Hubbard Brook (cid:493)(cid:484)(cid:478)(cid:483)(cid:476)(cid:493)(cid:479)(cid:3)(cid:495)(cid:17)(cid:3)(cid:483)(cid:490)(cid:487)(cid:488)(cid:480)(cid:494)(cid:3)(cid:476)(cid:489)(cid:479)(cid:3)(cid:482)(cid:480)(cid:489)(cid:480)(cid:3)(cid:480)(cid:17)(cid:3)(cid:487)(cid:484)(cid:486)(cid:480)(cid:489)(cid:494) Hubbard Brook (cid:495)(cid:483)(cid:480)(cid:3)(cid:494)(cid:495)(cid:490)(cid:493)(cid:500)(cid:3)(cid:490)(cid:481)(cid:3)(cid:476)(cid:3)(cid:481)(cid:490)(cid:493)(cid:480)(cid:494)(cid:495)(cid:3)(cid:480)(cid:478)(cid:490)(cid:494)(cid:500)(cid:494)(cid:495)(cid:480)(cid:488) NEW HAVEN AND LONDON Frontispiece: The Gorge on the mainstem of Hubbard Brook Yale University Press books may be purchased in quantity for (Photo by N. L. Cleavitt) educational, business, or promotional use. For information, please e- mail [email protected] (U.S. office) or [email protected] Published with assistance from the Mary Cady Tew Memorial Fund, (U.K. office). and from the President’s Office of Dartmouth College, with special thanks to Carol L. Folt, and from Furthermore: a program of the Designed by Richard Hendel J. M. Kaplan Fund. Set in Utopia and Aller type by Tseng Information Systems, Inc. Printed in China. ISBN 978- 0- 300- 20364- 6 (cloth : alk. paper) Library of Congress Control Number: 2015948837 A catalogue record for this book is available from the British Library. Copyright © 2016 by Richard T. Holmes and Gene E. Likens. This paper meets the requirements of ANSI/NISO Z39.48- 1992 All rights reserved. (Permanence of Paper). This book may not be reproduced, in whole or in part, including 10 9 8 7 6 5 4 3 2 1 illustrations, in any form (beyond that copying permitted by Sections 107 and 108 of the U.S. Copyright Law and except by reviewers for the public press), without written permission from the publishers. Preface vii Acknowledgments ix Timeline: From the Glaciers to the Present xi Prologue: Step into the Forest—Today (cid:506) (cid:491)(cid:476)(cid:493)(cid:495)(cid:3)(cid:635)(cid:17)(cid:3)(cid:495)(cid:483)(cid:480)(cid:3)(cid:481)(cid:490)(cid:493)(cid:480)(cid:494)(cid:495)(cid:3)(cid:480)(cid:478)(cid:490)(cid:494)(cid:500)(cid:494)(cid:495)(cid:480)(cid:488)(cid:3)(cid:476)(cid:494)(cid:3)(cid:476)(cid:3)(cid:487)(cid:476)(cid:477)(cid:490)(cid:493)(cid:476)(cid:495)(cid:490)(cid:493)(cid:500) (cid:506) Ecosystem and Ecological Studies at Hubbard Brook (cid:514) (cid:507) The Small Watershed- Ecosystem Approach (cid:506)(cid:512) (cid:478)(cid:490)(cid:489)(cid:495)(cid:480)(cid:489)(cid:495)(cid:494) (cid:491)(cid:476)(cid:493)(cid:495)(cid:3)(cid:636)(cid:17)(cid:3)(cid:478)(cid:483)(cid:476)(cid:493)(cid:476)(cid:478)(cid:495)(cid:480)(cid:493)(cid:484)(cid:494)(cid:495)(cid:484)(cid:478)(cid:494)(cid:3)(cid:490)(cid:481)(cid:3)(cid:495)(cid:483)(cid:480)(cid:3)(cid:498)(cid:476)(cid:495)(cid:480)(cid:493)(cid:494)(cid:483)(cid:480)(cid:479)(cid:16)(cid:480)(cid:3) (cid:478)(cid:490)(cid:494)(cid:500)(cid:494)(cid:495)(cid:480)(cid:488)(cid:494) (cid:508) Physical Setting and Climate (cid:507)(cid:510) (cid:509) The Forest: Past and Present (cid:508)(cid:508) (cid:510) A Rich Array of Organisms and Their Interactions (cid:509)(cid:514) (cid:491)(cid:476)(cid:493)(cid:495)(cid:3)(cid:637)(cid:17)(cid:3)(cid:496)(cid:489)(cid:479)(cid:480)(cid:493)(cid:494)(cid:495)(cid:476)(cid:489)(cid:479)(cid:484)(cid:489)(cid:482)(cid:3)(cid:481)(cid:490)(cid:493)(cid:480)(cid:494)(cid:495)(cid:3)(cid:480)(cid:478)(cid:490)(cid:494)(cid:500)(cid:494)(cid:495)(cid:480)(cid:488)(cid:3)(cid:3) (cid:494)(cid:495)(cid:493)(cid:496)(cid:478)(cid:495)(cid:496)(cid:493)(cid:480)(cid:3)(cid:476)(cid:489)(cid:479)(cid:3)(cid:481)(cid:496)(cid:489)(cid:478)(cid:495)(cid:484)(cid:490)(cid:489) (cid:511) How Is Energy Transformed? (cid:512)(cid:510) (cid:512) Hydrology: Water Balance and Flux (cid:514)(cid:505) (cid:513) Biogeochemistry: How Do Chemicals Flux and Cycle? (cid:514)(cid:510) (cid:514) The Discovery of Acid Rain at Hubbard Brook (cid:506)(cid:506)(cid:509) (cid:491)(cid:476)(cid:493)(cid:495)(cid:3)(cid:638)(cid:17)(cid:3)(cid:479)(cid:484)(cid:494)(cid:478)(cid:490)(cid:497)(cid:480)(cid:493)(cid:484)(cid:480)(cid:494)(cid:3)(cid:481)(cid:493)(cid:490)(cid:488)(cid:3)(cid:487)(cid:490)(cid:489)(cid:482)(cid:16)(cid:495)(cid:3) (cid:480)(cid:493)(cid:488)(cid:3)(cid:494)(cid:495)(cid:496)(cid:479)(cid:484)(cid:480)(cid:494)(cid:3)(cid:3) (cid:476)(cid:489)(cid:479)(cid:3)(cid:480)(cid:499)(cid:491)(cid:480)(cid:493)(cid:484)(cid:488)(cid:480)(cid:489)(cid:495)(cid:476)(cid:487)(cid:3)(cid:488)(cid:476)(cid:489)(cid:484)(cid:491)(cid:496)(cid:487)(cid:476)(cid:495)(cid:484)(cid:490)(cid:489)(cid:494) (cid:506)(cid:505) The Consequences of Acid Rain and Other Air Pollutants (cid:506)(cid:507)(cid:512) (cid:506)(cid:506) The E(cid:420)ects of Forest Harvesting and Other Disturbances: Whole- Watershed Manipulations (cid:506)(cid:508)(cid:513) (cid:506)(cid:507) How Does the Forest Ecosystem Recover After Harvesting and Other Disturbances? (cid:506)(cid:509)(cid:513) (cid:506)(cid:508) How Stream Ecosystems Are Integrated with Their Watersheds (cid:506)(cid:510)(cid:510) (cid:506)(cid:509) What Causes Population Change in Forest Birds? (cid:506)(cid:511)(cid:512) (cid:506)(cid:510) Scaling Up: Ecosystem Patterns and Processes Across the Valley (cid:506)(cid:513)(cid:511) (cid:506)(cid:511) How Is Climate Change A(cid:420)ecting the Forest Ecosystem? (cid:507)(cid:505)(cid:506) (cid:491)(cid:476)(cid:493)(cid:495)(cid:3)(cid:639)(cid:17)(cid:3)(cid:477)(cid:493)(cid:490)(cid:476)(cid:479)(cid:480)(cid:493)(cid:3)(cid:484)(cid:488)(cid:491)(cid:476)(cid:478)(cid:495)(cid:494)(cid:3)(cid:476)(cid:489)(cid:479)(cid:3)(cid:487)(cid:490)(cid:490)(cid:486)(cid:484)(cid:489)(cid:482)(cid:3)(cid:495)(cid:490)(cid:3)(cid:495)(cid:483)(cid:480)(cid:3)(cid:481)(cid:496)(cid:495)(cid:496)(cid:493)(cid:480) (cid:506)(cid:512) Reaching Out: Hubbard Brook(cid:343)s In(cid:422)uence on Environmental Policy(cid:11) Management(cid:11) and Education (cid:507)(cid:506)(cid:510) (cid:506)(cid:513) A Look Ahead: The Forest Ecosystem in the Future (cid:507)(cid:507)(cid:510) Epilogue: Step into the Forest—(cid:507)(cid:505)(cid:511)(cid:510) (cid:507)(cid:508)(cid:508) (cid:476)(cid:491)(cid:491)(cid:480)(cid:489)(cid:479)(cid:484)(cid:499)(cid:3)(cid:635)(cid:17) Scienti(cid:421)c Units: Conversions and Abbreviations (cid:507)(cid:508)(cid:512) (cid:476)(cid:491)(cid:491)(cid:480)(cid:489)(cid:479)(cid:484)(cid:499)(cid:3)(cid:636)(cid:17) Scienti(cid:421)c (cid:45)ames and Lists of Selected Organisms (cid:507)(cid:508)(cid:514) (cid:45)otes (cid:507)(cid:509)(cid:508) Bibliography (cid:507)(cid:509)(cid:514) Index (cid:507)(cid:511)(cid:510) The Hubbard Brook Ecosystem Study, now under way for more than 50 years, has been an extraordinarily productive source of ecological information, derived from the research efforts of dozens of scientists from a large number of institutions. The research, conducted mostly in the Hubbard Brook Experimental Forest and nearby Mirror Lake in north central New Hampshire, was initiated in 1963, and has developed into one of the longest- lasting and most comprehensive investigations of forest and associated aquatic ecosystems anywhere. It has also served as a model for (cid:491)(cid:493)(cid:480)(cid:481)(cid:476)(cid:478)(cid:480) other ecosystem studies worldwide. Using the forest as a laboratory, Hubbard Brook This small corner of (cid:45)ew Hampshire has become the scientists have combined intensive field investigations most intensely studied piece of landscape on Earth and with powerful, long- term manipulative experiments the pioneering studies which have (cid:422)owed from this and modeling at a variety of spatial scales that have idea have made the name Hubbard Brook world famous been designed to answer critical questions about the among ecologists and foresters. structure, function, and temporal development of (cid:341)(cid:3)(cid:475)(cid:480)(cid:472)(cid:485)(cid:476)(cid:3)(cid:475)(cid:492)(cid:484)(cid:472)(cid:485)(cid:486)(cid:490)(cid:482)(cid:480) forest and associated aquatic ecosystems and their component parts. Awareness and understanding gained from this research undergird the long- term management of natural resources for water supply, water quality, wildlife, timber yield, and sustained forest growth in the region and beyond. More than 1,500 peer- reviewed scientific publications from this effort have contributed new understanding about the structure, function, and change of terrestrial and aquatic ecosystems, and have been widely and frequently cited in the scientific literature. As the project celebrated its 50th anniversary in 2013, however, we perceived a need to summarize and highlight the major findings, and to make them more accessible to a wider audience, from naturalists and educated general readers to land managers, policy makers, students, and professional biologists, including ecologists who might not be familiar with the Hubbard Brook studies. The book is organized in five parts. The first introduces the conceptual framework, the initial research plans, and the origin of the research. The second describes the forest ecosystem at Hubbard Brook, its setting in the White Mountains of New Hampshire, its history, and its biological vii characteristics. Part 3 highlights research findings groups but also by our many colleagues, collaborators, related to the structure and functioning of these forest students, and technicians as contributors to the Study. ecosystems. The fourth and longest section highlights When we use the first person plural (“we did this” or some of the major discoveries from long- term studies “we studied that”), we intend the usage to encompass and experimental manipulations, including the effects these many individual scientists and their research of atmospheric pollution (particularly acid rain) and teams, in the spirit of the collaborative research climate change. The last section, Part 5, covers the efforts that have been a long- standing feature of educational, policy outreach, and other applications the Hubbard Brook research community. We extend of the research findings, including the programs of thanks to our many colleagues who have been and the Hubbard Brook Research Foundation, established are still conducting research at Hubbard Brook for in 1993 as a support and policy outreach arm of the their important contributions over the years, and Hubbard Brook Ecosystem Study (hereafter the acknowledge their foresight, intellectual input, and Study). hard work that have led to the findings presented Although “Hubbard Brook” is the name of the river in this volume. A full roster of the Hubbard Brook draining the Hubbard Brook Experimental Forest, scientists, as well as a comprehensive and searchable the label has gained popular colloquial use as well, list of publications from Hubbard Brook, can be found referring to both the place and the studies that have on the Study’s website (http://hubbardbrook.org). gone on there. We use the term “Hubbard Brook” in Although this book is intended as a general this broad sense—for example, “research was done at synthesis of the research effort at Hubbard Brook, Hubbard Brook.” When we refer to the river and the it has not been possible to include everything that context is unclear, we use “mainstem Hubbard Brook,” has been achieved or discovered. We hope that the which specifically refers to the major stream that flows results we have discussed will engage our readers, and from the Hubbard Brook valley into the Pemigewasset encourage them to look further into areas that interest River. Individual tributaries in the valley that feed into them and have not been fully addressed. Finally, the the mainstem have their own names—Falls Brook and writing of this book has been a cooperative effort by Zig- Zag Brook, for example. the two of us, and any critical omissions or errors of As noted, this book contains the results of research interpretation are ours alone. conducted not only by ourselves and our research viii (cid:487)(cid:489)(cid:476)(cid:477)(cid:472)(cid:474)(cid:476) We would like to acknowledge the many institutions and foundations that have funded research at Hubbard Brook. Multiple grants from the U.S. National Science Foundation (NSF) have been the backbone of funding for the research. In more recent years, support from the Long- Term Ecological Research (LTER) program at NSF has provided core funding for a number of diverse studies, and several grants from the NSF’s Long- Term Research in Environmental Biology (LTREB) program have funded long- term biogeochemical monitoring and the bird population (cid:476)(cid:478)(cid:486)(cid:489)(cid:490)(cid:498)(cid:487)(cid:480)(cid:479)(cid:482)(cid:488)(cid:480)(cid:489)(cid:495)(cid:494) studies. Additional support has come from The Andrew W. Mellon Foundation, the Environmental Protection Agency (EPA), the National Oceanic and Atmospheric Administration (NOAA), and from many of the researchers’ home universities. We particularly acknowledge the support of Dartmouth College, Cornell University, University of Connecticut, and the Cary Institute of Ecosystem Studies in our research and professional pursuits. The U.S. Forest Service has been a partner in the Study from the beginning. Dr. Robert S. Pierce initiated hydrological, meteorological, and soil research at Hubbard Brook in 1956, and co- founded the Hubbard Brook Ecosystem Study in 1963, with Gene E. Likens, F. Herbert Bormann, and Noye M. Johnson. His successors, Dr. Chris Eagar and Dr. Lindsay Rustad, and scientists and staff at the Northern Research Station of the U.S. Forest Service have all made important contributions to the research results and to the long- term maintenance of this research program. We especially acknowledge the importance of W. E. Sopper, H. W. Lull, C. A. Federer, J. W. Hornbeck, J. S. Eaton, C. W. Martin, and T. G. Siccama for their contributions to the development of this research program. The White Mountain National Forest is acknowledged for its maintenance of critical infrastructure, such as roads, inside the forest. We have benefited from the input and help of many colleagues during the writing of this book. The following individuals have offered helpful comments and suggestions on various drafts: John Aber, Amey Bailey, Scott Bailey, John Battles, Emily Bernhardt, Don ix