Crescimento de uma floresta estacional decidual, em três estágios sucessionais, no município de Santa Tereza, RS, Brasil

Abstract

The changes in the floristic composition, its phytosociological structures and the dynamic processes of the growth as ingrowth, increment in basal area and mortality, were studied in three successional phases of Deciduous Seasonal Forest, which were named Dense Brushwood, Secondary Forest and Mature Forest. The area, located in the county of Santa Tereza, State of Rio Grande do Sul, was sampled during the period from 1996 to 2000, considering the arboreal individuals with diameter at breast height larger or equal to 3,2 cm (10 cm of circumference). The floristic analysis and its phytosociological structures have not showed significant changes during the study period. On the other hand, it was observed that there was a substitution hierarchy and importance of botanical families and of distinct sucessional categories of species groups in the course of the forest succession. The intolerant species to the shade are gradually substituted by tolerant species, if the analyzed subseres be considered as a cronosequence. The annual rates of mortality were larger than the one of the ingrowth; therefore, in the Dense Brushwood the number of trees reduced 1,25% annually; in the Secondary Forest 2,55% and in the Mature Forest 0,84%. However, the Dense Brushwood increased 0,4727 m² ha-¹ year-¹; the Secondary Forest 0,0326 m² ha-¹ year-¹ and the Mature Forest 0,2860 m² ha-¹ year-¹. The medium rates of increment in diameter and basal area were, respectively, of 0,14 cm year-¹ and 0,226.10-³ m² year-¹ in the Dense Brushwood; 0,10 cm year-¹ and 0,271.10-³ m² year-¹ in the Secondary Forest; and of 0,17 cm year-¹ and 0,609.10-³ m² year-¹ in the Mature Forest. The growth in diameter quite influenced by the class of vitality of the tree, amount of incident light on the cup and thickness of the log. The category sucessional of the species was not related to the growth. For the trees of the Deciduous Seasonal Forest of the studied area, the annual periodic increment in basal area can be estimated through specific equations developed for each successional phase, or through a general equation, independent of the successional phase, without loss of precision of the estimates.