Mudanças florístico-estruturais e variação do estoque de carbono em formação de vereda

Abstract

Veredas are formations of the Cerrado biome, characterized by herbaceous grasses and shrubby trees (Ribeiro and Walter 2008). Tropical communities, like veredas, constitute a mosaic of stages, with arrangements of species and individuals in different phases of regeneration, and subject to more or less periodic disturbances (Arruda et al. 2015; Reis et al. 2017). Thus, based on information about the vegetation in vereda areas, it is possible to assess changes in its horizontal and vertical structure, based on mortality, recruitment, and growth rates of its individuals, and also based on the natural regeneration of its vegetation (Felfili 1995; Braga and Rezende 2007; Branco et al. 2019). Due to the hydrological, social, and ecological importance of veredas, studies are needed to understand the temporal changes in vegetation in veredas with different levels of conservation. Furthermore, these are Permanent Preservation Areas, responsible for the perennial nature of the watercourses in the hydrographic basins and for assisting in the permanence of the drainage network (Augustin et al. 2009; Neves 2015; Nunes et al. 2022). In this sense, this work aims to evaluate the temporal changes in the plant community in the different habitats of the vereda (a type of wetland), over a period of five years. We evaluated the structure (importance value and basal area) and dynamics of the shrub-tree vegetation (mortality, recruitment, loss and gain) in the different environments of the veredas studied over a five-year interval; we evaluated the change in species composition between the two periods in the different habitats of the veredas; we evaluated how the aboveground biomass of the sampled woody species (AGWB – Mg) and the carbon stock vary between the periods and habitats of the sampled veredas (Almescla - more preserved and Peruaçu - advanced stage of drying). Data were collected in two Conservation Units: the Rio Pandeiros Environmental Protection Area (APA Rio Pandeiros) and the Veredas do Peruaçu State Park (PEVP). The Peruaçu stream shows advanced drying, with loss of springs and retraction of the humid portion. Furthermore, according to residents' reports and observations, the stream has burned sections, with high tree mortality leading to a change in the landscape. This is evidenced by changes in vegetation composition at various points along its course and the high invasion of Cerrado species. The Almescla stream, on the other hand, is in an intermediate stage of drying, still possessing a constant water table cycle (Nunes et al. 2022), but already shows the occurrence of species from other Cerrado formations in its open area. For sampling the plant community in the studied areas (Almescla stream and Peruaçu stream), the plot method was used (Mueller-Dombois and Ellenberg, 1974). For a better characterization of the sampled wetlands, these are defined in two zones that were delimited due to topography and soil drainage: hygrophilous forest (FH) and open area (AB), where 68 plots of 20x20 m were established in the Almescla wetland (30 in FH and 38 in AB) and 27 transects in the Peruaçu wetland (30 in FH and 27 in AB). During the second inventory in 2022, survivors were measured again, new individuals were added, and dead individuals were recorded. Species richness showed little variation between the habitats of the Almescla wetland, with the hygrophilous forest showing the highest number of tree and shrub species in the first sampling period compared to the open area habitats. In total, counting the species from both environments, 54 species were sampled in 2017 and 60 species in 2022. Regarding beta diversity, in the Almescla wetland, both open areas and hygrophilous forests showed high values, mainly due to species turnover, regardless of the sampling period. However, beta diversity did not differ between the years evaluated for the entire community or for the environments separately. For the Peruaçu wetland, turnover was also the main component of variation in species composition during the sampled periods. Comparing all environments of the Peruaçu wetland between the two sampled periods, turnover was relatively higher in 2017 compared to 2022, but did not show a difference between the periods for the environments evaluated separately. Regarding aboveground woody biomass (AGWB), comparing the two wetlands, the Almescla wetland had higher AGWB values ​​compared to the Peruaçu wetland in both sampling periods. Regarding the maintenance and reduction of carbon stock in the studied wetlands, the Almescla wetland had higher values ​​(2017: x̅ = 0.56, t = 2.44; p = 0.01; 2018: x̅ = 0.54, t = 4.06; p < 0.00001) compared to the Peruaçu wetland (2017: x̅ = 0.41, t = 2.44; p = 0.01; 2018: x̅ = 0.36, t = 4.06; p < 0.00001) in both sampling periods. These differences were also significant.