Artigo Estrutura Poço

Artigo Estrutura Poço

(Parte 1 de 3)

232APR 2009, VOL. 34 Nº 4

KEYWORDS / Atlantic Forest / Floristic Similarity / Lowland Forest / Structure / Received: 09/29/2008. Modified: 03/16/2009. Accepted: 03/18/2009.

Alexandre Gabriel Christo. Agronomic Engineer. M.Sc. in Botany, Escola Nacional de Botânica Tropical (ENBT), Brazil. Instituto de Pesquisas Jardim Botânico do Rio de Janeiro (JBRJ), Brazil. Address: Jardim Botânico do Rio de Janeiro, Rua Pacheco Leão, 915, 2.460-030 - Rio de Janeiro, RJ, Brazil. e-mail: achristo@jbrj.gov.br

Rejan R. Guedes-Bruni. Biologist. D.Sc. in Ecology, Universidade de São Paulo (USP), Brazil.

Senior Researcher, JBRJ, Brazil. e-mail: rbruni@jbrj.gov.br

Felipe de Araújo P. Sobrinho. Forest Engineer. M.Sc. in Botany, ENBT, Brazil. Doctoral student, USP, Brazil. e-mail: felipesobrin@yahoo.com.br

Ary Gomes da Silva. B.Sc. in Pharmacy. D.Sc. in Plant Biology, Universidade Estadual de

Campinas (UNICAMP), Brazil. Professor, Centro Universitário Vila Velha, Brazil. e-mail: arygomes@uvv.br

Ariane Luna Peixoto. Naturalist. D.Sc. in Plant Biology, UNICAMP, Brazil. CNPq Fellow, Associate Researcher, JBRJ, Brazil. e-mail: ariane@jbrj.gov.br

ALExANDRE GABRIEL CHRISTO, REJAN R. GUEDES-BRUNI, FELIPE DE ARAúJO P. SOBRINHO, ARY GOMES DA SILvA and ARIANE LUNA PEIxOTO fter five centuries of occupation and the effects of various economic cycles, the Brazilian Atlantic Forest has been reduced to about only 7.6% of its original extension (MMA, 1998). This drastic deforestation was driven by anthropogenic pressure on the forest, principally due to the selective extraction of valued arboreal species, agricultural expansion, lumbering and the use of wood as firewood by many industrial sectors

0378-1844/09/04/232-08 $ 3.0/0

(brick and tile manufacturing, residential expansion, etc.).

Within this historical context, remnant tracts of lowland forests in Rio de Janeiro State are now mostly limited to granite hillocks <300m in altitude and to fluvial plains along the coast. These low hills are surrounded by alluvial forest areas that have been occupied by homes and agricultural plots due to their leveled topography, even though they are often swampy (Guedes-Bruni et al., 2006a).

The forests that cover the low hills are generally altered remnants of the native vegetation that existed before anthropogenic processes dominated the lowland regions around Rio de Janeiro. These low hills are often totally deforested, but they are sometimes covered by remnant forests of different dimensions and in diverse successional states. Cattle-raising is the most evident sign

The present study describes and evaluates the horizontal and vertical structures of a lowland forest fragment on a hillock in the municipality of Silva Jardim, Rio de Janeiro State, Brazil (22o31’56’’S and 42o20’46’’W). Twenty plots (10×2m) totaling 0.5ha were laid out following the slope grade using DBH≥5cm as the inclusion criterion. A total of 734 individuals were encountered, yielding a total density of 1468 ind./ha and a total basal area of 10783m2. The richness values (129 species/41 families), Shannon-Wiener diversity (4.2) and equitability (0.87) indices indicated an accentuated floristic heterogeneity and low ecological dominance. Lauraceae, Myrtaceae, Fabaceae and Euphorbiaceae showed the greatest species richness, corroborating other studies that indicated these species as the most representative of Atlantic Forest areas in southeastern Brazil. The species with the greatest importance values (VI) were Aparisthmium cordatum, Guapira opposita, Lacistema pubescens, Xylopia sericea, Tapirira guianensis and Piptocarpha macropoda. The high diversity observed was influenced by earlier anthropogenic actions and by the current successional stage. The forest fragment studied demonstrated closer floristic similarity to areas inventoried in a close-by biological reserve than to fragments dispersed throughout the coastal plain. Similarities in soil type, degree of soil saturation and use-history of forest resources all support these relationships. The fragmented physiognomy of the central lowland in this region and the use-history of the landscape make these small remnant forest areas important in terms of establishing strategies for landscape restoration and species conservation.

APR 2009, VOL. 34 Nº 4233 of human intervention, and hand in hand with fire has determined the alteration of these landscapes and the species growing there (Guedes- Bruni et al., 2006a).

Although greatly fragmented, the lowland Atlantic Forest in the central region of Rio de Janeiro State is of great ecological importance, not only because of the species typical of this vegetation formation but also because it is the only habitat of the Golden-Lion- Tamarin (Leonthopitecus rosalia Lesson, 1940), a primate species endemic to this region and threatened with extinction.

Numerous authors have contributed to the knowledge of the composition and floristic structure of this environment, which is characterized by extensive fragmentation and a diversity of successional stages in the remnant areas (Guedes, 1988; Borém and Ramos, 2001; Borém and Oliveira-Filho, 2002; Carvalho et al., 2006a, Guedes-Bruni et al., 2006a; Pessõa and Oliveira, 2006: Carvalho et al., 2007; and others).

The present study describes and evaluates the horizontal and vertical structure of a section of lowland forest growing on hillocks and provides information that can contribute to conservation programs in the region.

Study area

The study area is part of the Santa Helena farm (22o31’56’’S and 42o20’46’’W; Figure 1), located along the BR 101 federal highway in the municipality of Silva Jardim (RJ), ~5km from the Poço das Antas Biological Reserve (Rebio) in an area of Dense Ombrophilous Lowland Forest (IBGE, 1992). The forest fragment examined covers 4.25ha and is surrounded by agricultural and grazing areas. The regional climate is classified as As by the Köeppen system: rainy-tropical, with a winter dry season (Bernardes, 1952). Average annual rainfall and temperature are 1995mm and 25.5oC, respectively (Lima et al., 2006).

The topography of the region is predominantly plain, with hillocks in the coastal lowlands (granite outcrops), whose height ranges from 19-200m, separated by flood plains and swamps (IBDF/FBCN, 1981). The surroundings of Rebio are in full field of Tertiary and Quaternary plains, with dated rocks of Pre-Cambrian and typical of the Coastal Complex Fluminense (IBDF/ FBCN, 1981). The classes of soil (EMBRA-

PA, 1999) are divided, basically, between Oxisols, Ultisols, Incepitsols (Aquepts).

Methods

Twenty plots (10×25m) were laid out along the line of the hill slope, covering a total sampling area of 0.5ha. In laying out the plots a minimum distance of 20m was maintained from any trail so that, essentially, only the central area of the fragment was sampled. All plants with trunk diameters at 1.3m above soil level (DBH) ≥5cm were measured and identified. All testimonial material was deposited in the herbarium of the Rio de Janeiro Botanical Garden (RB). The taxonomic system adopted followed APG (2003).

To elaborate a vegetation profile, a 50×5m plot was established following the slope of the hillock according to the methodology suggested by Melo (2002). The profile diagram was elaborated in true height and diameter scales, using the AutoCAD 2000 software program.

Sampling effort was measured by determining the simple linear regression line (Zar, 1999) of the accumulation of taxon richness (Whittaker, 1975) in regards to the accumulated number of observations (Loss and Silva, 2005), corresponding to the sequential implantation of the plots.

Structural analyses were made by calculating the absolute and relative values of density (DR), frequency (FR) and dominance (DoR), whose sum, in relative terms, defines the Importance Value (VI) of the species. Estimations of vegetation structure were obtained according to Müeller- Dombois and Ellenberg (1974). The Shannon- Wiener diversity index (H’) and equitability (J) were calculated according to Magurrán (1988) and Pielou (1975), respectively. The Fitopac 1 software package was used to calcu- late all phytosociological parameters (Shepherd, 1995).

The 10 species with highest VI were grouped into three categories, pioneers, early secondary and late secondary, according Gandolfi et al. (1995), and complemented on the basis of Paula et al. (2004) and Carvalho et al., (2006a).

To evaluate the horizontal structure of the vegetation, frequency histograms of diameter classes at 5cm intervals were elaborated for all individuals encountered. The vertical structure, as a characterization of the forest layers studied, was evaluated based on the allometric relationships between diameter and height (log transformed; Sneath and Sokal, 1973), identifying the canopy with a dotted line as seen on the correlation diagram, and characterizing the canopy individuals as having a specified diameter and height, confirmed by verifying the first discontinuity among the points in the diagram (Guedes- Bruni, 1998).

A graph was elaborated of the vertical space occupied by the sampled species that attained 75% of the VI. To determine the minimum number of classes, as well as their amplitude, the formula proposed by Spiegel (1977) apud Lopes et al. (2002) was used.

Relationships of floristic similarity were sought between the study area and other forest fragments inventoried in this coastal plain region. To that end, a presence/absence matrix was elaborated of the species encountered in this study and combined with 17 other areas (totaling 279 species), eight of which were on private lands and nine of which were within the Rebio Poço das Antas. The private lands are represented by Fazendas Imbaú (Faz. Imb.), Andorinhas (Faz. And.), Estreito (Faz. Est.), Afetiva-Jorge (Faz. Aft.) and Sítio do Professor (Faz. Stp.) reported by Carvalho et al., 2006a; Santa Fé (Faz. Sfe) from unpublished data; and two topographic sequences at the Biovert Agroflorestal farm: F. Bio TPA (Borém and Ramos, 2001) and F. Bio TMA (Borém and Oliveira-Filho, 2002). The studies at the Rebio Poço das Antas covered Rebio 20a and 40a (Neves, 1999), Rebio Mor (Guedes-Bruni et al., 2006a), Rebio Aluv (Guedes-Bruni et al., 2006b), Rebio Fr1, Fr2 and Fr3 (Pessõa and Oliveira, 2006) and Rebio Ari and Cam (Carvalho et al., 2006b).

Any species only recorded at a single area was excluded from the list, as they do not cause any variation in the analysis. Based on the obtained matrix, Sorensen’s similarity coefficient was calculated for all

Figure 1. Map of Rio de Janeiro State with studied area located.

234APR 2009, VOL. 34 Nº 4 the areas, forming a dendrogram by the UPGMA method. Calculations were performed utilizing the Fitopac 1 software package (Shepherd, 1995).

Results and Discussion

The results indicated a high species richness in the area, which is probably far from the real richness, as the sampling effort diagram exhibits a still ascending curve not highly significant different from a straight line in terms of the richness of the sampling points (Figure 2), indicating that there were still other taxa to be collected in the area. The vegetation sampling encountered 734 live individuals, yielding a total density of 1.468 ind/ha, a total basal area of 10783m2, and generating a taxon richness index of 19.85.

Among the sampled individuals were 129 species, subordinated to 41 families. The species, with their respective parameters, are listed in Table I in decreasing order of importance value (VI). Shannon- Wiener diversity index (H’) was 4.2 and equitability (J) was 0.87.

Earlier studies in central lowland forests (Neves, 1999; Borém and Ramos, 2001; Borém and Oliveira-Filho, 2002; Guedes-Bruni et al., 2006a, b; Pessõa and Oliveira, 2006; Carvalho et al., 2007) yielded H’ values from 1.75 to 4.57, corroborating the general pattern of the local landscape that has suffered from continuous anthropogenic interferences, whether as a result of fire or the establishment of small farm plots or grazing areas. Added to these alterations was the construction of the Juturnaíba reservoir in the 1970s, which had a strong impact on vegetation cover along the valley of the São João River (Cunha, 1995).

The families with the greatest abundance values were Euphorbiaceae, Lauraceae, Myrt- aceae, Annonaceae, Nyctaginaceae, Rubiaceae and Fabaceae. When their importance values were considered together, these families were found to be responsible for ~50% of the total VI. Previous studies in lowland and montane forests of Rio de Janeiro (Guedes-Bruni, 1998) have reported similar results, which reflect the wide geographic distribution of the species that integrate this vegetation type.

The families with the greatest species richness in the forest fragment studied were: Lauraceae (18 spp.), Myrtaceae (17), Fabaceae (1), Euphorbiaceae (8) and Meliaceae (6). These families together were responsible for 46.51% of all the species collected, with Myrtaceae alone yielding 13.95%.

Oliveira-Filho and Fontes (2000) analyzed 125 areas of Atlantic Forest (sensu lato) and reported that the families Myrtaceae, Rubiaceae, Euphorbiaceae and Melastomataceae had the greatest species richness in ombrophilous forests in southeastern Brazil. This data corroborates with that of other authors (Borém and Ramos, 2001; Borém and Oliveira-Filho, 2002; Carvalho et al., 2006a; Guedes-Bruni et al., 2006a, b; Pessõa and Oliveira, 2006; among others) in floristic analyses of the central coastal region of the state of Rio de Janeiro.

Myrtaceae and Lauraceae are characteristic in more mature forests (Tabarelli, 1997). Therefore, despite their representation in species richness, both families with many late successional species, contributed little in the composition of the VI.

The distribution of 10 species with higher VI (3.65% of sampled individuals) in successional groups showed a predominance (90%) of early secondary species, indicating that the forest is in a development process, or that there is some factor(s) preventing the full development of this fragment. Among these factors is the selective felling of some species (Euterpe edulis and Xylopia sericea), which was observed during data collection.

The families Euphorbiaceae, Lauraceae, and Annonaceae all contributed with 39.0% to the total basal area. The elevated number of individuals of the first two stood out, while

Annonaceae showed the highest average basal area of individuals.

In terms of the sizes of the various populations occurring in the fragment, the species Aparisthmium cordatum, Guapira opposita, Lacistema pubescens, Myrcia anceps and Bathysa mendoncaei stood out as having the largest numbers of individuals. As this forest was in an intermediate stage of succession, large numbers of individuals of these species were to be expected. Xylopia sericea, Jacaranda micrantha and Piptocarpha macropoda had the largest individuals (26, 23, and 21m, respectively) encountered in the survey, while an individual of Licaria sp had the largest recorded diameter (51.3cm). A schematic physiognomic structural profile of the vegetation is shown in Figure 3.

(Parte 1 de 3)

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