Remote Sensing-Based Assessment of the 2005–2011 Bamboo Reproductive Event in the Arakan

14 Pages·2017·3.36 MB·English

remote sensing
Article
Remote Sensing-Based Assessment of the 2005–2011
Bamboo Reproductive Event in the Arakan Mountain
Range and Its Relation with Wildfires
FrancescoFava1,*andRobertoColombo2
1 InternationalLivestockResearchInstitute,P.O.Box30709,Nairobi00100,Kenia
2 RemoteSensingofEnvironmentalDynamicsLab.,Dept.ofEarthandEnvironmentalSciences,
UniversityofMilano-Bicocca,PiazzadellaScienza1,Milano20126,Italy;[email protected]
* Correspondence:[email protected];Tel.:[phone]
AcademicEditors:KrishnaPrasadVadrevu,RamaNemani,ChrisJustice,GarikGutman,IoannisGitas,
ClementAtzberger,LarsT.WaserandPrasadS.Thenkabail
Received:26July2016;Accepted:11January2017;Published:18January2017
Abstract: Pulseecologicaleventshavemajorimpactsonregionalandglobalbiogeochemicalcycles,
potentiallyinducingavastsetofcascadingecologicaleffects. Thisstudyanalyzesthewidespread
reproductiveeventofbamboo(Melocannabaccifera)thatoccurredintheArakanMountains(Southeast
Asia)from2005to2011,andinvestigatesthepossiblerelationshipbetweenmassivefuelloadingdue
tobamboosynchronousmortalityoverlargeareasandwildfireregime. Multipleremotesensing
dataproductsareusedtomapthearealextentofthebamboo-dominatedforest. MODISNDVItime
series are then analyzed to detect the spatiotemporal patterns of the reproductive event. Finally,
MODISActiveFireandBurnedAreaProductsareusedtoinvestigatethedistributionandextension
ofwildfiresbeforeandafterthereproductiveevent. Bamboodominatesabout62,000km2offorestin
Arakan. Over65%oftheregionshowsevidenceofsynchronousbambooflowering,fruiting,and
mortality over large areas, with wave-like spatiotemporal dynamics. A significant change in the
regimeofwildfiresisobserved,withtotalburnedareadoublinginthebamboo-dominatedforestarea
andreachingalmost16,000km2. Wildfiresalsoseverelyaffecttheremnantpatchesoftheevergreen
forest adjacent to the bamboo forest. These results demonstrate a clear interconnection between
the2005–2011bambooreproductiveeventandthewildfiresspreadingintheregion,withpotential
relevantsocio-economicandenvironmentalimpacts.
Keywords: bamboo; reproduction; wildfires; MODIS; Arakan; pulse event; food security;
biodiversityconservation
1. Introduction
The important role of pulse ecological events, defined as infrequent, large-magnitude, and
short-durationeventsofincreasedresourceavailability,onregionalandglobalbiogeochemicalcycles
hasbeenincreasinglyacknowledgedinrecentliterature[1].Inthiscontext,mastflowering,themassive
andsynchronizedfloweringandfruitingofaplantspeciesacrosslargeareas, canbeconsidereda
typicalpulseevent,potentiallyinducingavastsetofcascadingecologicaleffects[2]. Mostmasting
plant species are iteroparous (i.e., they flower several times during their life cycle), and have a
relativelyshortintermastinterval(3–7years)[3]. Anoticeableexceptionisrepresentedbyseveral
woodybamboospeciesdistributedinsubtropicalandtemperateevergreenordeciduousforests[4],
whicharesemelparous(i.e.,theyfloweronceanddie)andhavetypicalintermastintervalsbetween
20and60years[5]. Thesebamboospeciesarecharacterizedbyaggressiverhizomatousgrowthand
developlargeclonalclumpsthatmaycoverhundredsofsquaremeters[6].
RemoteSens.2017,9,85;doi:10.3390/rs9010085 www.mdpi.com/journal/remotesensing
RemoteSens.2017,9,85 2of14
Alarge-scalemastfloweringeventofthebamboospeciesMelocannabacciferahasbeenreported
startingfrom2005intheArakanmountainrange,whichspansabout1000kmparalleltotheeastern
edgeoftheBengaligulfinMainlandSoutheastAsia. Widespreadandsynchronousbambooflowering
wasdescribedinseverallocationsinMizoramandManipur(India),EastChittagong(Bangladesh),
ChinandRakhine(Myanmar). Followingthebamboofloweringandfruiting,therewereextensive
reportsofrodentoutbreaks(alsoknownas“ratfloods”),causingseriousdamagetoriceandother
crops,andleadingtofoodinsecurityacrosstheregion[7,8]. Similarevents,locallycalled“mautam”,
werealreadydocumentedin1863,1911,and1959,withanapproximaterepeatingcycleof48years[9].
Despitethewideenvironmentalandfoodsecuritysignificanceofthisevent,mostscientificand
publicmediaattentionhasbeenaddressedtowardstherodentoutbreakdynamicsandimpacts,while
studiesonthespatialandtemporalpatternsofthereproductiveeventsandotherpossiblelargescale
ecologicalconsequenceshavebeenlacking. Consideringthesocio-economiccentralityofthetropical
andsub-tropicalforestsforextremelyvulnerablelocalcommunities[8],aswellastheirhighvaluefor
biodiversityconservation[10],afullunderstandingoftheimpactsofthispulseeventisessentialfor
futurelandmanagementandconservationplanning.
Previous research suggested that the mass mortality of bamboo after fruiting could favor
fire ignition and propagation as a result of synchronous and widespread fuel load [11,12]. This
considerationwasalsooneofthemajorargumentstosustainanexplanation,knownas‘fire-cycle
hypothesis’, for the highly specific reproductive strategy of mast flowering and semelparity in
bamboos[11]. Thishypothesisstimulatedastrongdebate[13,14],butonlyafewstudiesaddressedthe
possiblelinkagebetweenmastfloweringeventsandfireusingempiricaldata,andmostofthemwere
onlyatthelocalscale[15–17].
Long time series of satellite remote sensing data are now widely available for regional and
continental scale vegetation monitoring, and recent studies have demonstrated their potential for
mapping bamboo flowering, fruiting, and mortality in the Amazon [18]. In addition, a number
of algorithms and operational remotesensing productsare nowavailable for regional monitoring
of active fires and burned area dynamics [19,20]. This opens a unique opportunity to study the
interactionbetweenbamboomastfloweringandwildfiresduringregionalscalepulseevents. Based
ontheseconsiderations,thisstudyaimsatanalyzingtimeseriesofsatellitedataandderivedburned
area/active fire products in the Arakan region to assess the spatial and temporal patterns of the
bambooreproductiveevent,andtoinvestigatepossibleimpactsonwildfireregime. Specifically,the
followingscientificquestionsareaddressed:
(a) Whatistheextentandgeographicdistributionofthebamboo-dominatedforestinArakan?
(b) Whichspatialandtemporaldynamicscharacterizedthebambooreproductiveevent?
(c) Wasthewildfireregimeimpactedbythebambooreproductiveevent?
Giventhereporteddramaticeffectsonfoodsecurityassociatedwiththerodentoutbreaks,which
followedthisreproductiveevent,theproductionofregionalmapsofthebamboo-dominatedforest
andofthedynamicsofthereproductiveeventwouldprovidekeyinformationnotonlytounderstand
the ecology of the event, but also for planning and coordinating future interventions to support
local communities and policy makers in adopting strategies to prevent crop damage and food
shortage. Moreover, under the hypothesis that wildfires could increase because of the enormous
fuelloadgeneratedbythesynchronousmortalityofbamboo,thiscouldrepresentanotherimportant
consequenceofthemastingevent,whichsofarhasbeenpoorlydocumentedbutposesaseriousthreat
tolocalpopulationsandtoecosystemsofhighconservationalvalue.
2. MaterialsandMethods
2.1. StudyAreaandFieldSurvey
ThestudyareaislocatedintheArakanmountainrange,whichspansforabout1000kmparallel
to the eastern edge of the Bengali gulf from Cape Negrais, west of the Irrawaddy Delta, and the
Remote Sens. 2017, 9, 85 3 of 14
southern Manipur State of India, touching Myanmar (Rakhine and Chin), Bangladesh (Chittagong),
and India (Mizoram and Manipur) (Figure 1). Geologically, the Arakan mountain region belongs to
the northern portion of the Burmese-Java arc of the Himalaian system of folding, and it is
characterized by Cretaceous-Tertiary flysch sediments with basalt and ultramafic deposits and
metamorphic rocks. The terrain of the region is rugged, with steep slopes and elevation reaching
over 3000 m (Mt. Victoria). The region is characterized by a tropical monsoon climate, with
RemoteSens.2017,9,85 3of14
precipitation concentrated between the months of May and October. The mountains act as a barrier
for the southwest monsoon rains, generating a strong rainfall gradient between the western (over 3000
mm) and eastern (1000–3000 mm) slopes. This gradient is also reflected in the vegetation
southernManipurStateofIndia,touchingMyanmar(RakhineandChin),Bangladesh(Chittagong),
distribution, which shifts from tropical evergreen forest in the west to moist upper deciduous forest
andIndia(MizoramandManipur)(Figure1). Geologically,theArakanmountainregionbelongstothe
in the center and dry deciduous forests in the east. Anthropic activities and intensive agriculture
northernportionoftheBurmese-JavaarcoftheHimalaiansystemoffolding,anditischaracterizedby
exert strong pressure on the environment, especially on the east side of the region. At the same time,
Cretaceous-Tertiaryflyschsedimentswithbasaltandultramaficdepositsandmetamorphicrocks. The
shifting cultivation is common everywhere.
terrainoftheregionisrugged,withsteepslopesandelevationreachingover3000m(Mt. Victoria).
Bamboo species, such as Melocanna baccifera, Bambusa polimorpha, and Bambusa tulda, are widespread
Theregionischaracterizedbyatropicalmonsoonclimate,withprecipitationconcentratedbetween
in the study area. Bamboo-dominated forests have not been mapped as an independent class in
themonthsofMayandOctober. Themountainsactasabarrierforthesouthwestmonsoonrains,
previous land cover maps of the region (e.g., [21–25]), as they are generally included in broader
generatingastrongrainfallgradientbetweenthewestern(over3000mm)andeastern(1000–3000mm)
forest cover classes. Although bamboo can be associated with other species in degraded forests or as
slopes.Thisgradientisalsoreflectedinthevegetationdistribution,whichshiftsfromtropicalevergreen
part of the deciduous and evergreen forest understory, very large and almost pure Melocanna
forestinthewesttomoistupperdeciduousforestinthecenteranddrydeciduousforestsintheeast.
baccifera stands are common in the Arakan Mountains, especially in the southern portion of the area
Anthropicactivitiesandintensiveagricultureexertstrongpressureontheenvironment,especiallyon
(Chin and Rakhine) [26].
theeastsideoftheregion. Atthesametime,shiftingcultivationiscommoneverywhere.

Figure 1. Study area. On the left, the study area border is evidenced on the mainland South East Asia
Figure1.Studyarea.Ontheleft,thestudyareaborderisevidencedonthemainlandSouthEastAsia
topographic map. On the right, the main administrative regions included in the study area are
topographicmap.Ontheright,themainadministrativeregionsincludedinthestudyareaarereported
reported (i.e., Rakhine and Chin-Myanmar, Chittagong-Bangladesh, Mizoram-India).
(i.e.,RakhineandChin-Myanmar,Chittagong-Bangladesh,Mizoram-India).
To support satellite image analysis and interpretation, a field survey was carried out in 2013
Bamboospecies,suchasMelocannabaccifera,Bambusapolimorpha,andBambusatulda,arewidespread
in Southern Rakhine (i.e., Rakhine Yoma Elephant range) to collect ground information on
inthestudyarea.Bamboo-dominatedforestshavenotbeenmappedasanindependentclassinprevious
bamboo-dominated forest areas. The remoteness of the area did not allow a systematic validation
landcovermapsoftheregion(e.g.,[21–25]),astheyaregenerallyincludedinbroaderforestcoverclasses.
study, but qualitative observations along transects crossing the mountain range provided evidence
Althoughbamboocanbeassociatedwithotherspeciesindegradedforestsoraspartofthedeciduous
of very large areas dominated by young Melocanna baccifera plants with scattered trees, which could
andevergreenforestunderstory,verylargeandalmostpureMelocannabacciferastandsarecommonin
be easily discriminated as an independent vegetation cover class. In addition, in all bamboo-dominated
theArakanMountains,especiallyinthesouthernportionofthearea(ChinandRakhine)[26].
To support satellite image analysis and interpretation, a field survey was carried out in
2013 in Southern Rakhine (i.e., Rakhine Yoma Elephant range) to collect ground information on
bamboo-dominatedforestareas. Theremotenessoftheareadidnotallowasystematicvalidation
study,butqualitativeobservationsalongtransectscrossingthemountainrangeprovidedevidenceof
verylargeareasdominatedbyyoungMelocannabacciferaplantswithscatteredtrees,whichcouldbe
easilydiscriminatedasanindependentvegetationcoverclass. Inaddition,inallbamboo-dominated
RemoteSens.2017,9,85 4of14
areasthatweredirectlysurveyed,thereproductiveeventwasreportedandevidenceofrecentfireswas
found(i.e.,burnedbamboostubbles)belowtheyoungbamboocanopy. Thiswasconfirmedfurtherby
interviewswithlocalfarmers,reportingthebambooreproductiveeventandsubsequentlargefires.
2.2. BambooForestMapping
The identification of forests dominated by Melocanna baccifera, as well as other land cover
typologies,hasbeenperformedbyintegratingdifferentcartographicproductsandsatelliteimagery.
TheforestmapofSouthEastAsia[21,22],obtainedfromclassificationofSPOTVEGETATIONimages
acquired between 1998 and 2000 with 1 km geometric resolution, was used as a reference for the
forest type classification of the study area before the bamboo reproductive event. Since the forest
map legend includes bamboo forest in a broader class (i.e., “Evergreen wood and shrubland and
regrowth mosaics”), the Landsat GEOCOVER mosaic 2000 product [27] was used to refine the
bamboo-dominatedforestclassificationbyvisualinterpretationofthemosaicat1:250,000,exploiting
the distinct spectral features of bamboo mature forests [18] (cf. Figure S1). Finally, the potential
distributionmapofthebamboospecies[28,29]wasusedtodefinetheborderfortheareadominated
by Melocanna baccifera. Overall, four vegetation cover classes were used for the purposes of this
study: bamboo-dominatedforest,tropicalevergreenforest(mergingevergreenmountainforestsand
evergreenlowlandforestsclassesof[22]),deciduousforest(mergingdeciduousforestsanddeciduous
woodandshrublandandregrowthmosaicsof[22]),andcrops(otherlandclassof[22]).
2.3. BambooReproductiveEventDetection
Previous studies demonstrated that different bamboo life stages determine clear spectral
reflectancevariations,whichallowtheirdetectionfromMODISandLANDSATTM/ETMmultispectral
imagery[18]. Inthisstudy,MODISNormalizedDifferenceVegetationIndex(NDVI)imageswereused
todetectthespatialandtemporaldynamicsofthebambooreproductiveevent. Specifically,NDVI
time series between 2000 and 2014 generated by the BOKU (University of Natural Resources and
LifeSciences,Vienna,Austria)dataserviceplatform(http://ivfl-info.boku.ac.at/,accessedon1July
2016)[30]wereused. Amongtheoptionsofferedbytheservice,thecombinedMODISTERRA/AQUA
(MOD13andMYD13)smoothedNDVItimeserieswith16-daytemporalfrequencyand250mspatial
resolution was selected for the study region. For smoothing and gap filling, the BOKU service
appliestheWhittakermethod,deemedaccurateandcomputationallyefficientforglobal-scaleNDVI
analyses[31–33].
Mappingthebambooreproductiveevent(i.e.,flowering,fruiting,andmortality)wasbasedonthe
analysisofthephenologicalbehaviorofMelocannabacciferaforestsduringthereproductiveseason[9]
andontheconsequentgreennessvariations. Figure2schematicallyillustratestheexpected(Figure2a)
andanexampleoftheobserved(Figure2b)trajectoriesofgreenness/NDVIduringanon-reproductive
and a reproductive season. In addition, the seasonal frequency distribution of wildfires is shown
inFigure2a. AccordingtothisconceptualmodelandobservedNDVItimeseries,thepresenceofa
significantNovember/DecemberNDVInegativeanomaly,withrespecttopreviousyears,wasselected
asanindicatoroftheongoingreproductiveevent. Thisistheperiodwhenobservedanomaliescould
beclearlyassociatedtotheongoingbambooreproduction,withminimalexpectedimpactofwildfires
onthesignal.
Basedonthisassumption,thefollowingstepswereperformedontheMODISNDVItimeseries
todetectthereproductiveevent:
(i) ComputationofNovember-DecembermeanNDVI(NDVI ).
ND
(ii) Startingfromtheyear2005(asnobamboofloweringwasreportedbefore2005[7–9],at-testwas
appliedtoidentifystatisticallysignificantanomalies(p<0.001)betweenNDVI oftheyeari
ND
andmeanandstandarddeviationofNDVI fortheperiod2000—yeari−1. Theseseasons
ND
weremarkedas‘reproductiveseasons’.
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Remote Sens. 2017, 9, 85 6 of 14
RemoteSens.2017,9,85 6of14
analysis, as the size of the reproductive event and burned area patches was much larger than the
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3. Results and Discussion
3. ResultsandDiscussion
3.1. Bamboo Forest Extent and Reproductive Event Dynamics
3.1. BambooForestExtentandReproductiveEventDynamics
The use of multiple imaging products and of the Melocanna baccifera potential distribution
TheuseofmultipleimagingproductsandoftheMelocannabacciferapotentialdistributionmap
map allows for identification of the bamboo-dominated forest’s areal extent. According to this
allowsforidentificationofthebamboo-dominatedforest’sarealextent. Accordingtothisclassification,
classification, bamboo forests cover approximately 63,000 km2 in the Arakan mountain range (Figure 3a).
bambooforestscoverapproximately63,000km2intheArakanmountainrange(Figure3a). Thecentral
The central and southern parts of the region, which are mainly composed of Rakhine and Chin, are
andsouthernpartsoftheregion,whicharemainlycomposedofRakhineandChin,arecharacterized
characterized by large continuous bamboo-dominated forests locally alternated with dense evergreen
bylargecontinuousbamboo-dominatedforestslocallyalternatedwithdenseevergreenforestpatches
forest patches and shifting cultivations. The northern part of the region, located in Chittagong and
andshiftingcultivations. Thenorthernpartoftheregion,locatedinChittagongandManipur,ismore
Manipur, is more fragmented, especially in the northeastern portion. Bamboo forests are mainly
fragmented,especiallyinthenortheasternportion. Bambooforestsaremainlylocatedonthewestern
located on the western slopes of the mountain range, at elevations ranging approximately from 50 to
slopesofthemountainrange,atelevationsrangingapproximatelyfrom50to1050ma.s.l. (Figure3b).
1050 m a.s.l. (Figure 3b). This is the wetter side of the range due to the orographic effect, with rainfall
Thisisthewettersideoftherangeduetotheorographiceffect,withrainfallrangingfrom2000toover
ranging from 2000 to over 4000 mm per year [36,37]. The entire region is characterized by Cambisols:
4000mmperyear[36,37]. TheentireregionischaracterizedbyCambisols: DystricCambisolsinthe
Dystric Cambisols in the Chittagong Hill region and Western Mizoram, Humic Cambisols in Easter
ChittagongHillregionandWesternMizoram,HumicCambisolsinEasterMizoramandChin,and
Mizoram and Chin, and Ferralic Cambisols in Rakhine [38] (Figure 3c). These soils are moderately
FerralicCambisolsinRakhine[38](Figure3c). Thesesoilsaremoderatelyfertile,buttheyarealso
fertile, but they are also prone to severe soil erosion, especially when located over steep slopes [39].
pronetoseveresoilerosion,especiallywhenlocatedoversteepslopes[39].

Figure3.DistributionofMelocannabaccifera(a)superimposed(whitestripes)totheelevationmap(b)
andthesoilmap(c)ofthestudyregion.
Figure 3. Distribution of Melocanna baccifera (a) superimposed (white stripes) to the elevation map
(b) and the soil map (c) of the study region.
Thespatialandtemporalpatternsofthereproductiveevent,asderivedfromtheMODISNDVI
analyTsihse, asrpearteiaplo arntedd tienmFpigourarel p4a.tFtierrsntsd oefte tchtea brleepflroodwuecrtiinvge eepviesnotd, easso dcecruirvreedd firno2m0 0t5hein MthOeDnIoSr tNhDeaVstI
caonranleyrsiosf, Maraen irpeuproarnteddi ninn oFritghuerren R4.a kFhirinste .dTehteenct,abbeltew feleonw2e0r0in6ga nedpi2s0o0d9e,sw oidcecsuprrreeadd iflno w20e0r5in gint otohke
Remote Sens. 2017, 9, 85 7 of 14
RenmoortethSeenass.t2 0c1o7r,n9,e8r5 of Manipur and in northern Rakhine. Then, between 2006 and 2009, wides7porfe1a4d
flowering took place all over the region. In 2010 and 2011 the last large bamboo patches flowered in
the southernmost portion of Arakan, mainly in Rakhine. Over these years, the large scale
placeallovertheregion. In2010and2011thelastlargebamboopatchesfloweredinthesouthernmost
reproductive event affected about 65% of the mapped bamboo area. These patterns are fully
portionofArakan,mainlyinRakhine. Overtheseyears,thelargescalereproductiveeventaffected
consistent with the ones evidenced by local scale studies, which mainly focused on rodent
about65%ofthemappedbambooarea. Thesepatternsarefullyconsistentwiththeonesevidencedby
outbreaks, reporting general information about bamboo flowering in different areas [9]. The main
localscalestudies,whichmainlyfocusedonrodentoutbreaks,reportinggeneralinformationabout
region where there is no evidence of the occurrence of the bamboo reproductive event is located in
bamboofloweringindifferentareas[9]. Themainregionwherethereisnoevidenceoftheoccurrence
the northeastern portion of the study region. In this area, the bamboo-dominated forest is more
ofthebambooreproductiveeventislocatedinthenortheasternportionofthestudyregion. Inthis
fragmented and may include different vegetation types affecting the NDVI seasonal trajectory and
area,thebamboo-dominatedforestismorefragmentedandmayincludedifferentvegetationtypes
hampering the detection of the event.
affectingtheNDVIseasonaltrajectoryandhamperingthedetectionoftheevent.

FiFgiugruere4 .4M. Mapapo fotfh tehee setsimtimataetdedy eyaeraro foof coccucrurrernecneceo fotfh teheb abmambobooore rperpordoudcutcivtievee veevnetn.tF. oFrort htehem maianin
rerperpordoudcutcivtievese saesaosnosn(si .(ei..e,.2, 020060–62–021001)0t)h teheN NDDVIVNIDNDt etemmppoorarallt rterennddi sisr erpepoortretdedi ninF FigiguurereS 2S.2.
RRepeprorodduuctcitvivee evevenentsts oocccucurrrerded sysynnchchroronnoouuslsyly (i(.ie..e,., dduurirningg ththee sasmamee sesaesaosonn)) oovverer rartahtherer
hhoommooggeneneoeouussp patacthcheess( F(Figiguurere4 )4.). PPaattcchh ssizizee wwaass hhigighhlyly vvaarriaiabblele aaccrorosssst htheer ergegioionna nandds hshoowwssa a
ppowowere-rl-alwawd disitsrtirbibuutitoionn( c(cf.f. FFiigguurree SS33)).. AA ffeeww llaarrggee ppaattcchheess ((ii..ee..,, oovveerr 110000 kkmm2)2 )rerpeprerseesnent tovoevre r606%0% of
ofthteh eaareraea, ,aanndd tthhee llaarrggeesstt ppaattcchh rreeaacchheess oovveerr 33000000 kkmm22.. TThhee bboorrddeerrss aammoonngga addjajacceennttp paatcthcheessw wereere
ggenenerearlallylys hsharaprpa nanddw welelldl defiefnineded,s, ismimilialrart otot htheer erseusultlstsr erpeporotretdedb yby[ 1[81]8,]s, usugggegsetsitninggt hthatatp popopuulaltaitoinonss
mmayayb ebsep astpiaaltliyalelyxc leuxscivlues.iTvhe.e sTphaet iaslpdaitsiatrli bduitsitornibouftitohne roefp rtohdeu crteipvreoedvuecnttivpea tcehveesnta cproastscheelesv aatciroonss
deoleesvnaotitosnh doowesa nnyotr esghuolwar atneym rpeogruallapr attetmerpno(rcaf.l FpiagtuterrenS (4c)f.. NFiegvuerret hSe4l)e. sNs,eovneratvheerlaegsse,, o6n0% avoefrapgaetc, h6e0s%
floofw pearetcdhiens cfolonwtigeureodu siny ecaorns,tisguugoguess tyinegartsh, espuogsgseisbtiilnitgy tohfea pnoosns-irbainlidtyo mof dai sntroibnu-rtaionndo[1m8] .dAislttrhibouutgihon
th[e18m].e tAhlotdhooluogghy atphpe limedetihnotdhoislostguyd yapispnlioetdi nitne ntdheids tsotumdayp issi nngolet bianmtebnodoedp otpou lmataiopn ss,inbgulteo nbalymtbhoeo
repgoiponualaltsiopnasti, ablupta totenrlyn stohfe threegrieopnraol dsupcattiivael epvaettnetr,ntsh eosfe trhees urletpsrsoedemucsticvoen esivsetennt,t twhietshe threesfluoltws esreienmgs
wcaovnesihsytepnott hweisthis t[h4e0 ]fltooweexrpinlagin wbaavme bhoyop’ostghreesgisa r[i4o0u] stofl eoxwpelariinng bsapmabtioaol’asn gdretgemarpiooursa lfldoywnearminigcs sopvateiral
RRememooteteS Senens.s.2 2001177,,9 9,,8 855 88o off1 144
and temporal dynamics over large regions. Nevertheless, the event did not show any clear
largeregions. Nevertheless,theeventdidnotshowanyclearunidirectionalspreadingdynamic,but
unidirectional spreading dynamic, but followed more complex spatial patterns [18,40].
followedmorecomplexspatialpatterns[18,40].
3.2. Analysis of Wildfire Dynamics
3.2. AnalysisofWildfireDynamics
The total burned area before and during the reproductive event is reported in Figure 5. Overall,
ThetotalburnedareabeforeandduringthereproductiveeventisreportedinFigure5. Overall,
the total burned area almost doubled during the years 2007–2011 (i.e., following the main reproductive
thetotalburnedareaalmostdoubledduringtheyears2007–2011(i.e.,followingthemainreproductive
event periods, which mainly occurred from late 2006 to 2011) compared to previous years (2001–
eventperiods,whichmainlyoccurredfromlate2006to2011)comparedtopreviousyears(2001–2006),
2006), with total burned area reaching almost 16,000 km2 (i.e., 25% of the total bamboo forest cover).
withtotalburnedareareachingalmost16,000km2(i.e.,25%ofthetotalbambooforestcover).

Figure5.(a)Mainlandcoversofthestudyarea;(b)totalburnedareabefore(2000–2006);and(c)during
Figure 5. (a) Main land covers of the study area; (b) total burned area before (2000–2006); and (c)
(2006–2012)thebambooreproductiveevent.
during (2006–2012) the bamboo reproductive event.
TThheea naanlaylsyissios fothf etihnet erin-atnern-uaanlnduyanl admyincsamoficbsu ronfe dbuarrenaedin abraema biono -dbaommbinoaot-eddofmoriensattsecdo nfofirremstss
tchoantfairsmtrso nthgaitn acr setarsoenign ibnucrrneaedsea irne abtuoronkedp laarceeac otonocku rprleanctely cwonitchurthreenrtelyp rwodituhc ttihvee reevpernotdpuecrtiiovde, ewvietnht
ppeearkiosdin, w20it0h9 paenadks2 0in10 2(0F0i9g uarned6 2a0).10F r(oFmigu2r0e1 16ao)n. wFraormd, 2y0e1a1r loynbwuarnrde,d yaeraeralyg braudrnueadll yardeeac rgeraasdeudatloly
vdaelucreesacsoemd ptoa rvaabllueetso cyoemarpsabreafbolree ttoh eyereaprsr obdeufocrtiev teheev reenptr.oHdouwcteivveer e,vinecnrte.a Hsionwgbevuernr,e idncarreeaasdinugri bnugrtnheisd
paerreiao ddumriignhgt tbheisa plseoritohde cmoingshetq buee naclseoo tfhfea cctoonrsseoqthueerntchea onf tfhaectroerpsr oodthuecrt itvheanev tehnet ,repprirmodauriclytivder oeuvgehntt,
aptrriemgaiornilayl sdcraolue.gThot taets trethgiisonhaylp oscthalees.i sT,oth eteSstta nthdias rdhyizpeodthPerseicsi,p itthaet ioSntaannddarEdvizaepdo trParsepciirpaittiaotnioInn daenxd
(SEPvEapI)o[t4r1a]spwiarastuiosned Itnodeevxa l(uSaPtEeIi)f m[4a1j]o rwdaros uugshetde ptios oedveasloucactue rrief dmcaojnocru rdrreonutlgyhwt iethpitshoedbeus rnoecdcuarrreead
incocnrecausrer.eSnPtlEyI twimiteh sethriee sbauvrenraedge daroevae rinthcreesatsued. ySaPrEeaI htiimghel igsherteieds twavoedraroguedg htoveperis otdhees sdtuurdiny gatrheea
pheiagkhlyiegahrtsed(F tiwguor ed6robu),gshutg egpeisstoindgesth dautrdinrogu tghhet pceoaukld yaelasros h(Faivgeubreee 6nba), kseuyggdeestetirnmgi nthaantt dorfotuhgehbtu cronuedld
aarlesao inhcarveea sbeeiennt hae kreeyg iodne.teFrimguinrean7ts hoof wthset hbeurrenleadti oanrsehai pinbceretwaseee ninS PthEeI arnegdiobnu.r nFeigduarree a7 bsehfoorwesa nthde
druelraintigonthsheirpe pbreotdwuecetniv SePeEvIe natnpde briuordn.eTdh aertewa obreefogrrees asinodn dmuordinegls thhaev reespirmoidlaurctsilvoep eesv,ebnut tpdeurrioindg. tThhee
rtewproo rdeugcrteisvseioyne amrsoadeslisg nhiafivcea nsitmlyihlairg hsleorpienst,e brcuetp dtuwrainsgo bthsee rrveepdro(pdu<c0ti.v00e1 y,ecaf.rsT aab sliegSn1if)i,craenstulylt ihnigghoner
aivneterarcgeepitn waanso ovbesretrwveodt o(pt h<r e0e.0-f0o1l,d cifn. cTraebalsee Sin1)b, urersnueldtinarge aond uarvienrgagthe eine vaenn tofvoerr ctowmop taor athblreeeS-PfoElId
vianlcureesa.sTe hinis binudrniceadte asraeas tdrounrigngef ftehcet eovfetnhte froerp croomdupcatrivaebleev SePnEtoI nvawluiledsfi. Trehsisd yinndaimcaitcessa an dstrsounpgp oerfftesctth oef
htyhpe ortehpersoidsuthcatitvteh eevmenats soinv ewfiuldeflilroeasd dgyennaemraictse danbdy stuhpepreoprtrso tdhuec htiyvpeoetvheensitsc trheaatt ethdet hmeacsosnivdei tfiuoenls lofoard
lagregneerwaitleddfi rbeys ’tohcec urrerpernocdeuacntdivpe roevpeangta tciorena.ted the conditions for large wildfires’ occurrence and
propagation.
RReemmoottee SSeennss.. 22001177,, 99,, 8855 99 ooff 1144
Remote Sens. 2017, 9, 85 9 of 14

FFiigguurree 66..( a()a2)0 0200–0200–12301ti3m etismerei esseorfiebsu ronfe dbaurrenaeidn baarmeab oino- dboammibnoaote-ddofomreinstast;eadn dfo(bre)sotfs;S taanndda r(dbi)z eodf
Figure 6. (a) 2000–2013 time series of burned area in bamboo-dominated forests; and (b) of
PStraencidpaitradtiizoenda nPdreEcvipaiptaottiroansp airnadti oEnvIanpdoetxra(sSpPiEraI)ti(othnr eIne-dmeox n(tShPtEimI)e (stcharlee)e-amveornatghe dtimoveesrctahlee)s tauvdeyraagreeda.
Standardized Precipitation and Evapotraspiration Index (SPEI) (three-month timescale) averaged
Bovlueer cthoelu smtundsye avriedae.n Bcleupeo csoiltuivmenSsP EevIivdaelnucees ,proesditcivoelu SmPnEsI nveagluaetisv, ereSdP cEoIlvuamluness n.egative SPEI values.
over the study area. Blue columns evidence positive SPEI values, red columns negative SPEI values.

FFiigguurree 77.. OOrrddiinnaarryy RReeggrreessssioionnm mooddeleslsb ebtewtweeenenm emaenaNn oNvoemvebmerb-eMr-aMyaSyP ESIP(Ei.Ie .(,i.der.,y dsreya ssoenasSoPnE IS)PaEnId)
Figure 7. Ordinary Regression models between mean November-May SPEI (i.e., dry season SPEI)
Banudrn eBdurAnreeda bAerfeoare bthefeorreep rthode urcetpivreodevuecntitv(e2 0e0v1e–n2t0 0(62)0a0n1–d2d0u06ri)n agntdh edrueprirnogd utchteiv reeepvreondtu(c2t0i0v7e– 2e0v1e2n)t.
and Burned Area before the reproductive event (2001–2006) and during the reproductive event
(2007–2012).
(2007–2012).
Figure8reportstheburnedareaandthenumberofactivefiresfordifferentlandcoversbefore
Figure 8 reports the burned area and the number of active fires for different land covers before
anddFuigruinrge t8h reerpeoprrtos dthuec tbivuerneevden atr.eIat iasnwd othrteh nnuomtinbgert hoaf tatchtievne ufimrebse froor fdaicffteivreenfit rleasnadn cdotvheersb buerfnoerde
and during the reproductive event. It is worth noting that the number of active fires and the burned
aarneda dounrlyinmg othdee rraetperloydiuncctrievaes eedveinntb. oItt his cwrooprtahn ndodtiencgid tuhoatu tshfeo rneusmt,bfuerrt hofe racstuivpep ofirrteins ganthde thspe ebcuifirncietdy
area only moderately increased in both crop and deciduous forest, further supporting the specificity
oarfetah eonrelys umltoodbetraaitneelyd ifnocrrebaasmedb oino -bdootmh icnroapte danfdo rdeesctsid.uHoouws efovreers,ta, fruerlethvearn stuinpcproeratsinego tfhbeu srpneecdifaicrietya
of the result obtained for bamboo-dominated forests. However, a relevant increase of burned area
wofa tshde erteescuteltd oabltsaoinweidth fionr tbhaemebvoerog-dreoemnifnoarteesdt cfolarsesst(sf.r oHmow2.e6v%ert,o a4 r.e1l%evoafntth ienctoretaalsee voef rbgurerennedfo arreesat
was detected also within the evergreen forest class (from 2.6% to 4.1% of the total evergreen forest
awraesa )d.eEtvecetregdre aelnsof owreitshtipna tthche eesvaerregroefetenn folorecastt ecdlawssi t(hfrionmo r2a.6d%ja cteon 4t.1to%t hoef tbhaem tbootaol- devoemrginreaetend foarreesat,
area). Evergreen forest patches are often located within or adjacent to the bamboo-dominated area,
area). Evergreen forest patches are often located within or adjacent to the bamboo-dominated area,
suggesting a possible indirect connection with the reproductive event. This hypothesis was tested by
suggesting a possible indirect connection with the reproductive event. This hypothesis was tested by
Remote Sens. 2017, 9, 85 10 of 14
RemoteSens.2017,9,85 10of14
calculating the relative contribution to the increase of burned area of evergreen forest patches
ssuhgagreinstgin (gEGasp)o asnsidb lneoitn-dshiraercitncgo (nEnGenctsi)o na bwoirthdetrh ewriethp rboadmucbtoivoe-deovmenint.aTtehdis fhoryepsot.t hBeusrinsewda asrteeas twedithbyin
cEalGcu plaatticnhgesth iencrerelaatsievde cfroonmtr i1b2u5ti oton 3to69t hkemin2 c(+re1a9s5e%o)f dbuurrinnegd raerperaoodfuecvtievreg ryeeeanrsfo, rweshtilpea otcnhlyes as hliamriintegd
(EinGcsr)eaasned fnroomt-s 3h1a3ri nkgm(2E tGo n3s2)0a kbmo2r d(+e2r.w4%ith) obcacmurbroeod- dfoorm EinGantse dduforriensgt .tBhue rsnaemdea preeariwodit.h TinheEsGe ppaattctehrenss
inclceraeralsye dshforowm a1 2s5idteo e3f6f9ecktm o2f (t+h1e9 r5e%p)rodduuricntigvree pevroednut cotniv ethyee alarsst, wrehmilaeionninlyg adleinmsiet eedvienrcgrreeaesne fforormest
3s1t3ankdms2 otfo t3h2e0 rekgmio2n(+. 2 .4%)occurredforEGnsduringthesameperiod. Thesepatternsclearlyshowa
sideeffectofthereproductiveeventonthelastremainingdenseevergreenforeststandsoftheregion.

Figure8. (a)Burnedareabeforeandduringthereproductiveevent. Theburnedareapercentwith
Figure 8. (a) Burned area before and during the reproductive event. The burned area percent with
respecttothetotalcoverisalsoreported;(b)Numberofactivefiresdetectedbeforeandduringthe
respect to the total cover is also reported; (b) Number of active fires detected before and during the
reproductiveevent.
reproductive event.
Acloseexaminationofthespatialpatternsofburnedareasinbamboo-dominatedforestsatthe
A close examination of the spatial patterns of burned areas in bamboo-dominated forests at the
regionalscaleshowsevidencethatincreasesinburnedareaarenotubiquitous(Figure5): astrong
regional scale shows evidence that increases in burned area are not ubiquitous (Figure 5): a strong
increase was mainly observed in the bamboo-dominated forest of Chin and Rakhine. These areas
increase was mainly observed in the bamboo-dominated forest of Chin and Rakhine. These areas
were mostly unaffected by large size wildfires before the bamboo reproductive event. However,
were mostly unaffected by large size wildfires before the bamboo reproductive event. However,
similarpatternswerenotevidentinManipurandChittagongHills,whicharecharacterizedbymore
similar patterns were not evident in Manipur and Chittagong Hills, which are characterized by more
fragmentedbamboocoverandhigherfireoccurrencebeforetheevent,oftenassociatedwithshifting
fragmented bamboo cover and higher fire occurrence before the event, often associated with shifting
cultivations. Twohypothesescouldexplainthisresult. First,thelargerpurebambooforestpatches,
cultivations. Two hypotheses could explain this result. First, the larger pure bamboo forest patches,
whichcharacterizeChinandRakhine,favoredignitionandpropagationofverylargewildfires,while
which characterize Chin and Rakhine, favored ignition and propagation of very large wildfires,
themorefragmentedlandscapesofMizoramandChittagonglimitedthefirepropagation. Second,
while the more fragmented landscapes of Mizoram and Chittagong limited the fire propagation.
bothIndiaandBangladeshmayhavebeensuccessfulinimplementingpolicyplanstomanagethe
Second, both India and Bangladesh may have been successful in implementing policy plans to
forecastedbambooreproductiveeventandrelatedfoodsecuritycrisis,includingfiremanagementand
manage the forecasted bamboo reproductive event and related food security crisis, including fire
suppression[42,43].
management and suppression [42,43].
Overall,theseresultsprovideevidencethattheregionalscalebamboomortalitypromotedthe
Overall, these results provide evidence that the regional scale bamboo mortality promoted the
occurrenceoflargewildfiresinthearea,withpotentiallystrongecologicalimpactsovertheregion
occurrence of large wildfires in the area, with potentially strong ecological impacts over the region
otherthanrodentoutbreaks,suchasdamagetohumansettlements; fireemissions; disturbanceto
other than rodent outbreaks, such as damage to human settlements; fire emissions; disturbance to
high conservation value ecosystems, including remnant patches of dense evergreen forests; and
high conservation value ecosystems, including remnant patches of dense evergreen forests; and
directorindirectimpactsonfaunaresidentofbamboo-dominatedhabitats. Sofar,severalstudies
direct or indirect impacts on fauna resident of bamboo-dominated habitats. So far, several studies
havehighlightedthatwildfirescouldfacilitatebambooinvasion[12,17],butnonehaveevidencedan
have highlighted that wildfires could facilitate bamboo invasion [12,17], but none have evidenced an
interconnectionbetweenbambooreproductionandwildfiresatregionalscale.
interconnection between bamboo reproduction and wildfires at regional scale.
Inaddition,theseanalysesprovidesomelevelofsupporttothefire-cyclehypothesis[11],asa
In addition, these analyses provide some level of support to the fire-cycle hypothesis [11], as a
clearchangeinfireregimewasassociatedwiththefloweringevent,especiallyinregionswithlarge
clear change in fire regime was associated with the flowering event, especially in regions with large
bambooforestpatcheswherenaturalfirepropagationdynamicscandevelop[44],includingprotected
bamboo forest patches where natural fire propagation dynamics can develop [44], including protected
areas. Nevertheless,otherevidence,suchastestingforcharcoalinsoilprofilesandcolluvialsediments,
areas. Nevertheless, other evidence, such as testing for charcoal in soil profiles and colluvial