Resumen: El porcentaje de madera juvenil en coníferas de crecimiento rápido es un factor determinante de las propiedades básicas, ya que su proporción aumenta a medida que disminuye la edad de rotación. Dicha madera se caracteriza por presentar menor longitud y espesor de pared de traqueidas y mayor ángulo micro-fibrilar, lo cual se traduce en menor densidad y propiedades elasto-resistentes más bajas. Para delimitar la edad transición de madera (juvenil-madura) se realiza el análisis radial de algunas de las características mencionadas. La importancia de establecer dicha edad, radica en la estimación de los volúmenes de ambos tipos de madera, su calidad y potencialidad de uso. El objetivo del trabajo fue determinar la edad de transición y comparar sus valores elasto-resistentes en Pinus contorta (lodgepole). Se trabajó con 9 muestras de 35 años, radios norte y sur para estudios anatómicos, y madera juvenil y madura para ensayos físico mecánicos. Las edades de transición resultaron entre los 12 y 16,5 años, dirección norte y sur, respectivamente. Las variables anatómicas, físicas y mecánicas se diferenciaron significativamente, siendo mayores en la madera madura. A fin de generar una base de datos de esta especie para la región, se sugiere continuar con estudios similares en otros sitios.

Abstract: The percentage of juvenile wood in fast-growing conifers is a determinant of the basic properties, since its proportion increases as the rotation age decreases. This wood is characterized by having less length and thickness of tracheids and greater microfibrillar angle, which translates into lower density and lower elasto-resistant properties. To delimit the transition age of wood (juvenile-mature), we carried out a radial analysis of some of the mentioned characteristics. The importance of establishing transition age lies in the estimation of the volumes of both woods, their quality and potential use. The objective of the work was to determine the transition age and compare its elasto-resistant values in Pinus contorta (lodgepole). Based on nine samples of 35 years-old, we have been working with north and south radius for anatomical studies, while we used juvenile and mature wood for physical-mechanical tests. The transition ages were between 12 and 16,5 years, north and south direction, respectively. The anatomical, physical and mechanical variables differed significantly, being higher in the mature wood. Repeating our analysis framework in other study sites could generate an informative database of this species for the region.

Abstract: In this work, the behavior of Eucalyptus globulus unpreserved wood exposed outdoor for a year in La Plata city, Argentina, was evaluated. The evolution of color and defects presence were analyzed, and also their relationship with some climatic variables and the wood moisture content. Fifty-four samples (2.5 cm x 12 cm x 50 cm) were placed in an outdoor exhibitor with a 45º inclination (north), in which color (CIELab*), moisture content and defects were determined monthly. A sample without outdoor exposure was considered as control. After 150-180 days starting the test, the values of L*, a* and b* reached values close to the minimum (49.22; -6.5; -1.90, respectively). At the end, the colorimetric parameters showed significant changes with respect to the initial values (∆L*=22.55; ∆a*=5.41; ∆b*=16.64; ∆E*total=29.10) and to the control. The values of solar radiation and rainfall did not significantly influence the color, while the temperature affected the parameter a*. The moisture content of wood correlated with the presence of some defects, but it was not correlated with the color. Weathering caused loss of natural color, acquiring a grayish tone (a* and b* close to 0 = achromatic and L*=47.6) and increasing the level of cracking; the first 150 days of exposure were key in this process.

Resumen: En el presente trabajo se evaluó el comportamiento de la madera de Eucalyptus globulus sin preservar, expuesta a la intemperie durante un año en la ciudad de La Plata, Argentina. Se analizó la evolución del color y la presencia de defectos, y su relación con algunas variables climáticas y con el contenido de humedad de la madera. Se colocaron 54 muestras (2,5 cm x 12 cm x 50 cm) en un expositor exterior con inclinación de 45º (norte) y sobre ellas se determinó mensualmente color (CIELab*), humedad y defectos. Una muestra sin exposición fue considerada testigo. Entre los 150-180 días de comenzar el ensayo, los parámetros L*, a* y b* alcanzaron valores cercanos al mínimo (49,22; -6,5; -1,90 respectivamente); al finalizar presentaron cambios significativos respecto a los valores iniciales (∆L*=22,55; ∆a*=5,41; ∆b*=16,64; ∆E*total=29,10) y al testigo. Los valores de radiación solar y precipitaciones no influyeron significativamente en el color mientras que la temperatura afectó al parámetro a*. El contenido de humedad de la madera se correlacionó con la presencia de algunos defectos, pero no afectó al color. El intemperismo provocó pérdida del color natural, adquiriendo un tono grisáceo (a* y b*cercanos a 0=acromático y L*=47,6) y aumentó el agrietado, siendo los primeros 150 días de exposición claves en este proceso.

RESUMO Os objetivos do trabalho foram: 1- determinar o efeito do estresse hídrico (sítios de implantação) e do genótipo (clone) na anatomia e densidade da madeira produzida em seis clones de salgueiros em três idades; 2- verificar como essas variações na anatomia impactam na condutividade hidráulica teórica do xilema (Ks) e no crescimento. Foram mostrados seis clones, de 13 anos de idade de origem do cruzamento Salix babylonica x S. alba (Ragonese INTA 131-25, 131-27 e 250-33), S. matsudana x S. alba (Barrett 13-44 e NZ 26992) e S. babylonica var sacramenta ´Soveny Americano´ implantados em duas situações com diferente estresse abiótico (sítio DM Delta Del Río Paraná com inundações recorrentes e sítio LH zona continental província de Buenos Aires, com menor disponibilidade da água e sem inundações). Foi determinado: morfometria dos vasos, densidade da madeira, Ks e incrementos correntes anuais em três idades (2, 7 e 12 anos). A interação clone x sítio foi a fonte de variação que maior impacto teve nas variáveis e foi significante para o diâmetro de vasos, densidade, Ks e crescimentos. Isso significa que dependendo do tipo de estresse sofrido no sítio de implantação, os clones respondem de maneira diferente em sua estrutura, funcionalidade e produção da madeira. Existem clones melhor adaptados ao estresse por inundação (americano e 26992) e outros mais adaptados nas condições moderadas de seca (131-25, 131-27, 250-33 e 13-44), obtendo respostas no nível do xilema, densidade e, portanto, a produção da madeira.

ABSTRACT The aims of the study were to evaluate the effects of abiotic stress (plantation site) and genotype (clone) on the wood anatomy and density of six Salix (willow) clones at three ages (2, 7, and 12 years), and the impact of these effects on the theoretical xylem hydraulic conductivity (Ks) and growth. The clones studied were ´Ragonese 131-25 INTA´, ´Ragonese 131-27 INTA´ and “250-33” (originated from crosses between Salix babylonica and S. alba), ´Barrett 13-44 INTA´ and “NZ 26992” (originated from crosses between S. matsudana and S. alba), and the clone S. babylonica var. sacramenta ´Soveny Americano´. They were planted in two sites of the province of Buenos Aires, Argentina, with different abiotic stress: i) the Paraná River Delta, a site with recurrent floods, and ii) a continental site with lower water availability and no floods. The vessel morphometry, wood density, Ks, and current annual increments at the three ages were determined. The clone x site interaction was the source of variation with greatest impact, being this significant for vessel diameter, Ks, wood density and growth. This means that, depending on the type of stress at the plantation site, the clones responded differently, showing differences in their structure, functionality, and wood production. The results showed that the clones Soveny Americano and 26992 were better suited to stress by flood, whereas clones 131-25, 131-27, 250-33 and 13-44 were better adapted to moderate drought conditions, with responses at the level of the xylem and wood density, and therefore at the level of wood production.