Spatial and seasonal variability of photosynthetically active radiation in the understory of a semi-decidual seasonal forest.

The Atlantic Forest is a global hotspot for biodiversity conservation; however, human actions threaten and unbalance the dynamics of the natural processes of the biome. The present study investigated the incidence of solar radiation within a fragment of semi deciduous seasonal forest in the area of the Atlantic Forest Biome in southeastern Brazil. In the four seasons of the year, the leaf area index (LAI) and photosynthetically active radiation (PAR) were measured in the understory vegetation. The measurements were made at one-meter height, in ten different locations in the forest fragment, with different terrain exposure and slope. The annual average LAI was 4.5 and the PAR transmissivity was 4.1%. However, the results showed a spatial and seasonal variability of the leaf area index in the studied forest fragment. The seasonal variation of PAR in the understory vegetation was due to the LAI and to the different slopes and terrain exposures. The spatial heterogeneity in PAR availability is indicative of high plant diversity in the forest fragment.