change. Involving stakeholders such as governmental and non-governmental institutions is also imperative. [ABSTRACT FROM AUTHOR]

Cattle are a major methane (CH) source from pasture ecosystems; however, the underlying landscape can be a significant and unaccounted source of CH. In general, landscape CH emissions are poorly quantified, vary widely across time and space, and are easily underestimated if emission hotspots or episodic fluxes are overlooked. In this study, CH emissions from subtropical lowland pastures were quantified using static chambers, eddy covariance, and mobile spectrometer surveys. Landscape emissions were the dominant CH source, and cattle were responsible for 19-30% of annual emissions. The entire ecosystem emitted 33.84 ± 2.25 g CH m y as estimated by eddy covariance-measured fluxes. Landscape emissions were highly variable, and seasonal flooding drove high magnitude emissions from the underlying landscape. Large CH emissions were observed from wetlands and, to a lesser extent, from the entire landscape during the wet season. In contrast, during the dry season, there were no appreciable landscape CH emissions, although canals, which cover only 1.7% of the total land area, were responsible for 97.7% of dry-season emissions. Ecosystem CH fluxes, measured by eddy covariance, varied seasonally and positively correlated to water table depth, soil and air temperatures, and topsoil water content. The results presented here are the first to use mobile spectrometers to map biogenic CH emissions at the landscape scale, and strongly suggest that the underlying landscape is a strong CH source that must be considered in addition to cattle emissions. [ABSTRACT FROM AUTHOR]

The article provides an analysis of various concepts of emergence related to ecosystem. Topics include biological tradition of teleological emergence, primary succession of a terrestrial ecosystem, dependence of vegetation in early succession on external sources of nutrients from the atmosphere, and emergence of tight nutrient cycles requiring feedbacks between soils and vegetation that coordinate mineralization.

The arctic forest-tundra ecotone (FTE) represents a major transition zone between contrasting ecosystems, which can be strongly affected by climatic and biotic factors. Expected northward expansion and encroachment on arctic tundra in response to climate warming may be counteracted by natural and anthropogenic processes such as defoliating insect outbreaks and grazing/browsing regimes. Such natural and anthropogenic changes in land cover can substantially affect FTE dynamics, alter ground albedo (index of the amount of solar energy reflected back into the atmosphere) and provide important feedbacks into the climate system. We took advantage of a naturally occurring contrast between reindeer grazing regimes in a border region between northern Finland and Norway which was recently defoliated by an outbreak of the geometrid moth. We examined ecosystem-wide contrasts between potentially year-round (but mainly summer) grazed (YRG) regions in Finland and mainly winter grazed (WG) regions in Norway. We also used a remotely sensed vegetation index and albedo to quantify effects on local energy balance and potential climate feedbacks. Although differences in soil characteristics and ground vegetation cover were small, we found dramatic differences in the tree layer component of the ecosystem. Regeneration of mountain birch stands appears to have been severely hampered in the YRG regime, by limiting regeneration from basal shoots and reestablishment of individual trees from saplings. This has led to a more open forest structure and a significant 5% increase in spring albedo in the summer grazed compared to the winter grazed regions. This supports recent suggestions that ecosystem processes in the Arctic can significantly influence the climate system, and that such processes must be taken into account when developing climate change scenarios and adaptation strategies. [ABSTRACT FROM AUTHOR]

Boreal forests are critical to the global carbon (C) cycle. Despite recent advances in our understanding of boreal C budgets, C dynamics during compositional transition to late-succession forests remain unclear. Using a carefully replicated 203-year chronosequence, we examined long-term patterns of forest C stocks and net ecosystem productivity (NEP) following stand-replacing fire in the boreal forest of central Canada. We measured all C pools, including understorey vegetation, belowground biomass, and soil C, which are often missing from C budgets. We found a slight decrease in total ecosystem C stocks during early stand initiation, between 1 and 8 years after fire, at −0.90 Mg C ha y. As stands regenerated, live vegetation biomass increased rapidly, with total ecosystem C stocks reaching a maximum of 287.72 Mg C ha 92 years after fire. Total ecosystem C mass then decreased in the 140- and 203-year-old stands, losing between −0.50 and −0.74 Mg C ha y, contrasting with views that old-growth forests continue to maintain a positive C balance. The C decline corresponded with canopy transition from dominance of Populus tremuloides, Pinus banksiana, and Picea mariana in the 92-year-old stands to Betula papyrifera, Picea glauca, and Abies balsamea in the 203-year-old stands. Results from this study highlight the role of succession in long-term forest C dynamics and its importance when modeling terrestrial C flux. [ABSTRACT FROM AUTHOR]

Mowing is known to favor plant diversity and influence ecosystem functioning in semi-natural grasslands. This effect could be influenced by climate variability, especially in regions with harsh climate, such as subalpine zones. In particular, short-term extreme weather fluctuations may induce rapid plant responses, affecting in turn the response to mowing. We tested the effects of concomitant summer weather manipulation and mowing on a subalpine grassland in the Central French Alps for two consecutive years. We addressed two questions: (1) How is a subalpine grassland affected by extreme summer weather? (2) Does extreme summer weather alter mowing effects on the grassland plant diversity and functioning? We used a multi-level, integrative approach assessing the responses of six abundant plant species, as well as effects on plant community structure, biomass production, and litter decomposition rates. Extreme summer weather was simulated by increasing summer temperature by 1.1°C, and decreasing summer rainfall by 80%-resulting in a 30% decrease in total annual precipitation. In addition, a heat-wave event was simulated during the first year of the experiment. This weather manipulation was combined with a late-summer mowing treatment (mown vs. unmown). Extreme summer weather mainly increased leaf senescence and decreased plant vegetative growth. Leaf litter decomposition was slowed, but only for species characterized by the fastest rates of litter decomposition. Mowing increased plant diversity by restricting the dominant grass species, thereby favoring subordinates. In the short term, this subalpine grassland was rather resistant to extreme summer weather, whereas mowing cessation remained the main factor affecting its biodiversity. [ABSTRACT FROM AUTHOR]

This study focused on unraveling the natural mechanism for the frequent shifts in alternative regimes in pristine shallow lakes of the Boreal Plains, Alberta, Canada. The lakes tend to be clear and dominated by submerged aquatic vegetation (SAV) or turbid and dominated by phytoplankton. We report on the inter-annual response of 23 lakes from 2001 to 2007. We explore the effect of fluctuations in annual precipitation on the lake response including water depth, total phosphorus (TP) concentration, turbidity, phytoplankton biomass, SAV biomass, and the proportion of clear and turbid lakes. The regime switches appear driven by the transient dynamics of phytoplankton, and dilution of nutrients, phytoplankton biomass, and turbidity during wet years, and evapoconcentration during dry years. Increased precipitation was correlated with decreased phytoplankton biomass, TP concentration, chloride concentration, and turbidity. In 2005, the wettest year, no phytoplankton-dominated lakes were observed. During the driest year (2002), the phytoplankton-dominant regime (>18 μg chl- a L) occurred in 22% of lakes, which was higher than the study period average. SAV biomass was not directly affected by precipitation, but was negatively associated with phytoplankton biomass and positively associated with the previous year's SAV growth. SAV biomass was carried over from year-to-year, and the occurrence of SAV-dominated (>25% cover) lakes was significantly higher in 2007 (90%) following 3 years of high precipitation levels. [ABSTRACT FROM AUTHOR]

In mixed forests, interactions among species influence ecosystem functioning but environmental conditions also play an important role in shaping relationships between biodiversity and ecosystem functioning. In the context of climate change, the carbon and water balance in pure versus mixed forest stands may be differentially influenced by changing soil water availability. To test this hypothesis, we compared the influence of biodiversity on stand water use efficiency (WUE) in boreal forests between wet and dry years. We assessed the carbon isotope composition ( δC) of tree rings in Betula pendula, Pinus sylvestris, and Picea abies growing in pure versus mixed stands. In addition, we tested whether differences in WUE affected patterns of stand basal area increment (BAI). No biodiversity effect was found for stand δC ( δC) during the wet year. However, there was a significant increase in δC between the wet and the dry year and a significant effect of biodiversity on δC in the dry year. The increase in δC in mixed stands was associated with both selection and complementarity effects. Although BAI decreased significantly in the dry year, changes in δC did not translate into variations in BAI along the biodiversity gradient. Our results confirmed that the physiological response of boreal forest ecosystems to changing soil water conditions is influenced by species interactions and that during dry growing seasons, species interactions in mixed stands can lead to lower soil moisture availability. This illustrates that biodiversity effects can also be negative in mixed stands in the sense that soil resources can be more intensively exhausted. Overall, our results confirm that in boreal forests, the biodiversity-ecosystem functioning relationship depends on local environmental conditions. [ABSTRACT FROM AUTHOR]

Intertidal blue mussel beds are important for the functioning and community composition of coastal ecosystems. Modeling spatial dynamics of intertidal mussel beds is complicated because suitable habitat is spatially heterogeneously distributed and recruitment and loss are hard to predict. To get insight into the main determinants of dispersion, growth and loss of intertidal mussel beds, we analyzed spatial distributions and growth patterns in the German and Dutch Wadden Sea. We considered yearly distributions of adult intertidal mussel beds from 36 connected tidal basins between 1999 and 2010 and for the period 1968-1976. We found that in both periods the highest coverage of tidal flats by mussel beds occurs in the sheltered basins in the southern Wadden Sea. We used a stochastic growth model to investigate the effects of density dependence, winter temperature and storminess on changes in mussel bed coverage between 1999 and 2010. In contrast to expectation, we found no evidence that cold winters consistently induced events of synchronous population growth, nor did we find strong evidence for increased removal of adult mussel beds after stormy winter seasons. However, we did find synchronic growth within groups of proximate tidal basins and that synchrony between distant groups is mainly low or negative. Because the boundaries between synchronic groups are located near river mouths and in areas lacking suitable mussel bed habitat, we suggest that the metapopulation is under the control of larval dispersal conditions. Our study demonstrates the importance of moving from simple habitat suitability models to models that incorporate metapopulation processes to understand spatial dynamics of mussel beds. The spatio-dynamic structure revealed in this paper will be instrumental for that purpose. [ABSTRACT FROM AUTHOR]

Unravelling the role of structural and environmental drivers of gross primary productivity (GPP) and ecosystem respiration ( R) in highly heterogeneous tundra is a major challenge for the upscaling of chamber-based CO fluxes in Arctic landscapes. In a mountain birch woodland-mire ecotone, we investigated the role of LAI (and NDVI), environmental factors (microclimate, soil moisture), and microsite type across tundra shrub plots (wet hummocks, dry hummocks, dry hollows) and lichen hummocks, in controlling net ecosystem CO exchange (NEE). During a growing season, we measured NEE fluxes continuously, with closed dynamic chambers, and performed multiple fits (one for each 3-day period) of a simple light and temperature response model to hourly NEE data. Tundra shrub plots were largely CO sinks, as opposed to lichen plots, although fluxes were highly variable within microsite type. For tundra shrub plots, microsite type did not influence photosynthetic parameters but it affected basal (that is, temperature-normalized) ecosystem respiration ( R). PAR-normalized photosynthesis ( P) increased with air temperature and declined with increasing vapor pressure deficit. R declined with soil moisture and showed an apparent increase with temperature, which may underlie a tight link between GPP and R. NDVI was a good proxy for LAI, maximum P and maximum R of shrub plots. Cumulative CO fluxes were strongly correlated with LAI (NDVI) but we observed a comparatively low GPP/LAI in dry hummocks. Our results broadly agree with the reported functional convergence across tundra vegetation, but here we show that the role of decreased productivity in transition zones and the influence of temperature and water balance on seasonal CO fluxes in sub-Arctic forest-mire ecotones cannot be overlooked. [ABSTRACT FROM AUTHOR]

Macrophytes influence the physical, chemical, and biological characteristics of lowland streams, so may be critically important in stream management. We investigated the role of macrophytes in regulating metabolism and nutrient cycling in three lowland, agricultural streams. We measured stream metabolism over the growing season and following experimental macrophyte removal, and used short-term nutrient additions of phosphate (P) and ammonium to assess macrophyte influences on nutrient uptake. Primary production was closely correlated with macrophyte cover across all streams and dates, and decreased greatly with macrophyte removal, whereas ecosystem respiration was not correlated with macrophyte cover and was not altered by macrophyte removal. Phosphate uptake velocity was negatively related to primary production, suggesting that macrophyte activity actually slowed P uptake. Ammonium uptake was not correlated with macrophyte cover or metabolism metrics. Stream nitrate concentrations typically exceeded concentrations of incoming groundwater, suggesting little net nitrate retention in these macrophyte-dominated streams. Phosphorous demand by macrophytes was 10-fold lower than observed uptake rates, indicating that macrophyte P demand was much lower than that of other stream biota. Nitrogen demand by macrophytes was nearly equal to ammonium uptake and was not sufficient to affect the high nitrate flux. These results indicate that macrophytes drive ecosystem metabolism but have limited influence on water column nutrient concentrations because macrophyte demand is much lower than the supply available from the water column. Thus macrophytes in our streams had a large impact on stream trophic state, but offered little potential to influence nutrient removal via management. [ABSTRACT FROM AUTHOR]

Migratory animals often transfer nutrients between ecosystems, enhancing productivity in the subsidized system. Most research on nutrient subsidies by migratory fishes has focused on Pacific salmon, whose semelparous life history is unusual among migratory fishes. To test whether iteroparous species can provide ecologically important nutrient inputs to stream ecosystems, we experimentally blocked the migration of suckers (Catostomidae) midway up an oligotrophic tributary of Lake Michigan. Comparing reaches upstream of the barrier to downstream reaches containing thousands of breeding fish, we found that suckers elevated phosphorus and nitrogen concentrations three- to five-fold. Algal accrual was doubled and caddisflies grew 12% larger in subsidized reaches relative to reference reaches. An enclosure experiment demonstrated that caddisflies with access to a fish carcass rapidly became enriched in N and C, and experimental carcass additions were rapidly colonized by high densities of caddisflies. However, under natural conditions below the experimental barrier, caddisflies became enriched in N but not C, indicating that fish-derived nutrients entered the stream food web primarily through indirect pathways rather than direct consumption of carcasses or gametes. At pupation, an average of 18% of caddisfly tissue N below the barrier was sucker-derived. In comparison to our focal stream, a reference stream with few suckers showed no seasonal or longitudinal patterns in nutrients and stable isotopes. These results demonstrate that iteroparous fish migrations can spur productivity via nutrient subsidies, despite low mortality rates. Thus, concerns about negative ecosystem-level consequences of blocking migrations of semelparous fishes are also applicable to iteroparous species when migrations are large. [ABSTRACT FROM AUTHOR]

Ecosystem management (EM) is a process for addressing environmental problems that involves research utilizing interdisciplinary approaches. The work presented here examines the perspectives on the interdisciplinary research process from researchers involved in generating knowledge to contribute to EM. The goal is to generate critically reflective discussions about interdisciplinary practice. We conducted a set of targeted key-informant, semi-structured interviews ( n = 15). Interviews followed a general questioning guide that included: experience doing interdisciplinary research; descriptions of the interdisciplinary process; understandings on how to conduct interdisciplinary research; interest in theories of interdisciplinarity; and interest in how the interdisciplinary process takes place. We coded interview transcripts to gain an in-depth understanding of how respondents perceive interdisciplinary research practice. Results indicate that discussions about how interdisciplinary research is conducted are not currently an important part of research activity among researchers contributing to EM. Rather, participants in the study see interdisciplinary practice as under theorized, spontaneous, and mainly intuition-based. They understand interdisciplinary research as a collaborative effort to integrate insights from different disciplines, but details about how to achieve integration remain hidden inside a 'black box.' Results suggest that researchers in EM would benefit from specific guidelines for integrating insights across disciplines. The work discusses how opening the 'black box' and considering explicit and detailed descriptions about the integration process might benefit interdisciplinary practice in research for conservation. This study contributes to future in-depth debates on how to generate dialectical engagement between EM researchers and those studying theories of interdisciplinarity in fields such as interdisciplinary studies. [ABSTRACT FROM AUTHOR]

Artificial reservoirs likely accumulate more carbon than natural lakes due to their unusually high sedimentation rates. Nevertheless, the actual magnitude of carbon accumulating in reservoirs is poorly known due to a lack of whole-system studies of carbon burial. We determined the organic carbon (OC) burial rate and the total OC stock in the sediments of a tropical hydroelectric reservoir by combining a seismic survey with sediment core sampling. Our data suggest that no sediment accumulation occurs along the margins of the reservoir and that irregular bottom morphology leads to irregular sediment deposition. Such heterogeneous sedimentation resulted in high spatial variation in OC burial-from 0 to 209 g C m y. Based on a regression between sediment accumulation and OC burial rates ( R = 0.94), and on the mean reservoir sediment accumulation rate (0.51 cm y, from the seismic survey), the whole-reservoir OC burial rate was estimated at 42.2 g C m y. This rate was equivalent to 70% of the reported carbon emissions from the reservoir surface to the atmosphere and corresponded to a total sediment OC accumulation of 0.62 Tg C since the reservoir was created. The approach we propose here allows an inexpensive and integrative assessment of OC burial in reservoirs by taking into account the high degree of spatial variability and based on a single assessment. Because burial can be assessed shortly after the survey, the approach combining a seismic survey and coring could, if applied on a larger scale, contribute to a more complete estimate of carbon stocks in freshwater systems in a relatively short period of time. [ABSTRACT FROM AUTHOR]

The flux of consumer-derived nutrients is recognized as an important ecosystem process, yet few studies have quantified the impact of these fluxes on freshwater ecosystems. The high abundance of bivalves in both marine and freshwater suggests that bivalves can exert large effects on aquatic food webs. The objective of our study was to determine the importance of unionid mussel-derived nitrogen (MDN) to the food web. We used a stable isotope tracer approach in conjunction with nutrient uptake and excretion experiments. We fed mussels ( Lampsilis siliquiodea, n = 249) a N-enriched algal diet and placed them into a N-limited stream for 63 days. Mussel hemolymph was non-lethally sampled over the course of the experiment to measure tissue turnover of δN and excretion experiments were done to model the amount of N mussels provided in comparison to stream N uptake demand. Multiple food web pools were sampled twice prior and five times following the mussel addition to trace the N through the food web. Our mussel excretion rates in comparison to areal uptake demand suggested that mussel excretion can account for 40% of the total N demand in this stream. Our enrichment showed that MDN was entering the food web and supplied up to 19% of the N in specific compartments of the food web near the mussel bed. When scaled to a natural mussel aggregation, our results suggest up to 74% of N in the food web may be mussel-derived. Our results show that N supplied by mussels can be an important nutrient subsidy that provides food web support. [ABSTRACT FROM AUTHOR]