Vertical structure of the arboreal component... VERTICAL STRUCTURE OF THE ARBOREAL COMPONENT UNDER REGENERATION PHASE OF A DECIDUOUS FOREST FRAGMENT, SANTA CATARINA STATE, BRAZIL

1 Received on 16.10.2014 accepted for publication on 07.03.2016. 2 Universidade Federal Fluminense, Centro Tecnológico, Escola de Engenharia Industrial Metalúrgica de Volta Redonda, Volta Redonda, RJ Brasil. E-mail: <wkfreitas@gmail.com>. 3 Universidade Federal Rural do Rio de Janeiro, Instituto de Florestas, Departamento de Ciências Ambientais, Seropédica, RJ Brasil. E-mail: <l.mauro@terra.com.br>. *Corresponding author.


INTRODUCTION
Seasonal Deciduous Forests (SDF) occur in regions with annual precipitation of less than 1,600 mm or in regions with intense cold, which results in more than 50% of leaf losses in trees of a forest (OLIVEIRA-FILHO et al., 2006).Santa Catarina State, Brazil has undergone strong anthropic pressures, first with logging and subsequently due to the extensive agriculture.Currently, the urbanization process has provided significant changes in the relationships of the resources on the edge and inside forest (MOTTER;FIGUEIRÓ, 2010;GASPER et al., 2012;VIBRANS et al., 2013a;SEVEGNANI;SCHROEDER, 2013).However, the territory of Santa Catarina has the largest area of remaining Atlantic forest, which represents 16% of SDF (IBGE, 2013;VIBRANS et al., 2013b).
By the end of the last century, the researches on plant composition in the west of the state were still insufficient, even with some important initiatives, such as the "Flora Ilustrada Catarinense" (NEGRELLE; SILVA, 1992).From the Forest Floristic Inventory of Santa Catarina (FFISC), new efforts have contributed to broaden the knowledge about remaining forests (GASPER et al., 2012).
According to Freitas and Magalhães (2012), the study of the horizontal structure is concerned about the sociological analysis of the species in the distribution of a sinusiae.Nevertheless, only this type of approach could not be enough for allowing a true characterization of the order of ecological importance of the species (FINOL, 1971).Thus, in order to get a more appropriate picture for the community knowledge, it is necessary to incorporate the arrangement of species along the vertical gradient (FARIAS et al., 1994).
The vertical structure defines the arrangement of different strata of a plant community (FREITAS; MAGALHÃES, 2012).The uneven-aged heterogeneous forests generally present a decrease in the availability of light along the vertical profile toward the ground, with greater differentiation of niches (SOUZA; SOUZA, 2004;MORAIS et al., 2013).Therefore, through the forest vertical stratification study, it is possible to obtain more detail about the richness, diversity, growth and biomass production (POLISEL, 2013).
Natural regeneration allows the effective analysis to diagnose the conservation state of the fragment and the response to the management as it represents the set of individuals that can be recruited for the later successional stages (SILVA et al., 2010).
According to Silva et al. (2010), the knowledge of the forest structure, combined with the analysis of natural regeneration, has a great importance for the elaboration of restoration plans, conservation and management of forest fragments, ensuring the maintenance of the community and composition species characteristics.However, when applied to a temporal scale, it contributes to a better understanding about the level of ecological stability and forest restoration velocity (SILVA et al., 2010).
This study aimed to evaluate the structure (horizontal and vertical) and the regeneration state of a Seasonal Deciduous Forest fragment located in the Santa Catarina Midwest region.

Description of the study site
The study was conducted in a SDF fragment located between the cities Piratuba and Ipira, Midwest of the Santa Catarina State (27° 25' 34" S and 51° 47' 18" W).The municipalities of Piratuba and Ipira have a population density of 33 and 30 inhabitants per km 2 , respectively (IBGE, 2013).In Piratuba, the industrial activities related to the agribusiness contribute to 50.6% of the GNP; in Ipira, the service sector and agriculture account for more than 80% of this indicator (SEBRAE, 2010a;SEBRAE, 2010b).
Vertical structure of the arboreal component... 11 °C to 20 °C, with the minimum monthly average amplitude from 6 °C to 16 °C (May to July) and the maximum average from 18 °C to 26 °C (December to February) (SPINELLI, 2012).
The study site is a secondary fragment of vegetation with about 120 ha, which is bounded for both urban perimeter of the municipalities and small farms, mostly with activities related to poultry and/or pig production.

Collection and data analysis
To assess the parameters of the plant community structure, 14 plots of 10 × 100 m (14,000 m 2 ) were used.In those plots, all trees with diameter at breast height (DBH) greater than or equal to 4.0 cm were identified and their DBH and height values recorded.For the Natural Regeneration analysis, it was considered the individuals with DBH less than 4.0 cm and equal to or greater than 2.0 cm in each of the 14 subplots of 40 m 2 (10 × 4 m), allocated in all transects, totaling 560 m 2 .
The botanical material was collected and identified in the field and subsequently had its identification confirmed using specialized literature and comparison with the Herbarium Collection of the Federal University of Santa Catarina (FLOR).The families were organized according to the Angiosperm Phylogeny Group III (2009).
To assess the sociological position of each species in the community, the population was divided into three strata of total height (h j ) (SOUZA; LEITE, 1993) as follows: lower stratum: h j < (h x -1S); middle stratum: (h x -1S) < h j < (h x + 1S); and upper stratum: h j < (h x + 1S).Where h x is the average height of the sampled individuals, S is the standard deviation of the total height of the stratum h j and h j is the total height of the j-th individual tree of the respective stratum.
The vertical stratification was obtained by using the estimates of Absolute Sociological Position (ASP i ) and Relative Sociological Position (RSP i ) per species (FINOL, 1971).
The Relative Natural Regeneration (RNR) was assessed by using the arithmetic average of Frequency, Density and size relative class of regeneration for each species present in this compartment (FINOL, 1971).
The parameter analyses of the forest structure were calculated by using the software Mata Nativa 2 (CIENTEC, 2006).
The similarity of species among the strata was analyzed using the Venn diagram, as proposed by Pinheiro and Durigan (2012).

RESULTS
It was sampled 2,125 individuals of the arboreal stratum in 14,000 m 2 , belonging to 34 families, 80 genera and 113 species (Table 1).The total density of arboreal individuals with DBH > 4.0 cm in the sampled fragment was 1,517 individuals ha -1 .
The middle stratum included the range of heights between 3.67 m < h j <9.24 m, totaling 1,630 individuals (76.7% of the total number of sampled plants), with a total density of 1,165 individuals ha -1 .Luehea divaricata Mart., Actinostemon concolor and Casearia sylvestris Sw. were represented by the greatest number of individuals, with 7% each (Figure 1).
In its turn, the upper stratum included the trees with total height greater than or equal to 9.24 m, totaling 305 individuals (14.3%).The total density of this stratum was 218 individuals ha -1 .The dominant species were Parapiptadenia rigida (Benth.)Brenan (9.5%) and Ocotea puberula (Rich.)Nees (8.9%) (Figure 1).The analysis of Sociological Position (SP) showed that among the 113 species found, six were exclusive to the lower stratum, 35 to the middle stratum, three to the upper stratum and 72 common to all strata (Figure 1).In the lower stratum, the exclusive species were Celtis brasiliensis (Gardner) Planch., Myrciaria floribunda   The natural regeneration counted on 189 individuals distributed into 24 families and 49 species, in addition to the dead individuals (Table 1), with total density of 3,500 seedlings ha "1 .Among the recruiters, the species that presented the highest value for natural regeneration was Actinostemon concolor (18.1%), followed by Guarea macrophylla Vahl (5.8%) and Matayba elaeagnoides Radlk (5.6%).About 20% of the species occurred only in this compartment, especially Piper gaudichaudianum Kunth, Eugenia pluriflora DC., Annona sylvatica (A.St.-Hil.)Martius, Peltophorum dubium (Spreng.)Taub and others.
The species Ocotea odorifera Rohwer is listed in the list of endangered species of the Brazilian Institute of Environment and Renewable Natural Resources in the State of Santa Catarina (BRASIL, 2008).The study showed the presence of just over 4% of exotic species, such as Cinnamomum triplinerve (Ruiz & Pav.) Kosterm., Citrus sp., Hovenia dulcis Thunb.and Morus nigra L. and Brugmansia suaveolens (Bonpl.ex Willd.)Bercht.& C. Presl (1.05%) (FLORA BRASIL, 2014).

DISCUSSION
In the Atlantic forest, particularly in Seasonal Deciduous Forest formations, studies of floristic composition and arboreal stratum structure have been widely disseminated, especially during the last decades, in the Brazilian states of Rio Grande do Sul (SEMA/ UFSM-RS, 2001;JURINITZ;JARENKOW, 2003;LINDENMAIER;BUDKE, 2006) and Santa Catarina (GASPER et al., 2012;GASPER et al., 2013).However, researches involving the assessment of the vertical distribution of arboreal species in this region are still poorly developed, especially due to the difficulty of identifying the species in juvenile stages (POLISEL, 2013).
Since the last century, some studies have been contributing to a better understanding of phytogeographical and floristic attributes of SDFs.Prado and Gibbs (1993) reported a tenuous connection between the vegetation of the Caatinga and the Argentine Chaco through species cross Brazil occurring in areas of seasonal forests of the Atlantic forest (Seasonal Forests of Central Brazil and the channel of the Uruguay River) and the Cerrado region.Most likely, this vegetation corridor has reached its maximum extent during the Pleistocene (dry and cold climate), which can be observed from the species widely distributed (RATTER et al. 1978;PRADO;GIBBS, 1993;OLIVEIRA FILHO;FONTES, 2000;PENNINGTON et al., 2000).
According to Moraes and Silva (2006), the more regular the distribution of individuals of a species in the vertical structure of a forest is, the higher its value in the Relative Sociological Position.This descriptor shows the importance of Luehea divaricata (RSP = 7.10%), Actinostemon concolor (7.00%), Casearia sylvestris (6.79%), Cupania vernalis (4.93%) and Parapiptadenia rigida (3.91 %) in the studied community structure.These species were also well represented in other studies conducted in deciduous forests in southern Brazil (FARIAS et al., 1994;LONGHI et al., 2000).
The great abundance of Actinostemon concolor in the natural regeneration corroborates the study of Jurinitz and Jarenkow (2003) when observe that it is a shrubby species and inhabit the lower stratum and understory of SDF.Peltophorum dubium, Eugenia pluriflora and Annona sylvatica were recorded only in the natural regeneration probably due to the randomness used in allocating the sample units.The species Piper gaudichaudianum has a shrubby habit and is common in clearings and forest edges (BARDELLI et al., 2008).The increase in sampling effort could better clarify the meaning of these numbers.
Considering the species with the highest EIV, Luehea divaricata, Casearia sylvestris, Cupania vernalis, Guarea macrophylla Vahl and Cabralea canjerana (Vell.)Mart.are considered as "supertramps", i.e., species that are widely distributed in various phytophysionomies of forest in the Atlantic area in Brazil (OLIVEIRA FILHO;FONTES, 2000).The other five (Actinostemon concolor, Parapiptadenia rigida, Nectandra megapotamica (Spreng.)Mez, Ocotea puberula and Apuleia leiocarpa (Vogel) J. F. Macbr.) are pointed out by Fontana and Sevegnani (2012) as widely spread in the SDF of the state.Among the above species, only Actionostemom concolor has no entry problems in the community, since it is well represented in the lower stratum and natural regeneration (Table 1), which suggests the expansion of the sampling effort of the natural regeneration.
In Santa Catarina, Hovenia dulcis has been identified as an important exotic species with invasive potential, as observed in the Fritz Plaumann State Park, Concórdia, SC, Brazil (DECHOUM; ZILLER, 2013).In this study, this species presented a density in the middle and upper strata of respectively 18 individuals ha "1 and 15 individuals ha "1 .However, in the lower stratum this species presented only 2 individuals ha "1 , which, at first sight, seems to corroborate the hypothesis of a problem associated with the invasion of species in the community.However, by observing the fragment as a whole, we observed a widespread occurrence of this species, both in the arboreal stratum and in regeneration.The presence of this species can be Vertical structure of the arboreal component... associated with plantation and/or restoration activities for multiple uses that occurred in the recent past or due to the process of randomness of sampling, since the species has a preference for habitats with higher solar radiation (heliophytic species), occupying forest edges and recent clearings (CARVALHO, 1994).The same applies to the exotic species Morus nigra L., abundant in the middle stratum, and Brugmansia suaveolensi, abundant in the natural regeneration (Table 1), which may cause problems of biological invasion in the future.The species Guarea macrophylla reached a moderate highlight in the regeneration (third place), in the lower stratum (second place) and in the middle stratum (fifth place).It is noteworthy that even native species, when considered dominants, may behave as invasive by some environmental disturbance, also requiring attention in the control and management of their populations (RICHARDSON et al., 2000).Thus, it is recommended to continue the study in order to assess the community dynamics compared to the possible effects of population dynamics of these species.
According to the CONAMA RESOLUTION from April, 1994(BRASIL, 1994), which establish the succession stage of the Atlantic forest for the State of Santa Catarina.The forest structure of the fragment is in the successional stage from initial to medium, mostly due to the high value of basal area (27.94 m 2 ha -1 ), but with anthropogenic interference signals in the floristic composition and in the recruitment of species in the community.
The results of this study can support important management measures for the fragment in question and others in the same physiographic condition.For example, the species Luehea divaricata (higher VI) could be used as anchor species for restoration models of forest fragments, resulting in a simpler and less costly strategy due to its greater adaptability to the current environmental conditions.

. CONCLUSIONS
The main highlights in the horizontal structure were the species Luehea divaricata (142 individuals and 7.9% of IV) and Parapiptadenia rigida (93 individuals and 5.3% of IV).When the vertical structure were analyzed, it is possible to observe a low recruitment of these species, indicating problems in the regeneration possibly caused by anthropogenic changes.On the other hand, Actinostemon concolor takes the second place in terms of EIV (7.0%) as a function of values obtained in its typical strata of occupation: natural regeneration (146 individuals), lower (29 individuals) and middle (116 individuals).In the community was also possible to identify the presence of exotic species with invasive potential (for example Hovenia dulcis).The presence of an endangered species (Ocotea odorifera) has been identified, in addition to others with economic potential (Apuleia leiocarpa and Cabralea canjerana), among species of high EIV.Given these facts, it is essential the implementation of management measures of forest fragments and the adoption of public policies aiming forest conservation in the region., v.26, n.1, p.69-77, 2013.