ABSTRACT Background: Litter is an important component of ecosystems, and its characteristics (e.g., production, decomposition, and nutrient and carbon content) are relevant for the ecological maintenance of different ecosystems. Previous studies on decomposition patterns have focused only on short time periods. Furthermore, there is no information regarding the actual decomposition time of organic matter in the Brazilian savanna biome known as the Cerrado. Thus, analysis of the total decomposition time can provide reliable estimates for other models. This study aimed to evaluate total litter decomposition (100%) and its relationship with seasonality and floristic composition in the savanna forest (Cerradão) formation in central Brazil. Litter bags were randomly distributed over the soil, with 10 samples collected per quarter from August 2014 to May 2020. Single- and double-entry linear regression models were used to analyze the total litter decomposition. Results: The half-life (time for which 50% of the litter was decomposed) occurred at 360 days, and 100% of litter decomposition occurred at 2070 days. The single-entry model was more satisfactory for estimating the decomposition speed. There was a positive correlation between litter decomposition and precipitation, and the floristic composition helped to explain the litter decomposition trends. Conclusion: Litter decomposition in the Cerradão is related to floristic diversity (quality of the material) and to the synergism of factors that occur mainly in the rainy season. Thus, the results of this study can contribute to conservation initiatives.

ABSTRACT This study applied a deforestation model for the entire State of Rondônia assuming three scenarios of deforestation: business as usual, optimistic and pessimistic. Those scenarios were constructed for the time-period of 2012-2050 using the Dinamica EGO software. Rondônia deforestation dataset was provided by the Agência Ambiental do Estado de Rondônia (Rondônia State Environmental Agency) and was used as input of the deforestation modeling. Based on this study results, we estimated that 32%, 37% and 47% of Rondônia’s native forest could be fully deforested by 2050 assuming the optimistic, business as usual and pessimistic scenarios, respectively. Regardless of the chosen scenario, we expect that deforestation will be spatially concentrated in Northern Rondônia in the next decades. The greatest concern, however, could be the integrity of the protected areas assuming the business as usual and/or pessimistic scenario. In addition, we expect a substantial increase of the forest fragmentation by 2050.

RESUMO O estudo teve como objetivo avaliar o estoque mensal e anual de serapilheira e sazonalidade em duas fitofisionomias (Cerrado stricto sensu e Mata de Galeria) e em um povoamento de eucalipto, localizados na Fazenda Água Limpa, DF. O estoque de serapilheira foi coletado mensalmente, pelo período de um ano, com auxílio de um gabarito metálico de 0,25 m2. O material foi separado manualmente nas frações folhas, cascas, galhos, raízes, flores/frutos e material particulado. O estoque de serapilheira na Mata de Galeria (9,36 t ha-1) foi estatisticamente igual ao observado no povoamento de eucalipto (9,12 t ha-1), valores maiores que o verificado no Cerrado Típico (6,08 t ha-1). A fração folha apresentou maior quantidade nas fitofisionomias e no povoamento quando comparada às demais frações. Verificaram-se dois padrões divergentes de sazonalidade do estoque de serapilheira: maior estoque no Cerrado Típico e no povoamento de eucalipto na estação seca e maior estoque na Mata de Galeria na estação chuvosa.

ABSTRACT The aim of this study was to evaluate the monthly and annual litter stock, and the seasonality in two phytophysiognomies (Cerrado stricto sensu and Gallery Forest) and one eucalyptus plantation, located in Fazenda Água Limpa, DF. The litter stock was monthly collected by using a metal jig of 0.25 m2, during one year. The material was manually sorted into leaves, bark, twigs, roots, flowers/fruits and particulate matter. There were no significant differences in the litter stock between the Gallery Forest (9.36 t ha-1) and the eucalyptus plantation (9.12 t ha-1), which were both higher than the Cerrado stricto sensu (6.08 t ha-1). The leaf fraction presented a larger amount in the three vegetation types when compared to the other fractions. There were two different patterns of litter stock seasonality: higher litter stock in the Cerrado stricto sensu and eucalyptus plantation in the dry season; and higher stock in Gallery Forest in the rainy season.

As espécies do gênero Eucalyptus são as mais plantadas no mundo, tornando-se solução para diminuir a pressão sobre as florestas nativas. Este trabalho objetivou avaliar a biomassa seca e sua distribuição nos diferentes compartimentos das árvores (folhas, galhos, casca, lenho e raízes), bem como examinar o conteúdo de macronutrientes dela e o balanço de nutrientes no sistema solo-planta, em um plantio de Eucalyptus urophylla x E. grandis, aos 60 meses de idade, na Fazenda Água Limpa, no Distrito Federal. Os dados foram obtidos de três árvores de eucalipto, que foram cubadas rigorosamente e tiveram as raízes escavadas até a profundidade de 60 cm. Esses dados foram submetidos à análise estatística pela correlação de Pearson. Grande parte da biomassa seca das árvores foi verificada no compartimento lenho (69,19 %), seguido de raízes (10,15 %), galhos (9,75 %), casca (6,06 %) e folhas (4,85 %). Os maiores teores de macronutrientes foram detectados nas folhas (N = 13,55 g kg-1; P = 1,33 g kg-1; K = 8,52 g kg-1; Ca = 7,12 g kg-1; Mg = 2,44 g kg-1; e S = 1,76 g kg-1), enquanto o lenho apresentou os menores (N = 1,73 g kg-1; P = 0,23 g kg-1; K = 0,34 g kg-1; Ca = 0,20 g kg-1; Mg = 0,03 g kg-1; e S = 0,43 g kg-1). A ordem dos conteúdos totais de macronutrientes verificada para a parte aérea foi: N > K > Ca >S > Mg > P, enquanto para as raízes, N > Ca > K > Mg > S > P. As raízes são responsáveis por acumular aproximadamente 11,90 % dos nutrientes contidos na biomassa das árvores; essa quantidade diminui com o aumento da profundidade. O balanço de nutrientes indica que P e S não são suficientes para um novo ciclo da floresta.

The species of the Eucalyptus genus are the most cultivated in the world and have become a solution for reducing the pressure on native forests. The aim of this study was to evaluate the dry biomass and its distribution in the different compartments of the trees (leaves, branches, bark, wood and roots), and assess their macronutrient content and nutrient balance in the soil-plant system in a Eucalyptus urophylla x E. grandis plantation at 60 months of age on the Água Limpa Farm in the Distrito Federal, Brazil. Data were obtained from three eucalyptus trees that had been rigorously scaled and the roots dug to a depth of 60 cm. Data were statistically analyzed by Pearson correlation. Most of the dry weight of the trees was observed in the wood compartment (69.19 %), followed by roots (10.15 %), branches (9.75 %), bark (6.06 %) and leaves (4.85 %). The highest levels of macronutrients were observed in leaves (N = 13.55 g kg-1, P = 1.33 g kg-1, K = 8.52 g kg-1, Ca = 7.12 g kg-1, Mg = 2.44 g kg-1, and S = 1.76 g kg-1), while the wood had the lowest concentrations (N = 1.73 g kg-1, P = 0.23 g kg-1, K = 0.34 g kg-1, Ca = 0.20 g kg-1, Mg = 0.03 g kg-1, and S = 0.43 g kg-1). The order of total contents of macronutrients observed for tree shoots was N > K > Ca > S > Mg > P while for the roots it was N > Ca > K > Mg > S > P. The roots accumulate approximately 11.90 % of the nutrients in the biomass of trees, and this amount decreases with increasing depth. The nutrient balance indicates that P and S are not enough for a new growth cycle in the forest.