ABSTRACT In the Brazilian planted forest sector, most of the species used are from the genus Eucalyptus. Even though Southern Brazil has a suitable climate for species of the genus Pinus, the planting of frost-resistant Eucalyptus species has been increasing annually. The objective of this study was to evaluate the basic density, fiber dimensions, and chemical composition of Eucalyptus benthamii, Eucalyptus dunnii, Eucalyptus saligna, and Eucalyptus cloeziana woods. The trees used were from a six-year-old experimental plantation located in Canoinhas, state of Santa Catarina. For each species, three trees were selected, and discs were removed from each tree at 0%, 25%, 50%, 75%, and 100% of the commercial stem height. To evaluate the quality of the wood, the basic wood density, fiber dimensions, and chemical composition of the wood were determined by comparing the values between species and between the heights in the stem. The highest basic density was that of the wood of E. cloeziana; this species also had the greatest length and width of fibers. E. dunnii had the lowest levels of lignin and the highest levels of holocellulose. The highest lignin content was found in the wood of E. benthamii, E. saligna, and E. cloeziana. The relationship between wood properties and stem height was not relevant. The results highlight the tendency for higher extractives to be found at taller heights (100%), and holocellulose and lignin content are similar at all heights.

RESUMO No setor de florestas plantadas brasileiro, a maioria das espécies utilizadas são do gênero Eucalyptus. Embora o Sul do Brasil tenha clima propicio para espécies do gênero Pinus, o plantio de espécies de Eucalyptus resistentes à geada vem aumentando anualmente. O objetivo deste estudo foi avaliar a densidade básica, as dimensões das fibras e a composição química da madeira de Eucalyptus benthamii, Eucalyptus dunnii, Eucalyptus saligna e Eucalyptus cloeziana. As árvores utilizadas foram provenientes de um plantio experimental de seis anos localizado em Canoinhas, estado de Santa Catarina. Para cada espécie, três árvores foram selecionadas e os discos foram removidos de cada árvore a 0%, 25%, 50%, 75% e 100% da altura do caule comercial. Para avaliar a qualidade da madeira, a densidade básica, as dimensões das fibras e a composição química foram determinadas comparando-se os valores entre as espécies e entre as alturas no fuste. A maior densidade básica foi a da madeira de E. cloeziana; esta espécie também apresentou o maior comprimento e largura das fibras. E. dunnii apresentou os menores teores de lignina e os maiores teores de holocelulose. O maior teor de lignina foi encontrado na madeira de E. benthamii, E. saligna e E. cloeziana. A relação entre as propriedades da madeira e a altura do fuste não foi relevante. Os resultados destacam a tendência de maiores extrativos serem encontrados nas partes mais altas (100%), e os teores de holocelulose e lignina são similares em todas as alturas.

Abstract To characterize the spatial variation behavior of the tree attributes of tropical species in agroforestry systems is important for its management, and in this sense, geostatistics stands out for using techniques able of characterizing this variation. In this work, geostatistical methods were used to evaluate and map spatial variability of diameter (dbh) at 1.3 m from the ground level, commercial height (hc) and commercial volume (vc) of trees Swietenia macrophylla King, planted in an agroforestry system in the Brazilian Amazon. The field sampling was carried out based on a grid of 50 m × 50 m, which resulted in 36 systematics point. At each point, a circular plot of 500 m2 was installed to measure the variables dbh, hc. The vc of trees in the portions was estimated with the best equation adjusted to the 108 trees cubing data. Next, the spatial distribution standard of these variable were modeled with geostatistics and ordinary kriging was used to generate maps with predictions and uncertainties of the variables. The Schumacher-Hall’s model resulted in the best equation for the estimation of vc, and the systematic grid was efficient to detect the spatial patterns of these variables, because the adjusted semivariograms models demonstrated the strong spatial dependence on the dbh, hc and vc, being possible, make precise interpolations, generating cross-validation results without trend, mainly for vc that presented the best adjusted theoretical model.

Resumen La caracterización del comportamiento de la variación espacial de atributos dendrométricos de especies tropicales en sistemas agroforestales es importante para su manejo y, en ese sentido, la geoestadística se destaca por utilizar técnicas capaces de caracterizar esa variación. Se utilizaron métodos geoestadísticos para evaluar y mapear la variabilidad espacial del diámetro a 1.3 m del nivel del suelo (dap), de la altura comercial (hc) y del volumen comercial (vc) de árboles de Swietenia macrophylla King, plantadas en un sistema agroforestal en la Amazonia brasileña. El muestreo de campo se realizó con base en una cuadrícula de 50 m × 50 m, que resultó en 36 puntos sistemáticos. En cada punto, se instaló una parcela circular de 500 m2 para medir el dap y la hc. El vc fue estimado con la ecuación mejor ajustada a los datos de cubicación de 108 árboles. Luego se modelaron los patrones de distribución espacial de las variables por medio de la geoestadística y se utilizó kriging ordinario para generar mapas con predicciones e incertidumbres de las variables. El modelo de Schumacher-Hall resultó en la mejor ecuación para estimar el vc y la cuadrícula sistemática utilizada mostró ser eficiente para detectar los patrones espaciales de esas variables. Los modelos de semivariogramas ajustados demostraron la fuerte dependencia espacial del dap, de la hc y del vc, lo que permitió hacer interpolaciones precisas, generando resultados de validación cruzada sin tendencia, principalmente para vc que presentó el modelo teórico mejor ajustado.