Light extinction coefficients specific to the understory vegetation of thesouthern boreal forest, Quebec

This study was conducted in six different forest types in Abitibi, Que., (i ) to identify the factors that most influence understory light transmission in the southern boreal forest and (ii) to develop light extinction coeffic ients (k), which could be used to simulate light transmission in the unders tory. Light availability and understory vegetation (cover, composition, ver tical distribution, and leaf area index) were characterized within three st rata (0.05-5 m) in a total of 180 quadrats. Calculated k values were based on measured light availability and leaf area index. These values varied amo ng forest types, strata, understory vegetation types, and cover in the uppe r stratum. The highest k values were generally associated with a dense stra tum of Acer spicatum Lam. We developed five sets of k values based on the f actors that most affected light transmission. Measured transmission (T-m) w as compared with transmission predicted (T-p) from each set of k values. Li ght transmission predicted using a single k value (mean k = 0.54) underesti mated T-m. More accurate predictions were obtained when we used the other f our sets of k values. Our results indicate that, in the southern boreal for est, the understory vegetation can be quite heterogeneous and patterns of l ight transmission cannot be accurately simulated using a unique k value. Ho wever, the various sets of k values developed in this study could be used i n prediction models of forest dynamics to obtain relatively good prediction s of understory light extinction in forest types similar to the ones studie d here.