Halfway through the life of the second edition, the human population passed the 6 billion mark. The world's population has more than doubled since I took my first university-level ecology course: an increase of 3.2 billion people. It is expected to increase by another 3 to 5 billion in the time it takes to grow a tree crop in many sustainably managed, multivalue, temperate or northern forests: 60 to 90 years, or approximately the life expectancy of my generation's grandchildren. The good news for the world's forests is that the rate of human population growth has slowed and may stabilize or even start to decline within this century.
Human pressure on the world's forests has followedbut lagged somewhat behindpopulation growth. The increasing replacement of forest exploitation by sustainable forest management and the combined results of forest protection, product substitution, technology, increasing public concern, and the recycling of wood products have slowed the rate of increase inhuman impacts on forests to less than the increase in human numbers. However, as people continue to increase the range of values that they desire from forests, as the slowing of population growth leads to increased wealth, and as it is increasingly recognized that wood from sustainably managed forests is a socially and environmentally "green" product, I expect that total human demand on forests for wood and nonwood values will continue to rise even after population levels have stabilized.
Forestry faces an ethical dilemma: how to balance the changing social and environmental needs and desires of today's generation against the needs and desires that we anticipate for our grandchildren, their grandchildren, and generations beyond. Forestry is defined as the art (skill), practice, science, and business of managing forest stands and forested landscapes to sustain the balance of values and environmental services desired by society. This definition requires that forest policies and practices change as society changes the balance of values that it desires, and responding to this change is the first responsibility of forestry. However, a second and equal responsibility is to reject current practices and oppose suggested changes that are not consistent with the ecology and sociology of the new desired balance of values and that will not provide our grandchildren and theirs with the range of values that we think they will want and need.
Fulfilling these two key stewardship responsibilities of forestry requires that this profession have a sound understanding of the ecology of the values that are to be sustained. Although forestry is first and foremost about people and their needs, preferences, and desires and only second about ecology, biodiversity, and other currently politically correct topics, without a biological and ecological foundation, it is very unlikely that either the present or the future generations will have access to the resource values, nonresource values, and environmental services that they will want. This is the rationale for the science of forest ecology. Our science can certainly exist outside this utilitarian focus, but the prospect of another 3 to 5 billion humans in the time it takes for most trees that we plant today at temperate and northern latitudes to reach economic maturity (or provide the other values offered by trees of that age) requires that forest ecology also serve society's needs for an ecological foundation for a sustainable relationship between humans and forests.
Since the first edition of the book (1987), great progress has been made in recognizing the importance of diversity: cultural diversity, economic diversity, biological diversity, and diversity in the way that we manage forests. Increasingly, forestry around the world is recognizing the importance of respecting the spatial diversity of forests. Forests differ in different climates, on different geologies and soils, and with different biological circumstances. Diversity in management practice from place to place, from ecosystem type to ecosystem type, is required if we are to respect this spatial diversity. Recognition of the equal importance of the temporal diversity of forests has developed more slowly. Most people dislike change, and there is widespread antipathy toward the visual, spiritual, and other changes that accompany natural or human-caused disturbance in forests. It is one of the duties of ecologists and foresters to make available to the interested public sufficient knowledge about the processes, products, and ecological role of natural and human-induced change in forests that they can comprehend and respond appropriately toward forest disturbance and change.
A metaphor for forest ecology and for forestry itself is ecological theater. There are ecological stages, or settings, that define the ecological plays that can be acted out. The ecological plays (ecosystem disturbance-recovery sequences) in turn define which ecological actors (species) will appear on the ecological stage and in what order over time. Ecological stages, or settings, are defined by ecological diversitythe diversity of climate, geology, topography, soil, and physical disturbance agents such as fire, wind, frost, flood, drought, and landslide. Ecological plays are the sequences of changes in the species composition, structure, function, complexity, and internal organization that occur in forests as a result of human and nonhuman disturbances. These sequences are a result of external disturbance events and the internal ecosystem processes of recovery toward predisturbance conditions or some new condition.
All metaphors are incomplete as a description of reality. There are many inconsistencies between the concept of theater and ecology, but there are also some useful parallels. Different plays require different settings or stages, and a particular setting or stage limits the plays that can be performed on it. Particular biotic communities and temporal sequences of communities can occur only in certain climatic, topographic, and soil conditions. Particular physical environments limit the species and species sequences that can occur there, and there is generally a broad similarity in ecosystem development over time after successive disturbances of a particular type and severity in a particular type of ecosystem.
A play has a story line that describes events and relationships and how they change over time. Like a play, ecosystems do not exist in a single, fixed condition. There is periodic disturbance that initiates an internal sequence of changes in ecosystem characteristics. During this sequence -of changes, there will be different species and different processes and different rates of particular processes, just as in a multiact play there are different groups of actors on stage acting out different parts of the story in the different phases (acts) of the play. Some actors appear throughout the play; some are specific to a particular act. During ecosystem change, some species may persist throughout, but many appear only at a particular part of the "play." However, whereas the story line of a play is repeated relatively unchanged every time the play is performed, ecosystems exhibit considerable variation between successive renditions of the overall "ecological play." Thus, differences between ecosystems and the metaphor of theater emerge as soon as one goes from the broad concept to the details.
Thankfully, society has become preoccupied with biodiversitynature's insurance policy in the face of disturbance and environmental change. It is a rich inheritance for humans and a legacy to be passed undiminished to future generations. However, a preoccupation with biodiversity before or outside the context of a consideration of ecological and temporal diversity is unlikely to be a successful foundation for biodiversity conservation and sustainable forest management. It is analogous to being preoccupied with the actors and ignoring the play and the stage setting. As in theater, all three must be considered in assessing the ecology and designing the management of forest ecosystems.
This third edition of Forest Ecology is structured around the ecological theater metaphor to emphasize the necessity of a comprehensive approach to establishing an ecological foundation for sustainable forest management. It deals with the spatial diversity of forest ecosystems in terms of ecological classification and the physical factors of climate (explored as solar radiation, temperature, precipitation, wind, and fire) and site (explored in terms of soil and water). These factors collectively define the ecological stage, and their variation from place to place constitutes ecological diversity. The book then examines biological diversity in terms of the processes and products of individual species populations and of communities of diverse species. It then considers temporal diversity by examining change over time in the components and processes of the forest ecosystem: the ecological play. Ecological attributes of individual speciesthe ecological actorsare touched on throughout the book, but this subject area lies more in the realm of autecology, ecophysiology, dendrology, behavioral ecology, and so on, a detailed treatment of which is beyond the scope of this book and of most courses in forest ecology.
The book commences in Part I, "People and Forests," with a trio of contextual chapters. These deal with the historical relationship between humans and forests (Chapter 1) and why and how forestry and the science of forest ecology developed (Chapter 2). Part II introduces the ecosystem as the basic unit of forest ecology (Chapter 3). Because the forest is an ecosystem and all subsequent discussions of spatial and temporal diversity need to be in the context of the forest as a system, Part II then examines the key functional processes that ultimately drive organic production and change in ecosystems: the capture, storage, and flow of energy through and out of forest ecosystems, thereby maintaining ecosystem structure and order (Chapter 4), and the inputs of nutrients into, their circulation within, and the loss of nutrients from forest ecosystems (Chapter 5).
Having established the ecosystem as the basic unit of forest ecology, with five key attributesstructure (including species composition), function, complexity, interactions and linkage between its component parts and processes, and change over timethe book turns in Part III to the spatial diversity of forests. In previous editions, classification of this diversity was delayed to Chapter 16, but here it is addressed earlier because it deals with the ecological framework for biological and temporal diversity and with the spatial ecological foundation for sustainable forest management. Unless you can recognize the spatial diversity of forests, it is difficult to apply your ecological knowledge to explain their differences from place to place. It is also difficult to design and apply ecosystem-specific management. Chapter 6 deals with ecological site classification as the mechanism by which to spatially stratify ecological and biological diversity. Chapters 7 to 10 then address the major physical factors of climate: light (solar radiation), temperature, wind, and water. Chapter 11 addresses the major nonclimatic, physical component of site: the soil. Chapter 12 examines what is the major physical disturbance factor in many of the world's forests: fire. These chapters collectively define ecological diversity and set the stage for the ecological play: the disturbance-recovery sequence of ecosystem change. Chapter 13 examines the consequences of this physical diversity for the diversity of biotic communities along environmental gradients.
Having established in Part III the major features of the ecological stage and the physical causes of new ecological plays, the book turns in Part IV to the biotic determinants thereof. Chapter 14 examines the biotic processes that operate within or directly affect single-species populations: population ecology. This chapter discusses many of the population-level processes that contribute to various measures of biological diversity and the biotic change over time that accompanies stand development and ecological succession. Chapter 15 investigates the interactions between different species in biotic communities and how interactions contribute to the composition of communities and how this changes over time. The genetics of the individual actorstheir genetically controlled "ecological personalities"is then briefly discussed because all biological processes and the response of all species to ecological diversity are mediated through the genetics of the organisms concerned (Chapter 16).
Having identified many of the key components of the ecological stage and some physical and biotic determinants of the ecological play, attention switches to temporal diversity in Part V Chapter 17 examines the overall processes, pathways, and patterns of both externally driven (allogenic and biogenic) ecosystem change and change mediated by processes internal to the ecosystem (autogenic). Chapter 18 considers the ecological role of disturbance and the current interest in emulating natural forest disturbance as a template for management of ecosystem succession and sustaining temporal diversity.
In Part VI, we return to the spatial diversity of ecosystems and landscapes that was introduced in Chapter 6 as ecological classification was discussed. Ecosystem management and landscape ecology have become the current focus and are the ultimate issues in forest ecology (Chapter 19) because this is the spatial scale at which many of the issues of sustainability and stewardship must be assessed. However, some ecosystem values and many aspects of the ecology of individual species relate to spatial scales that are smaller than forest stands. Scaling up from our largely stand-level knowledge of forest ecology to forest landscapes at various scales and scaling down to individual trees, groups of trees, and canopy gaps represents one of the major challenges in our science today.
The final part of the book, Part VII, examines the application of ecological knowledge in forestry. It begins with Chapter 20 by examining some current issues in the management and conservation of forests: "old growth"; aesthetics versus ecology; ecosystem health, integrity, and stability and their relationship to measures of diversity; and the role of forests in carbon cycles and climate change. Foresters have important responsibilities for these issues and need to be able to harness the knowledge of ecosystem ecology presented in earlier chapters to design management strategies that will achieve objectives with respect to these issues. Each of these topics is worthy of a separate book; only a brief introduction is provided here.
Chapter 21 then examines how such knowledge can be harnessed in quantitative forecasting and scenario analysis tools: multivalue ecosystem management simulators as well as single value predictive models. This chapter reviews types of models and modeling and their role in helping foresters and the public apply ecological knowledge to answer questions of sustainability and stewardship. A major goal of these modeling tools is to facilitate the definition of sustainability, renewability, and stewardship, topics that are discussed in Chapter 22.
The book ends on a philosophical note, seeking wisdom from one of the great thinkers and writers about issues of environmental ethics: Aldo Leopold and other, more recent commentators. There is an ethical responsibility for stewarding the world's forests that rests with the practitioners who actually manage the forests, with governments who legislate and regulate their management, and with public interest groups who lobby for change in the way forests are managed. Issues of intergenerational equity, the ethics of forest management, and stewardship are beyond the scope of this book but require a sound foundation in ecological sciences if they are to be solved.
A problem is an issue that does not get solved. An issue that gets solved is not a problem. Problem issues often persist because they are complex and people offer simple solutions that do not solve them. Ecology and other biophysical sciences on their own cannot solve problems in forestry. Neither can social sciences and considerations alone. There must be a marriagepartnershipbetween these two great bodies of knowledge, guided by ethics, if we are to be successful in achieving a sustainable relationship between the human species and the world's forests and broader environment.