Ecology and management of the natural resources of Roraima´s Savanna

The study was carried out in 20 permanent plots distributed in two research modules of the Program for Biodiversity Research (PPBio; https://ppbio.inpa.gov.br), managed by the Brazilian government, by means of the Ministry of Science, Technology and Innovation. Both modules are located in the municipality of Boa Vista, Roraima (Fig. 1):

Figure 1.  

Location of the two PPBio modules studied in the Roraima’s savanna (lavrado), northern Brazilian Amazon.

(i) Campus do Cauamé, Monte Cristo region (MC): belongs to the Federal University of Roraima - UFRR (498 ha) and is located at ~15 km north of the city of Boa Vista (02°38’07”N to 02°40’11”N / 60°49’25”W to 60°52’28”W). It has 12 permanent plots (10 of which were randomly selected for this study). The relief of the study area is characterized as plan to wavy, due to its proximity to the Apoteri Formation (Benedetti et al. 2011). The vegetation of the area is defined as a mosaic of shrubby savanna (Campo Seco in Brazil) with savanna park-land (Savana Parque in Brazil), following the Brazilian vegetation classification system (Brazil-IBGE 2012).

(ii) Campo Experimental Água Boa (AB): belongs to the Brazilian Enterprise for Agricultural and Ranching Research - Embrapa Roraima (616 ha). It is located at ~36 km south of the city of Boa Vista (02°51’49”N to 02°53’06”N / 60°44’14”W to 60°42’27”W). It has 22 permanent plots (10 of which were randomly selected for this study). The vegetation of the area is typically a mosaic between shrubby savanna with wet grassland, interspersed with small patches of savanna park-land (Araújo and Barbosa 2007, Barbosa et al. 2007b).

Both modules are within the climatic type Aw, according to the Köppen classification, and present approximately the same average annual rainfall as that of the city of Boa Vista (~1,650 mm), with dry period defined between December to March, and the peak of the rainy season between May to August (Barbosa 1997).

The study was supported by institutional project PPI-INPA (PRJ 015/122). MAMA was supported for a grant provided by CAPES, and RIB received CNPq productivity fellowship (Proc. 303081 / 2011-2). AESR and ISM were supported by the project "Riqueza e diversidade de Poaceae e sua relação com variáveis ambientais em áreas de savanas da Amazônia” (Museu Paraense Emílio Goeldi, MPEG - Belém/PA).

(i) Plots Structure: the 20 permanent plots are long (250 m in length), and they are oriented by the isoclines measured at the initial point of each of them (Fig. 2). This configuration is standard in PPBio and aims to minimize the variation in the abiotic factors that affect the different biological communities investigated in many studies (Magnusson et al. 2005, Magnusson et al. 2013, Pezzini et al. 2012). The floristic inventory was divided according to the life forms (herbaceous, sub-shrubs, shrubs and trees), which synthesizes the forms of life used by the international convention (Raunkiaer 1934) used in many other works in different areas of the Earth (Perrino et al. 2014, Silva and Batalha 2008). Herbaceous and sub-shrub plants were surveyed in a 2 m wide strip (1 m on each side of the plot central line), while tree and shrub plants were surveyed in a range of 10 m (5 m of each side of the plot central line) (Barbosa et al. 2010, Cavalcante et al. 2014).

Figure 2.  

Schematic representation of the sample unit (permanent plot) for the sampling of herbaceous and sub-shrub (2 x 250 m) and tree and shrub (10 x 250 m) plants in the PPBio-Roraima’s savanna modules.

(ii) Floristic inventory: floristic survey and collection of the botanical material were carried out between October 2012 to February 2013 in daily excursions between the end of the rainy season and the beginning of the dry season. All species were numbered and photographed. Excicates were prepared and deposited in the Herbarium of the Federal University of Roraima (UFRR - Boa Vista/RR). Unidentified specimens were subjected to the evaluation of specialists from the Herbaria of the Museu Paraense Emílio Goeldi (MPEG - Belém/PA), and from the Museu Integrado de Roraima (MIRR - Boa Vista/RR) for comparison with other materials.

(iii) Plant coverage: estimate of plants coverage was carried out by the Point Quadrat Method (Bullock 2006), according to the adaptations of Costa et al. (2005) and Magnusson et al. (2008). This method consisted by using a 2 mm thick and 1 meter height metal rod. The rod was vertically plotted in the soil along the transect line (250 m) that defines each plot. Each rod plotting was made at intervals of 50 cm throughout the permanent plot, totaling 500 points per plot.

(iv) Hydro-edaphic variables: fertility (sum of bases, Al, pH, P, Fe, Mn, Zn) and soil texture (% sand, % silt, % clay) data at 0-20 cm depth were obtained by previous samplings carried out in both modules by Pimentel and Baccaro (2011b) (UFRR / Cauamé) and Pimentel and Baccaro (2011a) (Embrapa / Água Boa). Each plot was classified according to the soil type (Gleysol, Oxisol, Ultisol) and to drainage class (well and poorly drained), following the Brazilian Soil Classification System (EMBRAPA-SOLOS 2006).

(v) Data Analysis: plots were clustered by the Ward Method using the coverage (%) of the plant species as a proxy of floristic similarity (correlation was used as similarity algorithm). Each group was defined as a specific phytophysiognomic type characterized by the soil type, drainage class, species composition, richness (S = number of species) and coverage (%) by life form. Plots were arranged using the multivariate NMDS technique (Non-metric Multidimensional Scaling) to identify the variables that better explain the species distribution and the organization of the phytophysiognomic structure. For this, the scores of Axis 1 (dependent variable) of the analysis were correlated with the environmental variables by simple linear regressions. All statistical analyses were performed using the R software (R Core Team 2016).

This study was carried out in two PPBio savanna modules located in the municipality of Boa Vista, Roraima, to the north of the Brazilian Amazon: MC - Campus do Cauamé, Monte Cristo region (498 ha); 02°38’07”N to 02°40’11”N / 60°49’25”W to 60°52’28”W, and AB – Campo Experimental Água Boa (616 ha); 02°51’49”N to 02°53’06”N / 60°44’14”W to 60°42’27”W.

Description: The scientific names of the species identified in the study were corrected by the search systems of the (i) Virtual Herbarium of the REFLORA Project (REFLORA – Brazilian Plants: Historic Rescue and Virtual Herbarium fo Knowledge and Conservation of the Brazilian Flora - http://reflora.jbrj.gov.br/reflora/PrincipalUC/PrincipalUC.do?lingua=pt), and (ii) The Plant List (http://www.theplantlist.org/). The families circumscription followed the APG-III (2009) classification.

We report 128 plant species (10,934 individuals) classified in 34 botanical families (Table 1). The species of higher richness were Cyperaceae (26 spp.; 20.3%), Poaceae (21; 16.4%), and Fabaceae (20; 15.6%). Only 11 species were identified to genus level only, and eight to family level. Of the total species observed, 61.7% (79 spp.) were herbaceous, 20.3% (26) were sub-shrubs, 8.6% (11) were shrubs, and 9.4% (12) were trees. Cluster analysis identified three distinct phytophysionomic clusters (habitats) according to the soil type and drainage class: (i) SAV-1, characterized by a mosaic of savanna park-land (Savana Parque in Brazil) with shrubby savanna (Campo Sujo in Brazil), prevailing well-drained red soil classes as Ultisol and Oxisol (n=7); (ii) SAV-2, shrubby savanna typically established in well-drained yellow Oxisol (n=8); (iii) SAV-3, wet grassland (Campo Limpo Úmido in Brazil) occurring in poorly drained soils (typically hydromorphic - Gleysol), where plots undergo seasonal flooding for 1 to 4 months every year (n=5). The highest species richness (S=90) was observed in SAV-1, followed by SAV-2 (71) and SAV-3 (61). Twenty-five species (generalists) occurred in the three groups, with special emphasis on the families Poaceae (T. spicatus, P. carinatum, A. aureus) and Cyperaceae (R. barbata and B. capillaris), both highly abundant and distributed in the three phytophysiognomic sets.

Coverage (%) with herbaceous plants (live + dead) was dominant in all the three groups (> 83%), with almost absolute predominance (~96%) in wet grasslands habitats (SAV-3) (Table 2). Coverage (%) of woody plants was higher in SAV-1 (2.5%) and SAV-2 (1.3%), where plots are well drained with no seasonal flooding problems. These two groups presented the highest concentration of exposed soil (13-14%), indicating lower densification among plants, despite they are richer and presenting higher tree and shrub coverage.

Linear regression analysis indicated that pH (p < 0.003) and exchangeable Al (p < 0.003) are the edaphic variables that best explain the distribution of species within the three sets of plots (Fig. 3). In general, shrubby savanna (SAV-2) and mosaic of savanna park-land with shrubby savanna (SAV-1) are well drained habitats, with lower Al toxicity (0.306-0.391 meq%), lower acidity (pH = 5.3-5.6), and higher sum of bases (Ca+Mg+K = 0.25 to 0.43 cmolc kg). These characteristics indicate environments with lower hydro-edaphic restrictions associated with higher species richness. Conversely, wet grasslands (SAV-3) undergo seasonal flooding (poorly drained), have higher Al toxicity (~0.512 meq%), higher acidity (pH ~4.9), and lower sum of bases (~0.14 cmolc kg), resulting in environments with higher hydro-edaphic restrictions and lower species richness.

Figure 3.  

Linear regression indicating the correlation between the groups of habitats formed by floristic similarity of the plots (Axis 1 = scores NMDS 1) and the variables pH (H₂O; Y = -1.4631 + 0.2747×X; R2 = 0.3591) and Aluminum (meq%; Y = 0.25472 - 0.65102×X; R2 = 0.3534). Groups of habitat: 1 – mosaic of savanna park-land with shrubby savanna / well drained (SAV-1); 2 – shrubby savanna / well drained (SAV-2); 3 – wet grassland / poorly drained (SAV-3).

Linear regression analysis also indicated that the phytophysionomical structure of habitats is partially explained by diversification of life forms and hydro-edaphic restriction. Predominance of herbaceous plants was significantly related (p < 0.005) to the habitats with lower richness and higher hydro-edaphic restriction (e.g., wet grassland) (Fig. 4). On the other hand, the coverage of woody plants (sub-shrub + shrub + tree) indicates to be related (p < 0.026) to habitats with greater diversification of life form and less hydro-edaphic restriction (shrubby savanna, and mosaic of savanna park-land with shrubby savanna).

Figure 4.  

Linear regression indicating the correlation between the groups of habitats formed by the floristic similarity of the plots (Axis 1 = scores NMDS 1) and the coverage (%) of herbaceous plants (live + dead; Y = 0.873429 – 0.009996×X; R2= 0.3199) and woody plants (sub-shrub + shrub + tree; Y = -0.07886 + 0.05336×X; R2=0.2042). Groups of habitat: 1 – mosaic of savanna park-land with shrubby savanna / well drained (SAV-1); 2 – shrubby savanna / well drained (SAV-2); 3 – wet grassland / poorly drained (SAV-3).

Results suggest that the most restrictive savanna habitats (wet grasslands) are characterized by phytophysiognomies with less structural complexity in relation to the habitats conditioned by less restrictive hydro-edaphic factors (shrubby savanna, and mosaic of savanna park-land with shrubby savanna; both well drained). This effect directly influences the composition and life form of the species that inhabit the different habitats studied in this research (Table 3). In the plots of less hydro-edaphic restriction, the species T. spicatus (Poaceae) was predominant (24-54%), while P. carinatum (Poaceae) was predominant in wet grassaland (~18%). Similarly, the tree species with the highest coverage (%) were observed in the mosaic of savanna park-land with shrubby savanna (C. americana - Dilleniaceae, 2.7%) and in shrubby savanna on Yellow Oxisol (B. crassifolia - Malpighiaceae, 1.1%).). In the habitat formed by plots with seasonal flooding (wet grassland), only rare woody sub-shrubs and shrubs individuals were observed.

The results indicate that even with a small number of sample units (20) and study sites (2), Roraima’s savanna presents habitats with distinct floristic and structural characteristics, suggesting an ecosystem with high beta diversity associated with environmental heterogeneity. High beta-diversity was favored by the large number of species with low coverage (few individuals), which seems to be common in the Amazonian savanna (Magnusson et al. 2008). Although the habitats investigated in this study have common floristic elements, the hydro-edaphic factors determined the occurrence and the coverage of groups of species, providing different proportions between life forms in the different phytophysiognomic structures.

The present study highlights the environmental heterogeneity and the biological importance of Roraima’s savanna regarding the conservation of natural resources from the Amazon. In addition, it points out the need for greater investment in floristic inventories associated with greater diversification of sites, since this entire ecosystem has been rapidly modified by agribusiness (e.g. Aguiar et al. 2014). Further studies on Roraima’s “lavrado” are necessary in order to broaden the discussion about the demand for the creation of environmental protection areas as a public policy for the conservation of the largest savanna area in the Amazon (Pinto et al. 2008, Pinto et al. 2014).

These data can be freely used, provided their source is cited.