In the present study, forest ecosystems in the Atlantic Forest biome were analyzed under the hypothesis of significant differences, when comparing equivalent succession stages. The following reasons motivated this analysis:
- the main criteria that guide the decision between deforestation or protection of native vegetation consider the successional stage;
- currently, the indicators employed to classify the succession stage disregard the potential particularities of each ecosystem; and
- in case of confirmation of the analyzed hypothesis, this study should provide support for revising the classification guidelines.
The similarity between forest ecosystems in the initial stage of succession was already expected. Greater homogeneity at the beginning of regeneration is mainly associated with the dominance of a few species (Siminski et al., 2011; 2021).
However, as observed in the present study, as the succession moves towards greater diversity, biotic interactions lead to greater complexity and, hence to traits divergence between ecosystems (Vitória et al., 2019; Chazdon and Guariguata, 2016). In this sense, the present study results are in line with Pastório et al. (2020), who also verified the existence of great variability in several structural and compositional parameters when comparing different types of forests in the Atlantic Forest biome.
The influence of environmental variations on the ecosystems in the Atlantic Forest, such as weather conditions and topographical aspects, has been reported in several previous studies (Pastório et al., 2020; Higuchi et al., 2012; Klauberg et al., 2010; Budke et al., 2007; Roderjan et al., 2001).
Regarding weather conditions, the DOF and SDF regions have a subtropical climate, without a dry season and a hot summer (Cfa). In contrast, although its subtropical climate without a dry season, the MOF ecosystem is a place of temperate summer and severe winters with extreme frosts (Cfb) (Alvares et al., 2013). Consequently, the harshest conditions in MOF regions leads to the occurrence of more adapted species, such as Araucaria angustifolia, Dicksonia sellowiana, and Ocotea porosa (Gasper et al., 2013; Martins et al., 2012; Lingner et al., 2015).
Muscarella et al. (2020) highlight that topography affects abiotic conditions that consequently may influence the structure and dynamics of ecological communities. The MOF occurs in the central-west portion of the study area, ranging from 500 to 1,500 m altitude and extending towards the borders with Argentina (Siminski et al., 2021). The DOF is located below altitudes of 700 meters along the coastal region, with high temperatures, humidity values, and cumulated precipitation (Linger et al., 2015). The SDF is limited to the Uruguay River Basin, with altitudes ranging from 200 to 600 meters, and is characterized by the loss of foliage during periods of climatic seasonality (Gasper et al., 2015; Siminski et al., 2021).
Oliveira et al. (2021) describe DOF as one of the main typologies in southern Brazil, with a high diversity of species. The greater diversity found in the DOF is related to the fact that this forest ecosystem has about 80% of all species found in Santa Catarina, southern Brazil (Vibrans et al., 2010; Gasper et al., 2014). According to Roderjan et al. (2001), the lower diversity in FOM areas, mainly those in higher altitude areas, is due to the climatic severity that exerts selective pressure on the species.
Marked by a nebular environment with high relative humidity, the MOF constitutes an ecologically selective ecosystem because of the lower incidence of solar radiation and low temperatures, often associated with shallow soils and higher organic matter concentrations (Higuchi et al., 2012; Martins et al., 2012; Klauberg et al., 2010).
The number of species (S) in the DOF was statistically much higher (p < 0.001) than in other forest ecosystems. This finding agrees with previous studies, which found that the DOF has the highest number of species, including endemic and exclusive ones, and expressive occurrence of epiphytes and palm trees (Gasper et al., 2014).
Siminski et al. (2021) highlighted that the DOF region holds around 85% of all arboreal species in the study area. In contrast, there is no statistical difference (p-value > 0.05) between MOF and SDF regarding the successional regeneration stages. This similarity may arise from the number of species (about a third) encountered simultaneously in MOF and SDF areas, as discussed in Orihuela et al. (2015).
Regarding the DBH indicator, lower values are observed in DOF compared to SDF and MOF, especially in the advanced stage (p < 0.0001). MOF was the forest ecosystem with the highest DBH and BA/Ha values. In a particular portion, the dominant presence of Araucaria angustifolia in the MOF, a characteristic species of this formation, is highlighted as the main factor for this result since it presents one of the most significant volumetric growths (Cordeiro and Rodrigues, 2007; Herrera et al., 2009; Klauberg et al., 2010; Gasper et al., 2013).
Despite these Brazilian guidelines being criticized as low-effectiveness, especially for the reference values and limits to differentiate the stages properly (Siminski et al., 2013; Andreacci and Marenzi, 2017; Pastório et al. 2020), previous studies like Siminski et al. (2013) did not consider the potential differences between forest ecosystems. Therefore, studies were still necessary to strengthen evidence to verify the existence of such differences and the importance of considering them.