Aspectos biométricos e energéticos de galhos de Araucaria angustifolia nativas

Abstract

Adult Araucaria crowns are an abundant component in native forests with the occurrence of this species; however, they are unexplored in forestry studies given the difficulties for accessing this compartment. This research aimed at evaluating the biometry of adult Araucaria angustifolia crowns in native forests, characterizing the energetic potential of its branches. Data emerges from 30 logged adult trees from an experimental forest management for which the base diameter of all branches were measured and two samples (base and medium) out of 195 whole branches were collected. Ten attributes were measured in the managed trees which were considered independent variables. As the variable number of branches is discrete, Generalized Linear Models with Poisson and Negative Binomial distribution have been applied. It was possible to adjust two equations from significant independent variables, through the stepwise method, and another two considering only the diameter at breast height (DBH). For the probability of occurrence in certain diameter classes of 1.0 cm branches, the Weibull 3p Probability Density Function was adjusted. Using an equation avalaible in literature, the amount of photosynthetic biomass was estimated by branch diameter class. Basal discs of the 195 collected branches were prepared to know its age and growth, modelling its growth using Chapman-Richards, Gompertz and Logistic Function models. Moreover, 30 branches divided into three treatments (Small: base diameter up to 6.0 cm; Medium: between 6.0 and 10.0 cm; and Large: greater than 10.0 cm) were subjected to analysis of basic density, immediate chemical analysis and calorific value comparing results among them as well as with literature values for other species. The significant variables to estimate the number of branches were crown length and diameter at 0.1 m height. DBH proved to be significant only when analysed separately. Only the model with DBH as an independent variable and the Poisson distribution are not recommended to estimate the number of branches. Weibull function exposed adherence in the adjustment by the Kolmogorov-Smirnov test. Regarding photosynthetic biomass, we identified that about 20% occurs in branches greater than 10.0 cm in diameter. Chapman-Richards model showed the best results for estimating base diameter growth of branches with bark, with an average increment of 0.34 cm.year-1 at 35 years. Considering the energetic properties, large and medium branches presented superior characteristics in relation to the small branches, especially in ash density and content; Araucaria branches nonetheless have shown energetic properties superior to diverse forest cultures normally used for bioenergy. We concluded that it is possible to estimate the number of branches by diameter classes of adult native Araucarias and that the larger branches are not the main contributors to photosynthetic rates. Branch growth modelling has exhibited adequate results to estimate the ages when branches reach certain diameters considering possible uses for this material. Araucaria branches, of all dimensions, have desirable characteristics for bioenergy uses, particularly for those branches with a diameter greater than 6.0 cm.