STRUCTURE AND DIVERSITY OF THE ARBOREAL COMPONENT IN CERRADO SENSU STRICTO IN NORTHERN MINAS GERAIS

Structure and diversity of the arboreal component in cerrado sensu stricto in northern Minas Gerais. Due to a rapid change in the land use in northern Minas Gerais State, southeastern Brazil, large amounts of cerrado have been converted into crops. There is little information about the structure and diversity of the remaining communities in the region. The present study aimed to characterize the structure of the tree vegetation in a cerrado sensu stricto area. We delimited thirty 20m x 20m plots and sampled tree individuals with diameter equal to or greater than 4.8 cm at 30 cm from the ground level (DGH30). We sampled a total of 2616 individuals of 76 species and 33 botanical families. The community showed a density of 2180 ind/ha and a basal area of 17.3 m/ha. Qualea grandiflora, Terminalia fagifolia, and Dimorphandra mollis showed high importance values. Standing dead individuals stood out in the community. The Shannon diversity index (3.10) and Pielou’s evenness (0.70) indicate that the community is in an intermediate stage of succession in comparison with others. Despite the signs of disturbance, the community still includes species of great social and economic importance for the local population. This community’s floristic and structural patterns can be used to reference extractive management, restoration, and conservation initiatives of other cerrado areas in the region.


INTRODUCTION
The Cerrado Biome covers more than 25% of the Brazilian territory, comprising 2,036 M km². However, 73% of its extension is already anthropized (INPE, 2018). This biome is likely to be modified entirely by 2030 if the occupation trends remain at an annual loss of 22 k km² (MACHADO et al., 2004). In the face of this threat, the Cerrado was elevated to the category of priority global "hotspot" for biodiversity conservation (MYERS et al., 2000;DURIGAN et al., 2011), not only due to the diversity it harbors but also because only 8.1% of its territory is under environmental protection in Brazil.
The northern Minas Gerais State stands out ecologically as a transition of three phytogeographic domains: Cerrado, Atlantic Forest, and Caatinga. After the inclusion of this region in the Superintendence for the Development of the Northeastern Region (SUDENE, acronym in Portuguese) operational area, there was a rapid change in the natural vegetation cover, with irrigated crops, industrialization, and reforestation projects for charcoal (ESPÍRITO SANTO et al., 2009). As soon as the SUDENE incentives were discontinued, many areas were abandoned, resulting in large tracts of degraded pastureland and remnants of native vegetation dominating FLORESTA, Curitiba, PR, v. 51, n. 1, p. 061-069, jan/mar 2021. Lima, P. M. et.al. ISSN eletrônico 1982 10.5380/rf.v51 i1. 67302 62 the landscape. However, the deforestation in the Cerrado persisted for many years. Between 2000 and 2015, suppression rates exceeded natural regeneration by twice. (ESPÍRITO SANTO et al., 2016). Approximately 42.4% of the original cerrado cover of the region has already been converted to human use. The deforestation rate of 2.8%/year surpassed that observed in the Amazon Basin (ESPÍRITO SANTO et al., 2016). This threat implies diversity loss and decreased ecosystem services, such as the water supply to a region with a marked water deficit.
Conservation policies and sustainable use of cerrado resources must be strengthened to minimize such losses. A central point of this issue is the knowledge of natural vegetation and its importance for traditional populations, whose subsistence and livelihood depend on available resources. . In this context, several studies on the structure and diversity of the arboreal component of the cerrado sensu stricto (hereafter s.s.) are available in the literature (NETTESHEIM, 2010). However, there is little information about the communities in northern Minas Gerais State (see NERI et al., 2007;COSTA et al., 2010;SANTOS et al., 2010). Thus, the present study aims to characterize the tree vegetation structure in the cerrado s.s. in northern Minas Gerais to generate support for conservation, restoration, and sustainable management strategies. Comparing this cerrado with those of other regions allows the implementation of similar restoration, conservation, and management practices (NETTESHEIM, 2010;PEREIRA et al., 2016).

Study area
The study was carried out in the municipality of Montes Claros, Minas Gerais State, southeastern Brazil in the Area of Experimentation and Training in Agroecology at the Alternative Agriculture Center (AEFA -CAA/NM, acronym in Portuguese), located at kilometer 35 of the highway BR 135 ( Figure 1). The study area corresponds to a remnant of cerrado s.s. with over 20 years of regeneration, totaling approximately 10 ha (16°25'33.54" S and 44°02'08.11" W). The prevailing climate is tropical savanna with dry winters and humid summers (Aw sensu Köppen).

Data collection
We sampled thirty 20 x 20 m (400 m²) plots systematically spaced by 10 m, totaling 1.2 ha. We sampled all tree individuals with a trunk diameter greater than 4.8cm, including dead standing trees. We took measurements at 30 cm from the ground level. (DGH30 ≥ 4.8). We used a measuring tape to measure diameters and a graduated stick to indicate tree height. We identified the species in the field or through the consultation of herbaria and specialized literature. Voucher material was deposited in the MCCA Herbarium of the Institute of Agricultural Sciences of the Federal University of Minas Gerais.

Data analysis
We calculated the tree component structure using the parameters: frequency, density, absolute and relative dominance, importance value (MORO; MARTINS, 2011), height, and abundance. We also calculated the Shannon diversity index (H ') and Pielou's evenness (J') (MAGURRAN, 2013). We used a script from Cristo and Higuch (2012) for these calculations. We plotted the rarefaction (interpolation) and prediction (extrapolation) curves to determine the sample sufficiency, simulating twice the sample of individuals (CHAO et al., 2014). We used the Hill number method (q = 0; species richness) and bootstrap to calculate the standard error with 1,000 randomizations in the iNEXT package (HSIEH et al., 2016). The data were processed using the R software (R CORE TEAM, 2017).

RESULTS
We sampled a total of 2,616 individuals of 76 species and 33 families ( Table 1). The average density and basal area were 2,181 ind/ha and 17.3 m 2 /ha, respectively. The rarefaction curve indicated sampling stability, with an increase of only 13% (10 species) if sampling was doubled ( Figure 2).  The most representative families were Fabaceae, with 19 species, Vochysiaceae (5), Myrtaceae (4), Apocynaceae (4), Malphiguiaceae (4), Bignoniaceae (3), Combretaceae (3), Nyctaginaceae (2), Malvaceae (2), Annonaceae (2), and Sapotaceae (2); other families showed one species each. The Shannon diversity index (H') was 3.10 nats/ind. This diversity is similar to those of other cerrado communities in the state, with values ranging from 3.1 to 4.12 nats/ind ( Table 2). The Pielou's evenness (J') was 0.70.   The five species with the highest importance values represented 53% of the total number of individuals, i.e., half of the total abundance. Qualea grandiflora stood out for occurring in all plots, showing an absolute density of 463 ind/ha (22% of the total) and a basal area of 4.05 m²/ha.
The high proportion of standing dead trees indicated disturbances in the community. They occurred in all plots and represented 16.28% of the relative density and 3.35 m²/ha of basal area, according to the highest IV (12% of the total). The diameter distribution curve (Figure 3) corroborates the disturbance premise, presenting an inverted "J" shape, with a predominance of diameters between 5 and 10 cm. The individual height ranged from one meter (Erythroxylum suberosum) to approximately 13 m (Hymenaea stigonocarpa), with an average of 4.36 m.

DISCUSSION
The structural and floristic patterns of the community analyzed portrays the current context of natural landscapes in northern Minas Gerais State, with a high deforestation rate and different succession levels (ESPÍRITO-SANTO et al., 2016). This community presents diversity and structure consistent with a certain disturbance level compared to other cerrado areas in the state, but it is at an advanced succession stage and with a flora compatible with other cerrado patches.
The predominance of Fabaceae and Vochysiaceae is evident in different cerrado communities ( Table 2). The appearance of Fabaceae as the richest family is common in savanna environments due to the wide plasticity and broad distribution of its species (FINGER;FINGER, 2015). The Shannon index showed an intermediate diversity level in the study area, with evidence of ecological dominance verified by evenness, which was lower than that of other studies (Table 2). Qualea grandiflora showed high importance in most surveys in Minas Gerais (seven out of eight articles surveyed) probably because this species accumulates aluminum and, therefore, its presence is favored in the acid soils of this phytogeographic domain (HARIDASAN, 2000). The dominance of standing dead trees in the community surpasses that of other studies in the state. Most of these individual trees corresponded to the species Senna canna and Eugenia punicifolia, with evidence of clonal reproduction at the site (SILVA; PINHEIRO, 2007). This finding shows a post-disturbance successional stage due to succession and the thickening of vegetation, as observed by Cardoso et al. (2009), who found a complete transformation of more open savanna formations into dense cerrado or cerradão after 18 years of disturbance. The inverted "J" shape found in the diameter classes corroborates the regeneration pattern observed (FINGER; FINGER, 2015).
As for phytosociological parameters, the density value (2.181 ind/ha) was higher than those of different studies in cerrado s.s. (ALVES et al., 2013), but lower than that of the cerrado s.s. of Senador Modestino (NERI et al., 2007). The density found is higher than that estimated for cerrado s.s. (between 664-1396 ind/ha) and compatible with cerradão (960-2082 ind/ha) (FELFILI et al., 1994). However, the criterion adopted in the present study (DGH ≥ 4.8cm) differs from that suggested for savanna physiognomies (DGH ≥ 3cm sensu MORO and MARTINS, 2011). Thus, the density in the present study may have been underestimated, with values close to those found by Neri et al., (2007) in cerrados of the region. Hence, we considered the cerrado s.s. studied here dense, distinguishing it from a cerradão by the presence of a grassy stratum and little canopy superimposition (EMBRAPA, 2019) Among the species found, we highlight Astronium fraxinifolium (Gonçalo-Alves), Copaifera langsdorffii (Pau-d'óleo), Plathymenia reticulata (Vinhático), Tabebuia aurea (Ipê), and Bowdichia virgilioides (Sucupira preta) due to their structural parameters and timber importance. Other tree species stood out due to their use in local gastronomy and commerce: Caryocar brasiliense (pequi), Byrsonima crassifolia (murici), Hancornia speciosa (mangabeira), and Hymenaea stigonocarpa (Jatobá). At last, some species provide secondary metabolites that can be extracted for medicinal use as antioxidants and anti-inflammatories: Dimorphandra mollis (Fava d'anta), Leptolobium dasycarpum (locally known as unha d'anta), Lafoensia pacari (Pacari), Stryphnodendron adstringens (barbatimão) . These species are important for extractivism and increase the potential for conservation and proper management of the area.

CONCLUSIONS
• We found clear evidence of disturbances in the community. Nevertheless, there was a high density of individuals and species with high economic and social importance for the local population. • This community's floristic and structural pattern can be used to reference extractive management initiatives for restoration and conservation of other cerrado areas in the region and selection of resistant species, such as Qualea grandiflora.