Abstract: According to the data of total solar radiation and Photosynthetically Active Radiation(PAR) in intensive and extensive silviculture poplar plantation, the equations of transforming from total radiation to ground PAR were established. Combined with the leaf Area Index(LAI) and its vertical distribution in the canopy, the extinction coefficients(k) and vertical distribution of PAR in the two stands were calculated respectively. The daily and seasonal change of K and PAR transmittance were discussed also. The relationship between PAR transmittance and cumulative LAI within the canopy was established, the result showed it is a linear model. Compared the absorbtion of PAR in two stands, since intensive culture stands with higher leaf area in the different layers of canopy, so the interception of PAR in intensive culture stand is higher than that in the extensive culture stand, this resulted the higher productivity in the former.

Key words: Poplar, Plantation, Leaf area index, Photosynthetically active radiation, Extinction coefficient