Ecological Studies, Vol. 116Analysis and Synthesis

Edited by

G. Heldmaier, Marzburg, FRGO.L. Lange, Wiirzburg, FRGH.A. Mooney, Stanford USAU.Sommer, Kiel, FRG

Ecological Studies

Volumes published since 1989 are listed at the end of this book.

SpringerNew YorkBerlinHeidelbergBarcelonaBudapestHong KongLondonMilanParisSanta ClaraSingaporeTokyo

Richard G. Lawford Paul B. AlabackEduardo FuentesEditors

High-Latitude Rainforests andAssociated Ecosystems of theWest Coast of the Americas

Climate, Hydrology, Ecology,and Conservation

With 83 Illustrations

Springer

Richard G. LawfordOffice of Global ProgramsNational Oceanic and Atmospheric

Administration1100 Wayne AvenueSilver Spring, MD 20920-5603, USA

Eduardo FuentesCatholic UniversityLaboratory of EcologyCastilla 114-DSantiagoChile

Paul B. AlabackSch001 of ForestryMontana Forest and Conservation

Experiment StationUniversity of MontanaMissoula, MT 59812-1063, USA

Cover Illustration: Schematic of the integrated effects of climatic, hydrological,and biological processes on ecosystems along the west coast of the Americas .Artwork prepared by Mr. Philip Gregory of the National Hydrology ResearchCentre in Saskatoon, Saskatchewan, Canada .

Library of Congress Cataloging in Publication DataHigh-latitude rainforests and associated ecosystems of the West Coastof the Americas : climate, hydrology, ecology, and conservation /Richard G. Lawford, Paul Alaback, Eduardo Fuentes, editors.

p . cm.-(Ecological studies : vol. 116)

ISBN-13: 978-1-4612-8453-6 e-ISBN-13: 978-1-4612-3970-3001: 10.1007/978-1-4612-3970-3

1. Rain forest ecology-America. 2. Rain forests-America.3. Rain forest conservation-America. I. Lawford, Richard G.II. Alaback, Paul B. III. Fuentes, Eduardo . IV. Series: Ecologicalstudies : v. 116.QHI01.H55 1995574.5'2642'097-dc20 95-5547

Printed on acid-free paper.

© 1996 Springer-Verlag New York , Inc.Softcover reprint of the hardcover Ist edition 1996

Copyright is not claimed for works by U.S. Government employees.All rights reserved. This work may not be translated or copied in whole or in part withoutthe written permission of the publisher (Springer-Verlag New York, Inc., 175Fifth Avenue,New York, NY 10010, USA) , except for brief excerpts in connection with reviews orscholarly analysis. Use in connection with any form of information storage and retrieval ,electronic adaptation, computer software, or by similar or dissimilar methodology nowknown or hereafter developed is forbidden .The use of general descriptive names, trade names, trademarks, etc., in this publication,even if the former are not especially identified, is not to be taken as a sign that such names,as understood by the Trade Marks and Merchandise Marks Act, may accordingly be usedfreely by anyone.

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98765 432 1

Foreword

The high-latitude rainforests of the earth represent one of the last biomesto be impacted substantially by human efforts to "mine," in the worstcases, or sustainably harvest , in the best cases, biotic resources. Many ofthese areas are remote and have inhospitable climates, difficult terrain,and poorly developed transportation infrastructures. As a result, theseregions, like the tropical wet forests, are among the last to experiencelarge-scale forest clearing and wholesale losses of large mammals. Theselast frontiers are now under assault, and their character is changing sorapidly that we have not even had an opportunity to learn how theseecosystems were formed and how they are organized and function. Thisknowledge is fundamental for sustainable development and for minimizingthe potentially detrimental impacts of the mechanized tools and practicesnow utilized for large-scale forest harvesting.

In this book, the nature of these forests and related systems, as well asthe environment that produces them, is explored. It is done in a com­parative context, with the goal of predicting the impacts of land usechange in general for all of these systems, wherever they may occur in theworld. The principal comparison is between the high-latitude rainforestsof the west coasts of the Americas. These regions share comparableclimates, physiography, and biome types. They have been separatedthrough geological time and, thus, the biotic systems have had differentorigins even though they appear to function in a similar manner. Thus

v

vi Foreword

comparisons between these regions have provided a powerful tool forexamining the generality of responses of systems, to perturbation forexample, that share common physical evolutionary constraints.

Even though these disjunct biotic systems may have comparable re­sponses to disruptions, the human-driven forces of change are not alwayssimilar. Differing societal and economic frameworks can lead to quitedifferent land patterns of essentially identical biotic resources , providingmany different scenarios for comparison. However , the rate and extent ofchange need be of a pace that is slow enough for us to learn from theseinadvertent experiments. Unfortunately, this is not proving to be the casein all situations.

The assessment of the origins, status, function, and responses of high­latitude rainforests contained in this volume stems from the activities of aresearch consortium of scientists from both North and South America(AMIGO - America's Interhemisphere Geo-Biosphere Organization) ,who are examining the responses of the components of the earth systemof the Americas to global change. Many of the analyses included in thisbook were first presented at a scientific meeting held in Victoria , Canada.The meeting was supported financially by the Canadian Royal Society'sGlobal Change Program ; the Canadian International DevelopmentAgency; the Inter-America Institute; the United Nations Education,Scientific and Cultural Organization; Environment Canada; and ForestryCanada.

Harold A. Mooney

Contents

ForewordHarold »: Mooney

Contributors

IntroductionRichard G. Lawford and Paul B 0 Alaback

v

Xl

XV

Section 1. Climate, Hydrology, and History

1. North-South Variations in West Coast HydrometeorologicalParameters and Their Significance for Earth Systems 3Richard Go Lawford

2. Factors Controlling the Climate of the West Coast of NorthAmerica 27GoA. McBean

3. Sulfur Cycling in Coastal Upwelling Systems and Its PotentialEffects on Climate 42S. Mary P. Benbow

4. Atmospheric and Geologic Constraints on the Biogeochemistryof North and South American Temperate Rainforests 57Lars 00 Hedin and Eugene D. Hetherington

vii

viii Contents

5. Past Changes in Climate and Tree Growth in the WesternAmericas 75Rosanne D. D'Arrigo and Gordon C. Jacoby

6. Constraints on Terrestrial Primary Productivity in TemperateForests Along the Pacific Coast of North and South America 89R.H. Waring and W.E. Winner

Section 2. Biotic Patterns

7. Biodiversity Patterns in Relation to Climate: The CoastalTemperate Rainforests of North America 105Paul B. Alaback

8. Phytogeographic Relationships and Regional RichnessPatterns of the Cool Temperate Rainforest Flora of SouthernSouth America 134Mary T. Kalin Arroyo, Magaly Riveros, Alejandro Penaloza,Lohengrin Cavieres, and Ana Maria Faggi

9. A Comparative Review of Forest Dynamics and Disturbancein the Temperate Rainforests of North and South America 173Thomas T. Veblen and Paul B. Alaback

10. Patterns of Terrestrial Vertebrate Diversity in New WorldTemperate Rainforests 214Peter L. Meserve

11. Avian Communities in Temperate Rainforests of North andSouth America 228Mary F. Willson, Toni L. De Santo, Carlos Sabag, andJuan J . Armesto

12. The Importance of Plant-Bird Mutualisms in the TemperateRainforest of Southern South America 248Juan J . Armesto, C. Smith-Ramirez, and Carlos Sabag

13. The Temperate Rainforest Lakes of Chile and Canada:Comparative Ecology and Sensitivity to AnthropocentricChange 266Doris Soto and John G. Stockner

Section 3. Forest System Responses to Human Activities

14. Implications of Patch Dynamics for Forested Ecosystems inthe Pacific Northwest 283G.A. Bradshaw, Frederick J. Swanson, andMaria R. Fiorella

Contents ix

15. Assessing and Responding to the Effects of Climate Change onForest Ecosystems 306David L. Spittlehouse

16. A Comparison of the Ecology and Conservation Managementof Cool .Temperate Rainforest in Tasmania and the Americas 320Michael J . Brown and Jennifer Read

17. Logging Effects on the Aquatic Ecosystem: A Case Study inthe Carnation Creek Experimental Watershed on Canada'sWest Coast 342Eugene D . Hetherington

18. Biodiversity of Canadian Forests, with Particular Reference tothe West Coast Forests 353Timothy J.B. Boyle

Section 4. Conclusion

19. Afterword 381Richard G. Lawford and Paul B. Alaback

Index 389

Paul B. Alaback

Juan J . Armesto

Mary T. Kalin Arroyo

S. Mary P. Benbow

Timothy J.B . Boyle

Contributors

School of Forestry, MontanaForest and ConservationExperiment Station, Universityof Montana, Missoula ,MT 59812-1063, USA

Laboratorio de Sistematica andEcologfa Vegetal , Universidad deChile, Casilla 653, Santiago, Chile

Departamento de Biologia,Facultad de Ciencias, Universidadde Chile, Casilla 653, Santiago,Chile

Department of Geography,University of Manitoba, Winnipeg ,Manitoba R3T 2N2, Canada

Canadian Forest Service, Hull ,Quebec KIA IG5 , Canada

xi

xii

G.A. Bradshaw

Michael J. Brown

Lohengrin Cavieres

Rosanne D. D'Arrigo

Toni L. De Santo

Ana Maria Faggi

Maria R. Fiorella

Lars O. Hedin

Eugene D. Hetherington

Gordon C. Jacoby

Contributors

USDA Forest Service, PacificNorthwest Research Station, ForestSciences Laboratory, Corvallis,OR 97331, USA

Forestry Tazmania, Hobart,B 7001, Australia

Departamento de Biologia,Facultad de Ciencias, Universidadde Chile, Casilla 653, Santiago,Chile

Tree-Ring Laboratory, Lamont­Doherty Geological Observatory,Palisades, NY 10964, USA

Forestry Sciences Laboratory, 2770Sherwood Lane, Juneau, AK 99801,USA

CEFYBO, CONICET, Serrano665, 1414 Buenos Aires, Argentina

USDA Forest Service, PacificNorthwest Research Station, ForestSciences Laboratory, Corvallis,OR 97331,USA

Section of Ecology andSystematics, Cornell University,Ithaca, NY 14853, USA

Forestry Canada, Pacificand YukonRegion, Victoria, British ColumbiaV8Z 1M5, Canada

Tree-Ring Laboratory, Lamont­Doherty Geological Observatory,Palisades, NY 10964, USA

Contributors xiii

Richard G. Lawford

G.A. McBean

Peter L. Meserve

Alejandro Penaloza

Jennifer Read

Magaly Riveros

Carlos Sabag

C. Smith-Ramirez

Office of Global Programs,National Oceanic and AtmosphericAdministration , 1100 WayneAvenue, Silver Spring, MD 20920­5603. Formerly of: AtmosphericEnvironment Service, 11InnovationBoulevard, Saskatoon,Saskatchewan S7N 3H5, Canada

Atmospheric Environment Service,Environment Canada , Toronto,Ontario M3H 5T4 Canada

Department of Biological Sciences,Northern Illinois University , DeKalb , IL 60115-2861 , USA

Departamento de Biologia,Facultad de Ciencias , Universidadde Chile, Casilla 653, Santiago,Chile

Department of Ecology andEvolutionary Biology, MonashUniversity , Clayton , Victoria ,3168, Australia

Instituto de Botanica, UniversidadAustral de Valdivia , Casilla 567,Valdivia, Chile

Laboratorio de Sistematica andEcologia Vegetal, Universidad deChile, Casilla 653, Santiago , Chile

Laboratorio de SistematicaEcologfa Vegetal , Universidad deChile, Casilla 653, Santiago, Chile

xiv

Doris Soto

David L. Spittlehouse

John G. Stockner

Frederick J . Swanson

Thomas T. Veblen

R.H. Waring

Mary F. Willson

W.E. Winner

Contributors

Facultad de Pesquerias yOceanograffa, Instituto de CienciasNaturales y Exactas, UniversidadAustral de Chile, Campus Pelluco,Casilla 1327, Puerto Montt, Chile

Research Branch, British ColumbiaMinistry of Forests, Victoria,British Columbia V8W 3E7,Canada

Department of Fisheries andOceans, West Vancouver Labora­tory, 4160 Marine Drive, Van­couver, British Columbia V7V 1N6,Canada

USDA Forest Service, PacificNorthwest Research Station, ForestSciences Laboratory, Corvallis,OR 97331, USA

Department of Geography,University of Colorado, Boulder,CO 80309, USA

Department of Forest Science,College of Forestry, Oregon StateUniversity, Corvallis, OR 97331,USA

Forestry Sciences Laboratory, 2770Sherwood Lane , Juneau, AK 99801,USA

Department of Botany, College ofScience, Oregon State University,Corvallis, OR 97331, USA

Introduction

Regional intercomparisons between ecosystems on different continentscan be a powerful tool to improve understanding of the ways in whichecosystems respond to global change. Large areas are often needed tocharacterize the causal mechanisms governing interactions between eco­systems and their environments. Factors such as weather and climatepatterns and land-ocean and land-atmosphere interactions all playimportant roles. Regional studies that hold as many factors constant overas large an area as possible are likely to yield the most useful insights intothe functioning of ecosystems and their responses to outside stresses.

As a result of the strong physical north-south symmetry between thewestern coasts of North and South America, many researchers have usedthis area as a focus for comparative marine and terrestrial studies. Thesimilarities in climate, coastal oceanography , and physiography betweenthese two regions have been extensively documented. Examples of thissymmetry are the mountains and oceans that introduce similar west-to­east climatic gradients and the latitudinal variations in radiation inputsthat result in similar north-south changes in day length, diurnal cycles oftemperature, and ecological adaptations to climate. However, climaticeffectsarisingfrom increasing concentrations of atmospheric carbon dioxideare expected to occur more rapidly in the Northern Hemisphere than inthe Southern Hemisphere, due to the buffering effect of the oceans in thesouth. Over time these asymmetries in the controls on ecosystems are

xv

-30 -20 -10 0 10 20 30 40 50 60 70Degrees of Latitude

xvi Introduction

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1- Elevation (m) IFigure 1. North-South transect from 700N to 55°S showing the dominant coastalvegetation cover..

likely to enhance the differences and minimize the similarities betweenthe hemispheres.

An understanding of parallel ecosystem processes and history in thesetwo regions is needed to serve as a baseline to assess the differentialeffects of climatic change and economic development . Figure 1, whichshows a schematic of the latitud inal distribution of vegetation, highlightsthe similarities and differences that exist in the distribution of biota alongthe two coasts.

Forests dominate the landscape in both hemispheres and play a keyrole in cycling and processing of nutrients between land , air, and sea ,and in providing habitats for wildlife. As it is used in the title of thisbook , the term high-latitude rainforests refers to all rainforests outsidethe tropical regions. These forests contain some of the most extensiveremain ing examples of pristine landscapes in the temperate zone. Wide­ranging wildlife species, such as predatory birds and mammals, whichhave increasingly become rare or extinct in other temperate forest typesare common in rainforests. Rainfore sts also include the vast majority ofold-growth and ancient forests in each hemisphere and are intimately tiedto some of the world's richest freshwater fish habitats. Coastal rainforestsare a key focus for debate on conservation and management , yet littlebaseline information exists on their overall history, ecology, and responseto management intervent ions.

High-latitude rainforests genera lly have persistent wet, cool, equitableclimates where fire is a relatively infrequent factor in natural disturbanceregimes. These rainforests are also highly structured and densely vegetated

Introduction xvii

as compared to other temperate-latitude forest types, reflecting both acomplex disturbance history and a moist, moderate climate.

Temperate and high-latitude rainforests are generally divided into fourdistinctive subtypes that can be defined by temperature, seasonality ofrainfall, and natural disturbance regimes. The highest-latitude rainforesttype, the subpolar rainforest , has high" rainfall equitably distributedthroughout the year but also a significant winter snowpack (especially inthe Northern Hemisphere). Subpolar rainforests also have low speciesdiversity and small, highly fragmented forest patches. Perhumid rainforestsare warmer , more extensive, and much more diverse but still haveabundant rainfall year-round. The seasonal rainforest type is transitionalto mesophytic temperate forests , in that summer rainfall is low andcatastrophic fires, although infrequent, playa key role in natural distur­bance regimes. The warm temperate rainforest is the lowest-latitude ex­tratropical rainforest type and has even less summer rainfall and a morefrequent occurrence of fire than the seasonal rainforest type. This foresttype is sometimes considered a wet subtype within the Mediterraneanclimatic zone.

Timber harvesting associated with development activities is a commonenvironmental stress on forests in both hemispheres. Temperate rainforestson the west coasts of North and South America are being exploited asquickly as tropical forests, but because they occupy a much smallerfraction of the global land base than tropical regions they are potentiallyat greater risk. Not only do these rainforests play an essential role in theglobal carbon balance, because they serve as a carbon sink, but they alsoare an important source of revenue to the resource-dependent economiesof American countries with coastal boundaries. In South America , theintroduction of new tree species to improve forest productivity is furtheraltering the biogeochemical balance, the regional hydrological cycle, andhabitats for plants and animals.

In this book , we examine both physical processes that drive ecosystemfunctions in temperate and high-latitude rainforests and the historicalfactors that led to the development of this unique biome. Importantlocal-scale effects arise from the complex biological interrelations thatoccur in these rainforests and from the effects of human uses on theirassociated ecosystems and landscapes.

Physical Processes and Patterns

The first section of this book deals with abiotic factors and processes thatinfluence the distribution of biotic patterns in both space and time and thecomplex interactions between these factors. The north-south variationsin forest structure are driven by climate as well as genetic pool structureand local geomorphology.

xviii Introduction

In order to establish the importance of latitudinal variations in climaticfactors for the structure of these rainforests , Lawford analyzes transectsof coastal patterns of temperature, precipitation, and other hydroclimaticvariables along the western coasts of North and South America . Althoughthe gross features of these patterns are similar between continents,there are many significant regional and local differences that controlecosystems at the landscape and smaller scales. For example , the dis­placement of the climatic equator northward from the geographical equatorand the dramatic influence of the Andes mountains on local atmosphericcirculation patterns led to broader bands of arid and semiarid conditionsin Chile and Peru than in North America. Upper-air circulation patternsin the Southern Hemisphere are more consistent from season to season ,leading to more stable zones of high precipitation along the west coast ofSouth America . Although the estimates of hydroclimatic fields presentedby Lawford have some inherent limitations , the general character of thefields reflects the large-scale controls on climate. However, it must berecognized that better models and more strategic data collection activitiesare needed to address the issues of land-atmosphere-biosphere links inthese coastal areas.

McBean provides a more detailed examination of the dynamic controlson climate over the area of the western coast stretching from 30°N to600N. He notes that variability occurs on different space and time scales,with response times being dependent on the spatial scale of the phenomenabeing considered and the medium (e.g. , atmosphere or ocean) in whichthe variation is occurring. The large-scale linkages between the atmos­pheric circulation pattern and the topography are reflected in the complexprecipitation patterns observed along the coast. Differences in the do­minant circulation regimes with latitude also influence the coastal ocea­nography. Upwelling of cold subsurface water is common between 300N

and 45°N due to the dominant offshore pressure pattern. Father north ,upwelling is much more irregular.

Benbow continues the theme of atmosphere-ocean interactions, as­sociating upwelling areas with certain climate influences, including thosearising from the production of dimethylsulfide. This volatile sulfur com­pound, whichis produced by marine phytoplankton, leads to the productionof cloud condensation nuclei with high sulfide content. Benbow assessesthe importance of phytoplankton-zooplankton interactions for DMS(dimethylsulfide) production. The major effects of atmospheric releasesof DMS on climate include enhanced production of cloud and increases inthe concentration of sulfur compounds in precipitation leading to dif­ferential chemical inputs to coastal forests.

Hedin and Hetherington document the differences between the atmos­pheric and geological inputs to coastal forests. In the Chilean rainforests,the inputs of sea-salt aerosols coupled with the low rates of weatheringconstitute a major biogeochemical constraint on forests. In contrast,

Introduction xix

inputs in North America forests represent a balance between atmosphericand geologic sources. Hedin and Hetherington suggest that temperaterainforests in the Southern Hemisphere may be sensitive to ENSO(El-Nifio-Southem-Oscillation) events and especially sensitive to humanactivities .

The effects of climate on trees allow for the derivation of historicalclimate records from the analysis of tree-ring data. Records from theNorthern Hemisphere are much more extensive than those in the SouthernHemisphere . As noted by D'Arrigo and Jacoby, these records allow forthe analysis of indices of ocean-atmosphere interactions in the PacificOcean. These dendrochronological records are best for inferring temera­tures from years prior to the instrumental record. Other issues that can beaddressed through dendrochronological studies include forest responsesto climatic change and CO2-induced growth enhancement.

Waring and Winner review the need for real-time monitoring and callfor a careful examination of forests in relation to current climate usingmeteorological data bases and remote sensing. Using their model, theyare able to quantify the effects of frost, drought, and humidity on forestsacross the steep coastal climatic gradient experienced in Oregon. Basedon the physiological adaptability of trees in North and South Americaand GCM (Global Climate Model) outputs, they conclude that climaticchange will result in higher productivity in South American forests andlower productivity in North American forests.

BioticPatterns

The second section of the book deals with the distribution of plants andanimals and their interactions. Alaback examines the distinctive climate,history, and biota for the four temperate rainforest types in North America.Although the current forest composition is relatively new (2000-5000years old), most of the dominant species are exceptionally well adapted tocurrent climatic conditions. Dominant conifer species are widespread andgenetically diverse throughout the coastal region . Few unique speciesoccur in the region, except near the transition between rainforests anddrier forests occurring in Mediterranean climates near the southern limitof forest. In North America, riparian rainforests are a key concentrationof species richness and plant-animal interactions, although they havebeen heavily affected by human uses. Species richness in North Americanrainforests is less than in equivalent forest types in Chile, even though theregional species pool is greater in North America. Contrasts in evolutionaryhistory, forest structure, species specialization, and genetic architecturesuggest that their responses to climate change may diverge over time.

Arroyo and her associates examine the biodiversity patterns of forestsin Chile and their historic and evolutionary causes as well as their rela­tionship to current climatic conditions. Temperate rainforests of South

xx Introduction

America are extremely isolated from other moist forest types yet havedeveloped and maintained a high level of species diversity. These forestsevolved under very different conditions than in North America , sincethey were once a part of a large, cool rainforest type that was continuouswith tropical rainforests and they were subject to much less climaticvariation than North American rainforests . Chilean rainforests have amuch greater richness of unique specialized species than in analogousforests in North America. Woody genera also dominate southern rain­forests to a much greater degree than in North America. Chilean rain­forests are likely to be more sensitive to environmental stresses caused byclimatic change and human activities than North American rainforests.

Veblen and Alaback study the role of natural disturbance in determiningforest structure and composition in temperate forests in both hemispheres.Infrequent large-scale catastrophic disturbances as well as small-scalelocalized disturbances play key roles in structuring rainforests in bothhemispheres. Windstorms are pervasive as chaotic disturbance agents inboth hemispheres, but stem breakage is the dominant mechanism for treemortality in North America , whereas rootthrow dominates in SouthAmerica. Some disturbances, such as earthquakes and landslides, are ofgreater significance in South America, but others, such as wildfires andsnow avalanches, are more important in North America . While a largedegree of similarity exists between the material disturbance regimes ofrainforests in North America and South America , many human-causeddisturbances , such as the introduction of exotic plants and animals andthe introduction of fire, have had a much greater effect in South Americathan in North America . Grazing, subsistence agriculture , and anthro­pogenic fire have had the greatest impact in South America , whereasloggingfor pulpwood export has had the greatest impact in North America .

Meserve describes the mammals and reptiles of the seasonal rainforestsof North America and the perhumid rainforests of Chile. Differentfamilies dominate in each hemisphere. Lizards dominate in the south ,while snakes dominate in the north. Fewer than half the number ofmammal species in northern rainforests occur in Chilean rainforests.As with rainforest plant species, Chilean mammals have a much higherdegree of uniqueness and have evolved in much greater isolation thantheir counterparts in North America . Logging, poaching, and resourcedevelopment activities have resulted in much greater declines in mammalspecies diversity in Chile than in North America .

Willson and her collaborators examine the community structure ofbirds inhabiting rainforests in the perhumid zone of both southern Chileand coastal Alaska. They find that the rainforests of sourthern Chilesupport similar numbers of regularly breeding bird species as their coun­terparts in coastal Alaska , but relative abundances of birds tend to behigher in Chile. The structures of bird communities are significantlydifferent in both regions as well, with a greater representation of upper-

Introduction xxi

canopy insectivores in Chile and a greater diversity of leaf gleaners andunderstory birds in Alaska. Much of the contrast in community structurebetween Chile and Alaska is hypothesized to be due to the architecturaldifferences between broadleaf and coniferous forests , but none of themeasures tested are able to explain the differences in community structurethat are observed.

Bird pollination and seed dispersal are important to the maintenance offorest species diversity in coastal temperate rainforests on Chiloe Island.Armesto and his coworkers found that one species of migrant frugiverbird accounts for nearly half the fruit consumption in these forests. Birdpollination is much more widespread and occurs throughout the year inChile. The effects of loggingand land-clearing activities on the maintenanceof species richness are particularly prominent in this rainforest, sincefragmentation tends to be associated with a decline in these key fruit­eating and pollinator bird species. Biotic interactions are more importantto the maintenance of biodiversity in Chile than in North America.

Freshwater ecosystems show parallel trends with rainforests in terms ofevolutionary history and unique community structures. Soto and Stocknercompare the physical and biotic features of lakes in Chile and correspondingrainforest regions in southern British Columbia. The lakes in both regionsare similar in chemistry, ontogeny , and geomorphology but contrast intemperature, productivity, and food web structure. These ecosystemfeatures suggest that they are similar in chemistry , ontogeny, and geo­morphology but contrast in temperature, productivity , and food webstructure. These ecosystem features suggest that Chilean lakes may bemore sensitive to introductions of exotic species and to the effects oflogging on water chemistry than lakes in British Columbia.

Forest System Responses to Human Activities

The third and final section of the book summarizes techniques availablefor assessing the influence of human activities on the high-latitude ecosys­tems and discusses some of the management strategies and policies thatare being undertaken or proposed to address the management of high­latitude forests. A new understanding of the importance of spatial gradientsis leading to the development of new tools for analyzing and managingterrestrial ecosystems at the landscape level.

Bradshaw and her associates report on a technique for analyzing scaleinteractions in forest environments, using the concepts of patch dynamicsand hierarchy theory. Landscape composition and rates of landscapechange are determined by local patch-matrix interactions and patterns.When the rates of landscape change due to local processes are slowrelative to large-scale changes, successional patterns will be more severelydisplaced. The results of these modeling studies raise additional questions

xxii Introduction

about the role of small-scale processes such as stand levelland conversionsthat may depend on latitude, geomorphology , or regional climate controls.

Spittlehouse notes the need to look at forest ecosystems and species ina broader sense, thereby eliminating the requirement to predict variabilityat the site level. By identifying and analyzing the sensitivity of keylimiting factors , he assesses the impacts of future climatic change onforests . In the seasonal rainforest zone of southern British Columbia , forexample, the key limiting factor to Douglas fir is available moisture .Consequently, an increase in temperature due to global change mayormay not affect survival and distribution of Douglas fir, depending on thechanges in precipitation that occur in conjunction with the warming.

Tasmania has a significant representation of both seasonal and perhumidtemperate rainforest but contrasts with Chile and North America inhistory of human occupation and environmental management. Theserainforests have many structural features in common with the rainforestsof Chile, but they differ in disturbance history and degree of isolation.Brown and Read show that in contrast with North America and Chile,catastrophic disturbances play only a limited role in maintaining standstructure in Tasmania . Anthropogenic fire has played a key role inTasmania for a much longer period than it has in rainforests in theAmericas. Tasmania has one of the most comprehensive protected areasstrategies of any rainforest region, with nearly 60% of the existing rain­forest in established or proposed reserves and another 15% to 20% indeferred status. However , management of human-caused fire remains oneof the most important challenges for the conservation of rainforests inTasmania , as it does in Chile.

The range of human-use effects on forests involves the effects of loggingon the wood, water , and air resources in the watershed . Hetheringtonassesses the influence of logging in a small stream ecosystem in a coastaltemperate rainforest area over a 20-year period. In the logged areas ,there was a reduction in evapotranspiration and increases in water yieldand ground-water levels. However, the magnitude and direction of changesin peak flows , sediment transport, water quality, and fish populationswere variable over time. This finding suggests that the rate and arealextent of logging is an important consideration in determining the overallimpacts of logging.

Boyle notes that the coastal rainforests of western Canada representsome of that nation's most diverse and productive forests and account foras much as 40% of Canada's wood exports. They also have great ecologicalimportance because of their high diversity of vertebrates in comparison toother Canadian forests. In addition , lichen and moss diversity is excep­tionally high in coastal forests. A higher proportion of species are habitator climate specialists in British Columbia rainforests than in forests ofother provinces, and fewer threatened species occur in this area . Boyleobserves that little protection exists for the most productive forests in

Introduction xxiii

Canadian rainforests , even though they represent significant elements ofregional biodiversity. Logging is generally thought to have the potentialof constraining species diversity in the high-latitude rainforests. Newgovernmental initiatives are being implemented to develop better guide­lines to more effectively conserve biodiversity in this region.

In concluding the book, we draw a number of lessons from thesecomparative studies. While the biotic and abiotic patterns along thecoasts of North and South America are generally understood, moredetailed field studies and analyses are needed to understand the complexinteractions between and within physical domains and biological com­munities. Natural systems are complex, and a small change can bringabout large changes in ecosystem functioning and structure, dependingon the state of the ecosystem. One of the best ways (and possibly theonly way) to study such problems in their natural setting is to under­take regional comparative studies such as the ones described here .These studies must be interdisciplinary in nature , because expertise andparadigms from many disciplines must be brought to bear on the scien­tific problems arising from the linkages between ecosystem processes.Furthermore, this work must be done within a framework that allows forthe propagation of perturbations from one scale to another, with move­ment from and to smaller scales. Finally, the human dimension must beincorporated into this research. Humans are the principal disturbers ofecosystems. However, through their institutional policies and personalactions, they can also address and correct the imbalances and distur­bances that they have introduced . Consequently, our conclusions call fora stronger socioeconomic component in future regional comparativeglobal-change studies so that more positive forces of change can beidentified and studied .

Richard G. LawfordPaul B. Alaback