## 2 Results and Discussion
### Influence Factors of Green FPAR and Vegetation Indices  
Green FPAR (FPAR\({}_{\text{PAV}}\)) is smaller than the total FPAR which includes light absorption of all components in the canopy. As well as green leaves, non-green components also absorb solar photons. Unfortunately, the energy is not used for photosynthesis. Under the given condition in this study, the ratio of FPAR\({}_{\text{NPV}}\) to the total FPAR varied from 0.26 percent to 56.93 percent in deciduous broadleaf forests, while the ratio varied from 0.26 percent to 56.89 percent in evergreen coniferous forests. The contributions from non-green components to the total FPAR are similar for two different forests ecosystems, but it varies with canopy structure. In order to more clearly illustrate the variations of FPAR\({}_{\text{NPV}}\) with canopy structure, we simulated green FPAR of six tree species based on spectrum of theirs components (Figure 7). It can be found that non-green contributions increased along with the increase of proportion of non-photosynthetic components in the canopy and the decrease of forests PAI. FPAR\({}_{\text{NPV}}\) values of six tree species were no more than 0.003 at PAI of 7 and the proportion of green component of 0.02. Even though non-green components accounted for a higher proportion in the canopy, FPAR\({}_{\text{NPV}}\) was still low if PAI is high. For instance, at a PAI of 7, FPAR\({}_{\text{NPV}}\) increased only by 0.12 when the proportion of non-green components varied from 2% to 50%. However, when PAI was below 1.0 and the proportion of non-green components in the canopy was 0.5, non-green components had more contributions than green leaves. This suggests that non-green contributions are more significant in forests with low PAI values and a large proportion of non-green components in canopies, while in forests with high vegetation coverage green contributions to the total FPAR will higher. Mature forests, whether broadleaf forests ecosystems or coniferous forests ecosystems, have generally closed canopies and high PAI values during the peak growing season. And at the time, the canopies are mainly domi  
Figure 6: The relationship between FPAR and vegetation indices for evergreen coniferous forest. are only a very small proportion of non-green components. In addition, leaves are located on the top of the canopy, so solar photons will firstly interact with leaves once light arrives at the canopy. In PAR spectral regions (400 nm-700 nm), solar photons in the visible regions are strongly absorbed by chlorophyll and carotenoids of green leaves [30]. Only photons scattered (reflected and transmitted) by green leaves have chance to interact with non-green woody components. If there is a dense leaf layer, leaves will intercept most of photons, and thus only little PAR can be absorbed by woody material. This may explain why FPAR\({}_{\text{PAV}}\) has high values, while FPAR\({}_{\text{NPV}}\) is so low in forests ecosystems with high PAI values and small proportion of nonphotosynthetic components. However, for open canopies, there are more gaps in canopies and solar photons can arrive at non-green components directly and interact with branches. In addition to direct sunlight, non-green components absorb light transmitted by leaves and reflected by ground. Non-green components absorb solar light without any transmission [31]. These factors make non-green components absorb more sunlight than green leaves in some cases. Canopies of six tree species with identical canopy structure, background and illumination conditions had different FPAR\({}_{\text{PAV}}\). Oak had the highest green FPAR values, and Alder followed it. PAR by absorbed by green leaves of Juniper was the least. When the canopy structure, background and illumination conditions were same, the only difference between tree species was the absorption capacity of green leaves. According to spectral data measured in the laboratory, Oak had the largest absorpt  
Figure 7: Variations of green FPAR with plan area index for six tree species. second was Alder (Figure 8).