Arboreal community of an Atlantic Forest hillside fragment in São Sebastião/SP

The urban expansion and the growth of economic activities related to tourism added to the port and maritime ones, resulted in the occupation of the Serra do Mar, in the municipality of São Sebastião/SP, increasing environmental degradation. The objective of the study was to evaluate the arboreal patterns in a 0.111 ha fragment around a 4.8 ha clearing in an area of Atlantic Forest in the city of São Sebastião (SP), allowing the revegetation plan to include native species observed in the region. The phytosociological analyses used the Point-Centered Quarter Method (PCQM), using 50 sampling points (30 in close areas, 10 in the forest edge, and 10 near one of the areas drains), with a minimum distance of 20 meters between them. The main variables analyzed were commercial height, diameter to chest height, successional category, and dispersion syndrome. Also, the number of individuals of each species was observed, as well as their basal area (G), absolute and relative density (DA and DR) and dominance (DoA and DoR), relative frequency (FR), and importance value (VI). The results indicate a higher proportion of non-pioneer species, with Guapira oppositte (Vell.) presenting the highest value of importance and density, and the Schizolobium parahyba (Vell.) Blake with the highest basal area. The survey data indicate the richness of species in the study area, serving as a basis for strategies for management and conservation of the environment. Phytosociological studies, although scarce, are important to support the analysis of preservation and the use of nature.


Introduction
In Brazil, the economic growth by activities such as agriculture, livestock, mining, urbanization, and industrialization was not always related to the preservation of the environment (AZEVEDO-SANTOS et al., 2017;SOARES-FILHO et al., 2014). Throughout its history, this continuous process of predatory interaction has led to a high amount of degraded areas and compromised provision of essential ecosystem services, as a major associated restoration liability (BRANCALION et al., 2016;REZENDE et al., 2018). Degradation levels vary between phytogeographic domains depending on the occupation history, with the Atlantic domain standing out concerning the others in association with the old occupation and its economic importance (BRANCALION et al., 2016;JOLY et al., 2014;REZENDE et al., 2018).

Study area
The study site is in the municipality of São Sebastião, southeast of São Paulo state on its north coast. It occupies approximately 410 km², of which about 70 % are in Serra do Mar state park. It is limited to the north with the municipality of Caraguatatuba, west-northwest with Salesópolis, and west with Bertioga (GARCIA, 2005). It is bathed by the Atlantic Ocean throughout the south and east-northeast sector by the São Sebastião Channel (FIGURE 1). The area is located near an Atlantic Forest fragment with 4,8 hectares, where the original vegetation was composed of a dense ombrophilous forest (JOLY et al., 2012). Nowadays the fragment is covered by pastures surrounded by native vegetation, both in the lateral and upstream slopes, where are the highest altitudes. The beginning of fragmentation and opening of areas for agricultural and urban exploration in the region began about 40 years ago slowly and gradually, by the residents themselves with the palm exploitation, the extract of wood for construction and daily use and also for the occupation for subsistence agriculture. Nowadays, the native population is aware of the importance of ecological balance, as they have noticed large differences in the environment after vegetation removal, being water scarcity one of the major concerns, as local supplies are largely linked to the springs that surround the area. Pereira and Nunes (1997), analyzing data from 25 years , made the rainfall compartmentalization of the municipality of São Sebastião/SP. The study area, according to the survey of the above-mentioned authors, is located where the annual average rainfall is about 1,702.0 mm.

Data collection and analysis
The Point-Centered Quarter Method (PCQM) was used for the elaboration of the vegetal recomposition model of the clearing, data were obtained through the floristic inventory. The PCQM has been often used to sample plant communities, particularly forests (BRITO et al. 2007;MOREIRA et al. 2007;RUSCHEL et al. 2009). Fifty sample points were launched in stretches of Dense Montana Ombrophylous Forest, 30 points in the closed-canopy area, 10 points in the forest edge, and 10 points near one of the area drains. Thus, it was contemplated the physiognomic variations present in the study area and its surroundings, sampling the largest number of species. The points had a minimum distance of 20 meters from each other, thus ensuring that the same individual was not sampled twice. In each point, the four nearest trees were included in the sample.
The main variables collected had scientific name; commercial height (visually estimated); diameter at breast height (DBH), successional category, and dispersion syndrome. Thus, for each species were obtained: the number of individuals sampled, the number of occurrences, and basal area. The number of individuals (NI) corresponds to the number of trees of the same species sampled; The percentage over the total (200 individuals) was also calculated. The number of occurrences (NO) refers to the number of times the species occurred, considering the sample points, in this case, the percentage over the total (50 points) was also calculated. The basal area (G) is an estimator of the horizontal spatial occupation of the tree (associated with its size), and its calculation is obtained from the tree trunk diameter at 1.30 m from the ground. The basal area presented by species refers to the sum of its individuals and the percentage over the total was calculated.
For the evaluation of phytosociological parameters (MÜELLER-DOMBOIS; ELLENBERG, 1974), it was estimated the basal area (G) of the sampled area, absolute density (DA) and relative density (DR), relative frequency (FR), absolute dominance (DoA) and relative dominance (DoR) and value of importance (VI). The estimation of the ecological importance of families in the studied ecosystem was made by their relative density and dominance (MORI; BOOM, 1983) and the cover value (VC) highlighting the ecological importance of species in terms of distribution, based on density and dominance. For these analyzes, the Microsoft Excel for Windows program was used.

Results and discussion
We sampled 200 individuals, distributed in 28 families, 55 genera, and 71 tree species. The families with the highest species richness were: Myrtaceae (14 species), Fabaceae (8 species), and Lauraceae (6 species), totaling 38.4 % of the sampled species (TABLE 1). The non-pioneer species was the most representative successional category, with 54 species (~76 %), while the pioneers are represented by 17 species (~24 %) (TABLE 1). The Zoochoric dispersion syndrome is the most common with 60 species (84.5 %), while Anemochoric dispersion syndrome is represented by 11 species (15.5 %) (TABLE 1). The main families found are very characteristic for forests in the state of São Paulo, however the richness varies according to the formation, degree of disturbance, and stratum. Joly et al. (2012) in a study on floristics and phytosociology in permanent plots of the Atlantic Forest also found that, in an area of dense montane forest, the families with the largest number of species were Myrtaceae, Fabaceae, Rubiaceae, and Lauraceae. Fabaceae and Lauraceae are typical of the canopy and emergent; Rubiaceae, Myrtaceae, and Melastomataceae are prominent in the understory; Euphorbiaceae and Sapindaceae participate in both strata; and Solanaceae is frequent in disturbed areas, in forest edges (MANTOVANI, 1993). According to Padgurschi et al. (2011), several studies show a high density of these families in the Montana Atlantic Forest (DIAS, 2005;GUILHERME et al., 2004;MANTOVANI, 1993;FONTES, 2000;ROBIM et al., 1990;MANTOVANI, 1999) being, therefore, characteristics of this phytophysiognomy. The results found greater participation of non-pioneer and zoochoric species indicate a high stage of conservation of the fragment, which is in accordance with the conservation status of the region. The largest number of non-pioneers plants to an advanced silvigenic stage, in which species characteristic of high successional stages are composing the community (OLDEMAN, 1983). The higher proportion of zoochoric indicates the participation of biotic agents in the ecological patterns of the landscape, as they act in the seed's dispersion (BUDKE et al., 2005;CARVALHO et al., 2010). This participation is probably also related to the conservation status of the region, which has conservation units that shelter native fauna.
Among the sampled species, Guapira oppositte (Vell.) Reitz showed a higher value of VI and consequently greater sociological importance, mainly due to their higher basal area and density values compared to other species. However, when analyzing the parameters of Schizolobium parahyba (Vell.) Blake, the third species in VI, it is noted that the superior value obtained for basal area indicates the sociological dominance of this species, even though it has a low relative density (1.5 %) and relative frequency (1.9 %) (TABLE 2). The importance of species is related to density, frequency, and dominance values (LAMPRECHT, 1990). High values of these three parameters represent the most important species when only the community structure is evaluated. However, species with low density, but high frequency and dominance represent dominant and isolated trees, in small numbers, but scattered with some regularity over relatively large areas. Basal area (G) may be an important indicator of the degree of the degradation of the area. Ramos et al. (2011) associated the low values of basal area to several anthropic factors that cause disturbances in these places. While higher values are related to a better conservation status (KURTZ; ARAÚJO, 2000;MORENO et al., 2003;SZTUTMAN;RODRIGUES, 2002). According to Table 2, it is observed that the species Schizolobium parahyba (Vell.) Blake. was the one with the highest basal area value when compared to the others.
The relevant numerical data that may support the plant recomposition project are the number of individuals per species, the number of occurrences of the species at the sampling points (frequency), and the value of importance. Arruda and Daniel (2007) state that phytosociological studies can constitute a theoretical basis to assist in the preservation and use of flora resources, contributing to the recovery of degraded sites.

Conclusion
The results indicate a higher proportion of non-pioneer species, with Guapira oppositte (Vell.), presenting the highest value of importance and density, and the Schizolobium parahyba (Vell.) Blake with the highest values of basal area.
The survey data indicate the richness of species in the study area, serving as a basis for strategies for management and conservation of the environment. Phytosociological studies, although scarce, are important to support the analysis of preservation and the use of nature.