Vegetation patterns and the influence of rainfall after long-term fire suppression on a woody community of a Brazilian savanna.

We evaluated the structural and floristic characteristics of a Brazilian savanna fragment occupied by cerradão (CD) and cerrado sensu stricto (CS) in response to the influence of rainfall and long-term fire suppression. We carried out floristic, phytosociological and remote sensing studies in a cerrado fragment located in Corumbataí (SP, Brazil) after 43 years of complete fire suppression. We surveyed 43 plots of 200 m2 each (17 plots in CS and 26 plots in CD) and all individuals ≥ 0.32 cm diameter measured at 30 cm from the ground were included in the sample. We calculated phytosociological parameters for each species and classified them in three ecological groups, namely savanna, generalist and forest species. The remote sensing analysis used aerial photographs and satellite images from 1962 to 2019 (i.e. 59 years). The structural study of community revealed high predominance of forest and generalist species when compared to savanna species. Non-linear correlation between CD expansion rates and total rainfall within the study period indicated a positive influence of the rainfall (R2 = 0.42). Thus, our analysis indicated a tendency of a continuous and fast expansion of CD over areas of CS in the long-term absence of fire combined with periods of heavy rain.

Spatial-temporal distribution of fire-protected savanna physiognomies in Southeastern Brazil.

The analysis of the influence of edaphic finer textures, as a facilitating factor for the expansion of forest formations in the absence of fire, was possible thanks to rare characteristics found in a savanna fragment located in the State of São Paulo, Brazil. The total suppression of fire for over four decades, and the occurrence of two savanna physiognomies, cerrado sensu stricto and cerradão, allowed the conduction of this study based on the hypothesis that cerradão, a physiognomy of forest aspect consisting of fire-sensitive tree and shrubs species, is favored by fire absence and higher soil hydric retention capacity. Edaphic samples were collected from a regular grid of 200 m(2) for the production of isopletic maps of the distribution of clay, fine sand, coarse sand and silt edaphic textures by the geostatistic method of ordinary kriging. Changes in the areas occupied by both savanna physiognomies, defined on the basis of aerial photographs taken over a period of 43 years, were assessed through mean variation rates. Besides corroborating the hypothesis of edaphic hydric retention as a facilitating factor for the expansion of forest physiognomies in savanna areas, we were able to infer the positive influence of higher precipitation on the increase in cerradão expansion rates.

Spatiotemporal evolution of dengue outbreaks in Brazil.

BACKGROUND: Dengue is a mosquito-borne febrile disease infecting millions of people worldwide. Identification of high-risk areas will allow public health services to concentrate their efforts in areas where outbreaks are most likely to occur. The present study focuses on describing the spatiotemporal evolution of dengue outbreaks in Brazil from 2000 to 2018. METHOD: To assess the pattern behaviour and spatiotemporal trend of dengue outbreaks, the non-parametric kernel estimator method and the Mann-Kendall test, respectively, were used. Bivariate global Moran's I statistic was used to test the spatial correlation between dengue outbreaks, temperature, precipitation and population data. RESULTS: Our results revealed that the transmission cycles of dengue outbreaks vary in different spatiotemporal scenarios, with intermittent periods of outbreaks. In the period of study, outbreak clusters were primarily concentrated in the Northeast region and the transmission of dengue extended throughout Brazil until 2018. The probability of occurrence of dengue outbreaks was higher in high temperatures. Further, these space-time fluctuations in the number of outbreaks in the different regions were probably related to the high mobility between the populations of these regions, circulating serotypes and susceptible populations. CONCLUSIONS: The distribution of dengue outbreaks is not random; it can be modified by socioeconomic and climatic moving boundaries.

The influence of urban heat islands and socioeconomic factors on the spatial distribution of Aedes aegypti larval habitats.

We addressed the potential associations among the temporal and spatial distribution of larval habitats of Aedes (Stegomyia) aegypti, the presence of urban heat islands and socioeconomic factors. Data on larval habitats were collected in Santa Bárbara d'Oeste, São Paulo, Brazil, from 2004 to 2006, and spatial and temporal variations were analysed using a wavelet-based approach. We quantified urban heat islands by calculating surface temperatures using the results of wavelet analyses and grey level transformation from Thematic Mapper images (Landsat 5). Ae. aegypti larval habitats were geo-referenced corresponding to the wavelet analyses to test the potential association between geographical distribution of habitats and surface temperature. In an inhomogeneous spatial point process, we estimated the frequency of occurrence of larval habitats in relation to temperature. The São Paulo State Social Vulnerability Index in the municipality of Santa Barbára d'Oeste was used to test the potential association between presence of larval habitats and social vulnerability. We found abundant Ae. aegypti larval habitats in areas of higher surface temperature and social vulnerability and fewer larval habitats in areas with lower surface temperature and social vulnerability.

Impact of environmental factors on neglected emerging arboviral diseases.

BACKGROUND: Brazil is a tropical country that is largely covered by rainforests and other natural ecosystems, which provide ideal conditions for the existence of many arboviruses. However, few analyses have examined the associations between environmental factors and arboviral diseases. Thus, based on the hypothesis of correlation between environment and epidemiology, the proposals of this study were (1) to obtain the probability of occurrence of Oropouche, Mayaro, Saint Louis and Rocio fevers in Brazil based on environmental conditions corresponding to the periods of occurrence of the outbreaks; (2) to describe the macroclimatic scenario in Brazil in the last 50 years, evaluating if there was any detectable tendency to increase temperatures and (3) to model future expansion of those arboviruses in Brazil based on future temperature projections. METHODOLOGY/PRINCIPAL FINDINGS: Our model assessed seven environmental factors (annual rainfall, annual temperature, elevation, seasonality of temperature, seasonality of precipitation, thermal amplitude, and daytime temperature variation) for their association with the occurrence of outbreaks in the last 50 years. Our results suggest that various environmental factors distinctly influence the distribution of each arbovirus, with temperature being the central determinant of disease distribution in all high-risk areas. These areas are subject to change, since the average temperature of some areas has increased significantly over the time. CONCLUSIONS/SIGNIFICANCE: This is the first spatio-temporal study of the Oropouche, Mayaro, Saint Louis, and Rocio arboviruses, and our results indicate that they may become increasingly important public health problems in Brazil. Thus, next studies and control programs should include these diseases and also take into consideration key environmental elements.

Spatial-temporal distribution of fire-protected savanna physiognomies in Southeastern Brazil

The analysis of the influence of edaphic finer textures, as a facilitating factor for the expansion of forest formations in the absence of fire, was possible thanks to rare characteristics found in a savanna fragment located in the State of São Paulo, Brazil. The total suppression of fire for over four decades, and the occurrence of two savanna physiognomies, cerrado sensu stricto and cerradão, allowed the conduction of this study based on the hypothesis that cerradão, a physiognomy of forest aspect consisting of fire-sensitive tree and shrubs species, is favored by fire absence and higher soil hydric retention capacity. Edaphic samples were collected from a regular grid of 200 m² for the production of isopletic maps of the distribution of clay, fine sand, coarse sand and silt edaphic textures by the geostatistic method of ordinary kriging. Changes in the areas occupied by both savanna physiognomies, defined on the basis of aerial photographs taken over a period of 43 years, were assessed through mean variation rates. Besides corroborating the hypothesis of edaphic hydric retention as a facilitating factor for the expansion of forest physiognomies in savanna areas, we were able to infer the positive influence of higher precipitation on the increase in cerradão expansion rates.

A influência de texturas edáficas finas, como fator de facilitação para a expansão de formações florestais sobre áreas savânicas, através da maior retenção hídrica edáfica, na ausência de incêndios, foi possível ser estudada graças às características encontradas em um fragmento savânico com 38,8 ha, situado em Corumbataí (SP). A supressão total do fogo por quatro décadas, e a ocorrência de duas fisionomias, cerrado sensu stricto e cerradão, permitiram a condução deste estudo. Amostras de solo foram coletadas em uma grade regular de 200 m², abrangendo toda a área do fragmento. Foram produzidos mapas iso-pléticos, com a distribuição das porcentagens de argila, areia fina, areia grossa e silte, utilizando-se o método geoestatís-tico krigagem ordinária. As mudanças nas áreas ocupadas por ambas as fisionomias foram definidas a partir de fotografias aéreas abrangendo um período de 43 anos. Essas imagens também permitiram o cálculo das taxas médias de ocupação das fisionomias nas quatro décadas. Além de corroborar a hipótese de retenção edáfica hídrica, como um fator de facilitação para a expansão de fisionomias florestais, sobre áreas savânicas, foi possível também inferir sobre a influência positiva de períodos de maior pluviosidade, para a expansão mais acentuada do cerradão.