Tree diameter, height and stocking in even-aged forests

Empirical observations suggest that in pure even-aged forests, the mean diameter of forest trees (D, diameter at breast height, 1.3 m above ground) tends to remain a constant proportion of stand height (H, average height of the largest trees in a stand) divided by the logarithm of stand density (N, number of trees per hectare): D = β( H−1.3) / ln ( N). Thinning causes a relatively small and temporary change in the slope β, the magnitude and duration of which depends on the nature of the thinning. This relationship may provide a robust predictor of growth in situations where scarce data and resources preclude more sophisticated modelling approaches

Planting density and initial growth of two tree species adapted to the semi-arid region

Planting densities influence several aspects of forest formation, including management practices, timber yield, quality, and extraction, and consequently its production costs. The objective of this study was to evaluate Mimosa caesalpiinifolia and Gliricidia sepium growth as a function of planting density (400, 600, 800, 1000, and 1200 plants ha-1) and plant age. The species were evaluated every 90 days for plant height (PH), crown diameter (CD) and root collar diameter (RCD) (10 cm above the ground), with the first evaluation performed at 90 days and the last at 720 days. When plants were one year of age and beyond, evaluations were conducted also for stem diameter at breast height (DBH) (1.30 m above the ground). A randomized block design with split-plots and three replicates was adopted. Species were assigned to plots, planting densities were assigned to subplots, and evaluation ages were assigned to subsubplots. The four traits in both species had their values decreased as planting density increased, but continually increased as plant age increased. For PH and RCD there was an alternation between species superiority, with gliricidia being superior to sabiá at some ages, while the opposite occurred at other ages. As to CD the species only differed in the last measurement, gliricidia being superior. With regard to DBH, gliricidia was superior starting from the second measurement. There was an effect of the species × ages interaction for the four traits and also an effect of the densities × ages interaction for CD and DBH

Genetic variation for carbon isotope composition in Juglans regia L.: relationships with growth, phenology and climate of origin

• Among the traits of breeding interest for the common walnut tree Juglans regia L., characteristics such as timing of budbreak and leaf fall, water-use efficiency and growth performance are regarded as being of utmost relevance in Mediterranean conditions. • The authors evaluated intraspecific variation in $\delta$$^{13}$C (carbon isotope composition, surrogate of intrinsic water-use efficiency, WUE$_{\rm i}$) for 22 J. regia families grown in a progeny test under supplementary irrigation, and investigated whether such variation correlated with climatic indicators of native habitats. The genetic relationships between $\delta$$^{13}$C, growth and phenology were also assessed during two consecutive years. • Overall, the most water-use-efficient families (i.e. with higher $\delta$$^{13}$C), which originated mainly from drought-prone provenance regions which have a high vapour pressure deficit and low rainfall, exhibited less height growth and smaller DBH. Using a stepwise regression procedure, $\delta$$^{13}$C was included as the main explanatory variable of genotypic variation in growth traits, together with growing season duration (for DBH in both years) and flushing (for height in 2007). • It was concluded that WUE$_{\rm i}$ is largely unconnected to phenology effects in the explanation of growth performance for J. regia, therefore suggesting the opportunity of simultaneously selecting for low WUE$_{\rm i}$ and extended growing period to maximise productivity in non-water-limited environments.Variation génétique de la composition isotopique du carbone chez Juglans regia L.: relations avec la croissance, la phénologie et le climat d'origine. • Parmi les traits d'intérêt pour la sélection de noyer commun Juglans regia, des caractéristiques telles que la précocité de débourrement et la date de chute des feuilles, l'efficience d'utilisation de l'eau et la performance de croissance sont considérées comme étant importantes dans les conditions méditerranéennes. • Les auteurs ont évalué la variation intraspécifique de composition isotopique en 13C ($\delta$$^{13}$C, substitut de l'efficience intrinsèque d'utilisation de l'eau, WUE$_{\rm i}$) dans 22 familles de Juglans regia cultivées dans un essai de descendance avec une irrigation d'appoint, et ils ont examiné si la variation était corrélée avec les indicateurs du climat des habitats d'origine. Les relations génétiques entre $\delta$$^{13}$C, croissance et phénologie ont également été évaluées au cours de deux années consécutives. • En général, les familles présentant les plus fortes valeurs de WUE$_{\rm i}$ (c'est-à-dire avec le $\delta$$^{13}$C le plus élevé), qui proviennent essentiellement des régions de provenance à sécheresse élevée et à fort déficit de pression de vapeur et faibles précipitations, présentent une croissance en hauteur moindre et un plus faible diamètre à 1,3 m. En utilisant une procédure de régression par étapes, $\delta$$^{13}$C a été inclus en tant que principale variable explicative de la variation génotypique des caractéristiques de croissance, de concert avec la durée de la saison de croissance (pour le diamètre à 1,3 m) et le débourrement (pour la hauteur en 2007). • Il a été conclu que WUE$_{\rm i}$ est en grande partie sans rapport avec la phénologie dans l'explication de la performance de croissance pour J. regia, suggérant donc la possibilité de sélectionner simultanément pour de faibles niveaux de WUE$_{\rm i}$ et une période de croissance prolongée pour maximiser la productivité dans des environnements où l'eau n'est pas limitante