Ecosystem Scale Research Articles

Influences of conifer encroachment and removal on oak woodland ecophysiology and biodiversity—a case study from northern California, U.S.A.

Oregon white oak (Quercus garryana) woodlands are threatened by conifer encroachment established during decades of fire exclusion. Widespread restoration efforts are underway to remove conifers from many oak woodlands in California, Oregon, and Washington. Using water potential, stomatal conductance, stable isotopes, and three metrics of biodiversity, we investigated the effects of Douglas‐fir (Pseudotsuga menziesii) encroachment and removal at the ecosystem scale across 3 years in a northern California woodland. We found that heavily encroached stands had the highest water potential and often the lowest stomatal conductance, compared to moderately encroached and open stands. Xylem water stable isotopes indicated that oaks and Douglas‐firs were likely not directly competing for water, as oaks appeared to use a relatively deeper water source. Under certain climatic conditions, heavily encroached oaks were more vulnerable to water stress than oaks in open or moderately encroached stands. Following low‐intensity conifer removal, thinned stands had slightly lower predawn water potential and higher gas exchange compared to unthinned stands, particularly under dry conditions. For ecosystem biodiversity, understory plant and bird diversity did not meaningfully vary with encroachment or thinning, but mammal diversity was greater in encroached stands compared to open stands. Findings from this work demonstrate that negative impacts of conifer encroachment on oaks are not due to increased competition for water, conifer removal is physiologically beneficial for shaded oaks, and that heavier thinning treatments are likely needed to yield long‐term responses and influence biodiversity.

Birch (Betula pubescens Ehrh.) Encroachment Alters Contribution of Plant Functional Groups to Ecosystem Carbon Cycling in a Rewetted Bog

ABSTRACTRewetted bogs with high water levels (WL) and mire‐specific vegetation are crucial carbon (C) sinks, but their function might be threatened by tree encroachment, a phenomenon widespread in the northern hemisphere that often coincides with low WL. This might impact C cycling both at the ecosystem and microform scale in multiple ways, but so far, data are lacking. We established two sites in the same former peat extraction area, one showing permanently high WL and mire‐specific vegetation (open site, OS), while the other one has more fluctuating WL and a dense birch (Betula pubescens Ehrh.) population (tree site, TS). We measured the carbon dioxide (CO2) exchange at ecosystem (eddy covariance) and plot scale (chamber measurements) for 1 year to clarify the differences between the sites and the impact of birch encroachment on the contribution of the different bog‐specific microforms and the trees to the ecosystem's CO2 balance. Overall, the OS had a CO2 balance of −262.4 ± 7.8 g CO2‐C m−2 year−1 indicating CO2 uptake, while the TS was close to neutral (−28 ± 5.1 g CO2‐C m−2 year−1). The smaller uptake at the TS was caused by higher (151%) ecosystem respiration, while gross primary production was 14% higher. However, the microform contributions to C uptake strongly differed: At the OS, both hummocks and hollows showed net uptake, while at the TS, most C (52%) was assimilated by the birches and the understory was a net CO2 source. This indicates a loss of peat C from the TS, while the successfully rewetted site was accumulating new peat. Accounting for plot‐scale CH4 fluxes, both sites were a weak source of greenhouse gases, but a distinctly stronger C sink occurred at the OS. Our data show the possibility of increasing C removal from the atmosphere by full rewetting and the establishment of mire‐specific vegetation.

Source vs sink limitations on tree growth: from physiological mechanisms to evolutionary constraints and terrestrial carbon cycle implications.

The potential for widespread sink-limited plant growth has received increasing attention in the literature in the past few years. Despite recent evidence for sink limitations to plant growth, there are reasons to be cautious about a sink-limited world view. First, source-limited vegetation models do a reasonable job at capturing geographic patterns in plant productivity and responses to resource limitations. Second, from an evolutionary perspective, it is nonadaptive for plants to invest in increasing carbon assimilation if growth is primarily sink-limited. In this review, we synthesize the potential evidence for and underlying physiology of sink limitation across terrestrial ecosystems and contrast mechanisms of sink limitation with those of source-limited productivity. We highlight evolutionary restrictions on the magnitude of sink limitation at the organismal level. We also detail where mechanisms regulating sink limitation at the organismal and ecosystem scale (e.g. the terrestrial carbon sink) diverge. Although we find that there is currently no direct evidence for widespread organismal sink limitation, we propose a series of follow-up growth chamber manipulations, systematized measurements, and modeling experiments targeted at diagnosing nonadaptive buildup of excess nonstructural carbohydrates that will help illuminate the prevalence and magnitude of organismal sink limitation.

Bioacoustic and Ecoacoustic Data in Audiovisual Core

Audiovisual Core (Audiovisual Core Maintenance Group 2023), is the TDWG standard for metadata related to biodiversity multimedia. The Audiovisual Core Maintenance Group has been working to expand the standard to provide the terms necessary for handling sound recordings. Audiovisual Core can now handle acoustic metadata related to biodiversity from single species (bioacoustics) to the ecosystem scale (ecoacoustics). Bioacoustics The Natural History Museum, London has a significant collection of recorded insect sounds (Ragge and Reynolds 1998) that are often directly linked to museum specimens (Fig. 1). The sound collection has previously been digitised and made available electronically through the BioAcoustica project (Baker et al. 2015). The BioAcoustica platform allows for annotation of audio files with tags including "Call" for deliberate sound made by an organism, "Voice Introduction" for metadata, and "Extraneous Noise." These boundaries are defined by their start and end times (in seconds) relative to the start of the file (Fig. 2). Ecoacoustics Ecoacoustics deals with the sounds present within an entire soundscape or ecosystem. The calls of individual species form the biological part of the soundscape (biophony) alongside sounds produced by non-living natural sources (geophony) and humans (anthropophony). Individual components are often defined by date and time boundaries, and sometimes by upper and lower frequency limits (Fig. 3). Regions of Interest The recently added concept of a "Region of Interest" (ROI) allows for the annotation of sound files, identifying multiple regions within a single recording with time and/or frequency bounds. However, the vocabulary of ROI*1 is not just intended for sounds. Equivalent terms also allow for regions to be specified with images and videos. The use of well-defined annotations has the potential to generate large amounts of training data for machine learning models and provide a standard for generating observation records from these models (e.g., BirdNet, see Kahl et al. 2021), which can be verified by linking them to audio segments within a much larger recording. The development of a metadata standard for regions of interest has several interesting possibilities, including linking multiple observation records to a single soundscape recording (the recording acts similarly to a voucher specimen) and aggregating regions across multiple datasets to create larger corpora for training machine learning models.

Drought conditions disrupt atmospheric carbon uptake in a Mediterranean saline lake

Abstract. Inland saline lakes play a key role in the global carbon cycle, acting as dynamic zones for atmospheric carbon exchange and storage. Given the global decline of saline lakes and the expected increase of periods of drought in a climate change scenario, changes in their potential capacity to uptake or emit atmospheric carbon are expected. Here, we conducted continuous measurements of CO2 and CH4 fluxes at the ecosystem scale in an endorheic saline lake of the Mediterranean region over nearly 2 years. Our focus was on determining net CO2 and CH4 exchanges with the atmosphere under both dry and flooded conditions, using the eddy covariance (EC) method. We coupled greenhouse gas flux measurements with water storage and analysed meteorological variables like air temperature and radiation, known to influence carbon fluxes in lakes. This extensive data integration enabled the projection of the net carbon flux over time, accounting for both dry and wet conditions on an interannual scale. We found that the system acts as a substantial carbon sink by absorbing atmospheric CO2 under wet conditions. In years with prolonged water storage, it is predicted that the lake's CO2 assimilation capacity can surpass 0.7 kg C m2 annually. Conversely, during extended drought years, a reduction in CO2 uptake capacity of more than 80 % is expected. Regarding CH4, we measured uptake rates that exceeded those of well-aerated soils such as forest soils or grasslands, reaching values of 0.2 µmol m−2 s−1. Additionally, we observed that CH4 uptake during dry conditions was nearly double that of wet conditions. However, the absence of continuous data prevented us from correlating CH4 uptake processes with potential environmental predictors. Our study challenges the widespread notion that wetlands are universally greenhouse gas emitters, highlighting the significant role that endorheic saline lakes can play as a natural sink of atmospheric carbon. However, our work also underscores the vulnerability of these ecosystem services in the current climate change scenario, where drought episodes are expected to become more frequent and intense in the coming years.

Food web bioaccumulation model for ecological risk assessment of emerging organic pollutants in marine ecosystems: Principles, advances and challenges

The bioaccumulation and trophic transfer of pollutants in marine ecosystem members determine their ultimate ecological risks. Food web bioaccumulation models are widely used in scientific and regulatory programs to assess the bioaccumulation and ecological risks of pollutants at the ecosystem scale. The food web models are mainly established through concentration- and fugacity-based modeling approaches and include some chemical, food web-related, physiological and environmental factors. The models applied in the “forward approach” predict bioaccumulation and conduct internal exposure level-based ecological risk assessment (IEL-ERA), whereas those in the “reverse approach” are used to back-calculate the IEL-based predicted no-effect concentrations (PNECs) or environmental criteria. However, some challenges still exist in the application of food web model integrated risk assessment, including the lack of standardized/generalized frameworks, the lack of chemical- and species-specific toxicokinetic data and internal exposure (or tissue residue)-based toxicity data, and the lack of uncertainty-control methods in model estimation and parameterization. There are urgent requirements to improve models, integrate methods and update study designs in the assessment and prediction of “system-scale risks” of marine emerging organic pollutants.

Widespread forest-savanna coexistence but limited bistability at a landscape scale in Central Africa

Abstract Tropical forest and savanna frequently coexist under the same climatic conditions, which has led to the hypothesis that they could represent alternative ecosystem states, stabilized by internal feedbacks. An implication of this hypothesis is that forest and savanna may be bistable and exhibit tipping behavior in response to changing conditions. However, we pose that the local presence of forest and savanna within coexistence landscapes is not sufficient evidence that these are alternative stable states at larger ecosystem scales. Therefore, we explore forest-savanna coexistence and bistability at landscape scale in Central Africa. Using remote sensing data on tree cover, we classify 0.1° × 0.1° (approx. 10 × 10 km) landscapes as homogeneous forest, homogeneous savanna, or coexistence, and analyze the roles of climate, topography and soil sand content in driving their distributions. We find that local coexistence of forest and savanna within landscapes is common and occurs for the whole range of mean annual precipitation in our study area. At low precipitation, however, coexistence increases with topographic roughness and is therefore likely driven by local redistribution of resources rather than internal feedbacks. Coexistence within intermediate and high precipitation landscapes remains unexplained by the studied variables, and may be caused either by heterogeneity in unmeasured drivers or by feedback-driven bistability. At landscape scale, the precipitation ranges for which homogeneous forest and savanna occur have only limited overlap, and this overlap can be largely explained by other external drivers, such as seasonality, soil sand content, and topography. This lack of evidence that homogeneous forest and savanna in Central Africa are alternative ecosystem states at this landscape scale means that transitions between them may be mostly local, resulting in coexistence states. Therefore, we conclude that the likelihood of large-scale tipping between homogeneous forest and savanna ecosystems may be lower than previously thought.

The Ecosystem Ecology of Coral Reefs Revisited

Early studies in coral reefs showed that simple measurements of ecosystem metabolism (primary production and ecosystem respiration) were useful for understanding complex reef dynamics at an ecosystem scale. These studies also helped establish the field of ecosystem ecology, but contemporary coral reef ecology has shifted away from these origins. In this manuscript, I describe the historical development of a theory of ecosystem metabolism that was foundational for the discipline of ecosystem ecology, and I update this theory to fully incorporate dynamics on coral reefs (and all ecosystems). I use this updated theory to (a) identify important controls on coral reef processes and (b) provide a rationale for patterns of coral reef carbon dynamics that allow me to generate hypotheses of coral reef ecosystem production. I then use existing data to broadly evaluate these hypotheses. My findings emphasize the importance of integrating measurements of ecosystem metabolism with current approaches to improve the development of theory and the efficacy of conservation and management of coral reefs.

Global patterns in vegetation accessible subsurface water storage emerge from spatially varying importance of individual drivers

Abstract Vegetation roots play an essential role in regulating the hydrological cycle by removing water from the subsurface and releasing it to the atmosphere. However, the present understanding of the drivers of ecosystem-scale root development and their spatial variability globally is limited. This study investigates the varying roles of climate, landscape, and vegetation on the magnitude of root zone storage capacity ( S r ) worldwide, which is defined as the maximum volume of subsurface moisture accessible to vegetation roots. To this aim, we quantified S r and evaluated 21 possible climate, landscape, and vegetation controls for 3612 river catchments worldwide using a random forest machine learning model. Our findings reveal climate as primary, but spatially varying, driver of ecosystem scale S r with landscape and vegetation characteristics playing a minor role. More specifically, we found the mean inter-storm duration as most dominant control of S r globally, followed by mean temperature, mean precipitation, and mean topographic slope. While the inter-storm duration, temperature, and slope exhibit a consistent relation with S r globally, the relation between precipitation and S r varies spatially. Based on this spatial variability, we classified two different regimes: precipitation driven and energy limited. The precipitation-driven regime exhibits a positive relation between precipitation and S r for precipitation of up to 3 mm d − 1 , above which the relation flattens and eventually becomes negative. The energy-limited regime exhibits a strictly negative relation between precipitation and S r . Using the random forest model based on these three dominant climate variables and the landscape variable slope, we generated a global gridded dataset of S r , which closely resembles other global datasets of root characteristics. This suggests that our parsimonious approach based on four globally available variables to estimate S r on a global scale has the potential to be readily and easily integrated into the parameterization of S r in global hydrological and land surface models. This may enhance the accuracy of global predictions of land–atmosphere exchange fluxes and hydrological extremes by providing a robust representation of both spatial and temporal variability in vegetation root characteristics.

Water quality–fisheries tradeoffs in a changing climate underscore the need for adaptive ecosystem–based management

Changes driven by both unanticipated human activities and management actions are creating wicked management landscapes in freshwater and marine ecosystems that require new approaches to support decision-making. By linking a predictive model of nutrient- and temperature-driven bottom hypoxia with observed commercial fishery harvest data from Lake Erie (United States-Canada) over the past century (1928-2022) and climate projections (2030-2099), we show how simple, yet robust models and routine monitoring data can be used to identify tradeoffs associated with nutrient management and guide decision-making in even the largest of aquatic ecosystems now and in the future. Our approach enabled us to assess planned nutrient load reduction targets designed to mitigate nutrient-driven hypoxia and show why they appear overly restrictive based on current fishery needs, indicating tradeoffs between water quality and fisheries management goals. At the same time, our temperature results show that projected climate change impacts on hypoxic extent will require more stringent nutrient regulations in the future. Beyond providing a rare example of bottom hypoxia driving changes in fishery harvests at an ecosystem scale, our study illustrates the need for adaptive ecosystem-based management, which can be informed by simple predictive models that can be readily applied over long time periods, account for tradeoffs across multiple management sectors (e.g., water quality, fisheries), and address ecosystem nonstationarity (e.g., climate change impacts on management targets). Such approaches will be critical for maintaining valued ecosystem services in the many aquatic systems worldwide that are vulnerable to multiple drivers of environmental change.

Global influence of soil texture on ecosystem water limitation

Low soil moisture and high vapour pressure deficit (VPD) cause plant water stress and lead to a variety of drought responses, including a reduction in transpiration and photosynthesis1,2. When soils dry below critical soil moisture thresholds, ecosystems transition from energy to water limitation as stomata close to alleviate water stress3,4. However, the mechanisms behind these thresholds remain poorly defined at the ecosystem scale. Here, by analysing observations of critical soil moisture thresholds globally, we show the prominent role of soil texture in modulating the onset of ecosystem water limitation through the soil hydraulic conductivity curve, whose steepness increases with sand fraction. This clarifies how ecosystem sensitivity to VPD versus soil moisture is shaped by soil texture, with ecosystems in sandy soils being relatively more sensitive to soil drying, whereas ecosystems in clayey soils are relatively more sensitive to VPD. For the same reason, plants in sandy soils have limited potential to adjust to water limitations, which has an impact on how climate change affects terrestrial ecosystems. In summary, although vegetation–atmosphere exchanges are driven by atmospheric conditions and mediated by plant adjustments, their fate is ultimately dependent on the soil.

Domesticating the wild through escapees of two iconic mediterranean farmed fish species

Extractive fisheries and marine aquaculture share space and target species. Several regional-scale examples exist of escapees entering wild fisheries landings, yet no study has assessed the influence of aquaculture on landings at an ecosystem scale. We examined the effects of farmed fish escapes on fisheries using FAO data and published escape rates for Gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax). Seabream landings were significantly correlated with the estimated biomass of escaped seabream entering the wild. There was a similar pattern for seabass until 2005, but the overall relationship between landings and escapes was not significant due to the dramatic drop in catches in recent years. We argue that seabass escapees’ relatively high mortality, lower capturability, and minor ‘leaking’ from farms may obscure their influence on landings. Significant positive fisheries regime shifts were detected for both species, matching the onset of aquaculture in the Mediterranean and the period when escapees from aquaculture surpassed landings. Our results suggest that fish escapes of these two iconic species may mask wild stock overexploitation, confound stock assessments, alter genetic diversity, increase the risk of spreading pathogens and parasites, and compete with wild conspecifics while boosting fisheries landings.

Long-term alien marsh grass in China brings high carbon uptake capacity but cannot sustain high-temperature weather

Coastal wetlands, crucial in the global carbon cycle, face increasing challenges brought by extreme climate events, particularly high temperatures above plant tolerance thresholds. These conditions often exert great impact on plant, thereby potentially reducing overall ecosystem productivity. However, it has been observed that alien species, typically exhibiting higher productivity compared to native plant. Would plant invasion offset the loss of productivity caused by high-temperature events at ecosystem scale? In this study, we utilized data from 2020 to 2023 in China's Yangtze Estuary to investigate the responses of Spartina alterniflora (alien) and Phragmites australis (native) to high-temperature stress. Our results demonstrate that though the alien vegetation exhibits higher productivity before high temperature events, it experiences significant declines during high temperatures. In average, net ecosystem productivity (NEP) and gross primary productivity (GPP) of alien plant drops by 21.03% overall, with a notable 29.59% reduction during Neap tide. In contrast, native vegetation maintains a more stable productivity profile under the same conditions. Spring tide alleviate the negative impact of high temperatures on the alien vegetation, exhibiting a distinct environmental buffering effect. Photosynthetic photon flux density emerged as a crucial factor driving productivity, yet its effectiveness was moderated by aerodynamic conductance for heat transfer (Ga_h). Through the application of the Michaelis-Menten model, we confirmed that both species maintain similar maximum light utilization efficiencies, yet native vegetation demonstrates greater resilience to thermal stress. Additionally, we observed a 33.82% overestimation in productivity by the vegetation photosynthesis model (VPM) under high temperatures, emphasizing the need to refine how Ga_h impacts are integrated, particularly when comparing the resilience of native and alien species. We emphasize necessity of incorporating canopy structure factors into ecological models and underscore the importance of maintaining tidal dynamics for coastal wetland management.

Evaluating variation of respiration:photosynthesis ratio in sagebrush species: Implications for carbon flux modeling

AbstractPlant respiration and photosynthesis are the two main processes influencing carbon (C) flux balance at leaf‐to‐ecosystem scales. The ratio of respiration to photosynthesis (R:A) or carbon use efficiency (CUE) is considered an important trait for determining global carbon storage in the near future. One school of thought assumes that R:A is constant in terrestrial productivity models, irrespective of biomass, climate, and species. Others believe it is variable, although within a limited range. Semiarid systems dominated by woody vegetation, such as sagebrush steppe, have been recognized as potentially important C sinks on regional to global scales in the context of future climate scenarios. Therefore, there is a critical need to study R:A over different organizational scales (i.e., at the leaf, whole plant, and ecosystem scales) to use this approach for future C flux predictions under climate change scenarios. The objective of this study was to compare leaf‐, shrub‐, and ecosystem‐scale R:A among three sagebrush (Artemisia spp.) communities, and to determine how R:A varies throughout the growing season (i.e., early, mid‐, and late summer) among these communities. We measured photosynthesis and respiration monthly in three sagebrush communities spanning a 685‐m elevation gradient at the Reynolds Creek Experimental Watershed and Critical Zone Observatory in southwestern Idaho. Consistent with our expectations, we found large seasonal variations in R and A at all scales, but with differences in A among the three sagebrush communities significant only at the leaf scale. The R:A ratio was not significantly different among the three species at all organizational scales. However, the R:A ratio did vary among months at the leaf level and there was a statistical interaction between species and month at both leaf and shrub levels. Our study indicates that the R:A ratio is generally conservative, although not tightly constrained (range: 0.12–0.77) among three sagebrush species. Therefore, approaches that assume conservative R:A ratios in terrestrial productivity models need to be considered carefully to evaluate the impact of projected climatic changes on future C cycling in shrub‐dominated rangeland ecosystems.

Reduced ligninase‐cellulase ratio enhances soil carbon sequestration following afforestation of agricultural land

AbstractIntroductionAfforestation of agricultural land is one of the most essential approaches to mitigate climate change by enhancing the sequestration of atmospheric carbon (C) into the soil. C‐degrading extracellular enzymes produced by soil microbes regulated the decomposition and fate of sequestrated soil organic carbon (SOC), with potential divergent variations following afforestation across different ecosystem scales. However, the feedbacks of different C‐degrading enzymes and their relationships with SOC following afforestation of agricultural land remain unclear.Materials and MethodsWe investigated the changes in enzyme activity and their relationships with SOC in soil aggregates across two typical climatic vegetation restoration regions in China, and explored the mechanisms through which changes in enzyme activity contribute to SOC sequestration following afforestation of agricultural land.ResultsAfforestation of agricultural land generally decreased ligninase activity and increased cellulase activity across various aggregate fractions, compared to the adjacent croplands in both subtropic (Danjiangkou Reservoir, DJK) and temperate (Maoershan, MES) region. Additionally, the ratio of ligninase to cellulase (L:C) was lower in afforested lands than in the croplands, with L:C as the major factor explaining the variations of SOC sequestration following afforestation. Specifically, ligninase and L:C were negatively correlated with SOC, whereas cellulase showed positive correlations with SOC. Further analyses suggested that microbial biomass C and nitrogen (MBC and MBN) and the ratio of SOC and total nitrogen (SOC:TN) were important factors influencing L:C and subsequently regulating SOC. These results suggest that shifts in microbial enzyme production from ligninase to cellulase following afforestation, reduced the decomposition of recalcitrant C, thus contributing to SOC sequestration.ConclusionOur work underscores the critical role of reduced L:C in enhancing SOC sequestration following the restoration of croplands to afforested lands. These findings advance the understanding of the influence of microbial community physiological adaptations on C sequestration across different land use types.

Self-organization in spatial ecology

Biologists have long known that populations of organisms - microbes, plants, animals - can self-organize into emergent patterns. Yet, the fact that such patterns can arise with remarkable symmetry at the scale of entire ecosystems remains astonishing, even as aerial imagery has documented their existence across all continents. As the enormous scale of landscape patterns makes them experimentally intractable, ecologists have relied on theoretical modelling - typically rooted in physics - to investigate the underlying pattern-forming mechanisms. Such models have succeeded in generating mechanistic hypotheses and indicate that self-organized spatial patterns can reflect the health of an ecosystem. However, most of these hypotheses remain untested. This essay reflects on our current understanding of the causes and consequences of ecosystem-scale pattern formation.

Divergent mechanisms driving nutrient stoichiometry in surface and deep soils of desert ecosystems on the Qinghai–Tibetan plateau

The ecological stoichiometric properties of desert soils determine nutrient availability and contribute to biodiversity and ecosystem stability. We obtained 1784 soil samples from 330 soil profiles distributed across the desert area of the Qinghai–Tibet Plateau (QTP). We measured the content of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), total potassium (TK), alkali-hydrolyzed nitrogen (AN), available phosphorus (AP), and available potassium (AK) to elucidate the vertical patterns of soil stoichiometric characteristics and their driving factors. We found a unique vertical distribution of SOC and soil nutrients in the QTP desert ecosystem: the proportions of SOC and nutrient storage in the topsoil (0–20 cm) were the highest that have been reported to date, especially for the proportion of SOC, which reached 54 %. The vertical distributions of SOC and AN fit an exponential function (r = 0.247 and 0.249), TN fit a linear function (r = 0.115), and TP, AP, and AK fit a curvilinear function (r = 0.127, 0.175, and 0.103), indicating that soil components exhibited a depth-dependent distribution in the alpine desert ecosystem. With increasing soil depth, C:N and C:P decreased significantly, AN:AP first increased and then decreased, and AP:AK first decreased and then increased. The factors that influenced soil nutrients and stoichiometry differed between the topsoil (0–20 cm) and deep soil (20–100 cm) layers. In the topsoil (0–20 cm), vegetation and precipitation were the dominant factors for soil nutrients and stoichiometry, while topography and climate affected soil nutrients and stoichiometry indirectly by influencing vegetation growth. In the deep soil (20–100 cm), silt particles and precipitation were the dominant factors for soil nutrients and stoichiometry, but climate affected soil nutrients and stoichiometry indirectly, mainly by influencing soil texture. The inconsistencies of nutrient stoichiometric driving mechanisms in surface and deep soils contributed to a comprehensive understanding of soil stoichiometric properties at the profile scale of desert ecosystems.

Heat tolerance varies considerably within a reef-building coral species on the Great Barrier Reef

Reef-building coral populations face unprecedented threats from climate warming. Standing variation in heat tolerance is crucial for evolutionary processes necessary for corals to persist. Yet, the spatial distribution of heat-tolerant corals and the underlying factors that determine heat tolerance are poorly understood from individual to ecosystem scales. Here, we show extensive variation in the heat tolerance of a foundational coral species complex across the Great Barrier Reef. Thermal thresholds of 569 individuals differed by up to 7.3 °C across scales from meters to >1250 km. Variation in thresholds among reefs was consistent with local adaptation and acclimatization to historical and recent thermal history. However, variation within reefs was sometimes greater than among reefs and largely unexplained by environmental predictors, putative host species, or symbiont communities. This indicates that within-reef heat tolerance differences may be informed primarily by other factors, such as adaptive genomic variation. We anticipate our findings will inform conservation and restoration actions, including targeting individuals for selective breeding of enhanced heat tolerance.

Measuring quantity in ecosystem markets and ecosystem accounts

AbstractThe quantity of ecosystem services produced from land cannot be readily measured at the site level needed for participation in ecosystem markets, or at a regional level needed to create ecosystem accounts. This paper applies biological scaling principles to develop a quantity metric in which areas of ecosystem (extent) scale allometrically to ecosystem services (a capacity measure) according to a scaling exponent defined by the fractal dimension of ecosystem vegetation. A key conclusion of this paper is that the quantity of ecosystem services arising from ecosystem degradation and conservation activities cannot be estimated unless information about the space‐filling properties of vegetation is observed and included in the quantity measurement methodology. The paper demonstrates how remote sensing techniques can be applied to systematically measure ecosystem extent and fractal dimension. It illustrates the economic efficiency and environmental outcome implications of such a quantity metric through comparison with current quantity estimation methods that assume isometric scaling. The quantity metric proposed has potential applications to ecosystem accounting. It enables information currently reported in land accounts to be combined with information reported in ecosystem condition accounts to create ecosystem stock accounts measured in physical units.

Whole-lake coarse woody habitat addition facilitates ecosystem regime restructuring in an oligotrophic lake

Preul-Stimetz T, Shaw SL, Sass GG. 2024. Whole-lake coarse woody habitat addition facilitates ecosystem regime restructuring in an oligotrophic lake. Lake Reserv Manag. XXX-XXX. The loss of vital littoral zone and riparian habitat due to lakeshore residential development is a pervasive issue across temperate aquatic ecosystems. Oligotrophic glacial lakes may be particularly vulnerable to reductions in coarse woody habitat (CWH) due to their lack of alternative structural habitat. Although influences of CWH on fish populations have been well documented, questions remain regarding CWH influences on lower trophic levels and water quality. We conducted a whole-lake CWH addition experiment within a BACI framework using 2 lakes, Sanford (treatment) and Escanaba (reference), in the Northern Highland Lake District of Wisconsin. Premanipulation monitoring began in 2015, trees were dropped in 2018, and data collection continued until 2023. We monitored limnological, planktonic, and benthic macroinvertebrate parameters to test whether CWH addition initiated trophic shifts and altered the structure of the aquatic food web. We found that CWH addition minimally affected water quality and changed some characteristics of Sanford Lake at lower trophic levels. Chlorophyll a concentrations in Sanford Lake significantly increased but Secchi depth was unaffected. The abundance of macrophytes increased in both systems; that in Sanford Lake increased more and was linked to the CWH addition. Dissolved oxygen significantly increased at multiple depth strata. Water temperature was unaffected. We observed declines in total zooplankton that were not related to CWH addition, but the decline in relative abundance of large grazers was. Our results provide a mechanistic understanding of the effects of habitat enhancement at an ecosystem scale and can help guide stakeholder and manager expectations following CWH addition.