CHARACTERISTICS OF SHORTWAVE AND LONGWAVE IRRADIANCES UNDER A DOUGLAS-FIR FOREST STAND

被引:147
作者
BLACK, TA
CHEN, JM
LEE, XH
SAGAR, RM
机构
来源
CANADIAN JOURNAL OF FOREST RESEARCH-REVUE CANADIENNE DE RECHERCHE FORESTIERE | 1991年 / 21卷 / 07期
关键词
D O I
10.1139/x91-140
中图分类号
S7 [林业];
学科分类号
0829 ; 0907 ;
摘要
Measurements of the spatial mean values of global irradiance, photosynthetic photon flux density, and the downward longwave irradiance under a 26-year-old, second-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forest canopy on a 26-degrees south-facing slope were made with a tramway system, which scanned a 20-m transect in 12 min. The diffuse solar irradiance under the canopy was measured with a stationary pyranometer equipped with a shadow band. The extinction coefficients for the direct, global, and photon components were derived as functions of the solar incident angle over the range of 15-degrees to 85-degrees. The extinction coefficient for the diffuse radiation was found to correlate well with the ratio of the direct to diffuse irradiance above the canopy. Complete diurnal cycles of the downward longwave irradiance were simulated with a simple model based on the air temperature inside the stand. Analyses of the measurements of all the shortwave and longwave components were made using an effective leaf area index, which was derived from the measurements of the direct irradiance above and below the stand. It was found that the distribution of the leaf inclination angle of a Douglas-fir canopy has strong planophile characteristics, and that in the case of a forest stand on a slope, it is critical to obtain the characteristics of the light transmission through the canopy over the entire incident angle range before effective leaf area index is calculated. Warren Wilson's 57.5-degrees approximation did not hold for the Douglas-fir canopy, which had distinct foliage clumping features.
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页码:1020 / 1028
页数:9
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