Resumo O crescimento populacional e as questões climáticas impõem desafios à sociedade, principalmente no que diz respeito ao abastecimento de alimentos e à manutenção de condições desejáveis do solo. Além disso, há uma evidente necessidade de reduzir as emissões de gases de efeito estufa, notadamente àquelas causadas por mudanças no uso do solo. Portanto, há necessidade de estudos que abordem o entendimento das condições do solo sob os diferentes usos do solo, uma vez que esses podem se tornar fontes de carbono dependendo das práticas de manejo. Este estudo foi conduzido em perfis de Plintossolos Amazônicos sob: florestas primárias, pastagens para pecuária e plantios mistos de restauração florestal. A densidade e o teor de carbono foram avaliados em quatro profundidades (0-5, 5-10, 10-20 e 20-40 cm), enquanto as propriedades físicas foram examinadas nas profundidades de 0-20 e 20-40 cm. Solos sob florestas primárias apresentaram as menores densidades e os maiores teores de carbono quando comparados a outros usos da terra. Esses solos também apresentaram o maior estoque de carbono. Entretanto, não foi observada diferença significativa pelo teste de Tukey para ambas variáveis. As pastagens apresentaram maiores estoques de carbono quando comparados aos plantios mistos (aos 10 anos). Nossos resultados indicaram que práticas de manejo adequadas são necessárias para a manutenção da capacidade produtiva do solo após a conversão de florestas para outros usos. Os Plintossolos, por suas características texturais e mineralógicas, apresentaram elevados teores de quartzo, notadamente nas camadas superficiais, demonstrando quão sensíveis às mudanças na paisagem. O estoque de carbono no solo é, portanto, sensível às mudanças na sua cobertura. Este estudo fornece informações úteis para o entendimento do estoque de carbono em Plintossolos na Amazônia Brasileira, bem como para aprimorar as estimativas realizadas no Inventário Nacional de Emissões de Gases de Efeito Estufa.

Abstract The population growth and the climate changes impose challenges to society, especially regarding food supply and the maintenance of desirable soil conditions. Besides, it is necessary to reduce greenhouse gas emissions. Hence, there is a necessity of studies addressing the understanding of soil conditions under different land uses, as soils can become carbon pools or sources depending on management practices. This study was conducted in soil profiles of Amazon Plinthosols under different land uses: undisturbed forests, cattle ranching pastures, and mixed crops. Soil density and carbon fraction were assessed at four depths (0-5, 5-10, 10-20, and 20-40 cm), while particle size and mineralogy were examined at 0-20 and 20-40 cm. Soils under undisturbed forests presented lower densities and higher carbon fractions when compared to other land uses. These soils also presented the highest carbon stock; however, the Tukey test indicated no significant differences. Soil densities were lower in forest environments. Cattle ranching pastures presented higher carbon stocks when compared to mixed crops (at age 10 years). Our results indicated that proper soil management practices are needed to maintain the soil productive capacity after converting forested areas for other uses. Plinthosols, due to its textural and mineralogical characteristics, presented high amounts of quartz, demonstrating how sensitive these environments are to changes in the landscape due to deforestation and how unstable the maintenance of carbon stocks is because of such conditions. This study provides useful information to the understanding of the carbon stock in Amazon Plinthosols. It may be helpful to improve the Brazilian Inventory of Anthropogenic Emissions and Removals of Greenhouse Gases and to understand the impacts of land-use change.

ABSTRACT Necromass play a significant ecological function, including the deposition of organic matter, which is essential for carbon cycling in forest ecosystems. Despite the devoted attention to the role of forest necromass into the global carbon cycle, international organizations such as IPCC and FAO have reported the lack of compatible data concerning the carbon stocks in forest necromass among different regions. This paper reviews the terminologies and sampling methods regarding the quantification of carbon stock in forest necromass. Volume, biomass and carbon content determination methods were examined into the literature and then notably in Brazil. We address the problems associated with sampling methods and spatial distribution in related studies. Conflict in nomenclatures, components and diameter threshold confound the comparison of regional results. Meanwhile, we present a standard terminology for similar studies. Coarse woody and non-woody (litter) necromass are frequently computed, although fine woody necromass stands ignored in most studies and reports. Finally, we provide recommendations on specific sampling and measurement methods, taking into account necromass size and spatial pattern for both necromass and litter.

ABSTRACT The objective of the study was to present mathematical models and strategies for fitting equations to estimate dry biomass for tree species in forest restoration areas. The presence of outliers was analyzed in each fitted equation using values of the matrix H, leverage points, means of standard and studentized residuals, and of influential points through DFFITS, DFBETAS and COOK distance values. Furthermore, the normality, homoscedasticity and independence of residuals were checked. The accuracy of the fitted equations was evaluated by means of the R2adj., Syx, analysis of residuals, and AIC and BIC criteria. The results showed that the model for estimating dry biomass as a function of the variables Dc2, DBH2, Hc2 and DBH provides the more accurate solution, with Syx = 40.91% and R2adj. = 0.92. We concluded that the performance of this equation improves when adjusted to data stratified by classes of height-diameter ratio, which reduces the value of the estimated error.