Natural Regeneration in Tropical Secondary Forest in Southern Amazonia , Brazil

Copyright © 2014 Alexandre Ebert et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In accordance of the Creative Commons Attribution License all Copyrights © 2014 are reserved for SCIRP and the owner of the intellectual property Alexandre Ebert et al. All Copyright © 2014 are guarded by law and by SCIRP as a guardian.


Introduction
The fabulous Amazon's biodiversity has been the subject of numerous debates in different social spheres.With the increasing demand for forest resources and prospects of population growth, these demands are expected to increase, particularly for tropical timber.With this in mind society has been put on alert.What is the carrying capacity of natural environments to resist human interventions and conserve the ecological and genetic interrelationships among species?The answer to this question needs to meet the needs of the present without compromising the needs of future generations as it was referred by Burtland in the report (Our Common Future) in 1987.
Sustainable forest management aims at using forest resources while keeping forest biodiversity and resilience.Studies of forest and natural regeneration enable a better understanding of the effect of the extraction of wood in tropical forests (Park et al., 2005;Zimmerman & Kormos, 2012), and as Araújo (2011) points out, it is important to know more about tree species behavior and natural regeneration to define the appropriate silvicultural management for forest species.
Forest management based on natural regeneration is accomplished by concentrating efforts on conserving biodiversity, therefore ensuring the vital functions of forests, as well as the continuity in the supply of various social and economic benefits (Nasi & Frost, 2009).It is determined by studies and surveys which help activities, inventory planning and exploitation of timber.
Natural regeneration is the renewing of trees in a forest and provides natural replacement of individuals.It becomes essential to take this into account when exposing large areas of forest logging.Many forest species are endangered mainly as a result of pressure by the intensive exploitation due to their high economic value (Fontana et al., 2003;IBAMA, 2008;Hubel et al., 2008).Thus, it becomes necessary to carry out surveys and studies on specific ways to lead to replacement of forest stock, with the maintenance of the natural reproductive processes of regeneration.
Studies of aspects related directly or indirectly to natural regeneration include auto ecology, success stage and the effects of forest exploitation (Higushi et al., 1985).They are crucial when compared with studies conducted for mature individuals, or considered as inventory growth and future exploration, (Scolforo, 1998).The importance becomes more evident when one considers that the quantitative and qualitative characteristics of mature forest are intimately related to the dynamic processes of biotic and abiotic natural regeneration, which consequently will continue the maintenance of forest biodiversity.
Several factors can influence natural regeneration.Calegario (1998), for instance, suggests successional stages as determinant interacting climatic factors, as well as biotic, edaphic, physiographic and anthropogenic.
In areas of the Amazon rainforest, the study of natural regeneration involves complex knowledge, due to the great diversity of species and functional processes related to ecological interactions, to microclimatic extracts provided by the forest and the diversity of geomorphologic environments.This study aimed to determine the floristic composition, diversity levels, size category, phytosociological, use group and the ecological group of species in the regeneration of rain forest the Southern Amazon, Brazil.

Materials and Methods
The study was conducted at São Nicolau farm, located in the municipality of Cotriguaçu, northwest of Mato Grosso state, Brazil (Figure 1).The farm belongs to the Brazilian branch of the Office National des Forêts (ONF Brazil), and has an area of 100,000 km 2 , of which 70,000 km 2 are covered with secondary open rain forest, reforestation of 20,000 km 2 with tree species intercropped with pasture and 10,000 km 2 ha with riparian areas fragmented.
The farm lays in a region where weather prevails belonging to group A tropical rainy climate, (Brazil, 1982), with type climate "Am", common to the short period of drought and rainfall below 60 mm in the driest period year (June to September).
For data collection permanent plots were allocated by the method of sampling for fixed area plots distributed systematically in two stages (Pellico et al., 1997).
The original vegetation types of the study area comprises the typology Open Tropical Rain Forest (Brazil, 1982), submontane formation with palm trees.Its physiognomy shows large trees spaced grouped with palm trees presenting a number of features with large leaves and rough bark.
Altogether, there were 50 plots subdivided into two sub-plots totaling 100 sampling units measuring 100 m 2 (10 × 10 m), in which were accounted all individuals measuring between 30 and 59 cm in circumference at breast height (HBC), 100 plots of 25 m 2 (5 × 5 m), for all young individual trees, measuring between 1.5 m in height and 30 cm in circumference and subplots of 4 m 2 (2 × 2 m) for regeneration of plants up to 1.5 m tall (Figure 2).
The identification and cataloging of species in the field were carried out by two practical identifiers and botanist Program Management of Tropical Forests PROMANEJO/FENF/UFMT.The identification and measurement of species, data were recorded on field sheets, containing botanical identification by common name, circumference at 1.3 m height above the ground, the circumference height and commercial height.
The data collected were processed in an MS-Excel ® spreadsheet obtaining results through natural regeneration phytosociological structure parameters such as density, frequency and index of value of importance.To calculate the diversity of natural regeneration was used the diversity index of Shannon-Weaver.
To determine the estimated natural regeneration it was used the methodology proposed by (Volpato, 1994), which uses the values of frequency and absolute abundance of each species in each size class.The abundance and relative frequency were calculated for each species in each class size, assuming that the denominator is constructed by summing the abundances and absolute frequencies of all species in all size classes.Further, it was estimated the natural regeneration by size class plant, adding partial values of relative frequency and relative abundance of natural regeneration by size class of plant studied, combining them into a unique expression as follows: ( ) where RNC ij = estimate of the natural regeneration of the ith species in the jth class of plant size in percentage.
Determined an estimated total natural regeneration by species using the equation: where RNT i = estimate of the Natural Regeneration total ith species.
The sum of the RNT of all species, as calculated above, equals 100.Thus, each individual value, either by size class or kind, is being expressed in percentage.

Floristic Composition
The survey for the inventory of natural regeneration of tree species identified a total of 610 individuals belonging to 82 species that are distributed in 34 botanical families.The families with the highest floristic diversity were: Fabaceae, with 17 genera and 18 species, Moraceae with 5 genera and 5 species, Melastomataceae with 3 genera and 4 species Burceraceae with 2 genera and 4 species, as shown in Table 1.
For diversity analysis, by calculating the diversity index of Shannon & Weaver (H') value obtained was H' = 2.77.

Analysis of the Distribution of Natural Regeneration in Succession Groups
Categorization of natural regeneration of species between ecological groups grouped into size classes resulted in the data listed in Table 2.
It is observed in the prevalence pioneer species, totaling 271 individuals in 33 species, following the climax species with 204 individuals in 19 species and 132 individuals with secondary in 28 species (Figure 3).
These results suggest that the forest in study underwent recent exploratory interventions and based on resilience the same, succession processes is still being established, forming an initial structure of natural regeneration.This process is commonly viewed in areas that suffered extensive logging.
In group use of the species studied (Table 3) considered the supply and demand for timber products and non-timber species in the region, detecting a satisfactory number of commercial species, total: 38 species, 31 timber species 5 and the second food producing latex and oil.In the clustering of non-commercial trees were identified 44 species, of which at least 5 are used by local communities for the production of medicines, crafts and tool handles.It is noteworthy in this context, the species Siparuna guianensis Aublet used to relieve headaches, and Co-

Phytosociological Parameters
The total density of natural regeneration was 8.320 individuals/ha, and the individuals who had the highest values were: Protium robustum, Maquira callophylla, and Mouriri fagifolium and Inga sp respectively.
The amounts related to abundance, and absolute and relative frequency of each species Importance Value Index expanded, are shown in Table 5.These values indicate the ecological importance of each species, i.e., its value in fitocenose studied.
The results related to the Amplified Importance Index Value which defines the ecological importance of the species within the community, allows making decisions about the management techniques based on guarantees replacement of existing individuals.
The species with the highest importance values obtained AIVI refer to tree and shrub species, highlighting the Protium robustum, a timber kind suffering strong pressure exploration in the Amazon region; however it is noted that the species responds positively to the processes natural regeneration.Figure 4 graphically illustrates the species that showed best AIVI.

Discussion
The current structure of the natural regeneration of the forest studied reflects intense logging in previous years, a fact that establishes succession stages presented.Despite not being able to establish the most intense period of exploration, it was noted that decades after logging still occur marked differences in the floristic composition and structure of ecological succession, especially in places where there were sharp impact on exploration, such as creating large clearings, stockyards and skid trails.The results obtained show that the structure of the forest is renewed by natural regeneration in face of disturbances caused by selective harvesting of timber.It's due probably by the high resilience of local environment.
The structure of natural regeneration in disturbed forests may suffer different arrangements according to the intensity.Hirai et al. (2012) and Garden et al. (2007) studying the effects of logging on natural regeneration in a forest, concluded that the floristic composition is modified in areas directly affected during exploitation, suffering changes along the years, occurring natural replacement of species serial stages.Species diversity was considered in a satisfactory level.Studies performed by Gamma et al. (2003), studying the natural regeneration in lowland forests in the Amazon estuary, they obtained similar results with H' = 3.05, for comparison.Almeida et al. (2012) evaluating phytosociology in managed forest in the municipality of Santarém, in Pará state, obtained H' = 4.39.Probably, the differences found in the results obtained in studies of diversity refer to different vegetation types, and/or the intensity of explorations carried out in previous years.
The distribution of the number of plants, as expected, decreased with increasing class size, put in categories 2 and 3 (changes and changes made) there was considerable decrease of plants, which can be attributed to interspecific competition or related syndromes pollination and/or dispersing agents.
Results show high incidence of commercial species representing the natural regeneration of trees possibly exploited in previous years.Gomes et al. (2011) concluded in their studies conducted in managed rainforest in Bolivia that natural regeneration of tree species exploited continues after the intervention and does not compromise the structure of the natural regeneration of commercial species.

Conclusion
The results obtained in this study lead which species may fuel demand for raw material for timber and non-timber forest products, showing a useful strategy that allows the perpetuation of natural forests, supporting exploratory practices that consider ecological parameters maintenance of intra-and interspecific relationships.

Figure 1 .
Figure 1.Location map of the study area.

Figure 4 .
Figure 4.Graphic illustration of the species with the highest Amplified Importance Index Value.

Table 1 .
List of species raised in the study area, in alphabetical order by family, common and scientific name and its associated ecological group, and ecological group.

Table 2 .
Relation between sizes classes of natural regeneration and their percenttages of individuals and number of species per stage successional.

Table 3 .
Number of species in natural regeneration by ecological group.Graphical representation of species by size class in succession stages.paiferaspwhich is extracted oil much used in healing wounds and sore throats.Values of Total Natural Regeneration of tree species with the highest importance, in descending order were; Protium robustum 16.42%, Maquira callophylla to 8.03% and Inga fagifolium with 7.76% , respectively (Table4).Can observe the values of natural regeneration studied, with the respective values of absolute abundance by size class of the studied plants.These values allow us to analyze the regeneration by plant size.

Table 4 .
Relationship of the species with their respective values of absolute abundance by size classes (CT) values and estimated percentage of Natural Regeneration (NR).

Table 5 .
List of species and their phytosociological parameters.AANR: Absolute Abundance of natural regeneration; ARNR: Abundance concerning natural regeneration; AFNR: Absolute frequency of natural regeneration; RFNR: Relative frequency of natural regeneration; AIVI: Index magnified importance.