## 2 Results and Discussion  
### The Variations of FPAR and Vegetation Indices  
FPARPAV (green FPAR), FPARNPV and the total FPAR of deciduous broadleaf forests demonstrated different modes with canopy structure variations (Figure 1). The total FPARand green FPAR had similar curves with plant area index. They increased as the canopy plant area index was rising. FPAR\({}_{\text{NPV}}\) demonstrated different trajectories from the total FPAR and green FPAR. FPAR\({}_{\text{NPV}}\) had maximum values when PAI was 2.0. As PAI was below 2.0, FPAR\({}_{\text{NPV}}\) increased with increase of PAI. However, when PAI was greater than 2.0, negative relations between FPAR\({}_{\text{NPV}}\) and PAI can be found. For a given PAI, green FPAR increased, while FPAR\({}_{\text{NPV}}\) and the total FPAR decreased along with the increase of the proportion of leaf area in the canopy. The maximum and minimum values of green FPAR were 0.9562, 0.0323 respectively, and those of the total FPAR were 0.9674, 0.0647 respectively. The minimum value of FPAR\({}_{\text{NPV}}\) occurred when PAI was smallest (0.1) and the proportion of leaf area was highest (98%). The maximum of FPAR\({}_{\text{NPV}}\) was 0.3257, which occurred at PAI of 2.0 and the proportion of leaf area of 50%. The total FPAR, FPAR\({}_{\text{PAV}}\), and FPAR\({}_{\text{NPV}}\) of evergreeniferous forests had similar modes with those of broadleaf deciduous forests (Figure 2). The total FPAR and green FPAR increased as canopy plant area index was increasing. At a plant area index of 0.1, their minimum values occurred, and they had maximum values when PAI was 7.0. Canopy FPAR\({}_{\text{NPV}}\) had more complicate trajectories, and at a PAI of 2.0, the maximum values of FPAR\({}_{\text{NPV}}\) occurred. Figure 1: FPAR of broadleaf deciduous forests canopies from the SAIL model. Figure 2: FPAR of evergreeniferous forests canopies from the SAIL model. For evergreen coniferous forests and broadleaf deciduous forests, the only difference in FPAR was the size of their values. The maximum values of FPARPAV, FPARNFV, and total FPAR for evergreen coniferous forests were 0.9515 (PAI, 7.0, proportion of leaf area, 98%), 0.323 (PAI, 2.0, proportion of leaf area, 50%), 0.963 (PAI, 7.0, proportion of leaf area, 50%), respectively. And their minimum values were 0.0316 (PAI, 0.1, proportion of leaf area, 50%), 0.0016 (PAI, 0.1, proportion of leaf area, 98%), 0.0631 (PAI, 0.1, proportion of leaf area, 98%). Four vegetation indices (NDVI, EVI, EVI2, and SAVI) of deciduous broadleaf forests were shown in Figure 3. As PAI was 7.0 and the proportion of leaf area was 98%, NDVI, EVI, and SAVI had their maximum values, which were 0.89, 0.69, 0.66, and 0.62, respectively. It is similar with the total FAPR and green FPAR. Of four vegetation indices, NDVI was generally greater than other three vegetation indices, and SAVI value was the least for a given canopy structure. Compared with EVI, EVI2, and SAVI, NDVI displayed less sensibility to the variability of proportion of leaf area in a canopy. Maximum increment of NDVI was only 0.035 when the proportion of leaf area increased from 50% to 98%, while for EVI, EVI2, SAVI, and the maximum increments were 0.084, 0.086, 0.069, respectively. The sizes of increments were related to canopy PAI. When PAI was 3.0, the influence of variation in the proportion of leaf area on vegetation indices was most significant. Variability of vegetation indices decreased with increase of the proportion of leaf area in a canopy as PAI was less or greater than 3.0. Compared with the proportion of leaf area, the canopy PAI had more significant influence on four vegetation indices. For instance, at the proportion of leaf area of 98%, NDVI, EVI, EVI2, and SAVI increased by 0.71, 0.57, 0.51, 0.47 respectively with PAI increasing from 0.1 to 7.0. The increments decreased when the proportion of leaf area decreased.