Abiotic disturbances and their influence on forest health: a review

  Disclaimer  ThispaperisoneofaseriesofFAOdocumentsonforestrelatedhealthandbiosecurityissues.The purposeofthesepapersistoprovideearlyinformationaboutongoingactivitiesandprogrammes, andtostimulatediscussion.  Thedesignationsemployedandthepresentationofmaterialinthisinformationproductdonotimply theexpressionofanyopinionwhatsoeveronthepartoftheFoodandAgricultureOrganizationofthe UnitedNations(FAO)concerningthelegalstatusofanycountry,territory,cityorareaorofits authorities,orconcerningthedelimitationofitsfrontiersorboundaries.Thementionofspecific companiesorproductsofmanufacturers,whetherornotthesehavebeenpatented,doesnotimply thatthesehavebeenendorsedorrecommendedbyFAOinpreferencetoothersofasimilarnature thatarenotmentioned.  Commentsandfeedbackarewelcome.  Forfurtherinformation,pleasecontact:  GillianAllard ForestryOfficer(ForestProtectionandHealth) ForestAssessment,ManagementandConservationDivision ForestryDepartment FAO VialedelleTermediCaracalla 00153Rome,Italy Tel:+390657053373 Email:gillian.allard@fao.org       Acknowledgements  TheauthorswouldliketothankFAOForestryDepartmentpersonnel,NoraBerrahmouni,JimCarle, ThomasHofer,DougMcGuireandPietervanLierop,forreviewingthisdocumentandproviding valuablecomments,andRobertoCenciarelliandTulliaBaldassarriHögervonHögersthalforthe designandlayout.    Coverphotos: Lightningstrikes,Canberra,Australia(flickr/PRESCOTT) Deadvegetationindroughtstrickenarea,Senegal(FAO/CH.ERRATH/12787) Chile’sLonquimayVolcanoerupting(FAO/R.GRISOLIA/21843) Icecoverstreesandpowerlinesafteramajorstorm,Canada(B.MOORE) Floodedforest,Hungary(FAO/M.KERESZTES/FO6082)  ©FAO2011

ForestHealthandBiosecurityWorkingPapers





























Abioticdisturbancesandtheirinfluenceonforesthealth



Areview

            









BeverlyA.MooreandGillianAllard





2011











ForestAssessment,Managementand

ConservationDivision

ForestryDepartment



WorkingPaperFBS/35EFAO,Rome,

Italy











Contents





Foreword...iv



EXECUTIVESUMMARY...1



INTRODUCTION...3



METEOROLOGICALEVENTS...6



Cyclones(synonymshurricanesandtyphoons)...6



Storms(wind,snow,ice,hail,dustandsand)...11



Tornadoes...14



Thunderstormsandlightning...16



CLIMATOLOGICALEVENTS...1 Drought...17



HYDROLOGICALEVENTS...19



Floodsandflashfloods...19



Avalanches...20



Landslidesandmudslides...22



GEOPHYSICALEVENTS...24



Tsunamis...24



Earthquakes...25



Volcaniceruptions...26



ANTHROPOGENICEVENTS...29



Fire...29



Oilspills...31



Airpollution...32



Radioactivecontamination...34



CONCLUSIONS...36



References...37





Foreword

 TheUnitedNationsdeclared2011tobetheInternationalYearofForestswhichaimstoincrease publicawarenessofforests’importantecological,economicalandsocialfunctions.Forestsprovide shelterforpeopleandhabitattobiodiversity.Theyareasourceoffood,medicineandcleanwater andplayavitalroleinmaintainingastableglobalclimateandenvironment.Withsuchimmeasurable values,protectingtheworld’sforestsfromdevastatingdisturbancesiscrucial.  Disturbancesareanaturalandintegralpartofforestecosystems.Whentheyexceedtheirnormal rangeofvariation,however,theimpactsonforestscanbeextremeaffectingentirelandscapes, causinglargescaletreemortalityandcompletedestructionofundergrowthandsoils.Globalclimate changeisexacerbatingmanyoftheseimpactsbymakingforestsmorepronetodamagebyaltering thefrequency,intensityandtimingofsomeeventssuchascyclones,landslides,insectanddisease outbreaks,andheatwavesanddroughtswhichincreasetheriskoflargescalefires.  Muchmoreinformationisavailableontheimpactsofbioticdisturbances,suchaspestoutbreaks,on foreststhanontheimpactsofabioticdisturbances,thosecausedbynonlivingfactorssuchasstorms, droughtandtsunamis.FAO’sGlobalForestResourcesAssessment(FRA),carriedoutatfiveyear intervals,providesthedataandinformationneededtosupportpolicies,decisionsandnegotiationsin allmatterswhereforestsandforestryplayapart.Forthefirsttimeever,countrieswereaskedto reportontheareaofforestdamagedbyabioticdisturbancesforFRA2010.Informationprovidedwas sparse,mostlyqualitativeanddidnotallowforanytrendanalysis.Tosupplementtheinformationin FRA2010,andinacknowledgementoftheincreasingimportanceofabioticinfluencesonforest health,FAOpreparedthismoredetailedstudy.  Abioticdisturbancesareexpectedtoincreaseinintensity,quantityandfrequency.Adaptiveforest managementisthereforeessentialtoprotecttheworld’sforestsresources.Effectivemanagement practicesandpoliciesarebuiltuponrelevantandtimelyinformationandaccuratedataon disturbancesandtheirimpactsonforests.Thispaperisafirststepinsynthesizingsuchinformationto assistwiththemanagementandprotectionofforesthealth.Takingcareoftheworld’sforestsand effectivelymanagingthemnotonlyensuresthattheymeettheirobjectivesbutalsoreducestherisk ofdamagefromfutureabioticdisturbancesandaddressesglobalclimatechangeconcerns.         JoseAntonioPrado Director,ForestAssessment,Management andConservationDivision FAOForestryDepartment

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XECUTIVESUMMARY



Abioticdisturbances,disturbancescausedbynonlivingfactors,areanaturalandintegralpartof forestecosystemsthathavemajorimpacts,positiveandnegative.Theyinfluenceforeststructure, compositionandfunctioningandcanbeimportantformaintainingbiologicaldiversityandfacilitating regeneration.Whendisturbancesexceedtheirnormalrangeofvariation,however,theimpactson forestscanbeextremeaffectingentirelandscapes,causinglargescaletreemortalityandcomplete destructionofundergrowthandsoils.Globalclimatechangeisexacerbatingmanyoftheseimpactsby makingforestsmorepronetodamagebyalteringthefrequency,intensityandtimingofsomeevents suchascyclones,storms,landslides,insectanddiseaseoutbreaks,andheatwavesanddroughts whichincreasetheriskoflargescalefires.  Thispaperreviewsthecurrentknowledgeontheimpactsofabioticdisturbances.Eventsare discussedwithinfivecategories: x Meteorological–cyclones,storms(wind,snow,iceandhail,dustandsand),tornadoes,and thunderstormsandlightning; x Climatological–drought; x Hydrological–floodsandflashfloods,avalanches,landslidesandmudslides; x Geophysical–tsunamis,earthquakesandvolcaniceruptions; x Anthropogenic1 –fire,oilspills,airpollutionandradioactivecontamination.  Almost4000abioticdisturbanceeventsoccurredfrom2000to2009,killingoveronemillionpeople, impactingover2.5billionpeopleandcostingalmostatrillionUSdollars(overUS$971billion)(IFRC andRCS,2010).Whileconsiderableinformationmayexistonindividualevents,oftenlittle informationisreadilyavailableonthespecificimpactsofaneventonforests.Globalreportingon suchimpacts,particularlyquantitativeinformationonareasaffected,islowandsporadic.Thedata thatisavailablehowever,indicatesthesignificance,magnitudeandseverityofabioticdisturbances. x Forexample,abioticfactorsdamaged1.2millionhectaresofforestinSwedenin2005.The majorityofthedamageoccurredasaresultofamajorstormthatcausedseverewindthrowinthe southofthecountry. x TropicalCycloneSidrhitBangladeshin2007affectingapproximately8.7millionpeople(FAO,2008) anddamagednearly1.5millionhousesand4.1milliontrees.Approximately20000–25000 hectaresoftheSundarbanmangroveforests,aUNESCOWorldHeritageSite,incurredsevere damagesandafurther60000hectareswerepartiallydamagedbythecyclone(FAO,2008). x The2004IndianOceanTsunamikilledapproximately230000people,displacedmorethanone millionpeople,andcausedbillionsofdollarsofpropertydamage.InIndonesia,thehardesthit country,itwasestimatedthatalmost49000hectaresofcoastalforests(notincludingmangroves) wereimpactedbythetsunamirepresentinganeconomiclossofUS$21.9millionand300750 hectaresofmangroveforestssufferedapproximately90percentdamagerepresentingalossof US$2.5million(UNEP,2005). x The2010earthquake,andsubsequenttsunami,incentralChilekilledmorethan700peopleand causedwidespreaddamageinmanypartsofthecountry.Temporaryshutdownsatmanyofthe country’spulpandpaperproducersoccurredraisingglobalpulpprices.LossestoChile’seconomy wereestimatedatUS$1530billion(UNEP,2011). x In2010,over32000firesintheRussianFederationburnedapproximately2.3millionhectaresof coniferandmixedforests,withsomeareasofpeatbogs,killing62peopleanddestroyinghundreds ofhomes(Williamsetal.,2011).





1 Theseanthropogenic,orhumancaused,disturbancesareincludedinthisreviewsincetheagentitself,i.e.fire orpollutants,isabioticornonliving.

x The2010floodsinPakistanaffectedover18millionpeopleandkilledapproximately2000people, ruinedcrops,anddamagedordestroyed1.7millionhomesaswellaslivestock,forestsandwildlife (UNEP,2011).Thefloodseverelydamagedthenaturalforests,plantations,communityforests, treesgrownforfuelwood,wildlifehabitatandconservationareas(Khanetal.,2010).  Theconditionofforeststhemselvescanhaveaninfluenceondisturbances.Forexample, deforestationorpoormanagementpracticescanincreasefloodingandlandslidesduringcyclonesand degradationofmangroveforestsmayincreasethedamagecausedbystormsurgesortsunamis.In someareas,climatechangeisincreasingtheincidenceofdroughtandheatwavesresultinginan increasedriskandincidenceofwildfireswhichinturncontributestoglobalwarmingthroughcarbon emissions.  Abioticdisturbanceswillcontinuetoincreaseinintensity,quantityandfrequency.Adaptiveforest managementisthereforeessentialtoprotecttheworld’sforestresources.Activitiessuchas diversifyingspecies,usingwindbreaksandmixedcroppingpatternsforresilienceandnotplanting susceptiblespeciesinareaspronetoabioticdisturbancescanallhelptoreduceordivertpotential impacts.Reducingtheeffectsofdisturbancesonforestswillcontributetocountries’effortstoreduce carbonemissionsfromdeforestationandforestdegradationthroughforestconservation,sustainable forestmanagementandenhancementofforestcarbonstocks(REDD+)2.Takingcareoftheworld’s forestsandeffectivelymanagingthemnotonlyensuresthattheymeettheirobjectivesbutalso reducestheriskofdamagefromfutureabioticdisturbancesandaddressesglobalclimatechange concerns.   





2 ReducingEmissionsfromDeforestationandForestDegradation(REDD)isanefforttocreateafinancialvaluefor thecarbonstoredinforests,offeringincentivesfordevelopingcountriestoreduceemissionsfromforestedlands andinvestinlowcarbonpathstosustainabledevelopment.“REDD+”goesbeyonddeforestationandforest degradation,andincludestheroleofconservation,sustainablemanagementofforestsandenhancementof forestcarbonstocks(UNFCC,DECISION1/CP.16).

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NTRODUCTION



Disturbancesareanaturalandintegralpartofforestecosystems.Theyinfluenceforeststructure, compositionandfunctioningandcanbeimportantformaintainingbiologicaldiversityandfacilitating regeneration.However,globalclimatechange,primarilytheresultofhumanactivities,isreportedly makingforestsmorepronetodamagebyalteringthefrequency,intensityandtimingofsomeevents suchasfires,cyclones,storms,landslides,andinsectanddiseaseoutbreaks.Whendisturbances exceedtheirnormalrangeofvariation,theimpactsonforestscanbeextreme.Poormanagement practicesandclimaterelatedshiftsintherangeofforestpestspeciescanfurtherexacerbateabiotic impactsonforesthealth.  Abioticdisturbances,disturbancescausedbynonlivingfactors,differinduration,rangingfromhours todaysforcyclonesorwindstorms,weekstomonthsforfires,anddaysorweeksforvolcanic eruptions(Turner,2010).Thetimingofmanydisturbancesislargelycontrolledbyclimate.Tropical cyclones,forexample,typicallyoccurfromApriltoDecemberintheNorthernHemisphereandfrom NovembertoAprilintheSouthernHemisphere,tornadoesinspringandautumn,floodsduring seasonsofprecipitationorsnowmelt,andfiresduringperiodsoflowfuelmoistureandhigh temperatures(Foster,KnightandFranklin,1998).  Socioeconomicimpacts Informationonthenumberofabioticdisturbances,someestimatesoftheirassociateddamage,and thenumberofpeopleaffectedareavailablefromseveralsources.TheInternationalFederationofRed Cross(IFRC)andRedCrescentSocieties(RCS),forexample,reportedintheir2010WorldDisasters Reportthatalmost4000sucheventsoccurredfrom2000to2009(Table1;IFRCandRCS,2010).Asia experiencedthemostnaturaldisturbancesduringthisperiod–1536eventsrepresentingover38 percentofallthosereported.TheAmericasexperienced943naturaldisturbances,Africa–716, Europe–661andOceania–158.Windstormsandfloodstogetheraccountedforapproximately70 percentofthetotalabioticnaturaldisturbancesreportedand72percentofthetotaleconomicloss. Estimateddamagefromwindstormsalonerepresentedover50percentofthetotalcostsforthe decade.Earthquakesandtsunamiswerethethirdcostliestdisturbanceatover18percentofthetotal. Itshouldbenotedthattheeconomicfigurescorrespondtothedamagevalueatthemomentofthe eventandusuallyonlyrepresentdirectdamage.Thenumbersarethetotalforallreporteddamage (i.e.damagetoinfrastructure,crops,housing,etc.);specificcostsforimpactsonforestsandtheforest sectorarenotavailable.Estimatesalsovarydependingonacountry’seconomyandthefinancial valuesplacedonitemsdamagedsuchasinfrastructure;valuesaremuchhigherindeveloped countries.Alsodataoneconomicdamagesaremissingfor67percentofdisturbancesthereforethese figuresshouldberegardedasindicative(IFRCandRCS,2010).Evenwithlargegapsinreportingof economicimpacts,itisquiteclearthatnaturaldisturbanceshavesubstantialimpacts.  Table1.Totalnumberofreportednaturalabioticdisturbancesandtheassociatedimpacts,2000 2009

Disturbancetype Number of events reported Numberof deaths reported Numberofpeople reportedaffected (thousands) Estimateddamage (US$millions) Droughts 273 230 181 1 025 446 26811 Earthquakes/tsunamis 290 453 553 82 612 183425 Extremetemperatures 237 90 743 85 651 39798 Floods,waves,surges 1739 53 795 949 112 186584 Forest/scrubfires 142 636 2 140 24651 Massmovement:dryand wet(landslides,avalanches) 201 7 905 1 574 1212 Volcaniceruptions 61 230 1 556 193 Windstorms 1054 172 334 400 144 508717 Totalabioticdisturbance 3997 1 009 377 2 548 234 971391 (Source:adaptedfromIFRCandRCS,2010)

Themostdevastatingimpactsofabioticdisturbancesarethelossofhumanlives,andtheimpactson thesurvivorsrelatedtothelossoffamilymembers,homes,livelihoodsandthebasicnecessitiesof life.Peoplemaydieasadirectresultofadisturbanceormaysuccumbintheaftermath.Overone millionpeoplediedasaresultofthereportedeventsfrom2000to2009(Table1;IFRCandRCS, 2010).Earthquakesandtsunamiswerethedeadliestevents,responsibleforapproximately45percent ofallreporteddeaths;themajorityoftheseattributabletothe2004IndianOceandisaster.Droughts resultedinthedeathsof23percentofallextremeweathereventsreportedandwindstormstookthe livesofapproximately17percent.Thetotalnumberofpeopleaffectedbyabioticdisturbancesduring thelastdecadeisimmense–over2.5billion–andillustratesthewidespreadimpactsoftheseevents. Droughtimpactedthegreatestnumberofpeople,followedbyfloodsandwindstorms.  Impactsonforests Seasonaltimingofextremeeventscontrolsthepotentialrangeofimpactinforestecosystems.Trees withleavesaremuchmoresusceptibletoblowdownbycyclonesandtornadoeswhereaslateseason storms,occurringafterleaffall,createdifferentimpacts(Foster,KnightandFranklin,1998).  Somedisturbancesmayoccurasindividualdiscreteeventsormayoccurconcurrentlyorinquick successionwithotherevents.Forexample,floodingandtornadoesoftenaccompanytropical cyclones,earthquakescantriggertsunamis,avalanchesorlandslides,andwinterstormscantrigger avalanchesandalsoleadtofloodinglaterintheseason.Suchcombinationsofdisturbanceswillhave animpactontheseverityandpatternoftheimpactsobservedinforests.  Eachdisturbanceeventaffectsforestsdifferently;somecauseextensivetreemortality,whereas othersaffectcommunitystructureandorganizationwithlittlemortality.Theycanreduceleaf function,deformtreestructure,causetreedeath,alterregenerationpatterns,disruptthephysical environmentthroughsoilerosionornutrientloss,andincreaselandscapeheterogeneityofforest communities(Daleetal.,2000).Thepotentialimpactsofadisturbancedependonitsseverityor intensity,frequencyofoccurrence,duration,spatialscale,andpoint(s)ofinteractionwiththe ecosystem(Lugo,2008).Theimpactsofdisturbancesareseenoverabroadspatialscale,fromaleaf throughtotheentireforestecosystem.  Considerableinformationmayexistonindividualeventsbutoftenlittleinformationisreadily availableonthespecificimpactsofaneventonforests.Globalreportingonsuchimpacts,particularly quantitativeinformationonareasaffected,islowandsporadic(Box1;FAO,2010).  Box1.Globalinformationonimpactsofabioticdisturbances Toattempttoquantifytheimpactsofthemanyfactorsthat affectthehealthandvitalityofaforest,FAO,throughtheGlobal ForestResourcesAssessment(FRA)2010,askedcountriesto reportontheimpactofinsectpestsanddiseases,fire,other bioticfactors(suchaswildlifebrowsing,grazingandphysical damagebyanimals),andabioticfactors(suchasairpollution, wind,snow,ice,floods,landslides,tropicalstorms,droughtand tsunami)ontheirforests.Countrieswereaskedtoprovidedata (areaaffected)averagedoverfiveyears,sothatlarge fluctuationsinasingleyeardidnotsignificantlyskewthe figures.Datawerethuspresentedfor1990(anaverageofthe period1988–1992),2000(averageof1998–2002)and2005 (averageof2003–2007).  Mostcountrieswerenotabletoprovidereliablequantitative informationbecausetheydonotsystematicallymonitorthese variablesformanyreasons.Verylittlequantitativedataexistfor

manyregions,andexistingdataareoftennotavailableinaneasilyaccessibleformat.Inadditionitis oftendifficulttodeterminethecauseofforestdamageordecline.Dataareoftencollectedonlyafter significantdamagehasbeencaused.Consistentdataontheimpactsofdisturbancesovertimeare notavailableformostregions.  Forabioticdisturbances,reportingwasmoredetailedinFRA2010thaninFRA2005however,in general,informationwashighlysporadic.Theremayonlybeoccasionalreportingafteramajorstorm orothereventandmostoftenthevolumeofwoodthatisdamagedisreported(e.g.throughsalvage fellingreports)butnottheareaaffected.  Datawereprovidedby45countriesontheareaofforestaffectedbyabioticfactorsotherthanfire forallthreereportingperiods,togetheraccountingfor24percentofthetotalforestarea.Afurther 15countriesprovideddataforthe2005reportingperiodonly.  Sweden,forexample,recorded1.2millionhectaresaffectedbyabioticfactorsincludingamajor storminJanuary2005whichcausedseverewindthrowinthesouthofthecountry,especially affectingmiddleagedandoldsprucestands.TheRussianFederationreportedthatabioticfactors affected1.3millionhectaresofforestsandItalyreportedsnow,stormanddroughtaffecting0.5 millionhectaresofforest.StormsandblizzardsinJanuary2008causedgreatdamageto18.6million hectaresofforestineightprovincesinChinaincludingHunan;1781stateownedfarmsand1200 nurserieswereseverelydamaged,while760tonnesoftreeseedand10billionseedlingswerefrozen (StateForestryAdministration,2008).  Mostinformationonforesthealthisdescriptive(i.e.qualitative)innatureandmanycountries describedavarietyofabioticdisturbancesaffectingtheirforests.Storms(snow,wind,ice)werethe mostreportedabioticeventespeciallyfromEuropeancountriesincludingBelgium,CzechRepublic, Denmark,Estonia,France,Iceland,Ireland,theNetherlands,Slovakia,Slovenia,Sweden,Switzerland, UkraineandtheUnitedKingdom.DamagefromstormswasalsoreportedfromcountriesinAfrica (Sudan,Togo),AsiaandthePacific(NewZealand,RepublicofKorea)andtheNearEast(Lebanon).  HurricaneswerereportedfromcountriesinAfrica(Madagascar,Mauritius,Mayotte,Réunion),Asia andthePacific(CookIslands)andLatinAmericaandtheCaribbean(Belize,Cuba,Jamaica, Martinique).DroughtwasreportedfromcountriesinAfrica(theGambia,Togo),AsiaandthePacific (Australia,SriLanka),Europe(Hungary,Slovakia)andtheNearEast(Yemen).Floodswerereported fromcountriesinAsiaandthePacific(RepublicofKorea),Europe(Estonia)andLatinAmericaandthe Caribbean(Panama).  InthePhilippines,anoilspillof2.1millionlitresofbunkeroildamagedmangroveforestsinthe provincesofGuimarasandIloiloinAugust2006.Eruptionofthevolcano,PitondelaFournaise,in Réuniondestroyedsectionsofoldnaturalforestbylavaflows;lavaflowsweresubsequently colonizedbyintroducedplantspecies.TheMaldivesreportedconsiderabledestructionoftreesand forestvegetationasaresultoftheIndianOceanTsunamiin2004.Avalancheswerereportedfrom Slovenia,earthquakesinPanamaandairpollutioninSlovakiaandSlovenia.  Aboutthisreview Thispaperreviewsthecurrentknowledgeontheimpactsofabioticdisturbances,suchasstorms, drought,tsunamisandoilspills,onforests.Examplesprovidedarenotanexhaustivelistofeventsbut aselectionofthoseoccurringmostrecentlyorthosehavingknownimpactsonforestsandtheforest sector.Anthropogenic,orhumancaused,disturbancesareincludedinthisreviewsincetheagent itself,i.e.fireorpollutants,isabioticornonliving. 

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ETEOROLOGICALEVENTS



Cyclones(synonymshurricanesandtyphoons) Cyclones(asystemofwindsrotatinginwardstoanareaoflowbarometricpressure)cananddooccur atanylatitudeandinanyclimate.Thoseoccurringwithin30degreesnorthorsouthoftheequator arecalledtropicalcyclones;thosefoundabove60degreesnorthorsouthoftheequatorarearcticor polarcyclones;andthosebetween30and60degreesarecalledextratropicalcyclones.  Whileextratropicalcyclonesarenotasstrongastropicalcyclones,theycanproduceveryintense thunderstorms,powerfulwinds,hailandtornadoes.Suchcyclonesareimpactingforestsaroundthe world.Forexample,theGreatStormof15–16October1987hitnorthernFranceandsouthernUnited Kingdomresultinginthelossof19lives,thedeathof25milliontreesaswellaswidespreaddamage tohomes,transportandinfrastructureandanestimatedeconomiccostofUS$2.3billionintheUK alone(RMS,2007).ThestormwasfeltfromSpaintoNorwaythoughdamagewasmostsevereinthe UKandFrance.TreesofgreatscientificandaestheticvaluewerewindblownordamagedintheUK includingtreesincollectionsinKew,Wakehurst,VentnorandBedgebury.  Tropicalcyclonesareareasofverylowatmosphericpressureovertropicalandsubtropicalwaters whichbuildupintoahuge,circulatingmassofwindandthunderstormsuptohundredsofkilometres across(IHRC,2011;WMO,2011).Surfacewindscanreachspeedsof200km/hormore.Cycloneshave averydifferentwindprofileanddistributionandsignificantlyhigherprecipitationlevelsthanstorms.  Theterms‘hurricane’and‘typhoon’areregionallyspecificnamesforastrongtropicalcyclone:inthe westernNorthPacificOceanandSouthChinaSeathetermtyphoonisused;intheAtlanticOcean, CaribbeanSea,andintheeasternNorthandcentralPacificOcean–hurricane;andintheIndian OceanandSouthPacificregion–tropicalcyclone(NOAA,2011;WMO,2011).  Asatropicalcyclonemakeslandfallitsenergyistransferreddirectlytocoastalregionsoveralarge areabyhighvelocitywinds,witheffectsextendinginlandforhundredsofkilometresduringsevere events(Stanturf,GoodrickandOutcalt,2007).Threeprimaryfeaturesofcyclonesthatcausedamage arerainfall,stormsurgesandwinds.   HurricaneHugodamage,SouthCarolina,USA BUGWOOD.ORG /R.L. ANDERSON /3036081  

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Torrentialrainsaccompanyingtropicalcyclonesfrequentlycauseextensiveflooding,leadingtotree mortalityfromanoxia(absenceofoxygen).Floodingandrainfallsaturatessoil,whichmayincrease susceptibilitytowindthrowinshallowsoils.Evenatsomedistancefromthecyclonecentreandwith lowerwindvelocities,heavyrainswithmoderatewindsmaycausewindthrow(Stanturf,Goodrickand Outcalt,2007).  Astormsurgeisalargedomeofwater,sometimesgreaterthanfivemetres,thatfloodsthecoastat highspeedandwithimmenseforceasthestormmakeslandfall(IHRC,2011).Stormsurgescancause extensivedamagetocoastalvegetationbybending,breakingoruprootingtrees.Scouringanderosion mayexposerootsystemsleadingtodesiccation,anddepositionmayleadtorootsuffocation.Salinity andinundationincreasedbythestormsurgecancauseplantandtreemortality(Stanturf,Goodrick andOutcalt,2007).  Windisthefeaturethatislinkedtoavastmajorityofacyclone’sdamage,bothdirectlyandindirectly, throughwavesandstormsurge.Thestrongestwindsoccurinasemicircletotherightofthestorm’s pathashortdistancefromthecentre.Asthestormmovesinlandanditsoceanicenergysourceis removed,itrapidlylosesenergyandweakens.Tornadoes(seefollowingsectiononTornadoes) frequentlyoccurembeddedwithintherainbandsthatspiraloutfromtheeyeofthecyclonethough theyaretypicallyshortlivedandlessintensethanordinarytornadoes(Stanturf,Goodrickand Outcalt,2007).  Themostcommonimpactsofwindincludedefoliation,looseningandshreddingofbark,andabrasion ofstemsurfaces(Stanturf,GoodrickandOutcalt,2007).Treescansway,twistandrock,andlarge branchesmaybreakoffandcausedamagetounderstorytrees.Individualstemsmaybend,breakor suffersomelevelofuprootingfromleaningtocompleteblowdownofthetree(Boose,Serranoand Foster,2004;Lugo,2008;Stanturf,GoodrickandOutcalt,2007).  Treemortalitycanfollowasaresultofalmostanyoftheimpactsnotedabove.Estimatesofplantand treemortalityfollowingacyclonevaryfromtwopercent(HurricaneDavid,1979inDominica)to95 percent(HurricaneBetsy,1956inPuertoRico)(Stanturf,GoodrickandOutcalt,2007).Injuriestothe treesandlossofvigourcanalsoincreasetheirsusceptibilitytootherdisturbancessuchasinsectpests andpathogens(Lugo,2008).SeeBox2forsomeexamplesoftropicalcyclonesandtheirimpactson forests.  Predictingthedamagecausedbytropicalcyclonesisdifficultwithavarietyoffactorsinfluencing forestsatalllevels.Attheindividualplantlevel,rootingconditions(soildepthandmoisture)and growthforminfluenceatree’sresistancetowindthrow(Boose,SerranoandFoster,2004).Atthe standlevel,theamountandtypeofdamageisrelatedtothecyclone’sintensityaswellastosite specificconditionssuchas:treeheight,age,healthandotherfactorsaffectingsusceptibilitytohigh winds;speciescomposition;standstructure,conditionanddisturbancehistory;andsoilconditions, geologyandotherfactorsaffectingrootingstrength(Kupferetal.,2008).Attheregionalscale, patternsofforestdamagearecontrolledbycyclonesize,intensity,andstormtrack;largetopographic featuresthatweakenstormssuchascoastlinesandmountainranges;andregionalvariationin vegetation(Foster,KnightandFranklin,1998).  Cycloneimpactscouldbeconsideredbeneficialecologically,atleastinnaturallyregeneratedforests. Lugo(2008)suggestedthemainecologicalrolesofcyclonesinclude:alteringtheecologicalspace availabletoorganisms;increasingtheheterogeneityofthelandscapeandthevariabilityinecosystem processes;rejuvenatingthelandscapeanditsecosystemsandredirectingsuccession;shapingforest structure,influencingspeciescompositionanddiversityandregulatingtheirfunction;andinducing evolutionarychange.   

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Box2.Examplesofmajortropicalcyclonesandtheirimpactsonforests  TropicalCycloneNargis CycloneNargismadelandfallinMyanmaron2May2008withwindspeedsofupto200km/handheavy rain.ThedamagewasmostsevereintheDeltaregionwheretheeffectsoftheextremewindswere compoundedbya3.6metrestormsurge.Thecyclonekilled84537peopleplus53836peoplemissingand 19359injured(TCG,2008).Morethan2.4millionpeoplewereestimatedtobesignificantlyaffectedbythe storm.ThetotalamountofdamageandlossesintheaffectedareasofMyanmarwasestimatedatabout US$4057million(TCG,2008).Todate,itisconsideredtheworstnaturaldisasterintherecordedhistoryof Myanmar.  Some17000hectaresofnaturalforestand21000hectaresofforestplantationsweredamaged(TCG, 2008).Thelossofmangroveforestsandassociatedecosystemgoodsandserviceswillhaveasignificant impactonlocalcommunitiesthatareheavilyorpartiallydependentonforestsfortheirlivelihood.Besides cashemploymentfromtheforestsector,villagersobtainconstructionmaterialandfood(i.e.fish)fromthe mangroveforests.  TropicalCycloneSidr On15November2007TropicalCycloneSidrhitBangladeshwithwindspeedsofupto240km/hcausing significantdamagetolife,livelihoodsandproductiveinfrastructure.Approximately8.7millionpeopleor nearly2millionhouseholdswereaffected(FAO,2008).Nearly1.5millionhousesandsome4.1million treesweredamaged.TheSundarbanmangroveforests,thelargestsuchforestintheworld(140000 hectares)andaUNESCOWorldHeritageSite,incurredseveredamages.Theyformanaturalbuffer protectingmillionsofpeopleinBangladeshfromtheBayofBengal.Inadditiontosignificantenvironmental andecologicalfunctions,theSundarbansalsoplaymajorsocialandeconomicfunctionsandmany communitiesdependonthemfortheirlivelihoods.Theareaisalsoknownforitswiderangeoffauna, including260birdspecies,theBengaltigerandotherthreatenedspeciessuchastheestuarinecrocodile andtheIndianpython(UNESCO,2011).   DamagetotheSundarbanmangoveforestsinBangladeshafterTropicalCycloneSidr  IntheSundarbanssome45percent(20000–25000hectares)offorestareawereseverelydamagedand nearly15percent(60000hectares)partiallydamagedbythecyclone(FAO,2008).Someintroduced species,whichwereplantedinvariouspartsoftheSundarbans,wereuprootedwhileintheseverely affectedareasalargenumberoftreeshadstembreakorwereuprooted.Inthepartiallydamagedareas manybrancheswerebrokenbutthemaintrunksremainedintact.  flick r



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HurricaneKatrina HurricaneKatrinamadelandfallinLouisiana,UnitedStatesofAmericaon29August2005damagingcoastal andinlandforestsofMississippi,Louisiana,andAlabama.Inadditiontostrongwinds,Katrinabrought massiveamountsofrainoveraveryshorttime;astormsurgeofupto8.5metresacrosssouthern LouisianaandMississippi;extensivewind,rainandtornadodamagethroughoutMississippi,western TennesseeandwesternKentucky;andhurricaneassociatedprecipitationasfarnorthasNewYorkState (OswaltandOswalt,2008).  HurricaneKatrinawasthecostliestnaturaldisaster,aswellasoneofthefivedeadliesthurricanes,inthe historyoftheUnitedStates.Atleast1836peoplediedintheactualhurricaneandinthesubsequent floods.TotalpropertydamagewasestimatedatUS$81billion.  ItwaspredictedthatHurricaneKatrinakilledorseverelydamaged320millionlargetreesinGulfCoast forestsandtheresultinglossofcarbonrepresented50to140percentofthenetannualcarbonsinkofall forestsintheUSA(Chambersetal.,2007).InitialestimatesinMississippiindicatedpotentialtimberlosses ofupto84.9millioncubicmetresacross1.4millionhectaresofdamagedforestlandwhichcorresponded toapproximately90percentofstandingtimberinseveredamagezones,andanaverageof37percentof standingtimberacrossalldamagezones(OswaltandOswalt,2008).Hardwoodsexperiencedseverebole damageandwindthrow.InLouisiana’sPearlRiverbasin,hurricanerelatedtreemortalitywasmorethan fourtimesgreaterthanannualpreKatrinamortalityrates(Chapmanetal.,2008).Theestimatedeconomic lossoftimberfromwinddamagewasbetweenUS$1.42.4billion(Stanturf,GoodrickandOutcalt,2007).  SatelliteimagesoftheNewOrleansarea,USA,beforeandafterHurricaneKatrina.Healthyvegetation appearsbrightgreenbeforethestorm,indicatinggrowingtrees(left);brightreddepictsplantmortality justweeksafterthestorm(right).  ForestsdamagedfromHurricaneKatrinaarecurrentlybeinginvadedbyexoticspeciessuchasChinese tallow(Triadicasebifera)(Chapmanetal.,2008).Thisspecies,whichwaspresentbeforethehurricanebut witharestricteddistribution,nowthrivesinsomeareasinthelargecanopygapscreatedbythehurricane winds.  TyphoonSudal InApril2004,TyphoonSudalpassedoverthestateofYapintheFederatedStatesofMicronesiawith impactsonmangroveforests.Practicallyalltreessufferedcanopydamage,andsignificantproportionsof treesweresnappedoruprootedbutthisvariedbyspecies.Mortalityofmangrovespeciesrangedfromsix to32percentamongstands(KauffmanandCole,2010).  TropicalCycloneGafilo CycloneGafilostruckMadagascarinMarch2004causingdevastatingdamage,killingapproximately250 people,injuringmanymoreandleaving300000peoplehomeless.Justoveronehundredpeopledied whentheferry'LeSamson'sankinheavyseasofftheComoros;onlytwosurvived.Heavyrainafterthe flick r



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cycloneresultedinwidespreadfloodinginthenorth,northwestand southwest ofthecountry. Soonafterthecyclonestruck,theMinistryfortheEnvironment,WaterandForests(MINENVEF)issued temporarypermitsforthecollectionofwoodthathadbeenwindthrownordamagedbythecyclone outsideofprotectedareasonly.Withlittleenforcementandthepostdisastereconomicstress,thiscleared thewayforillegalloggingoflargeamountsofpreciouswoodssuchasrosewood,palisandre,andebonies andsubsequentexportas‘salvage’;theamountsofloggedwoodbeingmuchgreaterthantheactual amountdamagedbythecyclone(Patel,2007).Hundredsoftonnesofrosewoodandebonywere confiscated,mostofwhichwereloggedwithinthetwolargestprotectedareasintheregion.Suchselective loggingthreatensthevaluableprotectedforestsandcanresultinincreasedincidenceoffireandspecies invasions,alteredhabitats,andlossingeneticdiversity.  TropicalCycloneWaka On31December2001,TropicalCycloneWakapasseddirectlyovertheVava‘uislandgroup,Kingdomof Tonga,withsustainedandmaximumwindspeedsof185km/hand230km/hrespectively.Cyclonerelated treemortalityaveragedsixpercentandvarieddependingonspeciestype:0–7percentforlowlandlate successionalspeciesand4–19percentforearlysuccessionalspecies(Franklinetal.,2004).Severedamage (i.e.uprooting,snappedstems)affected25percentofstemsmeasured;thehighestfrequencyofsnapped stemsoccurredinthesmallmediumdiametertrees(10–15cmdbh)whileuprootingwasmoreprevalent amonglargertrees(>20cmdbh)(Franklinetal.,2004).  HurricaneMitch HurricaneMitchisconsideredtheworstdisasterofthe20thcenturyinCentralAmerica.Thehurricanehit Hondurasandthenfrom29Octoberto3November1998,theslowmovinghurricaneandthentropical stormdroppedhugeamountsofraininHonduras,Guatemala,NicaraguaandBelize,resultinginmassive floodingandmudslides.Anestimated11000peopledied,withthousandsmoreunaccountedforand approximately2.7millionlefthomeless.Thefloodingandmudslidesdamagedordestroyedtensof thousandsofhomes,withtotaldamageamountingtooverUS$5billion,mostofwhichwasinHonduras andNicaragua.  Thehurricanecauseddamage,deforestationanddisruptionoftheforestsectoringeneral.Mangrove forestsinthecoastalzonesoftheAtlanticandPacificcoastswereseverelyimpactedbothdirectlyand indirectlybythestorm(Doyleetal.,2002;HenselandProffitt,2002).Windscausednearcomplete defoliationofthevegetationontheBayIslandofGuanaja,Honduras,includingmangroveforests,and tallertreeswereeitherbrokenoruprooted(HenselandProffitt,2002).Damagetomangroveswasalso causedbywavesandsedimentburial(HenselandProffitt,2002).  InthefiveyearsfollowingHurricaneMitch,over100000hectaresofpineforestinCentralAmericawere infestedwiththesouthernpinebeetle,Dendroctonusfrontalis,inassociationwithotherspeciesof DendroctonusandIpsspp.Theresultingextensivetreemortalityseverelyincreasedtheriskofwildfiresand negativelyaffectedwildlifeandrecreationcausingwidespreadandsignificanteconomicimpacts.  HurricaneHugo InSeptember1989,HurricaneHugostruckGuadeloupe,Montserrat,St.Croix,PuertoRico,Antiguaand SouthCarolina,USA.InGuadeloupe,tallmixedmangrovesexperienceda78percentdecreaseinaverage treedensityand71percentreductioninaveragebasalareaafterthestorm’spassage(Lugo,2008).The hurricanepassedoverthenortheastcornerofPuertoRicowithsustainedwindsofover166km/hresulting indefoliation,windthrowandlandslides(Turner,DaleandEverham,1997).Thestormalsoresultedin populationoutbreaksof15speciesofLepidoptera(mothsandbutterflies)inthesamecountry,including larvaeofSpodopteraeridania(Noctuidae)whichwerefeedingonearlysuccessionalplantspecies(Lugo, 2008).Theoutbreakoftheseinsectsendedwiththedeclineofthehostplants.Thisstormalsoimpacted forestsinSouthCarolina,UnitedStateswhereitcausedextensivedamagefor325kilometresinland (Stanturf,GoodrickandOutcalt,2007).  

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Storms(wind,snow,ice,hail,dustandsand) Stormsbringingwind,snow,iceorhailoracombinationofthesefactorshavealwaysimpactedthe healthofforestsandthusarearegularconsiderationinforestmanagementplans.Theycanoccuras catastrophiceventsaffectingentirelandscapes,thequalityofwildlifehabitats,andforeststand structure,whichcanleadtomajordisruptionsinmanagementgoals.Alternativelytheymayoccuras smallscaledisturbancesthataffectindividualtreesorgroupsoftreeswithinastandincreasingthe amountofdeadwoodanddiversifyingstandstructure,whichcanhavepositivebenefitsforbiological diversity.  Damagingwindsvaryfromshortlivedgusts,tostrongprevailingwinds,topowerfulhurricanes,to briefbutintensedowndraftsfromthunderstorms(LauranceandCurran,2008).Theimpactofwindon forestsisdeterminedbyacomplexofmanybioticandabioticfactorsandissimilartothose experiencedduringcyclones(Seeprevioussection).Stormdamagecanincludeinitialmechanical damagefromthestorm,subsequentdamagefromotherbioticorabioticfactors(i.e.insects,fire,sun, snow,ice,etc.),andlossofproduction.Theseverityandextentofwindstormdamageinforestsarea functionof:thedamagepotential(i.e.theamountofgrowingstockexposedtostrongwinds);the susceptibilitytowind,whichisdeterminedbytreeandstandcharacteristics(i.e.treespecies, tree/standheight,slendernessoftrees,crownandrootingcharacteristics,standdensity)andsite characteristics(i.e.soiltype,soilmoisturecontent,topography);andtheextentandseverityofthe eventitself(i.e.stormextent,windspeedandgusts)(MartinandOgden,2006;Seidletal.,2011; Usbecketal.,2010).Whethertreesareuprootedorbrokenisdeterminedprimarilybyitsposition withinthecanopyandbyitsrootingdepth(MartinandOgden,2006).  Insomeareas,stormshavebeencausingincreaseddamagetoforestsinrecentdecades(Schelhaas, NabuursandSchuck,2003).InEurope,forexample,stormscausemorethan50percentofalldamage toforestsandthustheyhavebecomesuchamajorconcerntotheforestsectorthattheDirectorate GeneralfortheEnvironmentoftheEuropeanCommissioncommissionedastudyintotheproblem.   Stormdamage,Slovakia   FAO/V.CABOUN/FO6095





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Thisstudyidentified130separatewindstormsthatcausedconsiderabledamagetoforestswithinthe last60years(Gardineretal.,2010).Byanalysinginformationonthesestorms,theauthorsnotedthat gustpeakwindspeedisstronglycorrelatedtothemaximumpotentiallevelsofdamage,treeheight hasanimportantimpactonitsvulnerability,andrecentthinning,particularlyinolderstands,isoften associatedwithincreaseddamage.  Spruceandpoplarappeartobeamongthemostvulnerablespeciesandsilverfirandoakamongthe leastvulnerableoftheconifersandbroadleavesrespectivelyalthoughsuchfindings,andthegenerally highersusceptibilityofconiferstodamage,arepossiblyrelatedmoretovariationsinmanagement andsite.Soilconditionhadalargeinfluenceontheextentofdamage.Rootanchoragestrengthis increasedbysoilfreezingandreducedbywaterlogging,heavyrainandbypoordrainagethatallows soilsaturationduringstorms.Withclimatechange,increasedtemperatureswilldecreasetheperiod oftimeinwhichsoilsarefrozen,particularlyinnortherncountries,potentiallyincreasingthedamage fromwind.Stormswillalsobeaccompaniedbyheavierprecipitationresultinginmoresaturatedsoils andincreasedriskofdamage.  Snowmostcommonlyimpactstreesbybreakingstemsbuttreescanalsobebentoruprooted (Nykänenetal.,1997).Theseverityofsnowdamageisrelatedtotreecharacteristics;factors controllingthestabilityoftreessuchasstemtaperandcrowncharacteristicsarethemostimportant (Nykänenetal.,1997).Conifersareparticularlydamagedbyheavysnowfall,whilebroadleavedtrees aregenerallymoreresistanttostormsandsnowinthelateautumnandwinterduetobetterroot systemsandlackoffoliage(FAO/ECE/ILO,1995).  Icestormsresultwhenliquidprecipitationfallsthroughalayerofcoldair.Ifthislayerofcoldairis thickenoughandtheairtemperatureisbelowfreezing,theprecipitationfreezesoncontactwith groundlevelobjects,formingacoatofice.Theleveloficeaccumulationvarieswithtopography, elevation,aspect,andtheamountofareaintheregioninwhichconditionsfavouriceaccumulation (Irland,2000).  Inamatterofminutesanicestormcandepositalayeroficeheavyenoughtobringdownpowerand telephonelinesandsnapbranchesfromtrees(WMO,2011).Impactsofindividualstormsarehighly patchyandvariable,anddependonthenatureofthestorm,itsseverity,frequency,timingand extent.Icestormdamagetoforestcanopiesisrelatedtocanopyarchitecture,treesize,age,health andthemechanicalpropertiesofthewooditself(Irland,1998).  Iceaccumulationontreescancauseminorbranchbreakage;majorbranchloss,uptototalcrown loss;temporarilyorpermanentlybendingoverofcrowns;rootdamage(whensoilisnotfrozen); breakageoftrunkswithinorbelowthecrown;andforsomehardwoods,splittrunks(Irland,2000). Freezingrainimmediatelyfollowingheavysnowfallscanbeverydamagingtovegetationbecauseof theincreasedloadingonbranches(Irland,2000).Softwoodsseemtosufferlessdamagethan hardwoods.Recentlythinnedstandscanbehighlyvulnerable,ascrownshavespreadintonewly openedspacebutbranchstrengthmaynotbefullydeveloped.Treesdamagedbyicestormsor windthrowcanbemoresusceptibletootherdisturbancessuchasinsectpestsorfire.  Icestorms,likeotherdisturbances,caninfluencestandcomposition,structureandconditionover wideareas(Irland,2000).Asarecurringeventtheyplayaroleindeterminingforestsuccessionand areimportantfactorsinfluencingthedynamicsoftheforestsinaffectedregions(Hooper,Ariiand Lechowicz,2001).Icestormsredistributelivinganddeadbiomassinforests,reducecanopyheight andstratification,increaseorganicinputstothesoilandexposemineralsoil(Hooper,Ariiand Lechowicz,2001).  InJanuary1998,amajoricestormoccurredaffectinglargeportionsofNewEnglandintheUSAand theCanadianprovincesofNewBrunswick,OntarioandQuebec.Millionsoftreesfell,andmore continuedtobreakandfallthroughouttherestofthewinterseason.Nonnativespeciesandtrees 

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Icecoverstreesandpowerlinesafteramajorstorm,Canada  plantedoutsidetheirnaturalranges,suchasRobiniaandSalixspp.,sufferedseverely,whilenearby nativespeciessufferedfarlessdamage(Irland,1998).InanoldgrowthhardwoodforestatMontSt. Hilaire,Quebecthestormbroughtdown19.9metrictonnesor33.6cubicmetresofwoodydebrisper hectarewhichrepresentedabout7–10percentofthetotalabovegroundbiomassinthisforestbefore thestorm(Hooper,AriiandLechowicz,2001).  AFebruary1994icestorminnorthernMississippihadmajorimpacts,includingdamageto1500000 hectaresofforestsandheavylossestourbantreesandpecanorchards(Irland,1998).Astormin November1996ineasternWashingtonandIdaho,USAcausedwidespreadtreedamageandheavy lossestogardenandstreettrees(Irland,1998).  Largehailstonesthatcanreachdiametersofover10centimetresandcanfallatspeedsofover150 km/h(WMO,2011)canalsocauseconsiderabledamagetoforests.  Atopicrelatedtotheimpactsoficeandsnowontreesistheimpactofdeicingsalts,suchassodium chloride,usedliberallyonroadstomaintainsafewinterdrivingconditionsinmanycoldregionsofthe world.Sodiumchloridecandamageroadsidevegetationandaffectsurfacewaterandgroundwater quality(Muncketal.,2010).Conifersaremoresusceptibletodamagefromsaltspraycomparedto hardwoodsbecausetheyretaintheirfoliagethroughthewintermonthswhensaltisappliedtoroads. Tipdiebackandleafscorcharethetypicalsymptomsassociatedwithsaltdamageonconifers.Salt ionscauseosmoticandionicstressinplantsandsoilsalinityinterfereswithbothwaterandnutrient uptakebyroots(Muncketal.,2010).  Duststormsandsandstormsarenaturaleventsthatoccurthroughouttheworld,especiallyin drylandareaswhichcoverapproximately41percentoftheearth’slandsurface(morethan6billion hectares)(MEA,2005).DrylandsoccurintheMediterraneanregion,SaharaandsubSaharanAfrica, CentralandSouthAsia,AustralianOutback,SouthAmericanPatagoniaandtheNorthAmericanGreat Plains.  Duststormsandsandstormsarearesultofwinderosionandaredrivenbypoorlandmanagement anddegradationofthedrylandvegetationcover.Strongwindsandfavourablesurfaceatmospheric conditions(i.e.turbulencelevel,stability,soilmoisture)canallowforlargeamountsofsandanddust tobeliftedfrombare,drysoilsintotheatmosphere.Everyyearoneandahalftonnesofsandand B.MOORE





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 DuststorminNewSouthWales,Australia,2009  dustareemittedfromdrylandsintotheatmospherewhereitcanbetransporteddownwindaffecting regionshundredstothousandsofkilometresawaydependingonmeteorologicalconditions(WMO, 2011).DustfromtheGobiDesert,forexample,iscarriedtothePacificcoastsofNorthAmericaand dustfromtheSaharaDesertiscarriedtotheCaribbeanislandsandtheAmazonbasin(MEA,2005).  Dustcanhavenumerousimpactsonhumanandveterinaryhealth,theenvironment,agriculture, marineecosystems,fisheries,transport,visibility,aviation,andweatherandclimateatlargerscales (WMO,2011).AmajorsandduststorminnorthwestChinaon5May1993illustratesthedevastation andseriouseconomiclossthatsuchstormscanproduce.Atotalof85peopledied,31peoplewere lostand264peoplewereinjured.Approximately373000hectaresofcropsweredestroyed,120000 animalsdiedorwerelost,16300hectaresoffruittreesweredamaged,90000individualtreeswere blowndownandthousandsofgreenhousesandplasticmulchingshedswerebroken(UNCCD,2002).  Insomecases,however,thedepositionofdustcanproducepositiveresults.Forexample,mineral richSaharandusttransportedacrosstheAtlanticOceantotheAmazonrainforestinSouthAmerica providesironandphosphorustothenutrientpoorrainforestsoilsactingasfertilizer(WMO,2011).  Measurestocombattheoccurrenceandimpactsofsandandduststormsincludetheuseof windbreaksorshelterbeltstoreducetheimpactofwindspeedsanddecreasesoilerosion(Sivakumar, MothaandDas,2005).  Tornadoes Tornadoesareshortlived,relativelysmall,complex,violentandunpredictablestormsthatcancause severedamagethoughusuallyinlimitedareas(Foster,KnightandFranklin,1998;Fujita,1971).They aremostcommoninspringinlateafternoonandareconcentratedininteriorcontinentalregions, particularlyinTornadoAlleyoftheGreatPlainsofNorthAmerica,buttheycananddooccur anywhere,especiallyintemperatelatitudes(WMO,2011).Tornadowindsgreatlysurpasstropical cyclonewindsinintensity,reachinganestimatedmaximumexceeding400km/h(Foster,Knightand Franklin,1998). Flickr/DABAYU





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 Tornadodamage,HoosierNationalForest,Indiana,USA  Theydevelopunderthreemeteorologicalconditions:longlivedsupercell3thunderstorms,which generatethelargestandmostdamagingtornadoes;ordinarythunderstorms;andincyclonesafter theymakelandfall(Foster,KnightandFranklin,1998).Thoseassociatedwithcyclonestendtobe moreshortlivedandlessintensethanothertornadoes(Stanturf,GoodrickandOutcalt,2007).  Tornadoescancreatecomplexdamagepatternsowingtotheirextremevariabilityinintensity,path length,width,andcontinuity;thepotentialformultipletouchdowns;andthehighfrequencyof multiplestormsinclusters(Foster,KnightandFranklin,1998).Damagetotreesandforestscanrange frombranchbreakandsingletreegapstoextensiveareasofcompleteblowdown.Peterson(2007) notedanincreaseintheprobabilityofwindrelateddamagewithincreasingtreediameterinastudy oftornadodamageacrosseasternNorthAmerica.Someofthedamagecausedbytornadoesmaybe positive.Thelossofcanopycanallowforotherspeciestoflourishtherebyincreasingbiodiversityand theconsequentincreasesinsoiltemperaturemayincreasemicrobialactivityandtherebyenhance nutrientcyclinginthesoil(Peterson,2000).  TornadoescausemorehumanmortalityintheUnitedStatesthananyotherweathereventexcept lightning(Peterson,2000)anddespitetheirsmallsize,theyhavemassiveeconomiccosts.Asingle NorthCarolinatornadocausedanestimatedUS$100millionindamageinNovember1988,asdidthe Catoosa,OklahomatornadoofApril1993(Peterson,2000).OtherexamplesincludeaNovember1992 tornadooutbreakthatcausedapproximatelyUS$291millionindamage,asystemoftornadoesin Mississippi,Alabama,GeorgiaandTennesseeon8April1998(US$300million),theOklahomaKansas tornadoesofMay1999(US$1billion),theArkansasTennesseetornadoesofJanuary1999(US$1.3 billion),andthecombinedfloodingandtornadoesofMarch1997intheMississippiandOhiovalleys (US$1billion)(Peterson,2000).  The2011tornadoseasonintheUnitedStatesiscurrentlyonrecordpaceandprovinglikelytobethe mostdamagingyet.Asof04July2011,1583tornadoeswerereported(someoftheseareyettobe confirmed)(NOAA/NWS,2011).Sincethebeginningoftheyear,537peoplehavedied,approximately 346fromtheoutbreaksoftornadoesinAprilalone. 





_{Asupercellisathunderstormwithadeeprotatingupdraftormesocyclone.} BUGWOOD.ORG /J.O’BRIEN/5059075





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Thunderstormsandlightning Severethunderstormsgiverisetosuddenelectricaldischargesintheformoflightningandthunder. Theyoftenbringheavyrainorhail,strongwindsandoccasionallysnowandinsomepartsofthe worldtheytriggertornadoes(WMO,2011).Inareaswherelightningisnotaccompaniedbyrain,so calleddrylightning,itmayalsobeasourceofignitionforforestfires(Päätalo,1998)asnotedinsome remoteareasofCanadaandtheRussianFederation(FAO,2007).Howeveritisgenerallyrecognized thatthemajorityofforestfiresarecausedbyhumansandnotbylightning(SeesectiononFireunder Anthropogenicevents).  Talltreestendtobethemostvulnerabletolightningstrikes,especiallythosegrowingsinglyinopen areassuchasonhills,infields,nearwaterorinurbanenvironments.Thelikelihoodofastrikeis greatestonexposedridges,summits,slopesandotherconvexsurfaces(Päätalo,1998).Lightningcan impactatree’sbiologicalfunctionsandstructuralintegrity.Alongthepathofthestrike,sapboils, steamisgeneratedandcellsexplodeinthewood,resultinginstripsofwoodandbarkpeelingor beingblownoffthetree(Clatterbuck,VandergriffandCoder,2011).Treesmaysurviveifonlyoneside ofthetreeshowsevidenceofalightningstrike;howeverwhenthestrikecompletelypassesthrough thetrunk,treesareusuallykilled.Manytreescansuffersevereinternalorbelowgroundinjury despitetheabsenceofvisible,externalsymptomswhenthelightningpassesthroughthetreeand dissipatesintheground(Clatterbuck,VandergriffandCoder,2011).Majorrootdamagemaycause thetreetodeclineanddie.Lightninginducedmortalitycancreategapsinforestcanopies (Magnusson,LimaanddeLima,1996).          Lightningstrikes,Canberra,Australia Flick r/PRESCOTT 





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Drought Droughtsarecausedbyadeficiencyofprecipitationovertimeandassuchcandevelopslowly, sometimesoveryears.OftenassociatedwiththearidregionsofAfrica,particularlytheSahel,in recentyears,droughtshavealsostruckIndiaandpartsofChina,theNearEast,theMediterranean, Australia,partsofNorthAmerica,SouthAmericaandEurope(WMO,2011).Increasesinthe frequency,duration,and/orseverityofdroughtandheatstressassociatedwithclimatechangecould fundamentallyalterthecomposition,structureandbiogeographyofforestsinmanyregions.Of particularconcernareincreasesintreemortalityassociatedwithclimateinducedphysiologicalstress andinteractionswithotherdisturbancessuchaspestoutbreaksandfire(Allenetal.,2010).  Allenetal.(2010)identified88welldocumentedepisodesofincreasedmortalityduetodroughtand heatthroughoutavarietyofforesttypes,frommonsoonalsavannaswithmeanprecipitation<400 mm/year,tosubalpineconiferforestswithaMediterraneanclimate,totropicalrainforestswithmean precipitation>3000mm/year,illustratingthatdroughtinducedmortalityisnotrestrictedtoforests normallyconsideredwaterlimited.Theynotedacomplexsetofmortalitypatternsrangingfrom small,shortlivedlocalincreasesinbackgroundmortalityratestoepisodesofacute,regionalscale forestdieoff,whichmayinvolvebioticdisturbancessuchasdiseaseorinsectoutbreaks.Regional scalemortalityofoverstorytreesisofparticularconcernasitrapidlyaltersecosystemtype, associatedecosystemproperties,andlandsurfaceconditionsfordecades(Breshearsetal.,2005).  Quakingaspen(Populustremuloides)inWesternCanadaexhibitedsteepproductivitydeclinesand diebackafteraparticularlyseveredroughtin20012003,witheffectscontinuingforyears(Hogg, BrandtandMichaelian,2008).Impactswereexacerbatedbyattacksofdefoliatingandwoodboring insectsandpathogens(HoggandBernier,2005;Hogg,BrandtandMichaelian,2008).Steepgrowth declinesandstandreplacementofEuropeanbeech(Fagussylvatica)attheloweredgeofitsrange hasbeenobservedinSpainandothersouthernEuropeancountriesinresponsetodrought(Jump, HuntandPeñuelas,2006).InItaly,SpainandPortugalnativeoaksaredecliningduetowarming,    Deadvegetationindroughtstrickenarea,Senegal  FAO/CH.ERRAT H/12787



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droughtorPhytophthoraspeciesandinSpain,Pinusuncinata,P.pinaster,andP.pineahavebeen exhibitingdeclineanddieback(RescodeDios,FischerandColinas,2007).Carniceretal.(2011) reportedageneralizedincreaseincrowndefoliationinsouthernEuropeanforestsfrom1987to2007 inresponsetodroughtconditions.  ParkWilliamsetal.(2010)concludedthatprojectedrisesintemperatureandaridityinthe southwesternUnitedStateswillsubstantiallyreducetreegrowthandlikelyincreasemortalityrates. Breshearsetal.(2005)reportedaregionalscalevegetationdieoffacrosswoodlandsinthesame regionin2002–2003inresponsetodroughtandassociatedbarkbeetleinfestations.Otherexamples ofrecentdieoffscausedbyelevatedtemperaturesand/orwaterstresshavebeenwelldocumented forsouthernpartsofEurope(Bigleretal.,2006;Bredaetal.,2006;Peñuelas,LloretandMontoya, 2001)andfortemperateandborealforestsofwesternNorthAmerica,wherebackgroundmortality rateshaveincreasedrapidlyinrecentdecades(vanMantgemetal.,2009)andwidespreaddeathof manytreespeciesinavarietyofforesttypeshasaffectedwellover10millionhectaressince1997 (Raffaetal.,2008).InsemiaridandMediterraneansystems,severalstudieshaverecentlyreported increasedplantmortalityratesanddieoffevents,reducedseedlingrecruitment,longtermshiftsin vegetationcomposition,reducedradialgrowth,andincreasedcrowndefoliationresponses(Carnicer etal.,2011).  Aprimaryresponseofforeststofuturedroughtwillbeareductioninnetprimaryproduction(NPP) andstandwateruse(HansonandWeltzin,2000).DroughtshavebeenreportedtoreduceNPPin: NorthAmericaandChina(2000);NorthAmericaandAustralia(2002);Europe(2003);Amazonregion, AfricaandAustralia(2005);andlargepartsofAustralia(20072009)(ZhaoandRunning,2010).  Forestdroughtusuallyresultsinreducedshootgrowth,reducednitrogenandwaterfoliar concentrations,andincreasedallocationtosecondarydefensivecompounds,suchastannins (Carniceretal.,2011).Droughtinducedreductionsindecompositionratesmaycauseabuildupof organicmaterialontheforestfloorwhichcouldinfluencenutrientcyclingandincreasesusceptibility tofire(HansonandWeltzin,2000).  Susceptibilityofforestecosystemstodroughtismainlydeterminedbysite(i.e.soiltexture,soildepth, waterholdingcapacity)andstand(i.e.leafarea,speciescomposition,androotingdepth) characteristics(Seidletal.,2011),standmanagementaswellashumanpressure.Youngplantssuch asseedlingsandsaplingsareparticularlysusceptibletodroughtwhereaslargetreeswithamore developedrootingsystemandgreaterstoresofnutrientsandcarbohydratestendtobelesssensitive, thoughtheyareaffectedbymoresevereconditions(HansonandWeltzin,2000).Shallowrooted treesandplantsaswellasspeciesgrowinginshallowsoilsaremoresusceptibletowaterdeficits. Deeprootedtreescanabsorbwaterfromgreaterdepthsandthereforearenotaspronetowater stress.  Strategiesforforestmanagerstoadapttofuturedroughteventsmightincludethinningstandsto reducecompetitionorselectingappropriategenotypes,suchasthosewithimproveddrought resistance.  AseveredroughthasbeenaffectingthecountriesofDjibouti,Ethiopia,KenyaandSomaliasinceearly 2011,theworstonetohittheregionforsixdecades.Theregionhasexperiencedtwoconsecutive seasonsofsignificantlybelowaveragerainfall,resultinginfailedcropproduction,depletionofgrazing resourcesandsignificantlivestockmortality.AsofJune2011,highlevelsofacutemalnutritionwere widespreadandmorethan8millionpeoplewereinneedofemergencyassistance.Impactshave beenworsenedbyhighfoodpricesandinsomeareas,conflict.Attimeofprint,theimpactson forestswerenotknown.   

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Floodsandflashfloods Floodsoccurwhentherateofwatersupplyexceedsthecapacityofstreamchanneldrainagesuchas duringperiodsofheavyrainsandrapidlymeltingsnowandice.Theycanbetriggeredbycyclones, severethunderstorms,tornadoesandmonsoonsorcanresultfromthebuildingofdams(i.e.by beavers)orbydambreakscausedbygeneralfailure,icejams,landslides,orbytectonicandother geologicalprocesses(Foster,KnightandFranklin,1998).Excessiverainfallonsaturatedsoilsinflat areascanalsocreatefloods.Incoastalareas,stormsurgescausedbytropicalcyclonesandtsunamis, orbyacombinationofhighriverflowsandbackwatereffectsasaresultofhightides,canalsocause flooding.  Theecologicaldamageofregularfloodingmaybeminorasfloodplainplantsandanimalsarewell adaptedtosuchconditions(Foster,KnightandFranklin,1998).Inaddition,themechanicalforceof floodwaterisnottypicallyadequatetoincreaseplantmortalityrates,especiallywhenfloodingoccurs inspringbeforebudbreakofdeciduoustrees.Oxbowformation,icescouring,andbankerosionmay causethedeathofsometreesandchangesinthelandscapemosaic,butimpactsaregenerally affectedonlyoverlimitedareas(Foster,KnightandFranklin,1998).Floodscausedbywaterloggingof large,flatareas,however,canpersistforseveraldaysandcausedamagetotreesandforests.Some examplesofrecentfloodeventscanbefoundinBox3.  Flashfloodscanoccurafterheavystormsorafteraperiodofdroughtwhenheavyrainfallsontovery dry,hardgroundthatthewatercannotpenetrate(WMO,2011).Sucheventsmayhavemuchmore impactonforests,especiallyinareasnotaccustomedtohighwaters.          Floodedforest,Hungary   FAO/M.KERESZTES/FO6082



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 Box3.Somerecentfloodevents BeginninginJuly2010,aheavierthannormalmonsoonseasonresultedindevastatingfloodsin Pakistanthatkilledapproximately2000people,ruinedcrops,anddamagedordestroyed1.7million homesaswellaslivestock,forestsandwildlife(UNEP,2011).Over18millionpeoplehavebeen affected.Thefloodseverelydamagednaturalforests,plantations,communityforests,treesgrownfor fuelwood,wildlifehabitatandconservationareas(Khanetal.,2010).Theremainingintactforestsare atriskoffurtherdegradationaslocalcommunitiesextracttimbertorebuildhomesandforfuelwood andfodder,andsellforestproductsandwildlifetoearncash(Khanetal.,2010).  SignificantfloodingoccurredinmanyareasofQueensland,AustraliaduringlateDecember2010and earlyJanuary2011.Threequartersofthestatewasdeclaredadisasterzoneandcleanupeffortsare expectedtocostbillionsofdollars.Thousandsofpeoplewereevacuatedfromtheirhomesandmore than200000peoplehavebeenaffected.Theimpactsonforestsremaintobeseen.  UnusuallyheavyrainfallsinceJanuary2011hascausedwidespreadfloodinginsouthernAfrica, particularlyinAngola,Botswana,Lesotho,Madagascar,Malawi,Mozambique,Namibia,SouthAfrica, ZambiaandZimbabwe.Theaffectedcountriesreportdeaths,displacements,evacuationsaswellas damagetocrops,housesandinfrastructure(OCHA,2011).InNamibia,thehardesthitcountry,flood watersaresubsiding,howeverthenumberofpeopleaffectedbythefloodscontinuestoriseasnew informationisreceived;itisestimatedthatthetotalnumberofpeopleaffectedis500000with65 relateddeathsandapproximately60000displacedand19000inrelocationcamps(asof02July 2011).InMalawi,14peoplehavedied,over61000peopleareaffectedandover3800hectaresof cropsdamaged(asof29April2011).Atleast234peoplediedinAngolawithapproximately254000 peopledirectlyaffected(asof02June2011).Impactsonforestsarenotyetknown.  TheMississippiRiverfloodsof2011areamongthelargestandmostdamagingalongthefloodprone USriverinthepastcentury.ComparisonsarebeingdrawntothemajorMississippiRiverfloodsin 1927and1993,thelatterinwhichmorethan10millionacresoflandwereflooded.InApril2011, twomajorstormsystems,alsoresponsibleforlargetornadooutbreaks,producedlargeamountsof rainfallacrossmuchofthevastMississippiRiverwatershed.Combinedwithspringtimesnowmelt, theriverbegantorisetorecordlevelsbyearlyMay.StatesexperiencingfloodingincludeIllinois, Missouri,Kentucky,Tennessee,Arkansas,MississippiandLouisiana.Theimpactsonforestsremainto beseen.  Avalanches Avalanchesarerapid,gravitydrivenmassflowsofsnow,airanddebris(Bebi,KulakowskiandRixen, 2009).Theycangenerallybeclassifiedintoloosesnowavalanches(startingatasingleareaorpoint) andslabavalanches(releaseofacohesivesnowlayerinitiatedbyafailureatdepthinthesnow cover).Theycanbehighlydestructive,movingatspeedsinexcessof150km/h(WMO,2011). Avalanchesclaimapproximately150livesperyearandthatnumbercontinuestoriseasmorepeople participateinwintersportstherebyspendingmoretimeinvulnerableareas.On17February2010,for example,anavalanchefuelledbyheavysnowfallsstruckseveraltownsinNorthWestFrontier ProvinceofPakistankillingover100people.  Avalanchedisturbanceregimesaretwowayinteractionsinwhichforeststructureandcomposition affectavalanches,andavalanches,inturn,affectforeststructureandcomposition(Bebi,Kulakowski andRixen,2009).Avalanchesprimarilyaffectsubalpineforests(thoseforestsclosesttouppertree line).Theycandamageorkillindividualtreesovertenstohundredsofhectaresinforeststhatare locatedinvulnerableareas.Atastandscale,avalanchestypicallyresultinforestcommunitiesthatare characterizedbysmallerandshortertrees,shadeintolerantspecies,lowerstemdensities,and 

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 Damagecausedbyalargeavalanche,Switzerland  greaterstructuraldiversity.Suchcommunitiesprovidevaluedhabitatforvariousanimalandplant speciesandcancontributetooverallhigherbiodiversity.Atabroaderscale,avalanchetracksprovide increasedlandscapeheterogeneityandedgedensityandcanserveasfirebreaks.  Theimpactsofavalanchesontreesarecloselyrelatedtothesizeandflexibilityofthetreeandwhere theavalancheoccursinrelationtothetree.Intreeswithlargerdiameters,thestressesexertedby avalanchescanexceedthebreakingstrengthofthetree,resultinginbolebreakageoruprootingof thetreeifthepressureishighenough.Ifatreeisflexibleenough,itmaybedeflectedandbelargely undamaged.Smalltrees(height<5metres)cantoleratesnowpressurebybendingandleaninginthe snowpack(Kajimotoetal.,2004).Criticaltreediametersforbreakagerangeforcommonsubalpine treespeciesfrom6to14centimetres,andarehigherforbroadleaved,relativelyshortlivedtreeswith flexiblestemssuchasBetula,Alnus,AcerorSalixspecies(Bebi,KulakowskiandRixen,2009).  Whenavalancheseverityand/orfrequencyarehigh,theycanbethedominantfactorthatcontrols survival,growthratesandgrowthformsoftrees.Withdecreasedseverityandincreasingintervals betweenavalancheevents,thegrowthoftreespeciesshiftsfromshrubstoerecttrees(Bebi, KulakowskiandRixen,2009).Standsthatarefrequentlydisturbedbyavalanchesaretypically dominatedbytreeswithsmallerdiameters,shorterstature,andslowannualgrowthratesin comparisontoundisturbedstands(Bebi,KulakowskiandRixen,2009).Disturbedstandsalsotendto becharacterizedbyadominanceofshadeintolerantspeciesandlowertreedensities(Butler,1979; Johnson,1987;Bebi,KienastandSchönenberger,2001).Forestrecoveryafteravalanchesisnormally bywayofsurvivingvegetationasopposedtonewspeciesestablishment.  Oneofthemostimportantecologicaleffectsofavalanchesisincreasedstructuralandcompositional diversity(Bebi,KulakowskiandRixen,2009).Inmontaneandsubalpineareas,coniferousforests composedofrelativelylargetreesusuallydominate;avalanchedisturbanceallowsforsmaller individualstodominateplantcommunities.Avalanchescreateopenhabitatinotherwiseclosed forestswhichcontributestothecomplexityanddiversityoftheecosystem.Bebi,Kulakowskiand Rixen(2009)notedthatthenumberofvascularplantspecieswasgreatestinareasofhighest disturbanceintensityandfrequencyasopposedtoareasthatexperiencedavalancheslessfrequently. FAO/T.HOFER/F O0346



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