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Floresta e Ambiente

Print version ISSN 1415-0980On-line version ISSN 2179-8087

Floresta Ambient. vol.26 no.4 Seropédica  2019  Epub July 29, 2019

http://dx.doi.org/10.1590/2179-8087.791408 

Original Article

Conservation of Nature

Influence of Edaphic Attributes on the Distribution of Tree Species in a Riparian Forest in Southern Brazil

Mônica Brucker Kelling1 
http://orcid.org/0000-0002-4416-3739

Maristela Machado Araujo1 
http://orcid.org/0000-0003-3751-8754

Daniele Guarienti Rorato1 
http://orcid.org/0000-0003-2751-7336

1Universidade Federal de Santa Maria (UFSM), Santa Maria, RS, Brasil

ABSTRACT

This study aims at identifying the formation of clusters and to evaluate the influence of chemical attributes in the soil on the groups and species in a riparian forest fragment in Campos de Cima da Serra, Rio Grande do Sul (RS). Thirteen plots (10 × 20 m) were demarcated to carry out the study. Forest inventory data were employed in a multivariate analysis using the Twinspan method and the correlation between vegetation data and chemical characterization of the soil was carried out by Canonical Correspondence Analysis (CCA). Thirty-one species were sampled (DBH ≥ 30 cm) and two floristic groups were identified. The results indicated a structural difference between the two environments, likely due to the steeper slope and less influence of groundwater. Variables such as sulfur, calcium and organic matter were explanatory of the vegetation grouping known as riparian forest of hillside and aluminum, aluminum saturation and copper of riparian forest with flat topography.

Keywords: conservation; cluster analysis; canonical correspondence analysis; Mixed Ombrophilous Forest

1. INTRODUCTION AND OBJECTIVES

The vegetation found along watercourses is generally referred to as riparian (Brasil, 2012), however, when this vegetation is not characterized as a continuous forest, it is often referred to as a gallery forest (Rodrigues, 2009). Regardless of the denomination, riparian forests play an important biological filter role by retaining substances or by filtering water runoff (Kageyama & Gandara, 2009), as well as forming ecological corridors that are fundamental for preserving the diversity of flora and fauna (Brancalion et al., 2010). Due to its importance, the development of researches related to the phytosociological parameters of the vegetation present in riparian forests is an important subsidy for planning conservation actions and enrichment of these areas.

In this regard, the use of multivariate techniques such as cluster analysis is an important tool to characterize vegetation in forest fragments, since it aims to cluster elements in homogeneous groups (Felfili & Rezende, 2003). Among the implemented techniques, the Twinspan (Two-Way Indicator Species Analysis) grouping analysis (Gauch, 1982) has been used by Araujo et al. (2010), thus allowing the detection of distinct vegetation clusters in forest remnants, which were defined according to environmental characteristics and specific species.

Moreover, as important as characterizing floristic and vegetation structure, as well as evidencing groupings of species in natural ecosystems, is the correlation of this information with environmental characteristics. This is possible through sorting methods such as the Canonical Correspondence Analysis (CCA), Principal Component Analysis (PCA) and Detrended Correspondence Analysis (DCA), which were used by Rodrigues et al. (2007). According to these techniques, these authors determined preferential habitats for species occurrence which were correlated with the type and characteristics of soils, topography and drainage.

Similarly, Avila et al. (2011) also used cluster analysis and CCA, respectively, to identify the presence of floristic clusters in natural regeneration mechanisms and the influence of environmental factors on the distribution of species and plots in the seedling bank in a Mixed Ombrophilous Forest fragment in southern Brazil. In this forest typology, the authors concluded that the formed clusters indicate differences in the regenerative processes of the forest. Understanding this information makes it possible to plan conservation and management strategies that are appropriate to each species and environment, and according to Rorato et al. (2015), allows one inferring about the biological conservation of these ecosystems, providing an indication of potential species to be used in programs and strategies for recovery and enrichment of degraded areas.

Thus, the objective of the present study was to identify and characterize groupings of species in the arboreal component and correlate them with soil variables in a riparian forest in Campos de Cima da Serra in RS, Brazil.

2. MATERIALS AND METHODS

The study was carried out in an area of riparian forest in a Mixed Ombrophilous Montana Forest fragment (IBGE, 2012) in the municipality of São Francisco de Paula, RS (29°26’52”S latitude and 50°35’02”W longitude), with average altitudes of 907 m. According to the Köppen climate classification, the climate in the region is Cfb (subtropical), constituting the coldest region of the state and with the greatest precipitation (Moreno, 1961).

The region is known as Campos de Cima da Serra, in which the fields form mosaics with the Mixed Ombrophilous Forest (Pillar et al., 2009) and the Campos Sulinos biome (IBGE, 2004). According to Streck et al. (2008), the predominant soils in the region are classified in the first categorical level as Cambisols and Neosols.

Systematic sampling was used for the vegetation survey with random selection of the first sample unit (plot), and all other units were then systematically distributed from there (Péllico Neto & Brena, 1997). Thus, eight strips perpendicular to the water course were demarcated, parallel to one another at distances of 100 m. The strips were drawn in the perpendicular direction to the drainage line in order to obtain a vegetation gradient from the fragment edge to the riverbed (Figure 1).

Figure 1 Location of the study area, highlighting the distribution of the strips and plots sampled in a Mixed Ombrophilous Forest fragment, São Francisco de Paula, RS, Brazil. 

A total of 13 plots of 10 × 20 m were demarcated throughout the eight strips in the fragment with a total area of 12.2 ha. Botanical identification and measurement of the individuals of the shrub-arboreal component of the diameter at breast height (DBH), according to class sizes, was carried out in each plot. All individuals with DBH ≥ 30 cm (Class I) were evaluated in the total area of each plot (10 × 20 m), while all individuals with 15 ≤ DBH < 30 cm (Class II) were evaluated in the 10 × 10 m subplots. The species were classified into botanical families according to the Angiosperm Phylogeny Group (APG IV) (Chase, 2016) and the scientific name updating was determined according to the List of Species of the Brazilian Flora (JBRJ, 2014).

In addition to the vegetation survey, three simple soil samples in the 0-20 cm layer were collected from eight of the 13 plots studied to form the composite sample. These samples were submitted to chemical analysis at the Universidade Federal de Santa Maria (UFSM) Soil Analysis Laboratory according to the methodology proposed by Tedesco et al. (1995) for determining the pH in water, V% (base saturation), m% (saturation by aluminum), H+Al, effective cation exchange capacity (CEC), pH7 CEC, and content of organic matter (OM), aluminum (Al), calcium (Ca), magnesium (Mg), potassium (K), sulfur (S), phosphorus (P), copper (Cu), boron (B) and zinc (Zn).

The cluster analysis only considered data from individuals of the arboreal stratum (Class I), while Class II was used to support possible biological and structural differences in each grouping based on the evaluated class sizes. Thus, tree vegetation data (individuals with DBH ≥ 30 cm) gave rise to a matrix consisting of 13 plots (lines) and 14 species (columns). Rare species (considered as those with less than three individuals) were removed from the cluster analysis. Rare or low-density species have little or no influence on the results and can be removed from the analysis (Gauch, 1982).

This matrix was used in a multivariate analysis according to the Twinspan method (Gauch, 1982) using the PC-ORDTM program for Windows version 5.10 (McCune & Mefford, 1997).

For characterization of the pseudospecies, the cut levels were determined based on the densities observed for the species in each plot with pseudospecies 1 (up to one individual), pseudospecies 2 (two to four), pseudospecies 3 (five to six), pseudospecies 4 (seven to nine) and pseudospecies 5 (10 or more individuals).

According to the formed groups, each one was then analyzed by parameters such as density, dominance, absolute frequency and value of importance regarding the species (Felfili & Rezende, 2003), seeking to distinguish differences in the forest structure, which in addition to density also allowed to infer about each group.

The correlation between vegetation data and soil chemical variables through the Canonical Correspondence Analysis (CCA) was carried out using the PC-ORDTM program for Windows version 5.10 (McCune & Mefford, 1997). The analysis was based on the formation of two matrices: one referring to the density of the individuals of each tree species in the eight plots from which soil samples were collected; and another one containing the chemical characteristics of the soil, in addition to the group as a categorical variable. However, the analysis is only possible when the number of environmental variables is smaller than the number of plots with vegetation data; a condition imposed by the software at the time of inserting the matrices in the program. Thus, a preliminary analysis was carried out to remove weakly correlated variables (correlation value less than 0.4).

As a result, CCA was processed using the main matrix of species density (Class I), composed by eight plots (lines) and 11 species (columns), and a secondary matrix with eight plots (lines) and seven environmental variables (columns). It was then possible to evaluate soil chemical variables that had the greatest influence on the groups according to the CCA results.

3. RESULTS AND DISCUSSION

For the arboreal vegetation (Class I, DBH ≥ 30 cm) of the studied forest fragment, 31 species belonging to 27 genera and 19 botanical families were sampled, while for the smaller class size (Class II, 15 ≤ DBH < 30 cm), the richness was represented by 19 species, 19 genera and 12 botanical families (Table 1). Ribeiro et al. (2007) verified the occurrence of 130 species with DBH ≥ 30 cm belonging to 79 genera and 45 botanical families in an arboreal community characterization of the Mixed Ombrophilous Forest in the National Forest (Flona) of São Francisco de Paula, RS, Brazil. These results differ from those found herein, probably due to the studied area belonging to a Flona and representing a typical Mixed Ombrophilous Forest, while the forest fragment in the present study is represented by a riparian forest remnant.

Table 1 Families and species observed in Class I (DBH ≥ 30 cm) and Class II (15 ≤ DBH < 30 cm) in a Mixed Ombrophilous Forest fragment. São Francisco de Paula, RS, Brazil. 

Family Species Popular name in Brazil Class
Anacardiaceae Lithraea brasiliensis Marchand Aroeira-brava I and II
Schinus lentiscifolia Marchand Aroeira-cinzenta I and II
Aquifoliaceae Ilex brevicuspis Reissek Caúna I and II
Ilex dumosa Reissek Caúna I
Araucariaceae Araucaria angustifolia (Bertol.) Kuntze Araucária I and II
Asteraceae Gochnatia polymorpha (Less.) Cabr. Cambará I
Celastraceae Maytenus aquifolia Mart. Cancorosa I
Cunoniaceae Lamanonia ternata Vell. Guaraperê I
Dicksoniaceae Dicksonia sellowiana Hook. Xaxim I
Euphorbiaceae Sebastiania brasiliensis Marchand Leiteiro I and II
Gymnanthes klotzschiana Müll.Arg. Branquilho I and II
Lauraceae Cinnamomum amoenum (Nees & Mart.) Kosterm. Canela I
Ocotea corymbosa (Meisn.) Mez Canela I
Ocotea porosa (Nees & Mart.) Barroso Imbúia I
Ocotea pulchella (Nees & Mart.) Mez Canela-lageana I and II
Melastomataceae Miconia cinerascens Miq. Pixirica II
Myrtaceae Acca sellowiana (O.Berg) Burret Goiaba-da-serra II
Blepharocalyx salicifolius (Kunth) O.Berg Murta I
Calyptranthes concinna DC. Guamirim-ferro I and II
Eugenia uruguayensis Cambess. Guamirim I and II
Myrceugenia cucullata D. Legrand Guamirim I and II
Myrcianthes gigantea (D. Legrand) D. Legrand Araçá-do-mato I and II
Myrciaria delicatula (DC.) O.Berg Camboim I and II
Podocarpaceae Podocarpus lambertii Klotzsch ex Endl. Pinheiro-bravo I and II
Primulaceae Myrsine coriacea (Sw.) R.Br. ex Roem. & Schult. Capororoca I
Proteaceae Roupala brasiliensis Klotzsch Carvalho-brasileiro I and II
Quillajaceae Quillaja brasiliensis (A.St.-Hil. & Tul.) Mart. Pau-sabão I and II
Rosaceae Prunus myrtifolia (L.) Urb. Pessegueiro-do-mato I
Salicaceae Casearia decandra Jacq. Guaçatunga I and II
Casearia sylvestris Swartz. Chá-de-bugre I
Sapindaceae Allophylus edulis (A.St.-Hil. et al.) Hieron. ex Niederl. Chal-chal I
Styracaceae Styrax leprosus Hook. & Arn. Carne-de-vaca I
Symplocaceae Symplocos uniflora (Pohl) Benth. Sete-sangrias I and II

Two floristic groups (eigenvalue: 0.3133) were observed in the cluster analysis for Class I: Group 1 (G1) and Group 2 (G2) (Figure 2). According to the characteristic of the observed vegetation, the studied forest fragment shows a great number of species of riparian forests. However, G1 differed from G2 because it occurred on flat relief, thus being referred to as riparian forest with flat topography, using Eugenia uruguayensis as an indicator. The area in G2 has a more pronounced topography, which can be characterized as a hillside riparian forest, in which the indicator species of this environment was Myrcianthes gigantea. Both indicator species are typical of riparian forests, as evidenced by Rorato et al. (2015) for Eugenia uruguayensis and by Backes & Irgang (2009) for Myrcianthes gigantea.

Figure 2 Classification of sampling units in two floristic groups for Class I (DBH ≥ 30 cm) in a Mixed Ombrophilous Forest fragment. São Francisco de Paula, RS, Brazil, as follows: Group 1: riparian forest with flat topography; Group 2: hillside riparian forest. 

The species Casearia decandra, Eugenia uruguayensis, Myrciaria delicatula, Myrsine coriacea, Roupala brasiliensis and Styrax leprosus are the preferential species of the riparian forest with flat topography (G1) (six plots) as represented by pseudospecies 1, which indicates a low density of individuals in the plots. In addition to these, we can highlight Eugenia uruguayensis and Ocotea pulchella, belonging to pseudospecies 2, which presented between two and four individuals; and Eugenia uruguayensis and Podocarpus lambertii, both of pseudospecies 3 with five to six individuals.

For the hillside riparian forest (G2) formed by seven plots, the species Myrcianthes gigantea was indicative of the group and also the preferred pseudospecies 1 and 2, while Gymnanthes klotzschiana was preferred as pseudospecies 2, 3, 4 and 5, considering that more than 10 individuals of this species were observed in both plots.

In the G1 structure, represented by the riparian forest present in areas with flat topography, approximately 1,008 individuals.ha-1 were found for Class I (DBH ≥ 30 cm), belonging to 24 species, 23 genera and 14 botanical families (Table 2).

Table 2 Phytosociological parameters of the species belonging to Group 1, considering Class I and Class II in a Mixed Ombrophilous Forest fragment. São Francisco de Paula, RS, Brazil. 

SCIENTIFIC NAME CLASS I CLASS II
AD ADo AF VI AD ADo AF VI
Podocarpus lambertii 225 15.1796 100 21.6
Eugenia uruguayensis 183.3 5.6272 100 13.5 50 0.4161 33.3 14.6
Araucaria angustifolia 75 7.3202 50 9.3 33.3 0.1391 16.7 6.8
Ilex brevicuspis 83.3 4.4565 50 7.6
Lithraea brasiliensis 58.3 3.548 66.7 6.7 16.7 0.0613 16.7 4.2
Gymnanthes klotzschiana 50 1.4577 66.7 5
Ocotea pulchella 25 3.0763 33.3 4.1
Casearia decandra 33.3 0.7983 50 3.4 66.7 0.3507 50.0 16.7
Roupala brasiliensis 33.3 0.7957 50 3.4 16.7 0.0454 16.7 3.9
Ocotea porosa 25 0.9721 50 3.3
Myrciaria delicatula 33.3 0.5764 50 3.3 66.7 0.2915 33.3 13.9
Myrsine coriacea 41.7 0.8915 33.3 3.2
Myrceugenia cucullata 33.3 0.4373 50 3.2 33.3 0.1025 33.3 8.1
Styrax leprosus 25 0.8268 33.3 2.6
Schinus lentiscifolia 8.3 0.6765 16.7 1.3
Dicksonia sellowiana 8.3 0.2155 16.7 1
Symplocos uniflora 8.3 0.1725 16.7 1 33.3 0.1767 16.7 7.5
Calyptranthes concinna 8.3 0.1434 16.7 1 16.7 0.0590 16.7 4.2
Cinnamomum amoenum 8.3 0.1226 16.7 0.9
Lamanonia ternata 8.3 0.117 16.7 0.9
Ocotea corymbosa 8.3 0.0998 16.7 0.9
Sebastiania brasiliensis 8.3 0.0722 16.7 0.9 33.3 0.1460 16.7 7.0
Casearia sylvestris 8.3 0.0637 16.7 0.9
Gochnatia polymorpha 8.3 0.0597 16.7 0.9
Miconia cinerascens 16.7 0.052 16.7 4.1
Myrcianthes gigantea 33.3 0.1599 33.3 9.0
TOTAL 1008.3 48.283 950 100 416.7 2.0004 300 100

AD: absolute density (individuals.ha-1); ADo: absolute dominance (m2.ha-1); AF: absolute frequency (%); VI: value of importance (%); Class I (DBH ≥ 30 cm); Class II (15 ≤ DBH < 30 cm).

The species present in the riparian forest with flat topography (G1) that showed the highest values of importance were: Podocarpus lambertii (21.6%), Eugenia uruguayensis (13.5%), Araucaria angustifolia (9.3%) and Ilex brevicuspis (7.6%), representing 52% of the group’s horizontal structure (Table 2). Of these, Podocarpus lambertii and Ilex brevicuspis were not represented in Class II (15 ≤ DBH < 30 cm), while Eugenia uruguayensis and Araucaria angustifolia were found in both studied classes, thus suggesting the greater possibility of preserving these species in the environment. In this group, it should also be noted that Casearia decandra, Myrciaria delicatula, Myrceugenia cucullata and Roupala brasiliensis were also found represented in both classes, with their propagation being favored in this environment.

For Class I (DBH ≥ 30 cm) of the hillside forest (G2), it was found the occurrence of 900 individuals.ha-1 belonging to 18 species, 17 genera and 11 botanical families (Table 3). The species that presented the highest value of importance were Araucaria angustifolia (20.6%), Gymnanthes klotzschiana (19.6%), Lithraea brasiliensis (14.1%) and Podocarpus lambertii (9,6%), representing 63.9% of the forest structure. Of these species, except for Araucaria angustifolia, all the others are present in both evaluated classes, indicating the possibility of their propagation over time.

Table 3 Phytosociological parameters of the species belonging to Group 2, considering Class I and Class II in a Mixed Ombrophilous Forest fragment. São Francisco de Paula, RS, Brazil. 

SCIENTIFIC NAME CLASS I CLASS II
AD ADo AF VI AD ADo AF VI
Araucaria angustifolia 128.6 13.3374 85.7 20.6
Gymnanthes klotzschiana 292.9 6.0145 71.4 19.6 257.1 1.1212 28.6 27.8
Lithraea brasiliensis 107.1 6.0347 100.0 14.1 28.6 0.1278 28.6 5.9
Podocarpus lambertii 85.7 3.4423 71.4 9.6 28.6 0.1484 28.6 6.1
Ilex brevicuspis 28.6 2.0645 42.9 4.9 14.3 0.0604 14.3 2.9
Myrcianthes gigantea 42.9 0.6563 57.1 4.9 14.3 0.0891 14.3 3.2
Eugenia uruguayensis 50.0 0.8867 42.9 4.7 57.1 0.2859 28.6 9.0
Myrceugenia cucullata 35.7 0.8953 42.9 4.2 100.0 0.7281 57.1 18.9
Ocotea pulchella 28.6 0.5401 42.9 3.6 14.3 0.0555 14.3 2.9
Myrsine coriacea 14.3 0.8684 28.6 2.7
Myrciaria delicatula 28.6 0.4493 14.3 2.1 14.3 0.0360 14.3 2.7
Quillaja brasiliensis 7.1 1.2467 14.3 2.0 14.3 0.2718 14.3 5.1
Prunus myrtifolia 14.3 0.2909 14.3 1.5
Cinnamomum amoenum 7.1 0.3869 14.3 1.3
Ilex dumosa 7.1 0.3396 14.3 1.2
Allophylus edulis 7.1 0.1365 14.3 1.1
Blepharocalyx salicifolius 7.1 0.0909 14.3 1.0
Maytenus aquifolia 7.1 0.0529 14.3 1.0
Acca sellowiana 42.9 0.1628 14.3 5.4
Casearia decandra 14.3 0.0860 14.3 3.2
Miconia cinerascens 28.6 0.0636 14.3 3.7
Schinus lentiscifolia 14.3 0.0745 14.3 3.1
TOTAL 900.0 37.7339 700.0 100.0 642.9 3.3111 300.0 100.0

AD: absolute density (individuals.ha-1); ADo: absolute dominance (m2.ha-1); AF: absolute frequency (%); VI: value of importance (%); Class I (DBH ≥ 30 cm); Class II (15 ≤ DBH < 30 cm).

The riparian forest with flat topography (G1) had a basal area expressed by absolute total dominance (ADo) of 48.28 m2.ha-1 (Table 2), while it was ADo = 37.73 m2.ha-1 for the hillside riparian forest (G2) (Table 3). The highest values found for G1 in relation to G2 regarding the number of species and number of individuals indicate a structural difference of these two environments, probably due to the greater slope and less influence of the water table on G2. On the other hand, even though G2 is located on higher ground, it clearly reflects the condition of a riparian forest considering the predominance of Gymnanthes klotzschiana, a typical species of these environments. The soil of the studied forest area was classified by Rorato et al. (2015) as Litholic Neosols. This soil class is characterized by recent pedogenesis and its occurrence on steep slopes (Streck et al., 2008), and it imposes root growth restrictions due to low depth and low nutritional content, thereby experiencing consequent colonization by plant species, as can be evidenced by differences in the phytosociological parameters of Classes I and II in both clusters.

Tables 2 and 3 show that species belonging to Class I with the highest value of importance are common for both groups, indicating the similarity of the floristic composition between these environments. Regarding Class II, we can verify that only 10 of the 24 species present in Class I are represented in this class in G1 (Table 2).

We can probably consider that the greater shading within the vegetation grouping characterized as hillside riparian forest (G2), due to its slope in relation to facing south and associated with the canopy cover, has created a better condition for the natural regeneration of Podocarpus lambertii in this environment than in that of riparian forest with flat topography (G1) (Table 3). On the other hand, Araucaria angustifolia had a higher natural regeneration in G1 due to the more heliophilous character in that region (Table 2).

The CCA results indicated the influence of the chemical attributes (Al, OM, S, Ca, Cu, m%) on formation of the groups (Figure 3). The eigenvalues of 0.431 for the 1st axis and of 0.285 for the 2nd axis were indicated in analyzing the distribution of plots and species in relation to environmental factors for the arboreal vegetation belonging to Class I (DBH ≥ 30 cm). Monte Carlo permutation test was significant, presenting an error probability of 0.004, thus indicating precision in the calculation of the correlations between the analyzed matrices.

Figure 3 Ordination diagram produced by Canonical Correspondence Analysis for the first two axes for groups analyzed with the environmental variables in a Mixed Ombrophilous Forest fragment. São Francisco de Paula, RS, Brazil. GR: Group; Axis: axes; P: Plots; Al: Aluminum; m: Aluminum saturation; Cu: Copper; Ca: Calcium; OM: organic matter; S: Sulfur. 

All the analyzed chemical attributes showed higher correlation with the first ordering axis. Figure 3 shows the “biplot” ordination diagram obtained as a result of the CCA with the distribution of environmental variables in relation to the phytosociological groups.

Despite presenting high sulfur (S) levels for both groups (10.1 mg.dm-3 for the riparian forest with flat topography (G1) and 12.1 mg.dm-3 for the hillside riparian forest (G2)) (Table 4), its higher values in G2 represent an explanatory variable for classifying this group. Regarding organic matter, this variable reached an average of 8.7% in G2, higher than that of G1 (5.8%) (Table 4). These are interpreted as high values (SBCS, 2004), being the consequence of a greater humidity in the soil, presence of basaltic material, altitude and cold climate, resulting in slow decomposition of organic matter, and consequently acidic pH (5.4) (Table 4).

Table 4 Soil chemical attributes for phytosociological groups in Mixed Ombrophilous Forest Fragment. São Francisco de Paula, RS, Brazil. 

Attributes Groups
Riparian forest with flat topography Hillside Riparian forest
Active acidity (water pH) 4.8 5.4
Potential acidity (H+Al) (cmolc.dm-3) 17.5 9.6
Aluminum (cmolc.dm-3) 3.9 1.3
Calcium (cmolc.dm-3) 2.9 9.5
Magnesium (cmolc.dm-3) 1.3 2.5
Potassium (mg.dm-3) 77.0 90.0
Phosphorus (mg.dm-3) 3.0 3.5
Sulfur (mg.dm-3) 10.1 12.1
Copper (mg.dm-3) 3.5 2.5
Zinc (mg.dm-3) 2.6 4.7
Boron (mg.dm-3) 0.5 0.5
Organic matter (%) 5.8 8.7
Saturation by aluminum (m%) 49.5 13.9
Base saturation (V%) 26.3 56.6
Effect CEC (cmolc.dm-3) 8.2 13.6
pH7 CEC (cmolc.dm-3) 21.8 21.9

Phosphorus extracted by Mehlich method; Effect CEC: Effective cation exchange capacity; pH7 CEC: Potential cation exchange capacity.

The diagram of Figure 3 shows that the soil chemical variables that most correlated the riparian forest with flat topography (G1) were Al, m% and Cu. In this group, the concentration of exchangeable aluminum in the soil (Al3+) was 3.9 cmolc.dm-3; higher than the one found in G2 (1.3 cmolc.dm-3), which can be attributed to the greater weathering of this environment and higher soil pH values.

The variables S, Ca and MO showed correlation with the hillside riparian forest (G2). Ca had the highest correlation of these, with mean values of 9.5 cmolc.dm-3 for this group (Table 4), which is considered a high value according to Sociedade Brasileira de Ciência do Solo (SBCS, 2004).

The correlation of saturation by aluminum (m%) and of copper with the riparian forest with flat topography (G1) may be related to higher concentrations of OM, since Cu is retained in the organic matter, forming stable complexes that play an important role in the mobility and availability of this micronutrient to plants (Abreu et al., 2007).

Therefore, it can be observed that specific environmental conditions in the studied riparian forest fragment have an influence in forming ecological niches, which despite being represented by similar species, occur in a differentiated manner in terms of density, dominance and frequency. A clear example was the Araucaria angustifolia, which stood out in the environment with less influence of the water table.

4. CONCLUSIONS

In the studied riparian forest fragment, there are two clusters of arboreal components, which despite having similarity in the floristic composition, presented differences in the vegetation structure due to topographic and consequently edaphic aspects.

Soil chemical attributes are indicators of ecological niches that even when represented by similar species, occur in different manners in terms of density, dominance and frequency.

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Received: April 02, 2014; Accepted: November 16, 2017

CORRESPONDENCE TO Mônica Brucker Kelling Universidade Federal de Santa Maria (UFSM), Av. Roraima, 1000, CEP 97105-900, Cidade Universitária, Camobi, Santa Maria, RS, Brazil e-mail: mbk@politecnico.ufsm.br

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