Disturbance Events Research Articles

Long-term spatial variations in turbidity and temperature provide new insights into coral-algal states on extreme/marginal reefs

Globally, coral reefs are under threat, with many exhibiting degradation or a shift towards algal-dominated regimes following marine heat waves, and other disturbance events. Marginal coral reefs existing under naturally extreme conditions, such as turbid water reefs, may be more resilient than their clear water counterparts as well as offer some insight into how reefs could look in the future under climate change. Here, we surveyed 27 benthic habitats across an environmental stress gradient in the Exmouth Gulf region of north Western Australia immediately following a marine heatwave event. We used multidecadal remotely sensed turbidity (from an in-situ validated dataset) and temperature, to assess how these environmental drivers influence variability in benthic communities and coral morphology. Long-term turbidity and temperature variability were associated with macroalgal colonisation when exceeding a combined threshold. Coral cover was strongly negatively associated with temperature variability, and positively associated with depth, and wave power, while coral morphology diversity was positively associated with turbidity. While moderate turbidity (long-term average ~ 2 mg/L suspended matter) appeared to raise the threshold for coral bleaching and macroalgal dominance, regions with higher temperature variability (> 3.5 °C) appeared to have already reached this threshold. The region with the least turbidity and temperature variability had the highest amount of coral bleaching from a recent heatwave event and moderate levels of both these variables may confer resilience to coral reefs.

Near real-time monitoring of tropical forest disturbance by fusion of Landsat, Sentinel-2, and Sentinel-1 data

The ability to detect forest disturbance rapidly relies heavily on the frequency of usable satellite observations. Combining optical and SAR data can provide the most usable observations in the tropics and hence has the potential to achieve more timely detection of forest disturbance than using any individual sensor system. A new algorithm (Fusion Near Real-Time, or FNRT) for near real-time monitoring of tropical forest disturbance by fusion of Landsat, Sentinel-2, and Sentinel-1 data fits a time series model to the data of each individual sensor system and produces a change score for each clear observation during the monitoring period. The change scores from the three different kinds of sensors are then combined for disturbance monitoring. Applying FNRT using all three data sources in eight selected sites in the Amazon Basin detected 69.8 ± 5% and 84.6 ± 4.1% of the forest disturbances within the first 30 and 60 days, respectively. FNRT using all three sensors reached a peak producer's accuracy of 91.6 ± 3.2% at approximately a 100-day lag time, compared to 86.4 ± 3.8% using the two optical sensors combined, and 71.7 ± 4.7% using Landsat only (the best-performing single-sensor). The user's accuracy of FNRT using all three sensors increased to 90.9 ± 3.3% when excluding false detections in non-forest areas. Overall, the model result using all three data sources had the highest detection rate with shorter lag times. Although modest, including Sentinel-1 data in the multi-sensor fusion approach improved the detection speed of some disturbance events. Given the abundance of optical data during the dry season in our study region, Sentinel-1 data would be more valuable during the wet season or in persistently cloudy regions such as Madagascar or coastal West Africa.

Fire‐produced coarse woody debris and its role in sediment storage on hillslopes

AbstractInteractions between vegetation and sediment in post‐fire landscapes play a critical role in sediment connectivity. Prior research has focused on the effects of vegetation removal from hillslopes, but little attention has been paid to the effects of coarse woody debris (CWD) added to the forest floor following fires. We investigate the impacts of CWD on hillslope sediment storage in post‐fire environments. First, we present a new conceptual model, identifying “active” storage scenarios where sediment is trapped upslope of fire‐produced debris such as logs, and additional “passive” storage scenarios including the reduced effectiveness of tree‐throw due to burnt roots and snapped stems. Second, we use tilt table experiments to test controls on sediment storage capacity. Physical modeling suggests storage varies nonlinearly with log orientation and hillslope gradient, and the maximum storage capacity of log barriers in systems with high sediment fluxes likely exceeds estimates that assume simple sediment pile geometries. Last, we calculate hillslope sediment storage capacity in a burned catchment in southwest Montana by combining high‐resolution topographic data and digitization of over 5000 downed logs from aerial imagery. We estimate that from 3500–14 000 m3of sediment was potentially stored upslope of logs. These estimates assume that all downed logs store sediment, a process that is likely temporally dynamic as storage capacity evolves with CWD decay. Our results highlight the role that CWD plays in limiting rapid sediment movement in recently burned systems. Using a range of potential soil production rates (50–100 mm/ky), CWD would buffer the downslope transport of ~35–280 years of soil produced across the landscape, indicating that fire‐produced CWD may serve as an important source of sediment disconnectivity in catchments. These results suggest that disturbance events have previously unaccounted‐for mechanisms of increasing hillslope sediment storage that should be incorporated into models of sediment connectivity.

Isotopic niche of New Jersey terrapins suggests intraspecific resource partitioning, and little variability following a major hurricane

Diamondback terrapins (Malaclemys terrapin) are sexually dimorphic generalist turtles that inhabit salt marshes and estuaries along the Atlantic and Gulf coasts of the United States. On October 29th, 2012, Hurricane Sandy made landfall in New Jersey, USA, directly impacting terrapin populations inhabiting central and southern Barnegat Bay. To examine potential food web mediated impacts to the terrapin population and their foraging dynamics we examined carbon and nitrogen stable isotope values collected from terrapin tissues (2011, 2015, 2019) and resource taxa (2015, 2019) within Barnegat Bay. Isotopic analysis revealed that mature females had lower carbon and higher nitrogen values than immature females and males with almost no isotopic niche overlap, whereas males and immature females had statistically similar values with overlapping niches. Terrapins and resources collected from island habitats contained higher carbon and nitrogen values than those from mainland habitats, with little overlap in niche between habitats. There were no significant temporal variations detected in either carbon or nitrogen values from terrapins between years, or within each habitat pre- and post-Hurricane Sandy. These findings suggest long-term terrapin foraging dynamics have remained relatively stable, signifying resilience to disturbance events within the study site.

Contrasting effects of urbanization and fire on understory plant communities in the natural and wildland–urban interface

AbstractAs human populations expand and land‐use change intensifies, terrestrial ecosystems experience concurrent disturbances (e.g., urbanization and fire) that may interact and compound their effects on biodiversity. In the urbanizing landscapes of the southern Appalachian region of the United States of America (US), fires in mesic forests have become more frequent in recent years. However, 80 years of forest management practices aimed at fire suppression in this region may have decreased landscape resistance or resilience to high‐severity fires. At the same time, housing development is rapidly expanding in the wildland–urban interface, creating opportunities to examine the combined effects of urbanization and fire disturbances on plant communities when fires occur. Here, we investigated how understory plant communities were affected by a fire that varied in severity at sites in Gatlinburg, TN, and in the adjacent Great Smoky Mountains National Park. Our goal was to investigate the individual and combined effects of fire and urbanization on plant community composition in the second growing season after a fire. Overall, we found a significant interaction effect of fire severity and urbanization on total plant abundance and richness, such that increasing fire severity was associated with lower abundance and richness in natural areas but higher abundance and richness in exurban areas. Shannon diversity was significantly affected by fire severity and urbanization, but not interactively. Plant composition was affected by fire severity, urbanization, and their interaction effects. Understory plant communities in exurban locations (low‐density residential areas near protected lands) were resilient following the pulse disturbance event (fire), likely because of their consistent exposure to a press disturbance (urbanization). Our study indicates a press disturbance may change the way a subsequent pulse disturbance affects plant communities. Our findings contribute new insights into how disturbances can interact to alter patterns of biodiversity in the southeastern US.

Intelligent Controller Design and Fault Prediction Using Machine Learning Model

In a solar power plant, a solid phase transformer and an optimization coordinated controller are utilized to improve transient responsiveness. Transient stability issues in a contemporary electrical power system represent one of the difficult tasks for an electrical engineer due to the rise in uncertain renewable energy sources (RESs) as a result of the need for green energy. The potential for terminal voltage to be adversely impacted by this greater RES raises the possibility of electrical device damage. It is possible to use a solid state transformer (SST) or smart transformer to address a transient response issue. These devices are frequently employed to interact between RES and a power grid. SST features a variety of regulated converters to maintain the necessary voltage levels. This method can therefore simultaneously lessen power fluctuations and transient responsiveness. In order to improve the quality of RES power injections and the electrical system’s transient stability, this work provides a controller design for a solar photovoltaic (SPV) system that is connected to the grid by SST. The optimization of a controller model is proposed by modifying a PI controller taken from a commercial one. With the use of IEEE 39 standard buses, the proposed controller is tested. When evaluating the effectiveness of a suggested controller, it is important to take into account a variety of solar radiation patterns as well as a time delay uncertainty that can range from 425 ms to 525 ms. According to simulation results, the proposed controller can be employed to lessen power fluctuation brought on by unpredictable RES. Additionally, the proposed coordinated regulation of SPV and SST can prevent catastrophic damage in the event of substantial disturbances like a circuit breaker collapsing to expand a power line due to a fault by inhibiting significant voltage cycles within an electronic appliance’s rated voltage limit. The results indicate that a transitory stability issue in a modern power system caused by an unforeseen increase in RES may be addressed utilizing the suggested controllers as alternatives.

Spatiotemporal Variability in Disturbance Frequency and Severity across Mexico: Evidence from Conifer Tree Rings

It is critical to understand the ecological processes of forest dynamics by identifying past forest disturbances to take appropriate management actions. Tree-rings are commonly used for this purpose due to their reliability and accuracy. Here, we used a network of ring-width data distributed along a broad ecological gradient for the spatiotemporal identification of forest disturbances in 15 species of 13 sites of young Mexican conifers. We found different spatial and temporal patterns in the occurrence of forest disturbance. The species with the highest disturbance rates were Pinus patula (Ppa; El Jacalón), Pinus montezumae (Pmo; La Cueva), Pinus hartwegii (Phc; Cerro El Moro), and Pinus teocote (Pts; Rancho Joyas del Durazno) of the Gulf of Mexico, and Pinus ayacahuite (Pay; Corral de los Borregos) of the Mexico Center. The highest number of disturbances was found in 1953, 1956, 1976, and 1980; however, we noted that the number of disturbances tended to increase from 1975 to 1990 and particularly from 2000 onwards. The species close to the Gulf of Mexico presented a higher frequency and severity of disturbances than those located close to the Pacific Ocean. Thus, our results demonstrate a spatiotemporal pattern of disturbance events, which deserves further analysis, including regarding the drivers of disturbance. This knowledge is crucial for a better understanding of the dynamics of contemporary species.

Trends in post‐1950 riparian vegetation recovery in coastal catchments of NSW Australia: Implications for remote sensing analysis, forecasting and river management

AbstractExtensive riparian vegetation clearance occurred in many rivers of southeastern Australia throughout the 19th and 20th century, post colonisation. With improvements in river management practices, coincident with a period of minimal flooding, vegetation recovery of riparian corridors has been occurring since the 1980s in all coastal catchments of New South Wales (NSW). However, the catchment‐by‐catchment spatial pattern and temporal trends, trajectories and rates of vegetative recovery remain unknown. We reconstruct a 70‐year time series of change in riparian vegetation coverage for all rivers in coastal catchments of NSW, utilising historical aerial imagery, Landsat and Sentinel data and a manual digitisation and machine learning method. We quantify and statistically analyse decadal trends in woody and non‐woody vegetation coverage along 19 485 km of stream length in 20 catchments. Across the region, there has been, on average, a 40% increase in vegetation coverage along riparian corridors since the 1950s, with some catchments increasing towards a current day coverage of between 60% and 80%. However, the trends vary by subregion and by catchment. An early logarithmic increase occurred up to 2004 on the North coast, and a recent and accelerated exponential increase since 1995 has occurred on the South coast. After a steep initial increase, riparian corridor vegetation coverage has fluctuated on the Central coast since about 1995. We used these linear, exponential and logarithmic regressions to undertake preliminary forecasts of possible future timeframes of riparian vegetation change, based on several climate, management and natural disaster disturbance scenarios. If the current trend continues, riparian vegetation coverage can reach 70% across the region by 2055. However, if management practices change or catastrophic disturbance events such as fire and flood occur, increases in riparian vegetation coverage could be set back by up to 30 to 40 years.

Perbaikan Tegangan dengan Menggunakan Kapasitor Bank 25 MVAR pada Gardu Induk Banda Aceh

The Nagan Raya coal-fired power plant in Aceh, Indonesia, serves as a major supplier of electricity to the region's power grid. However, the power generation unit of the plant, which supplies reactive power to the subsystem, often experiences disturbances that cause voltage values in the Banda Aceh substation system to decrease. This decrease in voltage can be detrimental to the quality of power supplied to the consumers. To address this issue, a capacitor bank with a capacity of 25 Mvar was installed at the end of 2016. The capacitor bank was successful in increasing the voltage value at the substation and proved to be an effective solution. However, with the anticipated growth in load in the coming years and the possibility of future disturbances in the power generation unit, it has been proposed that an additional capacitor bank unit with the same capacity be installed to further enhance the voltage quality at the Banda Aceh substation. To assess the feasibility of this proposal, simulations were carried out using ETAP 12.6.0 software. The simulation results show that the addition of a 25 Mvar capacitor bank unit would lead to an increase in the substation voltage value of around 5-6 KV. This increase in voltage would help to maintain the quality of power supplied to the consumers and ensure that the power grid remains stable even in the event of disturbances in the power generation unit. Overall, the proposed installation of an additional capacitor bank unit would be a cost-effective solution to enhance the voltage quality at the Banda Aceh substation and ensure the stability of the power grid. This solution could be adopted by other power plants facing similar issues in maintaining voltage quality in their power grid systems.

Linking disturbance history to current forest structure to assess the impact of disturbances in tropical dry forests

Tropical dry forests are widespread, harbour vast amounts of carbon and unique biodiversity, and underpin the livelihoods of millions. A variety of natural and anthropogenic disturbances affect tropical dry forest canopy, yet our understanding of how these disturbances impact on forest structure and ecosystem functioning, and how forests develop after different disturbances, is partial. This translates into knowledge gaps regarding long-term outcomes of disturbances on forest structure as well as which of these outcomes signify recovery vs forest degradation. Here, we use a rich dataset of remotely-sensed, high-resolution forest indicators in a multilevel Bayesian regression framework to understand the effect of different disturbance agents (partial clearing, fire, logging, drought and riparian changes) on aboveground biomass, and woody cover in the Argentine Dry Chaco. Our models show that post-disturbance trajectories of forest structural indicators differ markedly among different disturbance agents. For example, riparian changes affected biomass most strongly but had the fastest recovery, whereas logging had a generally lower impact and mostly affected tree cover, but recovery was slow or never occurred. Importantly, even three decades after the disturbance event, woody cover and biomass exhibited higher values for natural disturbances compared to anthropogenic disturbances. Furthermore, anthropogenic disturbances had slower recovery rates than natural disturbances. Overall, our approach shows the potential of remote-sensing indicators and space-for-time substitution to unravel the diverse vegetation response of different disturbance agents. Given the high and rising human pressure on dry forests in the Chaco and globally, our findings also show the long-lasting effects that anthropogenic disturbances have on these valuable forests.

Biotic homogenisation and differentiation as directional change in beta diversity: synthesising driver-response relationships to develop conceptual models across ecosystems.

Biotic homogenisation is defined as decreasing dissimilarity among ecological assemblages sampled within a given spatial area over time. Biotic differentiation, in turn, is defined as increasing dissimilarity over time. Overall, changes in the spatial dissimilarities among assemblages (termed 'beta diversity') is an increasingly recognised feature of broader biodiversity change in the Anthropocene. Empirical evidence of biotic homogenisation and biotic differentiation remains scattered across different ecosystems. Most meta-analyses quantify the prevalence and direction of change in beta diversity, rather than attempting to identify underlying ecological drivers of such changes. By conceptualising the mechanisms that contribute to decreasing or increasing dissimilarity in the composition of ecological assemblages across space, environmental managers and conservation practitioners can make informed decisions about what interventions may be required to sustain biodiversity and can predict potential biodiversity outcomes of future disturbances. We systematically reviewed and synthesised published empirical evidence for ecological drivers of biotic homogenisation and differentiation across terrestrial, marine, and freshwater realms to derive conceptual models that explain changes in spatial beta diversity. We pursued five key themes in our review: (i) temporal environmental change; (ii) disturbance regime; (iii) connectivity alteration and species redistribution; (iv) habitat change; and (v) biotic and trophic interactions. Our first conceptual model highlights how biotic homogenisation and differentiation can occur as a function of changes in local (alpha) diversity or regional (gamma) diversity, independently of species invasions and losses due to changes in species occurrence among assemblages. Second, the direction and magnitude of change in beta diversity depends on the interaction between spatial variation (patchiness) and temporal variation (synchronicity) of disturbance events. Third, in the context of connectivity and species redistribution, divergent beta diversity outcomes occur as different species have different dispersal characteristics, and the magnitude of beta diversity change associated with species invasions also depends strongly on alpha and gamma diversity prior to species invasion. Fourth, beta diversity is positively linked with spatial environmental variability, such that biotic homogenisation and differentiation occur when environmental heterogeneity decreases or increases, respectively. Fifth, species interactions can influence beta diversity via habitat modification, disease, consumption (trophic dynamics), competition, and by altering ecosystem productivity. Our synthesis highlights the multitude of mechanisms that cause assemblages to be more or less spatially similar in composition (taxonomically, functionally, phylogenetically) through time. We consider that future studies should aim to enhance our collective understanding of ecological systems by clarifying the underlying mechanisms driving homogenisation or differentiation, rather than focusing only on reporting the prevalence and direction of change in beta diversity, per se.

Multi-Temporal Trend Analysis of Coastal Vegetation Using Metrics Derived from Hyperspectral and LiDAR Data

Monitoring and modeling of coastal vegetation and wetland systems are considered major challenges, especially when considering environmental response to hazards, disturbances, and management activities. Remote sensing applications can provide alternatives and complementary approaches to the often costly and laborious field-based collection methods traditionally used for coastal ecosystem monitoring. New and improved sensors and data analysis techniques have become available, making remote sensing applications attractive for evaluation and potential use in monitoring coastal vegetation properties and ecosystem conditions and change. This study involves the extraction of vegetation metrics from airborne LiDAR (Light Detection and Ranging) and hyperspectral imagery (HSI) to quantify coastal dune vegetation characteristics and assesses landscape-level trends from those derived metrics. HSI- and LiDAR-derived elevation (digital elevation model) and vegetation metrics (canopy height model, leaf area index, and normalized difference vegetation index) were used in conjunction with per-pixel linear regression and hot spot analyses to evaluate hurricane-induced spatial and temporal changes in elevation and vegetation properties. These assessments showed areas with greatest decreases in vegetation metric values were associated with direct tropical storm energies and processes (i.e., overwashing events eroding beach and dune features), while those with the greatest increases in vegetation metric values were in areas where overwashed sediments were distributed. This study narrows existing gaps in dune vegetation data by advancing new methodologies to classify, quantify, and estimate critical coastal vegetation metrics. The tools and methods developed in this study will ultimately improve future estimates and predictions of nearshore dynamics and impacts from disturbance events.

Disentangling regeneration by vertical stratification: A 17-year gap-filling process in a temperate secondary forest

Forest gaps are widely spread in the forest ecosystems and play important roles in driving forest dynamics. However, long-term regeneration during the gap-filling process was less understood, especially species composition and dynamics along vertical gradients over time. We monitored tree regeneration in artificial gaps of a temperate secondary forest for 17 years and analyzed the gap-filling process both as a whole and by stratification (lower layer: 0∼3 m, middle layer: 3∼6 m, and upper layer: >6 m) for three shade-tolerance groups of tree species. We found that the interaction effects of gap size and shade tolerance could result in a growth difference of five to ten years among different regeneration groups, with the most significant effects in the large gaps for the light-demanding species such as Juglans mandshurica and Phellodendron amurense. Regeneration density in the large and small gaps eventually converged, but there were great differences in density dynamics. The regeneration density in the large gaps decreased gradually over time, while it decreased sharply in the small gaps after just one growing season of gap formation and consistently remained at low levels regardless of shade tolerance. Species richness decreased smoothly during the 17-year monitoring, but the richness in the large gaps was consistently higher than that in the small gaps, with all shade-tolerance groups existing, which underlined the importance of gap size in maintaining tree species diversity. Differences in the density, richness, and composition among regeneration layers reduced over time. However, vertical regeneration patterns diverged among shade-tolerance groups during the gap-filling process. Light-demanding species were likely to have only one chance for successful regeneration because almost no new recruitments appeared in the lower or middle layer as dominant stems reached the upper layer. Intermediate and shade-tolerant species, by contrast, were well-distributed in different regeneration layers, indicating a stronger capacity for resistance and resilience during uncertain disturbance events in the long run. Our results revealed the gap-filling strategies of tree species with different shade-tolerance groups, which explained why light-demanding species could not completely occupy a forest gap and highlighted the necessity of repeated gap disturbance for intermediate and shade-tolerant species regeneration.

Overview about E-Mobility Conducted Immunity Tests on ESA Communication Lines

Due to the complexity of the Automotive Electromagnetic Compatibility legislation in force, this article aims to describe a simplified overview of several technical standards relating to conducted immunity tests on electronic sub-assemblies, where communication lines are involved. The discussed automotive standards reported in this article are: ISO 11452-1 and ISO 11452-4 for continuous narrowband electromagnetic fields immunity test, bulk current injection and tubular wave coupler, IEC 61000-4-5 for immunity against surge events, IEC 61000-4-4 for electrical fast transient/burst events immunity, ISO 10605 for electrostatic discharge events immunity, ISO 7637-2 and ISO 7637-3 for transient disturbances events immunity. For each cited standard, disturbance bandwidth evaluation was performed. Practical examples are reported, with analysis and discussion of some of the adoptable disturbance countermeasures applicable on controlled area network communication lines, and possible design advantages and disadvantages with different types of filtering and suppression circuit solutions.

Tipping time in a stochastic Leslie predator–prey model

Critical transitions are usually accompanied by a decline in ecosystem services and potentially have negative impacts on human economies. Although some early warning signals based on a generic characteristic of local bifurcations, such as variance and autocorrelation, can be used to predict an imminent critical transition, studies have shown that these indicators are ineffective for purely stochastic transitions. In this paper, we propose to use the maximum likelihood state, based on the Fokker–Planck equation, to track the true state of a predator–prey model under noisy fluctuations. Then, we use the maximal likely trajectory to determine tipping times for the most probable transitions from a high biomass state to a low biomass one. Numerical results show that the tipping times of population collapse depend strongly on the noise intensity and the growth rate of predator. We uncover that the enhanced disturbance events promote ecosystem collapse and that an increase in predator growth rate significantly alleviates the influence, which is beneficial to the stability and biodiversity of an ecosystem. Based on this, we define a two-dimensional region, called the Safe Operating Set (SOS) of the population ecosystem. SOS boundary exhibits a trade-off such that increased predator growth rates can compensate to some degree for losses from environmental perturbations. To verify the above conclusions, we fix noise intensity and calculate the quasi-potentials of the corresponding high biomass state for different predator growth rates. We can see that the results for measuring the stability of the high biomass state derived from the perspective of quasi-potential are consistent with the results obtained from the analysis of tipping time.

Linked disturbance in the temperate forest: Earthworms, deer, and canopy gaps.

Despite the large body of theory concerning multiple disturbances, relatively few attempts have been made to test the theoretical assumptions of how and if disturbances interact. Of particular importance is whether disturbance events are linked, as this can influence the probability and intensity of ecological change. Disturbances are linked when one disturbance event increases or decreases the likelihood or extent of another. To this end, we used two long-term, multi-disturbance experiments in northern Wisconsin to determine whether earthworm invasion is linked to canopy gap creation and white-tailed deer browsing. These three disturbances are common and influential within North American temperate forests, making any interactions among them particularly important to understand. We expected both deer and canopy gaps to favor invasive earthworms, particularly species that live close to or on the soil surface. However, we found only partial support of our hypotheses, as both deer exclosures and canopy gaps decreased earthworms in each experiment. Further, earthworm density increased the most over time in areas far from the gap center and in areas with deer present. Deer exclosures primarily decreased Aporrectodea and Lumbricus species, while gaps decreased Dendrobaena and Lumbricus species. Our findings show that earthworm invasion is linked to deer presence and gap-creating disturbances, which provides new insight in multiple disturbance theory, aboveground-belowground dynamics, and temperate forest management.

Population dynamics and individual growth dynamics of Larix gmelinii under non-stand replacing fire

The population dynamics and individual growth dynamics of dominant tree species in boreal forests are associated with fire regimes. Fire regimes in the boreal forests of eastern Siberia are dominated by non-stand replacing (NSR) fire types. Fire drives population demographics by triggering tree mortality and births, and affects the post-fire growth dynamics of surviving individuals. When a non-stand replacing fire occurs, population dynamics fluctuate and individual growth changes occur simultaneously. The Great Xing’an Mountains is located at the southern edge of the eastern Siberia boreal forest and research on fire regimes and stand dynamics in this region are scarce. Understanding the effect of fire on the population structure and individual growth of the dominant species in the stand and the disturbance mechanisms are essential to understand the develop of boreal forests in the context of climate warming. In this study, three Larix gmelinii stands disturbed by NSR fire in the Great Xing’an Mountains were selected and established plots, and control stand plots were established at similar site conditions. We conducted a forest inventory and used dendrochronological methods to reveal the short- and long-term effects of NSR fire disturbance on the population dynamics and individual growth of the dominant species of L. gmelinii. Specifically, the effects of NSR fire on stand structure, the relationship between L. gmelinii demographics and disturbance, and the response of growth dynamics to disturbance were analyzed. Finally, the history of potential disturbance at stand level was reconstructed. The study found that common NSR fire affect the biomass and species composition of L. gmelinii forests. Fire disturbance contributes to the younger age structure of L. gmelinii populations. However, The NSR fire may limit the size of L. gmelinii populations but does not necessarily destroy population resilience depending on stand conditions. Irregular fluctuations in population survival and mortality curves are directly related to historical disturbance events. The NSR fire can inhibit the growth of surviving trees for 1–2 years, resulting in temporary growth asynchrony. The population dynamics fluctuations and temporal patterns of growth release signals can reconstruct historical disturbance events at the stand level. For example, the MH intra-group (Mohe Luogu River Nature Reserve burned stand&Mohe Luogu River Nature Reserve unburned stand) probably experienced a high-severity fire in 1880–1900, the TH intra-group (Tahe Nature Reserve burned stand&Tahe Nature Reserve unburned stand) experienced a high-severity fire around 1930, and THB (Tahe Nature Reserve burned stand) suffered stand-replacing. Overall, irregular fluctuations in population survival and mortality curves have been directly related to historical disturbance events. These findings provide direct evidence of the short- and long-term effects of fire on the survival and growth of L. gmelinii populations.

Multi-Stage Voltage Sag State Estimation Using Event-Deduction Model Corresponding to EF, EG, and EP

Knowledge of the disturbance of the concerned bus is essential to make decisions to mitigate voltage sags. The most commonly used method is to estimate the state of voltage sag in the absence of a monitor. However, the traditional state estimation method, which is designed for rectangular voltage sags, is difficult to apply to multi-stage voltage sags (MSVSs). This study proposes an MSVS state-estimation method based on event-deduction models. First, we propose a method to identify the causes of MSVSs. Second, we present a method to calculate the matrix of relay protection trips (MRPT), which corresponds to the fault clearing time of the relay protection and a method to calculate the fault power line set to reduce the computing workload of the MRPT-based estimation method. Third, we propose a method to calculate the impedance matrix of a power system under different disturbance events, resulting in different stages of the MSVS and an event-deduction model based on this impedance matrix to deduce these events. Furthermore, we present a model to estimate the state of voltage sag for MSVS based on the event deduction result. Finally, we use the IEEE-118 system to validate the proposed method.

The Nightmare Island: Representations of St. Barthélemy in Swedish Novels

The Nightmare Island: Representations of St. Barthélemy in Swedish Novels

Flemish Immigration and Geoffrey of Monmouth's De gestis Britonum

Flemish Immigration and Geoffrey of Monmouth's <i>De gestis Britonum</i>