Manejo da densidade em povoamentos de eucalipto

Abstract

In this work, we aimed to develop a density management diagram to help in taking care of eucalyptus stands, the most planted genus in Brazil when the silvicultural practice of thinning is implemented. The thinning consists in an essential intervention for producing sawlog, for instance, wherein removing some individuals in the plantation provides the regulation of the growth space, avoiding losses in growth or mortality due to the competition, leading to continuous timber production and reduction in production time of big logs. The research was performed in three parts. The first chapter describes the theme overview by means of literature review. In the second chapter, the stand density index (SDI) of Eucalyptus urophylla tree plantation, including its natural hybrids, was estimated by varying: (i) the selection intensity of plots; (ii) different models for describing the proportion of number of stems per hectare and the quadratic mean diameter; and (iii) methods of adjusting models. In the third chapter we developed the actual density diagram. We used here the SDI value estimated in the second chapter, and data related to growth in tree plantation volume, mean dominant and codominant height, quadratic mean diameter and number of stems per hectare, obtained from the continuous forest inventory of clonal tree plantations of Eucalyptus urophylla of the State of Minas Gerais. For establishing the range of suitable density, for tree plantation maintenance, we used the method of derivative of the logistic model in each intervention of thinning. The maximum limit of density corresponded to the inflection point of the sigmoidal curve, wherein the increase in volume is maximal. The minimum, however, corresponded to the beginning of decrease stage of the rate of increase of volume, indicated by the first critical point of the second derivative of the model. According to site quality, the range of density varied, affording distinct estimates in relation to quantity of trees, basal areas and removed volumes in each simulated thinning, besides influencing the plant age for silvicultural practice of thinning. Therefore, by defining the initial planting density and the diametric measurements at the end of the rotation, was possible estimating three basic variables for the practice of thinning, based on technical criteria and use of density diagram. These variables are, namely: (1) number of times required for the practice of thinning; (2) the plantation age on which thinning will be performed; and (3) number of trees, basal area, and volume that will be removed on each thinning.