The forest management, in broad terms, covers a set of information and activities related to the growth and production of plantations or from heterogeneous forests. If on one hand forest plantation presents homogeneous dendrometric characteristics, on the other hand in heterogeneous forests such a configuration does not exist, which requires the application of essential mathematical estimates for the forest management planning, for example, the prognosis of diametric structure. In this respect, refinements can be tested in traditionally used mathematical models, aiming at more accurate results. These facts substantiate the following hypotheses: the stratification of the diameter increments can provide estimates with greater accuracy and more precise results for the prognosis. With the stratification of diameter increment made it possible to get better results for the prognosis for a 4-year period, allowing the forest manager to better work with estimators either for diameter classes as well as for the forest to be managed. Using the data structure of trees (DBH ≥ 9.5 cm) of the National Forest of Sao Francisco de Paula, RS, Brazil, the diameter increment of species was stratified into four statistically different strata. Using data sampled between the years of 2000 to 2004, it was carried out prognosis for the year 2008, using the stratified and not stratified data. The estimates were compared with the observed values by the Kolmogorov-Smirnov (K-S) test, which attested goodness of fit only for the estimates from the stratified values. The prognosis estimated by means of stratified values also showed more accurate results, because the stratified variance was reduced nine times when compared with that obtained with the prognosis made without stratified data and to determine the Quotient of De Liocourt. Thus, the diameter growth stratification indicated to be effective to generate more accurate prognosis.