descrição estrutural do manguezal do rio cachoeira, ilhéus...

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REVISTA DE BIOLOGIA E CIÊNCIAS DA TERRA ISSN 1519-5228

Volume 13 - Número 1 - 1º Semestre 2013

Descrição estrutural do manguezal do Rio Cachoeira, Ilhéus, Bahia, Brasil

Patrick Thomaz de Aquino Martins1,2, Lorena Lacerda Santos3, Erminda Conceição Guerreiro Couto3

RESUMO

O presente estudo objetivou descrever as propriedades estruturais do manguezal do estuário do Rio Cachoeira, Ilhéus, Bahia. Os dados de estrutura da vegetação foram obtidos segundo o Método do Quadrante Centrado (PCQM) em oito transecções perpendiculares ao rio, considerando-se os indivíduos vivos com mais de 1,30m de altura. Foram registradas também as características gerais do ambiente, como presença de lixo e corte da vegetação. Durante o estudo, foram registradas três espécies: Rhizophora mangle, Laguncularia racemosa e Avicennia schaueriana. Foi encontrado um padrão na distribuição das espécies, onde os manguezais à montante apresentaram menor média de altura das árvores e predomínio de L. racemosa, espécie presente em todos os transectos, com exceção de um transecto, o qual apresentou as árvores com melhor sinal de desenvolvimento. Nos transectos intermediários a presença de R. mangle torna-se mais freqüente. A. schaueriana foi registrada somente nos dois transectos à jusante. Os transectos onde foram identificadas intervenções depredatórias, como o corte da vegetação, apresentaram também sinais de rebrota e berçário de plântulas. O retrato estrutural da vegetação registrado reafirma a influência dos tensores naturais e antrópicos como decisiva para o estado de conservação e desenvolvimento dos manguezais. Palavras-chave: PCQM, fitossociologia, propriedades estruturais.

Structural description of the Cachoeira River mangrove, Ilhéus, Bahia, Brazil ABSTRACT The present study aimed to describe the structural properties of the mangrove of the Cachoeira River estuary, located in Ilhéus, Bahia, Brazil. Vegetation structure data were obtained according to the Point-Centered Quarter Method (PCQM) in eight transects perpendicular to the river, considering all live individuals taller than 1.30m. The general characteristics of the environment were recorded as well, such as the presence of trash and cut vegetation. Three species were recorded during the study: Rhizophora mangle, Laguncularia racemosa and Avicennia schaueriana. A pattern was observed in species distribution, in which mangroves more upstream showed shorter average tree height and predominance of L. racemosa – a species present in all transects except the most downstream one, which in turn featured the most developed trees. In intermediate transects, the presence of R. mangle became more frequent. A. schaueriana was recorded only in the two downstream transects. Transects in which destructive interventions were identified – such as cut vegetation – also featured signs of regrowth and sapling nurseries. The structural portrait of vegetation reaffirms the influence of natural tensors and anthropic tensors as decisive factors for the conservation and developmental state of mangroves. Keywords: PCQM, fitossociology, structural properties.

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1 INTRODUCTION

Mangroves are regarded as PPAs (Permanent Protection Areas) due to their renowned ecological and economic importance in maintaining nutrient cycling, sheltering several different species and providing resources for mankind (Lugo & Snedaker 1974). They are resilient systems, in which abiotic factors play an important part in determining their structure, although current studies have shown the essential role of fauna in that regard (Proffit & Devlin 2005, Cannicini et al. 2008).

Plant species found in mangroves share common traits that allow them to survive in marshy and anoxic soils, facing periodic tide flooding. The study of the structural patterns formed by mangrove vegetation can be a useful tool, making it possible to measure the degree of development of the mangrove, observe vegetation response to environmental factors and compare different areas in their functional and ecological aspects (Schaeffer-Novelli & Cintrón 1986).

Mangroves cover an area of approximately 1.38 million hectares along the Brazilian coast (Kjerve & Lacerda 1993), with different structural characteristics in each region (Schaeffer-Novelli et al. 1990). In Bahia, there can be found the species Rhizophora mangle L. (red mangrove), Avicennia germinans (L.) Stearn (black mangrove), and A. schaueriana Stapf & Leechman ex Moldenke, and Laguncularia racemosa (L.) Gaertn. f. (white mangrove) (Ramos 2002).

Suppressive practices, such as cutting or leveling of vegetation and effluent release, have been responsible for disfiguring mangroves in Bahia. In the municipality of Ilhéus, in the state’s southern coast, this scenario can be confirmed in different mangroves (Andrade 2003, Martins et al. 2008, Martins & Wanderley 2009), resulting in 4.5% losses in the original mangrove area over a 58-year period (Faria-Filho et al. 2002).

Considering the functions and services provided by this environment, there is an evident need for studies aiming to understand the structure and dynamics of the system, in which a large part of the population has a close

relationship with the mangrove – particularly in the Ilhéus area. In order to obtain greater knowledge of this ecosystem, the objective of the present study was to describe the structural properties of the mangrove of the Cachoeira River estuary, located in Ilhéus, Bahia, Brazil. 2 MATERIAL AND METHODS

The estuary of the Cachoeira River features the largest area of mangrove remnants in the area (Figura 1), approximately 4 km² (Martins & Wanderley 2009).

Data on vegetation structure were obtained by the Point-Centered Quarter Method, PCQM (Schaeffer-Novelli & Cintrón, 1986, Mitchell 2004).

The PCQM is based on the establishment of points along a course that across the study area. Each point divides the course into four quarters, from a line perpendicular to the course. Data are collected only one tree per quadrant, which is nearest to the central point (Figure 2).

Eight transects were set perpendicular to the Cachoeira river (Figure 1), considering all live individuals taller than 1.30 m. With the use of remote sensing data was possible collect the geographical coordinates of the course established. The coordinates were identified in field with a GPS.

The points to collections were established every ten meters. For this was used a calibrated string, indicating the points.

The following variables were collected: tree height, distance of the tree to the central point and tree stem diameter (TSD). From these variables it was possible to measure the following parameters: density (absolute and relative), basal area (average, total and relative), frequency (absolute and relative), according to Schaeffer-Novelli & Cintrón (1986).

To determine the total density (stems/m²), the sentence imposed was 1/d², where d is the average distance of the trees to the reference point. The calculation of density species was performed by counting the number of individuals and by dividing this by the total. The product was multiplied by the total density.

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Figure 1 – Location of transects in the study area.

The acquisition of basal area (g) of the

tree was estimated using the following: g (m²) = 0,00007854 (TSD cm)²

Figure 2 – Squematic model of PCQM.

The basal area per species was obtained by summing the area all individuals of the same species; total basal area by multiplying the total density by the sum of basal areas of species; and

the average basal area (BA) by dividing the value of the total basal area by the number of individuals:

(BA) = g/n°

The percentage contribution by species in absolute and relative frequency, relative density and relative basal area, were valued by applying the following equations respectively: Absolute frequency = n° of points with species x 100

total points n°

Relative frequency = frequency of one specie x 100 frequency sum

Relative density = n° of individuals of one specie x 100

total individuals n°

Relative basal area = basal area of one specie x 100 basal area to all species

The average basal area was determined

from the product of the sum of the relative density, relative basel área and relative frequency. 3 RESULTS AND DISCUSSION

Three species were found in the Cachoeira River mangrove: Rhizophora mangle, Laguncularia racemosa and Avicennia

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schaueriana; the first two had already been identified at another local mangrove – Cururupe River, about 12 km south (Martins et al., to be published).

In mangroves more upstream, there was a predominance of L. racemosa (transects 1, 2, 3 and 4), while R. mangle had higher frequency values in intermediate transects. Specie A. schaueriana was recorded only in the two downstream transects (7 and 8).

In transects 1, 2, 3 and 4, L. racemosa was present at almost all points (absolute frequency) and quadrants (relative frequency). Another species identified in these initial

transects was R. mangle – only one individual in T1 and T2, absent in T3 and greater representativeness in T4 (Figures 2, 3, 4 and 5). Density and basal area values for R. mangle in transects 1 and 2 should not be observed too rigorously, as they do have representativeness in the featured mosaic.

The domain of L. racemosa in the first three transects evidences its greater representativeness in the other parameters (Table 1). This pattern can also be identified in tree height, averaging approximately 7.5 m, and taller trees that did not exceed 15 m.

Table 1 – Density, basal area and frequency values by species (Sp.) for each transect (T)

Rm = R. mangle; Lr = L. racemosa; As = A. schaueriana. In the first four transects, located

upstream, the shorter average height of trees and high absolute density (stems per hectare) – with particular attention to the values of L. racemosa – as well as the discontinuity of the parameters of those transects compared to the others, may denote areas of environmental imbalance. Jimenez et al. (1985) have confirmed this possibility, indicating that reduced structural development may be associated with anthropic changes.

Different situations may be occurring in these first four transects, which may be causing some type of tensor. Transect 1 is bisected by highway BR-415. For that reason, it comprises two sectors: one extending from the river to the edge of the road, and another from the other

side of the road to the end of mangrove vegetation (Figure 3). The sides of the road are characterized by the presence of ruderal vegetation, about 5 m deep on each side.

The differences between these two sectors are considerable. The sector on the side of the river has lower density and is almost monospecific, suggesting a more mature forest (Schaeffer-Novelli & Cintrón 1986), with the development of a L. racemosa nursery at all points. Conversely, the other sector on the other side of the road shows several dead stems and almost no signs of regeneration, likely because of the more hindered penetration of water from the estuary due to the asphalt of the road.

Among the anthropic interventions common to both sectors are the high rate of cut

Density Basal Area (m²) Frequency T. Sp. Absolute (ha) Relative (%) Average Total Relative (%) Absolute Relative

1 Lr 805.4 98.21 0.03 2.34 99.98 1 93.75 Rm 14.6 1.79 0.00 0.00 0.02 0.07 6.25

2 Lr 1050.2 98.15 0.01 0.91 86.47 1 93.33 Rm 19.8 1.85 0.07 0.14 13.53 0.07 6.67

3 Lr 1940 100 0.01 2.39 100 1 100

4 Lr 516 61.43 0.01 0.75 51.53 0.78 60.87 Rm 324 38.57 0.02 0.71 48.47 0.50 39.13

5 Lr 63.6 10.61 0.01 0.04 2.00 0.17 15 Rm 536.4 89.39 0.04 2.21 98.00 0.94 85

6 Lr 232.9 38.18 0.01 0.27 19.16 0.6 45 Rm 366 60 0.03 1.13 79.69 0.67 50 As 11.1 1.82 0.01 0.02 1.15 0.07 5

7 Lr 1400.8 54.72 0.00 0.15 5.67 0.64 47.37 Rm 917.7 35.85 0.02 2.08 79.34 0.57 42.11 As 241.5 9.43 0.02 0.39 15.00 0.14 10.53

8 Rm 941.4 85.59 0.03 3.06 87.19 0.93 76.47 As 158.6 14.41 0.03 0.45 12.81 0.29 23.53

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vegetation, with resprouting in some cases, indicating disturbance of the area (Couto 1996).

Thus, the structural characteristics of the sectors can be explained by the geographic location of this mangrove, more upstream, and by the construction of the highway, which would act as a barrier to the penetration of the tide and nutrients.

Figure 3 – Height profile of Cachoeira River mangroves, transect 1. The black-white alternate bars corresponds to 10m scale. RC = Cachoeira River.

This configuration explains the dominance of species L. Racemosa, which is associated with degraded areas (Kilca et al 2010) and with flooding deficits (Carvalho, 2000).

Transect 2 is located on a small island, at the same longitude of transect 1, and shares that space with ruderal species (Figure 4). Structurally similar to transect 1, this transect featured the highest rate of cut mangrove vegetation among all analyzed transects.

Figure 4. Height profile of Cachoeira River mangroves, transect 2. The black-white alternate bars corresponds to 10m scale. RC = Cachoeira River.

The site of this transect may be a complicating environmental factor, as it is situated approximately 2 m above water level.

Despite this scenario, the presence of a large nursery of R. mangle at cut vegetation points indicates mangrove regeneration in that environment. In that sense, it must be mentioned that even though the transect is dominated by L. racemosa, colonizing species belonged to the less dominant specie. This condition may be due to the combination of cutting and different factors, such as the fertile period of species and proximity of the fertile specie to the cut area.

The transect 3 is the only monospecific transect among all those analyzed, and also the one featuring the greatest amount of solid residue and landfills (urban pressure). With a very characteristic pattern, this forest features high density (1940 ind./ha. – the highest per species among all sampled transects) and low basal area value (2.39 m²/ha), although that value is the third highest for that variable. The structural pattern of this mangrove (Figure 5) may be linked to the landfill inherent to the urban expansion of the municipality (Martins & Wanderley 2009).


Transect 4 has a low level of

development, but is nevertheless is more developed than transects 1, 2 and 3. Within this transect, a few trees were observed close to the river edge, not sampled, which were separated from the mangrove by a stretch of ruderal vegetation, totaling 80m from the start of the

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mangrove. Thus, transect 4 features two different scenarios divided into 3 sectors: two dominated by L. racemosa and, between them, one dominated by R. mangle (Figure 6).

Although it has lower frequency (absolute and relative), the R. mangle forest stands out due to the level of development of its individuals. The absence of cuttings and other types of direct anthropic tensors in the

vegetation of that mangrove suggests these stands are poorly developed as the result of natural environmental conditions, such as the penetration of water bodies into the mangrove. The presence of preferential flow channels found in the R. mangle stand reinforces this theory.


Figure 7. Height profile of Cachoeira River mangroves, transect 2. The black-white alternate bars corresponds to 10m scale. RC = Cachoeira River. Even though it does not have tall trees –

average of 9.32 m – the mangroves in transect 5 have the lowest absolute density (600 ind./ha.) and largest average basal area per species (R.

mangle with 0.04 m²) out of all measured transects (Figure 7).

Transect 5 is nearest to the urban area of the municipality, while the mangroves in

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transects 4, 6 8 comprise the right margin of the river, more distant from any direct strong anthropic disturbance (Figure 1).

Transect 6 was the first along the estuary to feature all three mangrove types (Figure 8), in which R. mangle and L. racemosa showed the highest frequency and density values. Featuring 16 sampling points, the last ones constitute an ecotone where the mangrove shares space with ruderal vegetation, and a rock outcrop is present.


The mangrove in transect 7 was the densest of all found (Table 1). The mangroves in this transect features two distinct stages (Figure 9): one dominated by L. racemosa, the most frequent species (absolute and relative); and another dominated by R. mangle.

The stage dominated by L. racemosa is a typical mangrove forest with high environmental compliance. Indicators include the high density of this species, (1400ind./ha.), low average height (Figure 9) and low contribution in relative basal area (5.67%). Conversely, the section dominated by R. mangle is a mature stand in final stage of development.

In addition to featuring trees over 15 m tall, R. mangle species showed propagules during data collection, thus demonstrating their condition as adult individuals already in reproductive stages. A. schaueriana was also present in transect 7, although in low density and basal area contribution.

The lower anthropic action in that transect seems not to be the main factor for its lower development, as no cut vegetation was

recorded. The low amount of solid detritus may have been brought by one of the two rivers, or even by the tide.

The mangroves in transects 5, 6 and 8 showed the greatest values for height (Figures 7, 8 and 10) and are among those with lowest density and largest average basal area (Table 1), indicating a higher degree of development. R. mangle becomes more frequent in all three transects, whereas L. racemosa becomes more restricted to transition zones (edges). Specie A. schaueriana is recorded in two of the three transects (Figures 8 and 10).

Figure 9. Height profile of Cachoeira River mangroves, transect 2. The black-white alternate bars corresponds to 10m scale. RC = Cachoeira River; RI = Itacanoeira River.

The predominance of R. mangle stands may be related to the good development and better preservation of upstream mangroves, corroborating the description by Kilca (2010), at the Piauí River estuary, Sergipe.

As the largest transects (260 m and 280 m, respectively), transects 5 and 8 (Figures 7 and 10) have the most developed mangroves. The absence of L. racemosa in transect 8 may be the result of the greater influence of tides and greater shade cover (Ball 1980, McKee 1995). These factors reduce the competitive potential of that species compared to the other mangrove species found.

The presence of several R. mangle saplings throughout the transect is another indicator of the continuity of that stand should competition occur, from natural tree death.

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Figure 10. Height profile of Cachoeira River mangroves, transect 2. The black-white alternate bars corresponds to 10m scale. RC = Cachoeira River; RS = Santana River.

The expanse of transect 5 mangrove and

the absence of direct anthropic interventions, combined with natural resource conditions, can explain the favorable development of the mangroves in transects 5 and 8. Even though it features the mangroves closest to urban areas, the vegetation of that transect has no negative indicators, such as cutting or effluents. ACKNOWLEDGMENTS

To the National Council for Scientific and Technological Development for financial support (CNPq-CTHidro 14/2005 – 13 3343/2006); to Rui, Nino, Alexandra, Fabrício, Bruna, Vinícius, Victor and Alex, for their support during field trips; to the Coordination for the Improvement of Higher Education Personnel (CAPES), for providing a Master’s grant to the first author; and to the Foundation for Research Support of the State of Bahia (FAPESB) for providing a Master’s grant to the second author. REFERENCES ANDRADE, M. P. Ilhéus: passado e presente. 2. ed. Ilhéus: Editora Editus, 2003. 144p.

BALL, M. C. Patterns of secondary succession in a mangrove forest of south Florida. Oecologia, v.44, p. 226-235, 1980. CANNICINI, S.; BURROWS, D.; FRATINI, S.; SMITH, T. J.; OFFENBERG, J.; DAHDOUH-GUEBAS, F. Faunal impact on vegetation structure and ecosystem function in mangrove forests: A review. Aquatic Botany, v. 89, n. 2, p. 186-200, 2008. CARVALHO, E. A. Impactos ambientais na zona costeira: o caso da estrada Bragança-Ajuruteua, Estado Pará. 2000. Dissertação (Mestrado em Ciências do Ambiente), Universidade de São Paulo, PROCAM, 2000. COUTO, E. C. G. Caracterização estrutural do manguezal da foz da Gamboa do Maciel (Paranaguá - Pr). Brazilian Archives of Biology and Technology, Curitiba, v. 39, n. 3, p. 497-507, 1996. KJERFVE, B.; LACERDA, L. D. Mangroves of Brazil. In: LACERDA, L. D. (ed.). Conservation and sustainable utilization of mangrove forests in Latin America and Africa Regions. International Society for Mangrove Ecosystems. Technical reports, v.2, ITTO TS-13, v.1, p. 245-272, 1993.

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FARIA-FILHO, A. F., ARAUJO, Q. R.; NASCIMENTO, R. L. Degradação ambiental causada pela ocupação antrópica em áreas de manguezais de Ilhéus – Bahia. In: I Congresso Internacional sobre Desenvolvimento e Meio Ambiente Política, Desenvolvimento e Sustentabilidade. Fortaleza. Resumos... Fortaleza: PRODEMA, 2002. JIMENEZ, J. A., LUGO, A. E.; CINTRON, G. Tree mortality in mangrove forests. Biotrópica, v. 17, n. 3, p. 177-185, 1985. LIÇKA, R. V., COSTA, M. P., ZANINI, R. R., CARVALHO, F. A.; COSTA, A. F. Estrutura de manguezais em diferentes estágios sucessionais no estuário do Rio Piauí, Sergipe-Brasil. Pesquisas, Botânica, v. 61, p. 171-189, 2010. LUGO, A. E.; SNEDAKER, S. C. The ecology of mangroves. Annual Review of Ecology and Systematics, v. 5, p. 39-64, 1974. McKEE, K.L. Interspecific variations in growth, biomass, partitioning, and defensive characteristics of neotropical mangrove seedlings: Response to light and nutrient avaibility. Am. J. Bot., v. 82, n. 3, p 299-307, 1995. MARTINS, P. T. A.; WANDERLEY, L. L. Dinâmica de ocupação espacial de áreas contíguas (período 1987-2008) e sua relação com tensores de origem antrópica no manguezal do Rio Cachoeira, Ilhéus, Bahia. Sociedade & Natureza, v. 21, n. 2, p. 77-89, 2009. MARTINS, P. T. A.; COUTO, E. C. G.; DELABIE, J. H. C. Évolution récente de la zone estuarine d un microbassin côtier du Nordeste du Brésil soumis à différents types d impacts d origine humaine. Revue d'Écologie Terre et Vie, v. 63, p. 47-53, 2008. MARTINS, P. T. A., COUTO, E. C. G.; DELABIE, J. H. C. Fitossociologia e estrutura vegetal do manguezal do Rio Cururpe (Ilhéus, Bahia, Brasil). Revista da Gestão Costeira Integrada, v. 11, n. 2, p. 163-169, 2011.

MITCHELL, J. S. R. Quantitative Analysis by the Point-Centered Quarter Method. Hobart and Willian Smith Colleges. Disponível em: <http://people.hws.edu/mitchell/PCQM.pdf>. Acesso em: 26 set. 2004. PROFFITT, C. E.; DEVLIN, D. J. Grazing by intertidal gastropod Mellampus coffeus greatly increases leaf litter degradation rates. Marine Ecology Progress Series, v. 296, p 209-218, 2005. RAMOS, S. Manguezais da Bahia: breves considerações. Ilhéus: Editora Editus, 2002. 104p. ISBN: 85-7455-047-7. SCHAEFFER-NOVELLI, Y.; CINTRÓN, G. Guia para estudo de áreas de manguezal: estrutura, função e flora. São Paulo: Caribbean Ecological Research, 1986. 150p. SCHAEFFER-NOVELLI , Y.; CINTRÓN, G.; ADAIME, R. R. Variability of Mangrove Ecosystems Along the Brazilian Coast. Estuaries, v. 13, n. 2, p. 204-218, 1990. ______________________________________ 1 - Universidade Estadual de Goiás, Programa de Pós-Graduação em Recursos Naturais do Cerrado, BR-153, nº 3.105 - Fazenda Barreiro do Meio - Caixa Postal: 459, Anápolis, GO, Brasil. 2 - Universidade Estadual de Goiás, Unidade Universitária de Minaçu. Rua Santa Cruz, s/n, Vila de Furnas, 76450-000, Minaçu, GO, Brasil. 3 - Universidade Estadual de Santa Cruz, Programa de Pós-Graduação em Sistemas Aquáticos Tropicais (Ecologia), Departamento de Ciências Biológicas, km 16 Rodovia Ilhéus-Itabuna CEP 45662-000, Ilhéus, BA, Brasil.

descrição estrutural do manguezal do rio cachoeira, ilhéus...

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