Journal of Natural Disaster Science, Volume 30, Number 1, 2008, pp45-53

45

Quantitative Research on Vigor of Ginkgo Trees hit by Typhoon
0613 with Ground-based Digital Image Analysis

1

Fei WANG1, Haruhiko YAMAMOTO2 and Kiyoshi IWAYA2
The United Graduate School of Agriculture Science, Tottori University
2
Faculty of Agriculture, Yamaguchi University(Received for 18 Apr., 2007 and in revised from 18 Nov., 2008)

ABSTRACTThe center of typhoon No.13 (Typhoon 0613) in 2006 passed through the Japan Sea and shaved the southwest
corner of Yamaguchi Prefecture with characteristics of strong wind and less rainfall in Yamaguchi City. Many
ginkgo (Ginkgo biloba L.) trees showed leaf discoloration and defoliation after its hit in Yamaguchi City, Japan.
The crown of them can be clearly divided into green part and non-green part so that they were misrecognised as
special ornamental trees. In order to quantitatively study this phenomenon, the indices of green coverage ratio ofcrown (GCRC), crown coverage (CC), vigor index (VI), and so on were used to analyze the vertical sideward profile of ginkgo trees by ground-based digital image analysis. They reflected leaf discoloration and defoliation of
the crowns, and positively related to the distance from coastline (DC). Logistic functions between DC and these
indices were obtained, with square correlative coefficients being 0.913, 0.622, and 0.882, respectively for GCRC,
CC and VI. There is indication that ground-based digital image analysis can be an effective tool used in evaluating the vigor status of ginkgo trees hit by Typhoon 0613. In the paper, combined with analysis of meteorological
data, the reason for damage to ginkgo trees was considered as water stress induced by Typhoon 0613. Based on
multi-analysis of the research, there were significant differences of vigor status between coast and inland ginkgo
trees after hit by Typhoon 0613.

1. INTRODUCTION
Vigor of trees can be thought as one kind of ability to form aperfect individual and healthily grows, which varies with the cultivated conditions, increases with fine nurtures and decreases byserious pest damages, disaster destroys and various kinds of stresses, such as drought, salt, nutrition shortage. Under stressed situations, many unhealthy symptoms may be appeared like severe wilt,
defoliation, discoloration, chlorosis, necrosis, dieback and so on.
In some extent, it is a near synonym with tree viability or health.
Typhoons are one kind of disaster that can seriously damage toforests, trees and shrubs (Hayes, 1999; Yamamoto, 1979;
Takahashi et al., 1981). The typhoon No. 13 in 2006 (Typhoon
0613) was characterized by low precipitation and high wind speed
when it hit Yamaguchi City on Sep.17.2006. Its maximum windvelocity reached 20 m/s, the daily precipitation was only 24 mm
during its hit and this period of less rainfall persisted for more than
one month after its hit (refer to Table 2). Although there was noseverely mechanical damage to trees, such as uprooting, stem
breaking, bending, leaning, and so on in Yamaguchi City, it did
lead to reduce the health status of many tree species, especially tosome precious landscape trees. Apparent symptoms of leaf discoloration and defoliation appeared on windward of the crowns thatmade the crown obviously different between the windward and leeward of some deciduous trees, even half green and half brown,such as ginkgo.
Historically, a lot of researches had focused on the storm

effect on trees, even making trees as wind indicator, such as thewell-known Fujita Tornado Scale and Saffir-Simpson Hurricane
Scale, as well as the Griggs-Putnam and Yoshino tree deformationindex to predict wind speed and wind direction in meteorologicalfields (Cullen, 2002; Hennessey, 1980; Wade et al., 1979;
Robertson, 1987). Recently, most research works on storm damage to trees still use visual scale method (Okinaka et al., 1990;
Shimizu et al., 2004; Zhu et al., 2001). Visual assessments of tree
crown are also common in forest health investigations (Redfern etal., 2004). To some extent, they are observer specific and probably
affected by subjective judgment (Doswell et al., 1988; Solberg,
1999). There is a tendency of transformation to objective methods
for determining damage by typhoons and other disasters, especiallyusing imagery analysis nowadays.
Comparing to annual plants, trees have big bodies and complex three-dimensional structure, which makes them difficult to bemeasured. It is almost impossible to perfectly measure tree crowns
in a large-scale area for few researchers with common sampling
method. As a repaid, nondestructive, noninvasive method, groundbased digital image analysis has been used to measure leaf areaindex, gap fraction (Bréda, 2003), crop coverage (Purcell, 2000),
pest damage and so on. It has been remarked to be a potential
method in coverage research of grasses (Richardson et al., 2001),
crops (Iwaya, 2003; Purcell, 2000), and vegetation (Laliberte et al.,2006). Richardson et al. (2001) considered that digital image
analysis had potential in the study that the amount of green tissue
was an indication of health or growth, including injury ratings of

KEY WORDS: Ginkgo, Typhoon 0613, Ground-based digital image analysis, Vigor indices, Water stress46

F. WANG, H. YAMAMOTO AND K. IWAYA

various grasses and diseases or insect injury. It has also been usedin tree measurement and researched on the porosity of shelterbelts(Kenny, 1987; Guan et al., 2002; Wan et al., 2005). Kenny (1987)
concluded that the porosity of shelterbelt could be estimated towithin 2% at a probability level of 0.05 by silhouette method, andthe distance of taking photo has no appreciable effect on estimationof porosity. After improvement of photograph treatment method,
Guan et al. (2002) considered it was a proper way to measureporosity of shelterbelt with high accuracy. In this paper, distinguished from commonly used hemispherical image analysis
method, the overall profile of crown was quantitatively measured
after hit by Typhoon 0613 by using ground-based, vertical sideward digital images of the profile for ginkgo trees. The vigor status of ginkgo trees hit by Typhoon 0613 was quantitatively studied
using indices including the green coverage ratio of crown (GCRC),
crown coverage (CC), vigor index (VI) and so on. Combined withanalysis of meteorological data, the reason of reducing the vigor
status of ginkgo trees has also been studied.
2. MATERIALS AND METHODS
2.1 Research site and basic meteorological data during
Typhoon 0613 s hit
The research site is located in the area from 131°16 to 131°
45 east longitude and from 33°55 to 34°25 north latitude. The
investigation was practiced in a long, narrow area near Yamaguchi
Bay, Fushino River and Anno River, which was from seashore via
plain to canyon. It includes the circled sites of Ube, Aio, Ogori,
Yamaguchi, Miyano, Mitani and Tokusa, which don t match up
the administrated area with same name (see Fig. 1), and runs fromsouthwest to northeast.
The meteorological data comes from the AutomatedMeteorological Data Acquisition System (AMeDAS) and from thenearest observation station of the Hazard Protection Information
System in Yamaguchi Prefecture (HPISYP). The max wind speed
distributed from the highest of 27 m/s in Ube City to the lowest of
8 m/s around Tokusa Town during the hit by Typhoon 0613. The
distance to the nearest coastline is from the shortest of less than 1
km to the longest of more than 40 km (see Table 1).
2.2 Photo image taken method and standard of analysis
Photographs were taken 45 days after typhoon 0613 s hit. It
is characterized by horizontally taking photos of the vertical profile
of sample trees on the ground and by using a CCD digital camera(Canon IXY 6.0). The photo-taking distance was determinedaccording to the size of crown and making crown fit the screen of
the camera. The position of photo-taking was fixed by movingaround the sample tree until the crown could be clearly classified
into green part and non-green part, and the ratio of the green part tothe non-green part didn t change, so that we could obtain the exact
sideward photo image of sampled individuals. For trees whosecrown cannot be clearly divided into green part and non-green part,the position of photo taking was determined by wind direction,
local topography or by reference to other tree species etc. The
absolute geographical position of sampled trees was fixed by GPS
with Ricoh camera (Caplio 500SE). Photographs was taken
between 0900JST and 1600JST and at the light-ward.
In order to avoid effects by other trees and take photos easily,
most of street ginkgo trees were selected in open sites. Trees
exhibiting any of the following characteristics were excluded fromuse in this study to decrease the primary source of error, such as

Fig. 1 Integrated map for research area, meteorological data and green coverage ratio of crown (GCRC); Sampledcrowns were clearly divided into three groups, Group 1 (I), Group 2 (II) and Group 3 (III).

A QUANTITATIVE RESEARCH ON VIGOR OF GINKGO TREES HIT BY TYPHOON 0613 WITH GROUND-BASED DIGITAL IMAGE ANALYSIS

Table 147

Basic meteorological data for investigated areas during hit by Typhoon 0613 on Sep.17.2006

Fig. 2 Damaged crown and green part of Ginkgo biloba; Index of Green
Coverage Ratio of Crown (GCRC) was calculated by both of them.

Fig. 3 Images of silhouette and shadow for same crown; Crown Coverage(CC) index was calculated by both of them.

trees sheltered by houses, buildings, and other trees, newly planted
trees and newly pruned trees as well as trees with scars on the trunkand so on. To avoid errors in analysis, almost all of data used in
the results analysis are relative values from the same crown.

2.3.2 Crown coverage and vigor index
Another characteristic of ginkgo trees damaged by Typhoon
0613 is defoliation, which is expressed into increasing of opennessof the crown. In the study, the openness induced by defoliation of
ginkgo trees hit by Typhoon 0613 was estimated by CC index. It is
the pixel proportion of crown silhouette to crown shadow shown in
Fig. 3. It was measured by pixel method in reference to researches
by others (Kenny 1987; Guan et al., 2002). The detail proceduresof measurement include photo image processing and silhouetting
by decreasing the color depth to 2-color palette by using Paint
Shop Pro X in the pattern of the blue palette component, the nearest color reducing method, and non-palette weight. The pixels of
the image shadow were obtained from Photoshop CS. The calculating formula of CC is shown in Equation 2.

2.3 Establishment and measurement of indices2.3.1 Green coverage ratio of crown
In order to analyze the phenomenon of leaf discoloration ofcrown and the difference between green part and non-green part on
different trees quantitatively, GCRC was applied, which was a proportion of the pixels of green part to the pixels of overall profile ofthe crown. Firstly, the photo image was treated by image editor
software such as Photoshop CS, etc. to remove the parts out of thesampled crown. After obtaining pixels of overall crown, the partsout of green was removed by eraser (see Fig. 2) and then pixels ofgreen part of the crown were obtained. The detail of calculation
for GCRC by pixel proportion method is presented in Equation 1.

GCRC(%) =pixels of green part
¥ 100
pixels of overall crown(1)

Crown Coverage(%) =pixels of silhouette¥100
pixels of shadow(2)

The comprehensive index of VI for damaged trees was calculated by the average value of GCRC and CC (see Equation 3).

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F. WANG, H. YAMAMOTO AND K. IWAYA

VI (%) =(GCRC + CC )2(3)

2.3.3 Crown Ratio between Windward and Leeward (CRWL)
As a factor of symmetric characteristics of crowns for multianalysis, CRWL is the proportion of pixels from the shadows ofboth windward and leeward of crown divided by reference to themain stem. Firstly, the photo image was processed to remove theparts out of the crown. Then, the crown was divided into windward and leeward from main stem of the tree. After that, bothwindward and leeward were shadowed respectively and pixels
were obtained by using Photoshop CS. The CRWL was calculated
as Equation 4.

CRWL(%) =pixels for windward¥ 100
pixels for leeward(4)

2.4 Distance from coastline (DC) and average distance frommeteorological station to the coastlines of west, southwest,
south, and southeast (ADC)As a main analysis factor, the DC is the shortest distance fromtree sites to coastline measured by an electronic atlas named Atlas
Z Professional5.
The average distance from observation stations for AMeDAS
to the coastlines of west, southwest, south, and southeast was measured in Yamaguchi Prefecture to study the relation between windspeed and the distance from coastline. It was also measured byusing Atlas Z Professional5 and calculated by Equation 5.

ADC =west / 2 + southwest + south + southeast
4(5)

in which Dpq is the centroid distance between class p and class q.
x p is the cluster mean value in p class and x q is the cluster meanvalue in q class.
3. RESULTS AND ANALYSIS
3.1 Discoloration of ginkgo crowns hit by Typhoon 0613
Based on the calculation, the GCRC distributed from zero or
close to zero near the coastline to 100% in the valley far from thecoastline around Tokusa Town, corresponding to the overall crownbrown and overall crown green. From Fig. 4, although the GCRC
value for samples at the same site differ from each other for thereason of different site conditions and growth situations, it was not
so great as to significantly effect the relation to DC. A positive
logistic function relationship between GCRC and DC was
obtained, with a square correlative coefficient of R2= 0.913 at 0.01
probability level by screening among the regression equations oflogistic, logarithmic, exponential, linear, polynomial etc. The optimal equation determined by maximum correlative coefficient isshown in Equation 8. In addition, the equation was computed fromthe regression analysis of 36 sampled trees.

GCRC = 101.95/(1＋8.821e−0.183DC)

R2 = 0.913(8)

It indicates that the further is from the coastline, the greater
the green part of the crown is. In other words, the nearer is to thecoastline, the more the green leaf color of ginkgo loses. As the distance from coast to inland increases, the GCRC increases sharply,
then smoothly, and then becomes stable.
Further, the leaves on a damaged tree were analyzed by dividing them into groups of non-scorched, scorched, and dried leaves
by sampling method in order to analyze the pattern of leaf discol-where west/2 was used for the reason that the average width of thewest and east is about 2.3 times more than that of south and northfor Yamaguchi Prefecture.
2.5 Multiple statistic analysis
Principle component analysis and cluster analysis were carriedout using GCRC, CC, VI, CRWL, and DC mentioned above. The
analysis was conducted by commonly used software. The distanceused in cluster analysis is the square Euclidean distance (refer toEquation 6) for samples and cluster mean (centroid method andrefer to Equation 7) for classes.
1p2
d ( xi , x j ) = ÈÍ Â ( xik - x jk )2 ˘˙
Îk =1
˚

(6)

where d(xi, xj) is the Euclidean distance between sample i and sample j, i=1, 2, ……, n, j=1, 2, ……, n and k=1, 2, ……, p. xik is thedata of sample i at point k and xjk is the data of sample j at point k.
Dpq = d ( x p , x q )(7)Fig. 4 Relationship between Green Coverage Ratio of Crown (GCRC) andDistance from Coastline (DC); It was regressed from 36 ginkgo
trees from the sites of Yamaguchi, Ube, Mitani-tokusa, Miyano,
Aio and Ogori respectively.

A QUANTITATIVE RESEARCH ON VIGOR OF GINKGO TREES HIT BY TYPHOON 0613 WITH GROUND-BASED DIGITAL IMAGE ANALYSIS

oration. Fig. 5 showed the leaf component of samples from trees
with different DC. Almost all of the leaf samples from ginkgo
trees in Tokusa, with an average DC equaling 35.6 km, were composed of non-scorched leaves, with a non-scorched leaf rate of
93.7%, a scorched leaf rate of 6.3%, and a dried leaf rate of 0%.
The scorched leaves showed only scorch spots, which perhaps
were not induced by Typhoon 0613 since the scorch spots exist on
the leaves at both leeward and windward. Contrarily, the majorleaf samples from Ube, with DC equaling 1.7 km, were scorchedand dried leaves, with a non-scorched leaf rate of 1.6%, a scorchedleaf rate of 49.9%, and a dried leaf rate of 48.5%. The leaf samples
from Yamaguchi, with DC equaling 13.5 km, were in the middle
position with a non-scorched leaf rate of 39.3%, a scorched leaf
rate of 52.3%, and a dried leaf rate of 8.4%. So, it can be said thatthe difference of crowns in different areas mainly comes from different scorch components of leaves 45 days after Typhoon 0613 s
hit.
3.2 Defoliation of ginkgo trees hit by Typhoon 0613
Defoliation is widely used as an indicator for the vitality or
health of forest trees and the damage status in forest investigations,although it is still debatable (Zierl, 2004). It is observed different
defoliation occurred on ginkgo trees in varied site conditions after
hit by Typhoon 0613. From Fig. 6, it is evident that CC ranged
from 40% to 90% or so and almost no CC value of ginkgo trees
become zero or near zero because there were a lot of dead leaves
remained on the damaged trees until next spring. Meanwhile, theresult appears that there is a positive relationship between CC andDC, although the correlative coefficient is less than that of the relationship between GCRC and DC. The corresponding equation is:
CC = 101.34/(1＋1.0076 e−0.0535 DC)

R2 = 0.622(9)

The result showed that there is a difference in crown coverageamong the sampled trees and the further is from the coastline, thebigger the crown coverage of ginkgo trees is. In other words, defoliation occurred indeed and was more serious near coastline.
The further regression analysis by classifying samples into

Fig. 5 Percentage of leaf scorch for discolored ginkgo crowns from different sites with different distance from coastline

49

two groups of dense crowns and sparse crowns showed a positive
relationship between CC and DC, and the square correlative coefficient for regressive equations was 0.78 and 0.79 respectively forthe dense crown group and sparse crown group. It indicates thatthe relationship between CC and DC is affected by density ofcrowns. Therefore, sampled trees with much dense crown were
eliminated from the analysis.
3.3 Comprehensive vigor status of ginkgo trees hit by
Typhoon 0613
Tree’s vigor has been evaluated by various methods, which
includes foliage based indices, volume increment and height
growth rate based indices (Robichaud et al., 1991). However, thevigor of ginkgo tree to be estimated in this study is the status after
hit by strong Typhoon 0613, which is characterized by clear discoloration and defoliation of typhoon damaged trees. Therefore, discoloration and defoliation were used to establish the vigor index toresponse to the vigor status of ginkgo trees hit by Typhoon 0613.
GCRC and CC are two indices respectively response to them insome extents and the VI which integrated with index of GCRC andCC has potential to comprehensively model the vigor status ofdamaged trees. Fig. 7 gave a relation curve between VI and DC
and it shows that there is also a positive relationship between VI
and DC, with a square correlative coefficient of R2=0.882 andregressive Equation 10.
VI = 99.688/(1＋2.5366e−0.11DC)

R2 = 0.882(10)

3.4 Multi analysis and classification of ginkgo vigor status
Based on the principle component analysis by GCRC, CC, VI,
CRWL, and DC, samples from different areas were divided into
three groups showed in Fig. 8. Group 1 consisted of samples from
Tokusa and Mitani with DC of more than 30 km, GCRC of 100%or near 100%, average CC of 83.4%, and VI of 95.4%. Group 2
included samples from Miyano and Yamaguchi, with DC from 8 toFig. 6 Relationship between Crown Coverage (CC) and Distance from
Coastline (DC); It was also regressed from the same ginkgo trees
used in Fig. 4.

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F. WANG, H. YAMAMOTO AND K. IWAYA

Fig. 7 Relationship between Vigor Index (VI) and Distance from
Coastline (DC); Ginkgo crowns analyzed in it were also same as
Fig. 4.

Fig. 8 Classification of ginkgo crowns by principle component analysis.
36 crowns collectively distributed in three area of principle coordinate system and were classified into three groups, the first group isconcentrated in the first and fourth quadrant at the right side of thex axis, the second group around the datum point, and the thirdgroup in second and third quadrant at the left side of the x axis.

Fig. 9 Result of cluster analysis with centroid method, in which the crowns from Mitani-tokusa(○), Miyano (△), Yamaguxhi (X), Ogori (◇), Aio (*) and Ube (□), were also classified
into three groups.

20 km, GCRC from 40 to 90%, average CC of 67.3%, and VI of
67.5%. Group 3 came from samples from Ogori, Aio, and Ubewith DC from 0.2 to 4 km, GCRC from 0 to 39%, average CC of
54.2%, and VI of 21.1%.
The result of principle component analysis is evidence that thevigor of ginkgo trees were more seriously damaged by typhoon
0613 within 4 km from the coastline, and almost no injury occurredin the area out of 20 km from coastline and the ginkgo trees in thearea from 4km to 20 km were in the middle position.
Almost the same result has been obtained by Euclidean distance cluster analysis at the point of squared central distance equaling 6.05 with the data of GCRC, CC, VI, CRWL, and DC according to the discriminating standard of the starting point that thesquared central distance sharply increases. The samples from different areas also can be divided into three groups as showed in Fig.

9. The samples from Group 1 consisted of samples from Tokusa
and Mitani, Group 2, from Yamaguchi and Miyano, and Group 3,
from Ube, Aio, and Ogori except only one special sample from
Yamaguchi.
Fig. 10 shows a few of model of ground-based digital image
samples for Group 1, Group 2, and Group 3, respectively. A great
difference among the groups was shown and they are consistent
with the indices used in this research properly.
An outline of the research area (circled area), meteorological
data, GCRC index, and groups of classification were given in Fig.
1. In the figure, GCRC was scaled into 5 levels, and respectively
represent GCRC of 100, 60-90, 40-59, 1-39, and 0. Every sample,
with a consistent scale mark, was located on the map in the figure.
It can be observed that the classification result was consistent withthe research sites. For the first group, the DC is more than 30 km,

A QUANTITATIVE RESEARCH ON VIGOR OF GINKGO TREES HIT BY TYPHOON 0613 WITH GROUND-BASED DIGITAL IMAGE ANALYSIS

51

Fig. 10 Model samples of ground-based image for group1, group2 and group3 andrelated GCRC, CC and VI values

the second group is from 4 to 20 km, and the third group is lessthan 4 km and was in accordance with the gradient of wind andprecipitation. It can be seen that the further the sample tree is fromthe coastline, the slighter the damage by Typhoon 0613 is according to the indices by ground-based digital image analysis.
From Fig. 1, it is easy to see that there is a number gap
between scale 100 and scale 69-90 and it is not difficulty to finddiscontinuous topography between Miyano and Mitani-Tokusa,
which is located in the canyon. This discontinuous topography
formed a natural barrier for the trees, protecting them from strong
wind blown by typhoon, so that there was almost no sign of damage to ginkgo trees by Typhoon 0613 in this area. If there were noeffect of this discontinuous topography, the damaged ginkgo trees
might spread far inland and the number gap would not exist.
3.5 Meteorological data and relation analysis
Since the center of Typhoon 0613 brushed the southwest corner of Yamaguchi Prefecture, there was a tendency of wind speed
reduction from southwest to northeast in Yamaguchi Prefecture
according to the data from AMeDAS. Fig. 11 shows an inverse
exponential function relationship between average wind speed and
ADC with R 2 equaling 0.723. The investigated area of thisresearch also run from southwest to northeast and had a tendency
of decreasing wind speed from Ube in the southwest with a maximum wind speed of 27 m/s to Tokusa in the northeast with a maximum wind speed of 8 m/s (see Table 1) during hit by Typhoon
0613. A similar tendency was expressed for the above-mentioned
indices for vigor of ginkgo trees in the investigated area. In breif
we cannot affirm that there is no relationship between the vigor of
ginkgo trees and Typhoon 0613 blowing.
According to data from AMeDAS and HPISYP, the precipitation was only 24 mm during Typhoon 0613 s hit in Yamaguchi,
and only 8.5 mm from Sep.18.2006 to Oct.31.2006, which is theminimum record of 44 days after hit by strong typhoon (>=15 m/s)
for past 40 years (1967-2006). On the other hand, the precipitation
during and after Typhoon 0418 s hit was so great that it induced
regional flooding (see Table 2). Meanwhile, almost no such kindof damage to the vigor of ginkgo trees occurred in Yamaguchi after
the hit of Typhoon 0418. Evidently, it can be thought that heavy
rainfall can counteract damage by typhoons like Typhoon 0613.

Fig. 11 Relationship between average wind speed (AWS) and average distance from AMeDAS stations to the coastline of west, southwest,
south and southeast (ADC) during hit by Typhoon 0613

Ginkgo trees vigor is damaged by strong wind and lower precipitation together in Yamaguchi City during Typhoon 0613 s hit. In
other words, it is mainly caused by water stress induced by strong
wind from Typhoon 0613.
4. CONCLUSION AND DISCUSSION
Typhoons are one kind of disaster that can lead to serious
damage to forests, trees, and shrubs. Besides mechanical damage,vigor reduction is another kind of damage by strong typhoons like
Typhoon 0613, which is characterized by discoloration and defoliation of ginkgo crowns accompanying with not-eye-catching branchor twig dieback. By component analysis, leaves on damaged ginkgo trees are composed of leaves with different scorch areas at thetime of investigation. Results show that the further they are fromthe coastline, the fewer scorched leaves, and the closer they are to
the coastline, the more scorched and dried leaves. The relationshipbetween DC and indices of GCRC, CC, and VI show a similar tendency that the further they are from the coastline, the smaller the

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F. WANG, H. YAMAMOTO AND K. IWAYA

Table 2 Related precipitation data for Yamaguchi during Typhoon 0613 and 0418

damage by Typhoon 0613 is and the bigger the GCRC, CC, and VI
are. Based on the multi-analysis of this research, similar tendency
has been found. Because of the low land productivity in coastal
area, the landscape trees should be affected by more complicatedfactors, in which the salt injury may be one of the serious damage
factors (Boyce, 1954; Griffiths et al., 2003; Okinaka et al., 1990;
Munns, 1993).
Since the 1980s, a gradually increasing number of researches
on image analysis have been carried out (Wang, 2006). Most ofthem were focused on the area of space-borne or air-borne image
analysis for vegetation. Ground-based digital image analysis was
also mainly limited to the canopy of plants (Bréda, 2003). Almost
no research has been found on typhoon damaged tree crown studies
by sideward image, which cannot be detected by space-borne or
air-borne equipments. Although there were some reports on
typhoon damage with sideward photo as it is, they are not reallyquantitative researches. In this paper, ground-based digital image
analysis was applied in the quantitative research of ginkgo trees
vigor damaged by Typhoon 0613, and was characterized by analyzing sideward image of entire crown. Compared to the common
sampling method, it is more effective in application to field measurement of the vigor of trees damaged by severe typhoon with lesslabor and less time requirement. It may be an alternative tool to be
used in estimating or evaluating the degree of damage by typhoons
like Typhoon 0613.
As early as 1805, Salisbury noted that great leaf injury
occurred when rain was not associated with strong wind. A universal lower rainfall, averaging 21.7 mm in the investigated area during the hit by Typhoon 0613, reveals that the ginkgo tree s vigor
reduced by Typhoon 0613 is just like Salisbury s note. That is
why almost no such damage was found in Yamaguchi during
Typhoon 0418, which is characterized by heavy rainfall accompanied by a high wind speed even greater than that of Typhoon 0613.
It can be said that the damage to the crown of ginkgo trees by
Typhoon 0613 is caused by water stress induced by strong wind.
It is observed that lower vigor status of ginkgo trees, especially at limited site condition, seems not caused by one hit. It is morecommon that before they perfectly recover from one hit by a storm
another hit occurred. This kind of continued damages induced theasymmetric crown of ginkgo trees in the sites with limited conditions and should affect the vigor status to respond the further seri-

ous hit by storms like Typhoon 0613.
5. ACKNOWLEDGEMENTS
We would like to express our gratitude to the Research Lab. ofEnvironmental Ecology, Faculty of Agriculture of Yamaguchi
University for providing research conditions and thank all members who helped us in our field studies.
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2006 Annual conference of American Society for Photogrammetry andRemote Sensing.

A QUANTITATIVE RESEARCH ON VIGOR OF GINKGO TREES HIT BY TYPHOON 0613 WITH GROUND-BASED DIGITAL IMAGE ANALYSIS

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