POPULATION STRUCTURE AND REGENERATION OF ARBOREAL SPECIES IN THE NATIONAL FOREST OF S\uc3O FRANCISCO DE PAULA, RIO GRANDE DO SUL STATE

Este estudo teve como objetivo caracterizar a estrutura populacional e os aspectos da regenera\ue7\ue3o de Araucaria angustifolia (Bertol.) Kuntze, Blepharocalyx salicifolius (Kunth) O. Berg e Ilex paraguariensis A. St.-Hil em diferentes condi\ue7\uf5es ambientais e hist\uf3rico de perturba\ue7\ue3o na Floresta Nacional de S\ue3o Francisco de Paula - RS. Foram utilizados seis conglomerados de um hectare, com 16 parcelas (20 x 20 m) cada, nos quais foram amostradas as esp\ue9cies em tr\ueas classes de tamanho. A classe de tamanho II (CT II - di\ue2metro a altura do peito (DAP) 65 9,55 cm) foi inventariada nas 96 parcelas, a CT I (4,8 64 DAP < 9,55 cm) em 36 subparcelas de 10 x 10 m e a regenera\ue7\ue3o natural estabelecida (RNE) (1 64 DAP < 4,8 cm) em 36 c\ue9lulas de 3,16 x 3,16 m. Em todas as parcelas de 20 x 20 m foram avaliados o banco de pl\ue2ntulas (BP - altura 65 30 cm e DAP < 1 cm), a chuva de sementes (CS) e o banco de sementes do solo (BS). Os dados foram analisados considerando todos os ambientes conjunta e separadamente para os agrupamentos identificados em estudo pr\ue9vio na \ue1rea. Foram avaliadas a estrutura diam\ue9trica para a CT II e densidade e frequ\ueancia absoluta para todas as etapas do ciclo de vida (CS, BS, BP, RNE, CT I e CT II). Os resultados indicaram grande variabilidade na densidade destas esp\ue9cies nos diferentes ciclos de vida e ambientes florestais. Araucaria angustifolia demonstrou falhas no processo de regenera\ue7\ue3o em ambiente com menor hist\uf3rico de perturba\ue7\ue3o, n\ue3o apresentando padr\ue3o de distribui\ue7\ue3o \u201cJ invertido\u201d (CT II) e menor capacidade de regenera\ue7\ue3o em rela\ue7\ue3o \ue0s demais esp\ue9cies nos mecanismos de regenera\ue7\ue3o (CS, BS e BP). Ilex paraguariensis e Blepharocalyx salicifolius apresentaram melhor estabilidade populacional em ambiente com menor n\uedvel de interfer\ueancia antr\uf3pica (CT II). A primeira esp\ue9cie apresentou melhores condi\ue7\uf5es de regenera\ue7\ue3o em ambientes de solo com boa drenagem e a segunda esp\ue9cie demonstrou prefer\ueancia para solo mais \ufamido. Al\ue9m disso, falhas no processo de regenera\ue7\ue3o das popula\ue7\uf5es foram detectadas e variaram de acordo com as condi\ue7\uf5es ambientais e o hist\uf3rico de perturba\ue7\ue3o de cada \ue1rea. Assim, identifica-se a import\ue2ncia de considerar os diferentes ambientes florestais, a autoecologia das esp\ue9cies e de aplicar poss\uedveis interven\ue7\uf5es que visem melhorar a regenera\ue7\ue3o e equilibrar a din\ue2mica populacional destas esp\ue9cies.The aim of this study was to characterize the population structure and aspects of regeneration of Araucaria angustifolia (Bertol.) Kuntze, Blepharocalyx salicifolius (Kunth) O. Berg and Ilex paraguariensis A. St.- Hil. in different environmental and disturbance conditions in the National Forest of S\ue3o Francisco de Paula, RS state. Six conglomerates of one hectare were used, with 16 plots (20 x 20 m) each, where the species were sampled in three size classes. The size class II (SC II \u2013 diameter at breast height (DBH) 65 9.55 cm) was sampled in 96 plots, the SC I (4.8 64 DBH < 9.55 cm) in 36 subplots of 10 x 10 m, and the established natural regeneration (ENR) (1 64 DBH < 4.8 cm) in 36 cells of 3.16 x 3.16 m. The seedling bank (SB - height 65 30 cm and DBH < 1 cm), the seed rain (SR) and the soil seed bank (SSB) were sampled in all plots of 20 x 20 m. The data were analysed by taking into account all the different vegetation groups together and separately for each cluster identified in a previous study. For SC II, the frequency distribution of DBH was analysed combined with the analysis of absolute density and frequency for all life stages (SR, SSB, SB, ENR, SC I and SC II). The results indicated high variability in density of these species among the different life stages and environmental conditions. Araucaria angustifolia presented gaps in the regeneration process in areas that had low past disturbance, not showing the \u201creverse-J\u201d distribution (SC II) and with lower regeneration capacity in relation to the other species (SR, SSB and SB). Ilex paraguariensis and Blepharocalyx salicifolius showed higher population stability in environment with low level of human interference (SC II). The first species demonstrated preference for soils with good drainage, while the second species for humid soils. Moreover, gaps in the regeneration process of different populations were detected, which changed according to environmental conditions and disturbance levels. Therefore, the results suggest the importance of taking into account the different vegetation groups, the species autecology and to apply possible interventions that aim to improve regeneration and balance the population dynamics of these species