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Impact, Ecological
The observable or suspected effects of one or more perturbations on a factor (usually biological) of an environmental system. There are no value judgements, e.g., positive or negative impacts. An impact is simply an effect or a change of condition.
Impacts, Ecological, Types of
  1. accumulative - The sum of a variety of environmental changes and their total effect.
  2. acute - A person-induced ecological effect commonly resulting from a high level of disturbance but of short duration.
  3. beneficial - A person-induced ecological change which is useful to people and favorable to the system.
  4. chronic - A person-induced ecological effect commonly resulting from low levels of disturbance but often persisting over long periods of time.
  5. detrimental - A person-induced ecological effect which damages ecosystem structure or function.
  6. direct (primary impact) - Direct or primary impacts are those in which the causative agent impinges directly upon the responding ecological components, e.g., land clearing for construction causes direct loss of vegetation.
  7. indirect (secondary impact) - Indirect or secondary effects are those in which the person-caused change in the environment creates one or more intermediary effects in a chain of events leading to the impact being observed. Certain agencies (e.g., EPA) differentiate indirect and secondary impacts. For example, an indirect impact would occur when construction of a dam causes reduction of stream flow, in turn causing elimination of riverine wetlands downstream. Secondary impacts occur when a wastewater treatment project induces urbanization that in turn has environmental impacts.
  8. long-term
    1. which last the lifetime of the project or past the construction phase, or for the duration of maintenance and operation of the project, e.g., visual impact due to the design and building materials of a structure. It should be noted that some long-term impacts might be reversible. The time frame of reference should be stated when "long-term" impacts are discussed.
    2. "long-term" and "short-term" are two phrases that have caused considerable confusion in the environmental assessment process since there are no definitions for time periods encompassing either short-term or long-term. Perhaps a better selection of terms would be to divide the temporal phases of a project into pre-construction and planning, construction, immediate post-construction and initial operation, operation, and post-operation. In some cases, all of the above temporal phases, even through project operation, can occur over a short time period.
  9. moderate and severe - Moderate and severe effects are gradations of adverse impacts. Moderate could be characterized as partial elimination, dislocation, impairment or alteration of biota or use of resources and facilities. Total elimination, dislocation, impairment, or alteration of biota or use of resources and facilities could characterize "Severe".
  10. short-term
    1. Typically construction-induced impacts which last only as long as construction, or may be characteristic non-construction activities, such as spraying, or may occur during the operation of a facility, such as brief air pollution episodes due to temperature inversions. Since no strict definition of "short-term" exists, the time frame of reference should be stated.
    2. Any impact occurring over a relatively short period of time.
  11. significant - An impact resulting in measurable changes in indicator parameters, community dynamics and succession.
  12. synergistic - Impacts can have synergistic effects in that individually they may be relatively unimportant but together may form impacts which are "greater than the sum of their parts," e.g., timber harvesting practices may increase water temperatures, which make fish more susceptible to disease, while also decreasing the dissolved oxygen in the water, creating conditions of severe stress for fish.
  13. tertiary - Observed change resulting from a perturbation which directly impinges on the biota with two or more prior cause-and effect steps.
Incidents in which fish become caught and held by suction against intake screens at dams such as those utilized in power plant cooling systems.
Implementation Plan
A document for giving practical effect to, or ensuring the actual fulfillment of some regulatory standard or goal by specific measures.
Implementation Studies (Level C Plan)
One of the "levels of planning" for water and related land resources planning by Federal agencies whose activities involve planning and development of water resources as contained in the Principles and Standards of the Water Resources Council. Implementation studies are project feasibility studies undertaken by the Department. These studies may be conducted to implement findings, conclusions, and recommendations of framework and assessment studies, regional or river basin studies, other Federal-state investigations or at the request of local government organizations. Implementation studies are directed toward carrying out the project installation authorities of Public Law 83-566, Public Law 78-534, and the "Resource Conservation and Development" Program. Plan formulation for implementation studies focus on a recommended plan of action to follow within the next 10-15 years. Long-range projections of water and land resource needs will be considered; however, primary attention will be toward a plan to meet the near-term needs and alleviate problems. Plans will be directed toward a set of specific components of the two objectives (national economic development, and environmental quality, see Principles and Standards) which will be determined for the planning area. The plan formulation process will be responsive to the identified needs and problems that relate to the water and land resources in the area and the planning functions that may be employed to meet the needs.
A body of water formed by collecting and confining stream flow (as in a reservoir).
A short-term rapid learning process early in life (fixing young on parents or habitat) which is genetically irreversible. More prevalent in precocial young.
Improvement Cutting
Eliminating or suppressing less valuable (poor species, form, or genetics) trees to increase growth rates of more valuable trees, typically in mixed uneven-aged forest. A cutting is made in an immature stand to improve the stand composition and character.
Income Distribution Effects
Effects of proposed activities on the proportion of the total income of an area received by each segment of the population, e.g., "the rich get richer and the poor get poorer" is an example of income distribution effects. A doubling of everyone's income, so the shares of the total remain the same, has no income distribution effect.
Incommensurable Values
Resource yields for which no method yet exists for conversion to a common measurement scale or unit (such as dollars) for purposes of comparative evaluation of relative importance, e.g., comparison of the aesthetic benefits with the timber yields of land is difficult because it is often impossible to express the former objectively in dollar values or the latter in equivalent aesthetic units.
Incompatible Uses
Land uses which cannot exist together by reason of either competition for limited resources or use by products which prevent the alternative use, e.g., timber harvesting and wilderness preservation are incompatible uses for one piece of land.
Increaser Plant Species (Increaser)
Plant species (e.g., rangeland plants) of the original vegetation that increase in relative amount, at least for a time, under overuse.
Incrementalism (Muddling Through, Disjointed Incrementalism, Incremental Planning)
An alternative planning approach to comprehensive planning based on the assumption that due to practical difficulties, true comprehensive planning cannot exist. As an alternative, it is suggested that planners concentrate on a recursive process of choosing among policies based on incremental changes to existing policies without trying to set overall goals and without basing the policies on theoretical predictions of the consequences of the policies or on an understanding of the system being regulated. Instead the planners would rely heavily on the record of past experience with small policy steps to predict the consequences of similar steps extended into the future. Social scientists, politicians, or public administrators do not yet know enough about the social world to avoid repeated error in predicting the consequences of policy moves. Practicing incramentalism, a policy-maker consequently expects that his or her policies will achieve only part of what is hoped for. The policies, the same time, will produce unanticipated and undesirable consequences. If the policy maker proceeds through a succession of incremental changes, he or she avoids serious lasting mistakes in several ways. In the first place, past sequences of policy steps provide knowledge about the probable consequences of further similar steps. Second, big jumps toward goals are not needed, jumps that would require predictions beyond his or anyone else's knowledge. The policy maker never expects policy to be a final resolution of a problem. Each decision is only one step, one that if successful can quickly be followed by another. Third, the policy maker is able to test previous predictions about moves on each further step. Fourth, the incrementalist often can remedy a past error more quickly than if policy proceeded through more distinct steps widely spaced in time.

Because practitioners of this approach expect to achieve their goals only partially, they expect to repeat endlessly the sequence just described, as conditions and aspirations change and as accuracy of prediction improves. Any significant problem for planners or policy makers involves tradeoffs among conflicting values, and when dealing with incrementally different alternatives, this is always a problem of adjustments at a margin. But there is no practicable way to state marginal objectives or values except in terms of particular policies. The only practicable way to disclose one's relevant marginal values, even to oneself, is to describe the policy chosen to achieve them. Consequently no overall goal is developed and means and ends are simultaneously chosen. Ideally, rational-comprehensive analysis leaves out nothing important. But it is impossible to take everything important into consideration unless "important" is so narrowly defined that analysis is in fact quite limited. Limits on human intellectual capacities and on available information set definite limits to people's capacity to be comprehensive. Therefore, no one can practice the rational-comprehensive method for really complex problems, and every administrator faced with a sufficiently complex problem must find ways to simplify drastically. In the method of successive limited comparison, simplification is systematically achieved in two principal ways. First, it is achieved through limitation of policy comparisons to those policies that differ in relatively small degree from policies presently in effect. Such a limitation immediately reduces the number of alternatives to be investigated and also drastically simplifies the character of the investigation of each. The second method of simplification of analysis is the practice of ignoring important possible consequences of possible policies, as well as the values attached to the neglected consequences. Almost every interest has its watchdog. Without claiming that every interest has a sufficiently powerful watch dog, it can be argued that the current U.S. system often can assure a more comprehensive regard for the values of the whole society than any attempt at intellectual comprehensiveness.

Increment Borer
An auger-like instrument wilh a hollow bit, used to extract cores from trees for determining their growth and age.
Independent Peer Review
A review conducted using generally-accepted practices that does not allow individuals to participate in the reviews of documents they authored or coauthored. A peer is a person who has substantially equal knowledge and standing in relation to the authors or is likely to be able to make informed reasonable comment on a specified document.
Index (Index Number)
A ratio or composite numerical value derived from a series of observations which is used as an indicator or measure of conditions, properties, phenomena or trends. Also, a number used to indicate change in magnitude (as of cost, price or volume of production) of some complex variable as compared with its magnitude at some specified time -- usually taken as having a standard of 100.
Index, Economic
A measurable aspect of society which indicates the extent to which certain more complex aspects are present. [e.g., the "consumer price index"] Discloses the relative change, if any, of prices, costs, or some similar phenomena between one period of time and some other period of time selected as the "base period." The latter period is usually assigned the index number of 100. There are numerous methods of calculating an index number.
Indicative Planning
A method of planning (notably used in France) which primarily restricts itself to analyzing the economy and then making this information available to industry. The modern economy requires the employment of large investments the profitability of which may be profoundly affected by changes in the environment. These changes not only occur rapidly, they are difficult to predict. The individual business has no valid basis for such calculation. The entire economy is interdependent and beyond the analysis capabilities of a single firm. The guiding principle of "indicative planning" is to integrate all the effects of interdependence by, on a nationwide scale, studying the markets and making detailed analyses and forecasts. The instrument used in making these forecasts is the economic input-output analysis. This information is then distributed to the private sector, which is primarily left alone. With this complete information it is assumed that industry will adjust its production, use of resources, and investments to satisfy the projected demands, thus avoiding bottlenecks, smoothing business cycles, and increasing harmony and growth. The planning is implemented by "indicating" to all individuals involved the future consequences of their actions, helping individuals to arrive at a common view on the future of a particular economic activity in relation to the national development aims, demonstrating the advantages of conforming to this common view, and only occasionally coercing conformance. Thus, "indicative planning" is not planning for land managers, but planning for managers of societies and economics.
A measure or measurement of an aspect of a sustainability criterion (USFS, 2005). A quantitative or qualitative variable that can be measured or described and that, when observed periodically, demonstrates trends. Indicators are quantifiable performance measures used to assess progress toward desired conditions.
Indicator, Biologic (Ecological Indicator)
An organism or a class of organisms (such as a species) or an ecological community that is so strictly associated with particular environmental conditions that its presence is a fairly certain sign or symptom of the existence of these conditions. In select cases, an organism that exhibits identifiable responses to a pollutant at low levels.
Indicator Species (Index Species, Indicator Organism)
A plant or animal in a certain location or situation, the presence or absence of which, or its frequency or vigor, is a fairly certain sign that particular environmental conditions are also present, e.g., Escherichia coli bacteria in water indicates probable pollution by human fecal matter. A biologic indicator can be used to refer to signs or symptoms associated with any level of organic organization while indicator species only refers to those associated with the species level. For example, a particular plant might indicate a soil type or the presence or absence of an air or water pollutant. The arrangement of habitats (by tree species and age group) reflects requirements for selected wildlife species.
Indifference Curve or Map
A two-dimensional graph of a combination of indifference curves denoting an individual's preference system to various combinations of two goods or services. Each line of the family of curves represents equally desirable mixtures of the quantities in question. With different curves representing differing levels of satisfaction it is possible to determine what quantities an individual will consume when faced with different prices and incomes.
Indigenous Species
Species historically native to an area, not introduced by people.
Indirect Effect (Secondary Effect)
A condition caused by an action or inaction through intermediary causal agents. An effect for which the causal linkages to the action or inaction are not readily apparent. Contrasts with direct effect. This is not a measure of importance, but merely a classification by causal linkages. Direct effects are usually easier to detect and measure with certainty than indirect effects, but they may be either more or less important than indirect effects.
Individual Distance (Personal Distance)
The normal spacing maintained by non-contact animals; the distance two members of the same species experience stress of crowding. "Individual distance" and personal space interact to affect the distribution of persons. The violation of "individual distance" is the violation of society's expectations.
The flow or movement of water through the soil surface into the ground. This is distinct from percolation which is movement of water through soil layers or material.
Infiltration Rate (Infiltration Capacity)
The maximum rate at which the soil under various specified conditions (including the presence of an already excess amount of water) can absorb falling rain or melting snow.
Information System
A combination of personnel, efforts forms, formats, instructions, procedures, data, communication facilities and equipment that provides an organized and interconnected means (automated, manual, or a combination of these) for recording, collecting, processing, retrieving, transmitting, and displaying information in support of specific functions.
Infrastructure (Social Overhead Capital)
The basic equipment and facilities underlying a nation's, region's, or community's economy (transportation and communications systems, power facilities, schools, hospitals, etc.).
Inherent Erodibility
The natural qualities or properties of a soil to erode when subjected to erosive forces.
Initial Action
The prompt, pre-planned response to a wildfire.
(1) Data that are read into the computer. (2) Land, labor, or capital required for production processes. (3) Anything (often basic resources) that is taken in by or enters into the workings of a process or system, e.g., as nutrients or energy into an ecosystem, effort or information in to a planning process, silt into a stream.
Input-output Analysis (Inter-industry Analysis, Leontief Analysis)
A systematic technique for quantitatively analyzing the interdependence of producing and consuming units (sectors) in an economy. It studies the interrelations among producers as buyers of each other's outputs, as users of scarce resources and as sellers to final consumers. The technique has been useful for the study of the way in which the component parts of an economy fit together and influence each other, for short-run forecasting, and for policy guidance. A quantitative study of the interdependence of a group of activities based on the relationship between in puts and outputs of the activities. The basic tool of analysis is a square input output table, interaction model, for a given period that shows simultaneously for each activity the value of inputs and outputs, as well as the value of transactions within each activity itself. It has been applied to the economy and the industries into which the economy can be divided.
An agent or chemicals, typically used to destroy, prevent, or control insects and similar animals.
An animal that eats insects.
A stage in the development of an insect between two successive molts.
Institutional Land Uses
All buildings, grounds and parking lots composing the facilities for educational, religious, health, correctional and military installations.
A significant and persistent element (as a practice or relationship) in the life of a culture that centers on a fundamental human need, activity or value, occupies an enduring and cardinal position within a society and is usually maintained and stabilized through social regulatory agencies (e.g., the special legal status of the social institutions of marriage and the family unit).
Institutions, Legal
A society's system of legal rules and principles.
Institutions, Social
A set of informal and formal rules, behaviors, and practices that deal with a specific basic function in society. The five basic social institutions are: the economy, the political system, the educational system, the religious system, and the family.
Instream Flow
The minimum flow necessary for all the uses of water while it is flowing through streams. Some of those uses are fisheries, channel stability, maintenance, riparian habitat maintenance, and aesthetics.
Intangible Value (Imponderable Value)
Resource yields which are not directly quantifiable, or if quantifiable, cannot be valued by market mechanisms. The net yields from resource use extend beyond the concept of secondary benefits, and include psychic and indirect monetary benefits to the users. Normally intangible values accrue from the aesthetic, scientific, educational, historical, or recreational aspects of the natural environment.
Integrated Pest Management (IPM)
The comprehensive systems approach to achieving economical pest damage control in an environmentally acceptable manner. The individual components of integrated pest management in forestry include cultural, mechanical, manual, prescribed fire, biological, chemical, and regulatory means. A strategy which manipulates crop and forest pests to achieve resource management objectives. It is the planned and systematic use of detection, evaluation, and monitoring techniques, and all appropriate silvicultural, biological, chemical, genetic, and mechanical tactics needed to prevent or reduce pest-caused damage and losses to levels that are economically, environmentally, and aesthetically acceptable. Emphasis is on damage management, not necessarily reducing pest population abundance.Vertebrate damage management is recommended by the group of people working with those animals and associated problems.
Integrated Resource Management
A management strategy that emphasizes no resource element to the exclusion or violation of the minimum legal standards of others (USFS 2005)
Interaction Matrix (Matrix)
A table with actions, conditions, resources, effects, etc., listed along two perpendicular axes and a matrix structure so created where each position in the matrix corresponds to one element from each axis. By assigning values to the positions in the matrix structure, relations between pairs of elements (one from each axis) can be indicated.
The combination of two or more academic disciplines or fields of study; an example being a team of managers and researchers in a partnership of equals, even though each has different formal backgrounds, education, and experience. In contrast, a multi-diciplinary team consists of each person being a specialist, establishing his or her own method of operation, and turning out a personal product (output). Someone else combines or unifies the work.
Interdisciplinary Approach
The utilization of a team of individuals representing two or more areas of knowledge, learning, or skill working together on the same subject. This approach provides for integrating two or more mental processes into a common, problem-solving effort that is likely to be more effective than the independent thought processes of a single person trained or skilled in one area of knowledge. Contrast with Multidisciplinary.
Interdisciplinary Team (I.D. Team)
A group of individuals with skills from different resources. An interdisciplinary team is assembled because no single scientific discipline is sufficient to identify adequately and resolve issues and problems. Team member interaction provides necessary insight to all stages of the process. The members of the team develop a solution with frequent interaction so that each discipline may provide insights to any stage of the problem and disciplines may combine to provide new solutions. This is different from a multidisciplinary team where each specialist is assigned a portion of the problem and their partial solutions are linked together at the end to provide the final solution.
The cost or time value of money.
A shared boundary. Also a hardware component to link two devices. Also a portion of storage or registers accessed by two or more computer programs.
That portion of rainfall that infiltrates into the soil and moves laterally through the upper soil horizons until intercepted by a stream channel or until it returns to the surface at some point of infiltration.
Intermediate Cut
Any removal of trees from a stand between the time of its formation and the harvest cutting; generally includes cleaning, thinning, release liberation, improvement, sanitation, salvage, and sanitation cuttings. An example is a removal cut which removes seed source trees that are prominent in a seedtree or shelterwood cut. Thinnings are intermediate cuts in an immature stand to control tree density and to improve the growth, quality, yield and species composition of a stand. They may produce income but in some cases add costs.
Intermediate Harvest
Any removal of trees from an even-aged stand between the time of its formation and the regeneration cutting.
Intermittent Grazing
Grazing range or artificial pasture for indefinite periods at indefinite intervals.
Intermittent Road (Intermittent Use or Service Road)
A road developed and operated for periodic service and closed for more than 1 year between periods of use.
Intermittent Stream (Ephemeral Stream)
A stream or portion of a stream that flows only in direct response to precipitation. It receives little or no water from springs and no long-continued supply from melting snow or other sources. It is dry for a large part of the year, ordinarily more than 3 months. The groundwater table lies above the bed of the stream during the wet season but drops below the bed during dry seasons. During wet seasons the stream may receive a contribution from ground water. In many arid areas, the stream channels are always above the water table and therefore carry only surface runoff. Flow may also be interrupted by freezing of the groundwater to some depth below the streambed in smaller streams. A stream that flows only at certain times of the year when it receives water from springs or from some surface sources and is shown by a dashed line on USGS 7.5-minute quadrangle maps.
Internal Rate of Return
The rate of interest at which future project costs arid benefits, discounted to the present, are equal.
International Rule
See Log rules.
To set young trees among existing forest growth of similar age and size, planted or natural, to bring the stand to a fully stocked condition.
Interpretive Sites
A developed site at which a broad range of natural or cultural history is interpreted or described for the education or enjoyment of the public.
Intermixing of cover types, land uses, and conditions for wildlife for meeting year around needs of specific wild animal species. Many different small-size mappable units and many corners (where 3 or more types touch) are indexes to interspersion, an expression of landscape diversity.Only some species respond favorably to interspersion (not all "wildlife").
Intolerant Species
(1) Plant species that do not grow well in shade; (2) Plant and animal species that are unable to endure significant habitat or climate change.
Introduced Species
See Species, Exotic.
Rocks formed from solidification of fluid flowing into or between other rocks. Solidification occurs before surface contacts.
Plant species that were absent in undisturbed portions of the original vegetation and will invade under disturbance or continued overuse.
Invasive Species (Plants)
A species not native to the ecosystem under consideration (arriving after major settlement in the US) and if it causes or is likely to cause economic or environmental harm or impair human health.
Inventoried Roadless Areas
Those areas identified in a set of inventoried roadless areamaps, contained in Forest Service Roadless Area Conservation, Final Environmental Impact Statement, Volume 2, dated November 2000, which are held at the National headquarters of the Forest Service, or any update, correction, or revision of those maps.(USFS 2005)
Gathering of data and processing it on the quantity of physical entities (such as trees, lakes, etc.) in an area.
Inventory, Species
A sample survey to estimate the number of flora and/or fauna inhabiting a defined area. The level of resolution of such a listing varies with objectives and may range from only a few conspicuous or predominant species to a complete list for the area. A species inventory does not necessarily constitute an ecological baseline study and the two phrases should not be used interchangeably.
A stable layer of air having the temperature of the air increase with height.
Irreversible Effect
One of the categories of impacts specifically mentioned in section 102 of the National Environmental Policy Act (NEPA) for inclusion in the statement of environmental impacts required for Federal actions. Although not defined in NEPA, it has been the subject of judicial review. It is any effect of an action or inaction, that (due to physical, biological, or socioeconomic constraints) cannot be reversed (by returning the object of the effect to its previous condition), within a reasonable length of time. While a swamp that is channeled and drained after evolving for centuries may be returned to its pre-drained condition over many decades of being undisturbed, the time span involved is such that a reasonable person would consider the effect irreversible. Similarly, it may be physically possible to raze a city and plant a forest again, but socioeconomic constraints make this unlikely.
ISO 14001
A consensus standard developed by the International Organization for Standardization (ISO)and adopted by the American National Standards Institute that describes environmental management systems and outlines the elements of an environmental management system (36 CFR 219.16). (USFS 2005)
Travel-time zones, concentric lines each of which joins distances with equal travel times from some central reference point of concern.
Isohyetal Line
A line drawn on a map joining points that receive the same amount of precipitation.
Any lines on a map joining points of equal value, e.g., contour lines, isohyetal lines.
A controversial or debatable subject or topic. A subject or question of widespread public discussion or interest regarding management of wildlands. A point in question of law or fact. Something entailing alternatives between which to choose or decide. When the point of controversy can only be vaguely defined or when the causality relationships between use actions and undesirable results are more speculative than documentable, the dispute is referred to as a concern rather than an issue. It may reflect a great difference between an actual (B) and a desired condition (B*) or (B-B*). Within the National Forest System, issues may be
  1. a potential factor for determining need for change for a plan;
  2. specific resource concerns related to a proposed action under NEPA (FSM 1950);
  3. points of contention or disagreement, or
  4. a subject or question of widespread public interest relating to management of the National Forest System.
Issues and Concerns
A collective phrase used to include management concerns and public issues relating to management of the wildlands.
Item Type
A Designation of the way a component should be stored by the computer -- whether as alphanumeric characters or as numbers.

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Last revision January 17, 2000.