The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B7. Beijing 2008 
3.2. Statistical analysis 
Although there were some differences between sunlit and 
shaded leaves in absolute values of reflectance across the 
spectrum, we just focused on wavelength that related to 
chlorophyll content changes by using some indices. All 
indices listed in Table 2 are tested statistically for both 
illumination conditions for each species and different 
chlorophyll content among the species. Based on statistical 
results (Table 3) we can see that some indices are partly able 
to differ the shaded and sunlit leaves (Table 3). None of the 
vegetation indices shows significant difference for Ironwood 
and Hornbeam. Except for the mSR index all indices are 
sensitive to changing chlorophyll content of beech in 
illumination condition (p<0.0001). The illumination effect 
was significant at p<0.0001 for alder and oak by using mND 
and Vogelmann index (R 740 /R72o)- 
Species 
Vegetation 
index 
Alder 
Hornbeam 
Beech 
Ironwood 
Oak 
mND 705 
** 
NS 
** 
NS 
** 
1T1SR705 
NS 
NS 
NS 
NS 
NS 
Simple 
ratio 
NS 
NS 
** 
NS 
NS 
Vogelmann 
index 
** 
NS 
** 
NS 
** 
Datt index 
** 
NS 
** 
NS 
NS 
Table 3: T test result to investigate the differences between 
the index values for shaded and sunlit leaves. **: significant 
differences; NS: no significant differences (a= 0.01). 
R7*iJ R71VI 
Alder Hornbeam Baech Ironwood Oak 
R740/ ^720 
Alder Hornbeam Beech Ironwood Oak 
mSRjros 
Alder Hornbeam Beech Ironwood Oak 
Figure 4: Comparison of sensitive indices (R750/R700 and 
R740/R720) and non sensitive index (mSR 70 5) to chlorophyll 
content in each species in different illumination condition and 
between all five species to illustrate different behaviours. 
One-way analysis of variance was used to test statistically 
significant differences between species, both in sunlit and 
shaded leaves individually for those species that were 
significant in two exposed condition. The results show that 
the Vogelmann index (R740/R720) and simple ratio (R750/R700) 
used by Gitelson et al. 1996, are sensitive to chlorophyll 
content changing in different species (figure 4). Vogelmann 
index shows that hornbeam is different with beech, oak and 
alder as well as ironwood with alder and oak (p<0.0001, a= 
0.01). Beech and ironwood is statistically difference for sunlit 
leaves. There is no significant difference for any of the 
species in shaded position. Simple ratio index (R750/R700) is 
also sensitive to the chlorophyll difference between some of 
the species such as hornbeam with alder and ironwood with 
alder, beech and oak for sunlit leaves. Differences of Shaded 
leaves of hornbeam and ironwood, hornbeam and oak as well 
as ironwood and oak were significant. However mSR and 
mND indices showed different chlorophyll contents in the 
study of Sims and Gamon (2002), in this study we reached 
poor result compared to simple ratio indices. Maire et al. 
(2004) tested more than 60 published chlorophyll indices on 
the experimental and simulated data base, they could reach 
good result by using the Vogelman index and the Gitelson 
and Merzylak index for different forest tree species that 
confirmed our results. 
Our results highlight the importance of considering the 
illumination condition in canopy for those species that are 
especially present in dominant stairs and have more distinct 
shaded and sunlit leaves such as beech, alder and oak. This 
result is derived just by considering chlorophyll content as an 
important pigment in plant and could indicate that the other 
pigments that contribute in photosynthetic process might 
change in different exposed conditions. The strong 
relationships of the Vis with some biophysical parameters 
such as LAI can be somewhat expected in those Vis which 
are sensitive to chlorophyll absorption feature that is related 
to LAI. 
However, even though very important, leaf optical properties 
alone are not sufficient to unambiguously spectrally 
distinguish tree species. Also other canopy components such 
as branches, twigs, bark and understory need to be measured. 
The detection of statistically significant differences in 
intraspecific reflectance associates with illumination, leaf 
surface, non photosynthetic components such as twigs, 
branches and bark as well as habitat of sample collection 
suggest a potential for updating monitoring forest type maps 
and assess further the distribution of mixed forest stands. 
This study has produced the first spectral library of the most 
important forest tree species of the Caspian forest taking into 
account the range of spectral variability expected for the 
species measured under natural illumination conditions. The 
results provide a sound basis for mapping tree species in the 
north forest of Iran and beyond. 
ACKNOWLEDGEMENTS 
We acknowledge the contribution of the participating 
institutions. We wish to acknowledge the field work support 
we received from the staff of Geo-information department of 
Wageningen University and University of Tehran. 
294