Large-scale Ecosystem Processes Research Articles

In situ seasonal patterns of root auxin concentrations and meristem length in an arctic sedge.

Seasonal dynamics of root growth play an important role in large-scale ecosystem processes; they are largely governed by growth regulatory compounds and influenced by environmental conditions. Yet, our knowledge about physiological drivers of root growth is mostly limited to laboratory-based studies on model plant species. We sampled root tips of Eriophorum vaginatum and analyzed their auxin concentrations and meristem lengths biweekly over a growing season in situ in a subarctic peatland, both in surface soil and at the permafrost thawfront. Auxin concentrations were almost five times higher in surface than in thawfront soils and increased over the season, especially at the thawfront. Surprisingly, meristem length showed an opposite pattern and was almost double in thawfront compared with surface soils. Meristem length increased from peak to late season in the surface soils but decreased at the thawfront. Our study of in situ seasonal dynamics in root physiological parameters illustrates the potential for physiological methods to be applied in ecological studies and emphasizes the importance of in situ measurements. The strong effect of root location and the unexpected opposite patterns of meristem length and auxin concentrations likely show that auxin actively governs root growth to ensure a high potential for nutrient uptake at the thawfront.

Consistency Analysis of Multi-Source Remote Sensing Land Cover Products in Arid Regions—A Case Study of Xinjiang

Arid regions are considered to be among the most ecologically fragile and highly sensitive to environmental change globally, and land use and land cover conditions in the region directly influence large-scale ecosystem processes. Currently, thanks to diverse remote sensing platforms, geographers have developed an array of land cover products. However, there are differences between these products due to variations in spatio-temporal resolutions. In this context, assessing the accuracy and consistency of different land cover products is crucial for rationalizing the selection of land cover products to study global or regional environmental changes. In this study, Xinjiang Uygur Autonomous Region (XUAR) is taken as the study area, and the consistency and performance (type area deviation, spatial consistency, accuracy assessment, and other indexes) of the five land cover products (GlobeLand30, FROM_GLC30, CLCD, GLC_FCS30, and ESRI) were compared and analyzed. The results of the study show that (1) the GlobeLand30 product has the highest overall accuracy in the study area, with an overall accuracy of 84.06%, followed by ESA with 75.57%, while CLCD has the lowest overall accuracy of 70.05%. (2) The consistency between GlobeLand30 and CLCD (area correlation coefficient of 0.99) was higher than that among the other products. (3) Among the five products, the highest consistency was found for water bodies and permanent snow and ice, followed by bare land. In contrast, the consistency of these five products for grassland and forest was relatively low. (4) The full-consistency area accounts for 49.01% of the total study area. They were mainly distributed in areas with relatively homogeneous land cover types, such as the north and south of the Tianshan Mountains, which are dominated by bare land and cropland. In contrast, areas of inconsistency make up only 0.03% and are mostly found in heterogeneous areas, like the transitional zones with mixed land cover types in the Altai Mountains and Tianshan Mountains, or in areas with complex terrain. In terms of meeting practical user needs, GlobeLand30 offers the best comprehensive performance. GLC_FCS30 is more suitable for studies related to forests, while FROM_GLC30 and ESRI demonstrate greater advantages in identifying permanent ice and snow, whereas the performance of CLCD is generally average.

Consistency Analysis and Accuracy Assessment of Three Global Ten-Meter Land Cover Products in Rocky Desertification Region—A Case Study of Southwest China

Rocky desertification is one of the most critical ecological and environmental problems in areas underlain by carbonate rocks globally. Land cover and land use in the region affects large-scale ecosystem processes on a global scale, and many Earth system models rely on accurate land cover information. Therefore, it is important to evaluate current global land cover products and to understand the differences between them, and the findings of these studies can provide guidance to different researchers when using or making land cover products. Whereas there are many studies on the assessment of coarser resolution land cover products, there are few studies on the assessment of higher resolution land cover products (10 m). In order to provide guidance for users of 10 m data, this paper uses the rock deserted southwest region of China as the experimental area. We analyzed the consistency and accuracy of the FROM-GLC, ESA WorldCover 10 and ESRI products using spatial pattern consistency, absolute accuracy assessment of three validation samples, and analyzed their intrinsic relationships among classification systems, classification methods, and validation samples. The results show that (1) the overall accuracy of the FROM-GLC product is the highest, ranging from 49.47 to 62.42%; followed by the overall accuracy of the ESA product, ranging from 45.13 to 64.50%; and the overall accuracy of the ESRI product is the lowest, between 39.03 and 61.94%. (2) The consistency between FROM-GLC and ESA is higher than the consistency between other products, with an area correlation coefficient of 0.94. Analysis of the spatial consistency of the three products shows that the proportion of perfectly consistent areas is low at 44.89%, mainly in areas with low surface heterogeneity and more homogeneous cover types. (3) Across the study area, the main land cover types such as forest and water bodies were the most consistent across the three product species, while the grassland, shrubland, and bareland were lower. All products showed high accuracy in homogeneous areas, with local accuracy varied in other areas, especially at high altitudes in the central and western regions. Therefore, land cover users cannot use these products directly when conducting relevant studies in rocky desertification areas, as their use may introduce serious errors.

Landscape-scale characterization of Arctic tundra vegetation composition, structure, and function with a multi-sensor unoccupied aerial system

The Arctic is experiencing some of the most rapid climate change on Earth, with strong impacts on tundra ecosystems that are characterized by high land-surface and vegetation heterogeneity. Previous studies have explored this complexity using satellite remote sensing, however these typically coarse spatial resolution data have generally missed sub-pixel heterogeneity, leaving critical gaps in our understanding of tundra vegetation dynamics from the community to landscape scales. To address these gaps, we collected very high-resolution (1–5 cm) optical, structural, and thermal data at three low-Arctic tundra sites on the Seward Peninsula, Alaska, using a multi-sensor unoccupied aerial system (UAS). We examined the application of these data to studying tundra vegetation dynamics, by quantifying (a) canopy height and thermoregulation (leaf–air temperature) of representative plant functional types (PFTs), (b) fine-scale patterns of vegetation composition across landscapes, and (c) impacts of fine-scale vegetation composition on landscape-scale variation of canopy height and thermoregulation. Our results show that deciduous tall shrubs (those that can potentially grow >2 m) had a strong cooling effect, with canopy temperatures significantly lower than local air temperatures and other PFTs. Increased cover of tall shrubs also had the potential to reduce the cover of low-stature PFTs across the landscape, potentially associated with their closed canopy (i.e. increased light competition) and strong thermoregulation. To understand the connections between fine-scale vegetation composition and large-scale ecosystem processes, we produced a random forest model which showed that fine-scale PFT composition accounted for 86.8% and 74.2% of the landscape-scale variation in canopy height and thermoregulation, respectively. These findings highlight the importance of spatially detailed characterization of tundra PFTs to improve our ecological understanding and model representation of tundra vegetation, also transcend our study to show the need for continued collection of similar datasets to better understand the impacts of surface heterogeneity on the mapping and modeling of tundra ecosystem dynamics, as well as assist with conservation management and biodiversity monitoring strategies.

Tracking the resource pulse: Movement responses of fish to dynamic floodplain habitat in a tropical river.

Natural river floodplains are among the Earth's most biologically diverse and productive ecosystems but face a range of critical threats due to human disturbance. Understanding the ecological processes that support biodiversity and productivity in floodplain rivers is essential for their future protection and rehabilitation. Fish assemblage structure on tropical river floodplains is widely considered to be driven by dispersal limitation during the wet season and by environmental filtering and interspecific interactions during the dry season. However, the individual-level movement behaviours (e.g. site attachment, nomadism, homing) that regulate dispersal of fish on floodplains are poorly understood. We combined radiotelemetry and remote sensing to examine the movement behaviour of two large-bodied fishes (barramundi Lates calcarifer, forktail catfish Neoarius leptaspis) over the flood cycle in a tropical river-floodplain system in northern Australia to: (a) quantify movement responses in relation to dynamic habitat resources at a landscape scale; and (b) determine the extent of spatial 'reshuffling' of individual fish following the wet season. Both species altered their behaviour rapidly in response to changes in the availability and distribution of aquatic habitat, with most individuals undertaking extensive movements (up to ~27km from the tagging location) on the inundated floodplain during the wet season. Although there was considerable individual variation in movement patterns, overall barramundi distributions closely tracked the extent of floodplain primary productivity, whereas catfish distributions were most closely associated with the extent of flooded area. Most individuals of both species exhibited homing back to previously occupied dry season refugia during the wet-to-dry transition, even though other potential refugia were available in closer proximity to wet season activity areas. We postulate that homing behaviour modulates temporal variation in fish assemblage composition and abundance and limits the transfer of aquatic-derived energy and nutrients into terrestrial food webs by reducing fish mortality on drying floodplains. Our study demonstrates the importance of quantifying individual-level behaviour across the three stages of dispersal (emigration, inter-patch movement, immigration) for our understanding of how animal movement influences energetic subsidies and other large-scale ecosystem processes.

Rainfall and its possible hysteresis effect on the proportional cover of tropical tidal-wetland mangroves and saltmarsh–saltpans

Mangrove–saltmarsh tidal wetlands are highly dynamic ecosystems, responding and adapting to climate and physical conditions at all spatial and temporal scales. Knowledge of the large-scale ecosystem processes involved and how they might be influenced by climate variables is highly relevant today. For tidal-wetland sites well within the latitudinal range of the mostly tropical mangrove communities, we confirm that average annual rainfall influences vegetative cover, as well as species composition and biomass of tidal wetlands. On the basis of 205 largely unmodified, tropical and subtropical estuaries of northern Australia, a sigmoidal relationship, with a centroid inflection point ~1368mm, was derived between rainfall and the relative amounts of high-biomass mangroves and low-biomass saltmarsh–saltpan vegetation. The presence and probability of observed combinations of these community types were quantified using the wetland cover index, which is the ratio of total mangrove area to that of mangroves plus intertidal saltmarsh and saltpans. Accordingly, periodic changes in rainfall trends are likely manifest as either encroachment or dieback of mangroves along the ecotones separating them from tidal saltmarsh–saltpans. Presented is a new conceptual framework and model that describes how such ecosystem-scale processes take place in tropical and subtropical tidal wetlands.

Context-dependent consumer control in New England tidal wetlands.

Recent studies in coastal wetlands have indicated that consumers may play an important role in regulating large-scale ecosystem processes. Predator removal experiments have shown significant differences in above-ground biomass production in the presence of higher level consumers, or predators. These results indicate that predators play an important role in regulating biomass production, but the extent to which this regulation impacts additional ecosystem functions, such as nutrient cycling and organic matter accumulation, is unclear. This study evaluated the impact that consumers have on large-scale ecosystem processes within southern New England tidal wetlands and contributes to the general understanding of trophic control in these systems. I established enclosure cages within three coastal wetlands and manipulated the presence of green crab predators to assess how trophic interactions affect ecosystem functions. Findings suggest that although these consumers may exert some top-down effects, other environmental factors, such as other consumers not studied here or bottom-up interactions, may variably play a larger role in the maintenance of ecosystem processes within the region. These results indicate that the loss of top-down control as an important mechanism influencing ecosystem functions may not hold for all wetlands along the full extent of the New England coastline.

Flowers increase ecosystem biodiversity in Midwestern prairies

Loss of biodiversity due to anthropogenic factors, such as climate change and habitat conversion or loss, is among the largest problems affecting many native ecosystems today. Declines in plant diversity can often have detrimental effects on other forms of biodiversity through cascading trophic systems and negatively impact large-scale ecosystem processes. This is particularly relevant in grassland ecosystems, where in undisturbed systems grasses, forbs, and legumes coexist in diverse communities. Previous studies have explored the hypothesis that loss of plant species negatively impacts biodiversity of other trophic groups and can diminish whole ecosystem functions. In this study we tested how flowering plant species richness influenced arthropod order richness on eight sites in the Grand River Grasslands of south central Iowa, and whether that relationship depended on the vegetation height at which arthropods were sampled. We hypothesized that (1) flowering plant species richness would positively affect arthropod order richness, and that (2) a greater number of arthropod orders would be found 2 centimeters above the ground (hereafter “low”) than 1 meter above the ground (hereafter “high”) at given equal flowering plant species richness. With greater richness of flowering plant species, it is likely that this variety of vegetation supplies a greater amount of habitat available for arthropod communities. Counter to our expectations, flowering plant species richness was not significantly correlated with total arthropod order richness (p = 0.0785). However, richness of “low” arthropod order did increase with an increase in nectar richness (p = 0.0463). Further research including all plant species (rather than merely nectar producing species) and identifying arthropods to a finer taxonomic level may provide more conclusive results supporting our hypotheses. Results of such studies would contribute to the success of biodiversity conservation efforts that focus on bottom-up management practices that can enhance ecosystem functioning at higher trophic levels.

Herbarium specimens can reveal impacts of climate change on plant phenology; a review of methods and applications.

Studies in plant phenology have provided some of the best evidence for large-scale responses to recent climate change. Over the last decade, more than thirty studies have used herbarium specimens to analyze changes in flowering phenology over time, although studies from tropical environments are thus far generally lacking. In this review, we summarize the approaches and applications used to date. Reproductive plant phenology has primarily been analyzed using two summary statistics, the mean flowering day of year and first-flowering day of year, but mean flowering day has proven to be a more robust statistic. Two types of regression models have been applied to test for associations between flowering, temperature and time: flowering day regressed on year and flowering day regressed on temperature. Most studies analyzed the effect of temperature by averaging temperatures from three months prior to the date of flowering. On average, published studies have used 55 herbarium specimens per species to characterize changes in phenology over time, but in many cases fewer specimens were used. Geospatial grid data are increasingly being used for determining average temperatures at herbarium specimen collection locations, allowing testing for finer scale correspondence between phenology and climate. Multiple studies have shown that inferences from herbarium specimen data are comparable to findings from systematically collected field observations. Understanding phenological responses to climate change is a crucial step towards recognizing implications for higher trophic levels and large-scale ecosystem processes. As herbaria are increasingly being digitized worldwide, more data are becoming available for future studies. As temperatures continue to rise globally, herbarium specimens are expected to become an increasingly important resource for analyzing plant responses to climate change.

A meta‐analysis of zooplankton functional traits influencing ecosystem function

The use of functional traits to characterize community composition has been proposed as a more effective way to link community structure to ecosystem functioning. Organismal morphology, body stoichiometry, and physiology can be readily linked to large-scale ecosystem processes through functional traits that inform on interspecific and species-environment interactions; yet such effect traits are still poorly included in trait-based approaches. Given their key trophic position in aquatic ecosystems, individual zooplankton affect energy fluxes and elemental processing. We compiled a large database of zooplankton traits contributing to carbon, nitrogen, and phosphorus cycling and examined the effect of classification and habitat (marine vs. freshwater) on trait relationships. Respiration and nutrient excretion rates followed mass-dependent scaling in both habitats, with exponents ranging from 0.70 to 0.90. Our analyses revealed surprising differences in allometry and respiration between habitats, with freshwater species having lower length-specific mass and three times higher mass-specific respiration rates. These differences in traits point to implications for ecological strategies as well as overall carbon storage and fluxes based on habitat type. Our synthesis quantifies multiple trait relationships and links organisms to ecosystem processes they influence, enabling a more complete integration of aquatic community ecology and biogeochemistry through the promising use of effect traits.

Metabolomics and proteomics reveal impacts of chemically mediated competition on marine plankton.

Competition is a major force structuring marine planktonic communities. The release of compounds that inhibit competitors, a process known as allelopathy, may play a role in the maintenance of large blooms of the red-tide dinoflagellate Karenia brevis, which produces potent neurotoxins that negatively impact coastal marine ecosystems. K. brevis is variably allelopathic to multiple competitors, typically causing sublethal suppression of growth. We used metabolomic and proteomic analyses to investigate the role of chemically mediated ecological interactions between K. brevis and two diatom competitors, Asterionellopsis glacialis and Thalassiosira pseudonana. The impact of K. brevis allelopathy on competitor physiology was reflected in the metabolomes and expressed proteomes of both diatoms, although the diatom that co-occurs with K. brevis blooms (A. glacialis) exhibited more robust metabolism in response to K. brevis. The observed partial resistance of A. glacialis to allelopathy may be a result of its frequent exposure to K. brevis blooms in the Gulf of Mexico. For the more sensitive diatom, T. pseudonana, which may not have had opportunity to evolve resistance to K. brevis, allelopathy disrupted energy metabolism and impeded cellular protection mechanisms including altered cell membrane components, inhibited osmoregulation, and increased oxidative stress. Allelopathic compounds appear to target multiple physiological pathways in sensitive competitors, demonstrating that chemical cues in the plankton have the potential to alter large-scale ecosystem processes including primary production and nutrient cycling.

Historical patterns of exotic earthworm distributions inform contemporary associations with soil physical and chemical factors across a northern temperate forest

Understanding environmental factors related to exotic earthworm distributions across invasion stages (i.e., introduction, colonization, regional spread) is critical for assessing long-term impacts on previously earthworm-free forests. Studies following earthworm community establishment in North America, however, remain limited. We address this by characterizing historical and current exotic earthworm distributions in a regionally representative aspen-dominated forest, where their presence was first documented in the early 1900s. We map historic earthworm distribution records in a 360-km2 area surrounding our current study site, and re-analyze data collected nearly 60 years ago to inform contemporary associations between species densities and environmental factors. Field surveys were conducted over two years (2008–2010) using 10 permanent plots, with concurrent measurements of environmental ‘effect factors’ determined by large-scale ecosystem processes (leaf litter inputs, soil physical properties, soil C and N content), and environmental ‘response factors’ likely impacted by earthworm activity over short time scales (annual litter mass loss and soil isotopic values). Present-day communities included five exotic species with varying densities: Lumbricus rubellus ≥ Lumbricus terrestris >> Dendrobaena octaedra ≥ Aporrectodea spp. (Aporrectodea trapezoides + Aporrectodea caliginosa). These species were also present in the landscape in the early to mid-1900s though shifts in species composition, particularly the movement of L. terrestris into upland forest soils, were evident. Over two years, earthworm community composition did not show strong temporal or spatial trends characteristic of incipient invasions. However, species-specific associations with environmental factors were observed: L. terrestris and L. rubellus densities were positively associated with soil C and N content, Acer rubrum (red maple) inputs, and soil moisture; and were negatively associated with Pinus strobus (white pine) inputs. D. octaedra, and Aporrectodea spp. densities were positively associated with % sand; and negatively associated with plot-to-road distance. Soil moisture and texture were significant drivers of earthworm species abundance in historical surveys, though associations with soil C were only evident for Aporrectodea spp. Contemporary associations between earthworm species and soil C and N content suggest greater nutrient limitation in upland forest soils, while the importance of plot-to-road distance suggests the persistence of dispersal limitation and repeated introductions as a mechanism maintaining population densities. Species-specific associations with environmental response variables were also observed, where: surface soil δ13C depletion was associated with Aporrectodea spp. and D. octaedra biomass; δ15N enrichment was associated with total earthworm biomass, but negatively associated with L. rubellus biomass; and increased leaf litter mass loss was associated with L. terrestris and juvenile biomass. As soil C and N pools were not higher in plots with higher earthworm biomass, these results suggest earthworm activity may influence soil nutrient cycling by decreasing turnover times of nutrient pools over the long-term. Our results characterize exotic earthworm distributions at scales relevant to forest ecosystem processes, and allow for future extrapolation of laboratory and controlled field studies assessing impacts on soil nutrient cycling across northern temperate forests.

In vitro conservation of European bryophytes

The use of in vitro techniques for conservation has been rising steadily since their inclusion in The Convention on Biological Diversity and The Global Strategy for Plant Conservation. Unfortunately, bryophytes are often overlooked in conservation initiatives, but they are important in a number of large-scale ecosystem processes, i.e. nutrient, water and carbon cycling. There is a long history of the use of tissue culture in cultivating bryophytes, and many species respond well to in vitro techniques. For 6 yr (2000–2006), The Royal Botanic Gardens, Kew and the UK statutory conservation agencies supported a project for the ex situ conservation of bryophytes. Living and cryopreserved collections of UK threatened species were successfully established and the cryopreserved collection continues to be maintained. Other in vitro conservation collections are maintained over Europe, at botanic gardens, museums and by individual university researchers, but there is no coherent European collection of bryophytes for conservation, or standardisation of techniques. A major issue for many in vitro collections is the maintenance of within species genetic diversity. Such diversity is considered to be important, as it is the basis by which populations of species can adapt to new conditions and evolve. We are proposing to establish a European network for in vitro conservation of bryophytes. We envisage that this will include living collections, cryopreserved collections and spore collections. Conservation of genetic diversity would be a priority and the collections would provide a valuable resource for conservation initiatives and support research into rare and threatened species.

SPATIAL PATTERNS OF FOREST CHARACTERISTICS IN THE WESTERN UNITED STATES DERIVED FROM INVENTORIES

In the western United States, forest ecosystems are subject to a variety of forcing mechanisms that drive dynamics, including climate change, land-use/land-cover change, atmospheric pollution, and disturbance. To understand the impacts of these stressors, it is crucial to develop assessments of forest properties to establish baselines, determine the extent of changes, and provide information to ecosystem modeling activities. Here we report on spatial patterns of characteristics of forest ecosystems in the western United States, including area, stand age, forest type, and carbon stocks, and comparisons of these patterns with those from satellite imagery and simulation models. The USDA Forest Service collected ground-based measurements of tree and plot information in recent decades as part of nationwide forest inventories. Using these measurements together with a methodology for estimating carbon stocks for each tree measured, we mapped county-level patterns across the western United States. Because forest ecosystem properties are often significantly different between hardwood and softwood species, we describe patterns of each. The stand age distribution peaked at 60-100 years across the region, with hardwoods typically younger than softwoods. Forest carbon density was highest along the coast region of northern California, Oregon, and Washington and lowest in the arid regions of the Southwest and along the edge of the Great Plains. These results quantify the spatial variability of forest characteristics important for understanding large-scale ecosystem processes and their controlling mechanisms. To illustrate other uses of the inventory-derived forest characteristics, we compared them against examples of independently derived estimates. Forest cover compared well with satellite-derived values when only productive stands were included in the inventory estimates. Forest types derived from satellite observations were similar to our inventory results, though the inventory database suggested more heterogeneity. Carbon stocks from the Century model were in good agreement with inventory results except in the Pacific Northwest and part of the Sierra Nevada, where it appears that harvesting and fire in the 20th century (processes not included in the model runs) reduced measured stand ages and carbon stocks compared to simulations.

Across Space and Time: Social Responses to Large-Scale Biophysical Systems

The conceptual rubric of ecosystem management has been widely discussed and deliberated in conservation biology, environmental policy, and land/resource management. In this paper, I argue that two critical aspects of the ecosystem management concept require greater attention in policy and practice. First, although emphasis has been placed on the "space" of systems, the "time" -- or rates of change -- associated with biophysical and social systems has received much less consideration. Second, discussions of ecosystem management have often neglected the temporal disconnects between changes in biophysical systems and the response of social systems to management issues and challenges. The empirical basis of these points is a case study of the "Crown of the Continent Ecosystem," an international transboundary area of the Rocky Mountains that surrounds Glacier National Park (USA) and Waterton Lakes National Park (Canada). This project assessed the experiences and perspectives of 1) middle- and upper-level government managers responsible for interjurisdictional cooperation, and 2) environmental nongovernment organizations with an international focus. I identify and describe 10 key challenges to increasing the extent and intensity of transboundary cooperation in land/resource management policy and practice. These issues are discussed in terms of their political, institutional, cultural, information-based, and perceptual elements. Analytic techniques include a combination of environmental history, semistructured interviews with 48 actors, and text analysis in a systematic qualitative framework. The central conclusion of this work is that the rates of response of human social systems must be better integrated with the rates of ecological change. This challenge is equal to or greater than the well-recognized need to adapt the spatial scale of human institutions to large-scale ecosystem processes and transboundary wildlife.

Estimates of Down Woody Materials in Eastern US Forests

Down woody materials (DWMs) are an important part of forest ecosystems for wildlife habitat, carbon storage, structural diversity, wildfire hazard, and other large-scale ecosystem processes. To better manage forests for DWMs, available and easily accessible data on DWM components are needed. We examined data on DWMs, collected in 2001 by the US Department of Agriculture (USDA) Forest Inventory and Analysis (FIA) program on some plots in several states. We compiled DWM data from 778 plots to compute biomass for the following components: coarse woody material, fine woody material (three size classes), litter, duff, and shrub/herb cover. We developed regression equations to predict DWM components for extension to FIA’s more intensive plot network. Seven regression equations were applied to the FIA data to create maps of DWM biomass. As a first attempt to summarize FIA DWM measurements and extend them to plots without these data, our model produces reasonable results except possibly for duff and litter.