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ResumoEmbora a sazonalidade climática seja menos evidente nas regiões tropicais que nas temperadas, muitas espécies tropicais apresentam crescimento rítmico. A avaliação do crescimento em circunferência do tronco (CCT) permitirá obter informações sobre o desenvolvimento dos indivíduos de espécies arbóreas desta região. Esse estudo teve como objetivo avaliar o CCT de 11 espécies arbóreas de uma floresta estacional semidecidual no sul do Brasil, visando testar duas hipóteses: (i) existe sazonalidade no CCT das árvores e este crescimento está relacionado às variações climáticas da região de estudo; (ii) as características dos indivíduos (posição sociológica, altura da árvore, grau de ocupação por lianas, deciduidade e diâmetro à altura do peito) influenciam no incremento acumulado em circunferência. Para detectar a periodicidade do CCT foram implantadas faixas dendrométricas permanentes no tronco (altura do DAP) de 156 indivíduos. O acompanhamento do crescimento foi realizado mensalmente por um período de 18 meses. Foram feitas correlações do CCT mensal com a precipitação, temperatura e fotoperíodo para verificar a influencia dos fatores ambientais e análise de covariância para averiguar se as características dos indivíduos também interferiram no incremento acumulado em circunferência do tronco. As espécies apresentaram um padrão sazonal de CCT, com as maiores taxas de crescimento de outubro a dezembro, sendo que os parâmetros ambientais avaliados atuaram em conjunto -principalmente o fotoperíodo e a temperatura -promovendo essa sazonalidade e confirmando a primeira hipótese. Considerando as características dos indivíduos, somente o diâmetro do tronco correlacionou-se negativamente com o incremento acumulado em circunferência (b = -0,32; p = 0,02), aceitando parcialmente a segunda hipótese. Palavras-chave: deciduidade, floresta tropical, grupos sucessionais, Mata Atlântica, sazonalidade. AbstractAlthough seasonality is less evident in the tropics than in temperate ones, many tropical species present rhythmic growth. The stem circumference growth (SCG) evaluation will provide information on the development of tree species in this region. This study aimed to evaluate the SCG of 11 tree species of a tropical semi-deciduous forest in Southern Brazil. Two hypotheses were advanced: (i) seasonality of the trees SCG exist and it is related to climatic variations of the study area; (ii) individual characteristics (tree height, degree of occupancy by lianas, sociological position, deciduousness and diameter at breast height) influence the circumference cumulative growth. To detect the SCG periodicity, permanent dendrometric bands were fixed around the stem (diameter at breast height, or DBH) of 156 individuals. Growth was monitored monthly for a period of 18 months. Correlations of monthly SCG with precipitation, temperature and photoperiod were made to verify the environmental parameters' influence and a covariance analysis was performed to enquire if individual characteristics also affected cumulative increase in circumfer...

Structural differences in the secondary vascular tissues among habitats can contribute to understanding species performances, especially regarding water and photosynthate transport. The pattern of association between the secondary xylem tissue and water availability from the environment has been widely studied, unlike the secondary phloem, which has been barely explored. Here, we evaluated the structural variation of the secondary xylem and phloem in stems of four populations of two tropical tree species under contrasting water conditions. We also investigated the mirrored structure between both tissues. At dry sites, Moquiniastrum polymorphum had higher vessel density, thicker xylem fibers cell walls, and taller rays in both tissues commonly associated with safe transport, in agreement with our expectations. In contrast, the populations of Zanthoxylum rhoifolium had most features in disagreement with the water availability of each site. The perforation and sieve plates, the ray composition, and the axial parenchyma were similar in the two tree species’ xylem and phloem tissues. However, the quantitative descriptors of cell sizes were not correlated between the xylem and phloem. In general, there is a different pattern of morphological variation across sites in the two tropical tree species, highlighting that any generalization regarding the vascular system structure across environments should be avoided. Xylem and phloem revealed a mirrored structure in a few qualitative features, not followed by the dimensions of different cell types. Future research needs to explore the causes of the unexpected structural variation in the vascular system across populations in tropical tree species.

Structural differences in the secondary phloem suggest higher support and storage potential in stems than roots of Cytharexylum myrianthum Cham. (Verbenaceae)