Structure of the herb stratum under different light regimes in the Submontane Atlantic Rain Forest

This study aimed to characterize the structure of the herb stratum in relation to light availability in the Submontane Atlantic Rain Forest at the Carlos Botelho State Park, SP, Brazil. Fortyone 10 x10 m plots were established under the closed canopy (18 plots), small and medium canopy gaps (11) and large canopy gaps dominated by Guadua tagoara (Ness) Kunth (12). Inside each plot, the line intercept method was applied to assess soil coverage as an estimate of density of herb stratum vegetation. Hemispherical photographs were taken at the centre of the plots to evaluate the annual light regime. Overall, Calathea communis Wanderley and S. Vieira had the greater mean coverage, followed by woody seedlings, ground ferns and other herbs (mainly, Araceae, Acanthaceae, Amaranthaceae and Cyperaceae). There were strong correlations among several groups of the herb stratum, such as the negative correlations between woody seedlings with the coverage of C. communis and with rocks. The analysis of the hemispherical photographs confirmed the difference among environments that led to significant differences in the soil coverage of the herb stratum vegetation but woody seedlings. For instance, C. communis showed great coverage in large gaps while ferns were more abundant in small and medium gaps and in the understorey. Other herbs, in turn, demonstrated bigger soil coverage in small and medium gaps. Although this study represents a rough assessment of the structure and composition of the herb stratum, the results found here illustrated the evident relation between herb species density and the environmental variation promoted by changes on canopy structure and topography.