Abstract Litterfall and nutrient cycling are essential processes for the forest diversity and productivity maintenance. This study aims to characterize the litterfall and evaluate if it has correlations with climatic variables in the Semideciduous Seasonal Forest on advanced succession stage, in Southern Brazil. During the 2007-2010 period, the litterfall was collected every month, sorted into leaves, twigs, and miscellaneous fractions. The litterfall amount average was 7.75 Mg ha-1 year-1 and leaves constituted the highest litterfall percentage (75.0%), followed by twigs (14.7%), and miscellaneous (10.3%). Higher leaf amounts were recorded in August and September. The minimum air temperature was negatively correlated with the leaves and twigs production, that is, the litterfall amount increases when the air temperature decreases. The litterfall amount corresponds to values expected to advanced successional stage of the forest typology studied. In Semideciduous Seasonal Forest in Southern Brazil, the thermal stress exerts influence on the litterfall amount.

ABSTRACT Rainfall is one of the primary nutrient inputs to vegetation and its chemical composition is dependent on air quality as falling rain scavenges gaseous and particulate emissions from natural, industrial, and agricultural activities. The objective of this study was to evaluate whether the vegetation burn in a region of the Pampa biome influences the pH and chemical composition (anions) in incident rainfall. Nitrate, sulfate, and chloride concentrations, as well as the pH of the rainwater, were influenced by suspended particles in the atmosphere from biomass burning of native grassland and pasture renewal. The rainwater was acidified by, ash, and soot, which introduced large amounts of chloride and sulfate into the ecosystems caused by burning vegetation.

ABSTRACT We evaluated the nutrient input via incident rainfall in a Eucalyptus dunnii stand in the Brazilian Pampa biome. During the two-year study, we analyzed nutrient concentrations in incident rainfall (P), throughfall via drip (Pi), and stemflow (Et). Ion concentrations (NO2-, NO3-, PO43- , SO42-, Cl-, K+, Ca2+ , and Mg2+) were determined from the aqueous solution, and based on the water volume, the quantity per hectare (kg ha-1) was estimated for each element. Statistical differences observed by ANOVA and separation of means contrasts were subjected to Tukey’s test (5%), adopting a completely randomized design. Higher concentrations of SO4 2- in P; NO3- in Pi solution, and K+, Ca2+ , Mg2+, and Cl- in Et were observed. Greater amounts of nutrients such as Cl-, K+, Ca2+, and SO42 were incorporated via Pi.

RESUMO A expansão da silvicultura no Brasil e as consequentes práticas intensivas para o preparo do solo, com elevada demanda por fertilizantes, requerem ações de manejo nutricional sustentável dos sítios florestais. O objetivo do presente trabalho foi quantificar a biomassa e o estoque de micronutrientes, em um povoamento de Eucalyptus dunnii, aos 60 meses de idade, estabelecido em Alegrete, Rio Grande do Sul. O povoamento foi implantado em solo do tipo Argissolo Vermelho Distrófico típico, com baixa fertilidade natural e textura variando entre franco-arenosa e franco-argilo-arenosa. Para a amostragem da biomassa, doze árvores foram abatidas e seccionadas ao nível do solo, onde posteriormente houve o fracionamento nos componentes: raízes, folhas, galhos, casca do tronco e madeira do tronco, com determinação de massa seca e teores de micronutrientes. Verificou-se que a biomassa total do povoamento foi de 67,49 Mg ha-1, com sequência decrescente de alocação de massa na ordem de: madeira do tronco > raízes > casca do tronco > galhos > folhas. O estoque total de micronutrientes B, Cu, Fe, Mn e Zn na biomassa foi de 562,57; 401,46; 9.913,28; 31.877,82 e 766,96 g ha-1 respectivamente. Constatou-se maior acúmulo de zinco na madeira do tronco, elevado acúmulo de manganês especialmente na casca do tronco e de ferro nas raízes. Em função dos níveis de micronutrientes alocados na biomassa, enfatiza-se à prática de manutenção dos resíduos florestais no sítio após a colheita, indispensáveis para a nutrição florestal, que através da ciclagem de nutrientes propiciam a conservação da fertilidade.

ABSTRACT The expansion of silviculture in Brazil, and the consequent intensive practices for soil preparation with high demand for fertilizers require sustainable nutrient management of forest sites. The objective of this study was to quantify the biomass and the micronutrient stocks of a 60-month-old Eucalyptus dunnii stand established in Alegrete, Rio Grande do Sul. The stand was established in a Rhodic Paleudult soil with low fertility and texture varying between sandy loam and sandy-clay loam. For the sampling of stand biomass, twelve trees were harvested, sectioned at ground level, and subsequently fractionated into the components roots, leaves, branches, stembark and stemwood to determine the dry mass and micronutrient content. The total biomass of the stand was 67.49 Mg ha-1, with mass allocation in descending order from: stem wood > root > bark > branches > leaves. Total micronutrient stocks for boron (B), copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn) were 562.57, 401.46, 9913.28, 31877.82, and 766.96 g ha-1, respectively. In addition, we found greater accumulation of Zn in the wood, high Mn accumulation especially in the bark, and high Fe content in the roots. Therefore, based on these micronutrient levels and their allocation between biomass fractions, we emphasize that the practice of retaining forest residues on-site after harvest is essential for forest nutrition through nutrient cycling and for soil conservation and fertility.

RESUMO A produção de serapilheira é a principal responsável pela retenção e devolução de nutrientes para o solo em um povoamento florestal. O objetivo deste trabalho foi avaliar a devolução de nutrientes por meio da serapilheira produzida em um povoamento de Eucalyptus dunnii, no bioma Pampa. Para a quantificação da serapilheira produzida, foram demarcadas quatro parcelas de 420 m2, e no interior de cada parcela foram distribuídos quatro coletores de 0,50 m2. Para a coleta dos galhos grossos demarcou-se quatro sub-parcelas de 7,00 m2. O material coletado foi separado nas frações folhas, galhos grossos, galhos finos e miscelânea, com posterior análise química. A serapilheira produzida foi de 6,99 Mg ha-1 ano-1, distribuída em 61,57%, 17,34%, 13,83% e 7,26%, nas folhas, galhos finos, galhos grossos e miscelânea, respectivamente. A quantidade de macronutrientes na serapilheira foi de 160,22 kg ha-1 ano-1, sendo que, a ordem de transferência foi a mesma para as frações folhas, galhos finos e galhos grossos (Ca > N > K > Mg > S > P). Para os micronutrientes a quantidade foi 7,55 kg ha-1 ano-1, seguindo a ordem decrescente de Mn > Fe > B > Zn > Cu. A manutenção da serapilheira no sítio, principalmente em solos degradados ou de baixa fertilidade natural, como é o caso da região do bioma Pampa, poderá contribuir com possíveis melhorias nas características do solo.

ABSTRACT In a forest stand, litterfall is primarily responsible for the retention and return of nutrients to the soil. The objective of this study was to evaluate the return of nutrients through litterfall in a stand of Eucalyptus dunnii in a Pampa biome. For quantification of litterfall, four 420-m2 installments were marked; within each one, four 0.50-m2 collection plots were distributed. For the collection of thick branches, four 7.00-m2 sub-plots were staked out. The collected litterfall was separated into leaf, twig, thick branch, and miscellany fractions for subsequent chemical analysis. The total litterfall measured was 6.99 Mg ha-1 yr-1, and comprised 61.57% leaves, 17.34% twigs, 13.83% thick branches, and 7.26% miscellany. The total amount of macronutrients in the litterfall was 160.22 kg ha-1 yr-1, and the macronutrient transfer order was the same for the leaf, twig, and thick branch fractions (Ca > N > K > Mg > S > P). The total quantity of micronutrients was 7.55 kg ha-1 yr-1, and the transfer order was Mn > Fe > B > Zn > Cu. Maintaining litterfall on the site, especially in degraded or low fertility soils like in the Pampa biome, may contribute to possible improvements in soil characteristics.