AN EMPIRICAL-MODEL FOR PREDICTING THE GAP LIGHT INDEX IN AN EVEN-AGEDOAK STAND

An empirical model for predicting light levels under a canopy gap in a n even-aged oak stand is presented. The effects of gap size, distance from the gap, and directional position (noah-south) within the gap on gap light index (GLI) [sensu Canham, C.D. 1988. An index for understor y light levels in and around canopy gaps. Ecology 69, 1634-1638] are q uantified by multiple regression analysis. Data were obtained by the ' erasing method' (Yanagisawa et al., in preparation') which predicts th e GLI from computerized images of hemispherical photographs. Forty-fiv e 'virtual canopy gaps' were assumed, and at 945 points, light levels were calculated using HEMIPHOT [ter Steege, H. 1993. HEMIPHOT, A Progr amme to Analyze Vegetation Indices, Light and Light Quality from Hemis pherical Photographs. The Tropenbos Foundation, Wageningen, The Nether lands]. The model presented in this study has the advantage that the i ndices needed for the prediction can be measured easily in field surve y. The applicability of the model is discussed. (C) 1998 Elsevier Scie nce B.V.