Abstract
ABSTRACT Understanding the dynamics of forest species occupation in savanna and grasslands environments allows us to assess how forest expansion operates over time. For eleven years, the population dynamics of Tachigali rubiginosa (Mart. ex. Tul.) Oliveira-Filho was registered to evaluate the occupation strategy of this species in the ecotone between forest (Mata de Galeria) and grassland (Campo Sujo), located within the Capetinga stream basin, at Fazenda Água Limpa, Federal District. This area has been protected from wildfires since 1987. This study allocated thirty-one transects of 5 m x 100 m perpendicularly to the Capetinga stream, covering forest and grassland environments. The measurements were taken from adult trees (DBH ≥ 5 cm), young trees (height > 1 m and DBH < 5 cm) and seedlings (height ≤ 1 m and DBH < 5 cm). The results indicated that, in the studied period, the population of T. rubiginosa increased from 179.5 to 262.8 ind / ha. In 2007, of the total of 280 individuals in 1.56 ha, 96 of them were in the forest (0.22 ha), 103 in the ecotone (0.16 ha), and 81 in the grassland (1.18 ha). In 2018, this proportion changed when the number of individuals decreased in the forest (83 individuals), while the number increased in the ecotone (135 individuals) and in the grassland (194 individuals). In 2007, the young trees dominated with 71% of the total, followed by the adults trees (28.5%) and the seedlings (20.7%). In 2018, the young trees represented most individuals (39.2%), but there was a balance between the three size categories, as the seedlings represented 30.0% and adults trees 30.7%. Over the period of the study, there was an increase in the population of T. rubiginosa, especially of young individuals, which indicates persistence over time and an expansion of this forest species into grassland environments.
Highlights
Changes in the populations of plant communities occur over time due to the joint action of limiting factors that affect their density, spatial distribution, mortality, and recruitment, such as space limitations, competition, and climatic conditions, in addition to other factors
The results indicated that, in the studied period, the population of T. rubiginosa increased from 179.5 to 262.8 ind / ha
Over the period of the study, there was an increase in the population of T. rubiginosa, especially of young individuals, which indicates persistence over time and an expansion of this forest species into grassland environments
Summary
Changes in the populations of plant communities occur over time due to the joint action of limiting factors that affect their density, spatial distribution, mortality, and recruitment, such as space limitations, competition, and climatic conditions, in addition to other factors. The variation in population density depends on the magnitude of fluctuation in the environment, the inherent stability of the population, and the ecological characteristics of the species (Ricklefs and Schluter, 1993). Fluctuations in natural populations are practically unpredictable since individuals are affected by external factors (soil pH, temperature), which are correlated with the characteristics of a given ecosystem (Peroni and Hernández, 2011). The Cerrado biome has great biotic and abiotic spatial and temporal heterogeneity. These characteristics provide different environmental conditions that native species require in order to utilize available environmental resources and to minimize limiting factors (Ribeiro and Walter, 2008). Among the physiognomies that make up the different formations mentioned, Mata de Galeria and Campo Sujo represent quite distinct physiognomies when considering the tree density and the depth of the water table as examples (Felfili et al, 1998; Ribeiro and Walter, 2008)
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