Ecology and Management of Forest Soils

Dan Binkley, Richard F. Fisher

• Éditeur: Wiley-Blackwell
• Année: 2012
• ISBN:
  9781118422328
• Édition: 4
• Sujet: Scienze biologiche
• Sous-sujet: Ecologia

Forest soils are the foundation of the entire forest ecosystem and complex, long-term interactions between trees, soil animals, and the microbial community shape soils in was that are very distinct from agricultural soils. The composition, structure, and processes in forest soils at any given time reflect current conditions, as well as the legacies of decades (and even millennia) of interactions that shape each forest soil. Reciprocal interactions are fundamental; vegetation alters soil physical properties, which influence soil biology and chemistry, which in turn influence the growth and success of plants. These dynamic systems may be strongly influenced by intentional and unintentional management, ranging from fire to fertilization. Sustaining the long-term fertility of forest soils depends on insights about a diverse array of soil features and changes over space and time.

Since the third edition of this successful book many new interests in forest soils and their management have arisen, including the role of forest soils in sequestering carbon, and how management influences rates of carbon accumulation. This edition also expands the consideration of how soils are sampled and characterized, and how tree species differ in their influence on soil development.

Clearly structured throughout, the book opens with the origins of forest soil science and ends with the application of soil science principles to land management. This new edition provides:

• A completely revised and updated Fourth Edition of this classic textbook in the field
• A coherent overview of the major issues surrounding the ecology and management of forest soils
• Global in scope with coverage of soil types ranging from the tropical rainforest soils of Latin America to the boreal forest soils of Siberia
• New chapters on Management: Carbon sequestration; Evidence-based approaches and applications of geostatistics, GIS and taxonomies
• A clear overview of each topic, informative examples/case studies, and an overall context for helping readers think clearly about forest soils
• An introduction to the literature of forest soil science and to the philosophy of forest soil science research

This coherent overview of the major issues surrounding the ecology and management of forest soils will be particularly useful to students taking courses in soil science, forestry, agronomy, ecology, natural resource management, environmental management and conservation, as well as professionals in forestry dealing with the productivity of forests and functioning of watersheds.

Part I

Introduction to Forest Soils

Chapter 1

History of Forest Soil Science and Management

Overview

In this text, forest soils are considered to be soils that presently support forest cover. These soils differ in many ways from agronomic soils: they have O horizons, organic layers that cover the mineral soil; they have diverse fauna and flora that play major roles in their structure and function; they are often wet or steep, shallow to bedrock, or have a high stone content. Soil layers that occur at great depth are important to forests. The influence of soils on forests and other vegetation was known to the ancients, although our current understanding of soils did not begin to develop until the nineteenth century. The study of forest soils is as old as soil science itself. Researchers working on forest soils made many of the early discoveries that form the foundation of modern soil science.

In the broadest sense, a forest soil is any soil that has developed primarily under the influence of a forest cover. This view recognizes the unique effects of the deep rooting of trees, the role of organisms associated with forest vegetation, and the role the litter layer (forest floor, or O horizon) and the eluviation promoted by the products of its decomposition have on soil genesis. By this definition, forest soils can be considered to cover approximately one-half of the Earth's land surface area. Essentially, all soils except those of tundra, marshes, grasslands, and deserts were developed under forest cover and have acquired some distinctive properties as a result. Of course, not all of these soils support forests today. Perhaps as much as one-third of former forest soils are now devoted to agricultural, urban, or industrial use. A better definition of forest soils might be those soils that are presently influenced by a forest cover. Currently, forests of various types cover about one-third of the world's land surface.

The need for a separate study of forest soils is sometimes questioned on the assumption that a forest soil is no different from a soil supporting other tree crops, such as citrus, pecans, olives, or even a soil devoted to agronomic crops. Persons who are not well acquainted with natural ecosystems and who have failed to note even the most obvious properties of soils associated with forests generally make this assumption. Upon close observation of forests, one notices many unique properties of forest soils. The forest cover and its resultant O horizon provide a microclimate and a spectrum of organisms very different from those associated with cultivated soils or horticultural plantations. Such dynamic processes as nutrient cycling among components of the forest community and the formation of soluble organic compounds from decaying debris, with the subsequent eluviation of mineral ions and organic matter, give a distinctive character to soils developed beneath forest cover.

When European settlers arrived in what became North America, forests covered half of the land area, another two-fifths was grassland, and the remainder was desert or tundra. The eastern seaboard was almost entirely forested, and, largely as a consequence of the difficulties of clearing new land, agricultural settlement was mostly confined to the Atlantic slope until the end of the eighteenth century. Slowly, settlement began expanding westward, and extensive forest clearing for agriculture began in the central portion of the continent. By the middle of the nineteenth century, more than a million hectares of virgin forests had been cleared and the land converted to permanent agricultural uses.

This area of cleared forest land gradually increased until well into the twentieth century. As new and better farmlands were opened in the Midwest and West, millions of acres of former croplands were abandoned. Especially in the eastern regions, large areas of degraded farmland reverted to forests, and by 1950 forested areas had increased until they again covered nearly one-third of the total land area. The forest land base has continued to grow, and is projected to continue to grow slightly despite the relentless pressures of increasing urban and industrial development (Alig and Butler, 2004).

Few truly virgin forests exist today in populated regions of the globe. The conversion of forests to croplands and back to forests has gone through many cycles in sections of central Europe and Asia, as well as eastern North America and portions of South America. Large areas of non-forest soil now support forests, especially in Australia, New Zealand, and southern Africa. Deforestation continues at a rapid pace, particularly in the tropics. However, even there, degraded lands that were cleared of forest for agriculture are being reforested. Many European forestlands have been managed rather intensively for centuries. At the other extreme, relatively short-term shifts in land use occur in the tropics, where “swidden” agriculture or shifting cultivation, a form of crop rotation involving 1 to 3 years of cultivated crops alternating with 10 to 20 years of forest fallow, is practiced. Such practices alter many properties of the original forest soil.

In recent years, intensively managed plantation forests have been created in several countries of the world. Among these forests are several million hectares of exotic pine and eucalypt forests in the Southern Hemisphere and an even larger area of plantations employing native species in the Northern Hemisphere. The latter includes some 8 million ha of pine plantations in the coastal plains of the southeastern United States and large areas of Douglas fir plantations in the Pacific Northwest.

Because of the alteration in certain properties of forest soils as a result of intensive management, the distinction between forest soils and agronomic soils has become progressively less evident in some areas. Although some properties acquired by soil during its development persist long after the forest cover has been removed and the soil cultivated, other characteristics are drastically modified by practices associated with intensive land use. In this text, we will generally treat forest soils in the narrow sense as soils that presently support a forest cover, but we will also address the soils of intensively managed forest plantations, many of which were not developed under forests or have seen long periods of use in agriculture. Only cursory attention will be given to genesis and classification of forest soils. Emphasis will be placed on understanding various physical, chemical, and biological properties and processes and how they influence forest dynamics and the management of forests.

Forest Soils Differ in Many Ways from Cultivated Soils

The soil is more than just a medium for the growth of land plants and a provider of physical support, moisture, and nutrients. The soil is a dynamic system that serves as a home for myriad organisms, a receptor for Nature's wastes, a filter for toxic substances, and a storehouse for scarce nutrient ions. The soil is a product as well as an important component of its environment. Although it is only one of several environmental factors controlling the distribution of vegetation types, soil can be the most important one under some conditions. For example, the farther removed a tree is from the region of its climatic optimum, the more discriminating it becomes with respect to its soil site. This means that the range of soil conditions favorable to the growth of a species narrows under unfavorable climatic conditions for that species.

Many properties and processes characteristic of forest soils will be discussed in detail in later chapters. At this time, it will suffice to point out a few properties of forest soils that differ from those of cultivated soils. These differences derive, in part, from the fact that often the most “desirable” soils have been selected for agronomic use and the remainder left for native vegetation such as forests and grasslands. Fortunately, soil requirements for forest crops generally differ from those for agronomic crops. It is not unusual to find that productive forest sites are poor for agronomic use. Nevertheless, they may be used for agriculture because of their location with respect to markets or centers of population. Poor drainage, steep slopes, or the presence of large stones are examples of soil conditions that favor forestry over agriculture. However, the choice of land use often results from differences in crop requirements. Good examples are the wet flatlands of many coastal areas around the world. These important forest soils cannot be effectively used for agricultural purposes without considerable investments in water control, lime, and fertilizers.

Not all forest soils are nutrient poor. Some soils with excellent productive capacity for both trees and agronomic crops remain in forests today. This is generally because of location, size of holdings, ownership patterns, or landowner objectives. The fact that many forest soils contain a high percentage of stones by volume has a profound effect on both water and nutrient relations. Water moves quite differently through stony soil than it does through stone-free soil, and the volume of stones reduces proportionally the volume of water retained per meter of soil depth. Likewise, although stones contain weatherable minerals that release nutrient ions to the soil, the volume of stones reduces proportionally the soil's ability to provide nutrients for plant growth.

Forest trees customarily occupy a site for many years. Their roots frequently penetrate deeply into the subsoil and even into fractured bedrock (Fisher and Stone, 1968). During this long period of site occupancy, considerable amounts of organic material are returned to the soil in the form of fallen litter and decaying roots. As a result, a litter layer forms and exerts a profound influence on the physical, chemical, and biological properties of the soil.

The tree canopy of a forest shades the soil, keeping the soil cooler during the day and warmer during the night than cultivated soils. The presence of forest vegetation and the litter layer also results in more uniform moisture conditions, producing a soil climate nearly maritime in nature.

The physics of both overland and subsurface flow of water in steep forest soils are quite different from those in cultivated soils. Steep slopes under forests have their surfaces protected by the litter layer, their shear strength increased by the presence of roots, and their infiltration capacity enhanced by old root channels.

The more favorable climate of forest soils also promotes more diverse and active soil fauna and flora than are to be found in agronomic soils. The role of these organisms as mixers of the soil and intermediaries in nutrient cycling is of much greater importance in forest soils than in agronomic soils.

The deep-rooted character of trees leads to another unique feature of forest soils. Although the great majority of roots occur at or near the soil surface, deep roots also take up both moisture and nutrients. Thus, deep soil horizons, of little importance to agronomic crops, are of considerable importance in determining forest site productivity.

Agronomic soils may be described as products of human activity, in contrast to forest soils, which are natural bodies and exhibit a well-defined succession of natural horizons. This was certainly a valid contrast a few decades ago, and it continues to be valid in most areas today. But the contrast has diminished greatly in the exotic forests of the Southern Hemisphere and in the short-rotation forests of the southeastern United States, the Pacific Northwest, and much of western Europe. Clear-cut harvesting of trees disturbs the surface litter, resulting in short-term changes in the temperature and moisture regimes of the surface soil. Seedbed preparation by root raking or shearing, disking or plowing, and sometimes bedding incorporates the litter layer with the mineral soil, often enhancing microbial acti...

Table des matières

• Cover
• Title Page
• Copyright
• Dedication
• Preface
• Acknowledgments
• In Memoriam
• Part I: Introduction to Forest Soils
• Part II: Composition of Forest Soils
• Part III: Life and Chemistry in Forest Soils
• Part IV: Measuring Forest Soils
• Part V: Dynamics of Forest Soils
• Part VI: Thinking Productively about Forest Soils
• References
• Index