||Preface from Rob
Hilgard and Jenny
Related to Forest Soils
in Forest Soils
||Forest Soils in
Soil Factors Which Affect Tree Growth
Productivity - Site
Management and Forest Fertilization
Preface from Rob
Back to top
Due to the death of Professor Stanley P. Gessel during the writing of this chapter, and before acknowledgements were written, it is not possible to recognize each person that provided significant help to him, unless it was documented in writing, and I actually found it in his extensive notes and files. The junior author would particularly like to thank Chuck B. Davey, Earl L. Stone, Dick E. Miller, Gordon Weetnam and J. Stan Rowe for valuable inputs to this chapter.
|II. Introduction Back to top|
Forest trees depend directly upon the soil for physical support, temperature moderation, nutrition, and water but soils in forested areas contribute in many other ways to both the lives of trees, associated plants, microbes, animals and humans. However, the overwhelming importance of soils in the life and health of the forest has not been understood until recent years. This is perhaps best illustrated in the writings of an early agriculturist in western Washington, Erza Meeker, who was considered to be ahead of his time in the application of technology to Agriculture and Forestry. His principal occupation when he first moved into the Puyallup River Valley in Washington State in the late 1800's, was clearing the land of giant forest trees so that he could till the fertile alluvial soils in that region. This was a practice duplicated many times in the hundreds of major river valleys throughout North America. In Meeker's writings he observed that he could hold the ashes of even the largest of the giant forest trees in a small container, so he concluded that this indicated that the soil contributed little to the life of trees and that they must have received all their sustenance from the air. He wrongly concluded that soils could be ignored as an important factor in tree growth (Meeker, 1920). It is interesting to note that he recognized the high productivity of these fertile alluvial soils for agriculture compared to poorer fertility soils on ridges and slopes, but that he did not expand this to include tree growth.
Fortunately not all of the early observers of plant life and soil interactions reached this same conclusion. Professor S.A. Wilde (1958), of the University of Wisconsin, reviewed some of the early European history of soil and forests and states that as early as the year 1809 German scientists were actively trying to interest the established forestry profession in the study of soils and the role that soils played in forestry. Wilde also refers to a book authored by two German scientists (Grobe and Cotta) published in 1852 on forest soils and which deals with tree-soil interactions. Heinrich Von Cotta, born in 1763 in Thuringia, Germany, wrote extensively on the role of science in increasing wood production. He recognized that forest soils were most fertile where there were no removals of forest products, and poorest where removals were intensive. He wrote that good forest land managers, while not able to improve soils above the capabilities of nature, would produce the highest possible yield without reducing productivity while poor forest managers would neither obtain this yield or preserve the fertility of the soil (SAF, 1992).
Wilde in an earlier paper (1953) pointed out that both Virgil and the early Roman Boethius commented on the relationships of forest growth to soils. The historical evidence thus indicates that some early naturalists did observe and make use of some obvious relationships between the growth and size of native trees and properties of forest soils. However, these kinds of observations and use of information were for other areas of the world while the observations and thoughts about soil in relationships to forestry in North America were more dominated by the empirical (and not always correct) observations of the Ezra Meekers during the developing period in North American history.
Based on the above observations, it is therefore not surprising that soil science as a subject for study in the training of professional foresters, or as an object of research, did not command much attention in North America in the early years of settlement, expansion and development. It was true that at some forestry schools' students might take a soils course but these were given in the agricultural curriculum, with major emphasis on field crops. In some institutions a silvicultural course might have introduced the subject of soils but did not treat it in any depth as an important factor of forest management. This state of affairs existed generally through the 1930's with no significant improvement until the late 1940's, although several courses were taught which dealt with the importance of forest soils in tree growth by R.F. Chandler at Yale, T.S. Coile at Duke Harold Lutz at Cornell, and S.A. Wilde at Wisconsin prior to World War II.
As observations of the relationship between soil properties and forest growth became increasingly evident, the case for the study of forest soils was building slowly but surely in these early years prior to World War II, led by the diligent efforts of only a few individuals in North America. The contributions of these early people helped set the stage for the development of the modern forest soil science that we see today. Much as the concepts and application of modern physics originated and developed almost entirely outside of North America prior to World War II, but was embraced and greatly advanced by scientists in North America afterward, the application of science to the study of forest soils also was initially stalled, but blossomed in North America following World War II. Unfortunately, this abbreviated chapter on the history of forest soils in North America will not attempt to name everyone involved in this effort and will not evaluate all of their contributions. We will instead use authors' license and mention only a few names, events and organizations that we consider to be particularly significant or illustrative in our interpretation of the history.
In the early formative years of forest soil training and information development at least four institutions and four individuals played prominent roles. These institutions were Yale University, Cornell University, the University of Wisconsin, Pennsylvania State University and Duke University. Harold Lutz was initially at Penn State, then Yale University. Professor R.F. Chandler was at Cornell University. Lutz and Chandler worked together extensively, leading the efforts in North America to develop information on forest soils and bring this information into teaching programs at their universities. An outcome of these efforts was the production of the invaluable book "Forest Soils", which was first published in 1946 but is remarkably still in use today. Both Professor Lutz and Professor Chandler also had effective graduate training programs at their respective institutions and these three college professors produced some of the early leaders in forest soils.
Also in 1946, S.A. Wilde, who was teaching soils at the University of Wisconsin, published his book "Forest Soils and Forest Growth." Dr. Wilde was particularly effective at the graduate training and research level and a number of the early workers in forest soils took graduate degrees with him. He followed his first book with a second in 1958 "Forest Soils -- Their Properties and Relation to Silviculture" which is still also widely used. Wilde was strongly influenced by the European school of thought (particularly Russian soil science) with respect to forest soils, and therefore introduced some of these ideas into North American forest soils work. In an important paper that helped shape the nature of soil classification in North America, he chastises soil scientists for continuing to use the early, developmental soil classification system of K.D. Glinka, but not using his final work (Wilde, 1949).
Professor T.S. Coile at Duke University was a particularly prolific writer, having the distinction of publishing "Soils and Tree Growth" in volume 1 of "Advances in Agronomy" in 1952 (Coile, 1952). Coile's early work included research clearly establishing empirical relationships between soil properties such as surface horizon depth and forest growth rates in the pine forests of North Carolina.
By the 1930's, the study of soil science was firmly established as an absolutely necessary part of training programs in agricultural science and many kinds of specialized programs that included a consideration of soils developed. However, this was also true for the exploding interest in the subject matter of forestry and related natural resource studies such as Range and Wildlife. Interest in soils was intensified by the establishment of the Civilian Conservation Corps and the many projects conducted by that agency. As a result the number of Forest and Range schools increased so that most states in the United States ended up with at least one school and many with two. The same can be said for the Provinces of Canada. Initially many of these schools, and especially those at Land Grant institutions, depended upon their agricultural associates for any soils instruction. In some cases this is still true and agronomists and forest soil scientists still cooperate very successfully. However, by the late 1940's and early 1950's the almost complete dominance of agriculturally-based soils instruction began to change, pushed on by the influence of the early forest soil scientists previously mentioned. Over time forest soils became a valid area in the study of forest resources and worthy of study and research in its own right. Therefore, most forestry students now have direct contact with the subject matter of forest soils and how to apply it to forest land management. Many students also choose to specialize in the subject of forest soils at the graduate level.
In the remainder of this brief review we will consider those who we feel have made significant contributions to the development of forest soils. We also include organizations and organizational structures which have aided in that development and some of the major achievements made in the understanding of the function and properties of forest soils. We conclude with what we think are major information needs in different parts of North America, what we believe to be our current major soil-related forestry problems, and what information we will need to solve these problems in the future.
|III. Contributions of Hilgard and Jenny Back to top|
We chose to single out the contribution of these two scientists in this short history because we feel they were especially effective in advancing our understanding of forest soils. Although both received their initial backgrounds and show considerable influence from European science (Hilgard from Germany and Jenny from Switzerland), their contributions to the field of forest soils were distinctly North American. Although it is certainly debatable, we also believe that they would not had the considerable impact they did on the understanding of forest soils outside of the pristine natural laboratories they found in North America.
Hilgard, who grew up in a German colony near Belleville, Illinois, developed his career and made his early reputation as state geologist for Mississippi during the period 1855-1870. His 1860 report on the Geology and Agriculture of the State of Mississippi brought him considerable fame. The first half of the report dealt primarily with geology of the state, but the second half was devoted almost entirely to soils and it was this part that established his reputation. His many observations about the nature of soils and how to manage them for agriculture as well as for forestry established many principles we still use today. In recognition of his contributions he was made Professor of Experimental and Agricultural Chemistry at the University of Mississippi in the final years of his work there. In 1870 he moved to the position of Professor of Geology and Natural History at the University of Michigan. After 2 years he moved to a professorship in Soils at the University of California at Berkeley and spent the rest of his career there until his death in 1916.
In the course of his extensive field work in Mississippi, Professor Hilgard observed the fact that tree species distribution and general forest vigor and productivity have a direct relationship to occurrence of different soils. During many years of field and laboratory work in California he extended his observations and began to mention some of the relationships in his writings. Hilgard also recognized that factors other than geology appeared to determine the characteristics of a particular soil in a particular location.
Hilgard also established the concept of soil layers (the soil horizons of today) as being natural components of soils and that there are consistent differences between surface soil and subsoil. In 1895 he took these ideas a step further and published a paper that discussed particular characteristics of soil by depth. In Mississippi, Hilgard recognized low calcium status of soils by the presence of pines and absence of legumes. His observations regarding distribution of trees and soils were typically quite specific. For instance, one quote from his writing states "It is very essential, however, to take into account not only the species of trees, but also their mode of growth. The black-jack and post oak especially, as species, characterize the poorest as well as the richest upland soils, but their mode of development is very different in each case." Such observations of soil effects on forest growth are abundant in his writings.
That the work of Hilgard was visionary in terms of accurately describing soil properties can be clearly seen if one considers the fact that when a new soils map for the state of Mississippi was created in 1942 Hilgard's visionary work of the 1850's was used as the basis for the new map. In fact, Professor Vanderford commenting on the 1942 map wrote to Dr. Hans Jenny that "Many of the lines first drawn by Hilgard are still used on the present soil area map." Dr. Jenny paid tribute to Hilgard by publishing a special volume in 1961 entitled "E.W. Hilgard and the Birth of Modern Soil Science."
Though Hilgard contributed greatly to understanding soil effects on forests, it remained for the keen mind of Professor Hans Jenny to put the total picture of soil formation and distribution into sharp focus with his book "Factors of Soil Formation" in 1941. As stated previously, a number of early soil scientists had previously recognized that several different factors resulted in what we now call a "soil profile" forming in a particular spot; however, none had put the observations together and developed a unified theory about the formation of all soils until Jenny. His teachings and writings clearly established the role of each factor he considered to be of importance in soil formation. He developed his theory with a strong mathematical foundation and illustrated the role of each factor with many field examples and studies. His teachings and theoretical development of this important concept is now widely accepted across the world, and soils professional as well as most foresters have some concept of how soils develop under the influence of the five factors of climate, topography, organisms, different parent materials and time.
Due to the assimilation of previous ideas with new concepts introduced by Jenny, soil scientists have a basis to think of soils as a product of these soil-forming factors. Foresters and all those interested in soils are thus able to evaluate what soil characteristics and problems to expect in a given part of their landscape. Stated simply, the effort and contributions of Jenny enable us to actually put some order into the study and classification soils and not have to deal with a mass of unrelated facts. His contribution to soil science has been recognized thorough a special publication by the Soil Science Society of America resulting from a 50th Anniversary Symposium in 1991 (SSSA, 1994).
|IV. Organizations Related to Forest Soils Back to top|
As mentioned earlier, during the initial stages of the development of forest soils as a study area, forest soil scientists were heavily dependent for technical and instructional material on associates who were primarily interested in using soils information to manage agricultural lands. Forest soil scientists were also dependent upon the organizations they had developed to provide a basis for transfer of information and research discussions in the agricultural arena. We still use these original organizations for some aspects of our information transfer needs and therefore in this consideration of forest soils must take a look at the history of those organizations and their relationship to forest soils. The detailed history is available in papers by Lutz (1977) and Stone (1986).
The American Society of Agronomy (ASA), presently composed of three divisions including the Crop Science Society of America, the Soil Science Society of America (SSSA), and the Agronomy Society of America (commonly referred to as the "tri-societies") was the initial sponsor of much of the activity in forest soils. The American Society of Agronomy was organized in 1907 with sections of crops and soils specifically to further interest in agronomy programs at Land Grant Colleges. There have been (and continue to be) many changes in organization and incorporation of associated groups over the years. Therefore, we will only touch on the highlights as they relate to forest soils. Important events include the incorporation of the American Soil Survey Association (ASSA) into the organization in 1925. This was important because the first soil survey was started in 1889 with considerable expansion during the 1900-1922 period. In all of this time the American Soil Survey Association had well developed annual technical meetings. Early activity in forest soils was on soil surveys so this group had a special relationship to the needs of forest soils even though forest and range soil surveys as such were not initiated until later. For example, when the Weyerhaeuser Company decided to make forest soil information a part of their land management base in the 1950's they initially employed Dr. Eugene Steinbrenner to survey the soil of their forest land and afterward developed site quality information based on soil survey.
The fact that the American Soil Survey Association was very much interested in forest soils is shown by their sponsorship of a "Forest Soil Symposium" at their 1936 Annual Meeting. The papers given were published in the January 1937 Journal of Forestry (Anonymous, 1937) with abstracts in the official report of the Soil Science Society of America for 1936. Because of the historical interest we list the titles and authors of papers given at this early symposium:
John T. Auten,
Chairman, Forest Soil Committee,
American Soil Survey Association.
Some if not all of these names are familiar to those who have followed forestry and forest soils work during this century. John Auten, who did much to advance the study of forest soils, was chairman of the Forest Soils Committee at that time.
Another important event in the history of forest soils was the development of the present organizational structure and incorporation of forest soils into that structure. The Soil Science Society of America was formed by the combination of the Soils section of the American Society of Agronomy and the independent American Soil Survey Association. The current organization with the name Soil Science Society of America was proposed and voted on at a joint meeting of the American Society of Agronomy and American Soil Survey Association in 1935 and became official in 1936. It is worthy to note that Professor Emil Truog had the foresight to plead not to start the organization name with "American", but to start with "Soil", and he is the one that proposed "Soil Science Society of America" as the official name of the new organization. The modern name was thus adopted, and the new society avoided an embarrassing acronym. At the time of its formation, the Soil Science Society had six official subject matter sections as follows:
I. Soil Physics
II. Soil Chemistry
III. Soil Microbiology
IV. Soil Fertility
V. Soil Genesis, Morphology, & Cartography
VI. Soil Technology
Although some of the early workers in forest soils were members of American Society of Agronomy and SSSA their field of activity was not formally recognized as such in either society. The original constitution of the SSSA did not recognize forest soils in these six subject matter sections. However, Forest Soils was organized as Division V-A, under Soil Genesis, Morphology and Cartography. Records are incomplete, but Stone (1986) lists R.F. Chandler, Jr. as the first Chair of the Forest Soils Section. At the 1954 Annual meeting of the SSSA the president announced that a mail ballot had approved divisional status of S-7 and with the title "Forest and Range Soils." John C. Retzer was chairman of the Division at that time.
The present structure of the Soil Science Society of America recognizes the original six divisions (with the names of S-3, S-4, S-5 and S-6 changed) as well as three added official divisions and one recent provisional division. The divisions added so far are as follows:
S-1. Soil Physics
S-2. Soil Chemistry
S-3. Soil Biology & Biochemistry
S-4. Soil Fertility & Plant Nutrition
S-5. Soil Genesis, Morphology, and Classification
S-6. Soil & Water Management & Conservation
S-7. Forest and Range Soils
S-8. Nutrient Management & Soil & Plant Analysis
S-9. Soil Mineralogy
S-10. Wetland Soils (Provisional)
S-11. Environmental Quality (Provisional)
Though this chapter concentrates on the history of forest soils in North America there has always been a strong international focus and activity in forest soils, first seen by an influx of European thought into the study of forest soils, and now by a high amount of information flow in all directions both into and out of North America. It is important to consider international soil science activities and their impact on the study of forest soils in North America. The first International Conference of Soil Scientists was held in Hungary in 1909 with primary interest in soil classification and agricultural problems.
The fifth International Conference of Soil Scientists was held in Washington, D.C. in 1927. Remarkably, this fifth conference was officially termed the "First International Congress of Soil Science" and it was sponsored by the International Society of Soil Science, the American Society of Agronomy, and the American Soil Survey Association. This presentations at this early conference did show considerable interest in forest soils with a range of papers related to forestry. From the standpoint of the creation of an organization with a widespread, methodical approach to the study of forest soils with continental interest and distribution, this conference could actually be considered as the beginning of the organized study of North American forest soils. In 1933 there were three independent soils organizations in the United States (1) the Soils Section of American Society of Agronomy, (2) the American Soil Survey Association and (3) the American Section of the International Society of Soil Science. As mentioned earlier, in 1936 the American Soil Survey Association was merged with the Soil Science Society. In 1937 the American Section of the International Soil Science Society became part of the Soil Science Society of America. Thus, this one organization now represents major activities in both national and international relationships in soils. North American forest soil scientists do have a number of other avenues for international activities such as the International Union of Forest Research Organizations, but these will not be discussed further in this short history.
|V. Early Developments in Forest Soils Back to top|
Areas of scientific inquiry generally need organizational support in the form of societies which can bring groups together for reporting research, discussing problems, planning for the future, and responding to user needs. These scientific society organizations also act as training grounds for students and as mechanisms for facilitating interchange of faculty and students between other organizations. We have already reviewed the organizations which serve these needs in Agronomy and Soils and in which interest in forest soils was initially developed professionally. We will now review the development of organizations which are more specific to forest soils.
We begin by stating that the review will not be uniform for North America and readers may find coverage of their area is not included. We apologize for this but point out that contents of this chapter must come from local knowledge and personal contacts, since regularly published materials are so few on this subject. Because our careers are limited in geographical area, information available to us to write this chapter is incomplete for some areas. We hope that our effort will eventually result in the production of a more complete history of Forest Soils in North America as readers with more complete information become aware to us, and we encourage them to contact us with that information.
The senior author was appointed to the first faculty position dealing specifically with Forest Soils at the University of Washington beginning in September of 1948. At the time no formal local organization that was concerned with Forest Soils existed in North America as far as we have been able to discover, though several have been created since then.
With the help and support of many segments of the Forest Industry and Dean Gordon Marckworth at the University of Washington, the first action relative to development of interest in forest soils was to organize a conference. This was held in Portland, Oregon on September 15, 1948. This conference brought together representatives of both private and public forests who had an interest in what information about forest soils could contribute to the management of their forest land. The conference quickly disclosed that there was little existing information about forest soils in the Northwest, few people were working in the area, and that programs needed to be established in order to develop interest, information, and a forest soils "network" of professionals. Specific study areas that needed research priority were identified as follows:
1. Productivity--Site classification
2. Forest tree physiology, nutrition, and water in relationship to soils
3. Nursery soils
4. Forest management activities and soils
5. Physical, chemical, and biological properties of forest soils
However, a more long-lasting action of this conference was to organize and support "The Forest Soils Committee for the Douglas-Fir Region." A regular meeting schedule of two major meetings a year was established. One was a winter business and review meeting, and the second was a summer field trip for the purpose of reviewing forest soils research or problems. This schedule continues to be followed. This kind of an organization proved very useful and efficient, and now has counterparts in Northeastern and Southeastern and Northeastern United States as well as in California and Canada. The Committee has since changed its name to "The Northwest Forest Soils Council," and has sponsored many special short courses and conferences on various aspects of forest soils and published a text (Heilman, 1957) on the subject entitled "Forest Soils of the Douglas fir Region."
In the early years of the Committee, regular short courses on forest soils were held at the University of Washington and at Charles Lathrop Pack Forest to give practicing foresters a working knowledge of the subject matter of forest soils, with special discussions relative to soil damage, watershed management and productivity. As information about forest tree nutrition and forest fertilization was developed these subjects were also covered. These kind of short courses continue on a regular basis and were the forerunner of what is now called the "Silvicultural Institute", at the University of Washington and Oregon State University, which typically teaches 30-35 professionals per year on various aspects of forest management, including two modules on forest soils.
Another organization which has been very effective in promoting forest soils and disseminating information about current management of forest soils is the North American Forest Soils Conference. The structure of this group is designed to bring the major producers of soils information together with the users. The first meeting was held in 1958 at Michigan State University with a limited sponsorship but with a wide coverage of subjects. Thirty-one papers were given with the principal address by Charles Kellogg. In 1962 sponsorship was taken over by the Soil Science Society of America, the Society of American Foresters, the Canadian Soil Science Society and the Canadian Institute of Forestry.
As noted above the first Conference was in 1958 (MAES, 1958)and the 8th was in 1993 at the University of Florida. Proceedings of the conferences have all been published in individual book form so that 8 volumes of research results along with discussions about application to forest problems are now available. Organizers have attempted to direct each conference to highlight a particular subject matter. For example, the 2nd conference spent considerable effort on Soil Surveys of Forest and Range Lands, as that subject was of major concern in the 1960's. The 7th conference concentrated on Productivity Problems and Questions, and the proceedings are titled "Sustained Productivity of Forest Soils." Other conferences convered other subject matter.
The professional forestry society in the United States, the Society of American Foresters (SAF), has also moved to recognize the importance of soils through the establishment of a soils working group. This has been in operation for a number of years, with elected officers, and a program at the annual national meetings as well as at local levels. For example, the program at the 1994 annual meeting in Alaska was, Sustaining Long-Term Productivity--A Soils Based Approach (SAF, 1994). The soils working group of the SAF regularly publish a newsletter and are becoming an increasingly important communication group for forest soils professionals.
|VI. Forest Soils in Canada Back to top|
Although the title of this abbreviated history does say North America, the authors do acknowledge that the coverage is principally related to the United States. We hope to justify the more general title by including a section specifically related to Canada. We also acknowledge that the basic information for it was supplied by Professor Gordon Weetman of the University of British Columbia.
Although a number of forest soils researchers in British Columbia have been members of the Northwest Forest Soils Council and worked closely with U.S. soil scientists, there is a divergence, especially in relationship to teaching, management oriented research, and the use of soils information. Canadian forest soils research and teaching is centered on site classification. This was brought about after a rather large administrative and scientific debate over the period of 1950-1970 that centered on the approach Canada should take to classifying forest soil productivity. The site approach was taken because forests in Canada basically consist of a band of boreal conifer forests arranged in a somewhat consistent way across a glaciated landscape with strong physiographic and climatic control. In Canada, there is not the great diversity found in forest lands across the United States, which makes a national approach to classifying forest site productivity more simple than in the U.S. Most of the land is publicly owned and there has been no national soil survey as in the U.S. Therefore soil surveys of forest areas basically do not exist. For these reasons the study of forest soils has been centered on site, and site research has been dominant. We therefore must recognize that the United States and Canada have gone somewhat separate ways, with the common denominator only in pure soils research. The writings of Hills and Rowe explains the Canadian approach.
Professor Weetman lists some of the reasons the U.S. and Canada have gone separate ways: They are:
|VII. Achievements in Forest Soils Back to top|
In this section of the history we will attempt to give the reader a review of areas where we think significant progress has been made in our understanding of forest soils. This is not a literature critique but rather a recounting of what we believe has been achieved. Because of our research interests and lines of work there will be bias in this effort but we have attempted to include the entire field of forest soils. Regardless of this we think that everyone would agree that a major achievement of forest soils study has been to get the soil recognized as one of the major resources in forestry and one which must be carefully managed.
|VII. Achievements in Forest Soils a. Soil Surveys Back to top|
The first step in the wise use and management of a natural resource is knowing what exists and where. In the case of soils this means a soil survey. We already know that the American Soil Survey Association has existed since 1899 and its members were actively conducting soil surveys before that time. However, such activity was largely directed to lands either at that time under or destined for agriculture until about 1950. One of the first North American papers calling attention to the need to survey and map soils on forest areas was that of Lunt and Swanson (1949). In fact in this paper the authors substantiate the need by the statement "At a forest soils conference held in Portland, Oregon, last September (1948) it was agreed that the setting up of a soil survey program for forest land was first in importance for the Douglas-fir region. In this case they are referring to the conference of the "Committee for Forest Soils in the Douglas-fir Region" we have previously described.
The fact is that soil survey activity on forest land in the U.S. has gone very well and large areas of all classes of land ownership are now mapped. In the early years, large land owners such as Weyerhaeuser employed their own surveyors for both western and southern forests. The regular survey programs of the U.S. Soil Conservation Service (now the U.S. Natural Resource Conservation Service) expanded to gradually include all forest land, so that now most small forest land owners can expect to find maps and soil description in the updated standard county surveys. In future years, the NRCS hopes to enlist the aid of many professionals in the effort to develop better soil interpretations for forestry. Larger public land owners such as the U.S. Forest Service, the Bureau of Land Management, and State land agencies have also carried out surveys on their lands. The same is true for many of the forested Indian Reservations. As this review is for North America we should mention that this same picture of forest land soil survey and mapping is not true for Canada as the Canadians have taken a different approach as we described in the section on Canada. The adoption of Geographical Information System methods and more broad scale land management planning is rapidly changing the whole field of soil survey.
|VII. Achievements in Forest Soils b. Soil Factors Which Affect Tree Growth Back to top|
Soil, in concert with climate, is of primary importance in determining the potential for forests to be present in a particular area as well as the potential productivity or growth rates of those forests. Though soil itself is not specifically a necessary requirement for trees, soil supplies many of the growth requirements, including water and nutrients. In addition, soil offers a support medium for growing trees and a buffer against the extremes of temperature. Therefore, all soil properties which relate to any of these are important to tree growth. These are commonly expressed as physical, chemical, and biological properties. Forest soils researchers have worked on all of these and have advanced our understanding of each one in relationship to tree growth and health. In fact, the research effort is now quite specialized and educational institutions, research centers, and researchers are typically known for their contributions to specific areas, as well as overall forest management.
Water availability is one of the primary controlling factors for the presence of trees as well as vigor and growth rates. The problem with water on most forest areas in that there is either too little or too much. In the case of too much we have flooded and wetland conditions and these are assuming greater importance in overall management of forest lands. Many researchers have made significant contributions to our understanding of the water relationships of forest soils. The work of Zahner (Balmer, 1978) has been very useful. The Symposium "Soil Moisture--Site Productivity held in 1977 at Myrtle Beach, South Carolina reviewed the entire field of forest soil water relationships and provides a good reference point for this aspect of forest soils.
Many of the other soil physical properties have been studied in detail throughout the forest areas of North America so that we now have a good information base on the range of values to expect for such properties. Values have been used to predict tree growth rates, or site productivity, while others are used to evaluate the effects of forestry operations such as harvest effects.
Forest soils are habitat for large numbers of organisms from those very small and relatively immobile, such as bacteria and other microbes, to larger mobile insects and earthworms, to relatively large mammals, amphibians, reptiles and even birds. Although many studies have been conducted relative to these organisms and an extensive literature exists, our knowledge of the different kinds, and the roles they play in the forest ecosystem is rather incomplete, particularly as they relate to soil. Some organisms, such as the major decomposers, nitrogen fixing or disease causing organisms of large economic importance are well known and highly studied. For instance, the study of mycorrhizae was initially advanced by forest soil scientists. In this particular case, the agricultural soil scientists have followed the lead of forest soil scientists. Knowledge sometimes includes how we can affect population numbers and activities, but most have large degrees of uncertainty attached to them. Some organisms, such as the edible mushrooms, are becoming increasingly important in the management of forest areas as nontraditional sources of revenue, often with high value per area of forest land.
Chemical properties of forest soils have also been rather thoroughly investigated and described for most forest areas of North America and a very extensive literature exists. We therefore know what level of acidity (value of pH) to expect in soils of most of the forest areas and how this has or has not changed under the influence of man's activity. We also generally know the chemical composition of most of our soils and the status of the elements as to available, non-available, or exchangeable, even though we may not know in an extremely practical way how to interpret the information relative to forest growth. There is again an extensive literature on these aspects of forest soils for all areas of North America and many researchers have made significant contributions.
|VII. Achievements in Forest Soils c. Productivity - Site Back to top|
Although these terms have been historically used somewhat interchangeably in forestry we can review the contribution of forest soils to each. Site has been used to convey some concept of overall growing conditions and also specific productivity. A system of site classification called "site index" which has been developed for the major wood producing forest species, uses height of dominant or codominant trees at a specific age as an index. Many different concepts about productivity exist but in this review we will use the traditional biological context as stated by Hansen (1962) where productivity is "the total quantity of organic material produced in a given period by an organism." For forest tree species foresters have condensed this to merchantable or total volume and express it as cubic feet or cubic meters per unit area of land per year. In this short history we are not concerned with the philosophy of the terminology but rather the contribution of soils to our understanding of site and productivity and what we can do to maintain or improve productivity.
Forest soil researchers have contributed a great deal to our understanding of the factors which determine site. As a result we now recognize the role that some, but not all, soil physical, chemical, and biological properties play in determining site. This information has been put to practical use through the development of soil-site indices for given species in local areas. These contributions are well documented in an extensive literature specific to the local areas and species.
Productivity evaluation has assumed an increasingly important role in current discussions about the management of forest land. Some groups believe that forest harvest, and other uses by man, will reduce or destroy forest productivity, while others believe that we can have normal forest use and increase future production on a given area of land. Obviously, determining what will happen on any given area of land would involve understanding what factors determine productivity and whether or not and how much we change these factors in our use and management. Forest soils research has contributed substantially to our understanding of soil factors which are important in productivity and therefore can be used to predict or quantify changes due to land management.
Even though we believe that we scientifically understand the basis of forest productivity, the political and policy ramifications of the maintenance of forest productivity will be with us for a long time. This history therefore needs to point out that although many forest productivity studies have been completed, environmental attention in now focused on what is termed "Sustained Productivity" and a general literature is developing on how forest productivity can be destroyed. A major program in long term evaluation of forest productivity in different areas of the United States is the early developmental stage by the U.S. Forest Service and practically every forest research organization has some kind of a forest productivity program. Maintenance of soil and site quality is written into the management plan of each of the U.S. National forests, with monitoring plans designed to detect losses in forest productivity of 15 percent or greater being designed and implemented (Powers et. al., 1990). The potential for loss of inherent site quality and the ability to grow productive forests remains on the forefront of forest soil research, and is probably second only to biodiversity as a central issue in the management of North American forests.
Forest soil researchers will have ample opportunity for further contributions. Earl L. Stone made a major contribution to this area with his 1973 report on "The Impact of Timber Harvest on Soil and Water." Several new symposia on the general subject of maintaining forest productivity each year. The demand for forest products has been increasing both in per-capita and absolute terms, but the area of land devoted to forest production has been decreasing over that same time frame. Therefore there has been a growing interest in increasing the productivity of land for wood production through intensive management of forests. Intensive forest management basically increases wood production in two ways. The first method is by improving tree genetic potential and applying appropriate stocking, thinning, havesting and other silvicultural improvements. The second method is by improvement of soil properties that partially determine site. Improvement of site for forest management is probably best illustrated by the effort made in forest nutrient management and forest fertilization, which served as the underpinning for early forest soils research and continues to be a major soil manipulation that can improve site and thus forest productivity.
|VIII. Nutrient Management and Forest Fertilization Back to top|
Extensive early research work throughout all of North America has clearly shown that elemental deficiencies exist in many specific forest areas and therefore trees growing on those sites are not able to make full use of the other growth factors of the sites. In addition to reduced growth rates they may also be suffering decline in vigor and eventual death from nutrient deficiencies.
Research activity has not only been able to describe these nutrient deficiencies but has also shown how corrective action can be taken to eliminate them. Forest fertilization, or the adding of nutrients, is designed to add elements either lacking, or in low supply. To be successful, fertilization must be very specific to the needs of a given forest area and to the economics of forest management. In North America, forest fertilization is generally well-developed where the following three basic conditions exist:
In the future, increasingly stringent environmental considerations may restrict the ability of forest land managers to apply fertilizers, even where these three conditions make application profitable and attractive.
An extensive literature has been developed to cover this subject and many reports of special symposia and conferences exist. The development of the information base for good programs of forest fertilization in all of the major forest areas of North America has been an important contribution of forest soil research and the development of the relation of forest soils to tree growth. Again, many researchers have made significant contributions but they cannot be named in this short review.
Fertilization research and practice has also extended into the application of municipal waste to forest land and in many areas of North America programs for use of "Biosolids" (previously called sewage sludge) are well underway. We believe this use on forest land is an important contribution to recycling and environmental protection goals of society and that the program will expand in the fugure. Again an extensive literature covering all aspects of such use exists. One of the earliest books dedicated to the subject of application of wastes to forest land was published by Sopper and Kerr (1979), and coined the term "living filter" for the high ability of forests to retain nutrients added as waste materials.
The other important aspect of nutrient management on forest land which is now emerging very strongly is sustaining and improving forest productivity. We have previously referred to the great emphasis now being put on "sustained productivity" in the management of forest land. For many areas, researchers have developed nutrient cycles, which include the sizes of discrete forms or locations of nutrients (termed nutrient pools) and the relative movement of nutrients from one pool to another (termed nutrient fluxes). There is justified concern that one form of management or harvest may remove more of a particular element than the area can replace or sustain over a particular time period. If the harvest is repeated at frequent intervals then nutrient deficiencies may occur over time. Harvest at long intervals, and only partial crop removal constitutes less of a potential problem.
Solid research is badly needed in the area of the effect of nutrients on long-term productivity of forests, as some individuals and organizations have gone so for as to claim (with little or no data) that on some forest soils, as little as three harvest cycles would totally destroy productivity. As a result we are now in an era of expanded discussion and research on the question of "sustainable forestry" and what role our forest soils play as sources of nutrients for forest growth. There is a great deal of need for continuation and expansion of the research that early pioneers in forest nutrient cycling research conducted as forest management systems change.
|IX. Other Resources Back to top|
The increasing attention to the use of forest land, especially that in public ownership, for purposes other than wood production has expanded the need for a soils information base to serve these uses. Alternative uses of forest land will continue to expand with our increasing population and their changing desires for the use of that land. Forest soil research has responded by incorporating all of these alternative uses into research plans and information development and communication is well underway.
A very important use is that of water catchments and water supply for either agriculture, municipalities, or in some cases for wildlife such as salmon. In local areas this use of forests may have first priority, and management practices shifted to reduce water use by forest trees while still maintaining quality. An extensive literature exists in the area of water quantity and quality effects of forest management and a large number of researchers have contributed to our understanding throughout all of North America.
There remain many challenges that will need to be addressed in the future by forest soil scientists in order to utilize and protect the soil resource for the benefit of man and nature. The final section of the chapter on forest soil history will review important needs, realizing that many of the original questions asked several decades ago remain largely unanswered and many compelling new questions have been asked since then.
|X. Evaluation and Challenges Back to top|
Our final remarks will be directed toward an evaluation of where we are in forest soils and what major problems or challenges lie ahead for those now entering the field. We know that for both purposes we have many opportunities for being wrong and that some will disagree with us in our evaluation. There is a healthy difference of opinion in the forest soil's community. However, we will still make the effort and hope this will be a fitting conclusion to the history of the study of forest soils in North America.
Perhaps the most important accomplishment is the general recognition that soil is an independent natural body which plays an important role in the functioning of all natural terrestrial systems and knowledge of the soil is a critical part of our understanding of these systems. At the same time forest soils have been universally recognized as a legitimate object of study at all levels at most of the higher educational institutions in North America and are the subject of much research effort and reporting.
Having achieved a place for forest soils in education and research we believe that one of the greatest challenges to researchers and educators will be to keep on the right track in their research and instructional efforts. It will be easy to be sidetracked by the many charges of universal soil degradation and claims of inability to practice forestry while at the same time protecting forest soils now flowing in the environmental area. Forest soils are not magical entities, though their properties are often complicated and their form and functions fascinating to layman and advanced scientist alike. Some soils are very resilient and not highly subject to degradation by even the most intense forest management, while other soils are very fragile and should be highly protected from management that may degrade soil quality. Some of the concerns and charges of universal soil degradation have developed because so little attention was paid to forest soils for so long in forest management and even now most of the general populace know very little about forest soils. Clearly a very important area of soil research is to identify specific cases where soils can and cannot be easily degraded and to make that information available to forest management professionals as well as the public.
We do not attempt to play down the problems of expanding human populations, with resulting pressure on our land resources, and the need to maintain our soils in the best possible condition in order to maintain productivity. It is promising to observe that the latest Annual Report of the German Publication Prisma (German Advisory Council, 1994) focuses on the threat to soils and especially what is called soil degradation. The advisory council to this group came up with 12 syndromes for depicting the causes of soil degradation. One of these, the so-called "Sarawak Syndrome," that attributes the degradation to conversion or over-exploitation of forests that have delicate soils.
Another recent publication (Oldeman, 1994) takes a broader look at the subject by considering what is termed "Soil/Resilience and Sustainable Land Use." A number of papers in this volume deal with degradation of soils from many types of uses, including forestry. However, the concept of soil resilience and recovery is introduced and described. Therefore considerable emphasis is placed on the ability of the soil system to recover from degradation. Most of the soil degradation described in these publications has occurred in Asia, Africa and South America, with much smaller areas in Europe or North America.
Forests and forest land have been used for many purposes historically by man. Native peoples in forested areas, generally, but not necessarily few in numbers per unit area of land, used the forest mainly as a source of food and shelter, and typically without a great impact. However, in many areas they did use fire to bring about certain desired changes in conditions for grazing and agriculture and had widespread impacts on the land. Hilgard refers to this in his early writings about soils in Mississippi.
With ever-expanding human populations and greater pressure on all of our land there is indeed reason to give priority to managing our land resources to maintain or sustain basic productivity. However, in order to do this we must understand the factors which control forest productivity, especially the more critical ones, and how these may be affected by what we do.
Soil properties do play a central role in forest productivity, but so do many other factors. Soils also vary greatly from place to place on the earth's surface and also locally. Therefore, the effect of one forest crop harvest every 40 years may be very insignificant on one soil, but cause negative impacts on another. And this may happen over small distances. For instance, if we are concerned with essential elements as the negative factor, we must recognize that the amount removed in a given harvest may be quite small in relationship to either the total or available storehouse. We do know that some forest soils are deficient in one or more elements for good growth of trees under virgin or natural conditions. Although the practice of forest fertilization may not mesh well with some concepts of "sustained productivity" we also know that problems of nutrient deficiency can be corrected by applying the necessary essential elements, sometimes at minimal expense.
Much of the agricultural land in parts of North and South America, Europe, or other continents was developed by removing the forest cover, frequently by total area burning and then using the soil for intensive agriculture. In the early years of development this was typically done without the benefit of modern fertilizer and management practices. If total soil destruction could occur, we should certainly expect it under these more drastic conditions. A good case in point is the extremely large loss of topsoil due to soil erosion from agriculture in the Southeastern United States during the 1800's. This region today encompasses some of the most productive land with the highest forest growth rates in the U.S. Some of the highest growth rates measured in the Southeastern U.S. occurred on "old fields", which were considered so degraded as to be no longer acceptable for agriculture and therefore available for forestry.
The great increase in number of humans in the past 200 years, and resultant massive movements to relatively unpopulated areas, has brought many different demands on forest resources. To meet some of these needs and furnish raw materials, trees must be harvested. Man has of course devised many different methods for harvesting and removing trees from forest areas but depending upon how they are applied various kinds and degrees of impacts can be made on the forest system. For large areas of the world, and particularly in North America, the purpose of tree removal has been to convert to other land uses, especially agriculture. Unfortunately many of these efforts have been described as forestry in the popular literature, and much of the deforestation associated with land clearing for agriculture in the world is blamed on the practice of "forestry", and for maximum effect on the public, is often blamed on "multinational companies". Such blame of large "faceless" organizations is inviting, but often unwarranted. Conversely, in many cases, watchdog environmental organizations are reluctant to blame small farmers for deforestation, even when it is warranted. For instance, there is strong pressure to remove presently forested land from production forestry in the United States, but little pressure to require farmers to return some of the most productive tree growing land presently in agriculture to forestry. In Mexico there is tremendous pressure on the government to carve up and distribute large areas of land held by wealthy landholders. These areas are considered to be "unused" by reformists since the dominant acreage is not allocated to producing staple food crops. Many of these "unused" areas are heavily forested, and represent a significant amount of the forest production in Mexico.
Research has shown that the objective of fiber production from a forest can more efficiently be met by utilizing plantation forestry, which may mean the growing of a single tree species on certain tracts of land. Forest wood fiber production, especially when it involves plantation management and clearcutting of areas, has acquired a bad name among environmental groups and movements. In fact, great efforts are being expended to eliminate this part of forestry from many lands, especially those in public ownership. The literature is replete with statements that plantation forestry "destroys the soil" and after three rotations essentially everything is gone. Such statements are generally without merit, but they often have great effect on public opinion of the present effects of forest management. Unlike in agriculture, there is no significant scientific evidence to support widespread destruction of forests by forest management. In fact, there is widespread research evidence that shows that forest management in general is sustainable from the standpoint of nutrient cycling in most situations that have been studied. One of the important roles that forest soil scientists can play is to identify situations where a given level of forest management would or would not be sustainable, and to provide the range of possible corrections that would provide sustainability for all forest management.
In addition, it is important to note that natural systems are all resilient to a certain extent, with soils typically very much so, and forest land can and does recover from mismanagement. Though mismanagement of the soil resource may result in a period of time that a given area of land is unproductive, recovery of a natural system is typically a certainty, provided that the necessary organisms that might have been eliminated can enter the system. A good case in point is the frequent total destruction of forests in the Pacific Northwest by mudslides and volcanic eruptions, and the widespread incidence of other severe disturbances in many other areas. For instance, the example of the regeneration of forests on and near Mt. St. Helens offers a very good example of the resilience of "totally destroyed" forest systems. Such patterns of total destruction of forest ecosystems and their rebuilding over time dominate the landscape of many parts of North America. Damage to forest ecosystems by improper forest management are typically much less destructive than severe natural disturbances such as mudslides, and there is no valid reason to believe that such damage will be longer in duration just because it is man-induced and not natural.
The arguments for total destruction of the soil from present day forest harvesting appear to have been developed primarily to support the environmental movement's programs against any harvest of forests termed "old growth." The authors of this chapter choose not to make value judgements on the importance of protecting remaining old growth forests for environmental or aesthetic purposes and recognize the high ecological value of these resources. However, we do take issue with many of the methods used to provide old growth protection, including utilizing the myth of permanent ecosystem destruction due to normal forest management. We also point out that present-day old-growth forests often regenerated from previously disturbed systems, and the age class distribution of many old-growth stands in the Pacific Northwest indicate that disturbance may have been the original event that set those forests in motion.
|XI. Conclusions Back to top|
During this short consideration of the history of forest soils in North America, we have identified progress from the early times of forest soil science as simply recognizing forest soils are related to the type and productivity of a forest that grows on that soil. This initiated classification and mapping of forest soils in order to estimate potential forest productivity and concentrate management on productive areas. Later work showed that soil was a primary reservoir of critical nutrients for forest growth, and recognized that soil nutrients often limit forest growth, and that nutrients can be depleted or increased by forest management practices. The concept of the forest nutrient cycle provides a framework for evaluating the potential impacts of forest management on the nutrient capital of the forest ecosystem. In addition, methods of nutrient enhancement by fertilization or culture of certain species or tree/organism symbiotic associations provide a means of increasing nutrient availability and possibly forest productivity.
All of the earlier findings related to forest soils remain valid and useful at the present time, and are still active fields of study. The concept of forest soil as a component of a delicate forest ecosystem where constant linkages between all parts of the forest ecosystem are critical to long-term forest health is also not recent. In fact, the conservationist Aldo Leopold mentioned in his earliest writings that it is important not to throw away any parts of an ecosystem, or we couldn't put it back together in a way that would function, saying "The first rule of intelligent tinkering is to save all the cogs and wheels." However, the widespread acceptance of the forest ecosystem as a functioning "organism-like" unit is presently a subject of considerable debate, and the concept is by no means universally accepted. In fact, it has clearly been shown at least over short time scales that all parts of a natural forest ecosystem are not necessary for forests to "function". Some organisms may not serve a critical function, and some may be redundant for critical processes.
There are certainly instances of specific, widespread disasters where dominant species have been eliminated from forests such that the forest ecosystem changes but continues to function. Examples include the blight of the American Chestnut and the Dutch Elm disease. Such systems are certainly different, and in most ways less desirable than the original forest system, but they do function with many of the properties of the original forest due to the resiliency of the forest. The present authors are unaware of any instance where elimination of one or more "cogs" of an ecosystem cause a complete nonfunctioning of any future forest ecosystem to occur. It may be telling that the only instances of widespread continual deforestation in local sites that come to mind involve destruction of the soil resource. Thus, the challenges to future forest soil scientists include developing knowledge of forest soils both as an entity worthy of study in its own right, but particularly as a critical component with myriad linkages to the whole forest ecosystem. It is also clear that the primary importance of forest soil research in the future will be to assure and demonstrate that forest management be sustainable in the long term. Otherwise, forest management in North America may largely cease to be an acceptable land use option politically due to real or perceived losses in forest productivity.
|XII. References Back to top|
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