照片样线法测量人工草地覆盖度精度分析

The accuracy of artificial grassland coverage mea⁃ surement of photo line interception method

摘要:

草地覆盖度是评估植被情况的客观指标和重要的生态学参数。理想的草地覆盖度测量方法应该耗时短，工具简单，结果准确。将传统实地样线法的思路应用于样方照片分析，提出了草地覆盖度测量的照片样线法，通过实地拍摄样方照片，使用电脑中的虚拟刻度尺作为样线，进行覆盖度测量。以结缕草(Zoysia japonica)、白三叶(Trifolium repens)和雀稗(Paspalum thunbergii)3 种人工草地为研究对象，以照相法测量值为参考，对比实地目估法、照片目估法和实地样线法，分析了照片样线法的测量精度和适用性。结果表明：实地目估法、照片目估法和实地样线法测量误差分别为 5. 6%、14. 6% 和 2. 7%；每个 50 cm × 50 cm 草地样方采用实地样线法，野外测量时间约 3. 5 min。照片样线法测量误差平均为 3. 3%，每个 50 cm × 50 cm 样方需要消耗约 3. 7 min 室内测量时间。样线数量从 2 条(合计 1. 4 m)增加到 4 条(合计 2. 4 m)时，误差仅降低 0. 1%，增加样线数量不能明显提高测量精度，但耗时增加近 1 倍(3. 5 min)。因此，推荐用 2 条样线的照片样线法作为类似草地覆盖度测量方法，测量耗时短且精度较高。

Abstract:

Grassland coverage is the percentage of vertical projection area of plants in the total area of sample land. It is an objective index and serves as an important ecological parameter that is used to evaluate vegetation. An ideal method to measure the grassland coverage should be quick，requires few tools and must be accurate. In this study，the traditional field line interception method was applied to sample photo analyses，and the photo line intercep- tion method used to measure the grassland coverage was assessed. The grass coverage was measured by taking quad- rat photos in the field followed by using the virtual scale in the computer as the line interception. Three types of artifi- cial grassland，including Zoysia japonica，Trifolium repens and Paspalum thunbergii，were used as the research ob- jects. The photographic method was used as the reference，the accuracy of the measurement and the applicability of photo line interception method were analyzed by comparing the visual estimation of the field，visual estimation of the photos and the field line interception method. The results showed that the measurement errors of the field visual esti- mation，photo-visual estimation and field line interception method were 5. 6%，14. 6% and 2. 7%，respectively. It took approximately 3. 5 minutes to measure the field for each 50 cm × 50 cm grass quadrat using the field line inter- ception method. The average measurement error of the photo line interception method was 3. 3%；the measurement error of different grasslands was ＜5%，and it took approximately 3. 7 minutes to measure each 50 cm × 50 cm grass quadrat indoors. The increase of the number of interception lines did not significantly improve the accuracy of mea- surement. When the number of interception lines increased from 2(a total of 1. 4 m) to 4(a total of 2. 4 m)，the error was reduced by only 0. 1%，but the time taken was almost doubled (3. 5 minutes). The photo line interception method showed to be time-saving with a high degree of precision. Therefore，the photo line interception method with two interception lines is recommended to be used as a similar grass cover measurement method.