The boundary layer of the forest at which the energy exchange occurs and some insolation is returned directly to space is

The forest canopy acts as the primary boundary layer between the atmosphere and the forest ecosystem. It is the site where the most significant energy exchange occurs, as it receives the maximum amount of sunlight [1]. The canopy controls abiotic energy flow through its biomass distribution and optical characteristics. A portion of the arriving solar energy, known as albedo, is reflected directly back to space from this layer without being converted into heat [4]. This reflectivity is influenced by canopy nitrogen levels and foliar concentrations, which regulate shortwave surface energy exchange. While the forest floor and litter are active in nutrient cycling and moisture retention, the canopy layer is the specific interface responsible for returning insolation directly to space through reflection and scattering [4].

Sources

1. [1] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 3: MAJOR BIOMES > 1. Tropical Evergreen Rainforest Biome > p. 7
2. [4] https://pmc.ncbi.nlm.nih.gov/articles/PMC2593617/