Chuva de sementes e dinâmica da serapilheira em uma topossequência de floresta es tacional decidual

Abstract

The composition and distribution of flora in Seasonal Decid- uous Forests are heterogeneous. Understanding its dynamics in areas of floristic transi- tions between biomes are gaps in the knowledge to be filled. The aim of this study was to determine how the different topographic (slope and soil) and environmental (temperature and precipitation) variables influence the spatial dispersion patterns of native species in an area of the Serra da Bodoquena National Park (PNSB), MS, under the potential the mechanisms of natural regeneration, through the floristic composition of the seed rain and dynamics of the litter. In chapter 1, the composition of the seed rain was evaluated in a section of the PNSB with different altimetric variables (base, slope and top) where 15 col- lectors (1x1m) were installed per elevation level. Samples were collected every 30 days for 18 months. The evaluated patterns of seed rain were: density, life form, dispersion syndrome, seed size classes; and environmental variables. The Non-Metric Multidimen- sional Scaling (NMDS) was used to perform sorting between seed rain patterns and envi- ronmental and topographic variables. In chapter 2, it was estimated the monthly and an- nual litter productivity in each elevation, correlated with the environmental variables; a hollow square template (1 m2) was also used to collect the litter in the altimetric dimen- sions where it was evaluated: remaining dry mass, decomposition rates (k) and the half- life (t 1⁄2) at 30, 60, 90 , 120, 150 and 180 days after installation. Chemical analyzes of lit- ter and soil were also carried out. Statistically, the litter dynamics was represented by the analysis of the main components (PCA). In chapter 1, a total of 20,217 propagules were identified, belonging to 65 species and 30 families in the three altimetric levels, represent- ing 449.26 seeds / m2. Being the base holding most propagules (13,820 seeds). Of the 65 species found in the seed rain, 71% are arboreal, constituting zoochoric species (78%). Very small seeds were predominant and accounted for 53%. Our results indicate that there is heterogeneity in the floristic composition of the seed rain between the sampling sites in the toposequence, corroborating the hypothesis that the functional attributes of the seed rain are influenced by the topographic gradient in the PNSB. In chapter 2, the total litter production estimate was 1,447.28, t / ha-1. As for litter accumulation, the results obtained were 12,091 t / ha-1 (rainy season). For the dry season, the resultswere 12,980 t / ha-1, both in the rainy season and in the dry season, the base was the holder of the largest amount of litter. The decomposition constant (k) of litter in the period of 180 days at the base was 51.92%, slope 54.20% and top 53.06%. The average time to decompose 50% of the material was 190.86 days for the base, 204.04 for the slope and 253.27 days for the top. Corroborating the initial hypothesis, the results made it possible to infer that climatic seasonality, as well as the topographic gradient, has a strong influence on the dynamics of litter. This interaction is reflected in the characteristics of Deciduous Forests, which are heterogeneous ecosystems.