Dorothy Sue Dunn de Araujo

High abundance of dioecious plants in a tropical coastal vegetation

We examined the frequency of hermaphroditic, monoecious, and dioecious species of angiosperms in restinga (sandy coastal plain) vegetation in SE Brazil. The study site was a vegetation mosaic comprising nine plant formations, ranging from open types to forest. Dioecy (14% of 566 species) was similar to other tropical vegetations and strongly associated with woodiness and entomophily. However, more interestingly, there was an exceptionally high percentage (35%) of dioecious species among the dominant woody plants. This pattern has not been previously reported, and we discuss the extent to which it is ecologically driven. We argue that the high abundance of dioecious plants in this resource-poor environment can be attributed to ecological traits related to long-distance dispersal, ecological vigor, and possibly, vegetative reproduction.

Análise florística das pteridófitas do Parque Nacional da Restinga de Jurubatiba, Rio de Janeiro, Brasil

The Restinga de Jurubatiba National Park is located on the Northern coast of Rio de Janeiro State (municipalities of Macae, Carapebus and Quissama). There are 12 families, 21 genera and 32 species, with the following families present: Blechnaceae, Cyatheaceae, Davalliaceae, Dennstaedtiaceae, Dryopteridaceae, Gleicheniaceae, Lycopodiaceae, Polypodiaceae, Pteridaceae, Salviniaceae, Schizaeaceae and Thelypteridaceae. The most species-rich families are Pteridaceae (5 spp.) and Polypodiaceae (5 spp.). Nephrolepis, Polypodium and Thelypteris were the richest genera. Of the 32 species recorded for the area, 23 are terrestrial herbs, three are epiphytes, three are aquatics, two are arborescent and one is a hemiepiphyte. The periodically flooded forest was the richest in species and families; the beach thicket presented the lowest values. The fern flora of several areas of restinga on the Brazilian coast showed low similarity values; this is also true for restingas and Atlantic forest. Blechnum serrulatum and Polypodium triseriale are commonly found in areas of restinga. Of the 32 species studied, 17 have economic potential (medicinal, ornamental and food).

Estrutura de duas formações vegetais do cordão externo da restinga de Marambaia, RJ

Two plant communities (creeping psamophyte and palm scrub) are described from the outer Marambaia beach ridge, Rio de Janeiro State, Brazil, based on topography, vegetation physiognomy, and structure. Although the two communities can be distinguished visually, they are joined by a transition zone. Ipomoea pes-caprae, Ipomoea imperati, Remirea maritima, Allagoptera arenaria, Sporobolus virginicus, and Panicum racemosum were the most important species sampled in the creeping psammophyte community out of a total of 23. The halophyte community reported for other sandy coastal plains in Brazil was not observed at Marambaia due to the intense wave action on this beach. The palm scrub community was dominated by Allagoptera arenaria (56% of total importance value) out of a total of 64 species. Rhizome-geophytes dominate both communities.

Influence of Soil Physical Properties on Plants of the Mussununga Ecosystem, Brazil

Distribution ranges of plant species are related to physical variables of ecosystems that limit plant growth. Therefore, each plant species response to physical factors builds up the functional diversity of an ecosystem. The higher the species richness of an ecosystem, the larger the probability of maintaining functions and the higher the potential number of plant functional groups (FGs). Thus, the richness potentially increases the number of functions of the highly diverse Atlantic Rainforest domain in Brazil. Severe plant growth limitations caused by stress, however, decrease species richness. In the Spodosols of the Mussununga, an associated ecosystem of Atlantic Rainforest, the percentage of fine sand is directly related to water retention. Moreover, the depth of the cementation layer in the Mussununga’s sandy soil is a physical factor that can affect the plants’ stress gradients. When a shallow cementation layer depth is combined with low water retention in soils and with low fine sand percentage, the double stresses of flooding in the rainy season and water scarcity in the dry season result. This study aimed to identify FGs among Mussununga plant species responding to water stress gradients of soil and to verify the effects of the gradients on plant species richness of the Mussununga. A canonical correspondence analysis (CCA) of species abundance and soil texture variables was performed on 18 plots in six physiognomies of the Mussununga. Species richness rarefactions were calculated for each vegetation form to compare diversity. The two main axes of the CCA showed two FGs responding to soil texture and cementation layer depth: stress tolerator species and mesic species. Physical variables affect plant diversity, with species richness rising as the fine sand proportion also rises in the Mussununga. The effect of the cementation layer is not significantly related to species richness variation.

Regeneração e riqueza da formação arbustiva de Palmae em uma cronoseqüência pós-fogo na Restinga da Marambaia, Rio de Janeiro, RJ, Brasil

A estrutura e a riqueza da formacao arbustiva de Palmae foram analisadas em tres sitios numa cronosequencia de regeneracao (3, 12 e 84 meses apos a ultima queimada) na Restinga da Marambaia, registrando-se a presenca de 29, 41 e 64 taxons, respectivamente. No sitio com maior tempo de regeneracao, Allagoptera arenaria (Gomes) Kuntze representou 79% da dominância relativa (DoR), seguida das nanofanerofitas Inga maritima Benth. e Manilkara subsericea (Mart.) Dubard. Na area queimada ha 12 meses, A. arenaria representou 88% da DoR, seguida de Inga maritima, Setaria setosa (Sw.) P. Beauv. e Paspalum arenarium Schrad. No sitio com tres meses de regeneracao, a DoR de A. arenaria foi de 82%, acompanhada de Clitoria sp., Inga maritima e Portulaca mucronata Link. Nos tres sitios estudados, a forma de vida mais importante foi geofita rizomatosa, devido a dominância de A. arenaria. Camefita herbacea escaposa foi a forma de vida que apresentou maior numero de especies nos sitios com tres e 12 meses de regeneracao e no sitio queimado ha 84 meses, as nanofanerofitas acompanharam as camefitas herbaceas escaposas em numero de especies. Das 29 especies registradas no sitio com tres meses de regeneracao, so Portulaca mucronata e Sebastiania corniculata (Vahl) Mull. Arg. originaramse a partir de sementes, sendo que as demais rebrotaram ou se regeneraram. Sete dias apos a queimada A. arenaria apresentou, em media, 8cm de sua parte vegetativa regenerada e com 180 dias apresentou as primeiras inflorescencias.

Influence of environmental variation on Atlantic Forest tree-shrub-layer phytogeography in southeast Brazil

O presente trabalho analisou dados de 32 remanescentes florestais nos estados do Rio de Janeiro e Sao Paulo, atraves de analises multivariadas para responder a pergunta: Existem padroes floristicos do estrato arboreo-arbustivo da Floresta Atlântica relacionados a Serra do Mar e alargamento das planicies costeiras nos estados do Rio de Janeiro e Sao Paulo? Foram utilizadas tres analises multivariadas para investigar as relacoes entre a flora arboreo-arbustiva e a variacao ambiental das 32 areas. As analises demonstraram influencia de alteracoes geo-climaticas sobre a diferenciacao floristica das especies arboreas e arbustivas da Mata Atlântica. Este fato permitiu gerar grupos com as areas analisadas baseados em caracteristicas bioticas e abioticas, sustentando a existencia de padroes floristicos nos estados do Rio de Janeiro e Sao Paulo. Os grupos formados refletem a substituicao das especies arboreo-arbustivas entre as areas analisadas como consequencia de variacoes da precipitacao, altitude e temperatura media anual a medida que modifica o posicionamento da Serra do Mar e cresce a planicie costeira. Para cada grupo foram designadas especies preferenciais que devem ser consideradas em programas de restauracao e conservacao das regioes fitoecologicas por eles representadas.

Pollen analysis of Holocene sediments from the Poço das Antas National Biological Reserve, Silva Jardim, Rio de Janeiro, Brazil

The Poço das Antas National Biological Reserve is located in Rio de Janeiro State, southeast Brazil. This paper presents information on past environmental characteristics of the area through pollen analysis. Two sedimentary columns were collected and five samples were selected for radiocarbon dating. The following ages of the columns from bottom to top were detected: column 1 - 1.20-1.16 m: 6080 +/-40 years BP, 0.775-0.735 m: 4090 +/-40 years BP, 0.385-0.345 m: 1880 +/-80 years BP; column 2 - 1.22-1.18 m: 3520 +/-40 years BP, 0.23-0.19 m: 1810 +/-40 years BP. Three samples from column 1 and two samples from column 2 were selected for pollen analysis: 1.20 m, 0.77 m and 0.37 m of column 1 and 1.22 m and 0.21 m of column 2. Chemical treatment followed standard methodology. The palynological analysis shows that around 6080 years BP the study area was dominated by a rain forest and from around 4090 years BP the vegetation changed to a fragmented forest, restricted to low hills and surrounded by an open area of grassland and pioneer plants, swamps and peat areas. The pollen assemblage of the samples 3520, 1880 and 1810 years BP suggest the permanence of this kind of vegetation between 4000 years BP and the actual.

Biogeographic Features of Clusia, with Emphasis on South American and Especially Brazilian Species

Cox and Moore (1993), in their classic “Biogeography” text book, broadly define this discipline as “the study of living things in a spatial and temporal context”. They argue that biogeography studies will often provide answers to questions such as: “a) Why are there so many living things? b) Why are they distributed the way they are? c) Have they always occupied their current distribution patterns? d) Do man’s activities today affect these patterns and if so, what are the prospects for the future?” Ideally, therefore, whenever a complete account of Clusia biogeography is available, all these questions should be answerable. In order to reach this stage of knowledge, one should have enough relevant information on the three main biogeographic processes: migration, evolution and extinction (Shrader-Frechette and McCoy 1993). Since very little is known about these processes for Clusia, this chapter is by no means an attempt to provide a complete study of the biogeography of the genus. However, we use the four questions above as guidelines for this text.

Bryophytes of Restinga de Jurubatiba National Park, Rio de Janeiro State, Brazil

Este trabalho representa uma sintese do conhecimento floristico de briofitas do Parque Nacional da Restinga de Jurubatiba, com resultados de campo, material de herbario e publicacoes. Foram registrados 61 taxons de briofitas, pertencentes a 15 familias e 33 generos. Para cada taxon foram analisados a distribuicao geografica, o tipo de substrato e a forma de vida. A familia predominante foi Lejeuneaceae (25 especies), seguida de Jubulaceae (sete), Calymperaceae (quatro) e Sphagnaceae (quatro). Entre as especies, predominaram as de distribuicao Neotropical (35%). Com relacao ao substrato preferencial, a maior parte dos taxons e corticicola. A forma de vida predominante foi o tapete, seguido pelo tufo e a trama. O Parque possui brioflora bastante representativa no que diz respeito a vegetacao de restinga, com 45% dos taxons de briofitas conhecidas para as restingas no Brasil e 82% das conhecidas para as restingas do estado do Rio de Janeiro. E apresentada uma chave para identificacao das especies.

Tree community dynamics in a submontane forest in southeastern Brazil: growth, recruitment, mortality and changes in species composition over a seven-year period

In order to assess long-term community dynamics in tree populations, we investigated trees with a diameter at breast height (DBH) > 5 cm in an 11-ha fragment of submontane tropical forest in southeastern Brazil, at the beginning and end of a seven-year period. We observed a general tendency toward decreasing numbers of trees and toward stability in basal area. The stability in basal area was associated with an equilibrium between the loss of trees and the basal area gain from the horizontal growth of surviving trees, as well as from recruits The abundance of dead trees was significantly higher than was that of recruits. Changes in tree abundance occurred mainly in the lower DBH classes, whereas changes in basal area occurred mainly in the intermediate DBH classes. Among trees with a DBH > 10 cm, the observed rates of mortality and recruitment (2.4% yr-1 and 1.8% yr-1, respectively) were similar to those reported for other tropical forests. When we examined only trees with a DBH > 10 cm, we found the half-life to be 29.5 years, which places the forest fragment studied among the most dynamic of tropical forests. Over the seven-year period evaluated, the tree community lost ten species, with no new records. The most abundant species showed the highest rates of mortality and recruitment. Climax species, whether shade-tolerant or light-demanding, accounted for more species and individuals than did pioneer species, suggesting that the former group has a greater influence on forest dynamics. The results suggest that the tree community studied is in or is approaching a state of dynamic equilibrium, the changes in community structure and composition being attributed to periodic fluctuations.