利用半球图像反演祁连山区青海云杉(Picea crassifolia)林盖度

青海云杉是祁连山森林生态系统的主要建群种,具有重要的生态水文功能.冠层盖度是评估生态环境的一个重要参数, 但目前缺乏有效评估手段.半球摄影技术在估算林冠盖度方面已显示出潜在优势,但它受到环境条件例如天气的影响仍然没有报道.在祁连山排露沟流域利用半球摄影技术反演冠层盖度,界定不同天气条件对阈值的影响,评估与传统方法估算林冠盖度的差别,结果表明:分类阈值受天气状况的影响较大,阴天的最佳阈值为118,晴天的最佳阈值为149;另外传统观测与半球图像法获得的林冠盖度有一定的差异,其中最大差值17.88%,最小差值5.34%.该项研究对青海云杉林盖度估算提供新的方法,为生态水文过程模型提供有价值的输入参数.

Estimating the canopy coverage of Picea crassifolia forest using digital hemispherical photography in Qilian Mountains

Qinghai spruce (Picea crassifolia) is the dominant species in the forest ecosystem of Qilian Mountains and is critical to the eco-hydrological processes of the ecosystem. Canopy coverage of Qinghai spruce is an important indicator of ecosystem quality, but there has been a lack of effective methods for its estimation. Hemispherical photography has shown great potential for the estimation, while little is known about the effect of weather conditions on this method. This study estimates canopy coverage of Qinghai spruce in Pailugou watershed of Qilian Mountains using hemispherical photography. Specifically, the effect of weather conditions, such as cloudy vs. clear days, on the estimation of the threshold values is evaluated. The estimation is compared with that of a traditional method. Results show that weather conditions have noticeable effects on the threshold estimation. The average threshold values are 118 and 149 for the cloudy days and clear days, respectively. When comparing between the hemispherical photography and the traditional method, the maximum difference between the estimations is 17.88% and minimum is 5.34%. In sum, this study demonstrates a promising method for the estimation of canopy characteristics of forest ecosystem that are valuable parameters for eco-hydrological modeling.