## 4 Conclusions and Discussion  
In this study, hyperspectral reflectance data of _Quercus aquifolioides_ leaves measured by portable spectrometer and chlorophyll content measured synchronously were used. The spectral characteristics of _Quercus aquifolioides_ leaves, at different altitudes, were analyzed, and the statistical analysis methods of correlation analysis and stepwise regression analysis were used. Through systematic analysis of the selected typical spectral characteristic parameters, the optimal spectral characteristic parameters for monitoring the chlorophyll content of _Quercus aquifolioides_ were determined, and the estimation model of the chlorophyll content of _Quercus aquifolioides_ was established. The estimation model was tested and verified by using 3K-CV method in cross-examination. The conclusion was as follows. 1. The relative values of chlorophyll content of _Quercus aquifolioides_ at different altitude gradients were significantly different. From 2905 m to 3500 m, the relative chlorophyll content of _Quercus aquifolioides_ showed a trend of increasing first and then decreasing, which indicated that the environment at lower altitude or higher altitude was not conducive to chlorophyll synthesis and accumulation. At a low altitude of 2905 m, due to insufficient light and human destruction, its chlorophyll content was reduced. 3300 m above sea level was the most suitable growth area for _Quercus aquifolioides_. However, with the further increase in altitude (3500 m), due to the aggravation of unfavorable environment such as low temperature, thin atmosphere or strong ultraviolet radiation, the plant's resistance ability is limited, which also limits the growth and development of _Quercus aquifolioides_. 2. The trend changes of leaf spectral reflectance curves of _Quercus aquifolioides_ were generally consistent under different altitude gradients. In the visible light band (350-550 nm), the spectral reflectance was 3500 m \(>\) 3300 m \(>\) 2905 m. In the range of 550-700 nm, the reflectivity was 3500 m \(>\) 2905 m \(>\) 3300 m. In the near infrared band (750-1100 nm), the reflectivity was 2905 m \(>\) 3500 m \(>\) 3300 m.
3. In the range of 350-1800 nm, there were 4 main reflection peaks and five main absorption valleys in the leaf surface spectral reflection curve of _Quercus aquifolioides_, and their positions were basically the same. Visible light band was difficult to reflect the damage of host plants, while near infrared band (750-1400 nm) has the greatest degree of spectral reflectance discrimination. This band was the sensitive range of leaf spectral response of _Quercus aquifolioides_. At the same time, such variation characteristics were universal under different altitude conditions. 4. The red edge position and red valley position of leaf surface spectral curve move towards short wave direction with the elevation. This showed that, with the increase in altitude, the effect on the position of red edge and red valley on leaf surface becomes more severe. However, the yellow edge position and the green peak position move to the long wave direction first, and then to the short wave direction with the elevation. With the increase of altitude, the red edge area first decreases and then increases, the yellow edge area decreases and the blue edge area increases. 5. The correlation curve between the original spectrum of _Quercus aquifolioides_ leaves and chlorophyll relative content was the best between the wavelengths 509-650 nm, and the original spectrum hardly reflects the chlorophyll content information after 761 nm. The correlation between the first derivative spectrum and CCI value was the best and most stable at 450-500 nm, and the correlation in other spectral channels fluctuates greatly. 6. The correlation between red edge slope, blue edge slope, yellow edge slope, yellow edge position, green peak reflectance, water stress wave band reflectance, red edge area, yellow edge area and blue edge area and chlorophyll relative content value reached significant level.