封育条件下草地光谱反射特征及地上生物量估测*

 2005年7月至2006年4月,对云南省马龙县封育草地和过牧草地的光谱反射率、草层高度、覆盖度和地上生物量进行了测定,分析了归一化植被指数（NDVI）及比值植被指数（RVI）与地上生物量之间的相关性。结果表明:过牧草地封育1年之后,其草层高度、覆盖度和地上生物量显著增加,光谱反射特征也相应地发生明显变化。450~850 nm范围内,两种草地不同季相条件下在各波段的光谱反射率差异均达到极显著水平（P＜0.01）,覆盖度及季节变化对近红外波段的影响明显大于可见光波段。旺盛生长期（7月）和枯黄期（11月）,封育草地具有植被反射型特征,而自由放牧草地表现为植被-土壤型;返青期（4月）两种草地均表现为土壤型。过牧草地地上生物量与两种植被指数之间无显著相关性。封育草地地上生物量与NDVI,RVI之间存在显著的（P＜0.05）非线性相关,旺盛生长期和返青期NDVI与地上生物量的相关性强于RVI,枯黄期RVI与地上生物量相关性强于NDVI。

Spectral Reflectance and Aboveground Biomass Estimation of the Grassland under Protection Condition

From July 2005 to April 2006, the spectral reflectance, aboveground biomass of protected grassland and free grassland were measured and analyzed in Malong County of Yunnan province. The aims of this research were to understand the spectral reflectance under different coverage and aspectation conditions and quantify the correlation between vegetation indices and aboveground biomass of 2 different grasslands. It was showed that grassland coverage and aspection had significant effects on its spectral reflectance. After 12 months protection from using, the protected grassland had higher canopy, coverage and aboveground biomass, compared with free grazing grassland area, thus, significantly (P<0.01) increased or decreased its spectral reflectance in the near infrared wave bands or visible wave bands. During vigorous growth period (July) and dead ripe period (November), the protected grassland had reflectance type of vegetation, but free grazing grassland represented vegetation-soil type, due to the lower canopy, coverage and above ground biomass. During the greenup period (April), the protected grassland and free grazing grassland had the same spectral reflectance type of soil, although the reflectances were significantly different between both of them at all wavelengths. Spectral vegetation indices NDVI and RVI had significant (P<0.05) nonlinear correlation with the aboveground biomass of the protected grassland in three growth seasons. The protected grassland aboveground biomass could be estimated by NDVI both in vigorous growth period and dead ripe period and by RVI in greenup period.