MECHANICAL STABILITY OF THE Cabralea canjerana SAPLINGS SUBMITED TO LIBERATION IN SECONDARY FOREST, RS, BRAZIL

ABSTRACT The liberation of trees of interest by cutting competing trees, woody vines and other lianas is a very important silvicultural practice in the management of forest species of interest present in secondary forests. Thus, we aimed to know the influence of the liberation on the mechanical stability and what dimensional height limit of C. canjerana (Vell.) Mart. saplings must have so that there is no problem of buckling of the stem after the liberation. To this end, the liberation of 105 plants of the species was carried out and the diameter and height were measured before and annually for three years after the application of the treatment. Based on the Mechanical Design Theory, a regression model was generated to know to allocation mode of the diameter and height in the analized plants. The minimum diameter for buckling and the safety factor for all trees were calculated. The liberation resulted in the buckling of the stem of five trees, all below the safety limit, that is, with a real diameter smaller than the minimum diameter to support the weight of its height. According to the regression model generated the species grows proportionally in diameter and height. However, the liberation influenced the mechanical stability of the plants liberated, making a greater increment in diameter necessary so that the trees remained standing. The results demonstrate that the dimensions of the trees to be liberated should be considered in order to avoid problems of buckling of the stem after the treatment.

摘要：通过伐除竞争木、木质藤本及其他藤本植物以解放目标树种的作业，是次生林目标森林树种经营中极为关键的营林措施。据此，本研究旨在探究该抚育作业对植株机械稳定性的影响，以及C. canjerana (Vell.) Mart.幼苗需满足何种径高匹配阈值，方可避免抚育作业后出现茎干屈曲问题。为此，研究人员对该物种的105株植株实施了抚育作业，并在作业前及作业后三年内每年测量其胸径与树高。基于机械设计理论，本研究构建回归模型以解析供试植株的径高分配模式，并计算了所有植株发生茎干屈曲的最小胸径及安全系数。本次抚育作业导致5株植株的茎干发生屈曲，所有植株均低于安全阈值，即其实际胸径小于支撑自身树高重量所需的最小胸径。根据所构建的回归模型，该物种的径高生长呈比例关系；但抚育作业会降低已解放植株的机械稳定性，使得植株需具备更大的径生长增量方可维持直立状态。研究结果表明，为避免抚育作业后出现茎干屈曲问题，需对拟实施抚育作业的植株尺寸进行综合考量。