Forests in Time: The Environmental Consequences of 1,000 Years of Change in New England. David F. Foster and John D. Aber, eds. Yale University Press, New Haven, CT, 2004. 496 pp. $45.00 (ISBN 0300092350 cloth).
Little more than 20 years ago, when the ink was barely dry on my PhD certificate, David Foster and John Aber were already well on their way to joining the elite of North American forest ecologists. David Foster received his doctorate from the University of Minnesota and quickly established his reputation in forest history and disturbance ecology; he is now the director of Harvard Forest. John Aber earned his PhD from Yale University and made major contributions in the nutrient cycling arena while working with the Hubbard Brook team; he is currently a professor in the University of New Hampshire's Department of Natural Resources and the Institute for the Study of Earth, Oceans, and Space. Aber is also a principal investigator for the Hubbard Brook and Harvard Forest Long Term Ecological Research (LTER) sites. There are few disciplines in ecology not covered in Foster and Aber's research programs; they list over 300 scientific publications on their Harvard Forest Web sites.
Although Foster and Aber credit themselves mainly as editors of Forests in Time, it soon becomes clear that they are the primary authors as well. The work is organized into 5 major sections and 20 chapters. Foster and Aber are either lead author or coauthor of 15 of the chapters. There are approximately 50 other contributing authors, including several other Harvard University professors and many past and present research scientists and graduate students at Harvard Forest. The major sections of the book are “Forest Ecology and Change,” “Regional History and Landscape Dynamics,” “Modern Forest Landscape and Ecological Legacies,” “Forest Ecosystem Dynamics through Long-Term Experiments,” and “Lessons from the Forest and Its History.” Although the title of the book suggests that it covers all of New England, it really focuses on the long-term research conducted in and around Harvard Forest. That this site is located in Petersham, Massachusetts, in central New England, makes many of the findings relevant to the region as a whole.
The book starts with the background and framework for long-term ecological research at Harvard Forest, which was founded in 1907. The authors credit Walden, Henry David Thoreau's classic book about life on Walden Pond in Concord, Massachusetts, for the widespread interest in ecological research on human impact and land-use history in the New England countryside. In 1988, Harvard Forest became an LTER site funded by the National Science Foundation. The early chapters of Forests in Time discuss the period of New England's human settlement (first by Native Americans and then by Europeans), the physical environment (soils, topography, and climate), and natural disturbance factors (wind and fire). The authors synthesize this information using a discussion of witness-tree distribution (recorded in early land surveys) and paleoecology (pollen and charcoal profiles of bogs and lakes) to describe the original composition of the two major forest regions in New England: beech, maple, hemlock, and spruce forests to the north, and oak, chestnut, hickory, and pine forests to the south. The dramatic alteration of the New England forest landscape through logging, land clearing, and farming is discussed in detail, and the effects of this alteration in Petersham are illustrated with photographs of the well-known dioramas and models from the Harvard Forest museum.
Chapters by J. Fuller and colleagues and J. McLaclan and colleagues present a more detailed discussion of paleoecological data to illustrate forest responses and dynamics to land-use and climate change around the forest. These data are coupled with information on tree rings (dendroecology) and tree age structure to discern the relationship between tree recruitment and disturbances, and to learn how modern-day forests differed from forests of the past. Although the book is almost exclusively dedicated to plant and forest ecology, a chapter on wildlife dynamics is included to further illustrate species change in a constantly altered landscape. It contains a useful table on New England wildlife species that are now extinct or extirpated, declining, increasing, or introduced to the region. The research of a long-time Harvard Forest scientist, Glenn Motzkin, is synthesized in a subsequent chapter on forest landscape patterns, structure, and composition. The impacts of previous cultivation on soils and vegetation patterns in and around central Massachusetts are emphasized in this chapter. A related chapter follows on land-use legacies in soils. It discusses the long-term impacts of anthropological history on soil nutrients, nutrient cycling processes, and nitrogen storage.
The emphasis then changes from land and lakes to the forest–atmosphere interface. Over the last decade, a significant amount of the ecophysiological research conducted at Harvard Forest has emphasized canopy-level carbon and water vapor fluxes for the major tree species. Much of this research has been done in tower experiments using eddy flux measurements, and has documented diurnal, weekly, seasonal, and yearly variation in canopy fluxes. These data are used to model ecophysiological responses to climatic variation, including phenomena related to global change such as elevated carbon dioxide in the atmosphere and increasing temperature. They are also compared to data from other types of forest in North America.
The fourth major section of the book, on long-term ecosystem dynamics, begins with a chapter on the impacts of catastrophic hurricanes, a major recurring disturbance factor in New England. Research at Harvard Forest, including the early work of David Foster, led to a series of excellent papers documenting the effects of and responses to the 1938 hurricane that leveled the old-growth forests there and in the Pisgah tract in southern New Hampshire. So that scientists could better understand this phenomenon under more controlled conditions, trees were mechanically pulled down in an experimental hurricane simulation study, and the vegetation and soil impacts were monitored over a subsequent 12-year period as part of the LTER study. A major finding of this research is the remarkable ability of the affected ecosystem to “maintain internal functioning and resist major compositional changes.” This contrasts with other major findings reported throughout the book, suggesting that the imprint of human land use on the New England landscape is profound and very long lasting. It includes the homogenization of tree species distribution across central Massachusetts and other long-term legacies of past land use, such as Native American and early European settlement impacts.
The chapters that follow deal with pollution-mediated nitrogen saturation of ecosystems, with the impacts of soil warming as a consequence of global climate change, and with the DIRT (Detritus Input Removal and Transfer) experiment. Included here are a wide range of data and discussion of topics, including above- and belowground biomass, plant and soil nutrients, nitrogen mineralization, methane flux, and soil respiration. The far-reaching impacts of pollution, elevated levels of atmospheric carbon dioxide, increasing global temperatures, and manipulation of litter and root inputs on ecosystems processes are well developed in this section. The remainder of the book includes a chapter on experimental approaches to understanding forest regeneration and four synthetically oriented chapters on remote sensing, insights for ecology and conservation, global carbon budgets, and environmental change and the future health of regional forests.
Forests in Time is written in a concise and clear style. It can be understood and appreciated by a wide audience, from the weekend naturalist to the professional ecologist. The major strength of the book is that it synthesizes and discusses approximately two decades of intensive research on a wide variety of ecological topics. This is done in a step-by-step, chronological narrative that takes the reader from the pre-Columbian forests of New England, through the early European settlement period of logging, land clearing, and agriculture, to the present day. It covers many important ecological topics, ranging from land-use history to paleoecology and from nutrient cycling to ecophysiology. The book also assesses the impacts of major natural and anthropogenic disturbance factors (fire, wind, insects, and disease) and of ecosystem stressors (pollution and exotic invasive species).
One important message that I gleaned from the book echoes one that I have been writing about in my recent papers. Forests of the eastern United States undoubtedly have been affected by global change phenomena, but to date these impacts are not nearly as severe as the disturbances and stressors that resulted from the activities of European settlers. Anthropogenic effects on the ground have greatly outweighed those in the atmosphere. I believe, as I think the authors of the book do, that a dynamic equilibrium that existed for thousands of years in the forests of the eastern United States as a result of Native American activity and postglacial climate change was dramatically altered in the few centuries after European settlement (Abrams 2003). Indeed, this pattern now exists throughout much of the world. Evidence presented in this book suggests that the composition, structure, and ecology of New England forests will not return to anything that resembles the pre-European settlement condition in the foreseeable future. The loss of forested area to agriculture, the intensive logging and land-clearing, the introduction of exotic insects and diseases, and the suppression of fire that followed in the wake of the Europeans resulted in, among other things, the decline or extirpation of the once dominant chestnut, white pine, white oak, beech, sugar maple, and hemlock.
I probably wouldn't be doing my job if I didn't mention a few minor criticisms. The inclusion of some of the chapters seems a bit contrived, in that they don't fit well with the overall theme of book. For example, the wildlife chapter stands alone and is not well integrated. The chapter on experimental approaches to understanding forest regeneration likewise seems out of place in a section dominated by chapters on belowground processes. This chapter also lacks the historical bent and broad scope of the others. Nonetheless, all the chapters are of high quality. I should mention that anyone who has followed Foster and Aber's published work over the years would recognize many of the tables and figures included in the text. I was a bit disappointed by this, but others may find it helpful to have all this information available in one source.
Even more important than the data reported here are the approach and methodology used by the authors in conducting multiscale, multidisciplinary, long-term ecological research. You don't have to be from New England to appreciate the lessons, opinions, and other content. Any researcher in the field could be forgiven for feeling envious of the quality and quantity of the work that Foster and Aber have completed over the last 20 years. Harvard Forest has become a great venue for diverse scientists and for complex, multidisciplinary research. This book will become a must-read for anyone interested in the study of historical forest ecology and anthropogenic impacts on ecosystem dynamics.