Spectral comparison between diffuse PAR irradiance received under the shade of nine trees in different heights and a cloudy day in summer.

Spectral Solar Photosynthetically Photon Flux Density (PPFD) (380-780 nm) reaching the surface in different tree shade conditions and heights has been analyzed in order to better understand the different photosynthetic performance of plants depending on their spatial situation, the canopy density and height with respect to the floor. A comparison between the shadow of nine different trees in a sunny day and the case of a cloudy day in an open space has been studied. A poplar, laurel, amber tree, pine, olive tree, fir tree, cypress, elm tree and magnolia tree have been analyzed. The study has been developed in Valencia (Spain) during July and August 2022. Conditions with higher PPFD received are found to be, apart from those of a sunny day, those for cloudy day, and those for the shade of cypress. The case in which less amount of PPFD is received is that under the shade of olive tree. Both with a spectral maximum in the Blue region. It is also remarkable that the PPFD radiation is proportional to the height of measurement at 10 h, but this relationship changes, and at 13 h the relationship between irradiance received and height of measurement is inversely proportional.