tailieunhanh - Báo cáo lâm nghiệp: " The influence of drought and thinning on leaf area index estimates from canopy transmittance method"

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế, đề tài:" The influence of drought and thinning on leaf area index estimates from canopy transmittance method. | Ann Sci For 1996 53 595-603 Elsevier INRA 595 Short note The influence of drought and thinning on leaf area index estimates from canopy transmittance method A Cutini Istituto Sperimentale per la Selvicoltura Viale s Margherita 80 52100 Arezzo Italy Received 6 September 1994 accepted 15 December 1995 Summary Leaf area index LAI estimates from litterfall and from canopy transmittance measurements in photosynthetically active radiation PAR and total solar irradiance wave bands were compared in Turkey oak Quercus cerris L stands. The aim was to evaluate advantages and limits of the transmittance measurements method in estimating LAI and to determine whether the modifications due to silvicultural operations and to different climatic conditions affected the accuracy of this method. Data were collected in thinned and unthinned experimental plots established at two different locations Val-savignone in the Apennines with a wet climate wet site and Casein near the Thyrrenian coast with a longer and more severe summer dry period dry site . Differences in stand density and LAI due to silvicultural operations led to significant differences in transmittance but did not affect light extinction coefficient fc . On the contrary environmental constraints influenced canopy properties as transmittance and k. However the variability in canopy properties do no limit the capability of canopy transmittance measured in the PAR wave band to be a good predictor error 5 of LAI at stand level. Some considerations are made about kand its value in PAR and total solar irradiance wave bands and on variability in canopy structure of a given species in relation to drought. canopy properties leaf area index light extinction coefficient drought Quercus cerris Resume Influence de la sécheresse et des éclaircies sur la determination de I indice foliaire par la mesure de la transmittance. On analyse I indice foliaire LAI la transmittance - dans la bande de la PAR et du rayonnement global - et le .