Natural regeneration as an indicator of ecological restoration by applied nucleation and passive restoration

Abstract

Passive restoration and applied nucleation are important strategies for large-scale gains and cost reduction in ecological restoration projects. Passive restoration uses the natural regeneration potential while applied nucleation recreates microhabitats, which facilitates ecological succession. In this study, we assessed floristic composition, structure and functional groups as ecological indicators to compare passive restoration (fenced site 12 year ago), applied nucleation (7 years of dense seedling planting) and riparian forest. The study was carried out in a Seasonal Semi-deciduous Forest region in the Pampa biome, in the South of Brazil. We measured and identified all shrub and tree individuals greater than 30 cm in height. Analysis of variance (ANOVA) followed by the Tukey test (p < .05) was performed to compare composition (richness, abundance, diversity and evenness), structure (average height, maximum height, canopy cover, soil cover, leaf litter depth) and functional group variables (dispersion syndrome and shade tolerance). Riparian forest showed greater richness and diversity. Passive restoration and applied nucleation did not differ statistically in richness, abundance, maximum or average height, or for zoochoric species and zoochoric individual indicators. The leaf litter depth was statistically higher in the riparian forest. The applied nucleation presented a canopy cover similar to riparian forest, demonstrating ability to form habitats which are favorable to ecological succession. We can conclude that passive and applied nucleation restorations have been occurring in a slow process. This is the natural condition of the ecological succession in the Pampa biome, which is probably due to the subtropical climate. Although we could not verify the facilitation effect by functional groups in applied nucleation and expansion of the nuclei size, the floristic composition, diversity, canopy cover and leaf litter depth indicators suggest an acceleration in the ecological succession process. Long-term monitoring should be considered to assess the dynamics of ecological restoration in the subtropical region of Brazil.