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Ecosystems 

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Depth Profile of Soil Carbon and Nitrogen Accumulation over Two Decades in a Prairie Restoration Experiment
05. Januar 2021
Abstract Prairies converted from agriculture are known to accumulate carbon (C) and nitrogen (N) and are an important contribution to terrestrial C sequestration. However, estimates of decadal accumulation rates of C and N and their vertical distribution in the soil profile are highly variable among studies, in part due to the lack of repeated inventories of soil C and N stocks over long time periods. We determined the depth profile of soil C and N accumulation and bulk density following the transition from agriculture to planted prairie. Using 13 contiguous plantings...
Hydromorphologic Sorting of In-Stream Nitrogen Uptake Across Spatial Scales
08. Dezember 2020
Abstract Nitrogen (N) uptake is a key process in stream ecosystems that is mediated mainly by benthic microorganisms (biofilms on different substrata) and has implications for the biogeochemical fluxes at catchment scale and beyond. Here, we focused on the drivers of assimilatory N uptake, especially the effects of hydromorphology and other environmental constraints, across three spatial scales: micro, meso and reach. In two seasons (summer and spring), we performed whole-reach 15N-labelled ammonium injection experiments in two montane, gravel-bed stream reaches with...
Shade-Tree Rehabilitation in Vanilla Agroforests is Yield Neutral and May Translate into Landscape-Scale Canopy Cover Gains
07. Dezember 2020
Abstract Agroforestry can contribute to an increase in tree cover in historically forested tropical landscapes with associated gains in biodiversity and ecosystem functioning, but only if established on open land instead of underneath a forest canopy. However, declines in yields with increasing shade are common across agroforestry crops, driving shade-tree removal in forest-derived agroforests and hindering tree regrowth in open-land-derived agroforests. To understand trajectories of change in tree cover in forest- and open-land-derived agroforests, and the impacts of...
Long-Term Responses of Mediterranean Mountain Forests to Climate Change, Fire and Human Activities in the Northern Apennines (Italy)
02. Dezember 2020
Abstract Fagus sylvatica (beech) dominates the montane forests of the Apennines and builds old-growth high-conservation value stands. However, recent severe drought-induced diebacks raise concern on the future persistence of these forests and of Southern European mesophilous woodlands overall, growing at their dry edge. To explore the history of Apennine beech-dominated forests, we draw on the multiproxy paleoecological record from Lago Verdarolo, which includes a robust vegetation-independent temperature reconstruction. Numerical techniques are used to investigate the...
Divergent Controls on Stream Greenhouse Gas Concentrations Across a Land-Use Gradient
02. Dezember 2020
Abstract Inland waters can be significant sources of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) to the atmosphere. However, considerable uncertainty remains in regional and global estimates of greenhouse gas (GHG) emissions from freshwater ecosystems, particularly streams. Controls on GHG production in streams, such as water chemistry and sediment characteristics, are also poorly understood. The main objective of this study was to quantify spatial and temporal variability in GHG concentrations in 20 streams across a landscape with considerable variation...
Major Effects of Alkalinity on the Relationship Between Metabolism and Dissolved Inorganic Carbon Dynamics in Lakes
01. Dezember 2020
Abstract Several findings suggest that CO2 emissions in lakes are not always directly linked to changes in metabolism but can be associated with interactions with the dissolved inorganic carbon equilibrium. Alkalinity has been described as a determining factor in regulating the relative contributions of biological and inorganic processes to carbon dynamics in lakes. Here we analyzed the relationship between metabolic changes in dissolved oxygen (DO) and dissolved inorganic carbon (DIC) at different timescales in eight lakes covering a wide range in alkalinity. We used...
Transpiration of Dominant Tree Species Varies in Response to Projected Changes in Climate: Implications for Composition and Water Balance of Temperate Forest Ecosystems
01. Dezember 2020
Abstract The climate is changing in many temperate forests with winter snowpack shrinking and an increasing frequency of growing season air temperatures exceeding long-term means. We examined the effects of these changes on growing season rates of transpiration (sap flow) in two snow removal experiments in New Hampshire and Massachusetts, USA. Snow was removed during early winter, resulting in greater depth and duration of soil freezing compared to untreated plots. We examined the dominant tree species at each site, Acer saccharum at Hubbard Brook, NH and Acer rubrum...
Climate Warming Persistence Triggered Tree Ingression After Shrub Encroachment in a High Alpine Tundra
01. Dezember 2020
Abstract Climate warming can induce the encroachment of shrubs and may trigger treeline dynamics. However, the responses of shrubs and trees to climate change may be modulated by other environmental drivers such as land-use change and biological interactions. The European Alps are one of the three areas experiencing the most intense warming globally in the twentieth century. We analyse, through a multidisciplinary approach, the shrub and tree encroachment at the Stelvio Pass (Italian Alps) focusing on three target species (Rhododendron ferrugineum, Larix decidua, Pinus...
Simulated Increases in Fire Activity Reinforce Shrub Conversion in a Southwestern US Forest
01. Dezember 2020
Abstract Fire exclusion in historically frequent-fire forests of the southwestern United States has altered forest structure and increased the probability of high-severity fire. Warmer and drier conditions, coupled with dispersal distance limitations, are impeding tree seedling establishment and survival following high-severity fire. High-severity patches are commonly dominated by non-forest vegetation, a state that can be reinforced by subsequent fire events. We sought to determine the influence of fire probability on post-fire vegetation development in a severely...
Topographic and Host Effects on Arbuscular Mycorrhizal and Ectomycorrhizal Fungal Communities in a Forested Watershed
01. Dezember 2020
Abstract In a forested watershed, identity of tree species and topographical position could be important driving factors shaping mycorrhizal fungal communities. Here we aimed to disentangle the contributions of these two factors to mycorrhizal fungal community structure. We collected tree roots colonized by either arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi in a small, temperate, forested watershed of the Susquehanna-Shale Hills Critical Zone Observatory. Relative abundances of fungal OTUs were assessed using high-throughput DNA sequencing. The structures...
Silicon Dynamics During 2 Million Years of Soil Development in a Coastal Dune Chronosequence Under a Mediterranean Climate
01. Dezember 2020
Abstract Silicon (Si) in plants confers a number of benefits, including resistance to herbivores and water or nutrient stress. However, the dynamics of Si during long-term ecosystem development remain poorly documented, especially the changes in soils in terms of plant availability. We studied a 2-million-year soil chronosequence to examine how long-term changes in soil properties influence soil Si pools. The chronosequence exhibits extreme mineralogical changes—from carbonate-rich to quartz-rich soils—where a carbonate weathering domain is succeeded by a silicate...
Forest Vegetation Change and Its Impacts on Soil Water Following 47 Years of Managed Wildfire
01. Dezember 2020
Abstract Managed wildfire is an increasingly relevant management option to restore variability in vegetation structure within fire-suppressed montane forests in western North America. Managed wildfire often reduces tree cover and density, potentially leading to increases in soil moisture availability, water storage in soils and groundwater, and streamflow. However, the potential hydrologic impacts of managed wildfire in montane watersheds remain uncertain and are likely context dependent. Here, we characterize the response of vegetation and soil moisture to 47 years...
Effects of Extreme Disturbance Events: From Ecesis to Social–Ecological–Technological Systems
01. Dezember 2020
Abstract Ecologists addressed the effects of disturbances from the onset of the field by focusing on ecesis, which is the process by which organisms migrate and establish under the environmental conditions created by disturbances. Ecesis is the onset of succession, a self-organizing process whose nature, speed, and outcome depend in part on the outcomes of ecesis and the residual legacies remaining after disturbances. A by-product of succession after a disturbance is the reorganization of species dominance, or novelty. The degree of novelty in the outcome increases with...
A Small Nimble In Situ Fine-Scale Flux Method for Measuring Tree Stem Greenhouse Gas Emissions and Processes (S.N.I.F.F)
01. Dezember 2020
Abstract Tree stem methane emissions are gaining increasing attention as an overlooked atmospheric source pathway. Existing methods for measuring tree stem greenhouse gas fluxes and isotopes may provide robust integrated emission estimates, but due to their coarse resolution, the capacity to derive insights into fine-scale dynamics of tree stem emissions is limited. We demonstrate and field test an alternative method that is Small, Nimble, In situ and allows for Fine-scale Flux (‘SNIFF’) measurements, on complex and contrasting stem surfaces. It is lightweight and...
Snowpack, Tree Size, and Ecological Legacies Promote Seedling Establishment in Tree Islands at the Treeline
01. Dezember 2020
Abstract At a global scale, mean air or soil temperatures appear to be drivers of treeline position. However, at finer scales, seed availability and microsite conditions may limit the germination, establishment, and growth of tree seedlings—and therefore the position of treeline. Tree islands are features of many treelines, and they can alter microsite conditions by producing seed, providing shelter, and redistributing snow. Near Churchill, Manitoba, Canada, tree islands have higher seedling establishment than nearby forest and treeline sites and could be hot spots...
Patterns of Spring/Summer Open-Water Metabolism Across Boreal Lakes
01. Dezember 2020
Abstract Northern regions host the greatest density of surface water globally, but knowledge of lake metabolism in this vast yet remote landscape is limited. Here, we used an oxygen stable isotope approach to quantify patterns and drivers of surface layer metabolism in lakes throughout an approximately 106 km2 tract of boreal Canada. Ecosystem gross primary production (GPP) and respiration rates (R) were much higher than previously assumed for spring and summer months. Both rates were strongly linked to nitrogen (N) concentrations, not light availability, despite...
Long-Term Changes in Terrestrial Vegetation Linked to Shifts in a Colonial Seabird Population
01. Dezember 2020
Abstract Seabirds that form large colonies often act as biovectors that transport and concentrate large amounts of nutrients, metals, and contaminants from marine feeding areas to inland breeding grounds. This enrichment can potentially transform and structure primary productivity, vegetation communities, and species richness. In a previous paleolimnological study, we examined approximately 1700 years of population change in the world’s largest colony of Leach’s Storm-petrel (Hydrobates leucorhous) on Baccalieu Island (Newfoundland and Labrador, Canada) and, using...
A Mutualism Between Unattached Coralline Algae and Seagrasses Prevents Overgrazing by Sea Turtles
01. Dezember 2020
Abstract Seagrass meadows are threatened biodiversity hot spots that provide essential ecosystem services. Green sea turtles may overgraze meadows, further enhancing seagrass decline. However, we observed an unexpected, remarkable recovery of seagrasses in a previously overgrazed meadow with abundant unattached branched coralline algae, suggesting that turtle grazing had ceased. We hypothesize that this recovery is due to an effective grazing-protection mutualism, in which the spiny coralline algae structures protect the seagrass meadows from overgrazing, while the...
Biocrusts Modulate Responses of Nitrous Oxide and Methane Soil Fluxes to Simulated Climate Change in a Mediterranean Dryland
01. Dezember 2020
Abstract Little is known about the role of biocrusts in regulating the responses of N2O and CH4 fluxes to climate change in drylands. Here, we aim to help filling this knowledge gap by using an 8-year field experiment in central Spain where temperature and rainfall are being manipulated (~ 1.9°C warming, 33% rainfall reduction and their combination) in areas with and without well-developed biocrust communities. Areas with initial high cover of well-developed biocrusts showed lower N2O emissions, enhanced CH4 uptake and higher abundances of functional genes linked to...
Flow is more Important than Temperature in Driving Patterns of Organic Matter Storage and Stoichiometry in Stream Ecosystems
24. November 2020
Abstract Understanding the connections between biological communities and elemental cycles is increasingly important given that alterations to both are occurring on a global scale. Biological control of elemental cycles is tied to patterns of biomass and the elemental stoichiometry of organisms and organic matter (OM) pools that comprise ecosystems. The structure and size of these ecosystem components are, in turn, shaped by key environmental factors that influence species composition, functional traits, and OM and element storage. In stream and river ecosystems...