Distribution of biomass dynamics in relation to tree size in forests across the world.

Tree size shapes forest carbon dynamics and determines how trees interact with their environment, including a changing climate. Here, we conduct the first global analysis of among-site differences in how aboveground biomass stocks and fluxes are distributed with tree size. We analyzed repeat tree censuses from 25 large-scale (4-52 ha) forest plots spanning a broad climatic range over five continents to characterize how aboveground biomass, woody productivity, and woody mortality vary with tree diameter. We examined how the median, dispersion, and skewness of these size-related distributions vary with mean annual temperature and precipitation. In warmer forests, aboveground biomass, woody productivity, and woody mortality were more broadly distributed with respect to tree size. In warmer and wetter forests, aboveground biomass and woody productivity were more right skewed, with a long tail towards large trees. Small trees (1-10 cm diameter) contributed more to productivity and mortality than to biomass, highlighting the importance of including these trees in analyses of forest dynamics. Our findings provide an improved characterization of climate-driven forest differences in the size structure of aboveground biomass and dynamics of that biomass, as well as refined benchmarks for capturing climate influences in vegetation demographic models.

Demographic composition, not demographic diversity, predicts biomass and turnover across temperate and tropical forests.

The growth and survival of individual trees determine the physical structure of a forest with important consequences for forest function. However, given the diversity of tree species and forest biomes, quantifying the multitude of demographic strategies within and across forests and the way that they translate into forest structure and function remains a significant challenge. Here, we quantify the demographic rates of 1961 tree species from temperate and tropical forests and evaluate how demographic diversity (DD) and demographic composition (DC) differ across forests, and how these differences in demography relate to species richness, aboveground biomass (AGB), and carbon residence time. We find wide variation in DD and DC across forest plots, patterns that are not explained by species richness or climate variables alone. There is no evidence that DD has an effect on either AGB or carbon residence time. Rather, the DC of forests, specifically the relative abundance of large statured species, predicted both biomass and carbon residence time. Our results demonstrate the distinct DCs of globally distributed forests, reflecting biogeography, recent history, and current plot conditions. Linking the DC of forests to resilience or vulnerability to climate change, will improve the precision and accuracy of predictions of future forest composition, structure, and function.

Links between socio-economic circumstances and changes in smoking behavior in the Mexican population: 2002-2010.

While deleterious consequences of smoking on health have been widely publicized, in many developing countries, smoking prevalence is high and increasing. Little is known about the dynamics underlying changes in smoking behavior. This paper examines socio-economic and demographic characteristics associated with smoking initiation and quitting in Mexico between 2002 and 2010. In addition to the influences of age, gender, education, household economic resources and location of residence, changes in marital status, living arrangements and health status are examined. Drawing data from the Mexican Family Life Survey, a rich population-based longitudinal study of individuals, smoking behavior of individuals in 2002 is compared with their behavior in 2010. Logistic models are used to examine socio-demographic and health factors that are associated with initiating and quitting smoking. There are three main findings. First, part of the relationship between education and smoking reflects the role of economic resources. Second, associations of smoking with education and economic resources differ for females and males. Third, there is considerable heterogeneity in the factors linked to smoking behavior in Mexico indicating that the smoking epidemic may be at different stages in different population subgroups. Mexico has recently implemented fiscal policies and public health campaigns aimed at reducing smoking prevalence and discouraging smoking initiation. These programs are likely to be more effective if they target particular socio-economic and demographic sub-groups.

Links between childhood and adult social circumstances and obesity and hypertension in the Mexican population.

OBJECTIVES: This study examines links between early life circumstances and adult socioeconomic status and obesity and hypertension in the adult Mexican population. METHOD: We use data from the Mexican Family Life Survey (MxFLS) collected in 2002 for people aged 20 or older (N = 14,280). RESULTS: We found that men with low education and women with more education have significantly lower obesity. Women with higher education also have significantly less hypertension. Obesity triples the likelihood of hypertension among both men and women. Better childhood experiences are associated with less hypertension among women, but more hypertension among men in rural areas. DISCUSSION: Recent changes in income, nutrition, and infection in Mexico may be responsible for the observed high prevalence of overweight and obesity and the extremely high odds of hypertension among obese young adults.

The healthy migrant effect: new findings from the Mexican Family Life Survey.

OBJECTIVES: We used nationally representative longitudinal data from the Mexican Family Life Survey to determine whether recent migrants from Mexico to the United States are healthier than other Mexicans. Previous research has provided little scientific evidence that tests the "healthy migrant" hypothesis. METHODS: Estimates were derived from logistic regressions of whether respondents moved to the United States between surveys in 2002 and 2005, by gender and urban versus rural residence. Covariates included physical health measurements, self-reported health, and education measured in 2002. Our primary sample comprised 6446 respondents aged 15 to 29 years. RESULTS: Health significantly predicted subsequent migration among females and rural males. However, the associations were weak, few health indicators were statistically significant, and there was substantial variation in the estimates between males and females and between urban and rural dwellers. CONCLUSIONS: On the basis of recent data for Mexico, the largest source of migrants to the United States, we found generally weak support for the healthy migrant hypothesis.