tailieunhanh - Báo cáo khoa học: "Assessment of the spatial distribution of light transmitted below young trees in an agroforestry system S Meloni"

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế đề tài: "Assessment of the spatial distribution of light transmitted below young trees in an agroforestry system S Meloni. | Ann Sei For 1997 54 313-333 Elsevier Inra 313 Original article Assessment of the spatial distribution of light transmitted below young trees in an agroforestry system s Meloni H Sinoquet2 1 Cemagref domaine de Laluas 63200 Riom 2 Inra domaine de Crouelle 63039 Clermont-Ferrand cedex 02 France Received 15 November 1996 accepted 24 January 1997 Summary - Transmitted radiation under trees shows variability in space and time that may have implications for the understorey. Light measurements were made in a young agroforestry system to assess the radiation distribution below the tree canopy. Measurements show that the variability of the transmitted radiation is mostly due to the size of the tree shadow and to the irradiance distribution in the shaded area. The light measurements were used to test the predictive capacity of a three-dimensional radiative transfer model based on the turbid medium analogy. The model correctly simulates the fraction of sunlit area and the irradiance distribution in the shaded area. However it underestimates low radiation values and fails in describing the fine spatial pattern of transmitted radiation because of the stochastic nature of the radiation field. To obtain a mean error less than 15 of the incident radiation the distribution of transmitted radiation has to be described by elementary soil surface areas over m2. photosynthetically active radiation spatial distribution I canopy geometry agroforestry Prunus avium Resume - Repartition spatiale du rayonnement transmis sous de jeunes arbres en système agroforestier. Dans une plantation à large espacement le rayonnement transmis disponible pour la strate inferieure est très variable dans I espace et dans le temps. Cette hétérogénéité peut avoir des consequences sur le fonctionnement de la strate inferieure. Des mesures de rayonnement utile à la photo-synthèse ont Ểté effectuees pour étudier la distribution du rayonnement sous les couronnes de jeunes merisiers plantés à faible densité. .