How environmental factors condition natural regeneration in the altitudinal gradient of a montane rainforest

The response of plant species to the variation in abiotic factors affects the regeneration capacity and, consequently, the structure of the forest community. This study aims to describe the structure of the regenerating stratum in a Brazilian montane rainforest and investigate its relationship with environmental and spatial variables along an altitudinal gradient. Data on the height and diameter at soil height of regenerating individuals and environmental variables were collected from 28 sample units, distributed in seven altitudinal sites. To understand the spatial influence on species distribution, spatial variables (MEMs - Moran’s Eigenvector Maps) were created based on geographic coordinates. Phytosociological parameters were calculated by species. Floristic similarity between the altitudinal quota was determined by the Bray-Curtis index (UPGMA), and the species that characterize each group were determined by the Indicator Species Analysis. Redundancy Analysis (RDA) was performed, and generalized linear models were adjusted to verify the influence of environmental and spatial factors on regenerating vegetation. The species Palicourea sessilis had the highest Importance Value in the regenerating community. Two floristic groups were formed: the highest sites (1420 to 1550 m a.s.l.) were floristically more similar to each other (Group 1) than to the sites in the 1112 to 1391 m elevation range (Group 2). Overall, 11 species were indicators of Group 1 and only one of Group 2. Finally, a pattern of species substitution was verified as a function of abiotic factors. The first two axes of the RDA explained 51.02% of the variation in the floristic composition of the regenerating community. Natural regeneration demonstrated environmental preferences, being influenced by luminosity, abundance in adult components, calcium and sodium contents, plant litter accumulation, altitude, and the spatial structure of the environment. Altitude did not seem to influence the pattern of abundance or richness of regenerating species.