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Methane Emissions from Paludified Boreal Soils in European Russia as Measured and Modelled
20. September 2017
Abstract Spatial or temporal forest–peatland transition zones were proposed as potential hot spots of methane (CH4) emissions. Consequently, paludified soils are an important component of boreal landscape biogeochemistry. However, their role in the regional carbon cycle remains unclear. This study presents CH4 fluxes from two forest–peatland transition zones, two wet forest sites and two clear-cut sites which were compared to fluxes of open peatlands and dry forest. The median fluxes measured using the closed-chamber technique varied from − 0.04 to...
Soil Base Saturation Combines with Beech Bark Disease to Influence Composition and Structure of Sugar Maple-Beech Forests in an Acid Rain-Impacted Region
18. September 2017
Abstract Sugar maple, an abundant and highly valued tree species in eastern North America, has experienced decline from soil calcium (Ca) depletion by acidic deposition, while beech, which often coexists with sugar maple, has been afflicted with beech bark disease (BBD) over the same period. To investigate how variations in soil base saturation combine with effects of BBD in influencing stand composition and structure, measurements of soils, canopy, subcanopy, and seedlings were taken in 21 watersheds in the Adirondack region of NY (USA), where sugar maple and beech were...
The Landscape–Atmosphere Continuum Determines Ecological Change in Alpine Lakes of SE Tibet
15. September 2017
Abstract Remote alpine regions were considered to be largely unimpacted by anthropogenic disturbance, but it is now clear these areas are changing rapidly. It is often difficult to identify the causal processes underpinning ecological change because the main drivers (direct and indirect climate forcing, land use change and atmospheric deposition) are acting simultaneously. In addition, alpine landscapes are morphometrically complex with strong local environmental gradients creating natural heterogeneity which acts as a variable filter to climate and anthropogenic forcing...
Land Use Alters the Drought Responses of Productivity and CO 2 Fluxes in Mountain Grassland
15. September 2017
Abstract Climate extremes and land-use changes can have major impacts on the carbon cycle of ecosystems. Their combined effects have rarely been tested. We studied whether and how the abandonment of traditionally managed mountain grassland changes the resilience of carbon dynamics to drought. In an in situ common garden experiment located in a subalpine meadow in the Austrian Central Alps, we exposed intact ecosystem monoliths from a managed and an abandoned mountain grassland to an experimental early-summer drought and measured the responses of gross primary productivity...
Phosphorus Deposition in a Low-Phosphorus Landscape: Sources, Accuracy and Contribution to Declines in Surface Water P
14. September 2017
Abstract Atmospheric deposition can be an important source of phosphorus (P) to watersheds in geologically low-P landscapes like the Precambrian Shield, in south-central Ontario. Recent observations in this region of declining total P (TP) concentrations in streams and lakes, as well as P limitation in vegetation, prompted this investigation into the potential contributing role of atmospheric deposition. Long-term (1980–2014) measurements of bulk TP deposition at four monitoring stations, as well as wet-only deposition at one of the sites (2012–2014) and pollen...
Responses of Tree Transpiration and Growth to Seasonal Rainfall Redistribution in a Subtropical Evergreen Broad-Leaved Forest
14. September 2017
Abstract Precipitation changes such as more frequent drought and altered precipitation seasonality may impose substantial impacts on the structure and functioning of forest ecosystems. A better understanding of tree responses to precipitation changes can provide fundamental information for the conservation and management of forests under future climate regimes. We conducted a 2-year seasonal rainfall redistribution experiment to assess the responses of tree transpiration and growth to manipulated precipitation changes in a subtropical evergreen broad-leaved forest. Three...
Stream Resource Gradients Drive Consumption Rates of Supplemental Prey in the Adjacent Riparian Zone
11. September 2017
Abstract 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...
Overstorey–Understorey Interactions Intensify After Drought-Induced Forest Die-Off: Long-Term Effects for Forest Structure and Composition
07. September 2017
Abstract Severe drought events increasingly affect forests worldwide, but little is known about their long-term effects at the ecosystem level. Competition between trees and herbs (‘overstorey–understorey competition’) for soil water can reduce tree growth and regeneration success and may thereby alter forest structure and composition. However, these effects are typically ignored in modelling studies. To test the long-term impact of water competition by the herbaceous understorey on forest dynamics, we incorporated this process in the dynamic forest landscape model...
Driving Factors Behind Litter Decomposition and Nutrient Release at Temperate Forest Edges
07. September 2017
Abstract Forest edges have become important features in landscapes worldwide. Edges are exposed to a different microclimate and higher atmospheric nitrogen (N) deposition compared to forest interiors. It is, however, unclear how microclimate and elevated N deposition affect nutrient cycling at forest edges. We studied litter decomposition and release of N, phosphorus (P), total cations (TC) and C/N ratios during 18 months via the litterbag technique along edge-to-interior transects in two oak (Quercus robur L.) and two pine (Pinus nigra ssp. laricio Maire and ssp. nigra...
Aboveground Carbon Storage and Its Links to Stand Structure, Tree Diversity and Floristic Composition in South-Eastern Tanzania
06. September 2017
Abstract African savannas and dry forests represent a large, but poorly quantified store of biomass carbon and biodiversity. Improving this information is hindered by a lack of recent forest inventories, which are necessary for calibrating earth observation data and for evaluating the relationship between carbon stocks and tree diversity in the context of forest conservation (for example, REDD+). Here, we present new inventory data from south-eastern Tanzania, comprising more than 15,000 trees at 25 locations located across a gradient of aboveground woody carbon (AGC...
Biomass Stock and Productivity of Primeval and Production Beech Forests: Greater Canopy Structural Diversity Promotes Productivity
06. September 2017
Abstract Our knowledge of temperate broadleaf forest ecology is based mostly on the study of production forests, which lack the terminal stage of forest development and have a simpler stand structure than old-growth and primeval forests. How primeval and production forests differ in net primary production (NPP) is not well known. In three primeval and three nearby production forests of European beech (Fagus sylvatica) in the Slovakian Carpathians, we measured aboveground biomass stocks (live and dead), aboveground NPP (ANPP) and parameters characterizing canopy structural...
Effects of an Experimental Water-level Drawdown on Methane Emissions from a Eutrophic Reservoir
05. September 2017
Abstract Reservoirs are a globally significant source of methane (CH4) to the atmosphere. However, emission rate estimates may be biased low due to inadequate monitoring during brief periods of elevated emission rates (that is, hot moments). Here we investigate CH4 bubbling (that is, ebullition) during periods of falling water levels in a eutrophic reservoir in the Midwestern USA. We hypothesized that periods of water-level decline trigger the release of CH4-rich bubbles from the sediments and that these emissions constitute a substantial fraction of the annual CH4...
Climate, Topography, and Canopy Chemistry Exert Hierarchical Control Over Soil N Cycling in a Neotropical Lowland Forest
01. September 2017
Abstract Nutrient availability varies substantially across lowland tropical forests and constrains their responses to global change. However, interactions among regional, landscape, and local controls of nutrient availability are poorly understood. In that context, we explored the effects of rainfall, topography, and canopy chemistry on nitrogen (N) cycling across the Osa Peninsula (Costa Rica). We sampled soils from catenas in regions receiving 3000 versus 5000 mm y−1 rainfall. In both regions, we sampled catenas starting on narrow, knife-edged ridges, and in the...
Latitudinal Patterns and Climatic Drivers of Leaf Litter Multiple Nutrients in Chinese Broad-Leaved Tree Species: Does Leaf Habit Matter?
01. September 2017
Abstract Leaf litter nutrients play a key role in nutrient cycling in forest ecosystems, yet our current knowledge of the ways in which climate controls leaf litter nutrients remains uncertain, especially for broad-leaved tree species in China. We performed a meta-analysis of geographic patterns of leaf litter nutrients of Chinese broad-leaved tree species in relation to climatic variables and leaf habit (as a discrete classification of tree species). We found that mean leaf litter carbon (C), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg...
Estimating Ecosystem Nitrogen Addition by a Leguminous Tree: A Mass Balance Approach Using a Woody Encroachment Chronosequence
01. September 2017
Abstract Difficulty in quantifying rates of biological N fixation (BNF), especially over long time scales, remains a major impediment to defining N budgets in many ecosystems. To estimate N additions from BNF, we applied a tree-scale N mass balance approach to a well-characterized chronosequence of woody legume (Prosopis glandulosa) encroachment into subtropical grasslands. We defined spatially discrete single Prosopis clusters (aged 28–99 years), and for each calculated BNF as the residual of: soil N (0–30 cm), above- and below-ground biomass N, wet and dry...
Carbon Dioxide and Methane Fluxes From Tree Stems, Coarse Woody Debris, and Soils in an Upland Temperate Forest
01. September 2017
Abstract Forest soils and canopies are major components of ecosystem CO2 and CH4 fluxes. In contrast, less is known about coarse woody debris and living tree stems, both of which function as active surfaces for CO2 and CH4 fluxes. We measured CO2 and CH4 fluxes from soils, coarse woody debris, and tree stems over the growing season in an upland temperate forest. Soils were CO2 sources (4.58 ± 2.46 µmol m−2 s−1, mean ± 1 SD) and net sinks of CH4 (−2.17 ± 1.60 nmol m−2 s−1). Coarse woody debris was a CO2 source...
An Ecohydrological Cellular Automata Model Investigation of Juniper Tree Encroachment in a Western North American Landscape
01. September 2017
Abstract Woody plant encroachment over the past 140 years has substantially changed grasslands in western North American. We studied encroachment of western juniper (Juniperus occidentalis var. occidentalis) into a previously mixed shrub–grassland site in central Oregon (USA) using a modified version of Cellular Automata Tree–Grass–Shrub Simulator (CATGraSS) ecohydrological model. We developed simple algorithms to simulate three encroachment factors (grazing, fire frequency reduction, and seed dispersal by herbivores) in CATGraSS. Local ecohydrological dynamics...
Invasive N-fixer Impacts on Litter Decomposition Driven by Changes to Soil Properties Not Litter Quality
01. September 2017
Abstract Invasive nitrogen (N)-fixing plants often fundamentally change key ecosystem functions, particularly N-cycling. However, the consequences of this for litter decomposition, and the mechanisms that underpin ecosystem responses, remain poorly understood. Moreover, few studies have determined how nutrient pools and fluxes shift as invader density increases and whether these effects persist following invader removal, despite the importance of this for understanding the timing and magnitude of invader impacts in ecosystems. We tested how the decomposition rates of...
Detecting Multiple States of Trophic Connectivity Between Mangroves and Salt Marshes
01. September 2017
Abstract The productivity gradient between adjacent habitats can fluctuate over time due to seasonal cycles and lead to both habitats being alternately subsidized. Although this process is well known for prey subsidies in stream-riparian forest ecotones, few studies are available for other systems or subsidy types. Moreover, the effects of transport intensity on this expected alternate subsidy exchange are still poorly understood. We assessed whether subsidy input and allochthonous carbon assimilation by resident benthic invertebrates alternated between adjacent...
Interactive Effects of Vegetation Type and Topographic Position on Nitrogen Availability and Loss in a Temperate Montane Ecosystem
01. September 2017
Abstract 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...

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