scholarly journals Concerted changes in tropical forest structure and dynamics: evidence from 50 South American long-term plots

2004 ◽  
Vol 359 (1443) ◽  
pp. 421-436 ◽  
Author(s):  
S. L. Lewis ◽  
O. L. Phillips ◽  
T. R. Baker ◽  
J. Lloyd ◽  
Y. Malhi ◽  
...  
Keyword(s):  
Tropical Forest ◽  
Net Primary Productivity ◽  
Basal Area ◽  
Mortality Rates ◽  
Stem Density ◽  
Cross Sectional ◽  
The Cross ◽  
Stem Mortality ◽  
Over Time

Several widespread changes in the ecology of old–growth tropical forests have recently been documented for the late twentieth century, in particular an increase in stem turnover (pan–tropical), and an increase in above–ground biomass (neotropical). Whether these changes are synchronous and whether changes in growth are also occurring is not known. We analysed stand–level changes within 50 long–term monitoring plots from across South America spanning 1971–2002. We show that: (i) basal area (BA: sum of the cross–sectional areas of all trees in a plot) increased significantly over time (by 0.10 ±; 0.04 m 2 ha −1 yr −1 , mean ± 95%CI) as did both (ii) stand–level BA growth rates (sum of the increments of BA of surviving trees and BA of new trees that recruited into a plot); and (iii) stand–level BA mortality rates (sum of the cross–sectional areas of all trees that died in a plot). Similar patterns were observed on a per–stem basis: (i) stem density (number of stems per hectare; 1 hectare is 10 4 m 2 ) increased significantly over time ( 0.94 ± 0.63 stems ha −1 yr −1 ); as did both (ii) stem recruitment rates; and (iii) stem mortality rates. In relative terms, the pools of BA and stem density increased by 0.38 ± 0.15% and 0.18 ± 0.12% yr −1 , respectively. The fluxes into and out of these pools—stand–level BA growth, stand–level BA mortality, stem recruitment and stem mortality rates—increased, in relative terms, by an order of magnitude more. The gain terms (BA growth, stem recruitment) consistently exceeded the loss terms (BA loss, stem mortality) throughout the period, suggesting that whatever process is driving these changes was already acting before the plot network was established. Large long–term increases in stand–level BA growth and simultaneous increases in stand BA and stem density imply a continent–wide increase in resource availability which is increasing net primary productivity and altering forest dynamics. Continent–wide changes in incoming solar radiation, and increases in atmospheric concentrations of CO 2 and air temperatures may have increased resource supply over recent decades, thus causing accelerated growth and increased dynamism across the world's largest tract of tropical forest.

Creativity in Sociocultural Systems

2019 ◽  
pp. 269-284
Author(s):  
Dean Keith Simonton
Keyword(s):  
Macro Level ◽  
Historical Overview ◽  
Creative Activity ◽  
Cross Sectional ◽  
Individual Level ◽  
Short And Long Term ◽  
The Cross ◽  
Sociocultural Systems

Although psychologists typically see creativity as an individual-level event, sociologists and cultural anthropologists are more likely to view it as a sociocultural phenomenon. This phenomenon takes place at the level of relatively large and enduring collectives, such as cultures, nations, and even whole civilizations. This chapter reviews the extensive research on such macro-level creativity. The review begins with a historical overview before turning to the cross-sectional research on the creative Ortgeist, a subject that encompasses the factors that influence the relative creativity of both preliterate cultures and entire modern nations. From there the chapter turns to role of the Zeitgeist in affecting the creativity of civilizations across time—the rise and fall of creative activity. This research examines both quantitative and qualitative causes that operate both short- and long-term.

scholarly journals Investigating the Broken-Heart Effect: a Model for Short-Term Dependence between the Remaining Lifetimes of Joint Lives

2012 ◽  
Vol 7 (2) ◽  
pp. 236-257 ◽  
Author(s):  
Jaap Spreeuw ◽  
Iqbal Owadally
Keyword(s):  
Mortality Rates ◽  
Short Term ◽  
Numerical Work ◽  
Data Set ◽  
Multiple State ◽  
Multiple State Model ◽  
Insurance Data ◽  
Over Time ◽  
Assurance Contracts

AbstractWe analyze the mortality of couples by fitting a multiple state model to a large insurance data set. We find evidence that mortality rates increase after the death of a partner and, in addition, that this phenomenon diminishes over time. This is popularly known as a “broken-heart” effect and we find that it affects widowers more than widows. Remaining lifetimes of joint lives therefore exhibit short-term dependence. We carry out numerical work involving the pricing and valuation of typical contingent assurance contracts and of a joint life and survivor annuity. If insurers ignore dependence, or mis-specify it as long-term dependence, then significant mis-pricing and inappropriate provisioning can result. Detailed numerical results are presented.

Tree density, basal area and species diversity in a disturbed dry tropical forest of northern India: implications for conservation

2006 ◽  
Vol 33 (3) ◽  
pp. 256-262 ◽  
Author(s):  
R. SAGAR ◽  
J.S. SINGH
Keyword(s):  
Species Diversity ◽  
Tropical Forest ◽  
Basal Area ◽  
Tree Density ◽  
Dry Forest ◽  
Conservation Strategies ◽  
Stem Density ◽  
Dry Tropical Forest ◽  
Number Of Species ◽  
Northern India

Dry tropical forest communities are among the world's most threatened systems and urgent measures are required to protect and restore them in degraded landscapes. For planning conservation strategies, there is a need to determine the few essential measurable properties, such as number of species and basal area, that best describe the dry forest vegetation and its environment, and to document quantitative relationships among them. This paper examines the relationships between forest basal area and diversity components (number of species and evenness) for a disturbed dry tropical forest of northern India. Data were collected from five sites located in the Vindhyan dry tropical forest of India, selected on the basis of satellite images and field observations to represent the entire range of conditions in terms of canopy cover and disturbance regimes. These sites represented different communities in terms of species composition. The forest was poorer in species richness, and lower in stem density and basal area than wet forests of the tropics. Across sites (communities), the diversity components and tree density were positively related with total tree basal area. Considering basal area as a surrogate of biomass and net production, diversity is found to be positively associated with productivity. A positive relationship between basal area, tree density and species diversity may be an important characteristic of the dry forest, where recurring disturbance does not permit concentration of biomass or stems in only a few strong competitors. However, the relationships of basal area with density, alpha diversity and evenness remain statistically significant only when data from all sites, including the extremely disturbed one, are used in the analysis. In some sites there was a greater coefficient of variation (CV) of basal area than in others, attributed to patchy distribution of stems and resultant blanks. Therefore, to enhance the tree diversity of these forests, the variability in tree basal area must be reduced by regulating local disturbances. Conservation activities, particularly fuelwood plantations near human settlements, deferred grazing and canopy enrichment through multi-species plantations of nursery-raised or wild-collected seedlings of desirable species within the forest patches of low basal area, will be needed to attain restoration goals, but reforestation programmes will have to be made attractive to the forest-dwelling communities.

scholarly journals The influence of depth-to-groundwater on structure and productivity of Eucalyptus woodlands

2014 ◽  
Vol 62 (5) ◽  
pp. 428 ◽  
Author(s):  
Sepideh Zolfaghar ◽  
Randol Villalobos-Vega ◽  
James Cleverly ◽  
Melanie Zeppel ◽  
Rizwana Rumman ◽  
...  
Keyword(s):  
Aboveground Biomass ◽  
Net Primary Productivity ◽  
Basal Area ◽  
Tree Height ◽  
Stem Density ◽  
Aboveground Net Primary Productivity ◽  
Area Index ◽  
Mean Values ◽  
Huber Value ◽  
Eastern Australia

Although it is well documented that access to groundwater can help plants survive drought in arid and semiarid areas, there have been few studies in mesic environments that have evaluated variation of vegetation characteristics across a naturally occurring gradient in depth-to-groundwater (DGW). The aim of this study was to determine whether differences in groundwater depth influence structural attributes and productivity of remnant woodlands in south-eastern Australia. The study area was located in the Kangaloon bore-field area of New South Wales, where DGW varies from 2.4 m to 37.5 m and rainfall is plentiful. We examined structural (leaf-area index, basal area, stem density, tree height, Huber value (HV) and aboveground biomass) and functional (aboveground net primary productivity (ANPP)) attributes of seven woodland sites differing in DGW. We also used ∂13C analysis of sapwood across six sites, along with observed non-linear changes in structural attributes, to infer groundwater use by trees. Significant differences in structural attributes and ANPP were observed across sites. The three shallowest sites with 2.4 m, 4.3 m and 5.5 m DWG had significantly larger aboveground biomass and ANPP than did the four deepest sites (DGW ≥9.8 m). Across all attributes (except HV in the summer, where the mean values were significantly larger at sites where DGW was 5.5 m or less and across the four deeper sites (DGW ≥9.8 m), there were no differences in these three structural traits, nor in ANPP. Despite finding no significant differences in HV across sites in the summer, in winter, the two deepest sites had a significantly larger HV than did the two shallowest sites. Significant increases in ∂13C of sapwood occurred across five of the six sites, consistent with increasing water-use efficiency as DGW increased, reflecting the declining availability of groundwater with increasing DGW. This study has demonstrated that even in a mesic environment, putative access to groundwater can have important impacts on structural and functional traits of trees and, consequently, on woodland productivity.

scholarly journals The HIV/STI Epidemic Potential of Dynamic Sexual Networks of Men Who Have Sex With Men in Atlanta and San Francisco

2020 ◽  
Author(s):  
Emeli J. Anderson ◽  
Kevin M. Weiss ◽  
Martina M. Morris ◽  
Travis H. Sanchez ◽  
Pragati Prasad ◽  
...  
Keyword(s):  
San Francisco ◽  
Network Connectivity ◽  
Parameter Estimates ◽  
Sexual Networks ◽  
Age Group ◽  
Exponential Random Graph Models ◽  
Cross Sectional ◽  
The Cross ◽  
Over Time ◽  
Age Category

ABSTRACTBackgroundThe potential speed through which a pathogen may circulate in a network is a function of network connectivity. Network features like degree (number of ongoing partnerships) determine the cross-sectional network connectivity. The overall transmission potential of a pathogen involves connectivity over time, which can be measured using the forward reachable path (FRP). We modeled dynamic sexual networks of MSM in San Francisco and Atlanta to estimate the FRP as a predictor of HIV/STI epidemic potential.MethodsWe used exponential random graph models to obtain parameter estimates for each city’s sexual network and then simulated the complete networks over time. The FRP was estimated in each city overall and stratified by demographics.ResultsThe overall mean and median FRPs were higher in San Francisco than in Atlanta, suggesting a greater epidemic potential for HIV and STIs in San Francisco. At one year, in both cities, the average FRP among casual partnerships was highest in the youngest age group and lowest in the oldest age group, contrasting with the cross-sectional network parameters we estimated, where the youngest age category had the lowest mean degree and the oldest age category had the highest mean degree.ConclusionsThe FRP results correspond to the observed STI epidemics but not HIV epidemics between the cities. In San Francisco, rates of HIV have been declining over the last few years, whereas they have been steady in Atlanta. The FRP by age group resulted in fundamentally different conclusions about connectivity in the network compared with the cross-sectional network measures.

scholarly journals Malnutrition Rates in Chile from the Nitrate Era to the 1990s

2021 ◽  
Vol 18 (24) ◽  
pp. 13112
Author(s):  
Manuel Llorca-Jaña ◽  
Diego Barría Traverso ◽  
Diego del Barrio Vásquez ◽  
Javier Rivas
Keyword(s):  
Developed Countries ◽  
Mortality Rates ◽  
Adult Males ◽  
Sharp Decline ◽  
Low Levels ◽  
The 1960S ◽  
Chilean Population ◽  
Very High ◽  
Over Time

Following Salvatore and the WHO, in this article, we provide the first long-term estimates of malnutrition rates for Chile per birth cohort, measured through stunting rates of adult males born from the 1870s to the 1990s. We used a large sample of military records, representative of the whole Chilean population, totalling over 38 thousand individuals. Our data suggest that stunting rates were very high for those born between the last three decades of the nineteenth century and the first two decades of the twentieth century. In addition, stunting rates increased from the 1870s to the 1900s. Thereafter, there was a clear downward trend in stunting rates (despite some fluctuations), reaching low levels of malnutrition, in particular, from the 1960s (although these are high if compared to developed countries). The continuous decrease in stunting rates from the 1910s was mainly due to a combination of factors, the importance of which varied over time, namely: Improved health (i.e., sharp decline in infant mortality rates during the whole period); increased energy consumption (from the 1930s onwards, but most importantly during the 1990s); a decline in poverty rates (in particular, between the 1930s and the 1970s); and a reduction in child labour (although we are less able to quantify this).

scholarly journals Recalcitrant betas: Intraday variation in the cross‐sectional dispersion of systematic risk

2021 ◽  
Vol 12 (2) ◽  
pp. 647-682 ◽  
Author(s):  
Torben G. Andersen ◽  
Martin Thyrsgaard ◽  
Viktor Todorov
Keyword(s):  
High Frequency ◽  
Opposite Effect ◽  
Functional Limit ◽  
Cross Sectional ◽  
Macroeconomic News ◽  
Market Index ◽  
Cross Sectional Dimension ◽  
Large Panel ◽  
The Cross ◽  
Over Time

We study the temporal behavior of the cross‐sectional distribution of assets' market exposure, or betas, using a large panel of high‐frequency returns. The asymptotic setup has the sampling frequency of returns increasing to infinity, while the time span of the data remains fixed, and the cross‐sectional dimension of the panel is either fixed or increasing. We derive functional limit results for the cross‐sectional distribution of betas evolving over time. We demonstrate, for constituents of the S&P 500 market index, that the dispersion in betas is elevated at the market open and gradually declines over the trading day. This intraday pattern varies significantly over time and reacts to information shocks such as clustered earning announcements and releases of macroeconomic news. We find that earnings news increase beta dispersion while FOMC announcements have the opposite effect on market betas.

Multivariate Model for Defining Changes in Maximal Physical Working Capacity of Men, Ages 25 to 70 Years

1992 ◽  
Vol 36 (2) ◽  
pp. 171-174 ◽  
Author(s):  
Andrew S. Jackson ◽  
Earl F. Beard ◽  
Larry T. Wier ◽  
J. E. Stuteville
Keyword(s):  
Physical Activity ◽  
Body Fat ◽  
Multivariate Model ◽  
Percent Body Fat ◽  
Physical Working Capacity ◽  
Working Capacity ◽  
Cross Sectional ◽  
Exercise Habits ◽  
The Cross ◽  
Over Time

The purpose of this study was to develop a multivariate model with cross-sectional data that defined the decline in VO2max over time, and cross-validate the model with longitudinal data. The cross-sectional sample consisted of 1,608 healthy men who ranged in age from 25 to 70 years. VO2max was directly measured during a maximum Bruce treadmill stress test. Regression analysis showed that the cross-sectional age and VO2max relationship was linear, r = 0.45 and the age decline in VO2max was 0.48 ml/kg/min/year. Multiple regression developed the multivariate model from age, percent body fat (%fat), self-report physical activity (SR-PA), and the interaction of SR-PA and %fat (R = 0.793). Accounting for the variance in percent body fat and exercise habits decreased the influence of age on the decline of VO2max to just −0.27 ml/kg/min/year. This showed that much of decline in maximal physical working capacity was due to physical activity level and percent body fat, not aging. The multivariate equation was applied to the data of the longitudinal sample of 156 men who had been tested twice (Mean AgeΔ = 3.1 ± 1.2 years). The correlation between the measured and estimated change in VO2max over time (ΔVO2max) was 0.75. The results of the study showed that changes in body composition and exercise habits had more of an influence on changes in maximal physical working capacity than aging. The developed model provides a useful way to quantify the changes in physical working capacity with aging.

scholarly journals Information Percolation

2010 ◽  
Vol 2 (1) ◽  
pp. 100-111 ◽  
Author(s):  
Darrell Duffie ◽  
Gaston Giroux ◽  
Gustavo Manso
Keyword(s):  
Rate Of Convergence ◽  
Explicit Solution ◽  
Common Interest ◽  
Cross Sectional ◽  
Individual Agent ◽  
Large Market ◽  
The Mean ◽  
The Cross ◽  
Over Time

We study the “percolation” of information of common interest through a large market as agents encounter and reveal information to each other over time. We provide an explicit solution for the dynamics of the cross-sectional distribution of posterior beliefs. We also show that convergence of the cross-sectional distribution of beliefs to a common posterior is exponential and that the rate of convergence does not depend on the size of the groups of agents that meet. The rate of convergence is merely the mean rate at which an individual agent is matched. (JEL D83)

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