Main Article Content
The importance of technological progress for the Brazilian forest enterprises cannot be denied. Its influence comprehends all the activities, but can be summarized in the increase of income via yield increase or cost reduction and, mainly, in the two cases occurring together. Technological effects influence, among other aspects, the cutting age and the optimal time to renewal (a new plantinting or “reforma”) Eucalyptus plantations. Studies to determine these times are not so common in the literature since it requires both forestry and economic knowledge. Before renewing an Eucalyptus stand, it is necessary to technically and economically to define the optimal cut age the original planting and the coppicings and after how many cuttings the substitution of the plantations should be done. This study aimed at studying the optimal time to substitute Eucalyptus spp. Plantations, considering the gains earned through technological progress; to determine the cutting age of the population, the income being increasing and the cost being decreasing; to propose and verify the efficiency of a mathematical model which allows modeling the effects of technological progress; to study the substitution chain between 1960 and 2000 and between 2000 and 2040, considering technological progress; and to test the results in a case study. The Gompertz Function was employed to obtain the volumes at the various ages. The criterion employed for the economic evaluation of the projects was the Presente Net Value (PNV). The proposed model allowed the calculation of yields and costs through time, study the effect of yield increase and cost reduction and determine the rates of these increase and, or, reductions as well as determining rates which served as moderators so that the yield and costs did not reach unreal values. It was concluded that: The rotation, with current values, is at 7 years of age; the model proved to be efficient for estimates up to 40 years; with the income and costs from the sixties, considering technological progress from that point on, the number of cuttings before the renewal is currently 2; the substitution chain showed that the optimal substitution time went down with time, going from 18 cuttings in the sixties to 4 cuttings in the eighties, currently getting to 2 cuttings; a tendency to stick with 2 cuttings before substitution was verified for future cultivation, although little technological improvement in the coppice yield brings the optimal substitution Point to after the third cutting.