ABSTRACT: The natural regeneration process is essential for forest maintenance since it is critical for establishing new tree individuals. This study aimed to improve the understanding of the regenerative component dynamics of Araucaria Forests in Southern Brazil. We investigated the effects of climate, light, tree component structure and anthropogenic disturbance on tree species regeneration. Regenerating communities from six different fragments in forest remnants of the “Planalto Sul Catarinense” region was evaluated in permanent plots two years after the first inventory. The following demographic rates were determined: recruitment, mortality, net change in the number of individuals and the changes to both upper and lower height classes. The following variables were measured in each fragment: altitude, climatic variables, light environment, tree component density and cattle presence. Association between dynamics rates, regenerating species abundance and explanatory variables was verified by the fourth-corner and RLQ methods. A total of 4,379 and 5,268 individuals were sampled for the first and second inventories, respectively, with recruitment rate (21 % yr−1) higher than mortality rate (13 % yr−1). The dynamics pattern of the fragment with greater presence of cattle stood out for the intense height increase of regenerating species caused by the presence of fast growth and light-demanding species. Natural regeneration of forest remnants under study is facing a structuring process. The main conclusions of this study were: i) climate and altitude play a relevant role in defining floristic identity and ii) chronic disturbances may influence the definition of ecological strategies.

RESUMO Objetivou-se caracterizar a organização florístico-estrutural, a riqueza e a estrutura filogenética de comunidades arbóreas de fragmentos florestais altomontanos em diferentes estágios sucessionais, situados no Parque Nacional de São Joaquim em Urubici, Santa Catarina. Foram selecionados três fragmentos, dois em avançado estágio sucessional e um em estágio inicial, sendo cada um avaliado por meio de 20 parcelas de 10 x 10 m, distribuídas na forma de transecção de 20 x 100 m. Foram identificados e medidos todos os indivíduos arbóreos com DAP ≥ 5 cm. Os dados foram analisados por meio de rarefação, ordenação multivariada, análise de espécies indicadoras e métricas de estruturação filogenética. A riqueza encontrada em cada fragmento não apresentou relação com o estágio sucessional, uma vez que as áreas não difeririam quanto a este aspecto. A organização florístico-estrutural foi influenciada pela interação entre o estágio sucessional e as diferenças ambientais entre os locais. Na área em início de sucessão, foi observado o agrupamento filogenético das espécies, e nas áreas tardias, o padrão foi aleatório. Assim, os resultados evidenciaram variações na riqueza independentemente do estágio sucessional e que a sucessão florestal influenciou a composição florístico-estrutural e a estrutura filogenética das áreas.

ABSTRACT We aimed to describe the floristic-structural organization, the richness and the phylogenetic structure of tree components in highland forest fragments in different successional stages, at São Joaquim National Park, in the municipality of Urubici, Santa Catarina state. Three fragments were selected, two in an advanced successional stage and one in an initial successional stage, being each one evaluated by 20 10 x 10 m sampling plots, allocated as 20 x 100 m transects. All trees with dbh ≥ 5 cm were identified and measured. The data were analyzed through rarefaction, multivariate ordination, indicator species analysis and phylogenetic structure metrics. There was no relationship between the richness and the successional stage, once the studied areas did not differ in relation to the number of species. The floristic-structural organization was influenced by the interaction between the successional stage and the environmental differences among areas. Phylogenetic clustering of species was observed in the initial successional stage area and random phylogenetic pattern was observed in advanced successional stage areas. The results indicated independent variation in richness in relation to successional phase and, that the forest succession influenced the floristic-structural composition and phylogenetic structure of the study areas.

Este trabalho teve como proposta analisar as variações espaciais, florísticas e estruturais do componente arbóreo de um sistema de fragmentos de Floresta Ombrófila Mista no Planalto catarinense. Para isso, foram alocadas 50 parcelas de 200 m² (10 x 20 m) em quatro fragmentos, cujos indivíduos com diâmetro à altura do peito (DAP) > 5 cm foram identificados e medidos. Foi calculado o Índice de Valor de Importância e realizada a comparação florístico-estrutural entre os fragmentos, por meio de Análise de Variância Multivariada Não Paramétrica (NPMANOVA). Espécies indicadoras de cada fragmento foram determinadas por meio da Análise de Espécies Indicadoras (ISA). Foram identificadas 73 espécies, sendo a de maior valor de importância Araucaria angustifolia (Bert.) Kuntze. Houve diferença na estrutura do componente arbóreo dos fragmentos (p = 0,001), sendo possível identificar espécies indicadoras para os fragmentos 1, 2 e 3. Este estudo demonstrou que fragmentos próximos entre si podem apresentar variações florístico-estruturais, que devem ser consideradas na definição de estratégias de manejo e conservação florestal.

The goal of this study was to evaluate the spatial, floristic and structural variations of the tree component of a fragments system of Araucaria Forest in the uplands of the state of Santa Catarina, Brazil. For this sake, within four fragments, 50 parcels of 200 m² (10 x 20 m) were allocated; their individuals with diameter at breast height (DBH), measured at 1.30 m height, > 5 cm, were identified and measured. The Importance Value Index was determined and the floristic-structural comparison among fragments was analyzed, applying a non-parametric multivariate analysis of variance (NPMANOVA). Indicator species of each fragment was determined by Indicator Species Analysis (ISA). We found 73 species, being Araucaria angustifolia (Bert.) Kuntze the most important species. There was a difference in the tree component structure of the fragments (p = 0.001); it is possible to identify indicator species for fragments 1, 2 and 3. This study showed that fragments located close to each other may present floristic-structural variations, which should be considered during strategies definition for forest management and conservation.