Variety Of Ecosystem Processes Research Articles

Targeting Sagebrush (Artemisia Spp.) Restoration Following Wildfire with Greater Sage-Grouse (Centrocercus Urophasianus) Nest Selection and Survival Models

Unprecedented conservation efforts for sagebrush (Artemisia spp.) ecosystems across the western United States have been catalyzed by risks from escalated wildfire activity that reduces habitat for sagebrush-obligate species such as Greater Sage-Grouse (Centrocercus urophasianus). However, post-fire restoration is challenged by spatial variation in ecosystem processes influencing resilience to disturbance and resistance to non-native invasive species, and spatial and temporal lags between slower sagebrush recovery processes and faster demographic responses of sage-grouse to loss of important habitat. Decision-support frameworks that account for these factors can help users strategically apply restoration efforts by predicting short and long-term ecological benefits of actions. Here, we developed a framework that strategically targets burned areas for restoration actions (e.g., seeding or planting sagebrush) that have the greatest potential to positively benefit sage-grouse populations through time. Specifically, we estimated sagebrush recovery following wildfire and risk of non-native annual grass invasion under four scenarios: passive recovery, grazing exclusion, active restoration with seeding, and active restoration with seedling transplants. We then applied spatial predictions of integrated nest site selection and survival models before wildfire, immediately following wildfire, and at 30 and 50 years post-wildfire based on each restoration scenario and measured changes in habitat. Application of this framework coupled with strategic planting designs aimed at developing patches of nesting habitat may help increase operational resilience for fire-impacted sagebrush ecosystems.

Disentangling the roles of plant functional diversity and plaint traits in regulating plant nitrogen accumulation and denitrification in freshwaters

Abstract There is a growing recognition that functional measures of diversity, based on quantification of functionally important species traits, are useful for explaining variation in ecosystem processes. However, the mechanisms linking functional diversity to different processes remain poorly understood, hindering development of a predictive framework for ecosystem functioning based on species traits. The current understanding of how the functional traits of aquatic plants (macrophytes) affect nitrogen (N) cycling by regulating microbial communities and their activity in freshwater habitats is particularly limited. Denitrifying bacteria are typically associated with the roots of both aquatic and terrestrial plants and denitrification is the main cause of loss of N from ecosystems. Disentangling the interplay between plants and microbial denitrifiers is key to understanding variation in rates of denitrification from local to landscape scales. In a mesocosm experiment, we varied the species richness (monocultures or two‐species mixtures) and composition of macrophytes. We quantified effects of both macrophyte functional diversity, quantified as functional trait dissimilarity, and functional trait composition, quantified as community weighted mean trait values, on N removal in wetlands. We used structural equation modelling to disentangle the direct and indirect influences of traits on N accumulation in plant biomass, denitrification activity and abundance of key bacterial denitrification genes (nirS and nirK). Both functional diversity and functional trait composition regulated N removal, explaining 70%–94% variation in the underlying ecosystem processes. Increased macrophyte functional diversity increased plant N accumulation, and indirectly enhanced denitrification by increasing denitrification gene abundance. Among traits, greater plant relative growth rates, specific leaf area and above‐ground biomass increased plant N accumulation. Denitrification activity increased with increasing below‐ground biomass but decreased with increasing root diameter. These findings improve our understanding of N removal in freshwater wetlands dominated by macrophytes, and have broad ecological implications for wetland management targeting enhanced ecosystem services. Our results highlight the potential for optimizing denitrification and plant N accumulation in wetlands and thereby improving water purification by increasing macrophyte functional diversity and ensuring the presence of key traits in macrophyte assemblages. A free Plain Language Summary can be found within the Supporting Information of this article.

Above‐ground net primary productivity in regenerating seasonally dry tropical forest: Contributions of rainfall, forest age and soil

Abstract Identifying factors controlling forest productivity is critical to understanding forest‐climate change feedbacks, modelling vegetation dynamics and carbon finance schemes. However, little research has focused on productivity in regenerating tropical forests which are expanding in their fraction of global area have an order of magnitude larger carbon uptake rates relative to older forest. We examined above‐ground net primary productivity (ANPP) and its components (wood production and litterfall) over 10 years in forest plots that vary in successional age, soil characteristics and species composition using band dendrometers and litterfall traps in regenerating seasonally dry tropical forests in northwestern Costa Rica. We show that the components of ANPP are differentially driven by age and annual rainfall and that local soil variation is important. Total ANPP was explained by a combination of age, annual rainfall and soil variation. Wood production comprised 35% of ANPP on average across sites and years, and was explained by annual rainfall but not forest age. Conversely, litterfall increased with forest age and soil fertility yet was not affected by annual rainfall. In this region, edaphic variability is highly correlated with plant community composition. Thus, variation in ecosystem processes explained by soil may also be partially explained by species composition. These results suggest that future changes in annual rainfall can alter the secondary forest carbon sink, but this effect will be buffered by the litterfall flux which varies little among years. In determining the long‐term strength of the secondary forest carbon sink, both rainfall and forest age will be critical variables to track. We also conclude that detailed understanding of local site variation in soils and plant community may be required to accurately predict the impact of changing rainfall on forest carbon uptake. Synthesis. We show that in seasonally dry tropical forest, annual rainfall has a positive relationship with the growth of above‐ground woody tissues of trees and that droughts lead to significant reductions in above‐ground productivity. These results provide evidence for climate change—carbon cycle feedbacks in the seasonal tropics and highlight the value of longitudinal data on forest regeneration.

Aligning biodiversity conservation and ecosystem services in spatial planning: Focus on ecosystem processes

Although the consideration of socio-economic demands with biodiversity conservation is now high on the environmental policy agenda, it is not yet standard practice in spatial planning. This is argued to be related, among others, to a lack of awareness among stakeholders and practitioners of the underpinning role of ecosystem functioning and biodiversity to support human well-being. Meanwhile, there is mounting critique on the absolute focus of biodiversity conservation on static properties such as species and habitats. The establishment of more ecologically sensible objectives that include ecosystem processes besides species and habitats is put forward as a more effective way of environmental conservation. Methodological approaches increasingly consider ecosystem processes. However, the processes that are included mostly relate to aspects of biodiversity such as dispersal and productivity, and rarely do they include abiotic mechanisms that underlie biodiversity. We here report on the development of a method that integrates two principles which we identify as key to advance the integration of ecosystem services with biodiversity conservation in planning practice: (1) consider the variety of ecosystem processes, biotic as well as abiotic, that support biodiversity and ecosystem services, and (2) link the ecosystem processes to biodiversity and to socio-economic benefits to identify the common ground between seemingly conflicting objectives. The methodology uses a stepwise approach and is based on an extensive review of available knowledge on ecosystem functioning, expert consultation and stakeholder involvement. We illustrate how the methodology supports the setting of strategic goals to accomplish a healthy coastal ecosystem in Belgium, and exemplify how this may affect spatial plans. The aim of this paper is to demonstrate how including processes opens opportunities to align biodiversity and ecosystem services and how this increases chances to provide long-term benefits for biodiversity and human well-being. The paper may provide inspiration to advance current spatial planning approaches.

Experimental Evidence that Stochasticity Contributes to Bacterial Composition and Functioning in a Decomposer Community.

Stochasticity emerging from random differences in replication, death, mutation, and dispersal is thought to alter the composition of ecological communities. However, the importance of stochastic effects remains somewhat speculative because stochasticity is not directly measured but is instead inferred from unexplained variations in beta-diversity. Here, we performed a field experiment to more directly disentangle the role of stochastic processes, environmental selection, and dispersal in the composition and functioning of a natural bacterial decomposer community in the field. To increase our ability to detect these effects, we reduced initial biological and environmental heterogeneity using replicate nylon litterbags in the field. We then applied two treatments: ambient/added precipitation and bacterial and fungal dispersal using "open" litterbags (made from 18.0-μm-pore-size mesh) ("open bacterial dispersal") versus bacterial and fungal dispersal using "closed" litterbags (made from 22.0-μm-pore-size mesh) ("closed bacterial dispersal"). After 5 months, we assayed composition and functioning by the use of three subsamples from each litterbag to disentangle stochastic effects from residual variation. Our results indicate that stochasticity via ecological drift can contribute to beta-diversity in bacterial communities. However, residual variation, which had previously been included in stochasticity estimates, accounted for more than four times as much variability. At the same time, stochastic effects on beta-diversity were not attenuated at the functional level, as measured by genetic functional potential and extracellular enzyme activity. Finally, dispersal was found to interact with precipitation availability to influence the degree to which stochasticity contributed to functional variation. Together, our results demonstrate that the ability to quantify stochastic processes is key to understanding microbial diversity and its role in ecosystem functioning.IMPORTANCE Randomness can alter the diversity and composition of ecological communities. Such stochasticity may therefore obscure the relationship between the environment and community composition and hinder our ability to predict the relationship between biodiversity and ecosystem functioning. This study investigated the role of stochastic processes, environmental selection, and dispersal in microbial composition and its functioning on an intact field community. To do this, we used a controlled and replicated experiment that was similar to that used to study population genetics in the laboratory. Our study showed that, while the stochastic effects on taxonomic composition are smaller than expected, the degree to which stochasticity contributes to variability in ecosystem processes may be much higher than previously assumed.

Long-term continuity in land surface phenology measurements: A comparative assessment of the MODIS land cover dynamics and VIIRS land surface phenology products

Vegetation phenology contributes to, and is diagnostic of, seasonal variation in ecosystem processes and exerts important controls on land-atmosphere exchanges of carbon, water, and energy. Satellite remote sensing provides a valuable source of data for monitoring the phenology of terrestrial ecosystems and has been widely used to map geographic and interannual variation in land surface phenology (LSP) over large areas. The Visible Infrared Imaging Radiometer Suite (VIIRS) land surface phenology product provides global data sets characterizing the annual LSP of terrestrial ecosystems, and is designed to support long-term continuity of LSP measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS). We used data from VIIRS and MODIS to evaluate the agreement and characterize the similarities and differences between LSP data from each instrument. Specifically, we compare data from the Collection 6 MODIS Land Cover Dynamics (LCD) product with data from the newly developed VIIRS LSP product over the most common land cover types in North America. To do this, we assessed the overall agreement between time series of vegetation indices from VIIRS and MODIS, evaluated the correspondence between retrieved phenometrics from each instrument, and analyzed sources of differences between phenometrics from the each product. As part of this analysis, we also compared phenometrics from MODIS and VIIRS with phenometrics derived from Landsat Analysis Ready Data and PhenoCam time series. Results show that two-band enhanced vegetation index (EVI2) values from VIIRS and MODIS are similar (R2 > 0.81; root mean square deviation < 0.062), but that VIIRS EVI2 time series show more high frequency variation than time series from MODIS. Further, even though the VIIRS and MODIS products are generated using different instruments and algorithms, phenometrics from each product are similar and show only minor differences within and across land cover types. Systematic differences between phenometrics from the two products were generally less than one week (absolute bias 4.8 ± 3.0 days), and RMSDs were less than two weeks for most phenometrics across different land cover classes (10.7 ± 4.3 days). Comparison of VIIRS and MODIS LSP data with corresponding metrics estimated from Landsat and PhenoCam data consistently showed high agreement among the data sets. Overall, results from this analysis indicate that the VIIRS LSP product provides excellent continuity with the MODIS record. However, studies attempting to create high-fidelity long-term LSP time series by merging these products should exploit the overlap period of MODIS and VIIRS to estimate land cover-specific corrections for modest systematic bias in the MODIS LCD product relative to the VIIRS LSP product.

Feedbacks link ecosystem ecology and evolution across spatial and temporal scales: Empirical evidence and future directions

Abstract Unifying ecosystem ecology and evolutionary biology promises a more complete understanding of the processes that link different levels of biological organization across space and time. Feedbacks across levels of organization link theory associated with eco‐evolutionary dynamics, niche construction and the geographic mosaic theory of co‐evolution. We describe a conceptual model, which builds upon previous work that shows how feedback among different levels of biological organization can link ecosystem and evolutionary processes over space and time. We provide empirical examples across terrestrial and aquatic systems that indicate broad generality of the conceptual framework and discuss its macroevolutionary consequences. Our conceptual model is based on three premises: genetically based species interactions can vary spatially and temporally from positive to neutral (i.e. no net feedback) to negative and drive evolutionary change; this evolutionary change can drive divergence in niche construction and ecosystem function; and lastly, such ecosystem‐level effects can reinforce spatiotemporal variation in evolutionary dynamics. Just as evolution can alter ecosystem function locally and across the landscape differently, variation in ecosystem processes can drive evolution locally and across the landscape differently. By highlighting our current knowledge of eco‐evolutionary feedbacks in ecosystems, as well as information gaps, we provide a foundation for understanding the interplay between biodiversity and ecosystem function through an eco‐evolutionary lens. A plain language summary is available for this article.

Automated Estimation of Standing Dead Tree Volume Using Voxelized Terrestrial Lidar Data

Standing dead trees (SDTs) are an important forest component and impact a variety of ecosystem processes, yet the carbon pool dynamics of SDTs are poorly constrained in terrestrial carbon cycling models. The ability to model wood decay and carbon cycling in relation to detectable changes in tree structure and volume over time would greatly improve such models. The specific objectives of this paper were to: 1) develop an automated SDT volume estimation algorithm providing accurate volume estimates for trees scanned with terrestrial lidar in dense forests; 2) assess the volume estimation algorithm’s accuracy with respect to large and small branches; and 3) characterize the impact of occlusion with regards to volume estimation accuracy and the ability of the algorithm to mitigate challenges posed by lower quality point clouds. A voxel-based volume estimation algorithm, “TreeVolX,” was developed and incorporates several methods designed to robustly process point clouds of varying quality levels. The algorithm operates on horizontal voxel slices by segmenting the slice into distinct branch or stem sections then applying an adaptive contour interpolation and interior filling process to create solid reconstructed tree models. The concept of vertical point cloud resampling is introduced to facilitate the modeling of lower quality point clouds with a small voxel size. TreeVolX estimated large and small branch volume with a root-mean-square error of 7.3% and 13.8%, respectively, and the adaptive contour interpolation was shown to significantly reduce volume estimation errors in the case of significantly occluded point clouds.

Incorporation of Acoustic Sensors on a Coastal Ocean Monitoring Platform for Measurements of Biological Activity

AbstractOcean observing stations have mainly focused on data collection of physical parameters measured in the ocean and atmosphere and also, to some extent, of biogeochemical parameters. Robust sensors capable of measuring biological data reflective of higher tropic level function at the same time scales as other parameters are not yet commonly incorporated into the sensor array used on observing platforms. In this project, we reengineered a coastal ocean observatory to include two hydrophones for this purpose. One hydrophone (HTI 96-MIN) was used to record ambient acoustic signals of fish reproductive sounds, and a second hydrophone (Vemco VR2C) was used to receive transmissions from acoustic tags implanted in fishes. This project demonstrates that it is possible at a regional ocean observing station to collect data on biological-physical processes at the same time scales over long periods and on a cost-effective basis. This will allow a better understanding of natural variability in ecosystem processes and potential impacts on these from anthropogenic sources and climate change. Technical details of the reengineering methods used to make the station operational and URLs of data tables and archives are provided.

Temporal and Spatial Variation in Peatland Carbon Cycling and Implications for Interpreting Responses of an Ecosystem‐Scale Warming Experiment

Core Ideas We compared spatial vs. temporal variation in C cycle processes and drivers in a bog. The bog was indistinguishable as a C source or sink because of high spatial variation. Sensitive C cycle parameters in the model differed under ambient vs. warming scenarios. Characterizing pretreatment variability is necessary when interpreting warming effects. We are conducting a large‐scale, long‐term climate change response experiment in an ombrotrophic peat bog in Minnesota to evaluate the effects of warming and elevated CO2 on ecosystem processes using empirical and modeling approaches. To better frame future assessments of peatland responses to climate change, we characterized and compared spatial vs. temporal variation in measured C cycle processes and their environmental drivers. We also conducted a sensitivity analysis of a peatland C model to identify how variation in ecosystem parameters contributes to model prediction uncertainty. High spatial variability in C cycle processes resulted in the inability to determine if the bog was a C source or sink, as the 95% confidence interval ranged from a source of 50 g C m–2 yr–1 to a sink of 67 g C m–2 yr–1. Model sensitivity analysis also identified that spatial variation in tree and shrub photosynthesis, allocation characteristics, and maintenance respiration all contributed to large variations in the pretreatment estimates of net C balance. Variation in ecosystem processes can be more thoroughly characterized if more measurements are collected for parameters that are highly variable over space and time, and especially if those measurements encompass environmental gradients that may be driving the spatial and temporal variation (e.g., hummock vs. hollow microtopographies, and wet vs. dry years). Together, the coupled modeling and empirical approaches indicate that variability in C cycle processes and their drivers must be taken into account when interpreting the significance of experimental warming and elevated CO2 treatments.

Ecosystem Structure and Dynamics in the North Pacific Subtropical Gyre: New Views of an Old Ocean

The North Pacific Subtropical Gyre (NPSG) is one of the largest biomes on Earth. It has a semi-enclosed surface area of about 2 × 107 km2 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.

Water quality change in the Mississippi River, including a warming river, explains decades of wetland plant biomass change within its Balize delta

Ecosystem properties of riverine wetlands are known for high inter-annual variability. This multi-decadal study within the wetland complex of the Mississippi River’s Balize Delta, USA assesses how river parameters (temperature, discharge, and sediment load) impact wetland plant biomass over time and space. The Mississippi River’s annual temperature has increased 0.9°C/decade, while discharge and sediment load has varied without trend over the same period. End-of-season herbaceous biomass increased 14g/m2/year between 1988 and 2008, extrapolating to large (m-ton) area-wide increases. The river’s temperature, discharge and sediment impacted the Delta’s biomass in two ways: the increase in temperature had a positive impact on the growing season length which increased biomass; whereas discharge and load had negative impacts affecting the inter-annual variation without a temporal trend. The results explain natural variability in ecosystem processes in a dynamic deltaic system and likely trace a signal related to both climate warming and land use change within the drainage of the Mississippi River. The discovered decadal increase in herbaceous biomass has implications on carbon storage in the inshore and offshore receiving basins of the world’s riverine wetlands experiencing longer growing seasons.

Leaf Litter Mixtures Alter Microbial Community Development: Mechanisms for Non-Additive Effects in Litter Decomposition

To what extent microbial community composition can explain variability in ecosystem processes remains an open question in ecology. Microbial decomposer communities can change during litter decomposition due to biotic interactions and shifting substrate availability. Though relative abundance of decomposers may change due to mixing leaf litter, linking these shifts to the non-additive patterns often recorded in mixed species litter decomposition rates has been elusive, and links community composition to ecosystem function. We extracted phospholipid fatty acids (PLFAs) from single species and mixed species leaf litterbags after 10 and 27 months of decomposition in a mixed conifer forest. Total PLFA concentrations were 70% higher on litter mixtures than single litter types after 10 months, but were only 20% higher after 27 months. Similarly, fungal-to-bacterial ratios differed between mixed and single litter types after 10 months of decomposition, but equalized over time. Microbial community composition, as indicated by principal components analyses, differed due to both litter mixing and stage of litter decomposition. PLFA biomarkers a15∶0 and cy17∶0, which indicate gram-positive and gram-negative bacteria respectively, in particular drove these shifts. Total PLFA correlated significantly with single litter mass loss early in decomposition but not at later stages. We conclude that litter mixing alters microbial community development, which can contribute to synergisms in litter decomposition. These findings advance our understanding of how changing forest biodiversity can alter microbial communities and the ecosystem processes they mediate.

Linking water vapor and CO2 exchange from a perennial bioenergy crop on a drained organic soil in eastern Finland

With the aim of addressing the broader issues of land use, climate change and energy crisis, eddy covariance measurements of energy and CO2 exchange from a bioenergy crop (reed canary grass, Phalaris arundinaceae, L.) cultivated on a drained organic soil (a cutover peatland) in eastern Finland were initiated in the spring of 2004. Based on the climatically diverse dataset from the 2004 to 2010 period, the objectives of the work presented here are to characterize the interannual variability in water vapor exchange and to understand the linkage between energy and CO2 exchange from this perennial crop during two extreme growing seasons. Correcting the measured soil heat flux by accounting for the change in heat storage above the heat flux plates helped close the energy balance at this site. Interannual variability in ecosystem processes of energy and CO2 exchange were attributed primarily to marked differences in the amount and distribution of seasonal precipitation. Differences in the phonological development of the crop during seasons with contrasting climatic conditions were reflected in the normalized difference vegetation index (NDVI) estimated from the radiation instruments installed on the tower. Wet years were characterized by an even distribution of seasonal precipitation, low to moderate air and soil temperatures, lower solar and net radiation intensities (owing to reduced number of bright sunshine hours and therefore, higher amount of diffuse sky radiation), moderate to saturated soil moisture conditions and lower vapor pressure deficit. These climatic conditions resulted in high bulk surface conductance (gs), high evapotranspiration (ET) and low sensible heat flux with a peak seasonal Bowen ratio (β=0.1). These conditions were favourable for a high uptake of atmospheric CO2. Dry years, on the contrary, were marked by long dry spells during important phases of crop growth, climatic and soil moisture stress leading to high evaporative demand, low gs values, reduced evapotranspiration and high sensible heat flux (β=0.3–0.4). On a seasonal basis, the ET losses during a dry year were 13% lower compared to those during a wet year. The corresponding reduction in gross ecosystem productivity (GEP), however, was to the extent of 21%. Owing to the ability of this perennial crop to sequester large amounts of atmospheric carbon into its above- and below-ground biomass, the water use efficiency (defined as the slope of the linear regression of monthly values of GEP against ET) of this cultivation system was found to be 9.1g CO2 per kg of H2O lost as ET. The results stemming from this work further support our earlier conclusions that this bioenergy system is a suitable land use option on drained and abandoned cutover peatlands with a high potential for offsetting CO2 load to the atmosphere.

Trophic and functional cascades in tropical versus temperate aquatic microcosms

Inverse trophic cascades are a well explored and common consequence of the local depletion or extinction of top predators in natural ecosystems. Despite a large body of research, the cascading effects of predator removal on ecosystem functions are not as well understood. Developing microcosm experiments, we explored food web changes in trophic structure and ecosystem functioning following biomass removal of top predators in representative temperate and tropical rock pool communities that contained similar assemblages of zooplankton and benthic invertebrates. We observed changes in species abundances following predator removal in both temperate and tropical communities, in line with expected inverse effects of a trophic cascade, where predation release benefits the predator’s preys and competitors and impacts the preys of the latter. We also observed several changes at the community and ecosystem levels including a decrease in total abundance and mean trophic level of the community, and changes in chlorophyll-a and total dissolved particles. Our results also showed an increase in variability of both community and ecosystem processes following the removal of predators. These results illustrate how predator removal can lead to inverse trophic cascades both in structural and functioning properties, and can increase variability of ecosystem processes. Although observed patterns were consistent between tropical and temperate communities following an inverse cascade pattern, changes were more pronounced in the temperate community. Therefore, aquatic food webs may have inherent traits that condition ecosystem responses to changes in top-down trophic control and render some aquatic ecosystems especially sensitive to the removals of top predators.

Forest annual carbon cost: comment

Forest annual carbon cost: comment

Variation in decomposition rates in the fynbos biome, South Africa: the role of plant species and plant stoichiometry

Previous studies in the fynbos biome of the Western Cape, South Africa, have suggested that biological decomposition rates in the fynbos vegetation type, on poor soils, may be so low that fire is the main factor contributing to litter breakdown and nutrient release. However, the fynbos biome also comprises vegetation types on more fertile soils, such as the renosterveld. The latter is defined by the shrub Elytropappus rhinocerotis, while the shrub Galenia africana may become dominant in overgrazed areas. We examined decomposition of litter of these two species and the geophyte Watsonia borbonica in patches of renosterveld in an agricultural landscape. In particular, we sought to understand how plant species identity affects litter decomposition rates, especially through variation in litter stoichiometry. Decomposition (organic matter mass loss) varied greatly among the species, and was related to litter N and P content. G. africana, with highest nutrient content, lost 65% of its original mass after 180 days, while E. rhinocerotis had lost ca. 30%, and the very nutrient poor W. borbonica <10%. Litter placed under G. africana decomposed slightly faster than when placed under E. rhinocerotis. Over the course of the experiment, G. africana and E. rhinocerotis lost N and P, while W. borbonica showed strong accumulation of these elements. Decomposition rates of G. africana and E. rhinocerotis were substantially higher than those previously reported from fynbos vegetation, and variation among the species investigated was considerable. Our results suggest that fire may not always be the main factor contributing to litter breakdown and nutrient release in the fynbos biome. Thus, biological decomposition has likely been underestimated and, along with small-scale variation in ecosystem processes, would repay further study.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-010-1753-7) contains supplementary material, which is available to authorized users.

Biodiversity of Cold Seep Ecosystems Along the European Margins

During the European Commission's Framework Six Programme, HERMES, we investigated three main areas along the European margin, each characterized by the presence of seep-related structures exhibiting different intensity of activity and biological diversity. These areas are: (1) the Nordic margin with the Hakon Mosby mud volcano and many pockmarks, (2) the Gulf of Cadiz, and (3) the eastern Mediterranean with its hundreds of mud volcanoes and brine pool structures. One of the main goals of the HERMES project was to unravel the biodiversity associated with these seep-associated ecosystems, and to understand their driving forces and functions, using an integrated approach. Several multidisciplinary research cruises to these three areas provided evidence of high variability in ecosystem processes and associated biodiversity at different spatial scales, illustrating the hotspot nature of these deep water systems.

Functional identity is more important than diversity in influencing ecosystem processes in a temperate native grassland

Summary Experimental studies have provided significant knowledge of how biodiversity can influence ecosystem processes. However, there is a growing need to relate these findings to natural communities. Here we identify two major hypotheses for how communities may influence ecosystem processes: the ‘diversity hypothesis’ (the diversity of organisms in a community influences ecosystem processes through mechanisms such as complementary resource use), and the ‘mass ratio hypothesis’ (ecosystem processes are determined overwhelmingly by the functional traits of the dominant species). We then test which of these two hypotheses best explain variation in ecosystem properties and processes (biomass pools and fluxes, water use, light interception) in a temperate native grassland. We do this by applying various measures of diversity, functional diversity, and functional identity, whose significant relations with ecosystem processes would support either of the competing hypotheses. Mean trait values best explained variation in five of the eight ecosystem processes examined, supporting Grime's mass ratio hypothesis, which proposes that the functional identities of the dominant species largely determine ecosystem processes. Multi‐trait functional diversity indices also explained large amounts of variation in ecosystem processes, while only weak relationships were observed between species richness and ecosystem processes. To explore the mechanistic interactions between variables, we developed structural equation models (SEMs), which indicated that many of the community diversity and trait properties significantly influenced ecosystem processes, even after accounting for co‐varying biotic/abiotic factors. Synthesis. Our study is one of the first explicit comparisons of the ‘diversity’ and ‘mass ratio’ hypotheses, and our results most strongly support the mass ratio hypothesis, that is, the traits of the dominant species most influenced the ecosystem properties and processes examined. Our results suggest that the management of communities for the maintenance of ecosystem processes should focus on species dominance hierarchies.

Visible and invisible effects of hurricanes on forest ecosystems: an international review

Abstract Hurricanes have visible and invisible effects on forests. The visible effects are dramatic, noticeable over the short‐term and relatively well documented in the literature. Invisible effects are less understood as they require well‐focused research both in the short‐ and long‐term time scales. This review of the literature on hurricane effects focuses on the Neotropics and the temperate zone of North America. The material is organized according to a heuristic model that distinguishes between immediate effects (0 to 3 years), immediate responses (0 to 20 years), trajectories of responses (0 to 100 years) and long‐term legacies (&gt;100 years). It is suggested that the ecological role of hurricanes involves six principal effects: 1. they change the ecological space available to organisms; 2. they set organisms in motion; 3. they increase the heterogeneity of the landscape and the variability in ecosystem processes; 4. they rejuvenate the landscape and its ecosystems and redirect succession; 5. they shape forest structure, influence their species composition and diversity and regulate their function; and 6. they induce evolutionary change through natural selection and ecological creativity through self‐organization. A new approach to hurricane research will study hurricanes at the same scale at which they operate (i.e., across latitudes and longitudes and over disturbed and undisturbed landscapes). This research will require networks of observation platforms located along expected hurricane paths to facilitate forest structure and functioning observations across gradients of hurricane frequency and intensity. This research will also require use of remote sensing and automated wireless technology, hardened to survive hurricane‐strength winds and floods to assure real time measurements of the characteristics of hurricanes and ecosystem responses. No progress will be forthcoming in the understanding of hurricane effects if we do not learn to quantify objectively the energy dissipation of hurricanes on the full grid of affected forests as the hurricane passes over a landscape.