Currently, there is a lack of studies on the correct utilization of continuous distributions for dry tropical forests. Therefore, this work aims to investigate the diameter structure of a brazilian tropical dry forest and to select suitable continuous distributions by means of statistic tools for the stand and the main species. Two subsets were randomly selected from 40 plots. Diameter at base height was obtained. The following functions were tested: log-normal; gamma; Weibull 2P and Burr. The best fits were selected by Akaike's information validation criterion. Overall, the diameter distribution of the dry tropical forest was better described by negative exponential curves and positive skewness. The forest studied showed diameter distributions with decreasing probability for larger trees. This behavior was observed for both the main species and the stand. The generalization of the function fitted for the main species show that the development of individual models is needed. The Burr function showed good flexibility to describe the diameter structure of the stand and the behavior of Mimosa ophthalmocentra and Bauhinia cheilantha species. For Poincianella bracteosa, Aspidosperma pyrifolium and Myracrodum urundeuva better fitting was obtained with the log-normal function.

Dry tropical forests are a key component in the global carbon cycle and their biomass estimates depend almost exclusively of fitted equations for multi-species or individual species data. Therefore, a systematic evaluation of statistical models through validation of estimates of aboveground biomass stocks is justifiable. In this study was analyzed the capacity of generic and specific equations obtained from different locations in Mexico and Brazil, to estimate aboveground biomass at multi-species levels and for four different species. Generic equations developed in Mexico and Brazil performed better in estimating tree biomass for multi-species data. For Poincianella bracteosa and Mimosa ophthalmocentra, only the Sampaio and Silva (2005) generic equation was the most recommended. These equations indicate lower tendency and lower bias, and biomass estimates for these equations are similar. For the species Mimosa tenuiflora, Aspidosperma pyrifolium and for the genus Croton the specific regional equations are more recommended, although the generic equation of Sampaio and Silva (2005) is not discarded for biomass estimates. Models considering gender, families, successional groups, climatic variables and wood specific gravity should be adjusted, tested and the resulting equations should be validated at both local and regional levels as well as on the scales of tropics with dry forest dominance.

O objetivo deste trabalho foi comparar a regeneração natural de duas áreas de vegetação de caatinga com diferentes históricos de uso no agreste pernambucano. O estudo foi realizado em duas áreas: Área I de mata nativa, sem evidências históricas de eliminação total da vegetação para fins de cultivos agrícolas; e Área II, anteriormente ocupada com cultivo da palma forrageira, abandonada há cerca de 30 anos e que se encontrava em estágio de sucessão secundária. Para coleta dos dados da vegetação, foram utilizadas 24 parcelas de dimensões de 5 x 5 m, em 12 parcelas em cada área, sendo considerados indivíduos em regeneração natural as plantas que possuíram circunferência a 1,30 m do solo (CAP) < 6,0 cm e altura >1,0 m. No levantamento estrutural dos indivíduos regenerantes das duas áreas foram identificados 581 plantas pertencentes a 14 famílias botânicas, 26 gêneros e 30 espécies. As densidades totais obtidas neste estudo foram de 11.200 ind.ha-1 e 8.116 ind.ha-1, nas Áreas I e II, respectivamente. As espécies que obtiveram maiores densidades de regeneração natural na Área I foram: Croton argyrophyllus, Senegalia bahiensis, Croton blanchetianus e Coutareahexandra; e na Área II: Senegalia bahiensis, Poincianella pyramidalis, Zanthoxyllum sp, Croton blanchetianus e Croton argyrophyllus.

No presente trabalho objetivou-se estudar a estrutura e a composição florística do componente arbóreo de um remanescente de Floresta Atlântica na Reserva Ecológica (RESEC) de Gurjaú, no município do Cabo de Santo Agostinho, PE, visando contribuir para o conhecimento florístico e fitossociológico dos remanescentes florestais de Pernambuco. A RESEC está localizada no município do Cabo de Santo Agostinho e ocupa uma área de 1.077,10 ha. Sistematicamente, instalaram-se 40 parcelas de 250 m² (1 ha), distando 25 m uma das outras. Todos os indivíduos arbóreos com CAP > 15 cm foram amostrados e, nesta amostragem, registradas 112 espécies arbóreas, distribuídas em 31 famílias botânicas, das quais Moraceae e Myrtaceae contribuíram com maior número de espécies; essas espécies produziram um índice de diversidade de Shannon e Weaver (H') de 3,91 nats/indivíduo. A distribuição diamétrica da população amostrada apresentou padrão geométrico decrescente ("J" invertido). Esta configuração é prevista para uma floresta ineqüiânea secundária em estágios iniciais de sucessão. De modo geral, o remanescente estudado está desenvolvendo seu processo sucessional de forma eficiente, garantindo a sobrevivência da fitofidionomia da Floresta Ombrófila Densa no Estado de Pernambuco. Palavras-chave: árvores, estrutura horizontal, floresta ombrófila densa Phytosociologic of a arboreus component of the remanent of Atlantic Forest in the town of Cabo de Santo Agostinho, PE AB S TR ACT The present study aims to establish a support to the dynamic of arboreous species in a remanescent of Atlantic Forest in Cabo de Santo Agostinho, PE, therefore, contributing to the floristic and phytosociologic knowledge of remanescent Forest of Zona da Mata in Pernambuco. The Ecological Reserve (RESEC) de Gurjaú is located in the rural area Cabo de Santo Agostinho town (08º10'00''-08º15'00'' S and 35º02'30''-35º05'00'' W). RESEC's area is 1.077,10 ha. The vegetation is a Dense Ombrofilous Forest. A total of 40 sample of 250 m 2 (1 ha) were systematically installed in the area, 25 m apart from one another. All the individual adult with CBH > 15cm were sampled. The survey led to the identification of 112 arboreous species distributed in 31 botanic families. Moraceae and Myrtaceae were the families with greater number of species. These species produced a diversity index of Shannon e Weaver (H') of 3,91 nats/ individuals. The diametrical distribution showed a pattern typical of inequian, i.e., a curve in the shape of an inverted "J", which is expected for a secondary forest in initial succession phases. In general the Ecological Reserve in Gurjaú is developing its successional process in an efficient way and efficiently assuring the phytophysionomy for the Dense Ombrofilous Forest in the State of Pernambuco.

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