Dynamics Of Natural Ecosystems Research Articles

Partitioning the contribution of bees with different traits and hoverflies to flower-visitor interaction networks

Insect pollinators are key to maintaining biodiversity and providing important ecosystem services. Among them, bee species (i.e., Apidae) and hoverflies (i.e., Syrphidae) are two of the most important and well-studied taxa worldwide. Yet, their relative contribution to the structural and dynamic properties of plant-pollinator interaction networks remains poorly understood. This is an important gap in knowledge given that these phylogenetically and functionally different groups might play different roles within their communities and respond in contrasting ways to anthropogenic perturbations.Here, we study the relative contribution of bee species (with different traits) and syrphids to maintain network properties (i.e., nestedness, network specialization (H2), and interaction diversity) and their influence on the temporal dynamics of these network metrics. To this end, we simulate species removals in community-wide flower-arthropod visitor interaction networks. These interactions were extensively sampled across four years in two different near-pristine temperate ecosystems in Japan.We found that bee species contribute significantly more than syrphids or any random combination of species to network nestedness, low specialization, and interaction diversity across months and years. In addition, bees also played a particularly important role in maintaining the observed temporal dynamics over time. Conversely, although syrphids were an abundant and species-rich group, they did not contribute so prominently to network metrics or temporal dynamics, with the exception of network complementary specialization, to which they contributed positively. In addition, smaller bee species and those that were active for longer periods were particularly important for interaction diversity and the number of interactions, respectively, and to maintain observed network temporal dynamics.Our results support that bee species, and especially the small ones, are cornerstone contributors to plant-visitor communities by shaping network properties and network temporal dynamics in natural ecosystems.

Modelling changes in vegetation productivity and carbon balance under future climate scenarios in southeastern Australia

Australia, characterized by extensive and heterogeneous terrestrial ecosystems, plays a critical role in the global carbon cycle and in efforts to mitigate climate change. Prior research has quantified vegetation productivity and carbon balance within the Australian context over preceding decades. Nonetheless, the responses of vegetation and carbon dynamics to the evolving phenomena of climate change and escalating concentrations of atmospheric carbon dioxide remain ambiguous within the Australian landscape. Here, we used LPJ-GUESS model to assess the impacts of climate change on Gross Primary Productivity (GPP) and Net Biome Productivity (NBP) of carbon for the state of New South Wales (NSW) in southeastern Australia. LPJ-GUESS simulations were driven by an ensemble of 27 global climate models under different emission scenarios. We investigated the change of GPP for different vegetation types and whether NSW ecosystems will be a net sink or source of carbon under climate change. We found that LPJ-GUESS successfully simulated GPP for the period 2003–2021, demonstrating a comparative performance with GPP derived from upscaled eddy covariance fluxes (R2 = 0.58, nRMSE = 14.2 %). The simulated NBP showed a larger interannual variation compared with flux data and other inversion products but could capture the timing of rainfall-driven carbon sink and source variations in 2015–2020. GPP would increase by 10.3–19.5 % under a medium emission scenario and 19.7–46.8 % under a high emission scenario. The mean probability of NSW acting as a carbon sink in the future showed a small decrease with a large uncertainty with >8 of the 27 climate models indicating an increased potential for carbon sink. These findings emphasize the significance of emission scenarios in shaping future carbon dynamics but also highlight considerable uncertainties stemming from different climate projections. Our study represents a baseline for understanding natural ecosystem dynamics and their key role in governing land carbon uptake and storage in Australia.

Hurricane disturbance drives trophic changes in neotropical mountain stream food webs.

Food webs are complex ecological networks that reveal species interactions and energy flow in ecosystems. Prevailing ecological knowledge on forested streams suggests that their food webs are based on allochthonous carbon, driven by a constant supply of organic matter from adjacent vegetation and limited primary production due to low light conditions. Extreme climatic disturbances can disrupt these natural ecosystem dynamics by altering resource availability, which leads to changes in food web structure and functioning. Here, we quantify the response of stream food webs to two major hurricanes (Irma and María, Category 5 and 4, respectively) that struck Puerto Rico in September 2017. Within two tropical forested streams (first and second order), we collected ecosystem and food web data 6 months prior to the hurricanes and 2, 9, and 18 months afterward. We assessed the structural (e.g., canopy) and hydrological (e.g., discharge) characteristics of the ecosystem and monitored changes in basal resources (i.e., algae, biofilm, and leaf litter), consumers (e.g., aquatic invertebrates, riparian consumers), and applied Layman's community-wide metrics using the isotopic composition of 13 C and 15 N. Continuous stream discharge measurements indicated that the hurricanes did not cause an extreme hydrological event. However, the sixfold increase in canopy openness and associated changes in litter input appeared to trigger an increase in primary production. These food webs were primarily based on terrestrially derived carbon before the hurricanes, but most taxa (including Atya and Xiphocaris shrimp, the consumers with highest biomass) shifted their food source to autochthonous carbon within 2 months of the hurricanes. We also found evidence that the hurricanes dramatically altered the structure of the food web, resulting in shorter (i.e., smaller food-chain length), narrower (i.e., lower diversity of carbon sources) food webs, as well as increased trophic species packing. This study demonstrates how hurricane disturbance can alter stream food webs, changing the trophic base from allochthonous to autochthonous resources via changes in the physical environment (i.e., canopy defoliation). As hurricanes become more frequent and severe due to climate change, our findings greatly contribute to our understanding of the mechanisms that maintain forested stream trophic interactions amidst global change.

Landsat archive for detection of change in Mediterranean ecosystems: The case of Northern Morocco

The study of changes in land cover provides a better understanding of the interactions between humans and natural ecosystems. In this context, the present study focused on the dynamics of natural ecosystems in the Rif region of Northern Morocco. The methodology was based on the inspection and visual interpretation of Landsat and Google Earth image captures, the time series of five Landsat 4-8 image bands, and the Tasseled Cap indices for a random sample of 500 points from 1984 to 2022. The study found that changes affected practically the whole study region over the study period, with around a third of them being ignored due to their very tiny magnitudes or being false positives. The findings demonstrated a general declining trend in the measured changes, indicating a reduction in pressure on different ecosystems. Furthermore, this tendency may be due in part to the availability of Google Earth images during the 2000s, which has significantly reduced the number of false positives. In terms of the year of first change, only 5.7% of pixels experienced their first events after the year 2000, implying that these pixels underwent no change for at least the first 16 years of the study period. On the other hand, 2.5% of the pixels had their last events during the first ten years and have thus remained unmodified for at least 27 years. For the year 2020, the confidence rating of the visual land cover categorization is medium to high for 88.9% of pixels using high-resolution Google Earth photos, whereas the classification quality was inadequate for 64% of pixels in 1984. Despite the stresses on the ecosystems structured by shrubs/shrubs, forests, and herbaceous/shrubs caused by the different disturbances identified, the majority of these ecosystems have not been converted to new land cover classes. According to the study, agriculture is the primary driving force underlying the conversion of forests, herbaceous/shrublands, and even shrublands/shrublands. The area increases for the latter three ecosystems represent, on the one hand, their ability to regenerate themselves and, on the other, Morocco's restoration efforts.

Physiological cold tolerance evolves faster than climatic niches in plants.

Understanding how plants respond to thermal stress is central to predicting plant responses and community dynamics in natural ecosystems under projected scenarios of climate change. Although physiological tolerance is suggested to evolve slower than climatic niches, this comparison remains to be addressed in plants using a phylogenetic comparative approach. In this study, we compared i) the evolutionary rates of physiological tolerance to extreme temperatures with ii) the corresponding rates of climatic niche across three major vascular plant groups. We further accounted for the potential effects of hardening when examining the association between physiological and climatic niche rates. We found that physiological cold tolerance evolves faster than heat tolerance in all three groups. The coldest climatic-niche temperatures evolve faster than the warmest climatic-niche temperatures. Importantly, evolutionary rates of physiological cold tolerance were faster than rates of change in climatic niches. However, an inverse association between physiological cold tolerance and responding climatic niche for plants without hardening was detected. Our results indicated that plants may be sensitive to changes in warmer temperatures due to the slower evolutionary rates of heat tolerance. This pattern has deep implications for the framework that is being used to estimate climate-related extinctions over the upcoming century.

Metatranscriptomics reveals contrasting effects of elevation on the activity of bacteria and bacterial viruses in soil.

Soil microbial diversity affects ecosystem functioning and global biogeochemical cycles. Soil bacterial communities catalyse a diversity of biogeochemical reactions and have thus sparked considerable scientific interest. One driver of bacterial community dynamics in natural ecosystems has so far been largely neglected: the predator-prey interactions between bacterial viruses (bacteriophages) and bacteria. To generate ground level knowledge on environmental drivers of these particular predator-prey dynamics, we propose an activity-based ecological framework to simultaneous capture community dynamics of bacteria and bacteriophages in soils. An ecological framework and specifically the analyses of community dynamics across latitudinal and elevational gradients have been widely used in ecology to understand community-wide responses of innumerable taxa to environmental change, in particular to climate. Here, we tested the hypothesis that the activity of bacteria and bacteriophages codeclines across an elevational gradient. We used metatranscriptomics to investigate bacterial and bacteriophage activity patterns at five sites across 400 elevational metres in the Swiss Alps in 2015 and 2017. We found that metabolic activity (transcription levels) of bacteria declined significantly with increasing elevation, but activity of bacteriophages did not. We showed that bacteriophages are consistently active in soil along the entire gradient, making bacteriophage activity patterns divergent from that of their putative bacterial prey. Future efforts will be necessary to link the environment-activity relationship to predator-prey dynamics, and to understand the magnitude of viral contributions to carbon, nitrogen and phosphorus cycling when infection causes bacterial cell death, a process that may represent an overlooked component of soil biogeochemical cycles.

Microcosm experiment to test bacterial responses to perfluorooctanoate exposure

The impact of perfluoroalkyl and polyfluoroalkyl substances on microbial communities is challenging to investigate in situ because of the complexity and dynamics of natural ecosystems. In the present study, four microcosms were established to explore the impact of perfluorooctanoate (PFOA) on bacterial communities in riverine and marine settings. PFOA distribution between the aqueous and sedimentary phases fluctuated in both PFOA-amended and unamended control systems. PFOA was more rapidly partitioned into the sediment in marine than in riverine microcosms. Differences in iron concentration and salinity may influence PFOA exchange between water and sediment. In marine microcosms, the alpha diversity of bacterial communities was significantly correlated to PFOA concentration. PFOA tended to correlate more strongly with bacterial community composition in water than in sediment. At the whole system level, Lefse's analysis indicated Algoriphagus halophilus as biomarkers for PFOA exposure in both riverine and marine systems, and the family Flavobacteriaceae were also more abundant in the exposed systems. In terms of temporal variation (comparison between three time points in the systems), metastat analysis showed great variability of potential PFOA-sensitive bacteria at the genus level. As such, most PFOA-sensitive genera were transitory and variable and existed for a short term in different systems (river, sea, blank, and experiment) and phases. Compared with other PFOA-sensitive genera, we suggest that further research is carried out to explore the use of Limnobacter as a bioindicator for temporal monitoring of PFOA pollution.

Ratio-Dependence in Predator-Prey Systems as an Edge and Basic Minimal Model of Predator Interference

The functional response (trophic function or individual ration) quantifies the average amount of prey consumed per unit of time by a single predator. Since the seminal Lotka-Volterra model, it is a key element of the predation theory. Holling has enhanced the theory by classifying prey-dependent functional responses into three types that long remained a generally accepted basis of modeling predator-prey interactions. However, contradictions between the observed dynamics of natural ecosystems and the properties of predator-prey models with Holling-type trophic functions, such as the paradox of enrichment, the paradox of biological control, and the paradoxical enrichment response mediated by trophic cascades, required further improvement of the theory. This led to the idea of the inclusion of predator interference into the trophic function. Various functional responses depending on both prey and predator densities have been suggested and compared in their performance to fit observed data. At the end of the 1980s, Arditi and Ginzburg stimulated a lively debate having a strong impact on predation theory. They proposed the concept of a spectrum of predator-dependent trophic functions, with two opposite edges being the prey-dependent and the ratio-dependent cases, and they suggested revising the theory by using the ratio-dependent edge of the spectrum as a null model of predator interference. Ratio-dependence offers the simplest way of accounting for mutual interference in predator-prey models, resolving the abovementioned contradictions between theory and natural observations. Depending on the practical needs and the availability of observations, the more detailed models can be built on this theoretical basis.

Floristic Response of Herbaceous Flora to Intensive Cropping Systems: A Case of Ajibode-sasa Arable Agroecosystem, Ibadan, Southwest Nigeria

Agriculture a most significant land use types which alter natural ecosystem dynamics. Arable farming exerts much pressure on plant biodiversity, especially when practiced intensively in urban centers. There is dearth of information on floristic changes due to intensive arable farming in urban agroecosystems in developing countries. The study therefore assessed floristic changes resulting from and intensive farming practices at Ajibode-Sasa agricultural landscape. Ajibode-Sasa agroecosystem is a complex mix of arable cropping system between latitude N07°28′, E003°53′ and longitude N07°28′, E003°54. Comparative floristic surveys were conducted in 2016 and 2020 using quadrats (1 m2) systematically laid on 18 Transects ranging from 50 – 250 m long. A total of 224 and 184 quadrats were laid in 2016 and 2020 respectively. Reduction in numbers of quadrats laid resulted from physical anthropogenic development after the 2016 survey. Species identification followed standard procedures, and quantitative occurrence data were collected for determination of species composition and computation of relative importance values (RIV) and diversity indices. Land-use changes over four years period was determined using Google earth and QGIS. Herbacous plant composition with 123 cumulative number of species in both years reduced from 98 species in 2016 to 85 species in 2020 species RIV of species ranged from 0.038 – 14.803. Tridax procumbens had the highest RIV (14.803) in 2016, while it was Acmella brachyglossa (13.248) 2020. Species richness and floral diversity was high with Shannon-Weiner Index (3.081 and 3.088) and Dominance (0.09388 and 0.08746) in 2016 and 2020 respectively. Intensive cultivation favoured introduction and spread of invasive species like Tridax procumbens and Tithonia diversifolia. Eight introduced and invasive species were newly enumerated in 2020, with a total of 38 herbaceous species no longer encountered in 2020. Concerted efforts should be made to conserve native flora on the agroecosystem through sustainable practices like crop rotation and short fallow.

Динамика восстановления нарушенных земель горнодобывающей отрасли в соответствии с принципом самоорганизации природных систем и ее прогнозирование по спутниковым данным

Environmental issues associated with the development of mineral deposits are largely caused by the need to store mining and processing waste which becomes a source of environmental pollution. Large areas of dumped ore processing wastes determine the expediency of applying satellite data to monitor the environmental condition of the disturbed lands in order to make justified decisions on restoring the integrity of natural landscapes, which is crucial for the Arctic regions. The purpose of the research is to use the satellite data as the basis to reveal the dynamics of plant formation on the surrounding natural terrain when implementing the technology developed in the Mining Institute of the Kola Scientific Center of the Russian Academy of Sciences in accordance with the self-organizing principle of natural systems in the framework of the rock-biota system evolution. This is achieved by introducing a gramineous plant community without creating a fertile layer, which creates a biologically active environment. Analysis of the vegetation index obtained from a time series of the satellite data that characterizes the introduced vegetational change of the gramineous plant community on the bund wall slopes at the Khibiny group of apatite-containing ore deposits demonstrates the determinant influence of phytocoenotic factors on the recovery dynamics of natural ecosystems. A geobotanical study of the monitoring site has shown that in transition from the introduced gramineous to the forest stage of vegetational change, we observe a tier structure and large-scale resettlement of species from the adjacent natural areas, which is consistent with an increase in the vegetation index and allows to predict the dynamics of the natural ecosystem recovery.

Multitemporal Analysis of Deforestation in Response to the Construction of the Tucuruí Dam

The expansion of hydroelectric dams that is planned, and under construction, in the Amazon basin is a proposal to generate “clean” energy, with the purposes of meeting the regional energy demand, and the insertion of Brazil into the international economic market. However, this type of megaproject can change the dynamics of natural ecosystems. In the present article, the spatiotemporal patterns of deforestation according to distance from the reservoir in the vicinity of the lake of Tucuruí, and within a radius of 30 km from it, are analyzed. A linear spectral mixture model of segmented Landsat-thematic mapper (TM), enhanced thematic mapper plus (ETM+), and operational land imager (OLI) images, and proximity analysis were used for the mapping of the land-cover classes in the vicinity of the artificial lake of Tucuruí. Likewise, landscape metrics were determined with the purpose of quantifying the reduction of primary forest, as a mechanism of loss of ecosystem services in the region. These methods were also used for the evaluation of the influence of the distance from the reservoir on the expansion of anthropogenic activities. This methodology was used for the scenarios of pre-inauguration, completion of phase I, beginning of construction phase II, full completion of the Tucuruí hydroelectric project, and the current scenario of the region. The results showed that the highest deforestation rate occurred in the first period of the analysis, due to the areas submerged by the reservoir and due to the anthropogenic disturbances, such as timber extraction, road construction, and the conversion of forests into large areas of agribusiness.

Mechanistic insights into the role of large carnivores for ecosystem structure and functioning

Large carnivores can exert top–down effects in ecosystems, but the size of these effects are largely unknown. Empirical investigation on the importance of large carnivores for ecosystem structure and functioning presents a number of challenges due to the large spatio‐temporal scale and the complexity of such dynamics. Here, we applied a mechanistic global ecosystem model to investigate the influence of large‐carnivore removal from undisturbed ecosystems. First, we simulated large‐carnivore removal on the global scale to inspect the geographic pattern of top–down control and to disentangle the functional role of large carnivores in top–down control in different environmental contexts. Second, we conducted four small‐scale ecosystem simulation experiments to understand direct and indirect changes in food‐web structure under different environmental conditions. We found that the removal of top–down control exerted by large carnivores (> 21 kg) can trigger large trophic cascades, leading to an overall decrease in autotroph biomass globally. Furthermore, the loss of large carnivores resulted in an increase of mesopredators. The magnitude of these changes was positively related to primary productivity (NPP), in line with the ‘exploitation ecosystem hypothesis’. In addition, we found that seasonality in NPP dampened the magnitude of change following the removal of large carnivores. Our results reinforce the idea that large carnivores play a fundamental role in shaping ecosystems, and further declines and extinctions can trigger substantial ecosystem responses. Our findings also support previous studies suggesting that natural ecosystem dynamics have been severely modified and are still changing as a result of the widespread decline and extinction of large carnivores.

VA‐TRAC: Geospatial Trajectory Analysis for Monitoring, Identification, and Verification in Fishing Vessel Operations

AbstractIn order to ensure sustainability, fishing operations are governed by many rules and regulations that restrict the use of certain techniques and equipment, specify the species and size offish that can be harvested, and regulate commercial activities based on licensing schemes. As the world's second largest exporter offish and seafood products, Norway invests a significant amount of effort into maintaining natural ecosystem dynamics by ensuring compliance with its constantly evolving science‐based regulatory body. This paper introduces VA‐TRAC, a geovisual analytics application developed in collaboration with the Norwegian Directorate of Fisheries in order to address this complex task. Our approach uses automatic methods to identify possible catch operations based on fishing vessel trajectories, embedded in an interactive web‐based visual interface used to explore the results, compare them with licensing information, and incorporate the analysts’ domain knowledge into the decision making process. We present a data and task analysis based on a close collaboration with domain experts, and the design and implementation of VA‐TRAC to address the identified requirements.

From Lotka–Volterra to Arditi–Ginzburg: 90 Years of Evolving Trophic Functions

The trophic function, often called a “functional response,” determines qualitative properties in models of predator–prey dynamics. Many of the theoretical and empirical studies have demonstrated the problem of choosing and fitting a trophic function to experimental data. Notably the publication by Arditi and Ginzburg (1989) has stimulated a lively debate in scientific literature regarding the application of trophic functions. The authors highlighted contradictions between the observed dynamics of natural ecosystems and the qualitative properties of predator–prey models using Holling-type trophic functions. They suggested revising the theoretical models by means of the trophic functions that depend on the ratio of prey to predator abundances. By comparing this and other proposed trophic functions, we demonstrate that the Arditi–Ginzburg function offers the simplest way of accounting for mutual interference in predator–prey models. This trophic function effectively resolves contradictions between theoretical models and natural systems, including the paradox of enrichment, paradox of biological control, and the paradoxical enrichment response mediated by trophic cascades. We review the debate regarding the Arditi–Ginzburg model and present recent results obtained with continuous and individual-based models of animal foraging behaviour in predator–prey systems, which explain predator interference as an emerging property.

Landscape structure and climate drive population dynamics of an insect vector within intensely managed agroecosystems.

Characterizing factors affecting insect pest populations across variable landscapes is a major challenge for agriculture. In natural ecosystems, insect populations are strongly mediated by landscape and climatic factors. However, it has proven difficult to evaluate if similar factors predict pest dynamics in agroecosystems because control tactics exert strong confounding effects. We addressed this by assessing whether species distribution models could effectively characterize dynamics of an insect pest in intensely managed agroecosystems. Our study used a regional multi-year data set to assess landscape and climatic drivers of potato psyllid (Bactericera cockerelli) populations, which are often subjected to calendar-based insecticide treatments because they transmit pathogens to crops. Despite this, we show that psyllid populations were strongly affected by landscape and climatic factors. Psyllids were more abundant in landscapes with high connectivity, low crop diversity, and large natural areas. Psyllid population dynamics were also mediated by climatic factors, particularly precipitation and humidity. Our results show that many of the same factors that drive insect population dynamics in natural ecosystems can have similar effects in an intensive agroecosystem. More broadly, our study shows that models incorporating landscape and climatic factors can describe pest populations in agroecosystems and may thus promote more sustainable pest management.

Changes in Deadwood and Understory Vegetation 12 Years after Partial and Clearcut Harvesting in Mixedwood Stands of Western Quebec, Canada

AbstractEcosystem management promotes the integration of knowledge of natural ecosystem dynamics into forest-management planning and practices, and provides a useful framework for understanding and mitigating the impacts of timber harvesting on biodiversity and ecosystem functions. Understory vegetation and deadwood are involved in many ecosystem functions including nutrient and carbon, and tree-regeneration dynamics. The study objective was to compare the 12-year post-treatment effects on forest floor attributes of two intensities of partial harvesting (gap harvesting [62 percent basal area retention; BAR] and diameter-limit harvesting [35 percent BAR]) to clearcutting (10 percent BAR). We quantified the standing and downed deadwood abundance and the understory plant community composition in mixed, northern temperate forests, in western Québec, Canada. Our results suggest that moderate-intensity gap harvesting can best preserve a standing deadwood stem density and a diameter structure comparable to unmanaged stands. Downed deadwood abundance of all diameter classes was not altered, 12 years following the gap harvesting. Finally, understory plant communities in the gap treatment were more similar to those of unmanaged stands than those in diameter-limit and clearcutting treatments. These results illustrate the importance of tree retention levels for the maintenance of deadwood and understory plant species associated with closed-canopy or old-growth forests.

Adaptive Strategies of Desert Plants in Coping with the Harsh Conditions of Desert Environments: A Review

The low and erratic precipitation of desert habitats and the resultant drought have been a huge environmental challenge to the desert flora. Because these organisms must harmonize their structures and functions to thrive in their environments, they have evolved a range of strategies to survive the drought that characterizes the desert ecosystem. Desert plants have adopted some strategies like drought tolerance, drought escape, and succulence as the means to conserve and use water. Also, to minimize the rate of transpiration, they have evolved leaf sclerophylly. All these adaptations and more, play an important role in the organisms’ ability to conquer the harsh conditions of desert environments amidst the prevailing climate changes. It seems that some of these plants could potentially serve as models for understanding drought adaptation mechanisms and their potential uses. It is expected that understanding the response of plants to increasing drought would be important in the light of global and regional climate changes, not only to forecast population dynamics in natural ecosystems but also to adjust management processes in agronomy and vegetation management for improvement.

Soil nutrients, forest structure and species traits drive aboveground carbon dynamics in an old-growth temperate forest

Forests store a substantial amount of terrestrial carbon (C), but the drivers of forest C dynamics remain poorly understood, especially in old-growth forests. Here, we evaluate how aboveground C dynamics (i.e., net C change and its demographic processes: C gain from the growth of surviving trees (∆C-surv), C gain from the growth of recruited trees (∆C-recr) and C loss by tree mortality (∆C-mort)) are driven by vegetation attributes (diversity, trait composition and forest structure) and habitat conditions (soil properties and light environment), as well as how ∆C-surv, ∆C-recr and ∆C-mort contribute to net C change. Using 10-year interval demographic data from a 9-ha permanent plot in an old-growth temperate forest in northeastern China, we performed structural equation model to relate the C dynamics to the vegetation attributes and habitat conditions. The net C change is most strongly determined by ∆C-mort. High soil phosphorus concentrations increased ∆C-surv, soil moisture increased ∆C-recr, and leaf area index increased both ∆C-surv and ∆C-recr. Diversity (i.e., structural diversity) had a positive relationship with ∆C-surv but was not related to ∆C-recr or ∆C-mort. Trait composition was significantly related to all three demographic processes. Forest structure was the best predictor of ∆C-surv and ∆C-recr. The net C change increased with higher soil phosphorus concentrations and basal area and in communities dominated by conservative traits (i.e., high wood density). This study highlights that soil nutrients, forest structure and trait composition are important drivers of net C change in old-growth temperate forests. Better insights into C storage and productivity can be gained by simultaneously evaluating the vegetation attributes and habitat conditions of C dynamics in natural ecosystems.

A SD-MaxEnt-CA model for simulating the landscape dynamic of natural ecosystem by considering socio-economic and natural impacts

Background climate and socio-economy significantly affect the landscape dynamics of natural ecosystem. And the simulated method to understand the landscape dynamics of natural ecosystems in responding to human and natural effects is increasingly important for ecosystem management. In this study, we integrated system dynamics, MaxEnt and cellular automata models (called as SD-MaxEnt-CA model) to consider climatic effects and human activities during the simulation of natural ecosystems landscape dynamics. In the integrated model, the MaxEnt process was used for the interactive coupling of the top-down SD and bottom-up CA, which improve the model’s ability to accurately acquire the weights of each layer and transition rules during the simulation with the effects of climate changes. This proposed model was applied to simulate the landscape degradation of natural forest caused by the expanding of farmland, tea gardens and rubber plantations in Xishuangbanna from 2000 to 2010, one of the world’s 34 biodiversity hotspots. By the comparison with other algorithms, the MaxEnt achieve a good performance in acquiring the weights of each layer. The spatial consistent between simulated map and actual result reached to 84.2%, indicating the promising grid-to-grid agreement. Proposed model considered the driving of climate changes and socio-economy, which improved the accuracy of simulating the landscape dynamics of natural ecosystems. The method was further used in simulating the landscape dynamics of natural forest in Xishuangbanna from 2010 to 2030 under four different climate scenarios. The variation of conversion area among different climate scenarios is consistent with their response to climate changes. The simulation results demonstrate that the proposed model is effective for the landscape simulation of natural ecosystems.

Rosa multiflora’s performance under water stress: the role of positive and negative density-dependent intraspecific interactions

It is well known that biotic interactions may significantly alter plant population and community dynamics in natural ecosystems. Multiple studies have reported that density-dependent positive interactions can modify the effect of extreme stress on plant performance (in line with predictions by the stress gradient hypothesis, SGH). However, the performance of invasive species and the role of intraspecific density dependence, either negative or positive, in successful invasions are not well understood. In the present study, we tested if monocultures of Rosa multiflora, a highly invasive shrub, experience a group advantage under extremely low water availability. Using a manipulative greenhouse study, we tested the growth response of R. multiflora seedlings to a 4-level conspecific density treatment and a 4-level water availability gradient. Overall, our results provide preliminary evidence that biotic interactions under stressful conditions between R. multiflora individuals do not experience a group advantage, as predicted. Instead, our study indicates that seedling performance was strongly driven by negative density dependence, in which individuals grown at higher conspecific densities displayed lower plant performance, regardless of water availability. This demonstrates that R. multiflora experiences intense intraspecific competition even under a stressful, low resource environment. Thus, management efforts of R. multiflora need to ensure that re-sprouting of individuals after treatment is eliminated, as release from negative density dependence could lead the invader population to rebound.