Prognose da distribuição diamétrica e ciclo de corte de espécies arbóreas classificadas em grupos ecológicos em uma floresta tropical de terra firme.

Abstract

The Brazilian environmental legislation establishes an initial cutting cycle of 35 years for cut intensity of 30m3 / ha and minimum cut diameter (DMC) of 50 cm for ali species that do not have specific DMC. Thus, research is needed to help foresters to manage the forest for better use. In order to aid the research, one can analyze the diametrical distribution, group the species according to their characteristics in relation to the diametric growth, determining functional or ecological groups. The objective of this research was to estimate the cutting cycle for commercial tree species divided into ecological groups in a tropical mainland forest, through the Transition Matrix model and the Movement Ratio model. The results should answer the problem: what is the cutting cycle to be adopted for the tree species exploited in a Tropical Forest of Terra Firme? The work is divided into three specific questions, each of which has a hypothesis: 1) question: is it possible to detect ecological groups from the analysis of the diameter distribution? Hypothesis: the tree species can be divided into ecological groups after analysis of the diametric distribution; 2) question: which model has the greatest accuracy by ecological groups for the prognosis of the diametric growth in a Tropical Forest of Terra Firme? Hypothesis: a model in which the estimated data approaches the maximum of the real values will be the most suitable for prognosis in a Tropical Forest of Terra Firme; 3) Question: Is the cutting cycle established in environmental legislation compatible with the recovery and growth of tree species? Hypothesis: fast-growing species recover the harvested stock within the cutting cycle up to 35 years or less and slow-growing species do not recover. The experiment was conducted in 200 ha of a terra firme tropical forest at the EMBRAPA experimental field in Moju, state ofPará, where there was selective exploration in October 1997. Nine clearings were selected, around which sample plots were installed 10 mx 50 m, from the edge of the clearing into the forest, in the north, south, east and west directions, where ali individuais with DBH > 5 cm were measured. Data were collected from 1998 to 2010 totaling 12 years of monitoring. The prognosis was performed based on data obtained in 1998 and 2001, for the Transition Matrix and Moving Ratio models. The efficiency of the projections was verified based on the values observed, by means of the Kolgomorov-Smirnov test. Finally, from the methodology of greater accuracy, the prognosis ofthe commercial species divided into ecological groups for the year 2028 was carried out, in order to verify the ideal cutting cycle. It was verified that the diametric distribution can be used to classify the species into groups. The discriminant analysis showed that 92.4% ofthe species were correctly classified. The projections performed by the two methods did not present significant difference between the actual and projected values. Based on the results it is recommended the Transition Matrix method for the prognosis of the diametric distribution for the individuais belonging to the group of tolerant and intermediate species and it is indicated to use both models for intolerant species. It was found that tolerant and intolerant species recovered the harvested stock over a period of 16 years, going against the hypothesis that slow-growing species did not regain their volume in 27 years. The intermediate species presented a cut cycle of 22 years, 5 years less than stipulated by law. For forest exploitation it is necessary that the species be classified according to their ecophysiological demands and establish a Cycle of Cut compatible with the recovery of the volume extracted from each group, guaranteeing the environmental and financial sustainability of the activity.