Understory light regimes in old-growth and second-growth temperate forests of Northeastern China

Light penetration through the forest canopy affects the growth and survival of tree regeneration. We compared understory light regimes in an old-growth forest and a second-growth forest using hemispherical photography. From each photograph, we ascertained canopy openness (CO), light transmission (gap light index, GLI), sunfleck characteristics, and the spatial distribution of CO and GLI. Old-growth and second-growth forests differed significantly in CO, GLI and the mean number of sunflecks per day. The old-growth forest plot was more open and heterogeneous in its openness than the second-growth forest plot. Sunflecks were more abundant in the second-growth plot, but sunfleck duration was not significantly different between the two forest types. Our study suggests that the characteristics of understory light may be a distinguishing indicator of the different forest types.