HYDROLOGICAL PROCESSES Hydrol. Process. 24, 588–595 (2010) Published online 14 January 2010 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/hyp.7553 Detecting forest degradation in Kochi, Japan: ground-based measurements versus satellite (Terra/ASTER) remote sensing Bunkei Matsushita, 1 * Ming Xu, 2,3 Yuichi Onda, 1 Yuna Otsuki 1 and Mai Toyota 1 1 Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan 2 Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographical Sciences and Natural Resources, Chinese Academy of Sciences, Beijing 100101, China 3 Department of Ecology, Evolution and Natural Resources, Rutgers University, New Brunswick, NJ 08901-8551, USA Abstract: Forest degradation, due mainly to poor management, is of increasing concern in Japan. Major ecosystem functions, such as biodiversity, productivity, and soil and water retention, are being lost or weakened in Japan’s forests, especially in Japanese cypress (Hinoki; Chamaecyparis Obtusa Sieb.) plantations. Detecting forest degradation is critical to the restoration of the ecosystem in the Kochi area, but ground-based detection methods are labour intensive and difficult to implement in mountainous areas. In this study we examined the ecological characteristics (e.g. soil water content (SWC) and leaf water content) of degraded and healthy forests, based on in situ measurements and controlled experiments, and present a new method for mapping forest degradation based on remote sensing techniques. A field survey was carried out to record the locations and conditions of the degraded Japanese cypress plantations. Empirical relationships among the degraded plantation, SWC, fuel moisture content (FMC), and vegetation indices (VIs) were investigated by field survey and control experiments. We found that the SWC of the degraded Japanese cypress plantations was lower than that of the well-managed Japanese cypress plantations. We also found that the SWC, FMC, and VI are highly correlated (R> 0Ð80). In addition to the ground investigation, we used the advanced spaceborne thermal emission and reflection radiometer (ASTER) data and compared a number of VIs to determine their relationships to the biophysical/biochemical attributes of vegetation canopies. Our results showed that the ASTER thermal band was the most effective method used to detect degraded Japanese cypress plantations in the study area. Copyright 2010 John Wiley & Sons, Ltd. KEY WORDS ASTER thermal band; water-content-based index; unmanaged plantation; infiltration capacity; fuel moisture content Received 4 December 2007; Accepted 4 December 2008 INTRODUCTION Forests cover about 67% of the total land area in Japan, of which more than 40% are plantations. About 80% of the plantations are less than 45 years old, which means that they require appropriate management, such as timely thinning (Forestry Agency, 2003). However, these plan- tations, especially those of Japanese cypress (Hinoki; Chamaecyparis Obtusa Sieb.) which is a major com- mercial tree species (Miura et al., 2002), have severely degraded in recent years, due mainly to poor management (Onda et al., 2005; Onda et al., 2010). Although forest degradation does not change the forest’s overall classi- fication as with the deforestation occurring elsewhere, for instance in the Amazon Basin, Thailand, Malaysia, etc., these subtle changes nonetheless affect the charac- teristics and functions of the land cover (Turner et al., 1993). In fact, forest degradation is of increasing con- cern in Japan because some ecosystem functions, such as * Correspondence to: Bunkei Matsushita, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8572, Japan. E-mail: [email protected]sustaining biodiversity, productivity, and soil- and water- holding capacities, are being lost or weakened in many plantations (Hattori et al., 1992; Miura et al., 2002; Onda et al., 2010). Therefore, the detection of degraded forests is critical to effective forest and water resource manage- ment, assessment of the water conservation function of forests, and protection of downstream ecosystems and urban areas. Remote sensing techniques are probably the most effective means for detecting forest degradation in this region, because most of the affected forests are located in remote mountain areas which are difficult to access. Detecting forest degradation based on remote sensing can be achieved through measurement of differences in the biophysical/biochemical attributes of the canopy surfaces between healthy and degraded forests. Several vegetation indices (VIs) related to biophysical/biochemical attributes of vegetation have been proposed for monitoring the status of vegetation using remote sensing techniques. For example, the normalized difference vegetation index (NDVI), which mainly pertains to the chlorophyll con- tent (Rouse et al., 1974), the photochemical reflectance index (PRI), which mainly pertains to the xanthophylls Copyright 2010 John Wiley & Sons, Ltd.
Transcript
HYDROLOGICAL PROCESSESHydrol. Process. 24, 588–595 (2010)Published online 14 January 2010 in Wiley InterScience(www.interscience.wiley.com) DOI: 10.1002/hyp.7553
Detecting forest degradation in Kochi, Japan: ground-basedmeasurements versus satellite (Terra/ASTER) remote
sensing
Bunkei Matsushita,1* Ming Xu,2,3 Yuichi Onda,1 Yuna Otsuki1 and Mai Toyota1
1 Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan2 Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographical Sciences and Natural Resources, Chinese Academy of
Sciences, Beijing 100101, China3 Department of Ecology, Evolution and Natural Resources, Rutgers University, New Brunswick, NJ 08901-8551, USA
Abstract:
Forest degradation, due mainly to poor management, is of increasing concern in Japan. Major ecosystem functions, such asbiodiversity, productivity, and soil and water retention, are being lost or weakened in Japan’s forests, especially in Japanesecypress (Hinoki; Chamaecyparis Obtusa Sieb.) plantations. Detecting forest degradation is critical to the restoration of theecosystem in the Kochi area, but ground-based detection methods are labour intensive and difficult to implement in mountainousareas. In this study we examined the ecological characteristics (e.g. soil water content (SWC) and leaf water content) ofdegraded and healthy forests, based on in situ measurements and controlled experiments, and present a new method formapping forest degradation based on remote sensing techniques. A field survey was carried out to record the locations andconditions of the degraded Japanese cypress plantations. Empirical relationships among the degraded plantation, SWC, fuelmoisture content (FMC), and vegetation indices (VIs) were investigated by field survey and control experiments. We found thatthe SWC of the degraded Japanese cypress plantations was lower than that of the well-managed Japanese cypress plantations.We also found that the SWC, FMC, and VI are highly correlated (R > 0Ð80). In addition to the ground investigation, we usedthe advanced spaceborne thermal emission and reflection radiometer (ASTER) data and compared a number of VIs to determinetheir relationships to the biophysical/biochemical attributes of vegetation canopies. Our results showed that the ASTER thermalband was the most effective method used to detect degraded Japanese cypress plantations in the study area. Copyright 2010John Wiley & Sons, Ltd.
Received 4 December 2007; Accepted 4 December 2008
INTRODUCTION
Forests cover about 67% of the total land area in Japan,of which more than 40% are plantations. About 80% ofthe plantations are less than 45 years old, which meansthat they require appropriate management, such as timelythinning (Forestry Agency, 2003). However, these plan-tations, especially those of Japanese cypress (Hinoki;Chamaecyparis Obtusa Sieb.) which is a major com-mercial tree species (Miura et al., 2002), have severelydegraded in recent years, due mainly to poor management(Onda et al., 2005; Onda et al., 2010). Although forestdegradation does not change the forest’s overall classi-fication as with the deforestation occurring elsewhere,for instance in the Amazon Basin, Thailand, Malaysia,etc., these subtle changes nonetheless affect the charac-teristics and functions of the land cover (Turner et al.,1993). In fact, forest degradation is of increasing con-cern in Japan because some ecosystem functions, such as
* Correspondence to: Bunkei Matsushita, Graduate School of Lifeand Environmental Sciences, University of Tsukuba, 1-1-1 Tennoudai,Tsukuba, Ibaraki 305-8572, Japan.E-mail: [email protected]
sustaining biodiversity, productivity, and soil- and water-holding capacities, are being lost or weakened in manyplantations (Hattori et al., 1992; Miura et al., 2002; Ondaet al., 2010). Therefore, the detection of degraded forestsis critical to effective forest and water resource manage-ment, assessment of the water conservation function offorests, and protection of downstream ecosystems andurban areas.
Remote sensing techniques are probably the mosteffective means for detecting forest degradation in thisregion, because most of the affected forests are locatedin remote mountain areas which are difficult to access.Detecting forest degradation based on remote sensing canbe achieved through measurement of differences in thebiophysical/biochemical attributes of the canopy surfacesbetween healthy and degraded forests. Several vegetationindices (VIs) related to biophysical/biochemical attributesof vegetation have been proposed for monitoring thestatus of vegetation using remote sensing techniques.For example, the normalized difference vegetation index(NDVI), which mainly pertains to the chlorophyll con-tent (Rouse et al., 1974), the photochemical reflectanceindex (PRI), which mainly pertains to the xanthophylls
Copyright 2010 John Wiley & Sons, Ltd.
DETECTING FOREST DEGRADATION IN KOCHI, JAPAN 589
content (Penuelas et al., 1995), the normalized differencewater index (NDWI; Gao, 1996), the water index (WI;Penuelas et al., 1997) and the land surface water index(LSWI; Xiao et al., 2004), which mainly pertains to watercontent, have all been employed. In addition, the land sur-face temperature (LST), measured by the thermal-infraredbands of satellite sensors, has also shown strong corre-lation with the biophysical attributes of vegetation. Forexample, sparse or short vegetation shows a higher LSTvalue than dense or tall vegetation (Nemani and Running,1997).
The objectives of the present study are to (1) confirmthe locations and conditions of degraded and healthyJapanese cypress plantations based on a field survey;(2) investigate the relationships between the degraded/healthy Japanese cypress plantations and various VIsbased on the field survey and controlled experiments;(3) find the most effective remote-sensing-based indexor indices for detecting degraded forests and (4) mapthe degraded Japanese cypress plantations in the Kochiregion based on the selected index.
METHODS
Study area
The study area (Taisho town) is located in the KochiPrefecture, in western Japan (Figure 1). The annual totalprecipitation in the study area is about 2900 mm, withmost of the rainfall brought by typhoons during thesummer monsoon season. Plantations account for 63%of the total forest by coverage in the region, and 53% ofthe plantations are Japanese cypress plantations. Most ofthese plantations (83%) are between 30 and 45 years old.Forest management, such as timely thinning, is absent inthese plantations due to the lack of a sufficient labourforce and sluggish timber prices. As a result, most of theplantations in this area have severely degraded, whichhas been of increasing concern among local communities,scientists, and government agencies (Onda et al., 2005).
Characteristics of the degraded forests
Japanese cypress was extensively planted in the 1960sas a major commercial tree species following the clear-cutting of pre-existing forests (Fukuyama et al., 2005;Onda et al., 2005). The plantations have become highlydense recently, resulting in complete canopy closure.This in turn has prevented the development of under-story vegetation, such as shrubs and herbs, because oflight limitations. Additionally, the litter layer is absentin this type of plantation because the Japanese cypresshas scaly leaves that are easily fragmented after fallingto the ground. These leaves are then removed by heavyrainstorms because of the absence of shrub/herb lay-ers in the understory (Hattori et al., 1992). As a result,soil erosion and soil compaction/crusting from raindropshave impacted the forest floor directly and have severelychanged the soil hydrology, resulting in decreased soil
infiltration, flooding, increased sediment moving down-stream, and reduced ecosystem productivity (Yukawa andOnda, 1995). Figure 2 shows the mechanisms and pro-cesses of forest degradation in the Japanese cypress plan-tations in Japan.
In comparison with healthy Japanese cypress planta-tions, a degraded Japanese cypress plantation may feature(1) higher canopy density due to the lack of timely thin-ning; (2) lower chlorophyll-a content in leaves due to thesoil erosion and light competition affecting the ecosys-tem productivity and (3) lower leaf water content due tothe decreased soil infiltration and, hence, lower soil mois-ture content. We believe that all of these changes in thebiophysical and biochemical attributes of the degradedplantation should be reflected in the different VIs andcanopy surface temperature, which could be detected withremote sensing data.
In situ data collection
A field survey was conducted from August to Novem-ber 2004 with 100 sampling sites selected, of which88 sites were Japanese cypress plantations and 12 wereJapanese cedar plantations (sugi; Cryptomeria japonica).The locations of the investigation sites were measuredby global positioning systems (GPS) (GARMIN Ltd.,GPSmap76S), and several sites that were measured witha low level of accuracy were modified using a 1 : 25000 topographical map. Ten measurements of illuminancewere simultaneously obtained using an illuminometer atthe inside and outside of the forest at each site, and theaverage values were used to estimate the relative illumi-nance for the site. The percentage of understory vegeta-tion within a 2 ð 2 m frame was estimated from photointerpretation. Soil volumetric water content (SWC) inthe top 12 cm of the soil was measured in late October2004 using a HydroSense (Campbell Scientific, Inc.) at73 sites in the Japanese cypress plantations. The SWCat each site was obtained by averaging five measure-ments that were randomly located in a 5 ð 5 m plot. Leafsamples from Japanese cypress plantations were also col-lected from 24 sites to measure the fuel moisture content(FMC).
Controlled greenhouse experiment
To investigate the relationships between the SWC andFMC, and between the FMC and VI of Japanese cypressplantations, we carried out controlled experiments ina plastic greenhouse, located in the Agricultural andForestry Research Center, University of Tsukuba. Wepotted 12 Japanese cypresses (3 years old, 60 cm height)and divided them into two groups randomly. At first,we gave all 12 pots enough water for optimum growthconditions, and then we gave water continuously to onegroup and stopped giving water to the other group.SWC, FMC, and spectral reflectance were measured forboth groups. For SWC, we averaged the values of fivemeasurements using HydroSense (Campbell Scientific,Inc.) for every pot. For FMC, the fresh leaf weight (FW)
Figure 1. Location of the study area. The Terra/ASTER data were collected on 7 November 2001 (R : G : B D 5 : 4 : 1)
of Japanese cypress samples and the dry leaf weight (DW,oven-dried at a temperature of around 80° for 24 h) of thesame samples were measured in the laboratory, and theFMC was calculated using the following formula (Dansonand Bowyer, 2004):
FMC D �FW � DW�/DW ð 100 �1�
For spectral reflectance, we put the Japanese cypresssamples on a black board to minimize the backgroundeffects on the light field and measured the reflectanceusing FieldSpec Fr (Analytical Spectral Devices, Inc.,USA) in a darkroom with a 50-W halogen lamp as thelight source. Five VIs related to biophysical/biochemicalattributes of Japanese cypress samples were calculatedusing the following formulas:
NDVI D �R860 � R660�/�R860 C R660� �2�
PRI D �R531 � R570�/�R531 C R570� �3�
NDWI D �R860 � R1240�/�R860 C R1240� �4�
WI D R900/R970 �5�
LSWI D �R820 � R1600�/�R820 C R1600� �6�
where Ri is the reflectance at i nm wavelength.
Satellite data analysis
We used the Terra/ASTER data collected on 7 Novem-ber 2001 to map the degraded Japanese cypress plan-tations. The advanced spaceborne thermal emission andreflection radiometer (ASTER) is an imaging instrumenton the Earth Observing System (EOS) Terra satellite,which can obtain detailed information on the surfacetemperature, emissivity, reflectance, and elevation. It isused in conjunction with Moderate Resolution ImagingSpectrometer (MODIS), Multi-angle Imaging Spectrora-diometer (MISR), the Clouds and the Earth’s Radiant
Increased flooding,turbidity in downstreams.Reduced ecosystem function
Forest degradation
Decreased soil moisturecontent
Figure 2. Process of forest degradation
Energy System (CERES) sensors that monitor the Earthat moderate to coarse spatial resolutions, and serves as azoom lens for them because it is the only high-spatial-resolution instrument on the Terra satellite (Jensen, 2000).ASTER obtains data in 14 bands from the visible throughthermal infrared regions of the electromagnetic spectrum.The major characteristics of Terra/ASTER are summa-rized in Table I.
Geometric correction of the Terra/ASTER data wascarried out as a pre-processing procedure by using DigitalMap 25 000 (Map Image, Geographical Survey Institute,
Table I. Characteristics of advanced spaceborne thermal emissionand reflection radiometer
Japan) as reference data, and the root mean square error(RMSE) between Terra/ASTER and the reference datawas controlled within a pixel. We then extracted thecorresponding pixels from Terra/ASTER data with thelocation information from in situ data collections and setthe thresholds based on the extracted pixels. Finally, wemapped the degraded forest areas based on the selectedVI. Only the NDVI and LSWI were calculated in thisstudy because the Terra/ASTER does not provide banddistribution for PRI, NDWI, and WI calculations. Inaddition, we directly used the digital number (DN) valuesto represent surface temperature rather than using thetrue surface temperature because the DN values are indirect proportion to the surface temperatures (Abramset al., 2002). Atmospheric correction was not applied tothe satellite image because it has the same effect on thepixels both for degraded and healthy Japanese cypressplantations and thus has little effect on the differencesbetween them.
RESULTS
Soil water content among different forest conditions
Based on our in situ measurements, we divided the73 sites of Japanese cypress plantations into four groupsbased on the value of relative illuminance (threshold:5%) and status of the understory vegetation (thresh-old: 8%, the intermediate value of in situ data). Thuswe had four groups with the following combinations:(1) low illuminance C low understory coverage (LILU);(2) high illuminance C low understory coverage (HILU);
Figure 3. Comparison of SWC among four groups (group 1 (LILU):low illuminance C low understory coverage; group 2 (HILU): highilluminance C low understory coverage; group 3 (LIHU): low illuminanceC high understory coverage; and group 4 (HIHU): high illuminance C
high understory coverage)
(3) low illuminance C high understory coverage (LIHU);and (4) high illuminance C high understory coverage(HIHU). Figure 3 shows the comparison of soil mois-ture content among the four groups. It is apparent thatthe average SWC of group 1 (LILU) is lower than thatof group 4 (HIHU). The SWCs in groups 2 (HILU) and3 (LIHU) were between the SWCs of the group 1 (LILU)and the group 4 (HIHU), and the average SWC of group2 (HILU) was lower than that of group 3 (LIHU). Thesignificance of this comparison was found to be 5% inthis study.
Soil water content and fuel moisture content
Figure 4 shows the relationship between the SWC andFMC of Japanese cypress plantations. The data wereobtained from the in situ data collection (Figure 4a)and the controlled experiment (Figure 4b), respectively.Both datasets showed that SWC and FMC are highlycorrelated, with the correlation coefficient of 0Ð64 for thein situ field data and 0Ð80 for the controlled experimentdata. The results confirmed our speculation that drier soilswould result in drier leaves, as shown in the degradedJapanese cypress plantations. The results suggested thatwe might be able to differentiate degraded plantationsfrom healthy plantations by using remote sensing databased on the difference of their leaf water content becausethe dense degraded plantations might suffer a greaterwater deficit during the growing season.
Fuel moisture content and vegetation Index
The relationships between the FMC of Japanesecypress plantations and five VIs were compared on thebasis of the data obtained from the controlled experiment,and the results are shown in Table II. We found that thethree VIs (LSWI, WI, NDWI) were highly related to leafwater content, with the highest correlation coefficient of
y = 46.685Ln(x) + 17.935
R = 0.64
0
50
100
150
200
250
0 5 10 15 20 25
Soil Water Content (%)
Fuel
Moi
stur
e C
onte
nt (
%)
(a)
y = 57.632Ln(x) + 48.404
R = 0.80
0
50
100
150
200
250
0 5 10 15 20 25
Soil Water Content (%)
Fuel
Moi
stur
e C
onte
nt (
%)
(b)
Figure 4. Relationships between SWC and FMC of Japanese cypressplantations. (a) in situ data; (b) controlled experiment data
0Ð86 found between LSWI and the leaf water content. Incontrast, the other two VIs (NDVI and PRI) showed aweak correlation with leaf water content. These resultsindicate that water-content-based VIs (LSWI, WI, andNDWI) are more effective than pigment-content-basedones (NDVI and PRI) in detecting forest degradation.
Detecting degraded plantations using ASTER data
According to the previous studies, the decrease ofsoil infiltration capacity is due mainly to the lack ofunderstory (e.g. Yukawa and Onda, 1995). In other words,the understory plays an important role in vegetationwater content in the study area. Therefore, the absenceof understory in both groups 1 (LILU) and 2 (HILU)resulted in a similar SWC (Figure 3) and thus similarFMC and water-related spectral reflectance properties(Figure 4 and Table II). Likewise, the abundance of
Table II. Relationship between fuel moisture content and vegeta-tion indices
Vegetation index NDVI PRI NDWI WI LSWI
Correlation coefficient 0Ð62 0Ð61 0Ð72 0Ð84 0Ð86
Results based on the data obtained from controlled experiment inlaboratory.
Figure 5. Comparisons of (a) LSWI (using near-IR and mid-IR bands), (b) NDVI (using red and near-IR bands), and (c) DN of Band 14 (usingthermal-IR band) between degraded and healthy Japanese cypress plantations
understory in groups 3 (LIHU) and 4 (HIHU) alsogave them very similar properties. Accordingly, wemerged the above four groups into two new categories,degraded forest (groups 1 and 2) and healthy forest(groups 3 and 4), and expected that the water-content-based indices would be effective in differentiating thedegraded forest from the healthy plantations with theremotely sensed data. Surprisingly, we found that theTerra/ASTER-based NDVI with a 44% significance level(56% probability) and Terra/ASTER-based LSWI withan 82% significance level (18% probability) were bothpoor indices for detecting the degraded plantations in thestudy area (Figure 5a and b). However, we found that thethermal-IR band (band 14) of the Terra/ASTER data witha 7% significance level (93% probability) was effective indifferentiating the degraded and healthy Japanese cypressplantations (Figure 5c). Since the other thermal-IR bandsof Terra/ASTER such as bands 10, 11, 12, and 13 havehigh correlations with band 14 (data not shown), only thethermal-IR band 14 was used for analysis in this study.
Mapping forest degradation using Terra/ASTERthermal-IR data
In accordance with the above results, we mapped thedegraded forest areas on the basis of the Terra/ASTERthermal band (Figure 6). As the problem of forest degra-dation was found only in plantations, due mainly to theabsence of timely thinning, we first extracted the pixelsthat were classified as Japanese cypress/cedar plantationsbased on an existing vegetation map (Nature Conserva-tion Bureau, 1999) to improve the accuracy of detection.
33°17′N
132°54′Ε 132°56′Ε 132°58′Ε 133°0′Ε 133°2′Ε
33°16′N
33°15′N
33°14′N
33°13′N
33°12′N
33°11′N
33°10′N
33°9′N
Healthy Plantation
Degraded Plantation
Broadleaf Forest
Town, Road
River
2 0Kilometers
Scale
Figure 6. Map of degraded Japanese cypress plantations in Kochi, Japan
Table III. Error matrix, overall accuracy and kappa coefficient fordetecting forest degradation from Terra/ASTER thermal-IR band
Estimated Field survey Total User’s accuracy
Degraded Healthy
Degraded 20 13 33 0Ð606Healthy 9 20 29 0Ð690
Total 29 33 62Producer’s 0Ð690 0Ð606
Accuracy
Overall accuracy: 0Ð645.Kappa coefficient: 0Ð293.
Then, we used the Terra/ASTER thermal band to distin-guish the degraded Japanese cypresses from the healthyJapanese cypresses only for these extracted pixels. Themean of the intermediate values of the degraded andhealthy Japanese cypress groups was set as a thresh-old to distinguish the degraded Japanese cypresses fromthe healthy Japanese cypresses. As a result, we esti-mated that 52% of the Japanese cypress plantations in thisarea had been degraded as a result of mismanagement.Table III shows the error matrix, overall accuracy, andkappa coefficient for detecting forest degradation fromthe Terra/ASTER thermal-TR band. The field validationwas performed based on 62 field survey sites. Theseresults show that we can achieve an overall accuracy of65% in classifying and mapping the degraded Japanesecypress plantations in the Kochi area.
DISCUSSION
Forest degradation and soil water content
According to the processes of forest degradation inJapanese cypress plantations shown in Figure 2 (i.e.dense canopy reducing illuminance under the canopyand thus excluding understory vegetation), the group1 (LILU) is defined as the one with the highest levelof degradation, and the group 4 (HIHU) is defined aswell-managed Japanese cypress plantation. The group2 (HILU) indicates those degraded forest sites wherea timely thinning was carried out recently and thusresulted in a higher relative illuminance but still lowerunderstory coverage. In contrast, the group 3 (LIHU)indicates that the canopies of these sites have closed butunderstory vegetation has not disappeared completely,and thus can be considered as the halfway point betweenwell-managed and degraded Japanese cypress plantations.Therefore, it can be considered that the degradation levelof group 2 (HILU) is higher than that of group 3 (LIHU),but is lighter than that of group 1 (LILU). Overall, theSWC decreased with the increase of the degraded level.
Discrepancies between ground-based measurementsand satellite-based indices
According to the in situ measurements and controlledexperiments at the leaf level, we found that: (i) the
forest degradation in the Kochi area is highly associatedwith the decrease of SWC and thus the decrease ofthe FMC; (ii) the changes in FMC resulted in changesin the leaf spectral reflectance; (iii) the water-content-based VIs are more effective than pigment-content-based ones in detecting forest degradation. Therefore,the water-content-based indices could be used to detectforest degradation. This is because the leaf water contentresponded immediately to water stress during the dryingperiod, while the leaf pigment content remained almostunchanged in the first half of the drying period, until thewater stress severely reduced plant growth. However, thesatellite-based (Terra/ASTER) results showed that neitherthe water content nor the pigment-content-based indicesare effective in detecting forest degradation in the studyarea (Figure 5a and b), suggesting that the ground-basedleaf-level results may not be applied to the satellite-based canopy/stand scale. The vegetation at stand levelmight not experience severe water stress due to the largeamount of annual precipitation (about 2900 mm) in thestudy area. The coarse spatial resolution of the satellitedata provides evidence that the degraded forest features adenser canopy than the healthy forest, due to the lack oftimely thinning. Even though the LWC of per leaf volume(or mass) in the degraded forest was lower than that in thehealthy forest, the total canopy water content per pixelin a degraded forest may not necessarily be lower thanthat in a healthy forest (Figure 5a). This is probably whythe NDVI (one of the pigment-content-based VIs) wasnot significantly different between the degraded and thehealthy forests. The abundance of understory vegetationin the healthy forest may significantly contribute tothe total NDVI of the forest, thus making it similarto the degraded forest that features a denser overstorycanopy (Figure 5b). In conclusion, water-content-basedand pigment-content-based VIs obtained from satellitedata were not effective in detecting the degraded forestsin the study area.
Detecting forest degradation using thermal-IR bands
The thermal-IR band, a measure of surface temperatureof the Terra/ASTER data was more effective than thewater-content-based or pigment-content-based VIs (i.e.use of visible, near-IR, and mid-IR bands) in detect-ing forest degradation in Kochi, Japan (Figure 5). For-est degradation has resulted in the decrease of SWC(Figure 3). According to water availability and energybalance, one would expect the degraded Japanese cypressplantations to have higher surface temperatures than thoseof the healthy plantations. However, we found the oppo-site result in this study (Figure 5c). This may be partlydue to the lower canopy coverage of the healthy Japanesecypress plantation, as indicated by the NDVI values(Figure 5b). Based on the previous study, sparse or shortvegetation showed a higher LST than dense or tall vege-tation (Nemani and Running, 1997). It is also possiblethat the plants in the degraded forests did not suffermuch water stress due to the ample precipitation and
ground water supply, though the SWC was lower thanthat in the healthy forests. Further studies are needed toconfirm these speculations, and other biological and bio-physical processes may also need to be investigated inboth types of forest. In addition, satellite images witha finer spatial resolution (e.g. Landsat/ETM C data) arealso needed to improve the detection accuracy for futurestudies.
CONCLUSION
The results of this study can be summarized as follows.From in situ and controlled experimental data analysis(leaf level), it is shown that forest degradation resulted inthe decrease of SWC and the FMC of leaves; the changeof FMC resulted in changes in the spectral reflectanceproperty of the leaves. We found that the water-content-based indices could be used to detect forest degradation.However, satellite data analysis (canopy level) resultsshowed that it is difficult to use either water-content-based or pigment-content-based VIs to detect forestdegradation. In contrast, although the use of thermalbands was very effective for mapping the degradedforests, the coarse spatial resolution of the satellite imagesstill limits the application of satellite data in detectingforest degradation in the study area. The use of remotesensing data, especially the thermal bands with a higherspatial resolution (e.g. airborne data) may have a largepotential in mapping degraded forests in Japan andelsewhere.
ACKNOWLEDGEMENTS
This research was supported by the CREST project of JST(contract number 2754), and Grants-in-Aid for ScientificResearch of MEXT (contract number 17710003). MingXu was partly supported through the Bairen Program ofthe Chinese Academy of Sciences.
REFERENCES
Abrams M, Hook S, Ramachandran B. 2002. ASTER Users Hand-book Version 2 . Jet Propulsion Laboratory: Pasadena, Califor-nia. http://asterweb.jpl.nasa.gov/content/03 data/04 Documents/asteruser guide v2.pdf. Accessed April 23, 2008.
Danson F, Bowyer P. 2004. Estimating live fuel moisture content fromremotely sensed reflectance. Remote Sensing of Environment 92:309–321.
Forestry Agency. 2003. The Ministry of Agriculture, Forestry andFisheries of Japan. Annual Report on Trends of Forest and Forestry,Tokyo, 230, (in Japanese).
Fukuyama T, Takenaka C, Onda Y. 2005. 137Cs loss via soil erosion froma mountainous headwater catchment in central Japan. The Science ofthe Total Environment 350: 238–247.
Gao BC. 1996. NDWI-A normalized difference water index for remotesensing of vegetation liquid water from space. Remote Sensing ofEnvironment 58: 257–266.
Hattori S, Abe T, Kobayashi C, Tamai K. 1992. Effect of forest floorcoverage on reduction of soil erosion in hinoki plantations. Bulletinfor Products Research Institute 362: 1–34 (in Japanese with Englishsummary).
Jensen J. 2000. In Remote Sensing of the Environment: An Earth ResourcePerspective. Prentice Hall: Upper Saddle River, New Jersey; 544.
Miura S, Hirai K, Yamada T. 2002. Transport rates of surface materialson steep forested slopes induced by raindrop splash erosion. Journalof Forest Research 7: 201–211.
Nature Conservation Bureau. 1999. In the Dataset for GIS on the NaturalEnvironment of Japan, Version 2, CDROM. Japan EnvironmentAgency: Tokyo.
Nemani R, Running S. 1997. Land cover characterization usingmultitemporal red, near-IR, and thermal-IR data from NOAA/AVHRR.Ecological Applications 7: 79–90.
Onda Y, Gomi T, Mizugaki S, Nonoda T, Sidle RC. 2010. An overviewof the field and modeling studies on the effects of forest devastationon flooding and environmental issues. Hydrological Processes 24:527–534.
Onda Y, Tsujimura M, Nonoda T, Takenaka C. 2005. Methods formeasuring infiltration rate in forest floor in hinoki plantations. Journalof Japan Society of Hydrology and Water Resources 18: 688–694 (inJapanese with English summary).
Penuelas J, Filella I, Gamon J. 1995. Assessment of photosyntheticradiation use efficiency with spectral reflectance. New Phytologist 131:291–296.
Penuelas J, Pinol J, Ogaya R, Filella I. 1997. Estimation of plantwater concentration by the reflectance water index WI (R900/R970).International Journal of Remote Sensing 18: 2869–2875.
Rouse J, Haas R, Schell J, Deering D. 1974. Monitoring vegetationsystems in the great plains with ERTS. Proceedings of Third EarthResources Technology Satellite-1 Symposium , Greenbelt, NASA SP-351, 3010–3017.
Turner B, Moss R, Skole D. 1993. Relating land use and global land-cover change: a proposal for an IGBP-HDP core project IGBPReport no. 24, HDP Report no. 5, International Geosphere-BiosphereProgramme, Stockholm.
Xiao X, Hollinger D, Aber J, Goltz M, Davidson E, Zhang Q, Moore BIII. 2004. Satellite-based modeling of gross primary production inan evergreen needleleaf forest. Remote Sensing of Environment 89:519–534.
Yukawa N, Onda Y. 1995. The influence of understories on the infiltra-tion capacities of Chamaecyparis obtusa plantation (1) Experimentalresults using a mist type rainfall simulator. Journal of Japan ForestSociety 77: 224–231 (in Japanese with English summary).
![Detecting Carbon Monoxide Poisoning Detecting Carbon ...2].pdf · Detecting Carbon Monoxide Poisoning Detecting Carbon Monoxide Poisoning. Detecting Carbon Monoxide Poisoning C arbon](https://static.documents.pub/doc/80x56/5f551747b859172cd56bb119/detecting-carbon-monoxide-poisoning-detecting-carbon-2pdf-detecting-carbon.jpg)
![Detecting Carbon Monoxide Poisoning Detecting Carbon ...2].pdf · Detecting Carbon Monoxide Poisoning Detecting Carbon Monoxide Poisoning. ... the patient’s SpO2 when he noticed](https://static.documents.pub/doc/80x56/5a78e09b7f8b9a21538eab58/detecting-carbon-monoxide-poisoning-detecting-carbon-2pdfdetecting-carbon.jpg)
