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. RESUMO A liberação de árvores de interesse por meio do corte de árvores competidoras, videiras lenhosas e outras lianas é uma prática silvicultural muito importante ao manejo florestal de espécies de interesse comercial presentes em florestas secundárias. Diante disso, nós objetivamos conhecer a influência na estabilidade mecânica e qual o limite dimensional de altura que as plantas de C. canjerana devem possuir para que não haja problemas de flambagem do fuste após a liberação. Para isto, foi realizada a liberação de 105 plantas da espécie, que tiveram seu diâmetro e altura medidos antes e anualmente por três anos após a aplicação do tratamento. Baseado na Teoria do Design Mecânico, foi gerado um modelo de regressão para conhecer o modo de alocação de diâmetro e altura nas plantas analisadas. O diâmetro mínimo para flambagem e o fator de segurança foram calculados para todas as plantas. A liberação resultou na flambagem do fuste de cinco árvores, todas com bai