Ecological Informatics 12 (2012) 16–22

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Ecological Informatics
journal homepage: www.elsevier.com/locate/ecolinf

Image measurements of leaf scorches on landscape trees subjected to extreme
meteorological events☆
Fei Wang a,⁎, Kenji Omasa bab

Shandong Forestry Research Academy, 250014, Jinan, China
Graduate School of Agriculture and Life Sciences, the University of Tokyo, 113‐8657, Japana r t i c l e

i n f oArticle history:
Received 11 June 2012
Received in revised form 24 July 2012
Accepted 25 July 2012
Available online 29 July 2012
Keywords:
Landscape trees
Leaf scorch
Extreme meteorological events
Internal angle

a b s t r a c t
Trees grow in changing environments and are usually injured by many external factors including both abiotic andbiotic. Leaf scorch is a main symptom for many landscape trees when they are stricken by meteorological extreme
events, such as summer drought, strong typhoon and winter freezing and so on. In the study, the internal angle ofinjured area (IAIA) was deﬁned in relation to vein lines and measured non-destructively for some landscape tree
species. Meanwhile, the leaf scorch area percent (LSAP) and percent of scorched central vein (PSCV) were also
determined from RGB images. Positive relationships between IAIA and LSAP and between PSCV and LSAP were
found. The larger IAIA values for scorched leaves and smaller IAIA values for spot/anthracnose diseased leaves ofthe studied trees indicated that IAIA may be used as a diagnosing index of leaf scorch symptoms.
© 2012 Elsevier B.V. All rights reserved.

1. Introduction
Extreme meteorological events, such as strong typhoons andsummer droughts, in addition to root disease often induce tip and/or margin scorches on trees (Günthardt-Goerg and Vollenweider,
2007; Kozlowski, 1976; Vollenweider and Günthardt-Goerg, 2006;
Wang et al., 2009a, 2009b; Yapp, 1912) due to severe dehydration.
A variety of dieback and decline diseases of trees are favored by abiotic
stresses, such as drought, ﬂooding, extreme heat, mineral deﬁciency andair pollution. These diseases usually become severe after environmental
stresses render trees susceptible to organisms of secondary action(Kozlowski, 1985; Omasa et al., 2002; Schoeneweiss, 1981). Moreover,myxomycetes often conﬁne their attacks to the same regions of a leaf
(Yapp, 1912). Leaf scorches often showed systematic symptoms when
the trees are subjected to severe water stresses. Similar symptoms
may also be induced by several biotic agents, viruses and insects(Hammerschlag et al., 1986). However, pathogen-triggered injuries
generally cause unsystematic necrosis in a localized pattern and on
partial crowns of trees and shrubs. Leaf scorch symptoms originatingfrom extreme environmental events often appear in an inward spreading pattern. A type of inward leaf scorch symptom on dogwood trees
has been found in Yamaguchi, Japan, which was hit by a summer drought
in 2007 (SD2007) (Wang et al., 2009b). To identify the difference☆ Supported by the National Natural Science Funds of China. ID number: 301170671.
⁎ Corresponding author. Tel.: +86 0531 88557594; fax: +86 0531 88932824.
E-mail address: wf-126@126.com (F. Wang).
1574-9541/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ecoinf.2012.07.005

between abiotic leaf scorch and biotic damage, the parameters of internalangle of injured area (IAIA) and percent of scorched central vein (PSCV)
were deﬁned. The IAIA is a central angle corresponding to the scorchedleaf margin, and the PSCV is a length rate between the scorched partand the total length of the central vein in accord with the percent ofscorched leaf tip. They respond the scorch symptoms with respect totheir spreading from both radian and length.
Image analysis have increasingly become important tools to holistically study the characteristics of plants or trees (Adamsen et al.,1999, 2000; Jones, 2004; Omasa, 1990; Omasa et al., 2002, 2007;
Richardson et al., 2001; Wang et al., 2008a, 2008b). RGB image analysis has been recognized as a useful tool to determine the leaf scorcharea percent (Wang et al., 2009c; Zhao et al., 2012), and it has also
been used to directly measure the heterogeneousness of leaf living
parts and dead parts (Wang et al., 2009b). The common parametersof image analysis, such as distance, angle and area measurement,
are useful parameters to describe the morphology of plants andtrees (Bai et al., 2005; Bréda, 2003). In this study, it is aimed at objectively responding the ecological information from some landscapetrees and ﬁnding an easy and low cost way to diagnose the leaf
scorches that suffered extreme meteorological events by using thedigital image analysis. Another goal is focused on the proper parameteror index to describe the scorch symptoms. As a result, the IAIA value forleaf scorching, spot/anthracnose diseases and wind mechanical damage
as well as the PSCV for scorched dogwood leaves etc. was determinedby using the software of UTHSCSA Image Tool 3.00 to investigate thedifference among the symptoms caused by abiotic stress, biotic attack

F. Wang, K. Omasa / Ecological Informatics 12 (2012) 16–22

17

and mechanical damage. The positive result suggests that leaf scorch ofthese tree species is a systematic symptom which may be potentiallydiagnosed by using RGB image measurement.
2. Materials and methods
2.1. The studied position and tree species
This study was mainly carried out at Yamaguchi, Japan. The target
landscape trees and shrubs included the following species: kousa
dogwood (Cornus kousa Buerg.), which suffered severe SD2007 at
Yamaguchi Central Park; Japanese blue oak (Quercus glauca Thunb.)
and camphor tree (Cinnamomum camphora (L.) J. Presl.), whichwere struck by the strong dry typhoon 0613 (T0613); trident maple(Acer buergerianum Miq.) and zelkova (Zelkova serrata Murr.), whichwere hit by strong spring wind at Yamaguchi University; and Japanesespindle (Euonymus japonicus Thunb.), winter creeper (Euonymus
fortunei (Turcz.) Hand.-Maz.), Glossy Privet (Ligustrum lucidum Ait.)and red leaf photinia (Photinia glabra (Thunb.) Maxim.) supplement
shrubs in several hedges, which suffered winter injury at the Shandong
Forestry Research Academy in Jinan, China, and so on.
2.2. Preconditions and methods of image taking
Leaves were monitored before and after the symptom appearanceof leaf partial withering, disease and wind mechanical damage to
conﬁrm the origin of the symptoms. Leaf scorch events were recorded
soon after the symptoms appearance, when the leaf lesion color still
had the same color as the living part. During study of the partial freezing dehydration process of some broad evergreen tree species such as
Japanese spindle, Glossy Privet and so on; the freezing and thawing
process of their leaves were monitored.
The leaves were sampled from sampling trees and took photos
with a CCD camera (Canon IXY 6.0) or scanned with a ﬂat bed scanner(Canon d125u2). Images were stored in the form of Tiff format. Thereis no special constraint for the photograph taking in manual measurement of IAIA, PSCV and LSAP except the blurry images of leaf partial
withering symptom for most tree species. Images will be increased
luminance by using the adjust tool in Photoshop software if the object
leaf is too dim to be seen clearly. The number of sampled leaves foreach tree species is shown in the bracket following their names inthe ﬁgure captions (From Figs. 3 to 6).
In order to increase the sample numbers of diseased and scorchedleaves and to check multiple tree species, a large number of photographs from books and publishing papers have also been measured.
2.3. The deﬁnition and calculation of IAIA and PSCV values
The internal angle of injured area (IAIA) is a central angle when considering the farthest point that the injury has reached on the central
vein (or in the injured area if the injured area is beyond the centralvein) as tip point of the angle and considering the two lines from thispoint to the farthest points that the injury reached on both sides ofleaf edge as the two borders of this angle (Fig. 1b and c). The IAIA was
directly measured using the angle analysis tool in the software of
UTHSCSA Image Tool 3.00.
The PSCV was measured by using the distance tool in the softwareof UTHSCSA Image Tool 3.00 and calculated using Eq. (1) as follows:
PSCV% ¼ ðCV=TV Þ  100

ð1Þ

in which PSCV is the percent of scorched central vein, CV (from C to V
in Fig. 1a) is the pixel number of scorched part and TV (from T to V in
Fig. 1a) is the pixel number of total length of the central vein.

Fig. 1. Diagrams to show the internal angle of injured area (IAIA) and leaf scorch area
percent (LSAP). (a) A typical scorched kousa dogwood leaf with the non-scorchedgreen area (PGAL) and entire leaf area (POL) marked. (b) A scorched Japanese spindle
leaf with a typically obtuse IAIA. (c) A zelcova leaf mechanically damaged by wind witha signiﬁcant acute IAIA. The IAIA was measured by the tip point (TP) and side borders(BD).

2.4. Process and method to determine the LSAP
The target kousa dogwood trees were approximately 7 years
old and 3 to 4 m high, and these trees were planted around the
Yamaguchi Central Park. The number of sampled trees totaled 60. In
this study, the leaf scorch area percent (LSAP) values of the sampled
leaves were determined by image analysis. All of these trees weremonitored and analyzed by image measurement during the years of
2007, 2008 and 2009. In this study, 560 leaves were scanned with a
ﬂat bed scanner (Canon d125u2). Photoshop CS 12.0 software wasused to remove all objects except the leaves from the images. The
scorched area and overall leaf area was measured by using area tool in
the UTHSCSA Image Tool 3.00 software or directly read the pixels
from Photoshop. The LSAP was then calculated using Eq. (2) as follows:
LASP% ¼ 100−ð100  PGAL=POLÞð2Þ

where PGAL is the number of pixels in the green area of the leaf, and POL
is the number of pixels in the overall leaf (Fig. 1a).
A multivariate normality test has been carried out for the data of
IAIA, LSAP and PSCV, they are all consistent with the normal distribution
with the U checking value less than 1.96 and P> 0.05.
2.5. Meteorological data and related parameter
The precipitation data were obtained from the Automated Meteorological Data Acquisition System (AMeDAS) in Japan. The three month accumulated precipitation (TMP) was calculated with Eq. (3) to compare
the seasonal difference in precipitation among the years 2007, 2008 and2009 as follows:
TMP i ¼

2
XMPRiþjð3Þ

j¼0

where i=1, 2…10 and i=1 in January; j=0, 1 and 2; and MPRi+j is themonthly precipitation value in the month of i+j.
2.6. Leaf venation, water-trail and red-color-trail observations
Leaf venation of target tree species have been studied by using bothmethods of micro-distance photography and chemical treatment. In
which, most of tree species with transparent leaﬂets was directly
observed by using micro-distance photograph, while the tree species
with thick and nontransparent leaﬂets were ﬁrst treated with NaOH
solution to obtain the clear venation images.
By monitoring the leaﬂet of some evergreen arbor/shrub species,
the water-trail, a phenomenon of partial leaﬂet temporary water

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F. Wang, K. Omasa / Ecological Informatics 12 (2012) 16–22

deﬁcit with signiﬁcant visible trace during the process of occasional
winter frozen, was studied. Then, the red-color-trail has been
observed at the same area where water-trail has been found. They
are all similar to the permanent damage symptoms of leaf scorches
after extreme winter dehydration. Therefore, the “IAIA” of themwere measured with similar method to prove that they also result
from the water metabolism and imbalance of water system.
3. Results and analysis
3.1. Extreme meteorological events in 2007, 2008 and 2009 andresponses of several kousa dogwood trees in Yamaguchi
In the presence of meteorological changes in the world, theclimate in Yamaguchi, Japan ﬂuctuated among the years 2007, 2008
and 2009. The ﬂuctuations were mainly reﬂected in the threemonth precipitation values during these years (Fig. 2a). The meteorological environment in 2007 in Yamaguchi, Japan was characterized
by drought in almost all of the ﬁrst eleven months and by high temperatures in February, August, September and October. The annual
precipitation was 71.6% of the normal precipitation of this area, andthe precipitation for the ﬁrst nine months was only 60.1% of thenormal precipitation. From August 7th to August 18th in 2007, morethan 15 days of continual anticyclone weather occurred. During
these days, the average and minimum temperatures were higher
than normal (1971–2000), and no rainfall occurred. Meanwhile, therelative humidity values represented a U-shaped curve. Although
the precipitation during the ﬁrst half of the year in 2008 was similar
to normal years, the annual deviation of mean temperature in thesummer was 0.5 °C higher than normal, and the precipitation wasless than 80% of the normal precipitation at Yamaguchi. During thehottest days from July 22nd to August 14th in 2008, only 11 mm ofprecipitation was recorded at the Yamaguchi Observatory. The
maximum daily temperature during this period was higher than
33 °C. The characteristic precipitation in 2009 presented a different
tendency compared to the years 2007 and 2008, especially in thesummer. The prolonged Japanese rainy season and historical record
created heavy rainfall in July caused local ﬂooding in Yamaguchi.
More than 750 mm of monthly precipitation led to a peak in the
TMP as shown in Fig. 2a. After this period, less rainfall in September
resulted in a record of the third least monthly rainfall in Yamaguchi
meteorological history.
This strongly contrasting climate induced different responses fromlandscape trees in Yamaguchi, especially for the kousa dogwood trees
planted in the Yamaguchi Central Park (Fig. 2b). According to the
LSAP values of the 60 ﬁxed sampling trees, more than 40% of theleaf area was reduced by partial withering in 2007. The leaf scorcharea of 13% in 2008 for the same sampling trees may be a result of
the normal precipitation in the ﬁrst half of the year (Fig. 2a). In
2009, the LSAP was only 0.3%, which implied that almost no leaf
scorch occurred. According to the variation analysis, LSAP values
varied signiﬁcantly among 2007, 2008 and 2009 with an F-value
equal to 62.6 (P b 0.01). There was a consistency between the leaf scorcharea percent and precipitation during the summer days, especially in
July, August and September. The LSAP indirectly indicated that theheavy rain in the summer of 2009 counteracted the summer heat wave
and caused almost no leaf scorch occurrence on the kousa dogwood
trees planted in Yamaguchi Central Park. Similarly, the largest IAIA
value for kousa dogwood leaves was obtained in 2007, followed by the
IAIA values in 2008 and 2009. A signiﬁcant difference in the IAIA values

Fig. 2. Precipitation characteristics and responses of several kousa dogwood trees in Yamaguchi in 2007, 2008 and 2009. (a) Three month precipitation (TMP) during 2007 (△),
2008(●) and 2009( ); (b) Leaf scorch area percent (LSAP); (c) internal angle of injured area (IAIA) for 60 kousa dogwood sample trees planted around the Yamaguchi Central
Park; (d) Leaf scorch area percent values in 2007, 2008 and 2009 for two kousa dogwood sample trees (number 9 and number 33) with leaf scorch present in all of the three years.

F. Wang, K. Omasa / Ecological Informatics 12 (2012) 16–22

was measured among the years with an F-value of 144.76 (P b 0.01)(Fig. 2c).
There was almost no appearance of leaf scorch symptoms by
August 28th in 2009, which was the date of investigation in all
three years of the study period. Leaf scorch symptoms among the
kousa dogwood sample trees did not occur until the end of September
in 2009, which may have been attributed to the lower incidence ofrainfall in September of 2009. According to the investigation, only
two individual trees had leaf scorch symptoms on September 20th
after prolonged lack of rain and high temperatures. By comparison,
the LSAP of these two individual trees (N9 and N33) in 2009 was
far lower than that in 2007 and 2008 and could be considered
nonoccurrence as compared to 2007 and 2008 (Fig. 2d). Moreover,this result may provide further evidence that the leaf scorch of kousa
dogwood trees in Yamaguchi Central Park is associated with the water
stress induced by less rain and high temperatures during summer.

3.2. The LSAP, IAIA and PSCV of scorched kousa dogwood leaves
Careful observation of kousa dogwood leaves reveals that leaf veins
are thinner from the base to the tip and from the central vein to themargin. Similarly, leaf scorch caused by extreme meteorological events
usually starts from the leaf tip and margin of kousa dogwood leaves.
This phenomenon to some extent also appeared in this study bymeasuring the IAIA and PSCV, which reﬂect the radian and length of
the scorched area, respectively, of kousa dogwood leaf images. Thus,
as the IAIA and PSCV values increased, the tip and margin scorches
became more severe.
According to the measurement of these two parameters, a tendencyof the IAIA to increase as the LSAP increased (or a signiﬁcantly positive
exponent relationship) was found (Fig. 3a), with an R2 value of 0.556(Pb 0.01). Moreover, a statistically signiﬁcant and positive exponent
relationship existed between the PSCV and LSAP values (Fig. 3b), withan R2 of 0.841 (Pb 0.01). Thus, as the percent of scorched leaf area

Fig. 3. Relative curves of (a) leaf scorch area percent (LSAP) versus internal angle of injured
area (IAIA) and of (b) LSAP versus percent of scorched central vein (PSCV) (n=65).

19

increased, a larger area of the leaf tip and margin died of meteorologicalinjury. Therefore, the kousa dogwood leaves showed leaf scorch
symptoms starting from the tip and margin of the leaf.
3.3. The “IAIA” value of frozen dehydrated leaves with water-trail andred-color-trail
Persistent winter frozen dehydration induced similar symptoms toleaf scorches, such as water-trail (Fig. 4a-1, a-2, a-3 and a-4) andred-color-trail (Fig. 4a-5, a-6) on leaves of some landscape trees withlarger “IAIA” values (Fig. 4b-1, b-2, b-3, b-4, b-5 and b-6) of more than
250°. The water-trail is usually restorable and disappeared after thawof the frozen leaves. Permanent leaf scorch often occurred at the same
area as the frozen dehydration persisted for a longer time (Fig. 4a-2,tip), during severe drought or at the extreme stressed environment.
For example, in the winter from 2011 to 2012 only a few Japanese spindles around the yard of Shandong Forestry Research Academy in Jinan,
China appeared permanent symptoms of leaf scorch starting from tip
and margin. In which, some of them were newly transplanted seedlings
with imperfect root system; some of them grew on new branches
sprouting from an old root stock. Whatever, there has been a signiﬁcant
positive relation between water-trail area rate (w-rate) during frozen
dehydration and the green area rate (G-rate) of these leaves after permanent scorch (Fig. 4c). It suggests that the water and energy imbalance become the trigger of permanent scorch, the water-trail andred-color-trail symptoms, which start from the leaf tip and margin.
3.4. Comparison of multiple leaf partial injuries of several landscape trees
Direct image measurement of leaf wind break was seldom found.
In 2009, strong windy weather accompanied by heavy rainfall
occurred twice in Yamaguchi, in late spring and early summer(on April 20th and May 21st). The maximum gust wind speeds reached26.2 and 19.9 m/s on April 20th and May 21st, respectively. Due to thestrong wind on April 20th, severe mechanical damage was found on thejuvenile leaves of zelcova, Japanese blue oak and trident maple trees,
and the severity of the damage was also attributed to the early leaf
stage and leaf textures. One month later, however, the same intensityof strong wind had no inﬂuence on the leaves of these tree species
because the leaves were more developed and stronger, which allowed
them to endure the strong wind. The wind break damage to the leaves
occurred mainly on juvenile leaves and seldom on mature leaves. The
injured juvenile leaves usually had smaller IAIA values (Fig. 5a-3, a-4,
a-5, b-3, b-4 and b-5) similar to the anthracnose-diseased dogwood
leaves (Fig. 5a-1, a-2, b-1 and b-2). However, the strong and hot windduring the summer drought period in August of 2007 triggered leaf
scorch symptoms in most of the kousa dogwood trees planted aroundYamaguchi Central Park. The IAIA values of kousa dogwood leaves
after the summer drought period in 2007 were greater than 250°
(Fig. 5a-7 and b-7). In 2006, many landscape trees had leaf scorch on
the windward side of their crowns after being hit by strong wind caused
by T0613 accompanied with less rainfall. Some camphor trees andJapanese blue oaks were exceptional examples with large IAIA values(Fig. 5a-6, a-8, b-6 and b-8). A similar mechanism was not found simultaneously for both mechanical damage on younger leaves and leaf
scorch caused by extreme meteorological events. Interestingly, during
the winter injury process, with the average monthly temperaturefrom November 2009 to March 2010 being 1.4 °C lower than normal,
some evergreen shrub species planted in Jinan City, China presented
similar symptoms to those hit by extreme meteorological events during
SD2007 and T0613 in Yamaguchi, Japan with larger IAIA values(Fig. 5a-9, a-10, a-11, b-9, b-10 and b-11). Therefore, the symptoms
may be related to water stress as evidenced by the similar symptoms
after suffering from the extreme meteorological events of SD2007 andT0613. Winter injury has ever been considered to be the result of afrozen dehydration process (Pearce, 2001), especially in areas where20

F. Wang, K. Omasa / Ecological Informatics 12 (2012) 16–22

Fig. 4. The images of leaf water-trail (a, 1–4) and red-color-trail (a, 5–6), and the “IAIA” value (b) of some landscape tree species and the relation between water-trail area rate
(W-rate) of frozen dehydrated leaves and green area rate (G-rate) of permanently partial withered leaves of Japanese spindles (c) during or after the process of frozen dehydration.
In which, 1 is the Japanese spindle (n = 63), 2 the Glossy Privet (n = 26), 3 the Purpus Privet (n = 36), 4 the Wichura Rose (Rosa wichuraiana Crep.) (n = 11), 5 the winter creeper(n = 13) and 6 the red leaf photinia (n = 18).

there is a strong winter wind (Pirone, 1978). The IAIA values of theseevergreen tree species were similar to the IAIA values of leaf scorch on
the kousa dogwood trees caused by summer drought. Thus, theseresults suggested that the frozen dehydration process has similar
mechanism to desiccation or strong, dry typhoon strikes.
Theoretically speaking, the limitation value of the internal angle ofthe leaf spot disease should be the limitation of the circumferential
angle of a circle (or 180°), which is equal to half of the limitation of
the central angles of a circle (360°). Therefore, it can be deduced
that the IAIA value of an angular leaf spot disease of dogwood is lessthan 180°.

(1981) also showed larger IAIA more than 300° (Fig. 6G, H) except theAmerican elm leaf suffered bacteria leaf scorch (Fig. 6K, IAIA=76.9).
According to the measurement of three groups of leaf spot disease
and anthracnose disease from some plant disease books consisting of
16, 53 and 57 cases (CAAS, 1965; Ito and Aino, 1976; Pirone, 1978),the average IAIA values respectively equal to 119.7 ± 22.8° (Fig. 6-YT),
142.0 ±9.8° (Fig. 6-ZG) and 106.9± 8.3° (Fig. 6-BD). These results
were in accordance with the disease or mechanical damage samplings
shown in Fig. 6. They were far less than the mean IAIA values of leaf
scorch symptoms caused by SD2007, T0613 and prolonged winter injury with average IAIA values ranging from 250 to 320° with signiﬁcantstatistical differences due to the F value of 63.5 and P-value 6.58E−67.

3.5. Quantitatively measuring results of leaf scorch from historical reports

4. Discussion

The IAIA of leaf images measured from the past reports is aneasiest way to study the leaf scorch symptoms. By measuring thetypically scorched leaves from the reports of Yapp (1912), the larger
IAIA of all leaves tally with this conclusion even the linear leaf of
Buckhorn Plantain (Plantago lanceolata L.) (Fig. 6A; IAIA = 205.9).
The IAIA of the typically sampling leaves for the tree species ofCommon Oak (Quercus robur L.), Europea Beech (Fagus sylvatica L.),
European-haw (Crataegus oxyacantha), Poplar (Populous spp.) and
Rose (Rosa spp.) exposed to strong wind was even more than 300°
(Fig. 6B, C, D, E and F). Similarly, all leaves from America Linden (Tilia
spp.), Buckeye (Aesculus carnea), Kousa dogwood (C. kousa Buerg.) andAmerican elm (Ulmus Americana L.) suffered environmental stresses,with partial withering symptoms from the report of Schoeneweiss

Exogenous environmental factors become operative through theendogenous metabolic processes of trees. The origination and spreadof disease symptoms also can be considered as an interaction process
between pathogen intrusion and plant resistance. Pathogen spreading is a complex action, which includes the intrusion of a hypha into
host in the pattern of cell by cell. A hypersensitive response fromthe host usually conﬁnes the pathogen into a localized necrotic lesion
even the pathogen fails to further intrude into the host if it is incompatible. This type of host defense action varies among cultivars withdifferent sensitivities to the pathogen (Wharton et al., 2001) or varies
between attached leaves and detached leaves (Liu et al., 2007). Thiskind of leaf-pathogen interaction even can be detected by using thermography before symptoms appearance (Chaerle et al., 1999; Jones,

Fig. 5. Typical symptom (a) and internal angle of injured area (IAIA, b) of some landscape trees. (1) IAIA of leaf injury to kousa dogwood leaves caused by anthracnose disease(n = 5) in Yamaguchi, Japan. (2) IAIA of leaf injury to kousa dogwood leaves caused by both water stress and secondary disease (n = 26) in Yamaguchi, Japan. IAIA of leaf injury to(3) Japanese blue oak (n = 35), (4) zelcova (n = 28) and (5) trident maple (n = 4) leaves caused by strong wind during the leaf expanding stage in April 2009 in Yamaguchi,
Japan. IAIA of leaf injury to (7) kousa dogwood leaves (n = 25) triggered by SD2007, (6) IAIA of leaf injury to Japanese blue oak leaves (n = 31) and (8) camphor tree leaves(n = 34) induced by T0613 in Yamaguchi, Japan. IAIA of leaf injury to (9) Japanese spindle (n = 26), (10) winter creeper (n = 23) and (11) red leaf photinia (n = 6) leaves causedby severe winter frozen dehydration in Jinan City, China.

F. Wang, K. Omasa / Ecological Informatics 12 (2012) 16–22

400
350
300

IAIA

250
200
150
100
50
0

A

B

C

D

E

F

G

H

I

J

K YT ZG BD

Fig. 6. IAIA value measured from the reports on leaf scorch and diseases. It includes leaf
scorch on the linear leaf of Buckhorn Plantain (A), on the leaves of Common Oak (B), Europea
Beech (C), European-haw (D), Poplar (E), Rose (F (n=5)), America Linden (G), Buckeye (H),Kousa dogwood (I) and American elm (J (n=17)); bacteria leaf scorch (Bls) on Americanelm (K); and the anthracnose/spot diseases symptoms from different plant disease books(Yt (n=16), Zg (n=53) and Bd (n=57)).

2004; Omasa et al., 2002; Wang, 2010). Therefore, the necrotic lesion
on a diseased leaf is usually impeded by the living cells all around if
the intrusion point is located just within the leaﬂet. The spot/anthracnose disease induced by fungus as well as the mechanical damage induced by strong wind occurring on the juvenile leaves of sometree species had relatively smaller IAIA values because the symptom
spread was often resisted from all directions, except for the leaf margin in the case of margin intrusion.
By comparison, the leaf scorch caused by severe meteorologicalextreme events such as summer drought or winter damage of sometree species often presented the resistance coming from the living
tissues nearest to the major vein system. Kozlowski (1976) considered that visible symptoms of water stress responses of landscapetrees often show temporal delay, and the rapid appearance of symptoms after rehydration suggests that the symptoms are initiated bya response to water stress that cannot be completed without
adequate water. The symptom caused by this type of systematic
shock often has characteristics similar to the defense to the drying
back progress of the tissues furthest from water-way (Wang et al.,2009b). Leaf scorch caused by water stress appears as a pattern that
constructs a barrier along an isoline of water potential to protectfrom further water loss (Wang et al., 2009b). The different mechanisms of these stresses cause distinct symptoms. In this study, we
found that the leaf scorch originating from desiccation usually hadlarge IAIA and PSCV values due to the thinner veins at the tips andmargins of leaves. Thus, this result supports the hypothesis that leaf
scorch often starts from the leaf parts furthest from water-way(Günthardt-Goerg and Vollenweider, 2007; Yapp, 1912), and it alsosuggests that image analysis may be a useful tool for comparing leaf
scorch symptoms caused by desiccation and spot/anthracnose disease.
Leaf scorches often occurred on transplanting seedling/trees,
shade trees (Hammerschlag et al., 1986; Kozlowski, 1985) andextreme environment planted trees, and on leaves of watershoot,which easily present water imbalance during striking by meteorological extremes. Some shade trees of Japanese blue oak subjected to astrong wind at Yamaguchi University presented leaf scorch on thewindward side after T0613, which indicated that serious water imbalance occurred in the thin shade leaves facing the strong and dry
wind. However, the remaining green parts of the scorched leaves
maintained normal function for more than three years (Wang et al.,2009a). By comparison, the IAIA values of these leaves were signiﬁcantly different from the IAIA values of leaves that experienced

21

mechanical damage caused by strong early spring wind in 2009 andsimilar to the IAIA values of leaves that were hit by summer drought
events in 2007.
Some diseases and mechanical damage caused the leaves oflandscape trees to have similar symptoms with smaller IAIA values,
which implied that the symptoms did not cause systemic damage inthe trees. The leaf scorch symptoms caused by summer drought, dry
typhoons and persistent winter frozen dehydration presented similar
symptoms with larger IAIA values, which suggested that these results
all triggered systemic variation through water metabolism. The
recoverable symptoms of water–trail on some evergreen tree species
during the severe frozen dehydration may be the actual evidence of
its water imbalance. The red-color-trail appears at the same area of
the water-trail, which suggests that it is the internal responses oftrees to water stresses induced by extreme meteorological events.
In addition, the symptoms and injury mechanisms of polluted
plants are usually different from the leaf scorch symptoms causedby extreme meteorological events (Mudd and Kozlowski, 1975;
Omasa et al., 1981). Therefore, there is potential to diagnose thesymptoms of leaf scorch caused by extreme meteorological eventsfrom other damages (Vollenweider and Günthardt-Goerg, 2006). In
North America, bacterial leaf scorch is affected by both Xylellafastidiosa and water stress (McElrone et al., 2001; Wood et al.,1995). The dualism of their symptoms (Hammerschlag et al., 1986;
McElrone et al., 2001) irregular leaf scorch symptoms (Thorne et al.,2006) indicates that the diagnosing method described in this paper
may be used for morphologically determining which one is the
major factor between water stress and bacterial infection.
Although IAIA differences among distinct injuries are consistent, itremains unclear for the universality of most plant or tree species andit needs to be further proven by measuring a large number of samples.
The judgment of injuries was complicated because abiotic stresses
usually predispose the occurrence of disease (Blodgett et al., 1997;
Desprez-Loustau et al., 2006; Kozlowski, 1985; Schoeneweiss, 1981),
sometimes abiotic stress and disease coexisted on the same tree, andthe responses varied with tree species. Although the diseased leaves
usually showed local lesions at leaf margins with small IAIA, somelesions occasionally connected together, which made the lesions look
like the typical characteristics of water stress, especially during thesecond half of the disease process. Whatever, the typical disease characteristics can be statistically manifested when sample sizes are large
enough in the early stage of the disease. In contrast, partial leaves
from few water loss-resistant tree species, especially for some evergreen tree species with larger leaﬂets, sometimes presented local necrotic lesions away from the margin similar to disease symptoms. Treespecies with these types of characteristics usually contained venations
that lacked the veins with thin tip and margin or gradually thinnerveins from base to tip and from central vein to margin. Therefore, measurements should be perfected before the universality of the symptoms
on most plant or tree species is conﬁrmed.

5. Conclusion
The IAIA, LSAP and PSCV become effective indices to respond to
the scorch symptoms of dogwood trees etc. induced by extreme
meteorological events. Meanwhile, the larger IAIA values forscorched leaves and smaller IAIA values for spot/anthracnose
diseased leaves of the studied trees indicated that IAIA may be
used as a potential diagnosing index of leaf scorch symptoms after
further studies. This study suggested that digital image analysis
can be a useful and low-cost tool in distinguishing leaf scorch
symptoms from disease and mechanical damage on some landscape trees. It makes the study of leaf scorch being possible fromexperiential comparison to quantitative and statistical analysis in
the scope of ecological informatics.

22

F. Wang, K. Omasa / Ecological Informatics 12 (2012) 16–22

Acknowledgment
We express our gratitude to Guofan Shao, professor in Purdue University of USA, for his kindly help.
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