scholarly journals Spatial Patterns in Different Stages of Regeneration after Clear-Cutting of a Black Locust Forest in Central China

Forests ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 1066
Author(s):  
Zhang ◽  
Shen ◽  
Yang ◽  
Ma ◽  
Duan ◽  
...  
Keyword(s):  
Spatial Patterns ◽  
Stand Structure ◽  
Robinia Pseudoacacia ◽  
Spatial Relation ◽  
Dispersal Limitation ◽  
Central China ◽  
Variance Gamma ◽  
Clear Cutting ◽  
Variance Gamma Process ◽  
Underlying Mechanisms

Estimating underlying mechanisms and dynamics from observed tree patterns can provide guidance for plantation management. Robinia pseudoacacia can reproduce via clonally produced ramets, leading to a complex distribution of stems. Three second generation plots and three third generation plots (each plot 50 m × 50 m) were established across a wide age range after clear-cutting in a Robinia pseudoacacia plantation in central China. We measured spatial coordinates, diameter at breast height (DBH) or diameter at basal stem, and heights of all recruits, as well as the coordinates and base diameter of all stumps, in six plots. The spatial pattern in different plots and the spatial relation between stumps and regenerations after clear-cutting were analyzed. To estimate the underlying processes of the observed patterns, we fitted Matérn and Variance-Gamma cluster processes to the observed dataset. The results revealed that the percentage of ramets from stumps decreasing with age in the two types of stands (from 40.4% to 30.1%, from 57.6% to 35.7%), and trees exhibited an aggregated distribution in all plots, but the degree of aggregation exhibited a decreasing trend with age, and aggregation occurred at different scale. Furthermore, a large proportion of ramets had their nearest neighbor at a short distance (<1 m) based on analysis of the nearest neighbour function. The bivariate analysis revealed that the spatial relation between stumps and ramets changed with age, and a repulsion trend was found between them in all the six plots. The Variance-Gamma process with covariate of Cartesian coordinates fitted the observed patterns better than others. The observed pattern was likely driven by root dispersal limitation, seed dispersal limitation, human disturbance, and intraspecific competition. Spatial patterns are important characteristics in forest stand structure, and understanding the pattern change and its underlying mechanisms could allow for better timing of artificial disturbances to optimize stand structure and promote stand growth.

scholarly journals Prognostic and Classification of Dynamic Degradation in a Mechanical System Using Variance Gamma Process

Mathematics ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 254
Author(s):  
Marwa Belhaj Salem ◽  
Mitra Fouladirad ◽  
Estelle Deloux
Keyword(s):  
Mechanical System ◽  
Dynamic Environment ◽  
Machine Learning Algorithms ◽  
Maintenance Policy ◽  
Degradation Behaviour ◽  
Pump System ◽  
Variance Gamma ◽  
Variance Gamma Process ◽  
Operating Environments ◽  
Finite State

Recently, maintaining a complex mechanical system at the appropriate times is considered a significant task for reliability engineers and researchers. Moreover, the development of advanced mechanical systems and the dynamics of the operating environments raises the complexity of a system’s degradation behaviour. In this aspect, an efficient maintenance policy is of great importance, and a better modelling of the operating system’s degradation is essential. In this study, the non-monotonic degradation of a centrifugal pump system operating in the dynamic environment is considered and modelled using variance gamma stochastic process. The covariates are introduced to present the dynamic environmental effects and are modelled using a finite state Markov chain. The degradation of the system in the presence of covariates is modelled and prognostic results are analysed. Two machine learning algorithms k-nearest-neighbour (KNN) and neural network (NN) are applied to identify the various characteristics of degradation and the environmental conditions. A predefined degradation threshold is assigned and used to propose a prognostic result for each classification state. It was observed that this methodology shows promising prognostic results.

Avatars-Based Decision Support System Using Blockchain and Knowledge Sharing for Processes Simulation

2021 ◽  
Vol 17 (1) ◽  
pp. 72-92
Author(s):  
Vardan Mkrttchian
Keyword(s):  
Human Capital ◽  
Decision Support ◽  
Knowledge Sharing ◽  
Process Simulation ◽  
Efficient Algorithm ◽  
Capital Management ◽  
Human Capital Management ◽  
Variance Gamma ◽  
R Language ◽  
Variance Gamma Process

This article is an enhancement of the chapter “About Digital Avatars for Control in Virtual Industries” in the book Big Data and Knowledge Sharing in Virtual Organizations. The article discusses the capabilities of the R language for modeling Levy processes that currently most closely correspond to the nature of the organizational learning movements in sliding mode. The efficient algorithm of the CGMY process simulation as a difference of the tempered stable independent Levy is processed and programmed at R language. The efficient algorithm of variance gamma process simulation using variance gamma random variables is processed and programmed at R language. Overview of CGMY process simulation in practice is use for human capital management in the context of the implementation of digital intelligent decision support systems and knowledge management and for digital intelligent design of avatar-based control with application to human capital management.

scholarly journals Altitudinal Biodiversity Gradient and Ecological Drivers for Different Lifeforms in the Baotianman Nature Reserve of the Eastern Qinling Mountains

Forests ◽  
2019 ◽  
Vol 10 (4) ◽  
pp. 332
Author(s):  
Zhao ◽  
Wang ◽  
Yu ◽  
Zhang ◽  
Yao ◽  
...  
Keyword(s):  
Nature Reserve ◽  
Dispersal Limitation ◽  
Central China ◽  
Qinling Mountains ◽  
Dissimilarity Index ◽  
Β Diversity ◽  
Species Overlap ◽  
Predominant Process ◽  
Community Clustering ◽  
The Impact

Variation in species composition between two communities is so-called β diversity, or dissimilarity, and can be separated into two components: turnover and nestedness. However, the mechanisms underlying these two components remain ambiguous, particularly for different lifeforms. In this study, we examined the altitudinal gradient of biodiversity in the Baotianman Nature Reserve of the eastern Qinling Mountains in central China and found that turnover is the predominant process accounting for β diversity, that dispersal limitation is the main factor influencing species diversity, and that its effect on trees is greater than on shrubs, with herbs least affected. Nestedness, in contrast, is less prominent and generally affected by the richness deviation between communities, and the impact of richness deviation is stronger on shrubs than on trees, and in turn, stronger than on herbs. We zoned the altitudinal vegetation communities by pairwise dissimilarity index, and found that the peak value of turnover rather than β diversity indicates the existence of transitional zones; the higher the turnover index, the greater the diversity between communities. Comparatively, nestedness indicates species overlap between communities. The highest nestedness index usually occurs in the interior of vegetation zones. The result of community clustering by pairwise dissimilarity shows that understory species could have been mostly replaced upwards, while the dominant tree species may keep stable, indicating that dispersal limitation works differently for different lifeforms.

Influence of the landscape context on stand structure and spatial patterns of the doum palm (Hyphaene thebaica Mart.) in the Republic of Benin (West Africa)

2016 ◽  
Vol 90 (4) ◽  
pp. 591-605 ◽  
Author(s):  
Rodrigue Idohou ◽  
Achille Ephrem Assogbadjo ◽  
Fortuné Azihou ◽  
Romain Glèlè Kakaï ◽  
Aristide Adomou
Keyword(s):  
West Africa ◽  
Spatial Patterns ◽  
Stand Structure ◽  
Landscape Context ◽  
Republic Of Benin ◽  
The Republic

Shifts In Aquatic Insect Populations In A First-Order Southern Appalachian Stream Following A Decade Of Old Field Succession

1981 ◽  
Vol 38 (3) ◽  
pp. 353-359 ◽  
Author(s):  
John D. Haefner ◽  
J. Bruce Wallace
Keyword(s):  
Secondary Succession ◽  
Robinia Pseudoacacia ◽  
Aquatic Insect ◽  
Terrestrial Vegetation ◽  
Old Field ◽  
First Order ◽  
Clear Cutting ◽  
Southern Appalachian ◽  
Insect Populations ◽  
One Year

Aquatic insects of two first-order southern Appalachian streams were sampled monthly during one year. Sawmill Branch Watershed was subjected to several disturbances before 1968, including clear-cutting. Since 1968 Sawmill Branch Watershed has undergone natural secondary succession from terrestrial vegetation dominated by Gramineae to a herbaceous/coppice hardwood dominated by black locust, Robinia pseudoacacia. Grady Branch, the control stream, drains an undisturbed hardwood watershed. Aquatic insect densities on Sawmill Branch were about twice those of Grady Branch, which represent a dramatic reversal from results obtained by a similar study in 1968. It is suggested that change in riparian vegetation is a major factor influencing long-term changes in aquatic insect populations, and these changes are manifested through a shift toward an allochthonous energy base. The most conspicuous changes in macrobenthos on the disturbed watershed between 1968 and 1978 were a reduction in grazer organisms and a corresponding increase in shredder organisms, especially Peltoperla (Plecoptera).Key words: macrobenthos, secondary succession, watershed changes, clear-cutting, allochthonous detritus, food quality.

Long-term mortality rates and spatial patterns in an old-growth Pinus resinosa forest

2013 ◽  
Vol 43 (9) ◽  
pp. 809-816 ◽  
Author(s):  
Emily J. Silver ◽  
Shawn Fraver ◽  
Anthony W. D’Amato ◽  
Tuomas Aakala ◽  
Brian J. Palik
Keyword(s):  
Spatial Pattern ◽  
Spatial Patterns ◽  
Pinus Banksiana ◽  
Tree Mortality ◽  
Stand Structure ◽  
Pinus Resinosa ◽  
Mortality Rates ◽  
Stand Age ◽  
Initial Population ◽  
Dead Trees

Understanding natural mortality patterns and processes of forest tree species is increasingly important given projected changes in mortality owing to global change. With this need in mind, the rate and spatial pattern of mortality was assessed over an 89-year period in a natural-origin Pinus resinosa (Aiton)-dominated system to assess these processes through advanced stages of stand development (stand age 120–209 years). Average annual mortality rates fluctuated through time, yet were within the range reported in other studies (0.60%–3.88% depending on species and sampling interval). Tree mortality was attributed to multiple agents, including the senescence of the short-lived Pinus banksiana Lamb., windthrow, root-rot fungi (Armillaria ostoyae (Romagn.) Herink), and perhaps infrequent droughts. Despite the often contagious nature of many disturbance agents, the overall spatial pattern of mortality events (the arrangement of dead trees within the fixed initial population of live trees) was random at all scales tested. Similarly, the current spatial pattern of dead trees was predominantly random, despite clustering at small scales (2–4 m). These findings underscore the importance of studying mortality rates, agents, and spatial patterns over long time periods to avoid misinterpreting stochastic mortality events, and their influence on longer term stand structure and development.

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