FAO Decline and diebackdieback FORESTRY of tretreess and forestsforests PAPER 120

A globalgIoia overviewoverview

by William M. CieslaCiesla FADFAO Forest Resources DivisionDivision and Edwin DonaubauerDonaubauer Federal Forest Research CentreCentre Vienna, Austria

Food and Agriculture Organization of the United Nations

Rome, 19941994 The designations employedemployed and the presentation of material inin thisthis publication do not imply the expression of any opinion whatsoever onon the part ofof thethe FoodFood andand AgricultureAgriculture OrganizationOrganization ofof thethe UnitedUnited Nations concerning the legallega! status ofof anyany country,country, territory,territory, citycity oror area or of itsits authorities,authorities, oror concerningconcerning thethe delimitationdelimitation ofof itsits frontiers or boundarboundaries.ies.

M-34M-34 ISBN 92-5-103502-492-5-103502-4

All rights reserved. No part of this publicationpublication may be reproduced,reproduced, stored in aa retrieval system, or transmittedtransmitted inin any form or by any means, electronic, mechani-mechani­ cal, photocopying or otherwise, without the prior permission of the copyrightownecopyright owner.r. Applications for such permission, withwith aa statement of the purpose andand extentextent ofof the reproduction,reproduction, should bebe addressed toto thethe Director,Director, Publications Division,Division, FoodFood andand Agriculture Organization ofof the United Nations,Nations, VVialeiale delle Terme di Caracalla, 00100 Rome, Italy.Italy.

0© FAO FAO 19941994 FOREWORD

The periodic occurrence ofof lossloss ofof treetree vigour,vigour, branch diebackdieback andand treetree mortalitymortality for reasonsreasons unknown or difficult toto determinedetermine isis aa phenomenonphenomenon whichwhich has frustratedfrustrated resource managersmanagers andand intriguedintrigued scientistsscientists for manymany years.years. Referred toto as "dieback" or "decline", itit hashas becomebecome a subjectsubject ofof intensifiedintensified interestinterest asas forestforest scientistsscientists attemptattempt to achieve a better understanding ofof thethe dynamicsdynamics ofof forestforest ecosystems.ecosystems. ThereThere is also great concern onon thethe part of general public andand thethe scientific community that manymany instancesinstances of decline or diedieback back may bebe thethe result of human activities.activities.

Most cases of decline have been reportedreported fromfrom Europe, NorthNorth AmericaAmerica,, Australia and thethe Pacific RegionRegion.. HoweverHowever decline is by no meansmeans restricted to these regions.regions. There areare reportsreports ofof treestrees andand forests forests affected affected byby declinedecline throughout throughout the the world.world. WhileWhile the symptoms of declinedecline may be strikingly similar, theythey can be the resultresult ofof manymany different abiotic and bioticbiotic factors,factors, oftenoften interactinginteracting inin aa complex complex manner.manner. Some declines are thethe resultresult ofof processes whichwhich areare anan integral integral partpart ofof thethe dynamicsdynamics ofof forestforest communities. OthersOthers maymay bebe relatedrelated toto humanhuman activitiesactivities includingincluding landland managementmanagement practices, emissions from motor vehiclesvehicles or industrial processes.processes. InIn manymany instancesinstances thethe causal factors responsible forfor decline are notnot known.

The frequency of occurrence,occurrence, pattern and intensity ofof declinedecline oror diebackdieback maymay adversely affect the sustainablesustainable flow ofof goods goods andand servicesservices fromfrom forestsforests andand influenceinfluence forest management.management. DeclinesDeclines maymay alsoalso serve as indicatorsindicators of forest response toto climate change, an issueissue whichwhich isis currentlycurrently inin thethe forefrontforefront of scientific andand publicpublic interest. It is important.important, therefore, thatthat foresters,foresters, ecologists,ecologists, biologistsbiologists andand scientistsscientists fromfrom relatedrelated disciplines understand the mechanismsmechanisms and factorsfactors involvedinvolved in declinesdeclines so thatthat appropriate forest monitoring andand managementmanagement systemssystems cancan bebe implemented.implemented.

The purpose of this paper, which is based onon surveyssurveys ofof thethe publishedpublished literature,literature, unpublished reports, correspondence, personalpersonal eexperiencexperience and review by aa numbernumber ofof specialists, drawn fromfrom developeddeveloped and developing countries worldwide, isis toto provide provide anan overview of declinesdeclines andand diebacks in a globalglobal context.context. Similarities and differences between decline events are examined,examined, as are the mechanisms whichwhich are believed to cause decline. ThisThis paperpaper isis intendedintended toto serveserve asas aa referencereference sourcesource whichwhich describesdescribes case histories of declines fromfrom most of the'World'sthe·world's forestforest regionsregions andand isis designeddesigned forfor use by foresters, forestforest scientists,scientists, policypolicy analysts analysts andand decisiondecision makers.makers.

J.P. LanlyLanly Director, Forest ResourcesResources DivisionDivision Forestry Department ACKNOWLEDGEMENTS

The constructive commentscomments and additional information kindly providedprovided byby thethe many people whowho reviewed the draft paper,paper, "Dieback"Dieback andand DeclineDecline inin Forests:Forests: A GlobalGlobal Overview (FAO MiscMisc.. F0/275)F0/2/5) are gratefully acknovvledged.acknowledged. TheyThey were;were; ARGENTINAARGENTINA - Jose LuisLuis Darraidou,Darraidou, AUSTRALIAAUSTRALIA -- R.C. Ellis, Glen Kyle and KennethKenneth M.M . Old,Old, BANGLADESH -- MohammedMohammed Abdur Rahman,Rahman, BURKINABURKINA FASO - Laurent Magliore Some,Some, CANADA -- JeanJean ClaudeClaude MercierMercier andand J.J. PeterPeter Hall,Hall, CHILECHILE -- HernanHernan Peredo,Peredo, COLOMBIACOLOMBIA­ - Cielo Orozco JaramilloJaramillo andand WendyWendy Arenas Arenas Wightman, Wightman, COMISSION COMISSION OF OF EUROPEAN EUROPEAN COMMUNITIES -- BernardBernard MalletMallet,, COSTA RICA - Felix E. Scorza Reggio,Reggio, GERMANYGERMANY­ - U. Hoenish and O. Kandler, ISRAEL -- O.O. Bonneh,Bonneh, KENYAKENYA - -Garry Garry Hill, Hill, MALTAMALTA - Joseph BorgBorg,, NEW ZEALAND -- P.G. Cannon andand GordonGordon Hosking,Hosking, PAKISTAN - Bashir Ahmed Wani, PHILIPPINESPHILIPPINES -- Emilio Rosaria, SEYCHELLESSEYCHELLES - W.W. Andre,Andre, SIERRA SIERRA LEONELEONE -- E.K.E.K. Alieu,Alieu, SPAINSPAIN -- SantiagoSantiago MarracoMarraco and and Fernando Fernando RobredoRobredo Junco,Junco, SWITZERLAND SWITZERLAND -- R.R. Volz, TRINIDADTRINIDAD -- S.S. Faizool,Faizool, UNITEDUNITED KINGDOMKINGDOM -- EricEric Boa,Boa, J.N. Gibbs,Gibbs, UNITEDUNITED STATESSTATES - Allan Auclair, DieterDieter Mueller-Dombois,Mueller-Dombois, PaulPaul Hennon,Hennon, PaulPaul Manion, A.J.A.J . RebertusRebertus andand C.G. Shaw Ill,III, ZAMBIAZAMBIA - -O.O. ShakaciteShakacite and and ZIMBABWEZIMBABWE -- G.D.G.D. Piearce.Piearce.

Jim Ball,Ball, KlausKlaus Janz,Janz, MichelMichel Malagnoux,Malagnoux, ChristelChristel Palmberg-LerchePalmberg-Lerche andand PaulPaul Vantomme, FAO,FAO, ForestForest ResourcesResources Division,Division, ForestryForestry DepartmentDepartment in in RomeRome alsoalso providedprovided information, reviewreview commentscomments andand suggestions.suggestions. Shingo Shibata,Shibata, FAO,FAO, ForestryForestry Operations, AsiaAsia Desk,Desk, arrangedarranged for for the the acquistitionacquistition ofof photographs ofof firfir waves in JapanJapan..

ii TABLE OFOF CONTENTSCONTENTS

FOREWORD ...... • ..•..•.. • .. • ...... •...... •...... ii

ACKNOWLEDGEMENTS ..• . ..•..... • ..•..•..• . .. • ...... •.. . • ..•...... ii

TABLE OFOF CONTENTSCONTENTS ...... •...... •...... •...... iii

LIST OF TABLES ...... • .. • . . • . . •. . •. .•. . . • . ..•. . • ...... vii

LIST OF ILLUSTRATIONSIllUSTRATIONS ...... • ..•...•..•...•..•..•. . ... viii

CHAPTER 11 - INTRODUCTIONINTRODUCTION 1

CHAPTER 2 - DECLINE:DECLINE: WHAT ISIS IT?IT? .. .. .•. . •..•...... •... 3

2.1. DEFINITION OF TERMS ...... 3

2.2. DIEBACK AND DECLINEDECLINE AS SYMPTOMSSYMPTOMS OFOF DISEASEDISEASE ...... •.... 4

2.3. DECLINE ASAS A CLASSCLASS OFOF DISEASEDISEASE ...... •..•...... 4

2.3.1. THETHE HOST, HOST, STRESS, STRESS, SAPROGEN SAPROGEN CONCEPTCONCEPT ...... • .. . . 5

2.3.2. THETHE PREDISPOSING, PREDISPOSING, INCITINGINCITING AND CONTRIBUTINGCONTRIBUTING FACTORSFACTORS CONCEPTCONCEPT .. . ..• .. • . . • . ... 6

22.3.3..3 .3 .DECLINES DECLINES AS AS DISEASES DISEASES OF OF POORLYPOORLY UNDERSTOOD AETAETIOLOGYIOLOGY ...... •...... •... 6

2.4. DECLINE ASAS A PARTPART OFOF FORESTFOREST DYNAMICSDYNAMICS ...... • ...... 7

CHAPTER 3 -- EUROPEEUROPE ...... • ...... 10

3.1. SILVER FIR DECLINEDECLINE . . .. .•. .•.. • ...... • . .•. . •.. . • . ... 10

3.2. HARDWOOD DECLINESDECLINES ...... • ...... •...... 10

3.3. ACUTE YELLOWINGYELLOWING OFOF NORWAYNORWAY SPRUCESPRUCE ...... 13

3.4 REGIONAL DECLINE OF CONIFERS ANDAND HARDWOODS ...... • .. •.. 14

CHAPTER 44 - NORTH AMERICA .. . •...... •. ..• ... • . .•...... 18

4.1. BIRCH DIEBACK ...... •...... • ...... 18

4.2.4.2. POLE BLIGHT OF PINUS MONTICOLA ...... • .. . • . . ,. 18

4,3.4.3. ASH DIEBACKDIEBACK ...... • . . . •. . , ...... •.... 19

4.4. MAPLE DECLINEDECLINE ...... •...... •...... • . . .. 20

4.5. OAK DECLINEDECLINE . . ... • ..•..•...... •...... •.. . •... 20

III 4.6. BEECHBEECH BARK DISEASE ...... • ..•...•...... 23

4.7. LlTTLELEAFLITTLELEAF DISEASE OFOF SHORTLEAFSHORTLEAF PINEPINE ...... 23

4.8. DECLINEDECLINE ANDAND MORTALITY OFOF REDRED SPRUCESPRUCE ...... • .. .•.. 23

4.94.9.. FIRFIR WAVESWAVES ...... •. .• ...... • ... •. . .• . . • .. ... 24

44.10.10 YELLOW CEDARCEDAR DECLINEDECLINE ...... •...• ...... •. . 24

4.114.11.. X-DISEASE OF PINE IN SOUTHERN CALIFORNIA ..•...•... •.. • . . . 26

CHAPTER 55 - AFRICA ...... •..•..... 27

5.1. DECLINE OFOF AZADIRACHTAAZADIRACHTA INDICA ININ THETHE SAHELSAHEL . .. •...... •... 27

5.2. DECLINE OFOF ACACIAACACIA NILOTICA ININ THETHE SUDANSUDAN ...... •..•. . . 30

5.3. DIEBACK OF TERMINALITERMINALIAA IVORENSISIVORENSIS IN COTECOTE D'IVOIRE AND GHANA ...... •... , .... 33

5.4. DIEBACK OF CASUARINA EQUISETIFOLIAEQUISETIFOLIA ININ BENINBENIN ... • . .. • ..•... 34

5.55.5.. DECLINE OFOF OCOTEAOCOTEA BULLATABULLATA IN SOUTHSOUTH AFRICAAFRICA ...... •... 34

5.6. DECLINE OFOF PTEROCARPUSPTEROCARPUS ANGOLENSIS ANGOLENSIS ININ BOTSWANA,BOTSWANA, ZAMBIA AND ZIMBABWEZIMBABWE ...... •..... 34

5.7. DIEBACK ANDAND MORTALITY OFOF TROPICALTROPICAL RAIN FORESTS ININ UGANDA ...... , ...... 36

5.8. DIEBACK AND MORTALITY ININ MANGROVESMANGROVES ONON THE GAMBIA RIVERRIVER ...... •.. . •..•... . . 36

5.9. DIEBACK OF PINUS PATULA,PATULA, SAO HILLHILL PLANTATIONS, TANZANIA ...... •.. • ...... •.. •... . . 37

CHAPTER 66 - ASIA ...... • .. • ...... 39

6.1. DECLINE IN JAPAN ...... • ...... • ... .. 39

6.1.1. DECLINEDECLINE OF OF CRYPTOMERIA CRYPTOMERIA JAPONICAJAPONICA ...... 39

6.1.2. "SHIMAGARE""SHIMAGARE" DIEBACK DIE BACK IN IN HIGH HIGH ELEVATION ELEVATION ABIES ABIES FORESTS FORESTS . 4040

6.2. DECLINE IN CHINA ...... 4040

6.2.1. DECLINEDECLINE ANDAND MORTALITYMORTALITY OFOF PINUSPINUS MASSONIANA .. ...•.. 4040

6.2.2. CHLOROSISCHLOROSIS OFOF PINUSPINUS ARMANDIARMANDI ...... 4040

6.3.6.3. DECLINE ANDAND MORTALITY OF ABIESABIE S DENSADENSA ININ BHUTANBHUTAN ...... •.. 4242

6.4. DECLINE ANDAND MORTALITY OF SHOREASHOREA ROBUSTA IN INDIAINDIA ...... 4444

6.5. TOP DYINGDYING OFOF HERITIERAHERITIERA FOMESFOMES ININ BANGLADESHBANGLADESH ....• . .. , .. • .. 4545

ivIV 6.6. CANOPY DIEBACKOIEBACK ININ UPPERUPPER MONTANE FORESTSFORESTS IN SRI LANKA . . . . 47

CHAPTER 77 - AUSTRALIA, NEWNEW ZEALANDZEALAND ANDAND THETHE PACIFICPACIFIC ISLANDSISLANDS ...... 49

7.1. DECLINE OFOF ARAUCARIAARAUCARIA HETEROPHYLLAHETEROPHYLLA ON NORFOLK ISLAND ..... 49

7.2. DIEBACK OF MANGROVE FORESTSFORESTS ININ QUEENSLAND, AUSTRALIA . 49

7.3. DIEBACKS OF EUCALYPTS IN AUSTRALIA . . •...... •..• • .. 50

7.3.1. JARRAHJARRAH DIEBACK DIEBACK ..•..•..• . . •• .. •..• . . . •...... •.. 50

7.3.2. RURALRURAL DIEBACK DIEBACK ...... • . . . •...... •...... 50

7.3.3. NEWNEW ENGLAND ENGLAND DIEBACK DIEBACK ...... •... • ..... 51

7.3.4. EUCALYPTEUCALYPT DIEBACKS DIEBACKS ININ TASMANIA .. . . . • . ..• . .•...... 51

7.4. DECLINE ININ NEW ZEALAND ...... 52

7.4.1. STANDSTAND LEVEL LEVEL DIEBACKS DIEBACKS OF OF NOTHOFAGUSNOTHOFAGUS SP.SP. IN NEW ZEALAND ...... 52

7.4.2. STAND STAND LEVEL LEVEL DIEBACK DIEBACK OF OF METROSIDEROS METROSIDEROS SP.SP. ANDAND WEINMANNIA RACEMOSA,RACEMOSA, IN NEWNEW ZEALAND ...... 54

7.4.3. SUDDENSUDDEN DECLINE DECLINE OF OF CORDYLINECORDYLINE AUSTRALISAUSTRALIS ..• . . • ...... 54

7.5. STAND LEVELLEVEL DIEBACKDIEBACK ININ THETHE FORESTSFORESTS OFOF PAPUA NEW GUINEA ...... • .. . . 57

7.6. STAND LEVELLEVEL DIEBACKDIEBACK OFOF METROSIDEROSMETROSIDEROS POLYMORPHA,POLYMORPHA, IN THE HAWAIIANHAWAIIAN ISLANDS,ISLANDS, USAUSA ...... 58

CHAPTER 8 - LATIN AMERICAAMERICA ANDAND THETHE CARIBBEANCARIBBEAN . ... • ...... •...... 61

8.1. DECLINE ININ THE MEXICO CITY BASINBASIN ...... •...•.. • .. .•.... 61

8.2. OAK DECLINEDECLINE IN COLOMBIACO LOMBIA ...... • ...... 61

8.3. DIEBACK OF EUCALYPTUS SPSP.. IN SOUTH AMERICA .•...... 64

8.3.1.8.3.1 . BRAZILBRAZIL ...... 64

8.3.2.8 .3.2. COLOMBIACOLOMBIA .•...... • ...... •. ..•... • ..•..•... 64

8.3.3.8 .3.3. PERUPERU ...... • . ..•...... 65

8.4. CANOPY DIEBACK OF SCALESIA PENDUNCULATAPENDUNCULATA ININ THE GALAPAGOS ISLANDS,ISLANDS. ECUADORECUADOR ...... •... 65

8.58.5.. DECLINE ININ PARQUE ANCHORENA,ANCHORENA, URUGUAY ...... 66

8.6. DECLINE ANDAND MORTALITY OFOF AUSTROCEDRUSAUSTROCEDRUS CHILENSISCHILENSIS ININ ARGENTINA ...... •.. 67

v 8.7. DIEBACK OF FUEGO -- PATAGONPATAGONIANIAN NOTHOFAGUSNOTHOFAG US FORESTSFOR ESTS ...... 67

CHAPTER 9 - - DISCUSSIONDISCUSSION ANDAND CONCLUSIONSCONCLUSIONS ...... • .. •. . ... 69

9.1. DECLINE ANDAND DIEBACK AS AA GLOBALGLOBAL PHENOMENONPHENOMENON . .. •...... 69

99.2..2 . CAUSES OF DECLINE AND DIEBACKDIEBACK ...... •..... 69

9.2.1. NON-ANTHROPOGENICNON-ANTHROPOGENIC FACTORSFACTORS . ....•...... • ..•.... . 70

99.2.2..2.2. ANTHROPOGENICANTHROPOGENIC FACTORSFACTORS ... •. .. .. •...... •...... 71

9.2.3. CLIMATECLIMATE CHANGE CHANGE ...... •...... 74

9.3. MANAGMANAGINGING FORESTFOREST DECLINEDECLINE ...... •...... • .... 75

9.3.1. DIAGNOSISDIAGNOSIS OF OF DECLINESDECLINES AND DIEBACKSDIEBACKS ...... • ...... 75

9.3.2. MONITORINGMONITORING ANDAND ASSESSMENT ASSESSMENT ...... • ...... •... . 75

9.3.3. MANAGEMENTMANAGEMENT TACTICSTACTICS .....•...... • ..• ...... •.... 76

LITERATURE CITEDCITED ...... •...... 78

VIvi LIST OFOF TABLESTABLES

CHAPTER 2 - - DECLINE:OEClINE: WHATWHAT ISIS IT?IT?

TABLE 2.1 - EXAMPLES OF PREDISPOSING,PREDISPOSING , INCITING AND CONTRIBUTINGCONTRIBUTING FACTORSFACTORS WHWHICHICH INFLUENCEINFLUENCE OCCURRENCEOCCURRENCE OFOF DECLINEDECLINE ...... 7

CHAPTER 3 - EUROPE

TABLE 3.13.1 - DAMAGE RATINGRATING SYSTEMSYSTEM FORFOR ASSESSMENTASSESSMENT OFOF TREETREE CONDITIONCONDITION ININ EUROPE BASEDBASED ON DEGREEDEGREE OF DEFOLIATION ...... 16

TABLE 3.2 -- DAMAGE RATINGRATING SYSTEMSYSTEM FORFOR ASSESSMENTASSESSMENT OFOF TREETREE CONDITIONCONDITION ININ EUROPE BASEDBASED ON DEGREEDEGREE OF DISCOLOURATION ...... 16

CHAPTER 5 -- AFRICA

TABLE 5.15.1 - SUMMARY OFOF FORESTFOREST DECLINEDECLINE EVENTSEVENTS BYBY POSSIBLEPOSSIBLE CAUSAL FACTORS - AFRICA ...... 38

CHAPTER 66 - ASIA

TABLE 6.16.1 -- SUMMARY OFOF FORESTFOREST DECLINEDECLINE EVENTSEVENTS BYBY POSSIBLEPOSSIBLE CAUSAL FACTORS -- JAPANJAPAN AND CHINACHINA ...... 42

TABLE 66.2.2 - SUMMARY OFOF FORESTFOREST DECLINEDECLINE EVENTSEVENTS BYBY POSSIBLEPOSSIBLE CAUSAL FACTORS -- BHUTAN,BHUTAN, INDIA,INDIA, BANGLADESHBANGLADESH AND SRI LLANKAANKA ...... 48

CHAPTER 7 -- AUSTRALIA, NEWNEW ZEALANDZEALAND ANDAND THETHE PACIFICPACIFIC ISLANDSISLANDS

TABLE 7.17.1 - SUMMARY OFOF FORESTFOREST DECLINEDECLINE EVENTSEVENTS BYBY POSSIBLEPOSSIBLE CAUSAL FACTORS - AUSTRALIA ...... 53

TABLE 7.2 -- SUMMARY OFOF FORESTFOREST DECLINEDECLINE EVENTSEVENTS BYBY POSSIBLEPOSSIBLE CAUSAL FACTORS - NEW ZEALAND ...... 56

TABLE 7.3 -- SUMMARY OFOF FORESTFOREST DECLINEDECLINE EVENTS BY POSSIBLE CAUSALCAUSAL FACTORS - PACIFIC ISLANDSISLANDS ...... 60

CHAPTER 88 - LATIN AMERICA ANDAND THETHE CARIBBEANCARIBBEAN

TABLE 8.18.1 -- SUMMARY OFOF FORESTFOREST DECLINEDECLINE EVENTS BY POSSIBLE CAUSALCAUSAL FACTORS - LATIN AMERICAAMERICA ANDAND THE THE CARIBBEANCARIBBEAN ...... 68

VIIvii LIST OF ILLUSTRATIONS

CHAPTER 3 -- EUROPE

FIGURE 3.13.1 -- ABIES ALBA ININ BAVARIA,BAVARIA, GERMANY,GERMANY, WITHWITH SYMPTOMSSYMPTOMS OF OF SILVER SILVER FIRFIR DECLINE ...... 11

CHAPTER 4 4 - - NORTHNORTH AMERICAAMERICA

FIGURE 4.14.1 -- ACER SACCHARUMSACCHARUM WITHWITH SYMPTOMSSYMPTOMS OFOF MAPLEMAPLE DECLINE DECLINE (VERMONT,(VERMONT, USA) ...... 21

FIGURE 4.24.2 - OAK DECLINEDECLINE IN WESTERN NORTH CAROLINA, USAUSA ...... 22

FIGURE 4.34.3 -- FIR WAVES ONON THETHE SLOPESSLOPES OFOF LOOKOUTLOOKOUT MOUNTAIN,MOUNTAIN, ADIRONDACKADIRONDACK MOUNTAINS, NEWNEW YORK, USAUSA ...... 25

CHAPTER 55 - AFRICA

FIGURE 5.15.1 -- FOLIAGE OF A HEALTHYHEALTHY NEEMNEEM ININ NIAMEY,NIAMEY, NIGER NIGER ...... 28

FIGURE 5.25.2 -- DECLINING NEEMNEEM ININ NIAMEY,NIAMEY, NIGER WITHWITH "GIRAFFE NECK" SYMPTOMS 29

FIGURE 5.35.3 -- HEALTHY ACACIA NILOTICANILOTICA PLANTATIONPLANTATION ININ THE REMNANT OF ANAN OXBOW LAKE ALONG THETHE BLUEBLUE NILE IN THETHE SUDANSUDAN ...... 32

FIGURE 5.45.4 -- ACACIA NILOTICANILOTICA IN IN VARYINGVARYING STAGESSTAGES OFOF DECLINEDECLINE NEAR EDED DAMAZIN,DAMAZIN, THE SUDAN ...... 32

FIGURE 5.55.5 -- BUPRESTID LARVA LARVA ANDAND DAMAGEDAMAGE ININ BRANCHBRANCH OFOF DECLININGDECLINING ACACIAACACIA NILOTICA ININ THETHE SUDANSUDAN ...... 33

FIGURE 55.6.6 -- DECLINE OF PTEROCARPUS ANGOLENSISANGOLENSIS ININ ZAMBIA ...... •.. 35

CHAPTER 66 - ASIA

FIGURE 6.16.1 -- FIR WAVESWAVES ON THE SLOPES OFOF MT.MT. SHIMIGARE,SHIMIGARE, JAPAN ...... 41

FIGURE 6.26.2 -- NATURAL REGENERATIONREGENERATION FOLLOWINGFOLLOWING WAVE WAVE MORTALITY ONON HIGHHIGH ELEVATION ABIES FORESTS ININ JAPANJAPAN ...... 41

FIGURE 6.36.3 -- EXTENSIVE MORTALITY OFOF HIGHHIGH ELEVATIONELEVATION ABIESABIES DENSADENSA FORESTSFORESTS NEARNEAR CHELEILA, BHUTANBHUTAN ...... 43

FIGURE 6.46.4 -- ABIES DENSA IN BHUTAN WITH SYMPTOMSSYMPTOMS OFOF DECLINE.DECLINE. NOTENOTE "STORKS"STORKS NEST" FORMATIONFORMATION ININ UPPERUPPER CROWNCROWN AND NEWNEW GROWTHGROWTH ABOVEABOVE STORKSSTORKS NEST INDICATING RECOVERYRECOVERY FROMFROM DECLINEDECLINE ...... 44

FIGURE 6.56.5 -- HERITIERA FOMES WITHWITH TOP DYING IN THE SUNDARBANS, BANGLADESI46BANGLADES146

VIIIviii CHAPTER 77 - AUSTRALIA, NEWNEW ZEALANDZEALAND ANDAND THETHE PACIFICPACIFIC ISLANDS

FIGURE 7.17.1 - DIEBACK OF NOTHOFAGUSNOTHOFAGUS SP.SP, IN TONGARIROTONGARIRO NATIONALNATIONAL PARK,PARK, NEWNEW ZEALAND ...... 55

FIGURE 77.2.2 - WETLAND DIEBACKDIEBACK OFOF METROSIDEROSMETROSIDEROS POLYMORPHAPOLYMORPHA ...... 59

FIGURE 7.37.3 - STAND OFOF METROSIDEROS POLYMORPHAAFFECTEDPOLYMORPHA AFFECTED BY DRYLANDDRYLAND DIEBACKDIEBACK.. THIS PHOTOPHOTO SHOWSSHOWS VIGOROUSVIGOROUS REGROWTH,REGROWTH , AA SITUATIONSITUATION KNOWNKNOWN ASAS REPLACEMENT DIEBACK ...... 59

CHAPTER 88 - LATIN AMERICA AND THETHE CARIBBEANCARIBBEAN

FIGURE 8.18.1 - FOLIAGE OF HEALTHY ABIES RELIGIOSARELIGIOSA WITH THREETHREE TO FOURFOUR YEARSYEARS OFOF NEEDLE RETENTION ...... 62

FIGURE 8.28.2 - FOLIAGE OF ABIESABIES RELIGIOSARELIGIOSA SUFFERINGSUFFERING FROM FROM PHOTO-OXIDANT PHOTO-OXIDANT INJURY ININ THE PARQUEPAROUE NACIONAL DESIERTODESIERTO DE LOSLOS LEONESLEONES NEAR MEXICOMEXICO CITY,CITY, MEXICO. NOTENOTE THATTHAT ONLY ONLY THETHE MOSTMOST RECENT RECENT TWOTWO YEAR'SYEAR'S GROWTHGROWTH OFOF FOLIAGE IS RETAINED ...... 62

FIGURE 8.38.3 - ABIES RELIGIOSARELIGIOSA WITH SYMPTOMSSYMPTOMS OFOF DECLINE,DECLINE, PARQUEPAROUE NACIONALNACIONAL DESIERTO DE LOS LEONES, MEXICO ...... 63

CHAPTER 9 - DISCUSSIONDISCUSSION AND CONCLUSIONSCONCLUSIONS

FIGURE 9.19.1 -APPROXIMATE LOCATIONLOCATION OFOF DECLINEDECLINE EVENTSEVENTS DESCRIBEDDESCRIBED ININ THIS MPERPAPER ...... 70

IixX CHAPTER 11

INTRODUCTIONINTRODUCTION

Good forestforest health is essential forfor sustainablesustainable forestry.forestry. AA forestforest isis considered considered healthy vvhenwhen bioticbiotic and abioticabiotic factors do not threaten resourceresource management objectivesobjectives now or have the potential to do so in thethe future. ManyMany factorsfactors influenceinfluence forestforest health.health. These includeinclude climate,climate, soil, available moisture,moisture, managementmanagement practicespractices andand thethe effectseffects of fire,fire, insectsinsects andand disease.disease.

Decline or diedieback back of trees and forests isis aa conditioncondition characterizedcharacterized byby episodesepisodes of premature,premature, progressive lossloss ofof treetree or stand vigour without obviousobvious evidenceevidence of physical injuryinjury or attack byby aa primaryprimary disease oror pest.pest. ThisThis condition hashas affected thethe health of many forest ecosystemsecosystems andand hashas been the subject of widespreadwidespread concernconcern byby foresters, scientists and the general public.public. TheThe factorsfactors responsibleresponsible for manymany decline events have remained elusive, despite years of study.study. Decline has beenbeen consideredconsidered aa symptom of disease,disease, a distinct classclass ofof diseasedisease and as a part of forest dynamics.dynamics.

Episodes ofof declinedecline havehave beenbeen the the subjectsubject ofof intensified study duringduring thethe pastpast two decades.decades. ThisThis isis partiallypartially duedue to thethe efforts ofof forestforest scientistsscientists toto gaingain aa betterbetter understanding ofof the role of declines inin forest dynamics. ItIt is is also also duedue toto anan increasedincreased awareness andand concernconcern forfor thethe potentialpotential effectseffects of human activitiesactivities (e.g. emissions fromfrom motor vehicles or industrialindustrial sourcessources andand land management practices) on forest health.health. Furthermore, therethere is great interest worworldwideldwide inin reducingreducing thethe riskrisk ofof declinedecline andand otherother forest healthhealth problemsproblems inin forestforest plantationsplantations throughthrough properproper nurserynursery andand plantingplanting techniques and the matchingmatching ofof speciesspecies andand provenencesprovenences to sites.sites.

An indicationindication ofof thethe currentcurrent levellevel ofof interest interest and and concern concern aboutabout decline decline andand dieback is reflected in the numbernumber ofof symposiasymposia andand reviews whichwhich havehave beenbeen dedicateddedicated to thisthis subjectsubject inin recentrecent years.years. TheseThese include:include:

A symposium "Eucalypt"Eucalypt DiebackDieback inin ForestsForests andand Woodlands"Woodlands" heldheld inin CanberraCanberra Australia in 1980 (Old(Old et al 1981).1981 ).

A symposium "Canopy"Canopy DiebackDieback andand DynamicDynamic ProcessesProcesses" " heldheld inin conjunctionconjunction with thethe 15th15th Pacific Pacific Science Science Congress. Congress. (Papers(Papers publishedpublished inin PacificPacific ScienceScience 3737 (4),1983).

A workshopworkshop "Forest Decline and Reproduction: Regional and Global Consequences" sponsoredsponsored by by IASA,IASA, Laxenburg AustriaAustria andand held in Krakow,Krakow, Poland inin 1987 (Kairiuskstis(Kairiuskstis et al 1987).1987).

A symposiumsymposium "Stand"Stand LevelLevel DiebackDieback andand EcosystemEcosystem Processes:Processes: AA GlobalGlobal Perspective" held in conjunctionconjunction with thethe 15th15th International International Botanical Botanical Congress,Congress, Berlin, 1987 (Papers(Papers published inin GeoJournalGeoJournal 17(2)17(2) 1988).

A collectioncollection ofof paperspapers inin NevvNew ZealandZealand JournalJournal ofof ForestryForestry ScienceScience (19:2-3(19:2-3 1989). A historical review ofof hardwoodhardwood declinesdeclines in the eastern United St;ltesStates (Millers et al 1989).

A symposiumsymposium "Forest Decline Concepts"Concepts" heldheld inin conjunctionconjunction wwithith the jointjoint meeting of the AmericanAmerican Phytopathological Society and thethe Canadian Phytopathological Society,Society, August 1990 (Manion(Manion andand Lachance 1992).

Two IUFROIUFRO symposia on oakoak decline:decline:

Kornik, Poland, MayMay 1990 (Siwecki(Siwecki andand LeiseLeise 1991).1991). Brindisi, Italy, September 1992.

A review ofof MediterraneanMediterranean forestforest treetree declinedecline (Raddi(Raddi 1992)1992)

The publication "Forest Decline inin the Atlantic andand PacificPacific Region"Region" (Huettl(Huettl andand Mueller-Dombios 1993).

These symposiasymposia andand reviewsreviews have concentrated largely on decline events inin Europe, NorthNorth America, Australia and the PacificPacific RegionRegion and makemake relativelyrelatively fevvfew referencesreferences toto decline inin Asia, Africa, LatinLatin AmericaAmerica andand thethe Caribbean.Caribbean.

The purpose ofof this paper is to provideprovide anan overviewoverview ofof declinedecline andand diebackdie back inin aa global contextcontext.. It begins withwith a review of some basic terminologyterminology with regardregard to forestforest diseases andand anan examinationexamination ofof thethe evolutionevolution ofof thethe concept of decline. CaseCase historieshistories of decline eventsevents fromfrom various forest regions throughoutthroughout the world are presented. ThisThis is followed byby anan analysisanalysis of thesethese casecase histories from which conclusionsconclusions areare drawndrawn toto provide a better understanding ofof the causes of decline, its rolerole inin forestforest dynamics,dynamics, effects onon forestforest healthhealth andand toto aidaid inin thethe development development ofof management management strategiesstrategies toto minimize their impacts onon thethe sustainedsustained useuse ofof forestforest ecosystems.ecosystems.

2 CHAPTER 2

DECLINE: WHATWHAT IS IT?

2.1. DEFINITIONDEFINITION OFOF TERMS.TERMS.

What isis decline?decline? Several definitionsdefinitions have been developed but there isis still disagreement asas toto exactlyexactly what constitutesconstitutes decline.decline. It isis perhapsperhaps bestbest describeddescribed as:as: an episodic event characterized by premature, progressive loss of treetree and stand vigour and health over a given period without obviousobvious evidenceevidence ofof a a singlesingle clearlyclearly identifiableidentifiable causal factorfactor such as physical disturbance or attack byby anan aggressiveaggressive disease oror insect.insect.

The termsterms "dieback,"die back, decline,decline, forestforest dieback,dieback, standstand levellevel dieback,dieback, canopycanopy levellevel dieback, Waldsterben and Waldschäden"Waldschaden" havehave beenbeen used,used, moremore or less interchangeably,interchangeably, to describe this condition. DeclineDecline is is characterized characterized byby thethe presencepresence ofof symptomssymptoms suchsuch as reducedreduced growth,growth, shortenedshortened internodes,internodes, rootroot necrosis,necrosis, prematurepremature fallfall coloring (temperate forests)'forests), yellowingyellowing and loss of foliage,foliage, diebackdie back ofof twigstwigs and and branches branches generally beginningbeginning inin thethe upper crown, sprouting from adventitiousadventitious buds,buds, andand (or)(or) increasedincreased prevalenceprevalence and and pathogenicity pathogenicity of of root root decaydecay fungi fungi (Manion(Manion 1991).1991). AnotherAnother feature of declinedecline isis its progressiveprogressive nature and differences in thethe progressionprogression of symptoms between trees in thethe samesame stand.stand. SomeSome treestrees maymay havehave slightslight symptomssymptoms vvhilewhile othersothers areare inin an intermediate condition andand still othersothers areare dead.dead.

Additional terminology helpfulhelpful inin understandingunderstanding declinedecline isis defineddefined asas follovvs:follows:

A. PLANT DISEASEDISEASE - -AnyAny deviationdeviation inin thethe normalnormal functionfunction of aa plant caused by a persistent agent.agent.

B. AETIOLOGY (ETIOLOGY)(ETIOLOGY) - -The The science science associated associated with with determiningdetermining or assigning the causescauses of disease.disease.

C. ABIOTIC FACTORFACTOR - -A A non-livingnon-living oror nonnon-infectious-infectious factor capablecapable of causing disease.disease. Examples includeinclude non-anthropogenicnon-anthropogenic agents such as climatic factors (e.g.(e.g. drought,drought, highhigh winds,winds, excessiveexcessive rainfall),rainfall), saltsalt sprayspray from oceansoceans oror mechanicalmechanical injuryinjury andand anthropogenic anthropogenic (human(human caused)caused) factors such as air pollution from emissionsemissions ofof toxic chemicalschemicals or thethe burning of fossilfossil fuels,fuels, forestforest managementmanagement practices, construction, etc.etc.

D. BIOTIC FACTORFACTOR - - AA livingliving or infectiousinfectious diseasedisease causingcausing agent.agent. Non­Non- anthropogenic biotic factorsfactors includeinclude fungi,fungi, bacteria,bacteria, mycoplasma-like mycoplasma-like organisms (ML(MLOs), Os), virus,virus, insects,insects, mites,mites, nematodesnema todes andand parasiticparasitic higherhigher plants. Anthropogenic factorsfactors include introduced pests,pests, grazing ofof livestock inin forests,forests, thethe presencepresence of artificially highhigh populationspopulations of gamegame animals for hunting interests or forest management practicespractices which place forests underunder stress or favourfavour certaincertain pestspests oror disease.disease.

E. SYMPTOM -- AnAn expression ofof diseasedisease byby thethe hosthost plant.plant. SomeSome o'iseasesdiseases have unique symptomssymptoms which are helpfulhelpful inin identificationidentification of thethe pathogen. Other diseases areare characterizedcharacterized by by lessless specificspecific symptoms.symptoms. ExamplesExamples of symptomssymptoms includeinclude reducedreduced growth, deaddead branches,branches, decay, yellowingyellowing

3 or chlorotic foliagefoliage and abnormal growthgrowth such as cankers oror witches' brooms.

F. SIGN -- The visible presencepresence of of aa bioticbiotic pathogen suchsuch as the fruitingfruiting stage of aa fungus,fungus, thethe occurrenceoccurrence ofof aa parasiticparasitic plantplant oror aa damaging damaging insect. SignsSigns ofof disease disease areare notnot alwaysalways present.present.

G. STRESS - -Factors Factors which which weakenweaken treestrees andand increaseincrease theirtheir susceptibilitysusceptibility toto disease. ExamplesExamples of stressstress includeinclude soil deficiencies,deficiencies, drought, excessexcess moisture, mechanicalmechanical injury,injury, or aging.aging. Stress factors may occuroccur periodically oror bebe presentpresent continuously.continuously.

H. SYNDROME - -A A combination combination ofof symptomssymptoms and signssigns which characterize a disease.

In this chapter, declinedecline will bebe examinedexamined from threethree pointspoints ofof viewview -- asas aa symptomsymptom of disease, a type of diseasedisease and as aa partpart ofof the dynamics of forest ecosystems.ecosystems.

2.2. DIEBACK AND DECLINEDECLINE AS SYMPTOMS OFOF DISEASE.DISEASE.

The terms "decline""decline" andand "dieback""dieback" havehave bothboth beenbeen usedused toto describe describe diseasedisease symptoms. "Dieback""Dieback" refers refers to to death death of of branches branches and and can can be be associatedassociated withwith changes changes in soil moisturemoisture oror withwith virulentvirulent pathogens.pathogens. Cankers causedcaused byby thethe chestnutchestnut blight fungus,fungus, EndothiaEndothia oarasitica,parasitica, or the whitewhite pinepine blisterblister rustrust fungus,fungus, CronartiumCronartium ribicola,ribicola, forfor example,example, killkill branchesbranches and entire trees.trees. DiebackDieback can also be thethe resultresult ofof attack by insects as eexemplifiedxemplified by larvae of the mahogany shootshoot borers, HypsypylaHyosvoyla spsp.,., whichwhich bore into and kill the terminalterminal shootsshoots ofof treestrees ofof thethe familyfamily Meliaceae. Meliaceae.

"Decline" isis aa termterm oftenoften usedused toto describedescribe aa moremore generalgeneral set of symptomssymptoms oror syndrome associated with loss of tree vigour. TheseThese includeinclude reduced growth, reductionreduction in size and quantity of foliage,foliage, chloroticchlorotic foliage,foliage, deathdeath ofof twigstwigs and and branchesbranches and,and, inin some cases,cases, tree death. DiebackDieback cancan bebe partpart ofof thethe decline decline syndrome.syndrome.

Symptoms ofof declinedecline cancan bebe associatedassociated withwith aa numbernumber ofof diseasesdiseases causedcaused byby aa single factor. ForFor example,example, chloroticchlorotic foliagefoliage andand reduced growth areare common symptoms of soilsoil nutrientnutrient deficiencies.deficiencies. Sparse,Sparse, smaller smaller than than normal normal foliage,foliage, branchbranch dieback dieback and and epicormic branching are associatedassociated withwith prolonged periodsperiods ofof drought,drought, foliar injury by insects or mites,mites, or infectioninfection byby parasiticparasitic plants.plants.

2.3. DECLINEDECLINE ASAS A A CLASS CLASS OF OF DISEASE. DISEASE.

A numbernumber ofof forestforest pathologistspathologists considercO)lsider declinedecline asas aa distinctdistinct class class ofof disease, disease, one which isis stronglystrongly influencedinfluenced byby factorsfactors whichwhich predispose predispose treestrees underunder stressstress toto invasion byby agents which areare unableunable toto causecause disease in vigorous trees.trees. BecauseBecause ofof thethe complex interaction betweenbetween host,host, site,site, climateclimate andand oneone oror more pathogens, it is often difficult toto identifyidentify thethe factorsfactors involved.involved. The idea of declinedecline as aa classclass ofof diseasedisease isis discussed byby HoustonHouston (1967 (1967,, 1981,1992).1981, 1992), ManionManion (1991) and Sinclair (1965,1966).(1965, 1966).

4 2.3.1. THETHE HOST, HOST, STRESS, STRESS, SAPROGENSAPROGEN CONCEPTCONCEPT - -Houston Houston (1967, (1967, 1981,1981, 1992) considers declines as diseases causedcaused byby the the successivesuccessive actionaction ofof stress factorsfactors followed byby organismsorganisms ofof secondarysecondary actionaction (saprogens)(saprogens) which cancan onlyonly successfullysuccessfully attack weakenedweakened hosts. UnderUnder thisthis conceptualconceptual framework,framework, healthyhealthy treestrees are affected by somesome formform ofof environmental environmental stress.stress. Tree tissues altered byby that stressstress areare subsequently invadedinvaded by saprogens. TheThe diseasedisease condition develops,develops, tissuestissues andand treestrees decline and may ultimately die.die.

These events can be summarizedsummarized inin aa seriesseries of of word word equationsequations (Houston(Houston 1992):

1. Healthy treestrees ++ StressStress Altered treestrees (tissues)(tissues) (dieback begins)

2. Altered treestrees ++ More Stress Trees (tissues)(tissues) altered furtherfurther (dieback(dieback continues)continues)

3. Severely altered treestrees ++ MoreMore Tree (tissues)(tissues) alteredaltered Stress furtherfurther (dieback(dieback continues)continues)

* * * n. Severely altered treestrees ++ Trees (tissues)(tissues) invaded.invaded. organisms of secondary actionaction (Trees lose ability toto respond to improved conditions, decline andand perhaps die.)die.)

Using thisthis approach, aa decline of sugarsugar maple,maple, AcerAcer saccharum,saccharum, in NorthNorth America, which isis initiated by insect defoliation followed byby secondary invasion of fungi,fungi, is described as follows:

1. Healthy sugarsugar maple treestrees ++ Sugar maples altered defoliation (dieback begins)

* * *

n. Altered treestrees ++ secondarysecondary fungifungi

SteqonosporiumStegonosporium ovatumova tum Twig dieback accelerated

Armillaria sp.sp . Roots, root collars invaded, treestrees decline,decline, die.

5 The host/stress/saprogenhost/stress/saprogen conceptconcept implies that stressstress createscreates conditionsconditions favourablefavourable for invasion of treestrees by secondary biotic agents. ThisThis isis notnot alwaysalways thethe case.case. Certain endophyticendophytic fungifungi may infect trees and be presentpresent for longlong periodsperiods withoutwithout causing disease.disease. Disease symptomssymptoms dodo notnot appear untiluntil after treestrees areare exposedexposed to stress. ThisThis isis truetrue ofof severalseveral foliagefoliage diseasesdiseases in Europe. In addition, certain fungi, suchsuch as thosethose which invade root systems,systems, maymay bebe presentpresent on trees for manymany yearsyears andand not have visiblevisible adverseadverse effectseffects on treetree growthgrowth and vigourvigour eveneven thoughthough rootletrootlet mortality hashas occurred. WhenWhen aa stress,stress, suchsuch asas a prolonged drought occurs,occurs, treestrees infectedinfected by root ddiseaseisease areare moremore likelylikely toto develop decline symptomssymptoms or be attacked by barkbark beetles.beetles.

2.3.2. THE PREDISPOSING,PREDISPOSING, INCITING ANDAND CONTRIBUTINGCONTRIBUTING FACTORSFACTORS CONCEPT - -This This concept concept developed developed from from research research efforts efforts to to identifyidentify causes ofof three decldeclineine in thethe United States: ashash dieback,die back, maple decline and oak decline (Manion 1991).1 991). Sinclair (1965)(1965) waswas thethe firstfirst to to suggest suggest that that maple maple declinedecline andand similarsimilar problems was the resultresult of the interactioninteraction ofof threethree oror moremore sets of factorsfactors (Table(Table 2.1):

Predisposing Factors are longlong term,term, slowlyslowly changingchanging factorsfactors suchsuch asas soil,soil, sitesite andand climate. TheseThese factorsfactors alteralter the tree's ability toto withstandwithstand oror respondrespond to injury-injury­ inducinginducing agents.agents.

Inciting factors areare ofof shortshort durationduration andand maymay bebe physiologicalphysiological or biological in nature. They generallygenerally produceproduce diebackdieback ofof smallsmall branches.branches. Examples of incitantsincitants are defoliating insects,insects, latelate springspring frost,frost, droughtdrought andand saltsalt spray.spray.

Contributing factors areare those factors whichwhich subsequentlysubsequently furtherfurther weakenweaken andand u)timatelyultimately kill thethe tree.tree. ExamplesExamples includeinclude barkbark beetles,beetles, cankercanker fungi andand rootroot decay fungi.fungi. These factors are persistent and visible and are often wronglywrongly blamed for the death of treestrees.. ThisThis isis especiallyespecially true ofof barkbark beetlesbeetles (Coleoptera: Scolytidae), some species ofof which cancan reachreach epidemicepidemic levelslevels inin responseresponse toto stress and kill largelarge numbers ofof treestrees,, many of which maymay notnot havehave beenbeen directly affected byby thethe stress.stress.

2.3.3. DECLINES DECLINES AS AS DISEASES DISEASES OF OF POORLYPOORLY UNDERSTOODUNDERSTOOD AETIOLOGY - The concept of declinedecline as a class of disease isis notnot totallytotally accepted by forest pathologists. Manion (1993) acknowledgesacknowledges thatthat somesome expertsexperts considerconsider declinesdeclines asas aa collectioncollection ofof diseases withwith incompletelyincompletely understoodunderstood aetiologyaetiology and many situations werewere initiallyinitially designated as declines or diediebacks backs because theirtheir causescauses werewere unknown.unknown. SomeSome diseasesdiseases initially classifiedclassified asas declinesdeclines havehave eventually beenbeen shown toto havehave specific singlesingle causalcausal agents and were subsequently renamed.renamed. ForFor exampexample,le, when a portion of a decline of ash, Fraxinus sp.sp. in easterneastern NorthNorth AmericaAmerica was attributed toto infectioninfection by by a a mycoplasmamycoplasma or mollicute likelike organism (MLO),(MlO), it was renamed "ash yellows" (Mattenoni(Mattenoni andand SinclairSinclair 1985). Similarly when aa declinedecline of livelive oak,oak, QuercusQuercus virqinianavirginiana fusiforme, inin centralcentral TeTexas,xas, USA, waswas foundfound to be causedcaused by thethe oakoak wiltwi ltfungus fungus Oohiostoma Ophiostoma ((= = Ceratocystis)Ceratocystis) fagacearum,fagacearum, itit waswas consideredconsidered to to bebe a a form form ofof oakoak wiltwilt (lewis(Lewis 1977). In a more recentrecent attempt atat characterizingcharacterizing decline,decline, SinclairSinclair and Hudler (1988)(1988) indicateindicate that declinedecline can, in fact, bebe thethe resultresult ofof aa chronicchronic irritationirritation byby aa singlesingle factorfactor (e.g.,(e.g., thethe MLOMlO ininvolvedvolved in thethe ashash diebackdieback complex).complex).

66 TABLE 2.1

EXAMPLESEXAMPLES OF PREDISPOSING, INCITINGINCITING ANDAND CONTRIBUTING FACTORS WHICH INFLUENCEINFLUENCE OCCURRENCEOCCURRENCE OF DECLINE'DECLINE *

~--:-

I . PREDISPOSINGPREDISPOSING INCITINGINCITING CONTRIBUTING

I .. (Long(Long TermFactors)Term Factors) (Short(Short Term Factors) (Long(Long Term Factors) I.' '. .'. . '."

Genetic potential InsectInsect defoliation Bark beetles Age Frost Canker fungi Viruses Drought Root decay fungi (interacting with) Salt ClimateClimate Air pollutants Soil factors Mechanical injury Air pollution

•* Adapted from ManionManion (1991).(1991).

2.4. DECLINEDECLINE ASAS A A PART PART OF OF FORESTFOREST DYNAMICS.DYNAMICS.

Mueller-Dombois (1983,(1983, 1986, 1992a),1992a). workingworking withwith a a declinedecline ofof MetrosiderosMetrosideros polymorpha inin thethe HawaiianHawaiian Islands,Islands, USA,USA, concludedconcluded thatthat diebacksdiebacks areare notnot necessarilynecessarily a disease, butbut an integral part of forest dynamicsdynamics andand succession.succession. HeHe considersconsiders declinedecline as a complex condition which involvesinvolves aa number of interacting factorsfactors butbut arguesargues thatthat the primaryprimary andand predisposingpredisposing cause of declinedecline isis synchronous senescence of a number of treestrees inin oneone placeplace whichwhich hehe describesdescribes as cohort senescence. AA suddensudden trigger oror perturbation is required toto initiateinitiate declinedecline (e(e.g.,.g., drought,drought, floodflood oror wind).wind). RecoveryRecovery may occur if factorsfactors suchsuch asas insectsinsects oror fungifungi dodo notnot play playa a subsequent subsequent majormajor role.role. He defines decline as a stand or population level phenomenon, which is manifested in thethe loss of vigour ofof aa forestforest stand.stand. HeHe considers considers dieback dieback toto mean mean aa furtherfurther progressionprogression ofof decline which leadsleads to stag-headednessstag-headed ness ofof many trees.trees. Trees with diebackdie back cancan recover but in mostmost casescases the condition leads toto the death of many trees. HeHe furtherfurther definesdefines canopy dieback as all forms of stand-levelstand-level diebackdie back or forest decline,decline, whereverwherever the canopy and/orand/or sub-canopysub-canopy treestrees areare involved.involved. Situations wherewhere thethe undergrowthundergrowth vegetation is dyingdying andand wherewhere the overstoreyoverstorey remainedremained intact,intact, are not included. HeHe excludes all forms of stand-level death which havehave obvious causes. CanopyCanopy diebackdie back cancan take on two forms:forms:

A. Tree-to-TreeTree-to- Tree Dieback,Dieback, wherewhere many adjacent trees are affected.

B. Salt-and-Pepper Dieback,Dieback, wherewhere dyingdying treestrees occur repeatedly in a matrixmatrix of healthyhealthy trees.trees.

7 The concept ofof synchronoussynchronous cohortcohort senescencesenescence can be fit intointo thethe Predisposing,Predisposing, Inciting and Contributing FactorsFactors concept of SinclairSinclair and Manion by considering four generic causal factors (Mueller-Dumbois(Mueller-Dum bois 1992a):1992a):

A. Simplified forest structure leadingleading to instability.instability.

B. Edaphically extreme sites.sites.

C. Periodically recurring perturbations.perturbations. (e.g.(e.g . weather disturbancesdisturbances or catastrophic events)events)

D. Biotic agents.agents.

These cancan be relatedrelated toto the Sinclair/ManionSinclair/Manion concept as follows:

A. PredisposingPredisposing factors:factors:

1. Simplified cohortcohort structurestructure andand senescence.senescence.

2. Extreme edaphic and evolutionary stresses.stresses.

3. Pulse perturbations,perturbations, (e.g(e.g.. periodic shocksshocks fromfrom extreme weather or from seismicseismic disturbances.disturbances.

B. Inciting factor:

Pulse perturbation factorfactor (same as above)above) whichwhich triggerstriggers canopycanopy breakdown inin demographicallydemographically weakenedweakened stands.stands.

C. ContributingContributing factor:factor:

Biotic agents, such as pathogenicpathogenic fungi oror insectinsect pestspests whichwhich maymay overpower aa standstand weakenedweakened byby thethe precedingpreceding threethree causes.causes.

The role of climaticclimatic perturbationsperturbations as a universaluniversal inciting factor for declinedecline isis discussed byby AuclairAuclair etet al (1992). TheyThey suggestsuggest thatthat in in borealboreal andand temperatetemperate forests,forests, decline isis initinitiatediated by aa winterwinter thaw/freezethaw/freeze event.event. Thaws cause trees toto becomebecome physiologically active andand result inin prematurepremature bud swelling, sapsap ascent, rehydration of tissues and partial loss of frostfrost resistance.resistance. The onset ofof subsequentsubsequent deepdeep freezesfreezes results in xylem injury byby cavitationcavitation whichwhich rendersrenders treestrees moremore sensitive to drought.drought. Analysis of the onset of decline in relation toto climatic records indicate thatthat this scenario was common to severalseveral declinedecline eventsevents inin easterneastern Canada,Canada, western NorthNorth AmericaAmerica andand Europe (Auclair(Auclair et et al al 1990,1990, 1992, Auclair, in press).press). AnalysisAnalysis ofof declinedecline eventsevents in the Pacific Rim andand Southeast Asia indicate that they werewere associatedassociated withwith prolongedprolonged periods ofof wet, cloudycloudy weatherweather followedfollowed byby periodsperiods of clear,clear, bright,bright, hothot weather.weather. In these cases, thethe likely initiatinginitiating mechanismmechanism was rapidrapid treetree growthgrowth accompaniedaccompanied byby deposition ofof relativelyrelatively thin walledwalled vesselsvessels andand tracheidstracheids whichwhich cavitatecavitate underunder aa subsequent periodperiod ofof moisturemoisture stressstress (Auclair(Auclair 1992,1992, Auclair et al 1992).

8 Sinclair and Hudler (1988) consolidate thethe ideasideas of Sinclair, Houston,Houston, ManionManion andand Mueller-DomboisMueller-Dombois and describe decline as a premature, progressiveprogressive loss of treetree vigourvigour and health. TheyThey indicateindicate thatthat declinedecline cancan bebe explainedexplained in one of four ways:ways:

A . A tree may decline primarily as thethe result of a chronic irritation byby aa singlesingle agent.

B. A treetree maymay declinedecline becausebecause of damagedamage by secondarysecondary agents after anan event suchsuch asas defoliationdefoliation oror wounding.wounding. The same agents would notnot cause decline in an uninjured tree and the injury alonealone would notnot causecause decline.

C. Chronic irritation by oneone oror moremore agentsagents maymay diminishdiminish the tolerancetolerance oror resistance of a treetree toto anotheranother agentagent that that incitesincites decline.decline. VariousVarious factors,factors, includincludinging those which predisposedpredisposed thethe treetree andand incitedincited declinedecline maymay thenthen contribute to furtherfurther decline.decline.

D. Trees of similarsimilar ageage growing inin groupsgroups tendtend toto displaydisplay groupgroup behaviourbehaviour including prematurepremature senescencesenescence (synchronous cohort senescence)senescence) inin response to stress.stress.

In the sectionssections whichwhich follow,follow, aa number number ofof case case historieshistories ofof decline decline eventsevents are are described. Since most declinedecline eventsevents inin EuropeEurope andand NorthNorth AmericaAmerica havehave beenbeen wellwell documented inin thethe scientificscientific andand popularpopular literature,literature, theythey areare discusseddiscussed briefly. Descriptions ofof declinedecline eventsevents inin Africa,Africa ,Asia, Asia ,The The Pacific Pacific Region Region andand LatinLatin AmericaAmerica andand the Caribbean, are given inin greater detail.detail. ForFor thesethese regions,regions, causal factors associated with declinedecline eventsevents areare summarizedsummarized inin aa seriesseries ofof tablestables usingusing thethe Sinclair/Manion Sinclair/Manion concept of predisposing,predisposing, incitinginciting andand contributingcontributing factorsfactors (Tables(Tables 5.1, 5.1, 6 6.1,.1, 6.2,6.2, 7.1, 77.2,.2,7.3,8 7.3, 8.1).. 1 ).

9 CHAPTER 3

EUROPE

The existence of trees expressing symptoms ofof declinedecline has been widely reported in Europe.Europe. SomeSome reportsreports date toto the early part of thethe 18th18th century.century. Summaries of forest declinedecline events whichwhich havehave causedcaused concernconcern among scientists, resourceresource managersmanagers and the general public are presented inin thethe followingfollowing sections.

3.1 SILVER FIRFIR DECLINEDECLINE

One ofof the oldest known andand widelywidely reportedreported declinesdeclines ofof EuropeanEuropean trees is the Tannensterben (fir-death)(fir-death) associatedassociated with with AbiesAbies alba.alba. ThisThis isis aa diseasedisease ofof unknownunknown aetiology whichwhich has has spreadspread inin epidemicepidemic cyclescycles acrossacross centralcentral EuropeEurope since the beginning of the 19th19th century.century. ThereThere are are reports reports of of Tannensterben Tannensterben asas earlyearly asas 18101810 (Ruzicka (Ruzicka 1937).

This condition isis characterizedcharacterized byby defoliationdefoliation andand dyingdying ofof branches branches beginning beginning from the lowerlower crowncrown and and graduallygradually ascendingascending toto thethe toptop ofof the the tree tree and and anan abrupt,abrupt, longlong lastin9lasting incrementincrement reduction.reduction. TheThe apexapex of the crown isis flattenedflattened into a "stork's"stork's nest"nest" formation andand remainsremains green until latelate inin the syndromesyndrome when manymany treestrees diedie (Fig(Fig 3.1).3.1) . Others recover and show anan increaseincrease in incrementalincremental growth.growth.

The most recent occurrenceoccurrence of TannensterbenTannensterben beganbegan inin thethe 1950s and 1960s and peaked inin the 1970s1970s whenwhen aa series series ofof drydry summers summers occurred.occurred . Recovery of incremental growthgrowth began aboutabout 19801980 but improvementimprovement ofof crowncrow n conditionsconditions waswas delayed 44 toto 6 years (Kandler 1990,1990, 19921992,, 1993).1993).

3.2. HARDWOODHARDWOOD DECLINES DECLINES

Declines of hardwoodshardwoods havehave beenbeen reportedreported throughoutthroughout Europe.Europe. Of particularparticular concern is a recent increase in the incidence of the declinedecline ofof variousvarious speciesspecies ofof oaks,oaks, Quercus sppspp.. TheseThese have been discussed in twotwo recent international symposia;symposia; one one held held in 19901990 inin Kornik,Kornik, PolandPoland andand another in 19921992 inin SelvaSelva didi Fasano,Fasano, Brindisi, Italy.Italy. TheThe proceedings of the firstfirst ofof these these symposia symposia has has recently recently been been publishedpublished andand providesprovides anan excellent overview ofof thethe complexitycomplexity of of oak oak decline decline inin EuropeEurope (Siwecki andand LieseLiese 1991).

Hartmann andand Blank (1992)(1992) indicate that outbreaksoutbreaks ofof oakoak declinedecline havehave beenbeen recorded inin northernnorthern GermanyGermany during during the the periods periods 1739 1739 - -1748 1748,, 1911 1911 -- 1924,1924, 1929 - 1934 and 1939 - 1944.1944. TheseThese werewere attributedattributed toto cumulativecumulative andand interactive effects ofof insect defoliation, extremeextreme weatherweather conditions,conditions, powderypowdery mildewmildew and and otherother bioticbiotic agents.agents. A moremore recent episodeepisode of oakoak declinedecline inin northernnorthern GermanyGermany began in 1982,1982, increasedincreased markedly after 1985 and culminated in 1987 - 1989. AffectedAffected trees trees were were characterized characterized by marked reductions inin tree ring width betweenbetw een 19851985 andand 1987,1987, repeated repeated insectinsect

10 ne i decl fir silver of symptoms with 11

Germany, = Bavaria, in alba Abies Ciesla). . - W.M 3.1 by (Photo Figure defoliation, drought and deep winter frost. The only factor ofof simultaneoussimultaneous regionalregional occurrence waswas anan unusuallyunusually deep deep frost frost late late in in the the winters winters of of 1985,1985, 19861986 and 1987. Winter freeze damage ofof trees weakened by defoliationdefoliation and droughtdrought is believed toto be the primaryprimary causecause of dieback.die back. WeakenedWeakened treestrees werewere subsequentlysubsequently attackedattacked byby AgrilusAgrilus biguttatus (Coleoptera:(Coleoptera: Buprestidae)Buprestidae) and two fungifungi whichwhich causedcaused secondarysecondary barkbark lesions (Hartmann and Blank 1992).

According toto MarcuMarcu andand Tomiczek (1989),(1989)' symptomssymptoms ofof a a currentcurrent episode episode ofof oakoak decline first appeared inin easterneastern Austria,Austria, near thethe HungarianHungarian border border in in 1983. 1983. DetailedDetailed studies indicatedindicated that thethe occurrenceoccurrence ofof oakoak declinedecline waswas associatedassociated withwith prolongedprolonged periods ofof below normal precipitationprecipitation fromfrom 19751975 -- 1983. ExtremelyExtremely coldcold winterswinters fromfrom 1985 to 19871987 maymay havehave ledled to a further weakening of treestrees.. MoreMore recently,recently, TomiczekTomiczek (1990) hashas recoveredrecovered sapwoodsapwood nematodesnematodes ofof thethe genusgenus BursaphelenchusBursaphelenchus from oaksoaks wwithith symptomssymptoms ofof decline.decline. TheseThese areare believedbelieved to be transmitted by insect vectors in the families Buprestidae,Buprestidae, Cerambycidae and Scolytidae.Scolytidae. TheThe rolerole of these nematodes in the decline syndrome is not yet understood.understood.

Orlov and Osipov (1989)'(1989), in their reviewreview ofof QuercusQuercus robur forests inin thethe forest-forest­ steppe zone of centralcentral Russia,Russia, discuss the occurrence of decline and mortality whichwhich was observedobserved during the 1970s. FactorsFactors thoughtthought toto be be involvedinvolved inin thethe declinedecline includeinclude drought, frost,frost, insectinsect defoliationdefoliation andand fungalfungal diseases.diseases. Atmospheric pollutionpollution andand deposition ofof agriculturalagricultural chemicals chemicals in in the the soil soil are are also also consideredconsidered toto be be possiblepossible causalcausal factors. The most significantsignificant factorfactor responsibleresponsible for thethe declinedecline isis consideredconsidered toto bebe droughts which occurredoccurred during thethe 1960s and 70s, insectsinsects and a powderypowdery mildew fungus. AA significantsignificant recovery recovery was was observed observed inin 1980-1985,1980-1985, a a period period ofof higher higher rainfall.rainfall.

In Romania, aa formform of oak decline is characterized byby reductionreduction of annual shoot growthgrowth andand leafleaf sizesize and by yellowing, wilting andand loss of foliage. MLOsMLOs havehave beenbeen detected in the phloem ofof symptomatic trees by electron microscopy.microscopy. WhenWhen thesethese were transferred toto otherother plants,plants, similarsimilar symptomssymptoms appeared, appeared, suggestingsuggesting MLOMLO asas aa possiblepossible causal factor. TheseThese findings findings have have not not been been confirmed confirmed for for oak oak decline decline in in central central Europe Europe (Kandler 1990).

Decline andand mortalitymortality of Q.Q. ilexile x andand Q.Q. subersuber is occurring in portionsportions ofof Italy,Italy, Morocco, Portugal, Spain and Tunisia.Tunisia. ThisThis hashas been attributed in the pastpast to drought,drought, pollution and toto secondary attacksattacks by insects and fungi (Brasier 1992).1992). SymptomsSymptoms include sudden death witwithinhin oneone or two seasons,seasons, rootroot andand rootletrootlet necrosis,necrosis, epicormicepicormic shoots and a tarry exudation. In southern Spain, dying trees often occuroccur inin groupsgroups andand largela rge focifoci areare distributeddistributed alongalong streams,streams, valleysvalleys oror depressions. depressions. Decline is alsoalso associated withwith standing water duringduring winter monthsmonths oror withwith recentrecent soilsoil disturbancesdisturbances suchsuch as ploughingploughing oror roadroad construction. construction. TheThe root fungus, PhytophthoraPhytophthora cinnamomi, hashas been isolatedisolated fromfrom thethe rootroot systemssystems ofof symptomatic trees occurring on moistmoist sites. It is suggestedsuggested thatthat thisthis fungusfungus hashas recentlyrecently beenbeen introducedintroduced into thethe regionregion andand isis interacting with thethe effectseffects of of winter winter drought drought and and changing changing landland useuse patternspatterns toto bringbring about decline (Brasier etet al 1993).1993).

Key points which werewere mademade atat anan internationalinternational conferenceconference onon oakoak declinedecline inin Selva di Fasano,Fasano, Brindisi,Brindisi, ItalyItaly,, during September 1992 areare (IUFRO(lUFRO 1993):

A. Oak decline isis aa complecomplexx synsyndromedrome reportedreported toto havehave periodicallyperiodically occurred in thethe lastlast 100100 years years in in many many European European andand overseasoverseas countries.countries. ItItss

12 aetiology is still notnot completelycompletely known.known. Nevertheless,Nevertheless, the the phenomenon phenomenon seemed toto decrease inin intensityintensity duringduring thethe lastlast twotwo years.years.

B. While there are several common features of symptoms ofof oakoak declinedecline across Europe and even in North America,America, therethere areare alsoalso strongstrong regionalregional differences in factors (frost, drought,drought, airair pollution, root disease, etc.) thatthat are associated with thethe problem.problem.

C. The available resultsresults of intensive research carriedcarried outout until now seemseem toto prove thatthat all stress factors can reduce vitalityvitality ofof trees,trees, whichwhich maymay bebe easily damaged by secondary organisms (fungi, insects, etc.).etc.).

D. Lack of silviculturalsilvicultura' managementmanagement led to excessiveexcessive stoCkingstocking of oak trees. On dry sites,sites, thisthis predisposespredisposes oaksoaks toto decline,decline, especiallyespecially inin southernsouthern Europe. Sanitary felling should be carried out atat thethe appearanceappearance ofof decline symptoms, in orderorder to recoverrecover stump viability.

E. The possible rolesroles inin thethe declinedecline syndromesyndrome ofof endophyticendophytic fungi that maymay be normally present in asymptomatic trees were mentionedmentioned byby severalseveral papers. ThisThis presentspresents aa challengingchallenging new avenue of investigation.

F. The rolerole of severalseveral weakweak pathogenspathogens hashas beenbeen pointedpointed out.out. The epidemiological aspects of Armillaria spp. still needsneeds to bebe clarified.clarified.

G. A potentialpotential primaryprimary pathogen,pathogen, PhytophthoraPhytophthora cinnamorni,cinnamomi, hashas beenbeen foundfound inin association with thethe recentrecent rapidrapid oakoak declinesdeclines inin Iberia.Iberia. Its rolerole needsneeds to bebe investigated.investigated.

H. The results obtained from interdisciplinaryinterdisciplinary studies presentedpresented during the Congress helpedhelped toto clarify somesome aspectsaspects ofof thisthis complexcomplex disease disease andand marked thethe necessity to emphasizeemphasize thisthis kind of collaboration.collaboration.

Buchensterben is a decline of beech, Fagus sylvatica,sylvatica, which occursoccurs inin England,England, France, Germany,Germany, SwitzerlandSwitzerland andand PolandPoland.. The decline is characterized by brown toto black spots on the bark and branches of trees underneath which thethe cambiumcambium hashas died.died. The conditioncondition isis causedcaused byby thethe beech beech scale, scale, Cryptococcus Cryptococcus fagisugafagisuga (Homoptera:(Homoptera: Coccididael,Coccididae), whichwhich attacksattacks thethe bark andand buildsbuilds up up following following periodsperiods of of droughtdrought.. ThisThis predisposes trees trees to to attackattack by fungifungi ofof thethe genusgenus NectriaNectria andand secondarysecondary barkbark andand ambrosia beetlesbeetles (Coleoptera:(Coleoptera: Scolytidae).Scolytidae). Affected treestrees areare subjectsubject to windwind breakagebreakage (Schwerdtfeger 1981). TheThe beech beech scale scale hashas beenbeen introducedintroduced intointo NorthNorth AmericaAmerica andand isis now a factor inin aa conditioncondition knownknown asas "beech"beech barkbark disease"disease" whichwhich affectsaffects American American beech, E.F. grandifolia (see sectionsection 4.6).

3.3 ACUTEACUTE YELLOWING YELLOWING OFOF NORWAYNORWAY SPRUCE SPRUCE

An acute chlorosis or yellowing ofof thethe foliagefoliage ofof NorwayNorway spruce, spruce, Picea Picea abies,abies, hashas been reportedreported fromfrom centralcentral EuropeEurope sincesince the the early early 1970s. 1970s. TheThe symptomsymptom associated with this conditioncondition isis aa yellowingyellowing ofof olderolder needlesneedles whichwhich beginsbegins atat thethe needleneedle tiptip andand progresses toto thethe base. TheThe discolourationdiscolouration generallygenerally occursoccurs onon thethe upperupper oror illuminatedilluminated

13 side of the needles. SymptomsSymptoms areare confined to mountainous areas withwith acid soil derived from granite,granite, sandstonesandstone oror otherother rocksrocks poor poor in in available available magnesiummagnesium (Mg).(Mg).

This conditioncondition hashas beenbeen diagnosed as an Mg deficiency through studiesstudies whichwhich demonstrate that needleneedle yeyellowingllow ing is closely correlated withwith Mg content ofof thethe needlesneedles and availableavailable Mg in thethe soils.soils. In addition,addition, treestrees recoverrecover rapidlyrapidly whenwhen fertilizersfertilizers containing magnesiummagnesium areare applied.appl ied .

Some workersworkers believe thatthat thethe onset of acute yellowing isis atat leastleast indirectly duedue to increasesincreases in levels ofof aairir pollution. TwoTwo hypotheses hypotheses havehave formulated:formulated:

A. InIncreasedcreased levelslevels of atmosphericatmospheric ozoneozone and/orand/or otherother photochemicalphotochemical oxidants trigger oxidativeoxidative damagedamage to cellcell membranesmembranes andand chloroplastchloroplast pigments. This in combinationcombination withwith acidacid rainrain enhancesenhances leachingleaching ofof minerals. Because of of thethe loloww levelslevels ofof soil Mg,Mg, thethe plantplant cannotcannot compensate for lossloss of Mg.Mg.

B. The acidification/aluminum toxicitytoxicity hypothesis hypothesis assumes assumes an an increasedincreased soilsoil acidificationacidification byby depositiondeposition of pollutants.pollutants. ThisThis would would lead lead toto an an enhancedenhanced cation exchange andand aa shiftshift in the ratioratio ofof calciumcalcium toto aluminumaluminum andand subsequent inhibition of both CaCa and Mg uptake by the roots.

Kandler (1992)(1992) points outout that neitherneither hypothesishypothesis hashas beenbeen proven experimentallyexperimentally under ecologically relevantrelevant conditions.conditions. InIn additaddition,ion, he argues thatthat the development of acute yellowing duringduring thethe pastpast decadedecade isis not consistentconsistent with eithereither ofof thesethese hypotheses. IncreasedIncreased yellowingyellowing would would be be expectedexpected as as aa resultresult ofof continuouscontinuous exposureexposure to pollutants. AcuteAcute yellowing, yellowing, on on the the other other hand, hand, showsshows anan episodicepisodic development with frequent spontaneous re-greening andand a a low low raterate ofof treetree mortality.

3.4. REGIONALREGIONAL DECLINE DECLINE OFOF CONIFERSCONIFERS AND HARDWOODS.HARDWOODS.

Beginning inin thethe latelate 1970s, aa regional decline ofof both conifersconifers and hardwoods was reported in Europe. ThisThis decline received aa greatgreat dealdeal of of attentionattention byby thethe scientificscientific community, politicalpolitical leadersleaders andand thethe generalgeneral publicpublic andand hashas beenbeen widelywidely reported.reported. Declines described inin thethe preceding sectionssections (3.1(3.1 - 3.3) havehave frequentlyfrequently beenbeen includedincluded as part of the regionalregional decline. TheThe conditioncondition waswas rnostmost frequentlyfrequently reportedreported fromfrom andand most intensively studiedstudied inin Germany but occurs in many other countries as well.well. InIn thethe German literature,literature, this declinedecline waswas initiallyinitially designated designated asas WaldsterbenWa/dsterben (forest(forest death) death) and and later as neuartige WaldschädenWa/dschiiden (a(a newnew typetype ofof forest damage). GeneralGeneral reviews ofof thisthis decline are provided by SchuttSchutt andand CowlingCowling (1985),(1985), NiessleinNiesslein andand VossVoss (1985),(1985). Plochmann (1985),(1985), Steinbeck (1984).(1984), Kandler (1990,(1990, 1992,1992, 1993)1993) and and RaddiRaddi (1992).(1992).

Symptoms associated withwith thethe regionalregional declinedecline includeinclude foliagefoliage loss andand discolouratdiscolouration,ion, feederfeeder root mortality,mortality, radialradial growthgrowth reduction, reduction, premature premature senescence, senescence, abscission of foliage and shoots, altered leafleaf and branch morphology, abnormally heavy seed andand conecone cropscrops andand formationformation ofof bacterial wetwood.

Causal factorsfactors are still not wellwell understoodunderstood butbut several several hypotheseshypotheses havehave beenbeen formulated to explainexplain thethe decline.decline. These consider thethe deposition ofof toxic, nutrient,nutrient,

14 acidifying and/orand/or growthgrowth alteringaltering substancessubstances fromfrom anthropogenicanthropogenic sourcessources asas aa causalcausal factor andand areare summarized by Schutt and Cowling (1984) asas follows:follows:

A. Increased acidificationacidification of forestforest soils due toto deposition of acidic substances from the atmosphere which results in increased concentrationsconcentrations ofof solublesoluble aluminumaluminum ions and in turn results inin thethe deathdeath of finefine roots.roots.

B. IncreasedIncreased levelslevels ofof ozone inin thethe atmosphere resulting inin foliagefoliage lossloss andand growth reduction.reduction.

C. AAcceleratedccelerated leaching of calciumcalcium andand magnesiummagnesium from foliagefoliage andand soilssoils due to acid deposition which resultsresults inin soilsoil nutrientnutrient deficiencies.deficiencies.

D. Increased levelslevels of atmospheric pollution whichwhich leadsleads toto aa decreasedecrease inin net photosynthesis andand reducedreduced nutrient reserves making treestrees moremore susceptible to droughtdrought andand otherother stress.stress.

E. Air transport ofof growthgrowth alteringaltering substances.substances.

Kandler (1985),(1985), on the other hand, rejects the hypothesis of abiotic factors suchsuch as atmosphericatmospheric pollutants asas causal agents of the current wavewave ofof declinedecline andand proposesproposes an alternative "epidemic" hypothesis.hypothesis. HeHe postulatespostulates thatthat thethe declinedecline symptoms maymay bebe the resultresult ofof aa separateseparate andand distinctdistinct complexcomplex ofof environmentalenvironmental factorsfactors andand unknownunknown biotic agents. HeHe basesbases thisthis onon thethe factfact thatthat many many ofof the the present present declinedecline symptomssymptoms were previously described as separateseparate andand distinct distinct conditions.conditions. AA primeprime exampleexample is the decline of Abies alba (Tannensterben),(Tannensterben). whichwhich waswas first describeddescribed when levels of airair pollutants werewere muchmuch lower thanthan theythey areare today. InIn moremore recentrecent papers,papers, Kandler (1990, 1992) criticisescriticises EuropeanEuropean researchers for lumping symptoms ofof declinedecline fromfrom aa numbernumber of treetree speciesspecies and attributing thethe damagedamage to anan undefined complex of air pollutants.

Concern aboutabout neuartige Wa/dschadenWaldschäden and and the the futurefuture ofof Europe'sEurope's forestsforests prompted annual surveys to assessassess forest condition.condition. TheseThese vvere were begunbegun inin GermanyGermany inin 1983 andand areare nownow conductedconducted inin many many European European countries.countries. Trees areare classifiedclassified according to standardizedstandardized damagedamage categories based on defoliationdefoliation andand discolorationdiscoloration (Tables 3.13.1 & 3.2). 3 .2). TheseThese surveys surveys areare helpfulhelpful forfor monitoringmonitoring changechange inin treetree andand forestforest condition from year to yearyear butbut theythey dodo notnot relaterelate treetree conditioncondition toto causalcausal factors.factors. Results areare published onon anan individual countrycountry basis, byby the CommissionCommission for the European CommunityCommunity (CEC 1991)1991) and by thethe United Nations Economic Commission for Europe (GEMS 1991).

Results ofof surveys of regionalregional forest declinedecline in the formerformer WestWest GermanyGermany areare summarized by Kandler (1992).(1992). TheseThese indicateindicate anan increase in forest damage from 19831983 to 1984.1984. From 1984 toto thethe present,present, thethe level level of of damage damage has has remained remained relativelyrelatively constant. HeHe suggestssuggests thatthat the the sharp sharp increase increase inin damagedamage levelslevels betweenbetween 19831983 and and 1984 maymay havehave been due toto the fact thatthat notnot all all statesstates in in the the former former West West Germany Germany were using the same survey methods and that fieldfield personnelpersonnel were notnot fullyfully acquainted acquainted with thethe classificationclassification system.system.

15 TABLE 3.13.1

DAMAGE RATINGRATING SYSTEMSYSTEM FORFOR ASSESSMENTASSESSMENT OFOF TREE CONDITION IN EUROPEEUROPE BASED ONON DEGREE OFOF DEFOLIATIONDEFOLIATION *

CLASS DEGREE OF PERCENTAGE OFOF DEFOLIATION NEEDLE/LEAF LOSS

0 Not defoliated 0-10%0 - 10%

1 Slightly defoliateddefoliated 11 - 25%

2 Moderately defoliateddefoliated 26 - 60%

3 Severely defoliated > 60%60%

4 Dead

TABLE 3.2

DAMAGE RATING SYSTEMSYSTEM FORFOR ASSESSMENTASSESSMENT OFOF TREE CONDITIONCONDITION IN EUROPEEUROPE BASED ON DEGREE OFOF DISCOLOURATIONDISCOLOURATION *

CLASS DEGREE OF PERCENTAGE OF D1SCOLOURATIONDISCOLOURATION DISCOLOURATION

0 Not discoloureddiscoloured 0-10%0- 10%

11 Slightly discoloureddiscoloured 11 - 25%

2 Moderately discoloureddiscoloured 26 - 60%60%

3 Severely discoloured > 60%60%

4 (dead)

* Source, CEC (1991).

16 Landmann (1993),(1993), in a reviewre view ofof forestforest declinedecline inin France,France, concludesconcludes that thethe largelarge majoritymajority ofof declines recentlyrecently studiedstudied inin thethe context of "novel"novel forestforest decline"decline" (neuartige WaldschaVen)Waldschaden) presentpresent strongstrong similaritiessimilarities withwith decline events studied earlier. Natural factors (e.g.(e.g . climatic perturbations, stand dynamics) andand past forest management (in particular inappropriate selection of speciesspecies or provenances planted on certain sites) playplaya a majormajor rolerole inin thesethese declines.declines.

17 CHAPTER 4

NORTH AMERICA

DeclineDecline andand diedieback back eventsevents have been documented in both CanadaCanada and thethe United StatesStates sincesince thethe earlyearly 1900s.1900s. TheThe following sectionssections provideprovide a brief review of some of the moremore wellwell knownknown declinedecline events.events.

4.1. BIRCHBIRCH DIEBACKDIEBACK

A diebackdie back of yellowyellow birch,birch, BetulaBetula allegheniensis,allegheniensis, paperpaper birch,birch, B.a. papyrifera,papyrifera, andand grey birch, B.a. populifolia,populifolia, emergedemerged asas aa forestforest problem betweenbetween 1930 and 19501950 inin eastern Canada and the northeastern UnitedUnited States.States.

According to AuclairAuclair (1987),(1987)' birchbirch diebackdieback hadhad threethree noteworthynoteworthy featuresfeatures inin Canada:

A. DiebackDieback waswas preceded byby aa reductionreduction inin radial growthgrowth..

B. There waswas a pronounced east-westeast-west gradientgradient inin thethe intensity of diebackdie back with mostmost severesevere damagedamage occurringoccurring inin thethe eastern-mosteastern-most Provinces. Provinces.

C. By the 1950s,1950s, recoveryrecovery waswas apparent.apparent.

ThThee bronze birchbirch borer,borer, AgrilusAgrilus anxius (Coleoptera:(Coleoptera: Buprestidae), attacks and kills trees weakenedweakened byby birchbirch dieback.dieback. The root fungus,fungus, ArmillariaArmillaria sp.,1Sp.,' contributes to intensification ofof birch birch diebackdieback by by invadinginvading thethe rootroot systemssystems ofof weakenedweakened treestrees (Manion(Manion 19811981). ).

This decline is believed toto be the resultresult ofof aa prolongedprolonged warmingwarming trendtrend whichwhich increasedincreased average summer temperatures inin easterneastern CanadaCanada byby 1°,. C over a 10 to 2020 yearyear period (Hepting(Hepting 1963). ThisThis resulted resulted inin increasedincreased soil temperature which caused rootlet mortality. StandStand opening opening byby logging, logging, defoliationdefoliation and and leafleaf skeletonizing skeletonizing andand latelate springspring or early fall frosts cancan inciteincite birchbirch diebackdie back inin localizedlocalized areas.areas.

4.2.4 .2. POLEPOLE BLIGHTBLIGHT OFOF PINUSPINUS MONTICOLAMONTICOLA

Western whwhiteite pine,pine, Pinus monticola,monticola, iiss aa fastfast growing,growing, commercially important tree speciesspecies whichwhich isis foundfound inin thethe Pacific Pacific coastalcoastal regionsregions ofof British British Columbia, Columbia, Canada, Canada, IdahIdaho,o, Oregon, MontanaMontana and Washington,Washington, USA. ThisThis speciesspecies isis aa majormajor component ofof mixed coniferconifer forestsforests inin aa sub-regionsub-region knownknown asas thethe "Inland"Inland Empire",Empire", whichwhich comprisescomprises portions of easterneastern Washington,Washington, northern Idaho, western MontanaMontana in thethe USAUSA andand adjoiningadjoining portions ofof BritishBritish Columbia, Columbia, Canada.Canada .

1 MostMoSt citationscitations refer to Armillaria melleamerlea which,which, until recently,recently, waswas consideredconsidered toto bebe aa singlesingle variableva riable oror polymorphicpolymorphic speciesspecies with worldwideworldwide distribution.distribution. MoreMore recently, recently, the the genus genus has has been been reclassified reclassified intointo a a number number of of species species (Watling (Watling etet aI1991).al 1991). ThereforeTherefore thethe designation designation ArmillariaArmill aria sp.sp .is is usedused throughoutthroughout thisthis paper. paper.

18 A condition referredreferred to as "pole blight" waswas firstfirst notednoted inin IdahoIdaho in 19271927 andand waswas eventually found to occuroccur throughout the InlandInland Empire. SymptomsSymptoms intensifiedintensified during the 1930s1930s andand continuedcontinued untiluntil thethe 1950s1950s when when they they subsided. subsided. Assessment of thethe causes andand magnitudemagnitude ofof losses incurred byby pole blight werewere complicatedcomplicated byby thethe presence ofof whitewhite pine blister rustrust,, Cronartium ribicola, an introduced pathogen, which was also causing high levelslevels of damagedamage to P.E. monticola.monticola.

Recent reviewsreviews of pole blight areare providedprovided by Auclair et alal (1990),(1990)' HennonHennon (1990) and Manion (1991). SymptomsSymptoms consistconsist ofof chlorosis chlorosis ofof needles,needles, reductionreduction inin radial and height growthgrowth andand bolebole lesionslesions associatedassociated withwith resinosis. resinosis. Death usuallyusually began atat the topstops ofof trees trees and and progressed progressed downward.downward. Several species of fungi,fungi, includingincluding LeptographiumLeptographium sp. sp. and and Armillaria Armillaria sp. sp. werewere foundfound toto bebe associatedassociated with affected treestrees but were notnot thethe primaryprimary causecause of thethe blight.blight. Tree mortality waswas confined toto even-aged (pole-sized) stands stands ranging ranging from from 40 40 to to 100100 years ofof age.age. OlderOlder stands were unaffected.

Studies onon the aetiology of this diseasedisease indicatedindicated thatthat aa period ofof hot, drydry weather prevailed inin thethe InlandInland EmpireEmpire from from 19161916 toto 1940. ThisThis representedrepresented the mostmost adverse growthgrowth conditionsconditions forfor this speciesspecies during thethe past 280280 years.years. It waswas hypothesized thatthat moisture stress was the primaryprimary cause of polepole blight, causingcausing finefine rootsroots toto die. MoistureMoisture stressstress waswas broughtbrought aboutabout byby thethe combinationcombination of drought,drought, soilssoils with poorpoor waterwater holding holding capacitycapacity andand youngyoung pinespines inin maximummaximum growth phasephase havinghaving a high demanddemand forfor water.

4.3. ASHASH DIEBACK DIEBACK

Dieback of ash,ash, FraxinusFra xinus americana,americana, andand toto aa lesserlesser degree,degree, F..E. pennsylvanica,pennsylvanica, was first observedobserved inin thethe northeasternnortheastern UnitedUnited StatesStates andand adjoiningadjoining CanadaCanada in the 1930s but developed intointo a serious concernconcern inin thethe 1950s and early 1960s.

The onset of ashash diebackdie back is signalled by reduced growthgrowth of stemsstems andand twigs. This is followedfollowed byby deathdeath ofof terminal terminal buds buds and and branchesbranches andand thethe presencepresence ofof small,small, sparse andand chlorotic chlorotic foliagefoliage.. AffectedAffected crownscrowns oftenoften appearappear thin andand tufted. OnOn somesome trees, premature fallfall colouringcolouring andand early seasonal foliagefoliage lossloss.. Epicormic shoots develop as the trees progressivelyprogressively die back. EventuallyEventually treestrees die.die.

Reddish-brown to orange-yellow cankers develop on the branchesbranches and on the smooth bark of the main stem. TheseThese cankerscankers girdle twigs oror stemsstems andand contribute toto the dieback process. AtAt least least twotwo canker canker fungi, fungi ,Cytophoma Cytophoma pruinosa pruinosa andand FusicoccumFusicoccum sp, attack barkbark tissuestissues mademade susceptible by waterwater deficits.deficits.

One formform of ashash diebackdieback is believed toto be the result ofof stressstress associatedassociated with moisture deficit followedfollowed byby thethe invasioninvasion ofof secondary secondary cankercanker fungi.fungi. Other factors which maymay bebe involvedinvolved inin thethe dieback die back includeinclude virus,virus, mycoplasmasmycoplasmas andand airair pollutionpollution (Houston 19811981,, 1992). AA condition condition knovvn known asas "ash"ash yellows"yellows" isis caused caused byby anan MLO.MLO. Matteoni and Sinclair (1988) indicateindicate that ashash yellows isis probablyprobably the primaryprimary cause of ash diedieback back inin NewNew YorkYork State.State. Similar symptoms occur follofollowingw ing defoliation byby a rust fungus, PucciniaPuccinia sparganiodes (Houston(Houston 1992).

19 4.4. MAPLEMAPLE DECLINE DECLINE

Decline of sugar maple.maple, Acer saccharum,saccharum. and other species of maple,maple. hashas beenbeen reported from aa variety ofof situationssituations in in easterneastern CanadaCanada and the United States (Fig(Fig 4.1). Maples growing alongalong roadsides,roadsides. in sugar bushes (stands of maple from whichwhich sapsap isis extracted for sugar production) and in forests are affectedaffected (Manion 1991).

Many causal factors have been associatedassociated wwithith maplemaple decline including roadroad salt,salt. soil compaction.compaction, poor drainage.drainage, airair pollution.pollution, drought.drought, defoliating insects and root fungi. Different combinationscombinations ofof causal causal factorsfactors have have beenbeen suggestedsuggested forfor individualindividual episodesepisodes ofof maple decline. ForFor example,example. declinedecline ofof roadsideroadside maples is believed toto be thethe result of road saltingsalting duringduring winter.winter, overmaturity and water stress. Drought,Drought. defoliation,defoliation. heavyheavy grazing andand overtappingovertapping areare believedbelieved to to bebe associatedassociated with with mortalitymortality and diebackdie back of sugar bush maples.maples. InIn naturalnatural forests,forests. maplemaple decline isis thethe resultresult of insect defoliation followed byby invasioninvasion of secondarysecondary fungi (Houston 1981).

A regional decline ofof sugarsugar maplemaple overover portionsportions ofof Ontario Ontario and and Quebec,Quebec. Canada Canada began toto appear duringduring thethe late 1970s1970s andand increasedincreased in intensityintensity duringduring thethe earlyearly 1980·s.1980's. Many hypotheses were suggested forfor the causecause ofof thisthis declinedecline includingincluding harvesting accompanying treetree species,species. tree age.age, tappingtapping for syrup.syrup, livestock grazinggrazing and soil andand airair pollution.pollution. Short term factorsfactors includedincluded adverseadverse weather andand insectinsect defoliation. AA popular popular causal causal hypothesishypothesis was was acid acid rain rain becausebecause thethe regionregion receivesreceives highhigh loadingsloadings ofof acid deposits withwith the annual totaltotal being 4040 krn/ha/yrkm/ha/yr of wetwet sulphatesulphate (Linzon 1988). AA causal causal relationshiprelationship between between acid acid deposition deposition and and declinedecline hashas notnot beenbeen established however.

The results of a cooperative CanadaCanada - United States study onon sugar maple decline shows an apparent improvementimprovement in in thethe health ofof this speciesspecies since 1988 inin areasareas affected byby declinedecline (NAPAP(NAPAP 1992).

4.5. OAKOAK DECLINE DECLINE

Periodic eventsevents of decline and mortality ofof oaks,oaks. Quercus Quercus sp.,sp .• havehave beenbeen recordedrecorded Inin the easterneastern UnitedUnited StatesStates sincesince 19001900 (Fig.(Fig . 4.2). Trees areare weakenedweakened byby environmental stress such as drought.drought, excess water.water, frost oror fromfrom feedingfeeding injuryinjury caused caused by defoliating or sucking insectsinsects.. In recentrecent years.years, defoliationdefoliation by gypsy moth,moth. LymantriaLymantria dispar (Lepidoptera: LymLymantridae),antridael. anan insectinsect whwhichich was introduced intointo NorthNorth AmericaAmerica during the 19th century,century. hashas beenbeen a major inciting factor associatedassociated with oakoak decline.decline. The two linedlined chestnutchestnut borer,borer. AdrilusAgrilus bilineatusbilineatus (Coleoptera:(Coleoptera: Buprestidae),Buprestidael. andand thethe rootroot disease fungus.fungus, Armillaria sp.,sp .• areare often associatedassociated vvithwith declining trees.trees, but areare not thethe primary cause ofof declinedecline.. UsuallyUsually the progressionprogression of the decline isis sslow,low. occurring over a period of severalseveral years (Wargo et al 1983).

In thethe centcentralral United States.States, oak decline isis attributedattributed partially to firefire exclusionexclusion whwhichich hashas resulted in ththee invasion of prairie groves of fire resistant Quercus macrocarpa by species more sensitivesensitive toto both fire andand drought.drought. In addition.addition, clearingclearing of oakoak forestsforests from the 1880s1880s toto thethe 1920's,1920·s .followed followed by by attempts attempts to to farm farm these these landslands whichwhich endedended inin failure.failure, resulted in the formation ofof eveneven ageage QuercusQuercus forests.forests, many of sproutsprout origin.origin. These cohorts may bebe developingdeveloping senescence makingmaking themthem especially susceptiblesusceptible toto drought.drought, insect defoliation or otherother incitantsincitants whichwhich couldcould causecause standstand levellevel decline.decline.

20 ' ••, ;I. .

,

FigureFi gure 4.14.1 .- Acer saccharum with symptoms ofof maplemaple declinedecline (Vermont, USA).USA). (Photo by W.M. Cies(a)Ciesla)

21 ,

Figure 4.24 .2 - -OakOak decline decline in inwestern west ern North North Carolina, Carolina, USA. USA (Photo. (Photo by W.M.by W.M. Ciesla) Ciesla)

22 4.6. BEECHBEECH BARKBARK DISEASE DISEASE

Beech bark disease affectsaffects AmericanAmerican beech,beech, FaqusFagus qrandifgrandifolia, olla, in easterneastern NorthNorth America.America. SymptomsSymptoms includeinclude chloroticchlorotic foliage,foliage, thinthin crowns,crowns, branchbranch diebackdieback andand treetree mortality. The disease is initiatedinitiated whenwhen thethe beechbeech scale,scale, CryptococcusCryptococcus fagisugafagisuga (Homoptera: Coccididae), feeds on the bark of beechbeech trees.trees. FeedingFeeding causescauses crackscracks inin the barkbark tissuetissue whichwhich areare subsequentlysubsequently invadedinvaded byby aa cankercanker fungus,fungus, NectriaNectria coccineacoccinea faginata. TheThe fungusfungus killskills patches patches ofof bark bark which which are are subsequentlysubsequently invadedinvaded byby woodwood borers andand decaydecay fungi.fungi. BranchesBranches and sometimes entireentire treestrees maymay breakbreak offoff at these points (Houston(Houston 1981).1981). Beech Beech scale scale is is nativenative toto Europe,Europe, where itit isis also associated with a dieback of beechbeech (See(See section 3.2.).3.2.1 . This insect was accidentallyaccidentally introducedintroduced intointo Nova Scotia, Canada.Canada. It has since spread overover muchmuch ofof the natural rangerange of beechbeech inin eastern Canada and the northeastern UnitedUnited States.States.

4.7. LITTLELEAFLlTTLELEAF DISEASE DISEASE OF OF SHORTLEAF SHORTLEAF PINE. PINE.

The most seriousserious diseasedisease of shortleaf pine,pine, PinusPinus echinata, aa tree indigenousindigenous to the southern United States, is a conditioncondition knownknown as littleleaflittleleaf disease. This condition is prevalent on abandoned cotton growinggrowing landslands whichwhich havehave regeneratedregenerated naturallynaturally toto P. E. echinata. ThisThis conditioncondition waswas firstfirst reportedreported in the 1930s. AffectedAffected trees trees have have shortershorter than normal needlesneedles which oftenoften havehave aa yellowishyellowish castcast andand reducedreduced radialradial andand shootshoot growth. TreesTrees can can diedie withinwithin six six years years of of the the first first appearance appearance ofof symptoms symptoms (Manion(Manion 1991, MistrettaMistretta 1984).19841.

The disease isis thethe resultresult ofof a complexcomplex ofof factors which includeinclude the soil fungus, Phytophthora cinnamomi, low soilsoil nitrogennitrogen andand poorpoor internalinternal soilsoil drainage.drainage. In somesome cases nematodes andand fungifungi of the genusgenus PythiumPythium are associated with diseaseddiseased treestrees..

Littleleaf diseasedisease is present over 35% ofof thethe commercialcommercial rangerange ofof P.E. echinata andand is severesevere enough to influenceinfluence managementmanagement decisions decisions on on 560,000 560,000 haha of forestsforests dominated by E.P. echinata (Mistretta 1984).19841.

4.8. DECLINEDECLINE ANDAND MORTALITY MORTALITY OF OF RED RED SPRUCESPRUCE

Beginning inin thethe late 1970s1970s andand earlyearly 1980s,1980s, aa declinedecline ofof red red spruce,spruce, PiceaPicea rubens, was reported in thethe highhigh elevationelevation forestsforests ofof thethe easterneastern UnitedUnited StatesStates (Sicamma etet alal 1982, Johnson and Sicamma 1983,1983, Friedland etet alal 1984).1984). SymptomsSymptoms include a reductionreduction in thethe numbernumber ofof allall sizesize classesclasses ofof P.E. rubensrubens inin highhigh elevationelevation forests, aa reddeningreddening and loss of needles fromfrom thethe tipstips of branches and necroticnecrotic spotting on the older foliage (Bartuska 1990). SubsequentSubsequent studiesstudies indicateindicate thatthat thethe appearanceappearance of declinedecline symptoms waswas preceded preceded byby a a periodperiod ofof reducedreduced growthgrowth of of both both P. E .rubens rubens and and Abies balsameabalsa mea beginningbeginning in in thethe 1960s.1960s. HardwoodsHardwoods growinggrowing inin thethe samesame standsstands diddid not havehave reduced growth (Hornbeck(Hornbeck and Smith 1985, HornbeckHornbeck et al 1986).1986).

Reams andand PetersonPeterson (1992) (1992) conductedconducted an analysis ofof radial growthgrowth chronologies of PiceaPicea rubens inin Maine, USA andand detecteddetected twotwo periods of growth reductionreduction overover thethe past 60 years.years. InIn thethe earlyearly 1930s,1 930s, decreaseddecreased radial growth followed growthgrowth increasesincreases in the 1920s.1920s. TheThe 1920s 1920s increase increase was was attributed attributed to to the the release release ofof understorey understorey treestrees and recoveryrecovery ofof treestrees followingfollowing anan outbreak outbreak ofof spruce spruce budworm, budworm, Choristoneura Choristoneura

23 fumiferana (Lepidoptera: Tortricidae)Tortricidae) whichwhich killed manymany overstoreyoverstorey trees.trees. The trendtrend of reduced radialradial growthgrowth in the 1960s waswas precededpreceded by a growth increaseincrease inin the 1940s1940s which coincided withwith aa regionalregional declinedecline of BetulaBetula spp.

The possible role ofof climatic influences, winterwinter injuryinjury andand airair pollutionpollution asas causalcausal factors inin thethe declinedecline ofof P. .E. rubensrubens isis discusseddiscussed byby aa numbernumber ofof workersworkers (Sicamma (Sicamma etet al al 1982, JohnsonJohnson andand SicammaSicamma 1983, Friedland etet alal 1984, Pearl etet alal 1991). SeveralSeveral workers suggest that thethe primaryprimary mechanismmechanism ofof pollutantpollutant impactimpact on on.E. P. rubensrubens isis through alteration ofof thethe coldcold hardeninghardening processprocess leading to increased winter injury (Friedland(Friedland et al 1984,1984, FriedlandFriedland andand BattlesBattles 1987,1987, BartuskaBartuska 1990,1990, Adams Adams andand EagarEagar 1992).1992).

Surveys of the condition ofof highhigh elevation spruce-firspruce-fir forestsforests inin thethe easterneastern UnitedUnited States indicated significant involvement of aa numbernumber of bioticbiotic agentsagents inin thethe declinedecline ofof these forests.forests. TheseThese included included periodicperiodic outbreaksoutbreaks ofof the the spruce spruce beetle,beetle, DendroctonusDendroctonus rufipennis (Coleoptera: Scolytidael.Scolytidae), aa dwarfdwarf mistletoe,mistletoe, Arceuthobium pusillum, the root disease fungus,fungus, Armillaria sp,sp, andand aa cankercanker fungus,fungus, ValsaValsa kunzei,kunzei, onon P..E. rubensrubens (Weiss(Weiss and RizzoRizzo 1987).1987). Larvae ofof aa swiftswift moth, moth, Kotscheltellus Kotscheltellus qracilisgracilis (Lepidoptera: (Lepidoptera: Hepialidae) hashas beenbeen foundfound feedingfeeding onon rootsroots of A.A. balsameabalsamea andand P..E. rubensrubens inin highhigh elevation forests in Vermont (Tobi etet alal 1992).1992). ExtensiveExtensive mortalitymortality ofof AbiesAbies fraserifraseri in the southernsouthern AppalachianAppalachian Mountains isis largelylargely duedue toto infestations of thethe introducedintroduced adelgid, Adelges piceaepiceae (Homoptera: Adelgidae) (Dull et alal 1989).1989).

Discovery of the declinedecline of redred sprucespruce was roughlyroughly synchronous withwith that ofof neuartige WaldschädenWaldschaden inin Europe.Europe. This increasedincreased speculation that longlong distancedistance transport ofof anthropogenicanthropogenic pollutantspollutants might bebe aa causalcausal factor.factor. In addition, asas inin Europe, therethere waswas a tendencytendency to lump damage byby aa numbernumber ofof different causal factors across the natural range of PiceaPicea rubens intointo a single typetype of decline which waswas thenthen attributed toto airair pollution.pollution.

4.9. FIRFIR VVAVES WAVES

Mature, eveneven age,age, high elevation forests ofof balsam balsam fir,fir, AbiesAbies balsamea, balsamea, inin easterneastern North America are subject to aa phenomenonphenomenon known as "fir"fir oror regenerationregeneration waves".waves". These are bandsbands ofof diedieback back andand mortalitymortality which occuroccur generallygenerally parallelparallel to the contourcontour of the slopeslope (Fig(Fig 4.3). The dieback graduallygradually progressesprogresses upup slope.slope. In some cases,cases, several parallel bandsbands ofof waveswaves occur on thethe same slope.slope. AA newnew standstand ofof A.A. balsameabalsamea regenerates inin areas where trees havehave beenbeen killed.killed.

Fir waves are believed to be an integral part of thethe dynamicsdynamics ofof highhigh elevationelevation A. balsamea forests.forests. TheyThey areare triggeredtriggered by cold winterwinter windswinds strikingstriking exposedexposed forestforest margins (Sprugel(Sprugel 1976,1976, Sprugel andand Bormann 1981)1981) and serve as an example of synchronous cohort senescencesenescence in temperate forests (Mueller-Dombois(Mueller-Dombois 1986)1986) (See (See alsoalso section 6.1.2.

4.10. YELLOWYELLOW CEDAR CEDAR DECLINEDECLINE

Yellow-cedar, Chamaecyparis nootkatensis, has bright yellow, aromatic heartwood andand isis aa highly prizedprized timber species.species. It is presently the most valuable woodwood grown in the state of Alaska,Alaska, USA. ItsIts decaydecay resistantresistant woodwood allowallow yellow-cedaryellow-cedar to

24 Figure 4.3 - Fir waves onon thethe slopesslopes ofof Lookout Lookout Mountain, Mountain, AdirondackAdirondack Mountains, New New York, York, USA. USA. (Photo (Photo by W.M.by W.M. Cies(a) Ciesla) attain greatgreat longevity.longevity. Despite these characteristics,characteristics, yellowyellow cedarcedar isis experiencing experiencing extensive decline andand mortalitymortality on over 230,000 ha.ha. ofof unmanagedunmanaged forest inin coastalcoastal Alaska (Hennon(Hennon et al 1992).1992).

Decline isis concentratedconcentrated on wet, poorlypoorly draineddrained soilssoils at lowlow elevationselevations (Hennon(Hennon et al 1990a). Yellow-cedarYellow-cedar is is generallygenerally thoughtthought toto bebe toleranttolerant andand wellwell adaptedadapted toto thesethese conditions. Symptoms of decline include death of fine rootlets,rootlets, necroticnecrotic lesionslesions onon coarse roots and boles, reducedreduced radialradial growthgrowth and foliagefoliage thinningthinning throughoutthroughout the crown (Hennon etet alal 1990c).1990c). FineFine rootroot deathdeath maymay bebe the initial symptom thatthat leadsleads to slowslow tree death, oftenoften overover a period of 1515 yearsyears or more. MoreMore thanthan 5050 speciesspecies ofof fungi,fungi, aa species of barkbark beetlebeetle (Coleoptera:(Coleoptera: Scolytidae),Scolytidae), severalseveral nematodesnematodes andand brownbrown bearsbears have been investigated asas possiblepossible causalcausal factors.factors.

Studies on the epidemiology of yellow-cedar decline indicate that aa highhigh raterate ofof mortality beganbegan in about 18801880 andand continuescontinues onon thethe samesame sitessites todaytoday (Hennon(Hennon et alal 1990 a,b).a,b). An averageaverage ofof 65% ofof thethe volumevolume ofof yellow-cedar yellow-cedar hashas beenbeen killedkilled inin affected stands.stands. TreesTrees whichwhich died died over over 100 100 years years ago ago frequently frequently remain remain standingstanding asas snags and this hashas allowedallowed for aa reconstructionreconstruction ofof mortalitymortality patternspatterns overover time.time. Declining stands are notnot composed of cohort (same(same age) individualsindividuals andand mortalitymortality is not synchronous. TreesTrees diedie atat various ages, often between 100100 andand 400 years.years. ThisThis isis wellwell before the 1,0001,000 oror moremore yearsyears ofof ageage whenwhen theythey are are consideredconsidered toto naturallynaturally reach reach aa stage ofof senescence.senescence.

25 Some abioticabiotic factor is thought to bebe the primary stress mechanism. SeveralSeveral are nownow under investigationinvestigation.. TwoTwo hypotheses hypotheses are:are:

A . SoilSoil toxins,toxins, produced during anaerobic decompositiondecomposition in the wet, organicorganic soils damage fine roots of yellow-cedar.yellow-cedar.

B. ClimaticClimatic warming, whichwhich beganbegan aboutabout 100100 years years ago,ago, causescauses more winter precipitation toto fall asas rainrain ratherrather thanthan snow,snow, therebythereby reducingreducing thethe insulating snowpacksnow pack at lower elevations each winter where the shallow, fine roots ofof yellow-cedaryellow-cedar areare exposedexposed andand damageddamaged by freezingfreezing duringduring periods ofof cold continental weather.

The remote location, pristinepristine forest conditionsconditions andand earlyearly onsetonset ofof yellow-cedaryellow-cedar decline suggestsuggest thatthat this isis anan exampleexample ofof aa forestforest declinedecline whosewhose developmentdevelopment isis independent of human activities.

4.11. X - DISEASEDISEASE OFOF PINEPINE ININ SOUTHERNSOUTHERN CALIFORNIA

A condition knownknown as as XX - -DiseaseDisease ofof Pinus Pinus ponderosaponderosa andand P..E. ieffreviijeffreyii hashas been been known from thethe SanSan BernadinoBernadino mountains of southern California, USA since the mid 19501950's.'s. TheThe condition condition is is characterized characterized by by a a yellowingyellowing and and lossloss ofof foliage foliage accompaniedaccompanied by reduced growthgrowth and treetree mortalitymortality (Little 1992).

Studies by Miller et al (1982)(1982) implicatedimplicated ozoneozone (03)(03 ) asas the causalcausal agent for thisthis declinedecline.. DuringDuring the midmid 1970's,1970's, they they recorded recorded 2424 hour hour 030 3 concentrationsconcentrations duringduring MayMay to SeptemberSeptember inin thethe San Bernadino MountainMountainss rranginganging fromfrom a background level between 0.03 andand 0.04 ppmppm toto aa maximummaximum of 0.100.10 -- 0.120 . 12 ppm. ppm. SourceSource of of the the elevated elevated ozoneozone lelevelsvels isis motor vehiclevehicle emissionsemissions fromfrom thethe heavilyheavily populatedpopulated SanSan BernadinoBernadino Valley.Valley.

These emissions areare trappedtrapped byby thethe mountainsmountains and reactreact with sunlightsunlight toto produceproduce 03.0 3 , .EP.. ponderosaponderosa waswas foundfound toto be sensitivesensitive toto 24 hour 0033 levelslevels ofof 00.05.05 - 0.06 ppm.ppm. FoliarFoliar injury andand prematurepremature leafleaf fallfall causedcaused decreaseddecreased photosynthetic capacitycapacity resultingresulting inin reducreduceded increment,increment, seed productionproduction and nutrient retention.retention. TheThe pines pines became became moremore susceptible to rootroot diseasedisease causedcaused byby thethe fungusfungus HeterobasidiumHeterobasidium annosumannosum ((= = FomesFomes annosus) and thethe barkbark beetle,beetle, Dendroctonus Dendroctonus brevicomisbrevicomis (Coleoptera: (Coleoptera: Scolytidae).Scolytidae). Mortality ratesrates reached 22 - 33%% in some years.years. A long term effect ofof thethe declinedecline isis the replacement ofof the pinepine dominateddominated forest byby moremore 030 3 toleranttolerant speciesspecies suchsuch asas Libocedrus decurrensdecurrens andand AbiesAbies concolorconcolor (Little(Little 1992).1992).

26 CHAPTER 55

AFRICA

Forest decline events in thethe forestsforests of thethe AfricanAfrican continentcontinent are notnot wellwell documented. Hovvever,However, aa searchsearch of bothboth the publishedpublished literature andand of reports by national research institutes andand internationalinternational consultantsconsultants indicatesindicates that thethe phenomenonphenomenon isis widespread. TheThe followingfollowing sections sections detail detail case case histories histories of'of decline decline fromfrom Benin,Benin, Botswana,Botswana, Cote D'Ivoire,D'ivoire, TheThe Gambia,Gambia, the SahelSahel Region ofof West Africa, TheThe Sudan,Sudan, South Africa, Tanzania, Uganda, Zambia and Zimbabwe (Table 5.1).

5.1. DECLINEDECLINE OFOF AZADIRACHTAAZADIRACHTA INDICAINDICA ININ THETHE SAHELSAHEL

Neem, AzadirachtaAzadirachta indica,indica, isis anan importantimportant multipurpose treetree nativenative toto the IndianIndian subcontinent (Fig(Fig 5.1).5.1). The treetree is highlyhighly valued as a shadeshade tree,tree, for fuelfuel wood,wood, construction andand locallocal crafts. TheThe fruit, fruit, foliage foliage and and branches branches have have aa numbernumber ofof medicinalmedicinal and insecticidal propertiesproperties (National(National ResearchResearch Council 1992).1992). Neem has been widely planted in thethe tropicstropics andand isis anan especially especially importantimportant speciesspecies forfor shade,shade, forestforest andand windbreak plantingsplantings inin thethe westwest AfricanAfrican Sahel. Sahel.

During November 1990, neemneem expressing symptoms ofof declinedecline were reportedreported fromfrom south central Niger.Niger. TheThe conditioncondition was was subsequently subsequently found found to to be be widespread widespread in in NigerNiger and and has also been confirmedconfirmed in several neighbouring countries includingincluding thethe Cameroon,Cameroon, Chad,Chad, Mali and Nigeria (Boa 1992, USUS AID/Niger 1992).

The most conspicuous symptom ofof neemneem decline is a loss ofof older foliage.foliage. ThisThis isis often precededpreceded by aa yellowing ofof olderolder leaves.leaves. TheThe foliage foliage lossloss gives gives thethe normallynormally densedense crowns anan openopen appearanceappearance withwith clumpsclumps ofof foliagefoliage occurringoccurring atat thethe branchbranch apices.apices. InIn advanced cases, onlyonly aa smallsmall tufttuft of foliage remains atat the branch tiptip.. ThisThis conditioncondition hashas been describeddescribed asas a a "giraffe"giraffe neck"neck" (Fig.(Fig. 5.2).5.2). NewNew foliarfoliar growthgrowth isis abnormallyabnormally smallsmall andand often hashas a yellowyellow castcast (Boa(Boa 1992).1992).

Other symptoms associatedassociated withwith neemneem declinedecline includeinclude shortenedshortened internodesinternodes nearnear the apex ofof thethe branches,branches, exudationexudation ofof gumgum fromfrom branchbranch tips,tips, branch branch diebackdieback andand treetree mortality.

Some workers have reported the occurrenceoccurrence ofof aa deepdeep redred colourcolour inin thethe cambiumcambium layer on branches greater than one cm. inin diameter as being associated wwithith thethe decline.decline. There is disagreementdisagreement however if this is a symptomsymptom of thethe declinedecline oror a normalnormal characteristic ofof thethe treetree (Hodges(Hodges andand BeattyBeatty 1992)1.1992)' .

When initially discovered,discovered, declinedecline ofof neemneem waswas confusedconfused withwith damage damage causedcaused byby a scalescale insect,insect, Aonidiella orientalisorientali s (Homoptera:(Homoptera: Diaspididae),Diaspididae), whichwhich attacksattacks the the leaves leaves and and young stems of neem.nee m . ThisThis insectinsect waswas firstfirst recorded recorded onon neemneem inin AfricaAfrica inin thethe CameroonCameroon

, RecentRecent observatiobservationson s in IndoneIndonesiasia aandnd thethe SudanSudan iindicatendi cate tthathat indiindividualvidu al neemneem tretreeses hhaveave a cambiumcambium with aa deep red colour.col our. TheseThese treestrees diddid not no texpress ex press syn-iptoms symptom s ofof declinedec li ne (Ciesla,(Cies la , unpublishedunpu blished data).data).

27 Figure 5.15.1 - Foliage ofof a healthy neemneem in Niamey, Niger. Niger. (Photo (Photo by by W.M. W.M. Ciesla) Ciesl al

28 '-,\ l ... .-:. ~~ • ~ ,t;

Figure 5.25.2 - Declining neemneem inin Niamey,Niamey, NigerNiger with with "giraffe neck" symptoms.symptoms. (Photo by W.M.W .M . Ciesla)Ciesla)

29 inin 1972 andand laterlater inin thethe SudanSudan where itit isis believedbelieved toto havehave beenbeen introduced on citruscitrus trees. During thethe 1980s thethe insectinsect spreadspread intointo thethe LakeLake ChadChad BasinBasin wherewhere itit causedcaused heavyheavy damage (National(National ResearchResearch Council Council 1992). 1992). Infestations cause the foliage to have a burnt appearance. RecentRecent investigationsinvestigations concludedconcluded thatthat the the neem neem scalescale andand thethe neem neem declinedecline are twotwo distinctdistinct conditionsconditions andand thethe neemneem scalescale is not involvedinvolved asas a causalcausal factor in thethe decline of neem (Batra 1991, BoaBoa 1992).

The occurrence andand severityseverity ofof declinedecline roughlyroughly followsfollows the following patternpattern (Ciesla(Ciesla 1993a):

A. Trees of all ages are affected.

B. Single treestrees tendtend toto have fewer symptoms than treestrees growinggrowing inin groups.groups.

C. Most severe symptoms appear Inin forest plantings followed by windbreaks.

D. Trees growing inin villages tendtend to bebe leastleast affectedaffected althoughalthough declinedecline symptoms do appear,appear, especially areas whichwhich have heavyheavy useuse suchsuch asas outdoor market places.places.

E. Trees which havehave beenbeen pollarded tend to havehave healthyhealthy foliagefoliage andand densedense crocrowns.w ns.

F. At thethe presentpresent time, treetree mortalitymortality attributableattributable toto thethe decline decline isis minimal.minimal.

There is some question as toto whether thethe observedobserved decline is a new phenomenonphenomenon or whether itit hashas beenbeen goinggoing onon forfor somesome timetime andand onlyonly detecteddetected recently.recently. There areare photos of neemneem plantationsplantations in thethe SahelSahel exhibitingexhibiting thinthin crownscrowns andand abnormallyabnormally smallsmall foliage dating asas farfar backback asas 1963.1963. (Centre(Centre TechniqueTechnique ForestierForestier Tropical 1963)

At presentpresent therethere isis nono evidenceevidence ofof aa pathogenpathogen associatedassociated with thisthis decline.decline. It isis currently believedbelieved to bebe the result ofof oneone oror moremore environmentalenvironmental stresses. TheseThese couldcould include long dry periods,periods, competitioncompetition forfor availableavailable moisture,moisture, useuse ofof weakenedweakened plantingplanting stock, poorpoor plantingplanting techniquetechnique andand localizedlocalized soil nutrient deficiencies. ThereThere isis alsoalso somesome evidence of a long term trend in reduced precipitation which maymay havehave stressedstressed trees over a widewide areaarea (Hodges(Hodges and BeattyBeatty 1992).1992). In addition, neemsneems planted inin thethe SahelSahel areare believed toto be fromfrom a narrownarrow genetic basebase withwith little variability in susceptibility toto stress.stress. Several fungi, includingincluding NigrosporaNigrospora sphaericasphaerica andand CurvulariaCurvularia eragrostidiseragrostidis havehave beenbeen recovered from neems with symptomssymptoms ofof declinedecline butbut theythey areare secondary,secondary, recordedrecorded fromfrom other trees andand cropscrops andand notnot knownknown toto cause cause serious serious damage.damage.

5.2. DIEBACKDIEBACK OF OF ACACIAACACIA NILOTICA NILOTICA ININ THETHE SUDAN.SUDAN.

Sunt, Acacia nilotica, isis the mostmost valuablevaluable timber producingproducing species in the northern Sudan. It isis widelywidely usedused forfor railroadrailroad sleepers,sleepers, structuralstructural lumber,lumber, fuelfuel woodwood andand otherother purposes. This treetree occursoccurs inin pure, even ageage standsstands Whichw hich havehave beenbeen artificiallyartificially regenerated byby directdirect seeding inin flood plainsplains and remnants of oxbow lakeslakes alongalong majormajor river systems (Fig 5.3). AlongAlong thethe BlueBlue NileNile andand itsits tributaries,tributaries, A.A. niloticanilotica plantationsplantations areare managed intensivelyintensively on 20 or 3030 yearyear rotations.rotations.

30 Decline oror diebackdieback ofof AA.. nilotica was reported as early as thethe 1930s and attributed to attackattack byby a acambium cambium and and wood wood boring boring beetle, beetle, Sphenoptera Sphenoptera chalcicroachalcicroa arenosaarenosa (Coleoptera: Buprestidae) (Peake(Peake 1956)1956).. DuringDuring thethe 11980s, 980s, declinedecline was detecteddetected inin highhigh value plantationsplantations alongalong thethe BlueBlue NileNile betweenbetween Sennar Sennar Reservoir Reservoir andand ErEr RoseiresRoseires Dam.Dam. Occurrence ofof decline increasedincreased followingfollowing aa majormajor floodflood inin 19881988 which deposited up to 2 meters of silt in some plantations. TheseThese plantationsplantations are thethe country's primaryprimary source of railroad sleepers andand thethe declinedecline isis considered to to bebe thethe most importantimportant forestforest healthhealth problem inin thethe Sudan (EI(El Atta Atta 1988).

Decline isis expressedexpressed asas an an overall overall thinning thinning of of the the crown. crown. Other symptoms includeinclude abnormally small foliage, branch dieback and broken branches (Fig(Fig 5.4).5.4). ThereThere maymay bebe some recovery during the rainy season but symptoms reappear withwith the subsequentsubsequent dry season. TheThe declinedecline isis progressiveprogressive andand eventually leadsleads to treetree death.death.

The most abundant biotic factor associatedassociated withwith the declinedecline is aa complexcomplex ofof cambium andand wood boring beetles which attack andand eventuallyeventually killkill thethe branchesbranches ofof declining trees. AtAt least least two two species species are are involved; involved; a a buprestid, buprestid, presumably presumably Sphenoptera Sphenoptera chalcicroa arenosa (Fig 5.5).5.5), andand aa largelarge cerambycid. In addition, there isis evidenceevidence of aa stem boringboring lepidoptera.lepidoptera. Some areasareas ofof declining trees also have beenbeen defoliated byby unidentified lepidoptera.lepidoptera.

Ciesla (1993c)(1993c) proposes thethe followingfollowing "working hypothesis"hypothesis" toto explainexplain thethe eventsevents leading upup toto the occurrence of declinedecline of AcaciaAcacia niloticanilotica inin thethe Sudan:Sudan:

Predisposing factors factors -- A.A. nilotica occurs in pure, even age "cohort" plantations.plantations. This standstand structurestructure hashas beenbeen perpetuatedperpetuated andand intensifiedintensified byby thethe managementmanagement system presently inin place.place. Use of seedseed of unknownunknown oror mixedmixed originorigin in thethe establishment of some plantations may have resulted in establishment of certaincertain provenances ofof A.A. niloticanilotica in areasareas to to whichwhich theythey areare notnot suited.suited. While the soils of these sites may be relatively richrich inin nutrients, they are constantly changing with every year's deposit of silt.silt. Silt depositiondeposition gradually reduces thethe depth of thethe oxbow lakes. ConsequentlyConsequently theythey holdhold lessless water andand tend to dry out earlier.earlier. OverOver time they areare no longer suitablesuitable forfor growthgrowth of A. nilotica.nilotica. Periodic droughts areare aa more or less regularregular eventevent inin thethe SudanSudan.. Silt deposition andand periodic drought stressstress affects thethe larger,larger, olderolder standsstands toto aa greatergreater extentextent becausebecause theythey therethere isis moremore competition forfor availableavailable moisture.moisture. Any ofof thesethese factorsfactors couldcould contributecontribute to premature senescence ofof A. niloticanilotica andand predisposepredispose treestrees toto decline.decline.

Inciting factors -- The most likelylikely incitantincitant forfor thethe currentcurrent episodeepisode ofof declinedecline isis the massive floodingflooding andand siltsilt depositiondeposition which occurredoccurred in 1988.1988. Outbreaks ofof defoliating insect(s) and periods of drierdrier than normalnormal weatherweather couldcould alsoalso inciteincite decline.

Contributing factors-factors -TheThe complexcomplex ofof cambiumcambium andand woodwood boringboring beetlesbeetles which areare invading thethe affectedaffected trees are consideredconsidered to to bebe contributing contributing factorsfactors.. InsectsInsects ofof thethe families Buprestidae andand CerambycidaeCerambycidae typically typically attackattack treestrees which havehave beenbeen recently killed, howeverhowever somesome species attack livingli ving trees whichw hich havehave beenbeen severely weakened byby drought or site relatedrelated factors.factors. The role of rootroot diseasesdiseases inin thethe decline complexcomplex isis presently not known.

31 Figure 5.35.3 - HealthyHealthy Acacia nilotica plantation in the remnantremnant ofof anan oxbowoxbow lakelake along thethe Blue Blue Nile Nile in inthe the Sudan Sudan (Photo (Pho toby by W.M. W.M. C;eslal .

Figure 5.45.4- - AcaciaAcacia nilotica nilotica in in varying varying stages stages of of decline decline near near Ed Ed Damazin,Damazin, thethe SudanSudan (Photo by W.M. Ciesla).Ciesla).

32 Figure 5.5 - Buprestid larva and damage inin branchbranch ofof aa decliningdeclining AcaciaAcacia niloticanilotica in thethe SudanSudan (Photo !Phot oby b yW.M. W.M. Ciesla). Ci esla).

5.3. DIEBACKDIEBACK OFOF TERMINALIATERMINALIA IVORENSISIVORENSIS ININ COTECOTE D'IVOIRE AND GHANA

Terminalia ivorensis is a tropical hardwoodhardwood indigenousindigenous toto CoteCote D'Ivoire,D'ivoire, Ghana Ghana andand other West African countries in areas whichwhich receivereceive fromfrom 11501150 toto 1900 mm. of rainfallrainfall per year and have oneone distinctdistinct dry season.season. ThisThis speciesspecies becamebecame a popular treetree forfor reforesting cutcut-over-over lands durduringing the 1950s andand 60s.60s. TheThe tree tree produces produces aa goodgood lumberlumber forfor generalgeneral construction, has a highhigh growthgrowth rate,rate, isis easyeasy toto propagate propagate andand hashas otherother desirable desirable silviculturalsilvicultura! characteristics.charac teristics.

Growth in plantations of thisthis speciesspecies was apparently normal untiluntil the early 1970s when dieback waswas observedobserved in plantations in CoteCote D'IvoireD'ivoire and Ghana. Symptoms,Symptoms, asas described byby BrunckBrunck and MalagnouxMalagnoux (1976) andand Ofosu-AsiedoOfosu-Asiedo andand CannonCannon (1976),(1976). included branch diedieback back beginningbeginning atat the the crown crown apex,apex, chlorotic chlorotic andand wiltingwilting foliage,foliage, crown thinning andand sapwoodsapwood staining.staining. Other symptoms less frequently associated withwith thethe dieback, were barkbark necrosis,necrosis, exudationexudation of a black gummy liquidliquid from the trunk,trunk, development of epicormicepicormic branchesbranches and attacks byby barkbark beetlesbeetles and wood boringboring insectsinsects (Families(Families CerambyCerambycidae,cidae, Platypodidae and Scolytidae).Scolytidae).

Studies conduconductedcted in Cote D'IvoireD'ivoire indicated that therethere waswas aa markedmarked reductionreduction inin foliar nutrient contentcontent associatedassociated with treestrees expressingexpressing dieback. ThisThis ledled toto speculationspeculation that thethe diebackdie back was caused by a malfunction ofof thethe rootsroots oror vascularvascular system (Brunck(Brunck and MalagnouxMalagnoux 1976).

Studies in Ghana indicateindicate thatthat therethere werewere nono bioticbiotic agentsagents whichwhich could be identifiedidentified as the cause of ththee dieback. OnsetOnset ofof dieback dieback appearedappeared to bebe correlatedcorrelated withwith sixsix yearsyears

33 of drought whichwhich beganbegan in 1969,1969, followingfollowing aa yearyear ofof exceptionallyexceptionally highhigh precipitation.precipitation. IncidenceIncidence ofof ground fires were also shownshown toto have aa deleteriousdeleterious effecteffect on thethe survivalsurvival rate of I.T. ivorensisivorensis (Cannon(Cannon et al nono date).date).

5.4. DIEBACKDIEBACK OF OF CASUARINA CASUARINA EQUISETIFOLIA EQUISETIFOLIA ININ BENIN.BENIN .

Dieback and decline of CasuarinaCasuarina equequisetifoliaisetifolia plantationsplantations is described from the People's RepublicRepublic of of BeninBenin byby KaupenjohannKaupenjohann and and Zech Zech (1988). (1988). Symptoms are aa slow, progressive diedieback ba ck leading leading to to tree tree mortality. mortality. Symptoms occur in groups of trees in 5 to 10 year old plantations on coastal sandy sitessites inin theirtheir thirdthird rotation of C.~. equisetifolia.equisetifolia.

Studies on cacausesuses ofof thethe condition indicate shallow rootroot developmentdevelopment duedue toto aa highhigh water tabletable inin thethe rainyrainy season.season. In addition,addition, analysisanalysis ofof soils showedshowed increasedincreased acidification andand lowlow levelslevels of nitrogen, phosphorus,phosphorus, potassium and calcium.calcium. Foliar content of phosphorus and potassium waswas 00.04%.04% and 0.28% respectivelyrespectively forfor symptomaticsymptomatic treestrees and 00.21`)/0.21 % and and 0.85% 0.85% for healthyhealthy trees.trees.

5.5. DECLINEDECLINE OFOF OCOTEAOCOTEA BULLATABULLATA ININ SOUTHSOUTH AFRICA.AFRICA.

StinkwoodStinkwood,, OcoteaOcotea bullata,bullata, isis thethe mostmost economicallyeconomically importantimportant indigenousindigenous treetree species inin thethe forforestsests of thethe southernsouthern CapeCape and is widely usedused in furniturefurniture production.production. This tree isis thethe dominantdominant componentcomponent ofof thesethese forestsforests and and regenerates regenerates easilyeasily throughthrough coppice. StinkwoodStinkwood hashas aa thickthick barkbark whichwhich makesmakes itit firefire resistant.resistant.

A group diebackdie back of stinkwood occursoccurs in portions of southernsouthern Cape forests.forests. ThisThis dieback is associatedassociated with thethe rootroot fungus, fungus, Phytophthora Phytophthora cinnamomi,cinnamomi, waterlogging,waterlogging, fluctuating waterwater availability availability and and droughtdrought stress.stress . P..E. cinnamomi cinnamomi was was recovered recovered fromfrom areasareas of obviousobvious diebackdieback as well asas fromfrom areasareas ofof healthyhealthy forestforest wherewhere nono diebackdieback waswas observed. ThisThis fungusfungus hashas thethe characteristicscharacteristics ofof aa secondarysecondary pathogenpathogen in that affectedaffected stands and trees have a history of stressstress oror disturbance. DiebackDieback isis worseworse inin indigenousindigenous forests which areare disturbeddisturbed byby roadroad buildingbuilding oror plantationplantation forestryforestry activities.activities. These activities frequently affectaffect naturalnatural drainagedrainage patternspatterns and may assist in introducingintroducing the fungus into thethe soilsoil (Liibbe(Lubbe andand GeldenhuysGeldenhuys 1990, LObbeLubbe andand MostertMostert 1991).

5.6. DECLINE OFOF PTEROCARPUSPTEROCARPUS ANGOLENSIS ANGOLENSIS IN IN BOTSWANA,BOTSWANA, ZAMBIAZAMBIA ANDAND ZIMBABWE.

Pterocarpus angolensis,angolensis, locallylocally knownknown as muninga,muninga, mtumbati, mukulu, mukwamukwa oror bloodwood, is a common tree of savannas ofof South Central Africa.Africa. It is found inin Angola,Angola, Botswana, Malawi, Mozambique,Mozambique, Tanzania,Tanzania, ZambiaZambia and Zimbabwe where it is highly prized for furniturefurniture production,production, doors,doors, joinery,joinery, turnery,turnery, carvingscarvings andand aa varietyvariety ofof otherother purposes.purposes.

A decline of thisthis tree,tree, whichwhich hashas occurredoccurred inin portionsportions ofof Botswana,Botswana, ZambiaZambia andand Zimbabwe, is reviewedreview ed by Piearce (1979)(1979) and Piearce and and Calvert Calvert (1992). (1992). The condition isis characterized bbyy wiltingwilting and chlorosis of foliagefoliage followedfollowed byby defoliation,defoliation, progressiveprogressive diebadiebackck andand formationformation of epicormicepicormic shootsshoots leadingleading toto treetree deathdeath inin aa singlesingle seasonseason (Fig.(Fig. 5.6). SeriousSerious losseslosses firstfirst causedcaused concernconcern during the late 1950s1950s andand afterafter 1010 years, years, upup toto 60% of thethe merchantablemerchantable trees were affected within aa 4040 kmkm radiusradius ofof VictoriaVictoria Falls.Falls.

34 Figure 5.65.6 - Decline. Decline of Pterocarpusof Pterocarpus anqolensis angolensis in Zambia. in Zambia. (Photo (Photoby G.D. by G.D.Piearce, Piearce, Courtesy Courtesy of O.O. Shakacite,Shakacite, ZambiaZambia ForestForest Department, Kitwe, Zambia)Zambia)

35 The problem waswas originally describeddescribed as as "mukwa ''mukwa blight" blight" oror "quick decline" of unknown cause. StudiesStudies inin ZimbabweZimbabwe led toto the tentative conclusionconclusion that drought was primarily responsible for the decline.decline.

Research in in Zambia, Zambia, beginning beginning in in 1 1973, 973, led led to to thethe discoverydiscovery ofof a vascular wiwiltlt disease ofof .E.P. anqolensisangolensis caused by the soilsoil borneborne fungusfungus FusariumFusarium oxysporumoxysporum (Piearce(Piearce 1979). However,However, notnot all all casescases ofof declinedecline of this species cancan bebe attributedattributed toto infectioninfection by this fungus.fungus. ForFor example,example, mukwamukwa wiltwilt is is localizedlocalized andand most prevalentprevalent in young (up toto 30 years) trial plantings wherewhere thethe spread ofof thethe fungusfungus isis favouredfavoured byby monoculture monoculture conditions. However,However, deathsdeaths ofof many many maturemature treestrees inin naturalnatural woodlandswoodlands containingcontaining this species havehave occurredoccurred whichwhich could not be attributed ententirelyirel y toto.E. F. oxysporum.oxysporum.

Studies inin Matabeleland by a teamteam ofof researchersresearchers from from thethe UniversityUniversity of Zimbabwe indicate that thethe wiltwilt disease disease causedcaused byby F..E. oxysporum should bebe regarded asas aa contributing contributing factor in "stand"stand levellevel dieback"die back" and thatthat drought, frostfrost,, firefire andand infections by a mistletoe, Loranthus sp. were seen as predisposing oror incitinginciting factors.factors. In additionaddition toto slowslow growth and establishmentestablishment difficulties,difficulties, thisthis declinedecline is considered toto be aa furtherfurther disincentivedisincentive toto thethe use of this speciesspecies in industrialindustrial forestforest plantations.plantations.

5.7. DIEBACKDIEBACK AND AND MORTALITY MORTALITY OF OF TROPICAL TROPICAL RAIN RAIN FORESTS FORESTS ININ UGANDA.UGANDA.

Dieback andand mortalitymortality of severalseveral tropical rain forest speciesspecies was recorded in the KibaleKibale ForestForest adjacentadjacent to to exoticexotic coniferconifer plantations.plantations. WithinWithin aa restrictedrestricted areaarea of mortality,mortality, nearly all mature Newtonia buchananii hadhad dieddied byby 1984 and nearlynearly 90% ofof LovoaLovoa swynnertoniswynnertoniii and 45%45% of thethe AningeriaAningeria altissima hadhad dieddied byby 1986.1986. TwoTwo associated associated canopy trees, Mimusopts bagshawi and Celtis africanaafricana hadhad llowow rates of mortality.

The factor most highly correlatedcorrelated with thethe diebackdie back waswas thethe downslopedownslope proximityproximity to exoticexotic coniferconifer plantationsplantations ofof Pinus Pinus caribaea,caribaea, P..E. patula, P..E. radiataradiate andand CupressusCupressus lusitanica. There isis no explanationex planation givengiven asas toto why the proximityproximity ofof exoticexotic coniferconifer plantations would causecause diebackdie back and tree mortality in the nativenative forestforest (Struhsaker(Struhsaker etet alal 1989)

5.8. DIEBACKDIEBACK ANDAND MORTALITY MORTALITY IN IN MANGROVES MANGROVES ONON THETHE GAMBIAGAMBIA RIVER.RIVER.

Jimenez etet alal (1985)(1985) review an epidemic diedieback back andand mortalitymortality ofof mangrovemangrove forestsforests along the Gambia River.River. The mortality waswas attributedattributed toto aa gallgall causingcausing fungus,fungus, similarsimilar toto Cyclindrocarpon didymum whichwhich occursoccurs in in mangrovesmangroves inin Florida,Florida, USAUSA (Teas(Teas andand McEwanMcEwan 1982)1982).. RhizophoraRhizophora spp.spp. waswas thethe primaryprimary groupgroup ofof treestrees affected.affected.

Work by other investigators indicates that the mortality maymay bebe duedue to hydrologicalhydrological changes in the river basin (Jimenez 1985). TheThe GambiaGambia watershedwatershed hashas aa seasonalseasonal climate which isis dominateddominated byby aa 7 7 monthmonth drydry period.period. This allows for aa buildupbuildup of salinitysalinity inin thethe soils and mangroves.mangroves. Salinity isis flushed during the rainy seasonseason byby freshfresh water. water. MortalityMortality has beenbeen attributedattributed toto aa droughtdrought whichwhich occurred fromfrom 19721972 -1976-1976.. ChangesChanges inin thethe tidaltidal regimeregime havehave alsoalso beenbeen suggestedsuggested asas a a possible possible cause cause of of the the mortality mortality.. The high incidence of gall fungus infection maymay bebe relatedrelated to stressstress inducedinduced byby hydrologichydrologic changes.changes.

36 5.9. DIEBACKDIEBACK OF OF PINUSPINUS PATULA,PATULA, SAOSAO HILLHILL PLANTATIONS,PLANTATIONS, TANZANIATANZANIA

In 1975, TheThe WorldWorld BankBank financed an afforestationafforestation programme onon 33,00033,000 ha. at Sao HillHill,, located in the highlands of southern Tanzania. TheThe programmeprogramme was designed toto provide a source of rawraw materialmaterial forfor domesticdomestic productionproduction ofof pulp, pulp, paper paper and and lumber.lumber. Several speciesspecies ofof Eucalyptus and Pinus werewere planted. TheThe predominantpredominant speciesspecies plantedplanted was P..E. patula,patula, aa pinepine nativenative toto MexicoMexico whichwhich hashas beenbeen widelywidely plantedplanted inin easterneastern andand southern Africa.

One of the problems encountered in thethe implementationimplementation of this programmeprogramme was the occurrence of dieback.die back. OnOn.E. P. patula,patula, diebackdie back waswas confinedconfined toto thethe terminalterminal leaderleader which is killed backback toto thethe mostmost recentrecent whorlwhorl of lateral branches. Dieback results inin thethe formationformation of crooked stemsstems oror treestrees withwith multiple multiple leaders leaders and and aa subsequentsubsequent reductionreduction inin thethe volumevolume of useable timber.timber. TreeTree mortality directlydirectly attributableattributable to to this this dieback dieback was was minimal minimal (Cannon(Cannon 1985 a,b).a,b).

An early investigation ofof thethe problemproblem byby WaringWaring (1982)(1982) suggestssuggests thatthat thethe diebackdie back is thethe resultresult of thethe combined effectseffects of soisoil,l, light,light, water and competitioncompetition fromfrom weeds. HeHe recommended completecomplete cultivation,cultivation, plantingplanting of treestrees earlyearly duringduring thethe rainyrainy season, season, application of fertilizers, removalremoval ofof competingcompeting weedsweeds andand thinning at ageage 5 to 77 yearsyears as a means of reducing incidence of dieback.die back.

Later studiesstudies byby CannonCannon (1985 a,b)a,b) indicatedindicated thatthat dieback dieback waswas rare rare inin standsstands lessless thanthan 55 yearsyears old.old. However between ages 5 and 10,10, incidenceincidence ofof diebackdieback increasedincreased markedly. AfterAfter age age 10,10, incidence incidence ofof decline decline continuedcontinued toto increase,increase, butbut atat aa slowerslower rate.rate. Analyses of soils showed that incidenceincidence ofof diebackdieback waswas highesthighest onon soilssoils with aa highhigh bulkbulk density in the B horizon or with ferriciteferricite oror saprolitesaprolite parentparent rockrock nearnear the surface. TheseThese conditions inhibitinhibit rootroot developmentdevelopment and and predisposepredispose terminalterminal leadersleaders to dehydration duringduring extended droughts. PruningPruning ofof treestrees appearedappeared toto addadd anan additionaladditional stress.stress.

Proposed managementmanagement solutions solutions toto this diebackdie back problemproblem resultingresulting fromfrom thesethese studies included:

A. Avoid plantingplanting landland withwith aa problematicproblematic BB horizon.horizon.

B. Ripping thethe B horizon wherewhere it isis shallowshallow enoughenough andand wherewhere topographytopography permits.

C. Use of speciesspecies and provenances adaptedadapted toto periodicperiodic lossloss ofof soil moisture.

D. Changes in pruning practices.practices.

37 TABLE 5.15.1

SUMMARYSUMMARY OFOF FORESTFOREST DECLINEDECLINE EVENTS BY POSSIBLE CAUSAL FACTORSFACTORS AFRICA +•

DECLINEDECLINE EEVENTVENT FOREST PREDISPOSINGPREDISPOSING INCITING CONTRIBUTING SITUATION'SITUATION • FACTORSFACTORS FACTORS FACTORS

AzadirachtaAzadirachta PE LLongong dry seasonseason RainfRainfallall deficdeficitit SSecondaryecondary ffungiungi indicaindica Competition SSoiloil compactcompactionion (Sahel,5(Sahel, 5.1.).1 .) PoPooror planting technique NNarrowarrow geneticgenetic base

Acacia PI Senescence DrDroughtought InsectInsect attack nilotfeanilotica Changing FlFloodingooding andand BBuprestidsuprestids (The SudSudan,an, 5.2) habitat siltationsiltation Cerambycids DefoliationDefol iation

TermTermina//ainalia PI Nutrient Drought Bark beetles ivorensis deficiency FFireire Wood borersborers (Cote OD'Ivoire'ivoire & Sap stain Ghana, 5.3.) fungus

Casuarina PE HHighigh water tabletable UnknownUnknown None given equisetifo/iaequisetifolia Nutrient (Benin, 5.4) deficiency

Ocotea bullata N FluctuatingFl uctuating ChangesChanges inin Phytophthora (South AfAfrica,ri ca, 5.5.15.5.) water availabilityavailability water tabletable cinnamomi due to loggino,loggi ng, etc

Pterocarpus N Drought'Dr ought·· • Fungus, angolensisangolensis PI FrostFrost Fusarium ((Botswana,Botswana, ZambiaZambia FireFire oxysporium ZZimbabwe,imbabwe, 5.6.)5.6.) Mistletoe, Loranthus sp.sp.

TrTropicalopical N UnknownUnknown UUnknownnknown UnknownUnknown rainforests ((Uganda,Uganda, 5.7.15.7.)

MangrovesMangroves N LongLong drydry seasonseason DroughtDrought Gall fungusfungus (The(The Gambia,Gambia, 5.8.)5.8.) Soil salinitysalinity TidalTid al changechange

Pinus patula PPEE DenseDense rockyrocky DroughtDrought None listedlisted (Tanzania,(Tanzania, 5.9.)5.9.) soils

•* Causal fafactorsctors areare sumsummarizedmarized accordingaccording toto the predisposing, inincitingci ting and contcontributingributing factorsfa ctors conceptconcept ofof SinclairSincla ir and ManionManion (see sectsectionion 2.3.2).

*" *N =N natural= natural forest, forest, PI PI= plantation= plantati onwith with indigenous indigenous species, species, PE PE = plantationplantation with w ith exotic exoti cspecies. species.

**** *. ListedListed asas "predisposingnpredisposing oror inciting"inciting " factors.factors.

3838 CHAPTER 66

ASIA

A number of declinedecline events have beenbeen reported reported from from the the forests forests of of Asia.Asia. WhileWhile these events have not beenbeen as widely reportedreported in the scientific literatureliterature asas havehave events in Europe,Europe. North America andand thethe PacificPacific Region,Region. theythey havehave been ththee subject of considerable localloCal concern.concern. CaseCase historieshistories fromfrom Bangladesh,Bangladesh. Bhutan,Bhutan. China,China. JapanJapan andand India areare presentedpresented inin thethe following sectionssections andand areare summarized in tables 6.1 andand 6.2.6.2.

6.1. DECLINEDECLINE ININ JAPAN.JAPAN.

6.1.1 - DECLINEDECLINE OF CRYPTOMERIACRYPTOMERIA JAPONICA JAPONICA - - CryptomeriaCryptomeria japonica is anan important forestforest plantationplantation speciesspecies inin JapanJapan where it is used in the productionproduction ofof highhigh quality wood products.products. InIn the the Kanto Kanto Plains Plains ofof thethe centralcentral portionportion ofof the the island island ofof Honshu,Honshu. this species has been plantedplanted near religiousreligious shrinesshrines andand temples temples and and on on farms farms for for woodlots woodlots and windbreaks.

Dieback and decline of Cryptomeria japonica began toto appear duringduring thethe latelate 1970s and 1980s (Morikawa et al 1990). AA reportreport byby YokoboriYokobori (1981)(1981) indicatesindicates thatthat thethe declinedecline is widespread.widespread. Damage occursoccurs primarily in farmfarm windbreakswindbreaks andand smallsmall standsstands nearnear religious shrines on thethe KantoKanto Plains.Plains. Soil compaction,compaction. deposition of airair pollutants,pollutants. especially sulphur dioxide.dioxide, and fluctuations inin waterwater tabletable were were suggested suggested asas possiblepossible causal factors.

Studies by Inoue (1988) indicatedindicated that incidenceincidence of declinedecline waswas higherhigher inin smallsmall stands than in largelarge stands. ThereThere appearedappeared toto bebe nono relationshiprelationship betweenbetween incidenceincidence ofof decline,decline. stem diameter or age. However,However. therethere werewere indicationsindications thatthat dense dense standsstands hadhad aa higher proportion ofof decliningdeclining trees.trees.

Further studiesstudies by Waki (1988) indicatedindicated that therethere waswas considerableconsiderable variation in decline incidence between stands with aa tendency for symptomssymptoms toto bebe mdstmo'st prevalentprevalent onon sites with lowlow phph soils.soils.

Morikawa et alal (1990) indicateindicate thatthat crown crown damage damage isis observedobserved only in mature trees and height growthgrowth isis reduced. SymptomsSymptoms includeinclude crowncrown thinning,thinning. beginningbeginning inin thethe upperupper crown and gradually spreading toto thethe entireentire crown.crown, toptop dieback andand treetree mortality.mortality. TheyThey report that allall maturemature~. C. japonicajaponica within aa radiusradius ofof 6060 kmkm fromfrom central central Tokyo Tokyo have have died. died. The reason for this declinedecline hashas notnot beenbeen determined.determined. PossiblePossible causescauses areare reducedreduced rainfall and relative humidity in thethe KantoKanto Plains,Plains. a complexcomplex of airair pollutantspollutants fromfrom industrialindustrial sources andand populationpopulation centers.centers, and thethe physiological characteristicscharacteristics of mature trees.

Decline of Cryptomeria japonicajaponica andand ChamaecyparisChamaecyparis obtusaobtusa nearnear a coastal area was attributed toto aa combinationcombination of of salt salt spray, spray. Chlorosypha Chlorosypha needle needle blightblight and and thethe canker canker causing causing fungi,fungi. GuignardiaGuignardia cryptomeriae,cryptomeriae . DiaportheDiaporthe conorumconorum andand ValsaValsa abietis.abietis. Damaged trees eventually recoveredrecovered (Suzuki etet al 1987).

39 6.1.2. "SHIMAGARE DIEBACK" ININ HIGHHIGH ELEVATIONELEVATION ABIESABIES FORESTSFORESTS -- In Japanese, "shimagare" means stripesstripes ofof dead trees.trees. Mt.Mt. ShimagareShimagare (altitude 2,3952,395 m) m) isis located in the YatsugatakeYatsugatake Mountains inin thethe central region ofof thethe island of Honshu. OnOn the southwest slope,slope, fourfour toto fivefive bandsbands of dieback,die back, which runrun parallel toto thethe contour,contour, occur in natural subalpine forests ofof AbiesAbies veitchiiveitchii andand A.A . mariesii,mariesii, atat moremore oror lessless even intervalsintervals of about 100 m.m. TheThe name name ofof thethe mountainmountain comescomes fromfrom thisthis featurefeature ofof thethe landscape.landscape.

This pattern ofof diebackdieback isis commonlycommonly inin thethe upperupper subalpinesubalpine Abies forests in thethe mountains of centralcentral Honshu.Honshu. DiebackDieback frontsfronts movemove graduallygradually into purepure stands of AbiesAbies (Fig. 6.1). AsAs the the dieback dieback fronts fronts move move upslope, upslope, they they become become regeneratedregenerated withwith even even aged aged cohorts of AbiesAbies which comecome in the form of waveswaves (Fig.(Fig. 6.2). StudiesStudies onon thethe dynamicsdynamics of these forests suggestsuggest that desiccationdesiccation and and mechanicalmechanical damagedamage accelerated by prevailing winds trigger thethe directionaldirectional dieback.dieback. DiebackDieback is is alsoalso promotedpromoted byby overstocked,overstocked, eveneven agedaged stands (Kohyama 1988).

These waves ofof diebackdie back andand mortalitymortality areare virtuallyvirtually identicalidentical toto thethe fir waveswaves described from high elevation Abies balsamea forestsforests in the northeasternnortheastern United StatesStates (see sectionsection 4.9)4.9) and represent a remarkableremarkable simisimilaritylarity of ecosystem dynamics onon opposite sides of the worldworld (Sprugel(Sprugel 1976).1976).

6.2. DECLINE IN CHINACHINA

According toto BainBain andand YuYu (1992),(1992). largelarge areasareas of forestforest declinedecline havehave notnot beenbeen found in the People'sPeople's RepublicRepublic ofof ChinaChina (PRC).(PRC). HoweverHowever therethere areare localizedlocalized areasareas ofof decliningdeclining forests whichwhich havehave beenbeen detecteddetected nearnear largelarge cities,cities, industrialindustrial areasareas andand miningmining regions.regions.

6.2.1.6.2.1 . DECLINEDECLINE ANDAND MORTALITYMORTALITY OFOF PINUSPINUS MASSONIANA -- AnAn area of forestforest decline on approximatelyapproximately 2,0002,000 ha,ha, composedcomposed primarilyprimarily ofof Pinus Pinus massoniana, massoniana, nearnear Nanshan, a suburb of Chongquing,Chongquing, SichuanSichuan Province, has caused much public concern. Symptoms includeinclude tip necrosisnecrosis ofof thethe needles,needles, prematurepremature abscission,abscission, crown thinning,thinning, branch dieback and reduced radial growth.

Elevated sulphursulphur andand fluorinefluorine lelevelsvels werewere found in pinepine foliagefoliage collectedcollected fromfrom damaged sites. The main source of SO2SO , isis the burning of coalcoal forfor energyenergy production.production. Sources of fluorides include glass, cement and brick factoriesfactories.. TheThe areaarea alsoalso hashas aa high incidence of fog whichwhich isis acidifiedacidified byby thethe industrialindustrial sources.sources.

The affected areaarea also has aa historyhistory ofof insect damage. ThereThere have been outbreaks of the pinepine caterpillar, DendrolimusDendrolimus punctatus (Lepidoptera:(Lepidoptera: Lasiocampidae),Lasiocampidae). duringduring 2121 of the pastpast 3636 years.years. In addition, therethere havehave beenbeen epidemicsepidemics of barkbark beetles,beetles, weevilsweevils andand pine sawyers.sawyers. TheseThese areare considered to be secondarysecondary toto thethe anthropogenicanthropogenic pollutants (Bain(Bain and Yu 1992).1992).

6.2.2. CHLOROSISCHLOROSIS OFOF PINUSPINUS ARMANDIARMAND' - Decline and mortality ofof PinusPinus armandiarmandi planted in 19581958 onon WushanWushan Mountain,Mountain, SichuangSichuang ProvinceProvince inin southwesternsouthwestern ChinaChina isis described by Ma Guanging (1990(1990 a,b). SymptomsSymptoms includeinclude chlorosischlorosis ofof foliagefoliage beginningbeginning at age 10, followedfollowed byby lossloss ofof foliagef ol iage andand treetree mortality.mortality.

40 Figure 6.16.1 - Fir waves on the slopesslopes of Mt.Mt. Shimagare,Shimagare, Japan.Japan. (Photo(Photo courtesy of M.M. Yarnagata,Yamagata, NaganoNagano RegionalRegional Forest Office, NaganoNagano Prefecture, Japan)Japan)

Figure 6.2 - Natural regeneration following wavewave mortalitymortality on on highhigh elevationelevation AbiesAbies forestsforests in Japan.in Japan (Photo. (Photo courtesy courtesy of M. ofYarnagata, M. Yamagata, Nagano Nagano Regional Regional Forest Forest Office, Office, Nagano Nagano Prefecture, Prefecture, Japan)

4141 This area receives high levels of SO2SO, depositiondeposition duedue toto coal burning in villages near 3 the forest.forest. Soil SO2SO, contentcontent in the plantationsplantations rangesranges fromfrom 90-35090-350 mg3. mg •

A multidisciplinary studystudy vvaswas initiated to determinedetermine causes of decline inin 1984 byby the Chinese Academy of Forestry. PreliminaryPreliminary results ofof thesethese investigations indicateindicate thatthat foliar symptomssymptoms werewere mostmost notablenotable onon acidacid soils.soils. Levels of magnesium,magnesium, potassiumpotassium andand zinc were low in the current year'syear's needle.needle. ExchangeableExchangeable magnesiummagnesium in the soil of heavily damaged plantationsplantations was was lowerlower thanthan that ofof nearbynearby healthyhealthy forests.forests. Magnesium deficiency isis believedbelieved to bebe thethe predominantpredominant cause of this decline.decline.

TABLE 6.16.1

SUMIVIARYSUMMARY OF FORESTFOREST DECLINEDECLINE EVENTSEVENTS BY POSSIBLE CAUSALCAUSAL FACTORSFACTORS JAPAN AND CHINACHINA *•

DECLINE EVENT . FORESTFOK$T PREDISPOSING INCITING CONTRIBUTING SITUATION**SITUATION' , FACTORS FACTORS FACTORS

Japan (6.1.)(6.1.1

Cryptomeria PI Low PHPH soils?soils? Overmature trees?trees? None given japonicajaponica Air pollution?pollution? 16.1.1.J(6.1.1.) Reduced rainfall?

Fir vvaveswaves N Cohort senescencesenescence High winds None givengiven (6.1.2.)(6.1.2.1

China (6.2.)(6.2.1

Pinus ? Air pollution InsectInsect defoliation, Bark beetles rnassonianamassoniana (SO2)(50,1 Dendrolimus Wood borersborers (6.2.1.)(6.21.1 punctatuspunctatus

PinusPinos armand;armandi PI Air pollution Nutrient deficiency None given (6.2.2.)(6.2.2.1

* Causal factorsfactors are summarized according according to to the the predisposing, predisposing, inciting inciting and ad contributingcontributing factors conceptconcept ofof SinclairSinclair andand ManionManion (see(see section 2.3.2),2.3.2).

*** * NN = =natural natural forest, forest, PI PI = =plantation plantation with with indigenous indigenous species, species, PEPE = plantationplantation withwith exoticexotic species.species.

6.3. DECLINEDECLINE ANDAND MORTALITY MORTALITY OF OF ABIESABIES DENSADENSA ININ BHUTAN.BHUTAN.

The East HimalayanHimalayan fir,fir, AbiesAbies densa,densa, occursoccurs inin BhutanBhutan between between 30003000 andand 40004000 m. At the lowerlower elevationselevations itit isis intermixedintermixed withwith Picea Picea spinulosa,spinulosa, LarixLarix griffithianadriffithiana andand in the understorey withwith JuniperusJuniperus recurva and Rhododendron spp. spp. At the higherhigher elevations it

42 forms purepure stands overover largelarge areas. DeclineDecline andand mortality ofof Abies Abies densadensa waswas reportedreported inin high elevation forestsforests inin BhutanBhutan inin thethe earlyearly 1980s.1980s. TheThe conditioncondition waswas restrictedrestricted toto elevations aboveabove 3600-38003600-3800 metersmeters.. An estimated 10,000 to 12,00012,000 ha ha ofof AbiesAbies forests have died during this periodperiod (Donaubauer(Donaubauer 1993) (Fig(Fig 6.3).

Symptoms include reduction of height growth resultingresulting in a flattening of thethe crowncrown into a "storks"storks nest",nest", dyingdying ofof branches branches justjust belowbelow thethe crowncrown apex, apex, loss loss ofof older older needles,needles, epicormic branching,branching, wetwet woodwood andand decaydecay (Fig(Fig 6.4). TheseThese symptoms areare strikingly similarsimilar to thosethose reportedreported forfor declinedecline ofof A.A. albaalba inin EuropeEurope (See(See Section 3.1.)

Analysis of radialradial growth patternspatterns andand meteorologicalmeteorological data indicate that thesethese forests may have been stressedstressed byby droughtdrought duringduring thethe latelate 1970s1970s andand earlyearly 1980s.1980s. HighHigh elevation fir forests,forests, characterizedcharacterized byby aa highhigh proportionproportion ofof overmatureovermature stands,stands, decaydecay andand root disease caused by severalseveral fungifungi includingincluding Phellinus chonchatuschonchatus and ArmillariaArmillaria sp. were most severely affected. AnAn unidentified unidentified orange orange jellyjelly fungus,fungus, DacryomycesDacryomyces sp.,sp., waswas alsoalso collected fromfrom damageddamaged trees.trees. TheTherere waswas evidence ofof recoveryrecovery of decliningdeclining treestrees following aa returnreturn toto normalnormal rainfallrainfall conditionsconditions (Donaubauer(Donaubauer 19861986,, 1987).

An outbreakoutbreak of aa barkbark beetle,beetle, J.Q§lips schmutzenhoferi (Coleoptera:(Coleoptera : Scolytidae),Scolytidae)' occurred in forests ofof PiceaPicea spinulosaspinulosa in the samesame location and during the same period of time thatthat symptomssymptoms ofof declinedecline appearedappeared on 6.A. densa.densa. ThisThis outbreakoutbreak isis alsoalso believedbelieved toto have resulted from prolongedprolonged drydry weatherweather (Schrnutzenhofer(Schmutzenhofer 1987).1987).

Figure 6.3 - ExtensiveExtensive mortalitymortality of of high high elevation elevation Abies Abies densa densa forests forests near near Cheleila, Cheleila, Bhutan (Photo (Ph o tbyo by E. E. Donaubauer) Donaubauer)

43 Figure 6.46.4 -- AbiesAbies densadensa in in Bhutan Bhutan with with symptoms symptoms of of declinedecline.. Note "storks nest" formation inin upperupper crowncrown andand newnew growthgrowth aboveabove storksstorks nestnest indicatingindicating recoveryrecovery from decline. decline. (Photo (Pho byto byE. E.Donaubauer). Donaubauer).

6.4. DECLINEDECLINE ANDAND MORTALITY MORTALITY OF OF SHOREA SHOREA ROBUSTAROBUSTA ININ INDIA.INDIA.

Decline andand mortality ofof sal,sal, ShoreaShorea robusta, hashas beenbeen reported as early as 1907 (Joshi 1988). SymptomsSymptoms include include dieback dieback of of branches branches inin thethe upperupper crown extendingextending toto thethe lower crown overover time,time, epicormicepicormic branchingbranching andand eventualeventual treetree mortalitymortality andand havehave beenbeen attributed to drought,drought. overgrazing,overgrazing, firefire andand insectinsect attack.

Extensive mortalitymortality ofof S..s.. robustarobusta beganbegan in the earlyearly 1950s19505 inin thethe DaltonganjDaltonganj Division, Bihar ProvinceProvince andand reached reached catastrophic catastrophic levels levels during during the the 1960s. 1960s. Mortality waswas widespread over thousands ofof hectareshectares andand S..s.. robustarobusta ceasedceased toto bebe aa majormajor componentcomponent of the affected forestsforests (Boyce(Boyce andand Bakshi 1959, BakshiBakshi 1976).

Studies associated with declinedecline and mortality ofof S..s.. robustarobusta inin Uttar PradeshPradesh indicate that sitessites withwith highhigh mortalitymortality hadhad poorlypoorly draineddrained soils with aa highhigh siltsilt andand clayclay contentcontent (Sharma etet alal 1983).

44 6.5. TOPTOP DYING DYING OF OF HERITIERA HERITIERA FOMES FaMES ININ BANGLADESH.BANGLADESH.

Top dyingdying ofof sundri,sundri, HeritieraHeritiera fomes,fomes, inin thethe Sundarbans Sundarbans regionregion ofof BangladeshBangladesh isis considered to be the most serious of all tree diseases inin BangladeshBangladesh (Rahman (Rahman 1990). 1990). The Sundarbans coverscovers anan areaarea of of 571,502571,502 ha and is thethe largestlargest singlesingle tract ofof mangrovemangrove forestforest inin thethe world.world. SundriSundri is is the the most most important important tree tree species species in in thethe Sundarbans,Sundarbans, coveringcovering 52.7 percentpercent ofof thethe areaarea and constituting about 63.863.8 percentpercent ofof thethe standingstanding treetree volume.volume. Dieback andand mortalitymortality of this species waswas firstfirst recorded inin 1915, but overover the past 10-1510-15 years, has been veryvery damagingdamaging (Fig.(Fig. 6.5).6.5). In many cases, symptomaticsymptomatic trees develop galls and/or cankers on the twigs and,and, toto aa lesserlesser extent,extent, onon thethe main main branches branches andand trunks.trunks. Symptoms are seen onon saplingssaplings asas wellwell asas maturemature trees.trees. A fungus,fungus, BotryosohaeriaBotryosphaeria ribis, has beenbeen foundfound associatedassociated withwith gall andand cankercanker formation. formation. YoungYoung trees wwhichhich areare affected generally die.die.

Top dying ofof sundrisundri appearsappears as a declinedecline andand diebackdieback ofof thethe foliagefoliage andand twigstwigs in the crown. In older trees,trees, oneone oror twotwo branchesbranches maymay diedie initially.initiall y. Examination of suchsuch branches do not show a clearly defined area ofof infection.infection. CrackedCracked perennialperennial galls are often seen associatedassociated withwith dead branches. SymptomaticSymptomatic treestrees areare alsoalso attacked byby borersborers andand wood decay fungi. DeadDead branchesbranches areare subject to breakagebreakage by strong winds.

Possible causescauses ofof the conditioncondition areare (Rahrnan(Rahman 1990):1990):

A. Reduction ofof fresh water dischargedischarge through the SundarbansSundar bans as aa resultresult of upstream diversion of water duedue toto damsdams andand increased use ofof ground water for agriculturalagricultural andand industrialindustrial purposes.purposes.

B. Reduction inin thethe nutrient supplysupply due to reducedreduced vovolumeslumes of fresh water.

C. Reduction in fresh water flushflush hashas alsoalso beenbeen accompaniedaccompanied byby anan increaseincrease inin salinity. IncreaseIncrease inin salinitysalinity hashas exertedexerted anan increasedincreased osmoticosmotic stressstress onon thethe roots and thereby reduced avaiavailabilitylability andand uptakeuptake ofof water and nutrients.

D. A moratorium on tree felling inin thethe SundarbansSundarbans between 1972 andand 19761976 resulted inin an increaseincrease of of symptoms.symptoms. As the number of trees with diebackdieback increased,increased, thethe population of B.~. ribisribis alsoalso increasedincreased andand becamebecame moremore damaging.

E. Severely affectedaffected areas maymay bebe infectedinfected withwith a root pathogen.pathogen.

F. A change in the depth and duration ofof flooding due toto siltation of canalcanal banks may have also played a role in the developmentdevelopment ofof dieback.dieback.

A report by Chaffey et al (1985) indicates that the sensitivity ofof speciesspecies distribution inin thethe Sundarbans toto longlong termterm salinity patterns makes the forest particularlyparticularly susceptiblesusceptible to changeschanges in fresh water availability.availability. ThereThere isis concernconcern thatthat the the forest forest may may be be adverselyadversely affected byby reducedreduced stream flowflow inin thethe GangesGanges RiverRiver as a resultresult ofof developmentdevelopment upstream. The appearance ofof symptoms predatespredates this developmentdevelopment however.however.

45 Figure 66.5.5 - - HeritieraHeritiera fomesfomes withwith top top dying dying in inthe the Sundarbans, Sundarbans, Bangladesh. Bangladesh. (Photo (Photo courtesy of E.E. Boa, NaturalNatural Resources Institute,Institute, Overseas DevelopmentDevelopment AdministAdministration,ration, UKUK.).)

46 Boa andand Rahman (1988)(1988) report that B.g. ribis is aa weakweak pathogenpathogen andand cankercanker development doesdoes notnot significantly contribute to thethe crowncrown damagedamage ofof sundri.sundri. They conclude that the conditioncondition isis aa complexcomplex diseasedisease andand recommendrecommend replacement of sundrisundri with otherother species.species.

6.6. CANOPYCANOPY DIEBACK DIEBACK IN IN UPPER UPPER MONTANEMONTANE RAIN RAIN FORESTS FORESTS ININ SRISRI LANKALANKA

InIn Sri Lanka, remnants of upperupper montane rain forestsforests covercover thethe highlandshighlands aboveabove 1500 meters. TheseThese "mossy""mossy" forests forests occur occur in in a a zonezone ofof frequentfrequent fogfog andand rainfallrainfall betweenbetween 2000 andand 50005000 mm./year.mm./year. Trees are umbrella-shapedumbrella-shaped withwith gnarledgnarled branchesbranches andand coriaceous leaves. StemsStems andand branches coveredcovered withwith mosses, ferns and lichens.lichens. They are stunted and generally only reach aa heightheight ofof fromfrom 3 to 5 meters except on sites protected fromfrom high winds where they may reach aa heightheight ofof 2020 toto 25 meters.meters.

The dominantdominant tree species of these forestsforests are of thethe genusgenus CalophyllumCaloehyllum withwith lesser amounts ofof Syzygium spp. These form even-age "cohort""cohort" stands. SaplingsSaplings andand seedlings are scarce inin the understories ofof these stands whichwhich are dominated byby aa shrub ofof the genus Strobilanthes.

Patches ofof dead andand dyingdying treestrees werewere firstfirst reported on the slopes of the mountain Thotupolakanda andand other high regions above thethe Horton Plains inin 19781978 and continuedcontinued into 1980/81.1980/81. ByBy 1981, 1981, virtually virtually the the entire entire upper upper canopy canopy was was killed killed in in thethe affected affected areas. areas.

Werner (1988) reportsreports thatthat thethe diebackdieback occurredoccurred onlyonly inin stuntedstunted andand single-storiedsingle-storied forests of slopesslopes vvithwith a westerly exposureexposure and a strong wind influence,influence, shallowshallow soilssoils andand a low water storagestorage capacity. HeHe concludedconcluded thatthat thethe causecause ofof thisthis canopycanopy diebackdieback was not due to air pollutionpollution oror disturbancedisturbance ofof thethe hydrologicalhydrological regimeregime due to human activities. Instead,Instead, hhee relatedrelated thethe incidence ofof dieback toto a periodperiod ofof exceptionallyexceptionally drydry weatherweather between 1971 andand 19831983 and and suggestssuggests thatthat thisthis eventevent isis anan example of cohort senescence triggered by drought.

An aspect of this declinedecline event wwhichhich is particularly intinterestingeresting is thethe lifelife cycle of Strobilanthes which isis the dominantdominant understoreyunderstorey plantplant inin thesethese montanemontane forests.forests. Strobilanthes growthgrowth suppressessuppresses growthgrowth of otherother understoreyunderstorey plants,plants, includingincluding treetree regeneration. TheThe plantplant isis characterizedcharacterized byby cyclescycles ofof synchronoussynchronous floweringflowering andand seedseed production followedfollowed by death after a 6 to 1212 yearyear vegetativevegetative period.period. TheThe occurrenceoccurrence of canopy dieback inin 19781978 coincided withwith a periodperiod ofof floweringflowering ofof StrobilanthesStrobilanthes undergrowth.undergrowth.

Return toto normal rainfall resulted in some recovery of treestrees andand a small amount of natural regeneration.regeneration. InIn March 1986,1986, anan unusualunusual frostfrost occurredoccurred whichwhich causedcaused furtherfurther damage toto the montane vegetation.vegetation.

47 TABLE 6.2

SUMMARYSUMIVIARY OF FOREST DECLINE EVENTS ININ BHUTAN, INDIA, BANGLADESH AND SRI LANKA BY POSSIBLE CAUSALCAUSAL FACTORS'FACTORS *

. DECLINE EVENT FOREST PREDISPOSING INCITING CONTRIBUTING ., SITUATION"SITUATION** FACTORS FACTORS FACTORS

AbiesA bies densa N OvermaturityOvermaturity Drought Root disease (Bhutan 6.3.16.3.) Stem decay

Shorea robusta N Poorly draineddrained Drought None givengiven (India 6.4.16.4.) sosoilsils Overgrazing Fire

Heritiera fomes N None given Reduced seasonalseasonal Gall fungus, (Bangladesh 6.5.16.5.) flushes of fresh Botryosphaeria water. ribis

Canopy dieback of N Cohort senescencesenescence Drought None given montane forests ShallovvShallow soilsso ils (Sri(Sri LankaLanka 6.6.16.6.) High winds

•* CausaCausall factorsfactors are summarized according to the predisposing,predisposing, inciting andand contributingcontributing factors conceptconcept ofof SinclairSinclair andand ManionManion (see(see section 2.3.2),2.3.2).

*** * NN = =natural natural forest, forest PI I PI = plantation= plantation with with indigenous indigenous species, species, PE PE = plantationplantation with with exotic exotic species. species.

48 CHAPTER 7

AUSTRALIA,AUSTRALIA, NEWNEW ZEALANDZEALAND ANDAND THETHE PACIFICPACIFIC ISLANDSISLANDS

Forest decline events have been reportedreported fromfrom a number ofof forest ecosystemsecosystems inin Australia, NewNew ZealandZealand and thethe Pacific Islands.Islands. Many are wellwell documenteddocumented in thethe scientificscientific literature.literature. TheseThese areare describeddescribed inin thethe followingfollowing sectionssections and and summarizedsummarized inin tablestables 7.17.1 - 7.3.

7.1. DECLINEDECLINE OFOF ARAUCARIAARAUCARIA HETEROPHYLLA HETEROPHYLLA ONON NORFOLKNORFOLK ISLAND.

Norfolk Island isis a small, isolated islandisland in in thethe SouthSouth PacificPacific whichwhich isis part of Australia and home to severalseveral speciesspecies of endemicendemic plants.plants. The best known ofof thesethese endemics is Norfolk Island Pine, AraucariaAraucaria heterophylla.heterophylla. Captain James CookCook waswas thethe firstfirst to describedescribe thethe island's stately AraucariaAraucaria forests when he discovered itit inin 1774.

Crown deterioration andand tree mortality ofof NorfolkNorfolk IslandIsland pinepine waswas detecteddetected duringduring the 1970s and early 1980s. InIn addition,addition, itit waswas notednoted thatthat thesethese forestsforests hadhad little oror nono natural regeneration. Surveys,Surveys, usingusing large-scalelarge-scale colour aerial photography indicatedindicated thatthat one-third of the island's Araucaria forests were affected byby dieback. MostMost of of this this area area waswas severely damaged.damaged.

Studies into thethe causescauses ofof thethe dieback die back eliminatedeliminated climateclimate andand thethe fungus,fungus, Phytophthora cinnamomi, asas causalcausal factors. It isis believed thatthat the condition isis due to thethe manifestation ofof seriousserious ecologicalecological damagedamage due to severesevere competitioncompetition fromfrom introducedintroduced grasses andand shrubs, overgrazing andand nutrient depletion on landland originallyoriginally clearedcleared forfor agriculture (Benson 1980, BensonBenson and Myers 1978).1978).

7.2. DIEBACKDIEBACK OF OF MANGROVE MANGROVE FORESTS FORESTS ININ QUEENSLAND,QUEENSLAND, AUSTRALIA.AUSTRALIA.

Pegg etet alal (1980) reportreport onon thethe dyingdying ofof whitewhite mangrove, mangrove, AvicenniaAvicennia marina,marina, inin central coastal Queensland. TheThe foliage of affectedaffected treestrees droopsdroops moremore than normal, then becomes chloroticchlorotic and finallyfinally falls.falls. Lateral absorbingabsorbing rootlets,rootlets, which areare borneborne onon pneumatophores, become blackblack andand decayed.decayed. A trunk rotrot isis alsoalso occasionallyoccasionally evident.evident.

Only AA.. marinamarina was affectedaffected althoughalthough 1212 mangrovemangrove speciesspecies occur in thethe area.area. Dieback and mortalitymortality waswas observedobserved onlyonly inin large trees, however seedlings which appearedappeared healthy also had decayeddecayed rootlets.rootlets. TreesTrees growinggrowing onon sitessites subjectsubject toto diurnaldiurnal floodingflooding byby tides were most severely affected.

A fungus,fungus, PhytophthoraPhytophthora sp.,sp., (near(near vesicula)vesicula) waswas recoveredrecovered fromfrom damageddamaged tissue. This fungus producedproduced dark colouredcoloured lesions whenwhen inoculated into healthyhealthy A.A. marinamarina seedlings. PeggPegg et al (1980), however,however, questionquestion the the role role ofof Phytophthora Phytophthora as as an an aggressiveaggressive pathogen, capable of killingkilling vigorousvigorous trees.trees. They suggest that sincesince optimumoptimum saltsalt concentration for A. marinamarina is reported as 1.5%, the affectedaffected treestrees areare subject to stressstress caused by continual exposure toto high salines duedue toto the lack of estuaryestuary flushing.flushing.

49 7.3. DIEBACKSDIEBACKS OF OF EUCALYPTSEUCALYPTS ININ AUSTRALIA

Diebacks affectingaffecting a number of speciesspecies of EucalyptusEucalyptus havehave beenbeen reportedreported fromfrom Australia (Old(Old andand Podger,Podger, inin press).press). Increased incidenceincidence ofof diebackdieback duringduring thethe 1970s, both inin plantedplanted andand naturalnatural forests,forests, stimulatedstimulated surveyssurveys andand researchresearch toto determinedetermine thethe extent andand naturenature ofof thethe problem.problem. Initially many of thesethese diebacksdiebacks were attributed toto infection byby ArmillariaArmillaria sp.sp. andand Phytoohthora Phytophthora cinnamomi.cinnamomi. These are now seenseen asas contributing factorsfactors resulting resulting fromfrom stress stress induced induced byby aa numbernumber ofof abioticabiotic andand bioticbiotic agentsagents including drought, excessexcess moisture,moisture, humanhuman activitiesactivities andand insectinsect damage.damage.

Several distinctdistinct diebacks of eucalypts havehave been described fromfrom Australia. TheseThese bear names reflectingreflecting thethe host tree affected, geographicgeographic location of thethe dieback,dieback, oror thethe conditions under which thethe diebackdieback isis found.found . Examples includeinclude jarrah dieback, ruralrural diedieback, back, New EnglandEngland dieback, high altitude dieback, gully diebackdie back and regrowth dieback.die back.

7.3.1. JARRAHJARRAH DIEBACKDIEBACK - A A diebackdieback ofof drydry sclerophyllsclerophyll forestsforests dominateddominated byby jarrah,jarrah, I.E marginata,marginata, hashas been known fromfrom Western AustraliaAustralia sincesince 1920.1920. ThisThis condition is reviewed byby NevvhookNewhook and PodgPodgerer (1972).(1972), Jacobs et alal (1979)(1979) andand WesteWeste andand MarksMarks (1987). SymptomsSymptoms include include generalgeneral crowncrown decline,decline, foliarfoliar wilt,wilt, dieback,dieback, rootroot necrosisnecrosis andand mortality.

In 1975, thethe areaarea of jarrah forestforest affected by diebackdie back waswas estimatedestimated atat 282,000282,000 ha. and was increasing atat thethe raterate ofof 20,00020,000 ha annually.annually. ByBy 1982,1982, anan estimatedestimated 14%14% of thethe forestforest areaarea waswas affected.affected. In addition toto jarrah,jarrah, diebackdieback andand mortalitymortality hashas beenbeen reported from 59 indigenousindigenous plant species whichwhich occur in thesethese forests.forests. TheseThese represent 34 genera and 13 familiesfamilies (Weste(Weste and Marks 1987).

The root fungusfungus PhytoohthoraPhytophthora cinnamomi andand itsits role in the diebackdie back waswas firstfirst established in 1965 when it waswas isolatedisolated from root systems ofof symptomaticsymptomatic treestrees andand has been shown toto bebe pathogenic.pathogenic. Occurrence ofof this fungus appearsappears to bebe favouredfavoured byby human activitiesactivities.. DamageDamage toto jarrahjarrah andand other plants is associated withwith timber harvesting, roads, power lines and other disturbances (Jacobs etet alal 1979).

There is speculation that.E.that P. cinnamomi has beenbeen introducedintroduced intointo AustraliaAustralia and thatthat the fungusfungus entersenters jarrahjarrah forests via motor vehicles, toolstools andand thethe clothing of forestforest workers. OthersOthers believe believe thatthat thethe fungusfungus isis indigenousindigenous and that forest operationsoperations and other factorsfactors modifymodify thethe environmentenvironment toto createcreate conditionsconditions favourablefavourable forfor itsits development development (Newhook and Podger 1972).1972). WesteWeste andand MarksMarks (1987)(1987) concludeconclude thatthat.E. P. cinnamomicinnamomi waswas introduced into Australia. TheyThey basebase thisthis conclusionconclusion on its pathogenicity when introducedintroduced into sites whichwhich werewere previouslypreviously freefree of thethe fungusfungus andand thethe factfact thatthat entireentire plantplant communities areare damageddamaged in areas where this fungus isis present.present.

77.3.2..3.2. RURALRURAL DIEBACKDIEBACK - A dieback known asas "rural dieback"dieback" occursoccurs inin populatedpopulated regions ofof humid, sub-humid and semi-aridsemi-arid zoneszones of of Australia. Australia. Many species ofof eucalypts are affectedaffected.. TreesTrees in in woodlandwoodland andand forestforest communities communities areare damageddamaged but mostmost concernconcern has been expressed overover diebackdieback andand mortalitymortality ofof treestrees inin pastoralpastoral areas.areas.

Symptoms of ruralrural diebackdieback areare deaddead branchesbranches andand developmentdevelopment ofof epicormicepicormic shoots. Intensity ofof symptomssymptoms variesvaries byby speciesspecies and the nature and duration of stress.stress. Trees may die after a period of progressiveprogressive crown dieback.die back.

50 Many factors areare believed to be involved in thethe onsetonset ofof symptomssymptoms of ruralrural dieback.die back. These maymay change fromfrom one location to anotheranother andand includeinclude defoliationdefoliation byby insects,insects, drought, tree aging, soil salinity,salinity, mistletoe,mistletoe, rootroot fungi,fungi, ArmillariaArmillaria sp.sp. andand PhytoohthoraPhytophthora cinnamomi, andand animalanimal damage.damage.

Changes inin environmental conditionsconditions and and treetree condition are believedbelieved to bebe predisposing factorsfactors inin the occurrence ofof rural diedieback. back. CultivationCultivation andand grazinggrazing reducesreduces the probability thatthat naturalnatural regenerationregeneration ofof eucalyptseucalypts willwill survivesurvive andand replacereplace olderolder trees.trees. Many of the trees which presentlypresently occuroccur inin pastoralpastoral areasareas are overmature,overmature, in the range of 200 to 500500 yearsyears (Kile(Kile 1980).

7.3.3. NEWNEW ENGLAND ENGLAND DIEBACKDIEBACK - New England DiebackDieback isis aa formform ofof rural diedieback back described fromfrom thethe New EnglandEngland tablelandstablelands of of NewNew SouthSouth Wales.Wales. TheThe conditioncondition waswas reported as earlyearly asas the the 1850s.1850s. JonesJones et al (1990) reportsreports that thisthis diebackdieback isis associated with soilsoil type,type, geologygeology andand certaincertain characteristicscharacteristics ofof thethe woodland. woodland. Kile (1980)(1980) summarizes thethe causal factors involved in thisthis dieback.dieback. He indicates thatthat repeatedrepeated defoliation by insects together with frostfrost damagedamage are key factors associatedassociated with treetree death and decline.decline.

Mueller-Dombois (1991) summarizessummarizes the aetiology ofof NewNew EnglandEngland or rural diedieback back as follows:

The genus Eucalyptus evolved under isolationisolation into many species but it representsrepresents thethe onlyonly majormajor generic taxontaxon that isis overwhelmingly dominant in Australia. AtAt the the genus genus level, Australia's treetree floraflora isis taxonomicallytaxonomically impoverishedimpoverished relative to otherother continents.continents. Australia's soilssoils areare generallygenerally ancientancient andand nutrientnutrient poor,poor, particularlyparticularly inin phosphorusphosphorus andand other nutrients.nutrients. Moreover,Moreover, even even inin moremore humidhumid climates,climates, theythey areare adaptedadapted toto occasionaloccasional droughts and most have evolved to copecope withwith periodicperiodic fires. fires . Thus, eucalypts cancan bebe generally considered hardyhardy species.species.

Settlers trying toto makemake aa livingliving onon landslands dominateddominated byby thesethese poorpoor soilssoils inin thethe moremore humid zones ofof easterneastern AustraliaAustralia focusedfocused onon thethe sheepsheep industry. industry. ThisThis requiredrequired introductionintroduction of grazing-resistantgrazing-resistant grasses fromfrom otherother continentscontinents.. TheseThese pasturepasture grassesgrasses were mixedmixed withw ith legumeslegumes to increaseincrease productivity, butbut particularlyparticularly fertilizationfertilization withwith superphosphate superphosphate was practisedpractised inin thethe openopen grazinggrazing lands.lands. Eucalypt trees were allowed to remainremain inin thethe paddocks asas shadeshade treestrees andand asas forestforest and woodlandwoodland fragmentsfragments inin a formerly forested landscape converted to pastoralpastoral use.use.

Initially, the eucalypteucalypt trees benefitted fromfrom thethe additionaddition ofof nitrogennitrogen andand phosphorus,phosphorus, but their foliagefoliage becamebecame enriched with proteins.proteins. Their resistance toto insect feeding was weakened by fertilization. TheThe numbers numbers ofof insectivorous insectivorous birdsbirds werewere reducedreduced becausebecause ofof forest fragmentationfragmentation and lossloss ofof woodlandwoodland habitat.habitat. These factors, combinedcombined with occasional droughtdrought which further favoursfavours insectinsect feedingfeeding onon eucalypts,eucalypts, isis causingcausing trees to die at an alarming rate.

7.3.4. EUCALYPT DIEBACKS DIEBACKS IN IN TASMANIA TASMANIA - -At At least least three three distinct distinct typestypes of diebacks have been reported from TasmaniaTasmania andand are summarized by Felton (1980) andand OldOld and Podger (in press).press).

51 High altitude dieback is a conditioncondition which affects naturalnatural forestsforests ofof E. J; . delegatensisdelegatensis and can result in the death ofof trees ofof allall ageage classes. DiebackDieback occursoccurs inin areasareas whichwhich havehave not been burned forfor 50 to 7070 years.years. Soil disturbances associatedassociated withwith logging and fire result in recovery of symptomatic trees. DiebackDieback andand mortalitymortality ofof E.J;. delegatensisdelegatensis allows understorey Nothofagus cunninghamii andand otherother vegetation to becomebecome thethe dominantdominant components of the stand.stand. ThisThis dieback dieback maymay bebe partpart ofof the the natural natural successionsuccession ofof thesethese forests when firefire isis excludedexcluded from the ecosystem (Ellis(Ellis 1980).1980). MoreMore recentrecent work byby EllisEllis and Pennington (1992) indicatesindicates that soilsoil microbiologicalmicrobiological factors, specificallyspecifically mycorrhizal mycorrhizal associations which accompanyaccompany changes inin vegetative components of eucalypt stands,stands, could bebe the underlyingunderlying causecause ofof diebackdie back ofof all all ageage classesclasses ofof E. J;. delgatensis.delgatensis.

Gully dieback affectsaffects natural forests ofof E.J;. obliquaobligua whichwhich growgrow alongalong creekscreeks andand gullies in steeply dissected topography in northeastern TasmaniaTasmania.. This condition vvaswas firstfirst noted during the late 1960s andand early 1970s. StudiesStudies byby PalzerPalzer (1980) indicate that this diebackdie back isis the resultresult ofof aa severe severe droughtdrought accompaniedaccompanied by defoliationdefoliation by thethe leafleaf skeletonizer, UrabaUraba lugens (Coleoptera: ChrysomelidChrysomelidae),ae). andand subsequentsubsequent secondarysecondary attackattack by Armillaria sp.sp.

Regrowth dieback affects dominantdominant and co-dominant J;E.. regnans andand J;. E obliqueobligua in second growthgrowth (regrowth)(regrowth) forests older ththanan 3030 to 40 years.years. SymptomsSymptoms includeinclude crowncrown death, reduced growth, proliferationproliferation ofof epicormicepicormic branchesbranches and tree mortality. Despite intensive research,research, the aetiology ofof thisthis diebackdieback isis still unresolved.unresolved. ThereThere isis nono correlationcorrelation with standstand oror sitesite factors.factors. Although there is some insect defoliationdefoliation andand invasioninvasion byby Armillaria sp,sp, associated wwithith symptomatic trees, no pathogenpathogen or insect is consistentlyconsistently associated withwith thethe condition.condition. There is circumstantialcircumstantial evidenceevidence which linkslinks symptomsymptom development withwith droughtdrought eventsevents (Wardlaw(Wardlaw 1989).1 989).

7.4. DECLINEDECLINE ININ NEWNEW ZEALAND.ZEALAND.

7.47.4.1.. 1. STAND LEVELLEVEL DIEBACKS OFOF NOTHOFAGUS SPSP.. -- Southern beeches,beeches, Nothofagus spp., are the dominant treetree covercover ofof the montane forestsforests of both the NorthNorth and South Islands. TheyThey characteristicallycharacteristically formform eveneven ageage stands consisting of from oneone toto threethree speciesspecies overover extensiveextensive areas.areas. Periodic episodesepisodes ofof diedieback back and mortalitymortality areare aa characteristic of thesethese forests.forests. These events are described byby a numbernumber of workersworkers including Hosking (1989) andand WardleWardle and Allen (1984).(1984). They concludeconclude that periodicperiodic decline andand mortalitymortality is a natural process inin thesethese forests.forests. AsAs southernsouthern beechbeech forestsforests increase inin ageage,, theythey are predisposedpredisposed toto thethe impactsimpacts of events such as severesevere snowsnow storms resulting in breakage,breakage, earthquake disturbancesdisturbances,, windthrow andand severesevere drought.drought. Insects and fungi areare associatedassociated with thethe collapsecollapse ofof thesethese standsstands butbut areare consideredconsidered toto bebe contributing factors. OlderOlder,, even age stands are more sussusceptibleceptible thanthan younger, mixed stands (Fig. 7.1)

Examples ofof thesethese episodesepisodes include include mortality mortality ofof NN.. fusca in thethe MaruiaMaruia ValleyValley (Hosking and Kershaw 1985),1985), declinedecline ofof N.1[. truncatatruncata on on thethe Mamaku Mamaku Plateau Plateau (Hosking(Hosking andand Hutcheson 1986) and decline of N.1[. solandrisolandri var.var. cliffortioidescliffortioides inin thethe Kaweka Kaweka RangeRange (Hosking andand HutchesonHutcheson 1988).1988). StudiesStudies onon thethe dynamicsdynamics of thesethese forests indicateindicate that there areare three formsforms ofof stand-levelstand-level diebackdie back inin NewNew Zealand Zealand NothofaqusNothofagus forests:forests:

52 TABLE 7.17 .1

SUMMARY OFOF FORESTFOREST DECLINEDECLINE EVENTSEVENTS BY POSSIBLE CAUSAL FACTORSFACTORS AUSTRALIA *•

I DECLINEDECLINE EVENT · FOREST PREDISPOSING INCITINGINCITING CONTRIBUTING SITUATIOWSITUATION**.' FACTORS FACTORS FACTORS

Araucaria N Competition NNoneone given None given heterophylla Overgrazing 17.1(7.1.).1 Nutrient depletion

AAvicennia vicennia marina N None given Excess salinitysalinity of Phytophthora 17.2.1(7.2.1 water sp.

EEucalyptucalypt declinesdeclines 17.3.1(7.3.)

Jarrah dieback N ? Introduction of ? 17.3.(7.3.1.)1.1 PhytophrhoraPh ytophthora cinnamomi intointo forestforest soilssoils

RurRural/Newal/New N Grazing InInsectsect defoliation Animal damagedamage England dieback FFertilizationertilization Root fungi 17.3.2.,7.3.3.1(7.3.2.,7.3.3.)

High altitude N FirFiree exclexclusionusio n Unknown None given dieback (7.3.4.)17.3.4.1

Gully diebackdieback N UnknownUnknown Drought Root fungus, 17.3.4.1(7.3.4.1 InsectInsect defoliationdefoliation Armillaria sp.sp .

RegrowthRegrowth diebackdieback N SenSenescence?escence? Drought RootRoot fungus,fungus, 17.3.4(7.3.4.).1 InInsectsect defoliation Armillaria sp.sp.

•* Causal factors areare summarized according to the the predisposing,predisposing, incitinginciting andand contributingcontributing factorsfactors conceptconcept ofof SinclairSinclair andand ManionManion (see(see sectionsection 2.3.2).

••** NN = =natural natural forest, forest, PI PI = plantation= plantati on with w ith indigenous indigenous species, species, PE PE = plantationplantation with with exotic exoti cspecies. specie s.

A. Stands inin which therethere isis anan extensiveextensive declinedecline of thethe oldold canopycanopy butbut adequate regeneration.regeneration.

B. Stands with re-establishmentre-establishment problems followingfollowing breakdown of thethe oldold canopy.

C. Stands in which bothboth oldold andand youngyoung trees show clear symptoms ofof decline.decline.

Hosking (19891(1989) recommendsrecommends care in planningplanning of developmentsdevelopments suchsuch asas trails andand recreation sites in natural forests of southernsouthern beechbeech to minimizeminimize disturbances which mightmight trigger episodesepisodes of declinedecline and mortality.

53 Ogden (1988) concludesconcludes thatthat successfulsuccessful regeneration of N. solandri var. cliffortoides, aa short-lived,short-lived, lightlight demanding demanding species,species, isis dependentdependent onon thethe occurrenceoccurrence ofof decline and mortalitymortality of the upper canopy. NaturalNatural regenerationregeneration of N. fusca, on the other hand, can become established in small openings createdcreated byby thethe deathdeath ofof small patches of trees. If these species grow inin mixturemixture withwith N.H. menzeisii,menzeisii, aa shadeshade toleranttolerant species,species, theythey are destined to be replaced by it in the absence of disturbances which leadlead to declinedecline andand mortality ofof thethe upperupper canopy.canopy.

7.4.2. STAND LEVELLEVEL DIEBACKDIEBACK OFOF METROSIDEROSMETROSIDEROS SP.SP. AND WEINMANNIAWEINMANNIA RACEMOSA -- StandStand level dieback is aa phenomenonphenomenon ofof thethe rata, Metrosideros sp.-sp.- kamahi,kamahi, Weinmannia racemosa, forestsforests ofof NewNew Zealand.Zealand. This diebackdie back has beenbeen studied byby aa number of scientistsscientists andand isis summarizedsummarized byby BatchelerBatcheler (1983).(1983). The aetiology of thisthis condition isis complicated byby thethe browsingbrowsing ofof thethe AustralianAustralian possum,possum, TrichosurusTrichosurus vulpecula,vulpecula, which waswas introducedintroduced intointo NewNew ZealandZealand forestsforests aboutabout 7070 yearsyears agoago and and feedsfeeds inin thethe canopy of thesethese forestsforests inin epidemicepidemic numbersnumbers (Stewart 1989).1989). For many years,years, thethe possum was regarded as the majormajor causecause ofof dieback.die back. Recently, thisthis view hashas beenbeen challenged and assertions have been made thatthat some of these forests werewere inin aa poorpoor state of healthhealth beforebefore thethe possumspossums invadedinvaded andand thatthat theirtheir naturalnatural collapsecollapse waswas inevitable.inevitable. Batcheler (1983) rejectsrejects thethe latterlatter hypothesishypothesis andand presentspresents evidenceevidence that thethe possumpossum isis indeed thethe primary causal factor associatedassociated with thisthis dieback.die back.

According toto StewartStewart and and RoseRose (1988),(1988), thethe diebackdieback triggeredtriggered byby thethe possumpossum maymay be further accelerated by other factors which includeinclude windwind damage,damage, insect feeding, fungi and possibly drought.drought. DiebackDieback patternspatterns indicateindicate that notnot allall forestsforests areare uniformly affectedaffected by dieback.die back. TwoTwo major major predisposing predisposing factorsfactors cancan bebe identified;identified; thethe abundance abundance ofof seralseral shrub hardwoods preferred by the possumpossum and the proportion of oldold canopycanopy treestrees whichwhich have a low potentialpotential forfor recoveryrecovery fromfrom possumpossum browsing.browsing.

7.4.3. SUDDENSUDDEN DECLINE DECLINE OFOF CORDYLINECORDYLINE AUSTRALISAUSTRALIS -- TheThe cabbagecabbage tree,tree, locally known asas titi kouka, kouka, CordylineCordyline australis,australis, isis aa successional successional speciesspecies whichwhich colonizescolonizes bothboth naturally and artificially disturbeddisturbed sitessites suchsuch asas forestedforested areasareas damageddamaged by wind oror fire,fire, or affected byby timbertimber harvestingharvesting andand otherother forestforest operations.operations. During thethe early 1980s, there were reports of dying cabbage trees.trees. ByBy the latelate 1980s,1 980s, thethe deathdeath andand declinedecline of this species was widespread on the northern half ofof thethe NorthNorth Island.Island.

This decline is characterized by wilted foliage,foliage, collapsecollapse ofof thethe crowncrown and and eventualeventual tree death.death. Profuse flowering hashas alsoalso beenbeen reported.reported. An evaluationevaluation ofof thethe declinedecline indicated that itit waswas stronglystrongly associatedassociated withwith landland use,use, beingbeing mostmost commoncommon onon maturemature farmland andand grazedgrazed shrub land.land. Its occurrence was rarerare in undisturbed forestforest andand shrubshrub lands. SymptomsSymptoms werewere most most severe severe in in old old and and overmatureovermature treestrees while while seedling seedling andand pre-pre­ flowering treestrees werewere largelylargely unaffected.unaffected. TheThe most most severe severe damagedamage waswas associatedassociated with sudden changes in water table;table; areasareas whichwhich hadhad beenbeen floodedflooded oror drained.drained.

Hosking and HutchesonHutcheson (1992) concludeconclude thatthat suddensudden declinedecline ofof CordylineCordyline australisaustralis is thethe result of aging trees and sitesite modification with possiblepossible secondarysecondary invasioninvasion byby weak pathogenic agents. TheyThey recommendrecommend the following actionsactions toto protectprotect individual individual treestrees andand stands:

A. Protect residual treestrees or stands fromfrom browsing, especially by cattle.

54 Zealand. New Zealand) New '-COZ Park, Rotorua, National Institute, Tongariro Research in Forest sp. 55 Zealand New Nothofagus of Hosking, Gordon Dieback of - 7.1 courtesy (Photo Figure B. EncourageEncourage the the growthgrowth of natural shrub land associations withinvvithin significant stands of this speciesspecies to provideprovide moremore stable soilsoil moisturemoisture conditions.conditions.

C. RefrainRefrain fromfrom draindraininging wetlandswetlands whichwhich containcontain major populations ofof this species.

D. Continued research toto further investigateinvestigate thethe causescauses ofof suddensudden decline.decline.

Simpson (1993a)(1993a) presentspresents three three hypothesishypothesis for for thethe causecause ofof this decline;decline; aa pathogen, climate change which maymay havehave triggeredtriggered profuseprofuse flowering,flowering, andand changeschanges inin nutrient uptake possible stimulatedstimulated by profuse flowering. TheseThese hypothesishypothesis werewere basedbased on observations and a causecause andand effecteffect relationship which hadhad notnot yetyet been been established.established. More recently Simpson (1993b) reports the presencepresence of foreignforeign DNADNA belongingbelonging to aa mycoplasma-like organism (MLO)(MLO) inin symptomaticsymptomatic treestrees but not in healthy cabbagecabbage trees. He suggestssuggests thatthat the MLO may be an inciting factor inin treestrees stressesstresses byby environmentalenvironmental factors.

TABLE 7.27.2

SUMMARY OFOF FORESTFOREST DECLINEDECLINE EVENTSEVENTS BY POSSIBLE CAUSALCAUSAL FACTORS NEW ZEALAND •

DECLINE EVENT FOREST PREDISPOSING INCITING CONTRIBUTING SITUATION'SITUATION** , FACTORS FACTORS FACTORS

Nothofagus sp.sp. N Cohort Storms Secondary (7.3.1.)(7.3.1.) senescence Earthquakes insects High winds and fungi Drought

Metrosideros sp.sp. N Cohort Defoliation byby None given and WeinmanniaWeinmannia senescence? Australian racemosa possum (7.3.2.)(7.3.2.)

CordylineCordy/ine N Senescence Site modificationmodification Secondary australis Grazing MLO pathogens (7.3.3.)

, * Causal factfactorsors are summarized according to the predisposing,predisposing, inciting andand contributingcontributing factors conceptconcept ofof SinclairSinclair andand ManionManion (see(see section 2.3.2).

*** * NN = =natural natur alforest, forest, PI PI = plantation= plantation with w iindigenousth indigenous species, species, PE PE == plantation plantation with with exotic exotic species. species.

56 7.5. STANDSTAND LEVEL LEVEL DIEBACK DIEBACK IN IN THE THE FORESTS FORESTS OFOF PAPUAPAPUA NEWNEW GUINEA.GUINEA.

Arentz (1988)(19881 reviews reviews stand stand level level diebackdie back inin Nothofagus,Nothofagus, mangrovemangrove andand Eucalyptus degluotadeglupta forests inin PapuaPapua NewNew Guinea.Guinea.

The genus NothofapusNothofagus is represented byby 13 species in Papua NewNew Guinea.Guinea. They generally occur on ridge tops and upper slopesslopes betweenbetween 1000 and 3000 metersmeters aboveabove seasea level. AA speciesspecies maymay bebe locally dominant formingforming purepure stands which areare mosaics of groups of eveneven age trees. CanopyCanopy treestrees commonlycommonly developdevelop dead branches. DeathDeath of thethe upperupper crown maymay bebe followed byby developmentdevelopment ofof adventitiousadventitious shootsshoots butbut eventuallyeventually thethe aboveabove ground portion of thethe treestrees die.die. Mortality occurs simultaneously within aa group of largelylargely even age trees. Following episodes of dieback and mortality, regenerationregeneration of thethe samesame species ofof Nothofagus will occur, most commonly as clumpsclumps ofof vegetative shoots.shoots. ThereThere is generally nono evidence ofof chlorosis oror deathdeath inin thethe regrowth.regrowth. TheThe fungifungi PhytophthoraPhytophthora cinnamomi and Armillaria sp.sp. havehave beenbeen recovered fromfronn affectedaffected sites and three species of ambrosia beetles have been collected from decliningdeclining trees.trees. TheseThese agents agents are are consideredconsidered as secondary oror contributing factors.

Studies of diebackdie back ofof N.N. pulleipullei andand N. grandisgrandis on the slopesslopes of Mt.Mt. GiluweGiluwe havehave ledled investigators toto concludeconclude that thesethese episodesepisodes of diebackdie back areare anan exampleexample of cohortcohort senescence with with soil nutrient deficiencies,deficiencies, drought and heavy frost associatedassociated with drought serving as triggeringtriggering mechanismsmechanisms (Arentz 1983, AshAsh 1988,1988, Mueller-Dombois Mueller-Dombois 1986).

Patches of diebackdie back and mortality hashas beenbeen recordedrecorded inin mangrovemangrove forestsforests onon PapuaPapua New Guinea withwith areas of a radius upup toto 25 meters affected. ThereThere isis aa highhigh frequencyfrequency of lighteninglightening strikes in thesethese forestsforests andand itit is suggestedsuggested that thesethese maymay triggertrigger treetree mortality. TwoTwo species species of of Phytophthora Phytophthora havehave beenbeen recoveredrecovered from thethe soilsoil inin diebackdieback areas butbut pathogenicity has notnot been proven.proven. Water tests inin areasareas affected by diebackdie back indicated normalnormal levelslevels ofof salinitysalinity butbut thesethese werewere takentaken duringduring periodsperiods ofof normalnormal precipitation. ArentzArentz (1988) (1988) suggests suggests that that the the occurrence occurrence of of periods periods of of high high salinitysalinity during during drought periods could be a possible factorfactor which triggers diebackdieback and mortality.

Eucalyptus deglupta forms extensive stands of eveneven ageage forests rising terrace likelike along streamsstreams inin coastalcoastal rainrain forests,forests, primarily onon thethe islandisland ofof NewNew Britain.Britain. ThereThere isis nono natural regeneration of £.E. degluptadeplupta inin thesethese standsstands andand ifif leftleft undisturbed, will eventually be replacedreplaced byby otherother rainrain forestforest species.species. This treetree isis toleranttolerant ofof wet sites associated with streams but will notnot toleratetolerate waterwater logging.logging.

There areare aa few reportsreports ofof crowncrown declinedecline ofof E.£. deolupta.deglupta. In oneone instanceinstance Phytophthora palmivora waswas recovered fromfrom soilsoil inin diedieback back sitessites butbut itsits pathogenicitypathogenicity to this treetree hashas notnot yetyet been been demonstrated.demonstrated. £.E. degluptadeplupta isis potentiallypotentially susceptiblesusceptible toto twotwo opposing weather related stresses; excess water andand drought.drought. Because ofof itsits lack ofof tolerancetolerance to waterwater logging,logging, itit may may be be placedplaced underunder stressstress duringduring periodsperiods ofof heavyheavy rainfall.rainfall. The restricted distributiondistribution ofof natural natural stands stands of of this this species species to to areas areas ofof high high rainfallrainfall and and nono marked dry season suggestssuggests thatthat this species may be susceptiblesusceptible toto drought stress (Arentz 1988).

57 7.6.7.6. STANDSTAND LEVEL LEVEL DIEBACK DIEBACK OF OF METROSIDEROS METROSIDEROS POLYMORPHA,POLYMORPHA, IN THE HAWAIIAN ISLANDS, USA.USA.

The dominantdominant rain forest treetree onon thethe HawaiianHawaiian IslandsIslands isis thethe ohl'aohi'a lehua,lehua, Metrosideros polymorpha.polymorpha. This speciesspecies has longlong impressedimpressed botanists becausebecause of itsits morphological variability and ecological amplitude.amplitude. OnOn the islandisland of Hawaii,Hawaii, ohi'aohi'a lehualehua forms nearlynearly purepure standsstands onon lavalava flowsflows onon thethe slopesslopes ofof the the volcanoes volcanoes Mauna Mauna LoaLoa andand Mauna Kea.Kea.

During thethe early 1970s, a diebackdie back of ohi'aohi'a onon thethe islandisland ofof HawaiiHawaii becamebecame soso conspicuous thatthat a number ofof studies were initiated to determine its causes. SequentialSequential aerial photographs, taken ofof anan 80,00080,000 ha ha areaarea onon thethe slopesslopes ofof MaunaMauna KeaKea indicated that an area ofof severesevere decline,decline, withwith over 40%40% of the canopy dead or dying, increased fromfrom 120 ha in 1954 to 34,50034,500 haha inin 19721972 (Stemmermann (Stemmermann 1983).1983).

Investigations intointo thethe causecause of the diedieback back indicatedindicated thatthat the fungus,fungus, Phytophthora cinnamomi, and anan endemic,endemic, hosthost specificspecific borer,borer ,Plagithmvsus Plaqithmysus bilineatus,bilineatus, (Coleoptera: (Coleoptera: Cerambycidae) werewere associatedassociated withwith the decline but could not bebe implicated asas primaryprimary causal factors. Hodges etet al (1986) suggestsuggest that poorpoor soilsoil drainagedrainage maymay stressstress trees,trees, increasing theirtheir susceptibility toto borersborers andand rootroot disease.disease.

Stemmermann (1983)(1983) documenteddocumented differences differences in in the the distributiondistribution ofof differentdifferent morphological forms of ohi'a lehualehua on young and old lava flows andand suggests that therethere may be several successionalsuccessional formsforms ofof thisthis tree. SheShe considersconsiders the occurrenceoccurrence ofof diebackdieback in these forests asas a natural successional process.process. Mueller-DomboisMueller-Dombois (1986)(1986) regardsregards thethe diedieback back of thesethese forestsforests asas anan exampleexample ofof synchronous synchronous cohortcohort senescence senescence possiblypossibly triggered by excessexcess rainfall. HeHe hashas describeddescribed fivefive diebackdie back types on the windwardwindward slopesslopes of MaunaMauna KeaKea and Mauna Loa (Mueller-Dombois 1983)1983)::

A. Wetland Dieback - Usually a radical tree-to-tree diebackdieback onon poorlypoorly drained,drained, shallow, lava outcrop soilssoils (Fig(Fig 7.2).7.2).

B. Dryland Dieback - UsuallyUsually a salt-and-peppersalt-and-pepper or patchy diebackdieback onon wellwell drained, shallow lava rock outcrop soilssoils (Fig(Fig 7.3).7.3).

C. DisplacementDisplacetnent Dieback -- Found onon moderatelymoderately toto well draineddrained deepdeep soilssoils of organicaorganicallylly enriched and thereforetherefore fertile volcanic ash. Here,Here, treetree fernsferns areare so vigourousvigourous that they replacereplace the canopy Metrosideros whenwhen thesethese undergoundergo stand-level diedieback. back. MetrosiderosMetrosideros seedlingsseedlings may be abundant on thethe forest floor, butbut thethe treetree fernsferns shadeshade outout aa significantsignificant number.number.

D. Bog-Formation Dieback - Occurs also on deepdeep soilssoils ofof volcanicvolcanic ash, but here the ashash is relatively old,old , nutritionallynutritionally poorpoor andand permanentlypermanently soggysoggy oror waterwater soaked. ThisThis isis aa salt-and-pepper diebackdieback involving grovesgroves ofof dead dead treestrees andand non-dienon-dieback back trees in various patterns.patterns.

E. Gap-Formation DiebackDieback - - FoundFound onon the moderatelymoderately wellwell draineddrained ridgesridges dissecting the bog formation terrainterrain inin the northern half ofof thethe diebackdieback area. It ininvolvesvolves small tree groves or patches as inin thethe drydrylandland diebackdieback.. However,However, this formform ofof diebackdieback occursoccurs onon older,older, nutritionallynutritionall y depleteddepleted ash ash soils,soi ls, somesome of whichwhich areare suspectedsuspected to showshow aluminumaluminum toxicity.toxicity.

58 Figure 7.27.2 - Wetland- Wetland dieback dieback of Metrosideros of Metrosideros polymoroha. polymorpha. (Photo (Photo courtesy courtesy of D.of D. Mueller- Mueller­ Dombois, University of HawaiiHawaii atat Manoa,Manoa, USA.)USA.)

Figure 7.37.3 - Stand ofof Metrosideros polymorphaoolymorpha affectedaffected byby drylanddryland dieback.dieback. This photo shows vigorousvigorous regrowth,regrowth, a a situation situation known known as as replacement replacement dieback. dieback. (Photo (Photo courtesy of D.D. Mueller-Dombois,Mueller-D ombois, University of Hawaii at Manoa, USA.)

59 TABLE 7.3

SUMMARY OFOF FORESTFOREST DECLINEDECLINE EVENTS BY POSSIBLE CAUSAL FACTORSFACTORS PACIFIC ISLANDS ISLANDS •*

DECLINE EVENT FOREST PREDISPOSINGPREDI SPOSING INCITING CONTRIBUTING SITUATIONSITUATION**" FACTORSFACTORS FACTORS FACTORS

Nothofagus sp.sp . N Cohort senescencesenescence None given RootRoot fungus,fungus, (Papua New Guinea,Guinea, Phytophthora 7.47.4.).1 cinnamomcinnamornii WooWoodd borersborers

Metrosideros N CCohortohort senescencesenescence ExcessExcess rainfall RootRoot fungus,f ungus, polytnorphapolymorpha Phytophthora (Hawaiian Islands,Islands, cinnamomi UUSA,SA, 7.5.)7.5.1 Wood borer,borer, Plagithmysus bilineatusbilineatus

• CausaCausall factorsfactors areare summarizedsummarized according toto the predisposing, incitinginciting andand contributingco ntributing fafactorsctors conceptconcept ofof SinclairSinclair andand ManionManion (see(see sectionsection 2.3.21.2.3.2).

*** * NN = =natural natural forest, forest, PIPI i== plantationplantation vvithwith indigenousindigenous species,species, PEPE planplantationtation wwithith exoticexotic species.species.

60 CHAPTER 8

LATIN AMERICA ANDAND THETHE CARIBBEAN.CARIBBEAN.

Episodes of forest declinedecline inin Latin America andand the CaribbeanCaribbean have occurred inin bothboth natural forests andand plantations.plantations. SomeSome havehave involvedinvolved chronicchronic exposureexposure to airair pollutants.pollutants. Others have been associated withwith soil nutrientnutrient deficiencies,deficiencies, drought andand highhigh winds.winds. Included inin the followingfollowing sectionssections areare casecase historieshistories fromfrom Argentina,Argentina, Brazil,Brazil, Colombia,Colombia, Ecuador (Gallapagos(Gallapagos Islands),Islands), Mexico,Mexico, Peru andand Uruguay (Table 8.1).8.1).

8.1. FORESTFOREST DECLINE DECLINE ININ THETHE MEXICOMEXICO CITYCITY BASIN.BASIN.

In 1981,1981, extensiveextensive declinedecline and mortality ofof purepure forestsforests ofof AbiesAbies religiosareligiosa waswas detected in thethe ParqueParque NacionalNacional Desierto dede los Leones, southwestsouthwest of MexicoMexico City.City. Symptoms include discoloration of needles,needles, loss of olderolder foliage, reduced growth, deaddead branches and lack of cone crops (Figs 8.18.1 -- 8.3).8.3). TreeTree mortalitymortality is is thethe resultresult of of a a build-up build-up of twotwo species species of of bark bark beetles, beetles, Pseudohylesinus Pseudohylesinus variegatusvariegatus andand ScolytusScolytus mundosmundos (Coleoptera(Coleoptera:Scolytidae).: Scolytidae).

Forests ofof PinusPinus hartwegii, which areare locatedlocated atat anan elevationelevation zonezone immediatelyimmediately above the AA.. religiosa forests, have yellow foliar flecking characteristic ofof elevatedelevated levelslevels of ozone.ozone. TreesTrees areare beingbeing attackedattacked andand killedkilled byby thethe barkbark beetle,beetle, DendroctonusDendroctonus adjunctusadjunctus (Coleoptera:Scolytidae).(Co)eoptera :Sco)ytidae).

It isis believedbelieved that thethe declinedecline ofof bothboth AbiesAbies andand PinusPinus forestsforests isis duedue toto elevatedelevated levels of ozone which isis producedproduced when pollutant ladenladen air is trapped inin thethe Mexico City basin and exposed to sunlight. HighHigh levels levels of of ozone ozone have have been been measured measured inin thethe basinbasin andand street trees and vegetable crops in Mexico City havehave shown classicclassic symptoms ofof ozoneozone damage (Bauer andand KruperKruper 1990,1990, Cibrion TovarTovar 1989, CieslaCiesla and Macias Samano 1987).

8.2.8.2. OAKOAK DECLINE DECLINE ININ COLOMBIA.COLOMBIA.

The oak, QuercusQuercus humboldtii, isis aa valuablevaluable treetree inin ColombiaColombia becausebecause ofof itsits highhigh wood quality.quality. This tree occursoccurs in homogeneoushomogeneous standsstands in in thethe northernnorthern partpart of the Department of Antioquia wherewhere harvestingharvesting isis nownow regulatedregulated to protectprotect remainingremaining stands.stands.

A dieback, affectingaffecting bothboth youngyoung andand oldold trees,trees, hashas beenbeen reportedreported in thesethese forests. Symptoms include a progressiveprogressive death of individualindividual branchesbranches eventually affecting thethe entire crown,crown, marginalmarginal necrosisnecrosis and chlorosis of foliagefoliage andand aa vascularvascular discoloration of twigs,twigs, branchesbranches andand roots.roots.

Investigations into the causes of thisthis dieback indicated thatthat several fungi,fungi, parasitic plants (mistletoes), insects andand anan unidentified nematode were associatedassociated withwith symptomatic trees. TheThe following following fungi fungi were were recovered; recovered; PhialophoraPhialophora sp. from necroticnecrotic foliage,foliage, PestalotiaPestalotia sp. from bothboth chloroticchlorotic andand necroticnecrotic foliagefoliage andand DothiorellaDothiorella sp.sp. fromfrom dead branches.branches. Several familiesfamilies ofof insects were foundfound feedingfeeding onon thethe foliagefoliage andand secondary wood borers,borers, ants and termites werewere foundfound inin deaddead andand dying trees.trees.

61 Figure 8.18.1 -- Foliage ofof healthy Abies religiosa withwith three to fourfour yearsyears ofof needle needle retentionretention.. (Photo(Photo byby W.M. Ciesla)Ciesla)

Figure 8.28.2 - Foliage of Abies religiosa suffering from photo-oxidantphoto-oxidant injuryinjury inin thethe Parque NacionalNacional DesiertoDesierto dede loslos Leones Leones near near Mexico Mexico City, City, Mexico. Mexico. Note that onlyonly the most recent two year'syear's growthgrowth ofof foliage foliage isis retained.retained. (Photo(Photo by W.M.W.M. Ciesla)Ciesla)

62 los Figure Leones, 8.3 - Abies Mexico. religiosa (Photo by w W.M ith symptoms . its1 S 1 I IV C;eslal .. ie jlt 1,. .;,

63 I -. -40#41.. ilt-: ..0';:t ' . : 45% .. li ' v.' "':.0416Vg It- lii!': of , 4 1r - k!». decline, 1,4,- ..... :.

Parq ' ilk ipi ue Nacional Desierto de Ramirez CorreaCorrea (1988)(1988) concludesconcludes thatthat thethe diedieback back maymay bebe duedue toto several factorsfactors which could produceproduce similarsimilar symptoms.symptoms. He suggested studiesstudies leadingleading towardtoward a betterbetter understanding ofof the structurestructure ofof thesethese standsstands asas aa meansmeans ofof developingdeveloping strategiesstrategies toto protect themthem fromfrom damagingdamaging agents.agents.

8.3. DIEBACKSDIEBACKS OF OF EUCALYPTUS EUCALYPTUS SP.SP . ININ SOUTHSOUTH AMERICA.AMERICA.

Eucalypts areare widelywidely planted in manymany SouthSouth AmericanAmerican countries wherewhere theythey areare used forfor fuelwood, charcoal,charcoal, minemine timberstimbers,, structural lumber,lumber, poles,poles, posts and other wood products.products. TheyThey areare alsoalso usedused forfor windbreakwindbreak andand ornamentalornamental plantings. WhileWhile thisthis groupgroup of trees is well adaptedadapted to aa widew id e rangerange of climatic,climatic, topographictopographic andand edaphicedaphic conditions, there have been a number of problemsproblems associated withwith plantationplantation establishmentestablishment inin thethe region. SeveralSeveral ofof thesethese appear toto be thethe resultresult ofof aa complexcomplex ofof interactinginteracting factorsfactors which fit underunder thethe definitiondefinition ofof decline.decline.

8.3.1. BRAZIL -- EucalyptsEucalypts plantedplanted inin thethe Rio DoceDoce ValleyValley inin thethe state ofof MinasMinas Gerais areare affectedaffected by a disease ofof unknown aetiology which isis locallylocally knownknown asas MalMal do do Rio DDoceoce oror SecaSeca de de Ponteiros. Ponteiros. SomeSome 30,00030,000 ha. of plantationsplantations havehave beenbeen affected sincesince 1974. MalMal do do Rio Rio Doce Doce is is presently presently considered considered toto bebe thethe most most damaging damaging diseasedisease ofof eucalypts inin Brazil.Brazil.

Symptoms, which appear 88 toto 10 months afterafter transplanting toto thethe fieldfield following the first drydry season,season, include loss of foliage, shoot diebackdie back followed byby secondarysecondary branchingbranching which resultsresults inin poorpoor form,form, girdlinggirdling branch branch cankerscankers and reduced increment.increment. AA numbernumber ofof species, including most ofof thosethose ofof commercialcommercial importance,importance, havehave beenbeen affectedaffected (Dianese(Dianese and Moraes 1986).

A numbernumber of hypotheseshypotheses havehave beenbeen postulated asas to thethe causalcausal factorsfactors associatedassociated with thisthis disease.disease. TheseThese includeinclude unfavourableunfavourable soilsoil andand waterwater chemistry,chemistry, airair pollutionpollution andand acid rain. NoneNone ofof thesethese factorsfactors have have beenbeen confirmedconfirmed asas causalcausal agents, however,however, andand thethe aetiology ofof thisthis diseasedisease is still unknown.unknown. InIn addition, addition, no no pathogens pathogens have have been been recoveredrecovered to date from affectedaffected treestrees whichwhich couldcould bebe firmlyfirmly implicatedimplicated asas causalcausal factors otherother thanthan a few foliar andand stem fungi, notablynotably ColletotrichumColletotrichum qleosoorioides.gleosporioides. TheseThese areare believed toto be secondary factorsfactors (Dianese etet alal 1984, 1985).1985).

Certain provenances of E.I· saligna,saligna, E.I· Dellita,pellita, E.I · camaldulensis,camaldulensis, E.I· resinifera,resinifera, E.I· ounctata,punctata, aa cloneclone ofof E.I . qrandisarandis andand aa provenanceprovenance ofof E.I. saligna appear to be resistant toto thisthis condconditionition in the field.field. I.E. torelliana appears toto be highly resistant to MalMal dodo RioRio Doce.Doce. Utilization ofof resistantresistant speciesspecies oror varietiesvarieties appearsappears to bebe anan effective meansmeans ofof managingmanaging this diseasedisease even thoughthough the aetiology remainsremains elusive (Dianese etet alal 1984).

8.3.2. COLOMBIACOLOMBIA -- EucalyptusEucalyptus qlobulusglobulus isis oneone ofof thethe principleprinciple speciesspecies usedused for reforestation inin Colombia.Colombia. This treetree hasha s beenbeen widelywidely plantedplanted inin thethe DepartmentsDepartments ofof Cundinamarca, Boyaca, Tolima and NarifioNarino because itit is well adapted to cool climatesclimates andand provides anan important source ofof fuel wood,wood, posts,posts, structuralstructural lumberlumber andand otherother woodwood products.

In the DepartmentDepartment of Narifio,Narino, thisthis treetree hashas sufferedsuffered fromfrom aa progressiveprogressive diebackdie back (secamiento ascendente)ascendente) which which hashas affected affected anan estimated estimated 60% 60% ofof thethe plantations. TheThe

64 condition is initiallyinitially characterizedcharacterized by a reddening ofof thethe foliage, followed byby foliagefoliage andand branch necrosis and treetree mortality.mortality.

InvestigInvestigationsations intointo thethe causecause of thethe dieback,die back, including analysis of soils and foliage,foliage, indicate that affectedaffected plantationsplantations areare growing on soils deficient inin potassiumpotassium and, to aa lesser degree, phosphorus and boron.boron. Fungi recoveredrecovered fromfrom symptomatic trees includeinclude Pestalotia sp.,sp., which was recovered from necroticnecrotic foliagefoliage andand branches, and Botrydiolodia,Botrydiplodia, from necrotic rootroot tissue.tissue. TheseThese fungifungi werewere regardedreg arded as secondarysecondary factorsfactors affectingaffecting trees stressed by the nutrient deficientdeficient soils.soils.

Applications of aa 10-20-10 fertilizerfertilizer withwith borax borax (10.5%)(10.5%) resulted resulted inin somesome recoveryrecovery of the trees. TheThe investigatorsinvestigators recommendrecommend applicationapplication toto plantationsplantations lessless than three yearsyears of age with lessless than 50%50% ofof thethe treestrees affectedaffected byby dieback.die back. FertilizerFertilizer applicationsapplications shouldshould be made at thethe beginningbeginning ofof thethe winter w inter rainy rainy season season (Orozco (Orozco JaramilloJaramillo andand CopeteCopete Perdomo, no date)date)

8.3.3. PERU - - EucalyptusEucalyptus globulus olobulus has has been been wide widelyly plantedplanted inin portionsportions of thethe Andean highlands ofof Peru forfor many yearsyears.. SomeSome 59,00059,000 haha ofof plantations plantations havehave beenbeen established. TheseThese areare subject to periodicperiodic episodesepisodes of foliage yellowing andand witheringwithering (La(La marchitez del eucalypto).

Toward the end of 1983,1983, some some 6,0006,000 ha ha ofof eucalypteucalypt plantingsplantings inin thethe southeasternsoutheastern highlands of Peru were affected byby thisthis condition.condition. InitiallyInitially infection of rootroot systemssystems byby Phytophthora or a soil boron deficiencydeficiency waswas suspectedsuspected asas aa causa causall factor factor.. However field studies failed toto confirm the involvementinvolvement of eithereither ofof thesethese factors.factors.

An analysisanalysis of the geographicgeographic distributiondistribution ofof thethe condition showedshowed thatthat it waswas concentrated inin thethe ValleValle SagradoSagrado de los Incas, an areaarea whichwhich had sufferedsuffered from a severe drought during 1983 (18%(18% ofof normal normal precipitation).precipitation). VVithinWithin thethe areaarea affectedaffected by thethe drought, plantations which werewere establishedestablished on steep slopes withwith shallow,shallow, rockyrocky soilssoils were most severelyseverely damaged.damaged.

Guidelines for assessment of site conditions prior to plantingplanting werewere developeddeveloped whichwhich could be used toto identify sitessites bestbest suitedsuited forfor establishment. establishment. These These vvere were presented presented asas aa risk rating systemsystem whichwhich waswas basedbased onon topography,topography, soilsoi l conditioncondition andand precipitationprecipitation (Cannon 1984).

8.4. CANOPYCANOPY DIEBACK DIEBACK OF OF SCALES1A SCALESIA PEDUNCULATAPEDUNCULATA ININ THE GALAPAGOS ISLANDS, ECUADOR.

A diebackdieback ofof ScalesiaScalesia pedunculata,pedunculata, oneone ofof the majormajor canopycanopy speciesspecies of thethe Galapagos Islands,Islands, isis describeddescribed byby Itowltow and Mueller-Dombois (1988), LawessonLawesson (1988) and Mueller-DomboisMueller-Dombois (1988).(1988). ThisThis fastfast growinggrowing species,species, whichwhich maymay completecomplete itsits life cyclecycle inin 20 yearsyears and grow toto aa heightheight ofof 2020 meters, meters, apparentlyapparently evolvedevolved fromfrom aa forbforb inin thethe family Compositeae.Compositeae.

Scalesia pedunculatapedunculata isis thethe dominantdominant canopycanopy tree tree ofof thethe moistmoist forestforest zone, whichwhich isis well representedrepresented atat midmid toto upper elevatelevationsions (500(500 -- 700 m)m) onon thethe windwardwindward sideside ofof Santa Cruz island.island. The existence ofof large,large, eveneven ageage stands (cohorts) ofof thisthis speciesspecies maymay be the result of pastpast disturbancesdisturbances includingincluding wildfiresw ildfires duedue toto human human 'activities·activities andand heavyheavy

65 rains associated wwithith ElEI Niño.Nino. ThisThis forestforest goes goes intointo periodic periodic episodesepisodes ofof canopycanopy diebackdieback which isis usuallyusually followedfollowed byby abundantabundant regeneration.regeneration. TheThe dieback die back appears appears toto be be relatedrelated inin part to the stand demography resulting in aging cohort stands and inin part toto environmental triggers, suchsuch asas heavy rains associated withwith "El"EI Niño'Nino" oror otherother physiologicalphysiological upsets,upsets, suchsuch as droughtdrought..

Two diebackdieback events have occurred duringduring thisthis century.century. TheThe first occurredoccurred betweenbetween 1935 and 1940 whenwhen the forestforest thinned down to onlyonly a few scattered remnants. DuringDuring the early 11940s, 940s, heavy flowering, coincidentcoincident withwith a a drydry period, period, providedprovided seedseed toto restockrestock the areas whichwhich suffered fromfrom dieback.die back. AA moremore recentrecent diebackdieback eventevent occurredoccurred following the 1982/831982/83 El EI Niño,Nino, which which brought brought unusually unusually heavy heavy rainfall rainfall to to the the Galapagos Galapagos Islands.Islands.

Studies onon the ecologyecology ofof 12S.. pendunculatapendunculata forestsforests indicateindicate thatthat theythey areare characterized by:by:

A. A pioneerpioneer behaviour.behaviour.

B. Species-poor constitution.

C. An absenceabsence of youngyoung trees.trees.

D. The synchronous collapse of canopy treetree populations.populations.

E. A self cycliccyclic oror build-upbuild-up andand collapsecollapse succession.succession.

The dieback of these forests isis similarsimilar tato diebackdie back eventsevents inin otherother PacificPacific IslandsIslands (e.g. Hawaii, NewNew Zealand,Zealand, PapuaPapua New Guinea)Guineal and is believed to be another example of cohort senescence.senescence.

88.5.5 FORESTFOREST DECLINEDECLINE ININ PARQUEPAROUE ANCHORENA,ANCHORENA, URUGUAY.URUGUAY.

A declinedecline ofof bothboth nativenative andand exoticexotic trees trees has has recently recently beenbeen detecteddetected andand ininvestigatedvestigated inin Parque Anchorena,Anchorena, aa 13701370 ha national park locatedlocated somesome 208208 km west of Montevideo. ThisThis park park is is located located onon aa broad, broad, level,level, exposedexposed coastalcoastal plain.plain.

The condition were first detecteddetected inin DecemberDecember 19901990 andand intensified betweenbetween 19911991 and 1992. SymptomsSymptoms include include reducedreduced growth,growth, poorpoor vigour,vigour, foliagefoliage whichwhich isis smallersmaller than normal and either chloroticchlorotic or with aa greygrey castcast andand stemsstems andand rootsroots withwith cankers cankers andand necrotic areas. SpeciesSpeCies affectedaffected includeinclude CeltisCeltis spinosa,spinosa, EucalyptusEucalyptus spp.,spp., QuercusOuercus spp.,spp., Scutia buxifolia, SchinusSchinus spp. and other plants.plants.

Ramierez GrezGrez (1992) (1992) suggestssuggests involvementinvolvement ofof Phytophthora and StereumStereum butbut waswas unable toto make specificspecific identifications or determine the role ofof thesethese fungifungi inin thethe onset ofof decline. ExposureExposure of trees to episodes of high velocityvelocity southwesterly winds,winds, causingcausing barkbark damage andand creatingcreating infectioninfection courtscourts for fungi,fungi , isis aa probable probable predisposingpredisposing factor. A prolonged drought during 19881988 andand 19891989 may may have have placed placed anan addedadded stressstress onon thethe trees.trees.

Recommended actions actions includeinclude salvagesalvage ofof dead and dyingdying treestrees andand improvedimproved management of the park's flora and fauna including reduction of the park's introduced deerdeer population (Ramierez(Ramierez Grez 1992).

66 8.6. DECLINEDECLINE AND AND MORTALITY MORTALITY OF OF AUSTROCEDRUS AUSTROCEDRUS CHILENSISCHILENSIS ININ ARGENTINAARGENTINA

The conifer, AustrocedrusAustrocedrus chilensis,chilensis, isis indigenousindigenous to thethe AndeanAndean regionregion ofof centralcentral and southern ArgentinaArgentina andand Chile.Chile. In Argentina, a decline andand mortalitymortality of thisthis speciesspecies (Mal de cipres) has beenbeen observedobserved since since 1948. 1948. The condition is restricted toto ArgentinaArgentina where it isis causingcausing considerable damage damage to to a a tree tree whichwhich isis important both fromfrom anan ecological and economic standpoint.

Symptoms are uniformuniform and includeinclude discolourationdiscolouration ofof foliagefoliage followedfollowed by foliage loss, resinosresinosisis andand buttbutt and root rot.rot. FoliarFoliar symptoms are most prevalentprevalent duringduring thethe summersummer dry seasons.seasons.

Despite aa number ofof investigations,investigations, the causalcausal factorsfactors havehave notnot beenbeen identifiedidentified (Havrylenko etet alal 1989). AnAn analysis analysis ofof the the spatial spatial distributiondistribution ofof symptomatic symptomatic treestrees iindicatesndicates that theythey tendtend toto occuroccur in in patchespatches as as inin thethe case case ofof many many root root diseases diseases (Rosso(Rosso et alal 1989).1989).

8.7.8 .7. DIEBACK IN FUEGO-PATAGONIAN NOTHOFÁGUSNOTHOFAGUS FORESTSFORESTS

InIn the northernnorthern PatagoniaPatagonia region ofof Argentina,Argentina, overover anan west-eastwest-east distancedistance ofof approximately 50 km,km, thethe vegetationvegetation changeschanges fromfrom NothofagusNothofagus rainforestsrainforests throughthrough woodlands ofof AustrocedrusAustrocedrus chilensischilensis toto steppesteppe dominateddominated byby bunchbunch grass grass andand shrubs.shrubs. Pure standsstands ofof N.N. aantarcticantarctica dominate thethe forestforest-steppe-steppe marginmargir along the entire length of this vegetationvegetation gradient.gradient.

Dieback andand mortalitymortality of N.N. antarcticaantarctica hashas beenbeen noted asas a characteristiccharacteristic ofof thesethese stands. Its presence,presence, alongalong withwith otherother characteristicscharacteristics of thethe vegetationvegetation alongalong thisthis east-east­ west gradient,gradient, hashas beenbeen interpretedinterpreted asas anan indicatorindicator ofof regionalregional aridification.aridification. However, more recent investigations on the vegetation dynamics of this region showsshows that cessation of frequentfrequent burningburning ofof thethe steppe,steppe, firstfirst by by indigenous indigenous huntershunters andand laterlater byby European European settlers, hashas permittedpermitted treetree invasioninvasion ofof areasareas whichwhich werewere previously previously occupied occupied by by grasses grasses and shrubs.shrubs. Exclusion ofof fire from standsstands of N. antarctica,antarctica, aa shortshort livedlived species,species, rarelyrarely attainingattaining ages over 120 years,years, allowsallows themthem toto reachreach aa stagestage ofof senescence,senescence, setting thethe stage for episodesepisodes of crowncrown diebackdieback andand treetree mortalitymortality (Veblen (Veblen andand LorenzLorenz 1988).1988). NN.. antarctica isis oftenoften replacedreplaced byby N.N. dombeyidombeyi andand AustrocedrusAustrocedrus chilensischilensis (Veblen(Veblen andand Markgraf 1988).1988).

Rebertus etet al (1993) describedescribe several typestypes of gapgap formationformation andand diebackdie back inin Nothofagus forestsforests ofof PatagoniaPatagonia andand TierraTierra deldel FuegoFuego inin southernsouthern ArgentinaArgentina andand Chile. Chile. TheseThese includeinclude canopy diebackdieback andand mortalitymortality in NN.. pumiliodumilio and N. betuloides andand persistentpersistent partial crown diebackdieback in NN.. dumiliopumilio and N. antarctica.antarctica. PartialPartial wavewave mortalitymortality isis aa localizedlocalized expansion of gaps which superficially resembleresemble thethe cyclicalcyclical wave patterns in Abies in the United States and Japan (See(See sectionssections 44.9..9. andand 6.1.2).6.1.2). PartialPartial crowncrown diebackdieback isis believedbelieved to represent incomplete recovery from defoliating insects or wood borers although climaticclimatic factors andand thethe mistletoe-likemistletoe-like MisodendrumMisodendrum sp.sp. maymay alsoalso bebe involved.involved.

67 TABLE 8.18.1

SUMMARY OFOF FORESTFOREST DECLINEDECLINE EVENTSEVENTS BY POSSIBLE CAUSALCAUSAL FACTORSFACTORS LATINLATIN AMERICA ANDAND THETHE CARIBBEANCARIBBEAN •*

, DECLINE EEVENTVENT FOREST PREDISPOSIPREDISPOSINGNG INCITING CONTRIBUTING · ..... SITUSITUATION**A.TlON · • FACTORS .. , FACTORS FACTORS

MMexicoexico City BasinBasin N None given OOzonezone BarkBark beetles (8.1.1(8.1.)

Quercus N Unknown Insect Fungi humboldtii,humboldtli, defoliation? Nematodes ((Colombia,Colombia, 8.2.18.2.) Wood boringboring insectsinsects

EuEucalyptcalypt declines (8.3.1(8.3.)

Mal do Rio DoceDoce PE Soil and water Air pollution?pollution? Stem fungus ((Brazil,Bra zil, 8.3.1.18.3.1.) chemistry?chemistry? Acid rain?rain? Colletotrichum gleosporiodes

SSecamientoecamiento PE SoilSo il nutrient NoneNone given given Secondary fungi ascendente deficiencies (Colombia, 8.38.3.2.).2.1

La marchitez del PPEE SteepSteep slopesslopes DroughtDrought None given eucalypto Shallow,Shallow, rockyrocky (Peru 8.3.3.18.3.3.) soils

Scalesia N Cohort Heavy rainsrains None given pedunculata senescence DroughtDrought (Ecuador 8.48.4.).1

Parque Anchorena N HiHighgh windsw inds Drought Secondary fungifungi ((UruguayUruguay 8.5.18.5.1 PE

AAust US rocedrustrocedrus N UnUnknownknown UnknownUnknown RootRoot disease?disease? chilensischllensii' (Argentina(Argentina 8.6.)8.6.1

Nothofagus spp.spp. N FirFiree exclusion InsectInsect None given (Argentina(Arg entina 8.7.)8.7 .1 SeneSenescencescence defoliation High windswinds MistletoeMistletoe

•* CauCausalsal factorsfactors are summarizedsu mmariz ed accoaccordingrding to thethe predisposing,predisposing, incitinginciting andand contributingcontributing factorsfactors conceptconcept ofof SinclairSinclair andand ManionManion (see(see section 2.3.2).

••** NN = =natural natural forest, forest, PI PI = plantation= plantation with with indigenous indigenous species, species, PE PE = plantationplantation with with exotic exotic species. species.

68 CHAPTER 99

DISCUSSION AND CONCLUSIONSCONCLUSIONS

9.1. DECLINEDECLINE ASAS A A GLOBAL GLOBAL PHENOMENON. PHENOMENON.

The case histories described in thethe precedingpreceding sectionssections clearlyclearly establishestablish declinedecline asas a conditioncondition which can be foundfound throughoutthroughout thethe world'sworld's forests (Fig. 9.1)9.1).. DeclineDecline eventsevents are reported from boreal,boreal, temperatetemperate andand tropicaltropical forests.forests. TheyThey areare foundfound fromfrom highhigh elevation montane forests to coastal mangrove forests, in plantations and natural forests. They occuroccur inin thethe forestsforests ofof developing developing countriescountries asas wellwell asas inin industrializedindustrialized countries.countries. Decline has been reported from areas of heavy human influence andand fromfrom areasareas whichwhich are are still relativelyrelatively untouched.untouched.

Undoubtedly decline eventsevents have occurred inin addition to those describeddescribed in thisthis paper which have not been intensively studied oror wellwell documented. ForFor example,example, there are reports of diebackdie back in dipterocarpdipterocarp forests inin thethe Philippines',Philippines " diebackdie back ofof severalseveral treetree J species inin Pakistan'Pakistan' andand diebackdieback andand mortalitymortality of mangrovemangrove forestsforests in Trinidad'.Trinidad . Unfortunately the information base forfor these and otherother eventsevents waswas insufficientinsufficient for the development ofof case histories.histories. ThereThere are, no doubt, otherother cases which have either not been documented oror which havehave escapedescaped thethe attention ofof thethe authors.authors. Therefore this paper cannot bebe considered a complete globalglobal record ofof forestforest decline.decline.

There is also some evidenceevidence toto suggestsuggest thatthat additional studies could confirm that biotic agents may have a moremore dominant rolerole inin somesome declines.declines. OneOne exampleexample isis jarrahjarrah dieback in Western Australia (7.3.1)(7 .3.1) wherewhere P.E. cinnamomicinnamomi may be acting as the primaryprimary causal factor. AnotherAnother example example isis thethe declinedecline andand mortality ofof AustrocedrusAustrocedrus chilensischilensis in Argentina (8.6)4, the pattern of whichwhich maymay suggestsuggest infectioninfection byby aa yetyet undeterminedundetermined root disease.

9.2. CAUSES OF DECLINE AND DIEBACK.DIEBACK.

Complexes of interacting factorsfactors havehave beenbeen presentedpresented as the likely causes forfor most of thethe declinedecline eventsevents describeddescribed inin thethe precedingpreceding sections.sections. In a number of cases,cases, thethe aetiology of the decline event is still not well known.known. ForFor thosethose declinesdeclines whichwhich havehave beenbeen studied intensively the causalcausal factors can,can, inin manymany cases,cases, bebe orderedordered accordingaccording to thethe combined concepts of ManionManion andand Sinclair (Manion 1991) andand Mueller-DomboisMueller-Dombois (1992a) (Tables 5.15.1 - 88.1)..1).

1 Personal communication.communication, EmiEmiliolio Rosario, Director.Director, EcosystemsEcosystems Research andand DevelopmentDevelopment Bureau,Bureau, DepartmDepartmentent ofof Environment and Natural Resources, Republic of thethe Philippines.Philippines.

2 Personal communication,communication, Bashir Ahmed Wani, Deputy InspectorInspector GeneralGeneral of Forests,Forests, GovernmentGovernment ofof Pakistan.Pakistan.

33 Personal communication. communication, S. S. F Faizool,aizoel. Acting Acting Director,Director, FForestryorestry Division,Division, MinistryMinistry ofof Agriculture,Agricultu re, Land and Marine Resources, TrinidTrinidad.ad .

4A Numbers in parentheses referrefer toto thethe sectiosectionn in the text of thisthis paperpaper whichw hich describesdescribes the decline event.

6969 Figure 9.1 -- ApproApproximateximate location of declinedecline eventsevents describeddescribed in thisthis paper.paper.

There has been aa tendencytendency toto categorize forest declinedecline events into those whichwhich have occurred in the relativerelative absenceabsence of humanhuman influences (non-anthropogenic)(non-anthropogenic) andand thosethose which cancan be attributedattributed to humanhuman activities (anthropogenic),(anthropogenic), especiallyespecially industrialindustrial pollution.pollution. These will bebe discussed in the followingfollowing sections:sections:

9.2.1. NON-ANTHROPOGENIC NON-ANTHROPOGENIC FACTORSFACTORS - Many decline events havehave appearedappeared in remote locations, far removedremoved from sourcessources of pollution,pollution, timbertimber harvesting,harvesting, agriculturalagricultural operations or other identifiable anthropogenic influences. DespiteDespite thethe factfact thatthat they they have have occurred in areasareas which areare widelywidely separatedseparated geographically,geographically, theythey shareshare a numbernumber ofof common characteristicscharacteristics.. TheseThese include:include:

A. Low speciesspecies diversity.

B. Formation of even age stands (cohorts) on marginal sites,sites, usually following a catastrophic eventevent suchsuch asas aa volcanicvolcanic eruption,eruption, wildfirewildfire oror highhigh winds,winds, which hashas destroyeddestroyed thethe originaloriginal vegetation.vegetation.

C. Development ofof cohortcohort senescence.senescence.

D. A perturbation oror triggeringtriggering mechanismmechanism such as defoliation, drought,drought, excess rainfall oror highhigh winds.winds.

E. Invasion of decliningdeclining treestrees byby secondarysecondary pathogenspathogens oror insects.insects.

70 ----==-

Examples whichwhich showshow some, if not all,all, ofof thesethese featuresfeatures includeinclude wavewave generatedgenerated mortality of AbiesAbies spp.spp. inin thethe easterneastern UnitedUnited StatesStates andand Japan (4.9., 6.1.2.),6.1.2.), canopycanopy dieback in upper montane forests of Sri Lanka (6.6.).(6.6.), standstand level dieback of NothofagusNothofagus spp. in New Zealand, PapuaPapua New Guinea and thethe Fuego-Patagonia regionregion ofof South America (7.4.1.,(7.4.1. ,7.5,8.7),7.5, 8.7), stand stand level level dieback dieback of of Meterosideros Meterosideros oolymoroha polymoroha inin thethe HawaiianHawaiian IslandsIslands (7.6.), andand canopycanopy diebackdieback ofof ScalesiaScalesia oenduculatapenduculata in the Galapagos IslandsIslands (8.4). (8.4). These examples fitfit the modelmodel ofof cohortcohort senescencesenescence described by Mueller-Dombois (1992a) and can be consideredconsidered asas processesprocesses ofof ecosystemecosystem dynamicsdynamics resuresultinglting in eithereither pplantlant succession or re-establishment of new stands of the same species whichwhich dominated thethe forest canopy before the decline event took place.place. ThereThere is evidence thatthat the forest ecosystems affected by this sequencesequence of eventsevents havehave co-evolvedco-evolved withwith and and areare adaptedadapted toto these these processes. processes. InIn many cases, natural regeneration ofof the species affected is dependentdependent on the periodicperiodic occurrence ofof stand level diebackdie back or the recurrencerecurrence ofof the catastrophiccatastrophic event which created conditions for establishmentestablishment of the original cohort stands. TheThe declinesdeclines which fitfit this model are, therefore,therefore, natural andand essentialessential events events within within the the forest forest ecosystem.ecosystem. Our attention isis drawndrawn toto these these eventsevents because because ofof aa diminishing forestforest areaarea and concerns about adverse effectseffects of humanhuman activities onon forests.forests.

A notablenotable exceptionexception toto thisthis sequencesequence ofof eventsevents isis thethe decline decline ofof Chamaecyoaris Chamaecyparis nootkatensis in southeastern Alaska,Alaska, USAUSA (4(4.10)..10). StandsStands ofof thisthis speciesspecies dodo notnot appearappear to bebe even aged cohorts. ThisThis decline decline has has beenbeen aa moremore oror lessless continuous eventevent sincesince thethe late 1800s1800s andand doesdoes notnot appearappear toto bebe relatedrelated to episodicepisodic incitinginciting oror triggeringtriggering events.events.

In the case of otherother forestforest declinesdeclines whichwhich appearappear toto bebe primarilyprimarily relatedrelated toto non-non­ anthropogenic factors, thethe rolerole ofof thethe declinedecline inin thethe dynamicsdynamics ofof thethe affectedaffected forestforest is is less less clear. Examples includeinclude manymany ofof the declines which havehave beenbeen documented inin the temperate forestsforests ofof EuropeEurope and North America (eg.(eg. silver fir decline (3.1(3.1.).) and oak decline (3.2.)(3.2.) inin Europe,Europe, birch dieback (4.1.), pole blight (4.2.),(4.2.). ashash diebackdieback (4.3.) etcetc inin NorthNorth America).America) . TheThe oneone factorfactor thatthat thisthis groupgroup ofof declinesdeclines seemsseems to have inin commoncommon withwith the declines found in clearly definable cohort stands is the occurrenceoccurrence of aa perturbationperturbation oror triggering event.event. Various workers have related declinedecline occurrences toto outbreaks of defoliating insects,insects, drought,drought, excessexcess rainfallrainfall andand freezing.freezing. Auclair etet al (1992) presentpresent evidence which suggestssuggests thatthat thethe universaluniversal initiatinginitiating mechanismsmechanisms forfor forestforest declines declines are are climatic anomaliesanomalies (e.g.(e.g. winter thaw/freezethaw/freeze events oror excessexcess rainfallrainfall followedfollowed byby aa prolonged period ofof drydry weather)weather).. TheseThese cause xylemxylem cavitation which results in moisture stress and producesproduces decline symptoms.

Mangroves are dependent onon seasonalseasonal flushes flushes ofof freshfresh waterwater to regulate salinity.salinity. Failure ofof these flushesflushes duedue toto prolongedprolonged droughtdrought cancan stressstress mangrovesmangroves resultingresulting inin decline, dieback and mortality. ExamplesExamples includeinclude declinedecline ofof mangrovesmangroves inin GambiaGambia (5.8),(5.8), Bangladesh (6.5).(6.5), Australia (7.2.)(7 .2.) andand PapuaPapua New Guinea (7(7.5.)..5.).

9.2.2.9.2.2. ANTHROPOGENIC FACTORS FACTORS - Most- Most of of the the world'sworld's forests havehave beenbeen influenced toto oneone degreedegree or otherother byby humanhuman activity.activity. These influences have had far reaching effects onon ecosystemecosystem stabilitystability and and dynamicsdynamics and and havehave beenbeen associated with manymany cases of forestforest decline.decline.

Atmospheric deposition of pollutantspollutants hashas beenbeen widely discusseddiscussed as a cause of decline. TheThe effectseffects of of pollutants pollutants such such as as sulphur sulphur dioxide, dioxide, hydrogen hydrogen fluoridefluoride andand ozoneozone on vegetationvegetation areare wellwell known.known. Symptoms of exposureexposure to thesethese agentsagents havehave beenbeen described for many types of vegetation includingincluding trees (Jacobson(Jacobson and HillHill 1970, Malhotra

71 and Blavel 1980)1980).. SkellySkelly (1989)(1989) regardsregards airair pollutionpollution as potentially the most importantimportant pathogen confrontingconfronting modern day and futurefuture forests.forests. EffectsEffects havehave beenbeen demonstrated to includeinclude foliarfoliar injury,injury, growth responsesresponses and tree mortality near point sources (e.g. smelters, power plants, aluminum reductionreduction plantsplants etcetc.).) (Linzon(Linzon 1988) 1988).. In addition the detrimental effects ofof ozoneozone onon forestforest vegetation vegetation have have been been demonstrated demonstrated on on a a more more regional regional basis.basis. Examples includeinclude thethe California X-disease (4.11)(4.11) and the declinedecline ofof AbiesAbies religiosareligiosa andand Pinus patulap a tu lain inthe the Mexico Mexico CityCity BasinBasin (8(8.1)..1).

It has beenbeen suggestedsuggested thatthat some forestforest decline events, includingincluding thethe regionalregional declinedecline of hardwoodshardwoods andand conifersconifers inin EuropeEurope (3.4),(3.4), maplemaple declinedecline inin easterneastern CanadaCanada (4.4)(4.4) andand decline of Picea rubens inin thethe easterneastern UnitedUnited StatesStates (4(4.8).8) are at least in part due to longlong distance (transboundary) spreadspread of of airair pollutants.pollutants. While air pollution may be part of the complex of factorsfactors associatedassociated vvithw ith thesethese declines,declines, a conclusiveconclusive cause and effecteffect relationship has not yet been established. DiscussionsDiscussions of these declines,declines, accompanied by photos of forest devastation,devastation, havehave appearedappeared in articles in newspapersnewspapers and a number of popular andand semi-popularsemi-popular magazines.magazines. These havehave oftenoften attributedattributed thethe damagedamage to acid rain. While these articles have iincitedncited strong publicpublic opinionopinion andand concern, aa relationship betweenbetween acid rain andand suchsuch forestforest devastation as depicted in these articles does not yet exist (Skelly(Skelly 1989).

Other anthropogenic factors whichwhich havehave beenbeen linked toto declinedecline eventsevents include:include:

Use of ForestsForests and WoodlandsWoodlands for PastoralPastoral PurposesPurposes -- HeavyHe avy grazing in AcerAcer saccharum forestsforests in the eastern UnitedUnited States is one of manymany factorsfactors associatedassociated with maplemaple decline (4.4)(4.4).. TheThe useuse of woodwoodlandslands for pastoral purposes, introductionintroduction of exotic grassesgrasses and fertilization hashas beenbeen suggested as aa keykey factorfactor in the decline of eucalypts in Australia known as rural or New England DiebackDieback (7.3.2.,7.3.3.). (7.3.2., 7.3.3.). Severe competitioncompetition fromfrom introducedintroduced grassesgrasses and shrubs, overgrazing and nutrient depletion onon land originally cleared for agricultureagriculture hashas been implicated in the decline of AraucariaAraucaria heterophylla on NorfolkNorfolk IslandIsland (7.1.).(7 .1 .) . Site modificationmodification associatedassociated with grazinggrazing alsoalso hashas beenbeen suggested as a factorfactor in the sudden decline of Cordyline australis in New Zealand (7.4.3.).(7.4.3.).

Harvesting of ForestForest ProductsProducts - HeavyHeavy tapping of AcerAcer saccharumsaccharum inin thethe easterneastern United States and Canada forfor maple syrup production has been identified as a factor associatedassociated with maplemaple declinedecline (4.4.).(4.4.). Construction ofof logginglogging roadsroads andand resultant changeschanges inin local hydrologyhydrology stressesstresses treestrees andand createscreates conditionsconditions favourable forfor thethe developmentdevelopment ofof thethe fungusfungus PhytophthoraPhytophthora cinnamomicinnamomi whichwhich invades the weakenedweakened trees.trees. This sequence ofof events hashas beenbeen associated withwith declines of OcoteaOcotea bullata in SouthSouth AfricaAfrica (5.5)(5.5) andand EucalyptusEucalyptus marginatusmarginatus inin western Australia (7.3.1).(7.3. 1) .

Plantations - Single speciesspecies planplantations,tations, especially ofof exotics whichwhich maymay representrepresent a narrow genetic base,base, are generally consideredconsidered to to be atat high risk to damagedamage by pests andand diseases.diseases. Large areas of exoticexotic plantingsplantings havehave beenbeen establishedestablished throughout the world.world. AA recent recent assessment assessment ofof forest forest resources resources byby FAOFAO indicatesindicates that the totaltotal plantationplantation areaarea reportedreported in 90 tropical countries was 43.8 millionmillion haha as of thethe endend ofof 19901990 (FAO (FAO 1993).1993). In manymany cases,cases, theythey havehave performedperformed remarkably wewellll inin theirtheir neneww habitats with fasterfaster growth ratesrates thanthan inin theirtheir naturalnatural ranges. The performanceperformance ofof PinusPinus radiataradiata in thethe southernsouthern hemispherehemisphere andand eucalypts in manymany regionsregions ofof thethe worldworld serveserve asas goodgood examples.examples.

72 There are however,however, examples of plantation failurefailure bothboth duedue toto aggressiveaggressive insectsinsects and diseases and declines.declines. These areare oftenoften thethe result of failurefailure to selectselect treetree species, varietiesvarieties or provenances whichwhich are best suitedsuited to the site beingbeing planted.planted. Examples ofof declinesdeclines in variousvarious typestypes ofof tree plantations includeinclude AzadirachtaAzadirachta indicaindica inin thethe SahelSahel (5.1(5.1.),.), dieback of Terminalia ivorensisivorensis (5.3.)(5.3.) plantations establishedestablished onon nutrient poorpoor soils inin CoteCote d'Ivoired'ivoire andand Ghana,Ghana, declinedecline ofof PinusPinus patulapatula inin TanzaniaTanzania (5.9.) and diebacks of eucalyptseucalypts in South America (8.3.).(8.3.).

Because ofof increasingincreasing demandsdemands for for forestforest products due to anan increasingincreasing worldworld population and concerns about global climate change, the trend toward increasedincreased area of forestforest plantationsplantations isis expectedexpected toto continuecontinue intointo thethe foreseeable foreseeable future.future. Consequently thethe risk of damagedamage due toto all pests,pests, includingincluding declines,declines, willwill remainremain high.

Accidental Introduction Introduction of of Pest Pest Species Species - The gypsy moth, LymantriaLymantria dispar, which was introduced into North America in thethe latterlatter partpart ofof thethe 19th century and is nownow a major defoliatordefoliator of hardwood forests,forests, hashas beenbeen implicated as anan incitinginciting factorfactor in some episodes of oakoak declinedecline (4.5).(4.5). OccurrenceOccurrence ofof beech bark disease (4.6) inin North America is relatedrelated toto thethe introductionintroduction of beech scale, Cryptococcus fagisuga, from Europe.Europe. ScaleScale infestationsinfestations causecause aa dryingdrying andand crackingcracking of thethe barkbark surfacesurface which creates conditions favourable for the invasion of fungi ofof thethe genusgenus Nectria.Nectria. Browsing by the introduced AustralianAustralian possum,possum, TricosurusTricosurus vulpecula,vulpecula, isis aa factor inin stand level diebackdie back of MetrosiderosMetrosideros sp.sp . andand WeinmanniaWeinmannia racemosaracemosa forests inin NewNew Zealand (7.4.2.).

Phytophthora cinnamomi,cinnamomi, isis mentioned inin this sectionsection becausebecause somesome scientists believebelieve that thisthis fungusfungus maymay have have beenbeen introduced intointo Europe,Europe, Australia,Australia, New Zealand, Central and South America and portions of thethe UnitedUnited StatesStates fromfrom a location somewheresomewhere inin southeastsoutheast Asia.Asia. This is disputeddisputed howeverhowever andand otherother scientists argue that it isis anan indigenous componentcomponent of the soil microflora (Newhook and PodgerPodger 1972).1972). There is nownow aa general general consensusconsensus amongamong AustralianAustralian phytopathologists thatthat thisthis fungus fungus has has beenbeen introducedintroduced intointo AustraliaAustralia (Weste(Weste andand Marks 1987).1987) . .E.P. cinnamomi isis associated withwith a number of declinesdeclines worldwide including declinedecline andand mortality of QuercusQuercus ilexilex andand Q.Q. subersuber onon thethe Iberian Iberian Peninsula (3.2.1,(3.2.), littleleaf disease ofof shortleaf pine in the UnitedUnited StatesStates (4.7.),(4.7.) , decline of Ocotea bullata in South Africa (5.5.),(5.5.1, jarrahjarrah diebackdieback in Australia (7.3.1.)(7.3.1.) canopy level dieback of NothofagusNothofagus spp.spp. inin PapuaPapua NewNew GuineaGuinea (7.5) andand standstand levellevel dieback of MetrosiderosMetrosideros polymorphapolymorpha inin thethe HawaiianHawaiian IslandsIslands (7.6).(7.6) . .E.P. cinnamomi was also reported causing a root disease of American chestnut, CastaneaCastanea dentata,dentata, and several species of chinkapinschinkapins overover largelarge areasareas ofof thethe southeasternsoutheastern UnitedUnited States in the early partpart of thisthis century. ThisThis fungusfungus causedcaused extensiveextensive tree mortality before the chestnut blight,blight, causedcaused byby EndothiaEndothia parasiticaparasitica spreadspread intointo thesethese areasareas (Bowen etet al 1945).1945). In addition,addition, .E.P. cinnamomicinnamomi has been reported as a rootroot pathogen of AbiesAbies albaalba inin GermanyGermany (KOhne(Kuhne 1979) and ofof CastaniaCastania sativasativa andand Quercus rubra in France (Abgrall and Soutrenou 1991).

Since 1980, thethe numbernumber of introductionsintroductions ofof destructivedestructive forestforest insectsinsects hashas increased. TheseThese includeinclude thethe EuropeanEuropean pinepine shoot moth,moth, RhyacioniaRhyacionia buoliana,buoliana, intointo Chile; leucaena psyllid,psyllid, Heteropsylla cubana, into Asia, Australia, thethe PacificPacific IslandsIslands and Africa; cypresscypress aphid,aphid, CinaraCinara cupressi, intointo easterneastern andand southern AfricaAfrica andand thethe Asian form ofof thethe gypsy gypsy moth, moth, Lymantria Lymantria dispar, dispar, into into North North America America (Ciesla (Ciesla

73 1993b). While these insectsinsects havehave provenproven toto bebe aggressive,aggressive, singularsingular causescauses affecting the healthhealth of treestrees andand forests, somesome species suchsuch asas thethe AsianAsian formform ofof the gypsy moth couldcould bebe a factor inin futurefuture forestforest declinedecline events.events.

Fire Exclusion -- TheThe naturalnatural rolerole ofof firefire in the dynamics of forest ecosystemsecosystems hashas only recently been understood.understood. ChangesChanges in firefire frequency asas aa resultresult ofof forestforest fire protection oror landland useuse change can result in accumulations of vegetativevegetative biomassbiomass which isis inin excessexcess of thethe carryingcarrying capacitycapacity of thethe site.site. This causes stressstress andand increasesincreases susceptibilitysusceptibility toto invasioninvasion byby pests andand diseasedisease.. The occurrence ofof thethe eucalypt declinedecline knownknown asas "high"high altitudealtitude dieback"dieback" (7.3.4)(7.3.4) is relatedrelated toto firefire exclusion. The decline of NothofaqusNothofagus antarcticaantarctica in thethe PatagoniaPatagonia regionregion ofof Argentina (8.7)(8.7) isis alsoalso believedbelieved to bebe the result of senescence of stands which havehave become establishedestablished in in areasareas whichwhich werewere once frequently burned; initially byby indigenousindigenous huntershunters and laterlater byby EuropeanEuropean settlers.settlers. These landslands havehave beenbeen abandoned and and are are now now relativelyrelatively freefree fromfrom fire,fire, thus allowingallowing treestrees toto reachreach senescence.

Altered HydrologicHydrologic Systems - The sensitivity of mangrovesmangroves toto changes in water salinity has been mentionedmentioned in a precedingpreceding sectionsection (9(9.2.1)..2.1). TheseThese changeschanges cancan bebe the result of upstream diversion or impoundmentimpoundment ofof waterwater forfor irrigation or domestic uses. Decline of HeritieraHeritiera tomesfomes inin BangladeshBangladesh (6.5) has beenbeen attributedattributed toto upstream diversiondiversion ofof waterwater.. JimenezJimenez et al (1985), in an analysis ofof 2828 worldwide reports of massive mangrove mortality,mortality, attribute a number of events to siltation,siltation, impoundment and runoff diversion.diversion.

Altered drainage patternspatterns whichwhich result in excessivelyexcessively wet oror waterloggedwaterlogged soilssoils stresses trees andand createscreates conditionsconditions favourable for the developmentdevelopment of Phytophthora cinnamomi.cinnamomi. Altering of naturalnatural drainagedrainage patterns due to roadroad construction, plantationplantation establishmentestablishment andand timbertimber harvesting harvesting hashas been been suggestedsuggested as factors in the decline of Ocotea bullata in South Africa (5.5) andand in the dieback of Eucalyptus marginata in western Australia (7.3.1).

9.29.2.3..3. CLIMATECLIMATE CHANGE CHANGE - The earth'searth's climate has fluctuatedfluctuated throughout geologicgeologic history. These changes have influenced thethe existence,existence, abundance andand distributiondistribution of plants and animals. Today,Today, therethere isis muchmuch concernconcern thatthat increasesincreases inin thethe levelslevels ofof carboncarbon dioxide (CO2)(CO,) andand otherother greenhousegreenhouse gases gases in in the the earth's earth's atmosphere,atmosphere, largelylargely thethe resultresult of human activities, maymay bebe changingchanging globalglobal climateclimate atat anan acceleratedaccelerated rate.rate. Increases inin atmospheric CO2CO, andand methanemethane (CH(CH4)4 ) have have been been measured measured since since about about 1850. 1850. This has been accompanied by a 00.5°C.5°C rise in temperature. TheseThese increasesincreases areare duedue toto aa numbernumber of naturalnatural andand anthropogenicanthropogenic causes. TheThe leadingleading anthropogenicanthropogenic factors areare burningburning of fossil fuelsfuels andand biomassbiomass burningburning associatedassociated withwith deforestationdeforestation and and land land ·use use changechange (IPCC(lPCC 1990).

There areare predictionspredictions thatthat ifif presentpresent trendstrends continue, continue, thethe atmosphericatmospheric concentrationconcentration of CO2CO, willwill double from the pre-industrial revolutionrevolution level of around 260 partsparts perper millionmillion by the yearyear 20652065 (Pollard(Pollard 1985).1985). This isis expectedexpected toto influenceinfluence globalglobal andand regionalregional climates. AnAn increase increase ofof from from 2 2 to to 5°C 5°C is is predicted.predicted. TemperatureTemperature increases increases are are expectedexpected to increaseincrease with latitudelatitude andand thereforetherefore exertexert aa majormajor effecteffect on on northernnorthern ecosystems.ecosystems. Precipitation is also expected to change,change, generallygenerally increasingincreasing becausebecause ofof increasedincreased energyenergy available forfor evaporation. AccordingAccording toto severalseveral studies,studies, increased frequencyfrequency and intensityintensity of tropical storms maymay be associated withwith trends towardtovvard aa warmer, warmer, wetter wetter climateclimate.. TheseThese

74 changes couldcould havehave significantsignificant effectseffects on forestsforests includingincluding shiftsshifts in thethe distributiondistribution of tree species andand forest communities,communities, changes inin forest productivity,productivity, treetree physiologyphysiology andand growth. IncreasedIncreased occurrence occurrence ofof wildfires, wildfires, pest pest outbreaks outbreaks and and declinedecline eventsevents havehave alsoalso been predicted (Andrasko 1990).

The effects ofof globalglobal climateclimate changechange on the frequency and severity of forest declinedecline events are presently notnot known. However,However, sincesince climaticclimatic perturbationsperturbations suchsuch asas warmingwarming trends and thaw/freeze eventsevents havehave beenbeen implicatedimplicated as causal factors in somesome ofof thethe events described inin thisthis paper, an interaction betweenbetween thethe twotwo wouldwould seemseem to bebe aa reasonable assumption.assumption. Auclair et al (1992) hypothesize thatthat episodic, region-wideregion-wide forestforest dieback or decline may be drivendriven by global climate change.change. WithWith globalglobal warming,warming, therethere is a tendency forfor winterwinter and and springspring temperaturestemperatures toto increaseincrease moremore thanthan summersummer andand fallfall temperatures and forfor variability toto bebe highest during warm, dry periodsperiods.. ThisThis increasesincreases thethe probability of climatic conditionsconditions whichwhich causecause xylemxylem cavitationcavitation whichwhich isis believedbelieved to resultresult in moisture stressstress resultingresulting inin thethe onsetonset ofof decline. decline.

Mueller-Dombois (1(1992b) 992b) suggestssuggests that climateclimate changechange addsadds aa newnew dimensiondimension toto his concept ofof cohortcohort senescencesenescence because itit touches on all of the eventsevents whichwhich leadlead upup to decline.decline. Elevated levels of atmosphericatmospheric CO2,CO 2 , maymay increase netnet primary production inin trees. However many sites may be unableunable to supportsupport thethe increasedincreased ratesrates ofof plantplant metabolism. ThisThis couldcould shortenshorten thethe overalloverall lifelife spanspan ofof treestrees andand hastenhasten the advent of senescence.senescence. OnOn edaphicallyedaphically poorpoor sites,sites, thethe sitesite maymay bebe unable to support increasedincreased rates of plantplant metabolismmetabolism whichwhich couldcould bringbring aboutabout prematurepremature senescencesenescence even earlier. ClimaticClimatic disturbances which trigger decline events could increase inin frequencyfrequency andand intensity.intensity. TheThe activity ofof bioticbiotic agentsag ents whichwhich functionfunction asas contributingcontributing factorsfactors could could alsoalso increase withwith the advent of warmerwarmer temperatures.temperatures.

9.3. MANAGINGMANAGING FOREST FOREST DECLINEDECLINE

9.3.1. DIAGNOSISDIAGNOSIS OF OF DECLINESDECLINES AND DIEBACKS - -The The obvious obvious firstfirst stepstep in the management ofof a forest diseasedisease is itsits diagnosisdiagnosis and identificationidentification ofof causalcausal factor(s)factor(s) Diebacks andand declinesdeclines are are the the result result of of aa complecomplexx ofof interactinginteracting factors,factors, thereforetherefore itit is impossible toto establishestablish pathogenicitypathogenicity ofof causalcausal factorsfactors usingusing thethe classical classical approachapproach ofof Koch's postulates.postulates. Manion (1991) pointspoints outout thatthat diagnosisdiagnosis ofof declinedecline isis muchmuch moremore complex than diagnosisdiagnosis ofof otherother diseases. diseases. In the past,past, it waswas acceptableacceptable toto describedescribe declines based onon subjectivesubjective evaluationevaluation ofof obviousobvious factors.factors. ThisThis hashas ledled to disagreementsdisagreements and lack of progress. DeclinesDeclines havehave alsoalso beenbeen defined on the basisbasis of a few symptomssymptoms oror on selectedselected hypothesis of poorlypoorly defineddefined interactionsinteractions amongamong factors.factors. This hashas ledled to misconceptions andand hashas maskedmasked thethe truetrue identity ofof thethe associatedassociated factors.factors. It is appropriate toto recognize thatthat the causescauses of declinesdeclines are best identified onlyonly afterafter wellwell executed field surveys and statistical analysis.analysis. SimpleSimple correlationcorrelation oror multiplemultiple regression regression analyses are suggested as means of identifying causalcausal factors.factors. In the case of aa simplesimple correlation analysis, correlation of symptoms inin relation to signs, weather oror site variables will oftenoften showshow weakweak relationships.relationships. AA strong strong correlation correlation would would suggest suggest that that the the problem problem is not aa decline but the resultresult ofof aa singlesingle factor.factor.

9.3.29.3.2 MONITORINGMONITORING AND AND ASSESSMENT ASSESSMENT -- ManyMany EuropeanEuropean countries, CanadaCanada andand the UnitedUnited States havehave eithereither establishedestablished or are in the process of establishingestablishing systematic surveys to monitor overalloverall forest condition.condition. WhereWhere thesethese alreadyalready exist,exist. theythey are are annualannual surveys where permanentpermanent sample treestrees are rated for crowncrown condition,condition, foliagefoliage colour,colour, diebackdie back or other symptoms. TheyThey are are designeddesigned toto provideprovide anan overalloverall indicationindication ofof forestforest

75 condition oror healthhealth overover time inin relationrelation toto changingchanging environmentalenvironmental oror climatic conditions.conditions. While the needneed exists,exists, therethere are no such surveys being conductedconducted in developingdeveloping countries.countries. A similar monitoring programprogram hashas been recommendedrecommended for assessmentassessment ofof neem,neem, AzadirachtaAzadirachta indicaindica,, decline in the Sahel (Boa(Boa 1992,1992, Ciesla 1993a).1993a). ForestForest healthhealth monitoringmonitoring programsprograms are also needed in developing countries where industrial development is underwayunderway andand associated environmental pollutionpollution maymay increase (eg(eg.. ChinaChina and and Mexico).Mexico). SurveysSurveys cancan provide information on trends of overalloverall forest conditioncondition overover time,time, providedprovided theythey areare carried out in the samesame manner duringduring eacheach surveysurvey cycle.cycle. TheyThey willwill notnot provideprovide datadata onon the causescauses of anyany deteriorationdeterioration inin forestforest condition.condition.

9.3.3. MANAGEMENTMANAGEMENT TACTICSTACTICS - Management ofof a conditioncondition brought about by a complex interaction ofof factorsfactors presentspresents manymany challenges.challenges. ThisThis isis especiallyespecially true in cases where declines occur in unmanagedunmanaged forests and are triggered by climatic oror otherother eventsevents which cannotcannot bebe predictedpredicted with anyany degreedegree of reliability.reliability. One of thethe fewfew publishedpublished recommendations availableavailable to to addressaddress this this classclass ofof declinedecline isis byby Hosking (1989) whowho recommends care inin the planning and development of recreationalrecreational sites inin NewNew ZealandZealand Nothofagus forests toto minimizeminimize disturbancesdisturbances which couldcould increaseincrease susceptibility ofof standsstands to highhigh windswinds oror otherother eventsevents whichwhich couldcould triggertrigger decline.decline.

In cases of declines where anthropogenic factorsfactors are part ofof thethe causalcausal complexcomplex management practices havehave beenbeen suggested to reduce losses toto thethe forestforest resource where the specific cause(s)cause(s) of decline are known.known. TheyThey include:include:

A. Avoid overgrazingovergrazing and associated soil compactioncompaction in forests and woodlands which areare proneprone to declinedecline events.events.

B. When establishing plantations,plantations, selectselect species,species. varietiesvarieties andand provenancesprovenances which areare adapted toto the sites being planted.planted. Identify exposed,exposed, severesevere sites with poorpoor soilssoils usingusing riskrisk ratingrating criteriacriteria similarsimilar toto thosethose developeddeveloped byby Cannon (1984,(1984, 1985a,b).1985a,b) . SelectSelect species species whichwhich havehave aa knownknown tolerancetolerance to atmospheric pollution inin areasareas known toto havehave elevatedelevated levelslevels ofof depositiondeposition of anthropogenic pollutants.pollutants. PayPay attentionattention to to genetic genetic base. base. InIn cases cases where where the genetic basebase of aa plantationplantation speciesspecies isis narrownarrow (eg.(eg. clonalclonal plantations),plantations), plan for conservationconservation ofof aa widerwider geneticgenetic base base elsewhereelsewhere asas aa backup.backup.

C. Institute surveillancesurveillance atat ports ofof entryentry toto intercept intercept potentially potentially damaging damaging insects, fungi and otherother agentsagents which couldcould serveserve as eithereither incitantsincitants oror contributing factorsfactors inin declinedecline events.events. If pest species should be accidentallyaccidentally introduced, establish appropriate quarantine and integratedintegrated pest management tacticstactics to limitlimit theirtheir spread.spread.

D. In cases ofof decline which maymay bebe related to firefire exclusion,exclusion, considerconsider thethe useuse of prescribedprescribed fire to helphelp keepkeep the desired vegetation in a healthy condition (eg. High Altitude DiebackDieback inin TasmaniaTasmania (7.3.4)).(7.3.4)).

E. Experiments havehave shown that,that. in somesome cases,cases, aa fastfast andand sustained sustained revitalization ofof decliningdeclining forestforest ecosystemsecosystems cancan bebe achieved throughthrough liming and fertilization providedprovided that thethe declinedecline isis associatedassociated with aa soilsoil nutrientnutrient deficiency (e.g. acute yellowingyellowing of spruce (3.3). This hashas beenbeen demonstrated byby chemicalchemical andand histologicalhistological analysisanalysis ofof foliagefoliage andand byby visible visible improvement inin condition ofof treestrees andand stands.stands. Soil analysisanalysis havehave alsoalso

76 indicated a positive change vvhenwhen standstand andand sitesite specific fertilization hashas been done (Evers(Evers andand HOWHuttl 1990).1990). Fertilizer applicationsapplications inin forests isis expensive howeverhowever andand isis generally cost-effectivecost-effective ononlyly in fastfast growing,growing, intensively managedmanaged stands.stands.

F. Comprehensive environmental analysis prior to implementation of devedevelopmentlopment projects shouldshould bebe conducted where changes in the pattern oror volume of water flow inin riversrivers andand estuaries areare anticipated.anticipated. TheseThese analyses should iidentifydentify potentialpotential downstreamdownstream effectseffects suchsuch asas changes in thethe salinitysalinity of mangrove forests and identify mitigationmitigation measuresmeasures toto preventprevent undesirableundesirable effects suchsuch asas occurrenceoccurrence ofof widespreadwidespread dieback and mortality.

Vegetation damagedamage attributable to aa singlesingle pollutionpollution source,source, suchsuch asas aa smeltersmelter oror power generating plant, cancan be reduced through installation of effective emissionemission controlcontrol systemssystems.. EnvironmentalEnvironmental analysesanalyses can identify potentialpotential pollutionpollution hazardshazards and strategies for their mitigation priorprior toto sitesite construction.construction. TheThe management management of of decline decline events events believed believed to bebe at leastleast inin partpart thethe resultresult ofof longlong distancedistance spread of air pollutants are infinitelyinfinitely more complex, however, especially ifif the suspectedsuspected pollutantspollutants are originate from multiplemultiple sources and cross internationalinternational boundaries.boundaries. Actions to addressaddress thesethese eventsevents mustmust bebe taken at the countrycountry oror regionalregional levellevel andand willw ill involveinvolve establishmentestablishment ofof nationalnational oror regionalregional policies to control emissions.emissions. TheseThese cancan havehave widespreadwidespread effectseffects on on nationalnational economieseconomies and people's lifelife styles. ThereforeTherefore soundsound datadata which firmlyfirmly establishestablish a cause andand effecteffect relation between thethe suspectedsuspected pollutantpollutant and and declinedecline isis essentialessential to supportsupport suchsuch decisionsdecisions (See sectionsection 9.3.1).9.3.1). BecauseBecause declines areare complex complex conditions conditions wit withh anthropogenicanthropogenic factor(s)factor(s) being onlyonly aa partpart ofof thethe causal complex,complex, ifif they are ininvolvedvolved atat all,all, thesethese datadata areare difficult difficult to acquire.acquire. In addition, the issuesissues are often cloudedclouded by emotions.

Mueller-Dombois (1992a) states: "For"For evaluatingevaluating the impact ofof newnew anthropogenicanthropogenic stresses such as airair pollutionpollution,, climate change andand bioticbiotic impoverishmentimpoverishment onon forests,forests, itit is importantimportant to understandunderstand thethe natural processprocesseses of of forestforest dynamidynamics.cs. Only then will itit bebe possible toto untanguntanglele the real impact of human influencesinfluences on forest decline and dieback". This statement pointspoints outout thethe needneed for continuingcontinuing researchresearch to help identify thosethose factorsfactors responsible forfor indiindividualvidual declinedecline events, theirthei r ecological,ecological, economiceconomic andand socialsocial impacts,impacts, andand theirtheir role in the dynamics of forest ecosystems. ThisThis isis especiallyespecially true for tropical forestsforests and developing countries where relatively littlelittle isis knownknown aboytabo,lt declinedecline andand may experience more decline events as they becomebecome moremore industrializedindustrialized and as forestersforesters andand forestforest workers become more awareaware ofof forestforest health andand forestforest decldecline.ine. KnowledgeKnowledge obtained from these studies should be thethe basis forfor dedevelopmentvelopment ofof policy and action options. TheseThese studies should alsoalso identify thosethose casescases wherewhere managementmanagement ofof decline decline eventsevents is is desirable desirable to ensure sustainable flowsflows ofof goodsgoods andand services from forests and those where the event isis clearclearlyly aa partpart ofof thethe dynamicsdynamics andand regeneratregenerationion ofof naturalnatural forestsforests andand humanhuman interventionintervention to preventprevent oror managemanage thethe eventevent maymay notnot bebe appropriate.appropriate.

* * * * *

77 LITERATURE CITED

Abgrall, J.F. and A.A. Soutrenou,Soutrenou, 1991.1991. La forkforet etet ses ses ennemis. ennemis. CEMEGREF, Groupment de Grenoble, France, 399 pp.pp.

Adams, M.B. andand C.C. Eagar,Eagar, 1992.1992. ImpactsImpacts of acidicacidic depositiondeposition onon highhigh elevationelevation spruce-fir forests:forests: ResultsResults fromfrom thethe Spruce-Fir Spruce-Fir Research Research Cooperative.Cooperative. Forest Ecology andand ManagementManagement 5151:195-205. : 195-205.

Andrasko, K., 1990.1990. Global warmingwarming inin forests:forests: An overviewoverview ofof currentcurrent knowledge.knowledge. Unasylva 41/163:3-11.41/163:3-11.

Arentz, F., 1983.1983. NothofaqusNothofagus dieback on Mt.Mt. Giluwe,Giluwe, Papua,Papua, NewNew Guinea. Guinea. Pacific Science 37:453-458.37:453-458.

Arentz, F., 1988.1988. Stand-levelStand-level diebackdie back etiologyetiology andand itsits consequences consequences in the forestsforests ofof Papua NewNew Guinea.Guinea. GeoJournal 17:209-215.17:209-215.

Ash, J.,J., 1988.1988. Nothofagus Nothofagus (Fagaceae)(Fagaceae) forest onon Mt.Mt. Giluwe,Giluwe, NewNew Guinea. Guinea. New Zealand JournalJournal ofof Botany 26:245-258.26:245-258.

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Malhotra, S.S. and R.A. Blauel,Blauel, 1980.1980. Diagnosis ofof air pollutantpollutant andand naturalnatural stressstress symptoms on forest vegetation inin westernwestern Canada.Canada. EnvironmentEnvironment Canada, Canada, CanadianCanadian Forestry Service, Northern Forest RResearchesea rch Centre, Centre, Edmonton, Edmonton, Alberta, Alberta, InformationInformation report NOR-X-228, 84 pp.pp.

Manion, P.D.,P.O., 1991.1991. Tree diseasedisease concepts.concepts. (Second(Second edition)edition) Prentice-Hall Inc.,Inc., Engelwood Cliffs,Cliffs, N.J., 402 pp.pp.

Manion, P.D., 1987.1987. Decline as a phenomenon inin forests: pathologicalpathological andand ecologicalecological considerations inin Hutchinson, T.C.T.C. and K.M. Meema,Meema, EffectsEffects ofof atmosphericatmospheric pollutants on forests, wetlandswetlands andand agriculturalagricultural ecosystems. NATONATO ASIASI SeriesSeries GG 16, Springer Verlag, Berlin, Heidelberg pppp 268-275.268-275.

Manion, P.O.P.D. andand D.D. LachanceLachance (eds.l, (eds.), 1992.1992. ForestForest DeclineDecline Concepts. APSAPS Press,Press, St.St. Paul, MN, 249 pp.pp.

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85 •

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90 FAO TECHNICAL PAPERS

FAGFAO FORESTRY PAPERS

1 Forest utilization contracts on public land,land, 19771977 32 Classification and definitions of forest products, 19821982 (E F S)S) (Ar/E/F/S) 2 Planning forest roads andand harvestingharvesting systems,systems, 19771977 33 Logging of mountainmountain forests,forests, 19821982 (E(E FF S)S) ((EE F S)S) 34 Fruit-bearing forest trees, 19821982 (E(E F S) 3 World list of forestry schools, 1977 (E/F/S) 35 Forestry in China, 19821982 (C(C E)E) 3 Rev.1Rev.l World list of forestry schools,schools, 19811981 (E/F/S) 36 Basic technology in forest operations, 19821982 (E(E FF S)S) 3 Rev.2Rev.2 World list of forestry schools,schools, 19861986 (E/F/S) 37 Conservation and development of tropical forestforest 4/1 World pulp and paper demand, supplysupply andand trade resources,resources, 19821982 (E(E FF S)S) 1- Vol.Vol. 1,1, 19771977 (E(EFS) F S) 38 Forest productsproducts prices 1962-1981,1962-1981, 1982 (E/F/S)(E/F/S) 4/2 World pulp and paperpaper demand,demand, supplysupply andand tradetrade 39 Frame saw manual,manual , 19821982 (E)(E) -- Vol.Vol. 2,2, 19771977 (E(E FF S)S) 40 Circular saw manual,manual, 19831983 (E)(E) 5 The marketing ofof tropicaltropical wood,wood, 19761976 (E (E S)S) 41 Simple technologies for charcoal making, 19831983 6 National parks planningplanning,, 19761976 (E F S**)SU) (E F S) 7 Forestry forfor local community development,development, 19781978 42 Fuelwood supplies in the developing countries, 1983 (ArEFS)(Ar E F S) (ArEFS)(Ar E F S) 8 Establishment techniques for forest plantations,plantations, 1978 43 Forest revenuerevenue systemssystems inin developingdeveloping countries, 19831983 (ArCE*FS)(Ar C E* F S) (E F S) 9 Wood chips - production,production, handling, handling ,transport, transport, 19761976 44/1 Food and fruit-bearing forest species (C E S) -- 1.1. ExamplesExamples fromfrom easterneastern Africa,Africa, 19831983 (E(E FF S)S) 1010/1/ 1 Assessment ofof logging costscosts fromfrom forestforest inventoriesinventories 44/2 Food and fruit-bearing forest species in the tropicstropics -- 2.2. ExamplesExamples fromfrom southeasternsoutheastern Asia,Asia, 19841984 (E(E FF S) - 1.1. Principles Principles andand methodology, methodology, 1978 1978 (E (E FF S) S) 44/3 Food and fruit-bearing forest species 1010/2/2 Assessment ofof logging costscosts fromfrom forestforest inventoriesinventories -- 3.3. ExamplesExamples fromfrom LatinLatin America,America, 19861986 (E (E S)S) in the tropics 45 Establishing pulp and paper mills, 19831983 (E)(E) - 2.2. DataData collectioncollection andand calculations,calculations, 19781978 (E(E FF S)S) 46 Forest productsproducts prices 1963-1982, 1983 (E/F/S)(E/F/S) 11 Savanna afforestationafforestation in Africa,Africa, 19771977 (E(E F)F) 47 Technical forestryforestry educationeducation -- designdesign andand 12 China: forestry support forfor agriculture,agriculture, 19781978 (E)(E) implementation,implementation, 19841984 (E(E FF S)S) 13 Forest productsproducts pricesprices 1960-1977,1960-1977, 1979 (E/F/S) 48 Land evaluation for forestry,forestry, 19841984 (C(C EE FF S)S) 14 Mountain forest roads and harvesting,harvesting, 19791979 (E)(E) 49 Wood extraction with oxen and agricultural tractors,tractors, 14 Rev.1Rev.l Logging and transport inin steepsteep terrain,terrain, 19851985 (E)(E) 1986 (E F S)S) 15 AGRrSAGRIS forestry forestry -- world cataloguecatalogue of information and SO50 Changes in shifting cultivationcultivation inin Africa,Africa, 19841984 (E (E F)F) documentation services,services, 19791979 (E/F/S) SO/I50/1 Changes in shifting cultivation in Africa - sevenseven 16 China: integrated wood processingprocessing industries,industries, 19791979 case-studies, 19851985 (E)(E) (E F S) 51/1 Studies on the vovolumelume and yield of tropical forest 17 Economic analysis of forestry projects,projects, 19791979 (E(E FF S)S) stands -- 1.1. Dry Dry forest forest formations,formations, 19891989 (E(E F)F) 17 Sup.lSup.1 Economic analysis of forestryforestry projects:projects ;case case studies,studies, 52/1 Cost estimating in sawmillingsawmilling industries:industries: guidelines,guidelines, 1979 (E S) 1984 (E)(E) 17 Sup.2 Economic analysis of forestry projects:projects: readings,readings, 52/2 Field manual on cost estimationestimation inin sawmillingsawmilling 1980 (C E) industries, 19851985 (E)(E) 18 ForestForest products prices 1960-1978,1960-1978, 1980 (E/F/S)(E/ F/S) 53 Intensive multiple-use forest management inin Kerala,Kerala, 19/1 Pulping and paper-makingpaper·making propertiesproperties ofof fast-growingfast-growing 1984 (E F S)S) plantation wood speciesspecies 54 PlanificaciónPlanificaci6n del desarrollodesarrollo forestal,forestal, 19841984 (S)(S) - Vol.Vol. 1,1, 19801980 (E)(E) 55 Intensive multiple-use forestforest management in the 19/2 Pulping and paper-makingpaper·making propertiesproperties ofof fast-growingfast-growing tropics,tropics, 19851985 (E(E FF S)S) plantation wood speciesspecies 56 Breeding poplarspoplars forfor diseasedisease resistance,resistance, 19851985 (E) (E) - Vol.Vol. 2,2, 19801980 (E)(E) 57 Coconut wood -- ProcessingProcessing andand use, use, 19851985 (E(E S)S) 20 Forest tree improvementimprovement,, 19851985 (C(C EE F F S)S) 5658 Sawdoctoring manual,manual, 19851985 (E(E S)S) 20/2 A guide to forest seed handlinghandling,, 1985 (E S) 59 The ecological effects of eucalyptus,eucalyptus, 19851985 (C(C EE FF S)S) 21 Impact on soils of fast-growing species in lowland 60 Monitoring and evaluationevaluation of participatory forestryforestry humid tropics, 19801980 (E(E FF S)S) projects, 19851985 (E(E FF S)S) 22/1 Forest volumevolume estimation and yield predictionprediction 61 Forest products prices 1965-1984,1965-1984, 1985 (E/F/S) - Vol.Vol. 1.1. VolumeVolume estimation,estimation, 19801980 (C(C EE F F S)S) 62 World list of institutions engaged in forestry and 22/2 Forest vvolumeolume estimationestimation and yield prediction forest products research,research, 1985 (E/F/S)(E/F/S) - Vol.Vol. 2.2. YieldYield prediction,prediction, 19801980 (C(C EE FF S)S) 63 Industrial charcoalcharcoal making,making, 19851985 (E) (E) 23 Forest products prices 1961-1980,1961-1980, 1981 (E/F/S) 64 Tree growing by ruralrural people,people, 19851985 (Ar(Ar EE FF S)S) 24 Cable logging systems,systems, 19811981 (C(C E)E) 65 Forest legislation in selected African countries,countries, 19861986 25 Public forestry administrations inin LatinLatin America,America, 19811981 (E F) (E)(E) 66 Forestry extensionextension organization, 19861986 (C(C EE S)S) 26 Forestry andand rural development, 19811981 (E(E FF S)S) 67 Some medicinal forest plants of AfricaAfrica and LatinLatin 27 Manual of forest inventory,inventory, 19811981 (E(E F)F) America, 1986 (E)(E) 28 Small and medium sawmills in developing countries, 68 Appropriate forest industries, 19861986 (E)(E) 1981 (E S) 69 Management of forest industries,industries, 19861986 (E)(E) 29 World forest productsproducts,, demand and supplysupply 19901990 70 Wildland fire management terminologyterminology,, 1986 (E/F/S) 2000, 1982 (E(E FF S)S) 71 World compendium of forestry and forest products 30 Tropical forest resources,resources, 19821982 (E(E F F S)S) research institutions,institutions, 1986 (E/F/S)(E/FIS) 31 Appropriate technology inin forestry,forestry, 19821982 (E)(E) 72 Wood gas as engine fuel, 19861986 (E(E S) ~-

73 Forest products: world outlookoutlook projectionsprojections 1985-2000, 1985·2000, 113 Ex situsitu storage ofof seeds, pollenpollen and in vitro culturescu ltures 1986 (E/F/S) of perennial woody plantplant species,species, 19931993 (E)(E) 74 Guidelines for forestry information processing, 19861986 114 Assessing forestryforestry project impacts: issuesissues andand (E) strategies, 19931993 (E)(E) 75 An operational guide to the monitoringmonitoring andand 115 Forestry policies of selectedselected countries inin AsiaAsia andand thethe eevaluationvaluation of socialsocial forestry inin India,India, 19861986 (E)(E) Pacific,Pacific, 19931993 (E)(E) 76 Wood preservation manual,manual, 19861986 (E)(E) 116 Les panneaupanneauxx a base de bois,bois, 19931993 (F)(F) 77 Databook on endangered tree andand shrubshrub speciesspecies andand 117 Mangrove forest management guidelines,guidelines, 19931993 (E)(E) provenances, 19861986 (E)(E) 118 Biotechnology in forestforest treetree improvement,improvement ,1994 1994 (E)(E) 78 Appropriate wood harvestingharvesting inin plantationplantation forests,forests, 119 Les produits bois reconstitués,reconstitues, liantsIi ants et 1987 (E)(E) environnement, 19941994 (F)(F) 79 Small-scale forest-based processingprocessing enterprises,enterprises, 19871987 120 Decline andand diebackdieback ofof treestrees andand forestsforests -- AA global (E(E F S)S) overviewoverview,, 19941994 (E)(E) 80 Forestry extension methods, 19871987 (E)(E) 81 Guidelines for forest policy formulation, 19871987 (C(C E)E) Availability: FebruaryFebruary 19941994 82 Forest productproductss prices 1967-1986,1967-1986, 19881988 (E/(E/F/S)FIS) 83 Trade in forest products: a study ofof thethe barriersbarriers facedfaced Ar Arabic Multi!Multil --MultilingualMultilingual by the developingdeveloping countries,countries, 19881988 (E)(E) C Chinese * Out of print 84 Forest products: WorldWorld outlook projectionsprojections 1987-2000 1987-2000 E English ** In preparation - ProductProduct andand countrycountry tables,tables, 19881988 (E/F/S)(E/F/S) F French 85 Forestry extension curricula, 1988 (E/F/S)(EjFIS) P Portuguese 86 ForeForestrystry policies inin Europe,Europe, 19881988 (E)(E) S Spanish 87 Small-scale harvesting operations of wood andand non-wood forest products involving rural people,people, The FAOFAD Technical Papers are available through the authorized 1988 (E(E F S)S) FAO SalesSales AgentsAgents oror directlydirectly fromfrom DistributionDistribution and SSalesafes Section,Section, 88 Management of tropical moist forestsforests inin Africa,Africa, 19891989 FAO, VialeViale defledelle TermTermes di Caracalla, 0010000100 Rome,Rome, Italy.Italy. (E F P)P) 89 Review ofof forest management systems ofof tropicaltropical Asia, 19891989 (E)(E) 90 Forestry and food security,security, 19891989 (Ar(Ar EE S)S) 9191 Design manual on basic wood harvesting technology,technology, 1989 (E FF S)S) (Published only asas FAOFAO Training Series,Series, No.No. 18)18) 92 ForeForestrystry policiespolicies in Europe - AnAil analysis, analysis, 19891989 (E)(E) 93 Energy conservatconservationion in the mechanical forestforest industries,industries, 19901990 (E(E S)S) 94 Manual on sawmill operational maintenance, 1990 (E)(E) 95 Forest products prices 1969-1988,1969-1988, 1990 (E/F/S) 96 Planning and managing forestry research: guidelines for managers,managers, 19901990 (E)(E) 97 Non-wood forest products:products: the wayway ahead,ahead , 19911991 (E(E S)S) 98 Timber plantationsplantations in the humid tropicstropics ofof Africa,Africa, 1993 (E(E F)F) 99 Cost control in forestforest harvesting andand roadroad constructionconstruction,, 19921992 (E)(E) loa100 IntroductionIntroduction to ergonomics in forestryforestry inin developingdeveloping countriescountries,, 19921992 (E)(E) 101 Management and conservation of closed forests in tropical America,America, 19931993 (E(E F P S) 102 Research management in forestry, 19921992 (E(E S)S) 103 Mixed and pure forest plantationsplantations in the tropicstropics and subtropics, 19921992 (E)(E) 110404 Forest products pricesprices 1971-1990,1971-1990, 19921992 (E)(E) 105 Compendium of pulp and paper training and research institutionsinstitutions,, 19921992 (E)(E) 106 Economic assessment of forestry project impacts,impacts, 1992 (E)(E) 107 Conservation of genetic resources in troptropicalical forest manmanagementagement - PrinciplesPrinciples andand concepts,concepts, 19931993 (E)(E) 108 A decade of wood energy activities withinwithin thethe NairobiNairobi Programme of Action,Action, 19931993 (E)(E) 109 Directory of forestry research organizations, 19931993 (E)(E) 110 ProceedingsProceedings of the Meeting of ExpertsExperts on ForestryForestry Research,Research, 1993 (E(E/F/S)/ F/S) 111 Forestry policiespolicies in thethe Near East regionregion - AnalysisAnalysis and synthesis, 19931993 (E)(E) 112 Forest reresourcessources assessmentassessment 19901990 -- TropicalTropical countriescountries,, 19931993 (E)(E)