Abstract Forests play a crucial role in the global carbon cycle. Among the factors that can affect carbon stocks in forest stands, planting spacing stands out. This study verified the effect of spacing on biomass and carbon stock in a stand of Anadenanthera peregrina (L.) Speg at 56 months of age. They were planted with 3 x 2 m, 3 x 3 m, 4 x 3 m, 4 x 4 m and 5 x 5 m spacings. The biomass of the above-ground compartments (stem, branches, leaves and bark) and root biomass was quantified, totalling 16.42 and 6.68 Mg ha-1, respectively. The largest amount of biomass and carbon stock occurred in the denser spacings. Total biomass was twice as large at 3 x 2 m spacing compared to 5 x 5 m spacing. The root biomass represented 40.93% of the total biomass. The order of participation of the components in the total aboveground biomass was branches (44.99%), stem (40.77%), leaves (13.99%) and bark (4.90%). The denser spacings (3 x 2 m and 3 x 3 m) showed higher values of biomass and carbon stock than the wide spacings (4 x 3 m, 4 x 4 m and 5 x 5 m). There was no effect of planting spacing on carbon stock in necromass and soil.

Resumo As florestas desempenham um importante papel no ciclo do carbono. Dentre os fatores que podem afetar os estoques de carbono nos povoamentos florestais, o espaçamento de plantio tem grande relevância. O objetivo foi verificar o efeito do espaçamento na biomassa e no estoque de carbono em um povoamento de Anadenanthera peregrina (L.) Speg aos 56 meses de idade. O povoamento foi implantado nos espaçamentos 3 x 2 m, 3 x 3 m, 4 x 3 m, 4 x 4 m e 5 x 5 m. Quantificou-se a biomassa dos compartimentos acima do solo (madeira, galhos, folhas e casca) e da raiz, totalizando 16,42 e 6,68 Mg ha-1, respectivamente. A maior quantidade de biomassa e estoque de carbono ocorreu nos menores espaçamentos. A biomassa total foi duas vezes maior no espaçamento de 3 x 2 m em comparação com o espaçamento de 5 x 5 m. A biomassa abaixo do solo representou 40,93% da biomassa total. A ordem de participação dos componentes na biomassa aérea total foi galhos (44,99%), madeira (40,77%), folhas (13,99%) e casca (4,90%). Os espaçamentos mais densos (3 x 2 e 3 x 3 m) apresentaram maiores valores de biomassa e estoque de carbono do que os espaçamentos mais amplos (4 x 3 m, 4 x 4 m e 5 x 5 m). Não houve efeito do espaçamento de plantio sobre o estoque de carbono na necromassa e no solo.

ABSTRACT Background: Background: Eucalypt harvest residues are critical to nutrient balances and forest soil productivity mainly in areas with consecutive forest rotations. However, nutrient release and their relations over decomposition are still poorly understood in tropical sites. We aimed to understand how nutrients are released from leaves, branches, and bark (as harvest residues), and how nutrient concentrations could be limiting the decomposition of each fraction. We measured mass loss and nutrient release of Eucalyptus urophylla x Eucalyptus grandis harvest residues for 365 days in Southeast Brazil. Results: Results: Leaves fraction showed a faster decomposition rate than branches and bark, but nutrient accumulation was observed for all harvest residues, especially bark and branches at later stages of the decomposition. Decomposition of all harvest residues seemed to be P-limited with a stronger limitation occurring for leaf litter decomposers. The decomposition of more lignified residues such as bark and branches was less influenced by climatic variables than leaf decomposition. Conclusion: Conclusion: Eucalypt harvest residues had a great contribution to soil fertility, and retaining them in the soil systems will enhance soil fertility in the short (leaves) and long-term (branches and bark) and can partially supply the nutrients for the next rotation.