-(Seedling growth of fifteen Brazilian tropical tree species differing in successional status). Growth of seedlings of fifteen tropical tree species representative, at the adult stage, of different successional positions, was studied under field conditions. Seedlings were grown in three treatments: full sun (FS), artificial shade imposed by neutral screens (AS) and natural shade imposed by a closed canopy in a Forest Reserve in Southeast Brazil (NS). Most of the studied species survived in both shade treatments, although their growth was severely affected. Decreases in height, internode numbers, dry weight, leaf area, root:shoot ratio (R:S) and increases in leaf mass ratio (LMR), leaf area ratio (LAR) and specific leaf area (SLA) were common responses to shade. Relative growth rates (RGRs) and net assimilation rates (NARs) were consistently lower in the shaded treatments than in full sun. RGR was significantly correlated with NAR in the FS and NS treatments, whereas it was correlated with LAR in the AS treatment. Natural shade had more severe effects than artificial shade on leaf area reduction and RGR. Between-species differences in R:S, LMR, SLA and LAR were not related to the successional status of species. However, there was a tendency for early-successional species to have higher RGRs than late successional ones, regardless of the light environment. Late-successional species also showed less pronounced responses to shade than early ones. The characteristics presented by the late-successional species may be associated with shade tolerance, enabling their persistence under dense canopies.Key words -Seedling growth, shade, shade tolerance, successional species, tropical tree species RESUMO -(Crescimento de plântulas de quinze espécies árboreas tropicais pertencentes a diferentes estádios sucesionais). O crescimento de plântulas de quinze espécies arbóreas tropicais pertencentes a diferentes estádios sucessionais foi estudado sob condições de campo. As plântulas foram cultivadas sob tratamentos de radiação plena, sombreamento artificial proporcionado por telas sombrite e sombreamento natural imposto por dossel vegetal na Reserva Municipal de Santa Genebra em Campinas, SP, Brasil. A maioria das espécies estudadas sobreviveu aos tratamentos de sombreamento, com marcantes alterações no crescimento. Reduções de altura, número de entrenós, massa seca, área foliar e razão raiz/parte aérea (R/PA) foram respostas freqüentes ao sombreamento, assim como também aumentos da razão de massa foliar (RMF), razão de área foliar (RAF) e área foliar específica (AFE). As taxas de crescimento relativo (TCRs) e as taxas de assimilação líquida (TALs) apresentaram-se consistentemente mais baixas nos tratamentos de sombreamento. TCR se mostrou significativamente correlacionada com TAL nos tratamentos de radiação plena e sombreamento natural e com RAF no tratamento de sombreamento artificial. O sombreamento natural teve efeitos mais severos na redução da área foliar e da TCR. As diferenças inter-específicas nos parâmetros R/PA,...

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Seed germination and seedling establishment patterns have been used to classify species as shade tolerant or intolerant. The main objective of this research was to investigate, under controlled conditions, seed germination of species from different successional positions as well as to follow seed germination and seedling survival under natural shade in the field. The species studied were Solarium granuloso‐leprosum, Trema micrantha, Cecropia pachystachya, Croton piptocalyx, Bauhinia forficata subsp. pruinosa. Senna macranthera, Schizolobium parahyba, Piptadenia gonoacantha, Chorisia speciosa, Pseudobombax grandiflorum, Ficus guaranitica, Esenbeckia leiocarpa, Pachystroma longifolium, Myroxylon peruiferum, and Hymenaea courbaril. Field trials were carried out at Santa Genebra Municipal Reserve, Campinas, SP, Brazil, at the forest edge and in the understory. No significant correlations were detected between successional status and seed size or seed water content. Light‐regulated germination was present only in small‐seeded species. In field experiments, most species, including the light‐sensitive ones, were able to germinate under the canopy, where a low red/far‐red ratio predominates. Most species, mainly those of early‐ and intermediate successional positions, presented low seedling survival rates under shade. Myroxylon peruiferum was the most shade tolerant species, while 5. granuloso‐leprosum, C. speciosa, P. gonoacantha, F. guaranitica, T. micrantha, and 5. parahyba were the most shade intolerant. These latter species showed little or no survival under the shade conditions.

-(Germination of seeds of tropical pioneer species under controlled and natural conditions). Seed germination of eight tropical pioneer species (Cecropia hololeuca, C. pachystachya, C. glazioui, Solanum gracillimum, S. granuloso-leprosum, S. tabacifolium, Croton floribundus and Miconia chamissois) was studied. In controlled conditions, alternating temperatures were tested from 5 to 25°C. Low Red:Far Red ratios (R:FR) were also examined. In the field, germination was evaluated in gaps and under the canopy. With the exception of Croton floribundus, all other species were photoblastic in that higher germination percentages were found under light conditions (S. tabacifolium behaved as a negative photoblastic species at some temperatures). No relationship was found between germination percentage and alternating temperature. Germination was markedly reduced under low R:FR ratios. Alternating temperature is not the main factor affecting field germination. The low R:FR ratio under the canopy seems to be the crucial factor affecting germination. RESUMO-(Germinação de sementes de espécies pioneiras tropicais sob condições controladas e naturais). Foi estudada a germinação de sementes de oito espécies de pioneiras tropicais (Cecropia hololeuca, C. pachystachya, C.glazioui, Solanum gracillimum, S. granuloso-leprosum, S.tabacifolium, Croton floribundus e Miconia chamissois). Em condições controladas, foram testadas temperaturas alternadas usando amplitudes que variaram de 5 a 25°C. Também foram testadas baixas razões de vermelho:vermelho extremo. Em condições naturais, a germinação foi testada em clareira e sob o dossel. Com exceção de Croton floribundus, todas as outras espécies se mostraram fotoblásticas, sendo que altas porcentagens de germinação foram encontradas sob condições de luz (S. tabacifolium comportou-se como espécie fotoblástica negativa em algumas temperaturas). Não foi encontrada relação entre porcentagens de germinação e amplitude de temperaturas. A germinação foi drasticamente reduzida sob baixas razões de vermelho:vermelho extremo. Alternância de temperatura não foi o principal fator a influenciar a germinação em condições naturais. A baixa razão vermelho:vermelho extremo prevalecente sob o dossel parece ser o fator crucial que afeta a germinação.

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