1.A negative relationship between stand biomass and the density of stems is expected to develop during the self-thinning process in resource-limited forests; this leads to a large proportion of the total biomass occurring in large trees. Nevertheless, frequent disturbance regimes can reduce self-thinning and the accumulation of large trees. 2. We investigated size-density relationships and the contribution of large trees (dbh ≥ 70 cm) to stand biomass in 55 1-ha plots along a 600 km transect in central-southern Amazonia. The effects of natural-disturbance gradients (frequency of storms and soil characteristics) and seasonality on forest-structure components (density of stems and mean individual mass) and stand biomass were examined. 3. Contrary to self-thinning predictions, stand biomass increased in forests with higher stem densities. Large trees contained only an average of 5% of stand biomass, and half of the stand biomass was represented by small trees with diameters < 27 cm. These findings indicate that persistent or strong disturbance plays a critical role in forest structure and biomass in the central-southern Amazon. Frequent storms were identified as an important source of disturbance in the region. Forests under higher frequency of storms had trees with lower individual mass and higher stem packing. More physically restrictive soils seem to magnify the effects of exogenous disturbances limiting individual tree size. 4. Forests in areas with longer dry seasons had lower stem densities; however, individual mass was higher in these areas. These structural components of biomass seem to counterbalance each other in generating total stand biomass. Seasonality affected forest structural components but not stand biomass. 5.Synthesis. Forests of central-southern Amazonia are not resource limited and accumulate most part of their biomass in small-to mid-sized trees. The effects of environmental gradients on specific structural components of stand biomass differ such that strong positive effects on one component can mitigate strong negative effects on other component. Future work on the determinants of stand biomass should investigate forest structure and the contributions of individual components to stand biomass.

Abstract. In Amazonia, wetlands constitute about 30 % of its entire basin, of which ancient fluvial terraces located in vast interfluvial regions cover a large portion. Although the increased number of permanent plots in the recent years has contributed to improved understanding of regional variation in forest dynamics across the Amazon Basin, the functioning of large lowland interfluvial wetlands remain poorly understood. Here we present the first field-based estimate for tree ages, wood biomass productivity and biomass turnover rates for eight 1 ha plots in wetland and non-flooded forests distributed along the BR-319 Highway along a distance of about 600 km crossing the Purus-Madeira rivers interfluvial region in central-southwestern Amazon Basin. We estimate stand age, wood biomass productivity and biomass turnover rates combining tree-ring data and an allometric equation based on diameter, tree height and wood density and relate these structural parameters to physical soil and hydrological restrictions. Wood biomass and productivity varied twofold among the plots, with wood biomass stocks ranging between 138-294 Mg ha −1 and productivity varying between 3.4-6.6 Mg ha −1 yr −1 . Soil effective depth, topography, structure and mainly soil water saturation significantly affected stand age (64-103 yr) and forest dynamics in terms of annual biomass turnover rates (2.0-3.2 %). On harsher soils characterized by a poor structure, low effective depth and high water saturation, biomass turnover rates were increased and forests stands were younger compared to welldrained sites. We suggest that soil constraints, especially soil water saturation, limit the development of the stand structure, resulting in forests with younger stand ages and higher biomass turnover rates compared to forests growing on welldrained soils. We do not find, however, any relation between physical soil restrictions or hydrology and wood biomass productivity, but there is a trend of increasing wood biomass productivity and phosphorus concentrations at the soil surface. Based on our results we establish hypotheses for different dynamical processes between forests growing on waterlogged and well-drained soils and discuss how these results can be applied in the background of conservation as well as the potential development of forest management plans in this region, which will experience increased deforestation due to the construction of the BR-319 Highway crossing the interfluvial region of the Purus-Madeira rivers.

Background: Coarse woody debris (CWD) is an essential component in tropical forest ecosystems and its quantity varies widely with forest types.

The ongoing demand for information on forest productivity has increased the number of permanent monitoring plots across the Amazon. Those plots, however, do not comprise the whole diversity of forest types in the Amazon. The complex effects of soil, climate and hydrology on the productivity of seasonally waterlogged interfluvial wetland forests are still poorly understood. The presented study is the first field-based estimate for tree ages and wood biomass productivity in the vast interfluvial region between the Purus and Madeira rivers. We estimate stand age and wood biomass productivity by a combination of tree-ring data and allometric equations for biomass stocks of eight plots distributed along 600 km in the Purus-Madeira interfluvial area that is crossed by the BR-319 highway. We relate stand age and wood biomass productivity to hydrological and edaphic conditions. Mean productivity and stand age were 5.6 ± 1.1 Mg ha⁻¹ yr⁻¹ and 102 ± 18 yr, respectively. There is a strong relationship between tree age and diameter, as well as between mean diameter increment and mean wood density within a plot. Regarding the soil hydromorphic properties we find a positive correlation with wood biomass productivity and a negative relationship with stand age. Productivity also shows a positive correlation with the superficial phosphorus concentration. In addition, superficial phosphorus concentration increases with enhanced soil hydromorphic condition. We raise three hypotheses to explain these results: (1) the reduction of iron molecules on the saturated soils with plinthite layers close to the surface releases available phosphorous for the plants; (2) the poor structure of the saturated soils creates an environmental filter selecting tree species of faster growth rates and shorter life spans and (3) plant growth on saturated soil is favored during the dry season, since there should be low restrictions for soil water availability

Síndrome de Burnout e consumo de álcool em estudantes de Odontologia

Native vegetation across the Brazilian Cerrado is highly heterogeneous and biodiverse and provides important ecosystem services, including carbon and water balance regulation, however, land-use changes have been extensive. Conservation and restoration of native vegetation is essential and could be facilitated by detailed landcover maps. Here, across a large case study region in Goiás State, Brazil (1.1 Mha), we produced physiognomy level maps of native vegetation (n = 8) and other landcover types (n = 5). Seven different classification schemes using different combinations of input satellite imagery were used, with a Random Forest classifier and 2-stage approach implemented within Google Earth Engine. Overall classification accuracies ranged from 88.6–92.6% for native and non-native vegetation at the formation level (stage-1), and 70.7–77.9% for native vegetation at the physiognomy level (stage-2), across the seven different classifications schemes. The differences in classification accuracy resulting from varying the input imagery combination and quality control procedures used were small. However, a combination of seasonal Sentinel-1 (C-band synthetic aperture radar) and Sentinel-2 (surface reflectance) imagery resulted in the most accurate classification at a spatial resolution of 20 m. Classification accuracies when using Landsat-8 imagery were marginally lower, but still reasonable. Quality control procedures that account for vegetation burning when selecting vegetation reference data may also improve classification accuracy for some native vegetation types. Detailed landcover maps, produced using freely available satellite imagery and upscalable techniques, will be important tools for understanding vegetation functioning at the landscape scale and for implementing restoration projects.

O presente artigo visa tratar do “novo materialismo” na filosofia de Karl Marx após 1845, com a produção das chamadas <em>Teses ad Feuerbach</em>. Nesse sentido, buscaremos expor essa nova concepção filosófica através da reformulação da relação sujeito-objeto levada a cabo por Marx, que levou o autor a uma noção crítica de ciência, distinta daquela que vigorava no pensamento europeu e posteriormente caracterizada como tradicional, bem como da crítica da metafísica da economia política. A partir dessas críticas, a concepção marxiana se apresenta como uma continuação da chamada <em>deutsch Wissenschaft</em>, uma ciência filosófica, influenciada desde Hegel, que agora coloca o modo de produção capitalista como objeto crítico que constitui uma essência histórica específica e que deve ser conhecida enquanto tomada de consciência de si e por si apontando para a necessidade de rompimento com uma atividade científica instrumentalizada pelas necessidades do desenvolvimento das relações de produção e da valorização da riqueza capitalistas. Nesse sentido, a filosofia marxiana, tendo a negatividade como motor da razão, fundamenta uma teoria crítica e revolucionária da sociedade capitalista e reivindica uma práxis emancipadora e emancipada dos interesses e finalidades da produção capitalista estrita.

O artigo tem como objetivo analisar alguns elementos da passagem do jovem Karl Marx, especificamente seus experimentos poéticos influenciados pelo romantismo, ao hegelianismo ainda em meados dos anos de 1837-38 até o início dos anos 40, ou seja, dois anos após ele entrar na universidade e um período pouco tratado pelos estudiosos apologistas ou críticos de sua obra. Buscaremos aqui investigar em que medida essa transição do jovem, a partir de seus 19 para 20 anos, para o hegelianismo – e a forma como essa apreensão se deu – teve influência na constituição de sua concepção posterior, conjuntamente com Friedrich Engels, para a mesma crítica feita à filosofia de Hegel e os grupos pós-hegelianos nos anos seguintes. No final, evidenciaremos não apenas em que medida essa expressão romântica influenciou o modo como o jovem Karl Marx aderiu a filosofia hegeliana, senão também o que se conservou em sua crítica e concepção posterior.