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The characteristic of plants or plant parts that elicit a selective grazing or browsing response by animals. "Palatability" is controlled by the plant factors of chemical composition, proportion of plant parts, growth stage, external form of plant parts; influenced by environmental factors such as slope steepness, wind, sun or shade; and the animal factors of instinct, learning, physiological state, individual behavioral pattern variations and animal sensory responses.
Paleontological Area
Areas which have been Designated as containing significant remains (usually fossilized) of flora and fauna (nonhuman) of geologic time periods before the appearance of humans.
Vegetated wetlands dominated by trees, shrubs, and persistent emergents. It typically includes areas traditionally called marsh, swamp, bog, fen, prairie, and also includes small shallow, permanent or intermittent water bodies called ponds less than 6.6 feet deep. These wetlands, except for ponds, are situated shoreward of lakes, river channels, and large river embayments.
See People at One Time.
Paper Plan (Map Plan)
A term sometimes used to describe formal plan documents which consist mainly of a map on which land use regulation districts are indicated. While such explanatory written information as is necessary to convey its meaning accompanies a "paper plan", the basic regulatory document is the map. In contrast, plans whose basic regulatory document consists of a set of policies are sometimes called policy plans, whether accompanied or not by maps of the planning.
A collection of the major assumptions, concepts, and propositions in a substantive area of work or knowledge, a coherent body of ideas or an approach (though not a technique) attracting widespread acceptance and use and providing the conceptual and contextual status for a branch of knowledge. Paradigms serve to orient research and theorizing in an area, and resemble models. Paradigms describe "approaches" and compactly codify central concepts and their relations.
Tending to represent a paradigm. Tending to take a particular, nominal approach to a profession, discipline, or problem.
(1) A characteristic element or constant factor, such as an agency code, streamflow, aquifer type, etc.; (2) a word used as a symbol for a variable; (3) the name for a quantifiable variable or factor.
Parameter, Biological
(1) A quantitative measure that characterizes or describes a statistical population (e.g., a population height); estimated by a sample statistic. (2) Systems ecology context -- a quantified estimate or measurement of the value of an attribute of a component of an ecological system; e.g., 60 g/m is a measure of biomass for some species or group of species of organisms for a given site.
Parameter Code
A code established to identify a specific type of data collected, and stored in a database. An example is the eight-digit code that identifies the type of water-related data available from an organization.
Parametric String
A predefined command containing one or more variables for which the user supplies values at the time a computer command is invoked.
Parent Material
The unconsolidated, chemically weathered mineral or inorganic matter from which the upper layers (i.e., where living roots are primarily found) of soil develops.
Parent Plan
A plan establishing the decision framework in which other plans are made.
Parent Rock The original rocks from which sediments or soil were derived to form later rocks.
Pareto Optimum
In welfare economics, a concept that sets a condition necessary to maximize the economic wealth of a given society. The pareto optimum is achieved when it is impossible to make one person better off without making another (or others) worse off.
Part Per Million (PPM)
One part by weight of dissolved chemical, or suspended sediment, in 1 million parts by weights of water.
Partial Retention
A visual quality objective (VQO) in which human activities may be evident but must remain subordinate to the characteristic landscape.
Particle Size
The general dimensions (such as average diameter or volume) of the particles in a sediment or rock, or the grains of a particular mineral that make up a sediment or rock. It is usually measured by sieving, by calculating settling velocities, or by determining areas on an image.
An area devoted to producing forage (introduced or native); grass or other growing plants harvested by grazing and usually enclosed and separated from other areas by a fence or wall.
Pasture, Annual
A pasture consisting of introduced forage species planted for only one year or season's duration.
Pasture Management
The application of practices to keep pasture plants growing actively over as long a period as possible so that they will provide palatable feed of high nutritive value; to encourage the growth of desirable grasses and legumes while crowding out weeds, brush, and inferior grasses.
Pasture, Native
Land used for grazing on which the climax (natural potential) plant community is forest but which is used and managed primarily to produce native or naturalized plants for forage. Includes cutover forestland, pastureland, or cropland originally cleared from forest and managed for native or naturalized forage plants.
Pasture, Permanent
A pasture (usually created) consisting mainly of introduced perennial plants which are permitted to remain for a number of years.
Pasture, Rotation
A pasture of introduced perennial and/or self-seeding annual species, comprising a unit in a rotation (deferred, rest, etc.) of 5 years duration or less.
Land used and managed primarily for producing adapted domesticated forage plants to be grazed by livestock. Management practices usually include one or more treatments such as reseeding, renovating, mowing, liming, or fertilizing. Native pasture, because of location or soil limitation, may be treated like rangeland or included in this concept.
Patch Cutting
A clearcutting system variation in which the logging operation removes all merchantable timber in patches of about 10 to 100 acres, separated for as long as practicable (preferably until the regeneration is adequately shading the forest floor) by living forest, so as to secure both the optimum dispersal of seed and to avoid the high hazard of large continuous areas of logging debris. "Patch cuts" are logging operations of a size generally which does not include the entire stand of which they are a part.
Patented Mining Claim
See Mining Claim, Patented.
A living organism capable of causing disease in a particular species or range of species.
Pathology, Forest
The science that deals with diseases of forest trees or stands, and with the deterioration of forest products by organisms.
Pathological Rotation
The maximum age for a stand when reduced tree vigor occurs and before major insect and disease losses typically occur.
Payments to Towns
The money that is paid to local governments resulting from the presence of management activities on federal or state lands within a town boundary.
Peak Discharge
The maximum volume of flow attained at a given point in a stream during a runoff event.
A log from which veneer stock may he cut.
People at One Time (PAOT)
A unit of measure to indicate the capacity of developed recreation sites. One PAOT is the number of people that can comfortably occupy or use a facility or area at one time. Where 5 PAOT per individual camping or picnic site was the design, the capacity of a campground would be five times the total number of sites. The number of people in an area or using a facility at the same time. Generally used as "maximum PAOT" to indicate capacity of an area of facility to support peak usage loads.
The length of a rod, or a pole, i.e., 16.5 feet or 1/4th of a chain (old survey records) ; also the name of a game fish.
The downward movement of water within a soil, especially the downward flow of water in saturated or nearly saturated soil. Infiltration connotes entrance and exit of a substance through a soil.
Plants that form annual above ground vegetation and seed structures from underground roots that persist for many years.
Perennial Stream
Streams that flow throughout the year from source to mouth and are typically shown in solid blue on U.S.G.S. 7 1/2-minute quadrangle maps.
Performance Measure
Indicators used to quantify outcomes of desired conditions, goals, objectives, or outcomes.
The community of microorganisms that are attached to or live upon submerged surfaces.
Permanent Pasture
Artificial pasture consisting mainly of perennial plants that are permitted to remain for a number of years.
Permanent Water
A watering place that supplies water to wildlife and others at all times throughout the year or throughout a grazing season.
Permanent Wildlife Opening
An area of land that is managed to provide and maintain grass, low shrub, and/or herbaceous ground cover for wildlife habitat.
The readiness with which soil or rock allows water, air, or plant roots to penetrate or pass through. It is measured by the rate at which water can enter and move through soil in a given interval of time under standard conditions.
Permeability, Coefficient of
An expression of the rate of flow of a fluid through a unit cross section of porous mass under a unit hydraulic gradient, at a temperature of 60 degrees Fahrenheit. The standard coefficient of permeability used in the hydrologic work of the USGS is defined as the rate of flow of water at 60 degrees Fahrenheit, in gallons or million gallons a day, through a cross section of 1 sq. ft., under a hydraulic gradient of 100%.
Persistent Pesticides
Pesticides composed of compounds that retain their toxicity for long periods after application, e.g., DDT and other chlorinated hydrocarbons. Such pesticides do not deteriorate quickly, work their way up the food chain through various animals, and may accumulate in the fatty tissues of animals, including people, and remain there.
Persistence Time
The time required for a pesticide to become inert. Arbitrarily assumed to equal four half-lives when measured persistence time is not available.
Personal Distance
See Individual Distance.
Personal Space
An area with invisible boundaries surrounding a person's body into which intruders may not come without an effect. It is not necessarily spherical in shape. It does not extend equally in all directions. An invasion of "personal space" is an intrusion into another person's perceived boundaries of "self." Individual distance and personal space interact to affect the distribution of people.
People (or the count of such people) employed by an agency or land owner whose salaries or wages are paid from appropriated, allocated, or trust funds. It typically does not include contractors, cooperators, volunteers, or trainees.
Persons-At-One-Time (PAOT)
See People at One Time.
An observation having the effects of distance upon the perceived size and characteristics of objects.
Perspective, Aerial
The effects of distance from the viewer upon the color and distinctness of objects -- especially as due to the transparency of the intervening air. Typically objects become bluer, grayer, edges less distinct, and have reduced contrast of light and shade with increasing distance from the viewer.
Perspective, Linear
The effects of distance from a viewer upon the appearance of the size and form of objects.
Program Evaluation and Review Technique, also called "critical path method"; a planning aid, usually computerized.
Perturbation, Environmental
Either an action or results of an action; a disturbance that occurs in an environmental system, which results in a change on components of that system. Perturbations can be classified as active or passive. Evolutions may reveal whether they are "good" or "bad." An active perturbation is the dynamic direct result of some activity; it is dynamic in that it moves through time or space. Emissions of any type that are injected into the environmental system are active; a smokestack is considered passive: it impedes the wind; it casts a shadow.
A general term used to refer to chemicals used to destroy, prevent, or control plant or animal pests. There are several classes of pesticides, defined by the type of pest they will influence, (e.g., herbicides, insecticides, rodenticides, molluskicides, and fungicides.)
Parts hydrogen ("pH") is the intensity of the acid condition of a solution. It is the hydrogen ion activity expressed in moles per liter. The value is an exponent, 10 to the power of the measurement. A pH of 7.0 indicates that the water sample solution is neutral while readings lower than 7.0 denote increasing acidity and higher that 7.0 denote increasing alkalinity.
The study of the periodic occurrence of animal and plant phenomena and their relations to the weather and climate, e.g., the time of flowering in plants.
The tissue in higher plants which transports organic nutrients manufactured in the leaves to other portions of the plant.
A combination of several distinct photographic pictures so they often blend with or into each other to produce a composite picture. Also contrasting shots or sequences may be blended for the purpose of suggesting a total idea or impression, or developing a theme.
The duration of light during a 24-hour period.
A type of plant that habitually obtains its water supply from the zone of groundwater saturation, either directly from within the ground water level or from the capillary fringe just above it.
The interactive biological, physical, and chemical environment of plant leaf surfaces. These surfaces may have specialized biofilms and are invaded by bacteria, fungi, other microbes as well as insects.
Physical Life
That period of time that a facility exists, not necessarily in a useable condition or used. Often facilities are removed from active service and kept intact some years before they are junked or destroyed, or they may be just left in their service position but never used.
Physical Planning
A form of urban land use planning which attempts to achieve a physically attractive urban open space environment by regulating the physical relationships of structures to their sites and surroundings -- with such devices as set back requirements, building height controls, maximum lot coverage by structures and unnatural surfaces, etc. The intent of such physical standards is to avoid claustrophobic and ugly urban open space environments. They may result in monotonous cities.
Physiographic (Morphologic)
Descriptive of the surface form and features of the Earth, as bodies of air, water and land; equivalent to geomorphologic. Geomorphology is a study of landform genesis whereas "physiography" may be only descriptive.
Physiographic Climax
See Climax Community.
Physiographic Determinism
A theory that the natural elements of an environment should be respected in planning and given priority consideration in arriving at policy determinations. For example, "nature" should have priority in planning "aquifers" and wetlands, and the rest of nature's assets should be preserved in any development plan. It is equivalent to ecological determinism and biophysical determinism. "Physiographic" only refers to the nonliving elements of an environment while "physiographic determinism" encompasses the living elements as well.
Physiographic Production
Controls over the amount occurring or potential biotic productivity which are due to abiotic environmental factors such as regional climate, geologic materials, slope orientation, and elevation.
Physiographic Site Class
Units created by isolating areas within land-types on the basis of local climate considerations -- such as slope orientation, air temperature and humidity. Variation in plant communities is used as the principal indicator of climate variation.
Physiographic Site Phase
Created by adding information on the use requirements (e.g., beach slope and width, water depth, ridge tops, valley bottoms, toe-slopes, etc.) to a map of "physiographic site types". This is the smallest mappable unit land use or ecological unit. The various levels of G.A. Hills' categories in order of decreasing size, are site region, land-type, physiographic site class, physiographic site type, and physiographic site phase.
Suspended or floating plant organisms, such as diatoms and blue-green algae, which drift passively with water currents.
Injury to plants due to exposure to a chemical.
A device with a head similar to an axe but with a point rather thian a blade mounted on tie end of a handle which is used to assist in lifting and placing bolts of wood.
Round timbers to be driven into the ground to support other structures.
Pine Conversion
Establishing pines on sites that were formerly occupied by hardwoods to yield trees of high quality and volume per acre.
Making shallow pits or basins of adequate capacity and distribution on range to speed range improvement by retaining water from rainfall and snowmelt and by reducing competition to desirable species from a dense stand of less desirable vegetation.
Placer Claim
A mining claim located upon a mass of gravel, sand, or similar material (resulting from weathering, erosion and/or stream deposition) containing particles of gold, platinum, tin, or other valuable minerals and whose valuable mineral contents are extracted by concentration in running water. The maximum size of an individual "placer claim" is 600 by 1320 feet (10 acres). See Mining, Placer.
A plan is written ordered set of decisions, directions, policies, and a course of action to achieve a set of objectives. Plans are usually one or more documents or electronic messages include graphics, maps, and descriptions of areas and projects as well as findings, assumptions, and recommendations of the planning process. When adopted, "plans" become guides for administration and action. They are subject to change as policies change due to unfolding events, such as changing standards of life style, environmental factors, costs, and advancing technology. They display information relevant to managing a unit of the National Forest System (36 CFR 219.16).(USFS 2005).
Plan Area
The area of National Forest System lands covered by an individual land and resource management plan. The area may include one or more administrative units. (USFS 1999)
Plan Components
Broad guidance in a plan that identifies desired conditions, objectives, guidelines, suitability of areas, and special areas.(USFS 2005)
Plan Controls
Any of the various legal and administrative methods which are available for implementing a land use plan's goals, objectives, or policies, e.g., ordinances, zoning, and performance standards.
Plan Document
Information that documents the process of developing, amending, or revising a plan, including evaluation reports, documentation of the public involvement process, applicable approval documents, descriptions of the environmental management systems, and other information. This information also includes records that support analytical conclusions made, options considered by the interdisciplinary team throughout the planning process, and any new science or information added by the Responsible Official.
Plan Element
The major land use planning elements such as legal requirements and authorities, national and regional objectives and targets, management situations, basic assumptions, data collection, land capability, alternative considerations, plan selection, functional planning and documentation. Also a discrete topic area in an overall plan, e.g., housing, open space, recreation, transportation.
Plan Model
An ideal pattern that organizes the five plan components (2005) (see plan components) into three parts: the vision, strategy, and the design criteria.
  • The vision includes roles, contributions, and desired conditions.
  • The strategy includes objectives, identification of suitable and unsuitable land uses, and special area Designations.
  • The design criteria include guidelines and other statutory requirements.
Plan Selection
Selection of one plan from a set of alternative plans. Subjected to the planning process, a choice is made governed by a reasonable and rational perception of how the available resources can be most efficiently managed to achieve optimum multiple benefits for the people or a landowner. The process includes full consideration of the priorities and preferences expressed by the public or the responsible landowner at all levels to be affected by the plan.
Small (usually less than 2mm long) floating or drifting life forms in water bodies. Plankton includes both plants (phytoplankton) and animals (zooplankton) that are carried passively in the water currents. Those that can swim do so to change or adjust their depth in the water, not to move from place to place. Plankton is one of the 3 main divisions of aquatic life. The others being "nekton" (the animals that swim actively and may move long distances for feeding or breeding) and the "benthos" (organisms which crawl about on the bottom, or burrow into the bottom or grow attached to the bottom).
Planned Grazing System
A system of grazing in which two or more grazing units are alternately rested from grazing in a planned sequence over a period of years. Resting the land may be throughout the year or during the growing season of the key plant species.
Planned Ignition
A fire started by a deliberate management action.
Planned Unit Development (PUD) Zoning
See Zoning, Cluster.
Anyone who plans, e.g., a city planner, economic planner, public health planner, social planner, or landscape planner. One whose profession consists of identifying community needs, resources and the means to reduce the difference between a desired or imagined condition and the present status. One who assist citizens in making decisions on programs, and methods to create a physical, economic, and social environment in which the human conditions, activities, and benefits desired by the members of the community may flourish.
(1) Creating plans. A dynamic effort to use decisions to guide future actions and decisions, one element in the process of guiding the future. (2) Determining the objectives or goals of an enterprise and the selection, through a systematic consideration of alternatives, of the policies, programs, procedures, and schedules for achieving them reporting, and adapting to achieve effectiveness. (3) Designing a future organization, structure, and relationship of parts. (4) The process of finding alternative solutions to a problem. A way of thinking about and creating solutions for future problem. (5) A nondescript process oriented predominantly toward the future and deeply concerned with the relation of objectives to collective decisions in policy and program. (6) A process of conflict resolution (usually future) by designing optimum relationships between components without attempting to favor or eliminate any party in the (future) conflict. (7) With emphasis on material and inventory, an effort to attain some future objectives by rationally "determining" in the present the requisite resources, facilities, services, personnel, and procedures (and their future availability) needed to achieve those objectives. (8) Preparing a land use zoning map. (9) Preparing a schedule of activities. (10) Thinking about the future.
Planning Agent
The person(s) or organization actually doing the planning. A "planning agent" may be a person (an individual householder or entrepreneur), a family, a legal person (a corporation, a trade association), or various levels of government (Federal, state, county, public district).
Planning, Anticipatory
Any planning approach which operates by attempting to foresee potential issues or problems and develop solutions to them before they become real. An aspect of feedforward.
Planning Area
A specifically identified geographic area containing social and physical resources and land characteristics of a generally similar nature. Because general similarities in physical characteristics, resources, economics, and social needs give rise to similar management opportunities and constraints, therefore planning efforts, irrespective of administration or government boundaries, can often be coordinated. A variety of considerations may interact to determine the size and boundaries of a planning area; topography, vegetation or broad habitat type, climate, history of land use, populations -- human and animal, economy and the relationship of these and other elements to each other will affect the definition of a planning area. These areas may, and will likely, include several administrative boundaries. A planning area should be of sufficient size to allow for flexible patterns of land to develop and resources to be used. State and multi-county planning districts, and the integrity of counties, are strong considerations in establishing planning area boundaries. Commonality of boundaries will aid in cooperative planning and data exchange. The area should permit a maximum of agencies or governments to contribute and receive resource data and relate demand allocations with high compatibility. Coordinated demand projections for the resources within a land area can be efficiently gained in large planning areas.
Planning Criteria
Standards, terms, tests, rules, and guidelines by which the land and resource management planning process is conducted, and upon which judgments and decisions about the plan are based.
Planning Horizon
The overall period considered in the planning process that spans all activities covered in the analysis or plan, and all future conditions and effects of proposed actions which would influence the planning decisions. For timber resource planning purposes, the overall time period extends far enough into the future to assure that the allowable sale quantity can be achieved and maintained at the long-term sustained yield capacity. It is the last year of the planning period (fixed by the planner), the length of the planning period that will be considered in the planning process. For example, one 1995 plan had a "planning horizon" of 2025 AD.

In US FS, 2005, it was "the overall time period considered in the planning process to evaluate conditions and trends in the social, economic, and ecological resources that contribute to sustainability in the plan area."

Planning Level
The scale of a planning effort, usually the size of the project or the governmental level at which the planning is being done, e.g., site or project planning, county planning, state planning, interstate regional planning.
Planning Period
Usually one 10-year period. The time interval within the planning horizon that is used to show incremental changes in yields, costs, effects, and benefits.
Planning Problem
A major problem of long-range significance, derived from public issues and management concerns, to be addressed when formulating plans.
Planning-Programming-Budgeting System (PPBS)
A planning and decision-making tool that attempted to organize information and analysis so that the consequences of alternative policies are clearly revealed and fully comparable. Under PPBS (ordered instituted in each Cabinet agency by President Johnson in 1966), programs having the same purpose are grouped together under the same category and compared to see which represents the best use of the government's money. PPBS endeavors to display the allocation of resources in terms of the function; to gather quantitative information on the actual results of programs; and to analyze the cost of the various efforts to achieve similar ends and rank them in terms of their effectiveness per dollar.
Planning Unit
Geographic areas of land, varying in size, that are characterized by particular patterns of topography, climate, and land use. A unit may occur as one major drainage, several separate drainages, or portions of drainages. These are specific, identified, and delineated land areas large enough to encompass most of the meaningful or significant relationships within a drainage or series of drainages. Topographic features are logical places for planning unit boundaries because of the need to be able to identify boundaries on maps and photographs, and on the ground. Many factors influence the boundaries, size, and layout of planning units, among which are: (1) intensity of planning expected; (2) the resources available for doing planning, people and time; (3) presence or absence of unique features; (4) perceived complexity or homogeneity of the land features; (5) public involvement inputs; and (6) planning team judgment. The objective is to preserve as much uniformity as possible in relationships significant to land management. Such factors as existing transportation systems, population influences, current land use, topography, soils, industrial dependency, ownership, and public feelings are considered in establishing the boundaries for planning units. No two planning units are exactly equivalent in the factors that influence the boundaries of the planning unit. The purpose of planning units is to organize planning activities and concentrate them on areas small enough to be workable and large enough to enable a planning team to envision or predict the cause and-effect relationships of management alternatives. No size limits are arbitrarily established for planning units. Planning unit boundaries may cross both planning area and administrative unit boundaries.
An artificially reforested area established by planting or direct, seeding. Contrast with a natural forest stand which is established naturally.
Plant Community
Any named aggregation of plants having high uniformity in composition and structure and occupying an area of essentially uniform environment. Each of these communities is dominated by certain species which are conspicuous or which are rare. Even when areas of equivalent environment are encountered, whether continuous or detached, essentially the same plant assemblage reappears and there is a pattern to their appearance.
Plant Retrogression
The process of deterioration in vegetation whereby an area becomes successively occupied by different plant communities of lower (earlier) ecological order in succession.
Plant Species, Decreaser
Plant species of original range vegetation that will decrease in relative amount in population density or cover with continued grazing or overuse.
Plant Species, Increaser
Plant species of the original vegetation that increase in relative amount, at least for a time, under overuse.
A forest crop or stand raised artificially, either by seeding or planting of young trees.
Planting Bar
A hand tool used in making a slit-hole in which trees are planted.
Planting Levels
Five tree-improvement program intensity levels ranked by increasing complexity based on workloads and potential genetic gain that can be realized.
A scale drawing of essential data pertaining to boundaries, subdivisions, and ownership(s) of a tract of land, as determined by survey.
An area of land usually less than 1 acre on which trees and sometimes other vegetation are measured during a cruise (or inventory).
A description of society that contends that political power is distributed among a variety of groups and institutions. Pluralist theory argues that political resources -- wealth, education, prestige, skill, and votes -- are divided and that no group has a monopoly over all resources. In contrast, elitist theories of power argue that small groups of individuals rule a country in their own economic interest. Pluralists agree that only small numbers of citizens participate directly in decision-making, but they argue that these elites compete for economic rewards, differ on policy, are open for others to join, and are indirectly influenced by voters. "Elitists" contend that members of the ruling power-elite share a pro-capitalist ideology, are unified by a similar upper-class background, and are linked by institution and personalities.
Pluralistic Society (Cultural Pluralism)
A society in which there are widely differing and often conflicting points of view as to how the access to or use of a particular resource (or resources in general) should be allocated. The United States is often cited as the prime example of a pluralistic society.
Any person who illegally takes for personal or group benefits a wild animal or wild plant. The act or acts related to purposefully attempting to take or actually taking a wild animal or plant of improper species, sex, time of year, excessive numbers, or area classify any person of any description as a poacher. People seem to be opportunistic and given a special situation may act as described above, thus becoming a poacher for the first time. Once a person has poached, there are (2005) no categories for those who will never do so agin, those who have stopped, or who are full-time engaged in the acts. Some people include all people engaged in all aspects of taking, processing, and selling wild animals and plants or their parts as poachers.
Point-Source Pollution (Point Pollution Source)
Pollution the source of which is specific rather than general in location. Particulate matter emanating from a specific smokestack or toxic effluent from a pipe is point source pollution.
Pole and Pole Timber
A young tree 4 inches or more in diameter breast high.(1)As used in timber survey, a size class definition, trees 5.0 to 8.9 inches in DBH. The maximum size of poles is usually though not invariably taken to be some diameter breast high between 8 and 12 inches. (2)As used in logging operations, trees from which pole products are produced, such as telephone poles, pilings, etc.
Police Power
A state's inherent and plenary power over persons and property that enables the society to prohibit or regulate all things inimical to its comfort, safety, health, and welfare.
A decided course or method of action selected by a governmental agency, institution, group or individual. It is selected from among alternatives and, in the light of given conditions, to guide and usually determine present and future decisions and actions. It is a guiding principle, typically a set of major constraints, influencing a specific decision or set of decisions.
Policy Issue
An action or set of circumstances that has bearing on current or future policy, resulting in proposed policy, alternative policies, or an identified need for a policy.
Policy Plan
A formal plan document consisting entirely of a set of policies unaccompanied by maps differentiating the planning area where some policies apply while others do not. In contrast, a plan whose formal plan documents consist mainly of a map on which land use regulation districts are indicated is sometimes called a paper plan or "map plan". While "paper plans" are accompanied by explanatory written information necessary to convey their meaning, the basic regulatory document is still the map.
Political Boundary
A boundary which marks the limits of a political jurisdiction. The boundaries of cities, counties, states and nations are political boundaries. Lesser political boundaries limit tax districts, legislative districts, etc.
Political Determinism
A particular point of view in planning which advocates that all resource use and allocation decisions should be made via the political process -- i.e., by elected representatives and legislation. In theory, politics is society's means for attaining some needed resolution of issues via compromise from the often-conflicting demands on a resource by different groups. This point of view is that elected representatives' decisions are responsive to and representative of the collective judgments of their constituents. Politics thus is viewed as the process by which society makes group choices about resource use allocation, passes final judgment upon interim administrative decisions, and conveys the right (via legislation) to regulate resource use or the exercise of private property rights. It is believed that because political decisions are societal choices they are the best choices that can be made and thus should be the basis for making planning decisions.
Political Institutions
A society's system of legal rules, principles, and organizations.
(1) Concentrations of substances or radiation in excess of those for which there has been a collective genetic experience by communities. (2) Any substance or energy form (heat, light, noise, etc.) which alters the state of the environment from what would naturally occur. Especially associated with those altered states which human value judgements have decreed as bad. (3) An activity of people, which directly or indirectly results in adding to water, air, or soil, matter or energy which has a deleterious effect on living organisms or structures it is desirable to preserve, or which reduces the quality of water, air, or soil for any subsequent use. In this context, such terms as natural pollution and visual pollution (not referring to decreased visibility due to air pollution) are meaningless and should not be used. (4) The presence of matter or energy (usually undesirable) in an unusual or unintended place. (5) The presence in the environment of one or more contaminants or nuisances in sufficient quantities and of such characteristics and duration as to be injurious or irritating to human, plant, or animal life, to health, or to property, or to unreasonably interfere with production or with the enjoyment of life or property.
A small impoundment of water, usually 0.5 to 4.9 acres in surface area, usually with fish.
An aggregation of individuals of the same species inhabiting a given area at a time.
Population Dynamics
(1) The totality of changes that take place during the life of a population. (2) A study of changes, and the reasons for those changes, in the numbers of individuals in populations. (3) A study of the changes among sub-populations over a landscape.
Population/Habitat Unit
A discrete association of individual elk bonded together by traditional use of a habitat.
Population Pressure
The combined effects exerted by the individuals of a population upon the other organisms in a community and upon their physical environment.
Porosity, Effective
The ratio, usually expressed in percentage of (a) the volume of water or other liquid which a given volume of rock or soil, after being saturated with the liquid, will yield under any specified hydraulic conditions, to (b) the total volume of soil or rock.
A short timber up to 16 feet in length used in an upright position to support other structures for fencing.
Post Market
The market of trees to be used as fence posts. They are normally 4 inches to 10 inches in diameter and 6 to 10 feet long.
Potable Water
Water suitable for human drinking.
Potential Wilderness Area
An area including those previously identified in the Forest Service Roadless Area Conservation, Final Environmental Impact Statement, Volume 2, dated November 2000, in a unit plan, or in a land management plan, which remain essentially roadless and undeveloped, and which have not yet been Designated as wilderness or for non-wilderness uses by law.
Potential Yield
The maximum yield of timber that can be obtained annually on a sustained yield basis by utilizing intensive forestry management practices.
Poverty, Absolute
A standard of living below the minimum needed for maintenance of life and health.
Poverty, Relative
A condition characterized by a scarcity rather than a lack of economic necessities. A relatively poverty-stricken person is poor in comparison with a majority of others in his society, but his or her level of living usually does not constitute an immediate threat to life or health.
See Planning-Programming-Budgeting System.
See Parts Per Million.
Practical Maximum Capacity
The maximum potential recreation visitor days produced by the recreation opportunity spectrum.
An extensive tract of level or rolling land, usually with deep fertile soil, that was originally treeless and grass covered.
Young born with eyes open, down or fur covered and quite mobile in the first day or two of life, e.g. ruffed grouse young.
Pre-commercial Thinning
Reduction of the number of trees to improve the growth rate and quality of the remaining trees on areas where the trees that are cut do not have an economic value or market.
Activities required in advance of fire occurrence to ensure an effective suppression action. Included are (1) recruiting and training fire forces; (2) planning and organizing attack methods; (3) procuring and maintaining fire equipment; and (4) maintaining structural improvements necessary for the fire program.
The discharge of water, in liquid or solid state, out of the atmosphere, generally upon a land or water surface.
Pre-Commercial Operations
Cutting conducted in forest stands which removes wood of a size too small to be marketed. Such operations usually are designed to improve species composition and increase quality, growth, and vigor of the remaining trees.
A bird or mammal species that feeds upon live animals; a carnivore.
Preferable Species
Plant species that are preferred by animals and are grazed during first choice.
Preferred Alternative
The alternative recommended to be implemented.
Preparation Cut
The removal of trees near the end of a rotation to open the canopy and enlarge the crowns of seed bearers to improve conditions for seed production and natural regeneration, as typically done in the shelterwood method.
Preparatory Cut
See Shelterwood Cut.
Prescribed Burn
Skillful intentional controlled application of fire to wildland fuels in either their natural or modified state, under such conditions of weather, fuel moisture, soil moisture, etc. as allow the fire to be confined to a predetermined area and to produce the intensity of heat and rate of spread required to further certain planned objectives of silviculture, wildlife management, grazing, fire-hazard reduction, etc. It seeks to employ fire so as to realize maximum net benefits with minimum damage and at acceptable cost. The fire may result from either planned or unplanned ignitions.
Prescribed Fire
Any wildland or rural fire ignited by management actions and burning under certain predetermined conditions to meet specific objectives such as those related to hazardous fuels, forest or range regeneration, or watershed or faunal space management. (Debated: whether The fire may result from either planned or unplanned ignitions.) A planned fire used to dispose of fuels, control unwanted vegetation, restore or stimulate growth of desired vegetation, change successional stages, maintain fire dependent communities, reduce arthropod disease vector abundance, increase grazing wild faunal or livestock forage, and improve viewscapes in order to meet wildlife, recreation, wilderness, watershed, or timber management objectives.
A document for a timber compartment (or similar unit of land) which: (1) provides data about the age, forest type, and conditions of the stands in the compartment; (2) determines the type of silvicultural and other treatment needed by the stands; and (3) specifies management that is needed to secure the desired benefits from the land over the long-run.
Present Net Value (PNV)
The difference between the discounted aggregate value (benefits) of all outputs to which monetary values or established market prices are assigned and the total discounted costs of managing the area during a stated period and at a stated discount rate.
Present Worth
The series of benefits or costs that occur with a program or project over time discounted back to present time. That amount of money a person would have to deposit now, at a given rate, to accumulate to a stated future value for either benefits or costs.
(1) A visual quality objective that allows for natural or ecological changes only. (2) Complete protection, no use, and minimum management.
Pressure Group (Interest Group, Special Interest Group)
Any group of people with special interests which actively advocates for special consideration of its resource use goals. These are usually politically active groups with a common set of goals, values, or ideology about resource use allocation. They may influence decisions on resource use allocation in excess of their proportional representation in the planned-for populace by seeking preferential consideration for their resource use choices, such as lobbying, raising money for political campaigns, promising to "deliver" votes on election day or workers in political campaigns, developing some special expertise, or having some special relationship with an agency in the government bureaucracy. Pressure groups may be distinguished from the broader category of special interest groups by their somewhat more formal organization and their more noticeable activity over time. Interest groups are the most important unit of analysis in pluralist theory, for they mediate between an individual citizen's desires and the political parties. Two major differences between American parties and interest groups are that parties compete for office, whereas interest groups do not, and interest groups present a homogeneous interest whereas parties have a heterogeneous clientele.
Presuppression, Fire
Activities in advance of fire occurrence to insure effective suppression action. Includes recruiting and training, planning the organization, maintaining fire equipment and fire control improvements, and procuring equipment and supplies.
Prevent Significant Deterioration (PSD) Permit Program
The permitting program run by States with the objective of protecting the air quality from damage from new pollutant emitters.
Price Index
Published values per unit volume by tree species that are used to determine the actual price of cut timber. If the the index is lower at the time of cut that at the time of sale, the sale price is reduced by the decrease. If the index is higher, the sale price is increased by half of the increase.
Price-quantity Relationship
A schedule of prices that would prevail in a market for various quantities of the output exchanged.
Primary Conversion
The initial steps in the process of converting a felled or fallen tree to lumber, e.g., topping, trimming limbs, removing bark, and sawing into logs.
Primary Facility
Access and service to large land areas encompassed and served by a public transportation system. They include public transportation facilities and form the basic framework around which the transportation network is designed. A substantial percentage of the traffic served by these facilities is public service traffic, and emphasis is given to travel speed and efficiency.
Primary Output
The main goods, services, or environmental conditions of a resource element - the key quantitative indicators for determining if objectives have been attained (e.g.,animal-unit-months of forage for livestock or board feet of timber harvested).
Primary Productivity
The rate at which organic matter is produced by the photosynthetic and chemosynthetic activity of autotrophic organisms (chiefly green plants) using inorganic material as a carbon source and sunlight as an energy source.
Primary Wastewater Treatment (Primary Treatment, Primary Sewage Treatment)
The first treatment given to raw sewage collected from household and commercial sources. Typically the process first separates floating solids by screening. The undigested material is then piped into settling tanks where, depending on the temperature and length of stay, varying amounts of suspended solids are removed by gravity precipitation. Primary treatment removes most of the floating solids, 50 percent of the suspended solids, and at best only about 35 percent of the organic waste and biochemical oxygen demand from wastewater.
Prime Agricultural Land
(1) Land meeting any of the following four criteria: [1] Class 1 or 11 of the U.S Soil Conservation Service land capability classification scheme, [2] a Storie index rating of 80 to 100, [3] a carrying capacity (see Carrying capacity, range) of one animal unit per acre, [4] a gross annual revenue of $200 (price-index adjusted, 1969) per acre in unprocessed, plant production, for 3 of the past 5 years, or [5] land in fruit or nut-bearing trees, vines or bushes that have less than a 5-year nonbearing period and return not less than $200 (price-index adjusted, 1969) per acre. (2) Land identified (after considering the long-term productive potential and topographic position of the soil(s) climatic factors, and availability and quality of water) as being required for the economic production of specific agricultural commodities that are Designated by local units (of government).
Primitive Area
(1) A large tract typically within a U.S. National Forest set aside for preservation in natural condition with no alteration or development beyond measures for fire protection being permitted. This Designation according to the Wilderness Act of 1964 ceased in 1974. By that date appropriate Primitive Areas were reclassified as Wilderness Areas. (2) As defined in the 1929 U.S. Forest Service regulation, primitive areas will have "maintained primitive conditions of environment, transportation, habitation, and subsistence, with a view to conserving the value of such areas for purposes of public education, inspiration, and recreation. Within any area so Designated no occupancy under the special-use permit shall be allowed, or the construction of permanent improvements by any public agency be permitted, except as authorized by Confounding instruction subsequently sent indicated that "the establishment of a Primitive Area ordinarily will not operate to withdraw timber, forage or water resources from industrial use, since the utilization of such resources, if properly regulated, will not be incompatible with the purposes for which the area is Designated." These areas are extensive natural, wild and undeveloped areas, usually in a setting far removed from the sights, sounds, and smells of civilization. Essential characteristics are that the natural environment has not been disturbed by commercial utilization and that the areas are without mechanized transportation. The area must be large enough and so located as to give the user the feeling that he or she is enjoying a wilderness experience. Activities in Primitive Areas involve camping out on one's own without mechanized transportation, permanent shelter, or other conveniences. People are only transitory visitor. There is no development of public roads, permanent habitations or recreation facilities except trails. No mechanized equipment is allowed except that needed for management and protection purposes. Some people use the terms "primitive" and "wilderness" interchangeably to refer to all areas displaying no obvious evidence of present or previous human uses-other than foot or pack animal trails. Others make a distinction between the two, using "primitive" to refer to all areas possessing wilderness qualities and restricting the use of "wilderness" to only those portions of the larger primitive area which have been Designated as "Wilderness Areas" according to the Wilderness Act of 1964.
Primitive ROS Class
The classification of the recreation opportunity spectrum characterized by an essentially unmodified environment, where trails may be present but structures are rare, and which probability of isolation from the sights and sounds of people are extremely high.
Principles and Standards
Guidelines for water and related land resources planning established by the U.S. Water Resources Council for Federal agencies whose activities involve planning and development of water resources (Federal Register; 38(174): 24777-24869, "Water and Related Land Resources, Establishment of Principles and Standards for Planning"). The "Principles" provide the broad framework for planning activities and include the conceptual basis for planning. The "Standards" provide for uniformity and consistency in comparing, measuring, and judging beneficial and adverse effects of alternative plans. The "Principles and Standards" specify two main objectives to be reflected in the planning: national economic development and enhancement of environmental quality. Also specified is the accounting system that gives four required accounts in which all effects of programs are to be discussed: national economic development, regional economic development, environmental quality, and social well being.
Private Property
The exclusive right to the possession, use or disposal of property or goods. Private property can be real property, land, and the buildings fixed on it, or personal property that is movable property. The concept of "private property" is the creation of people in a society and thus property is subject to such intrusions upon it as society requires for the general welfare.
A Designated set or sequence of actions, some of which are developmental, moving progressively from one point to another on the way to completion. Land use planning is often described as being a dynamic "process" rather than a single, finite, irreversible event in time or space.
An organism which can synthesize organic material using inorganic material and an external energy source (light or chemical).
Producer Organism (Producer, Autotrophic Organism)
An organism, usually a green plant, that can utilize radiant energy (i.e., sunlight) to synthesize organic substances from inorganic materials.
Producer Surplus
In economics, the difference between the price at which a producer sells a good or service and the amount that he or she would actually be willing to accept in exchange for the good or service.
Production Function
A mathematical relationship (frequently presented as a graph) which shows how inputs of various physical factors are related to changes of output, e.g., the effect of different amounts of fertilizer or thinning on the rate of timber production. Expressions of wood or forage production over time are a special type of production function.
Productive Capacity of Ecosystems
The continuing productivity of an ecological system, including its ability to sustain desirable conditions such as clean water, fertile soil, riparian habitat, and viable populations of plants and animals; and to sustain desirable human uses; and to renew itself following disturbance.(USFS 1999)
Productivity (Biological Context)
(1) The rate of production of organic matter produced by biological activity in an area or volume (e.g., grams per square meter per day, or other units of weight or energy per area or volume and time). (2) The innate capacity of an environment to produce plant and animal life. (3) The capacity of a soil to produce a certain kind of crops under a defined set of management conditions. (4) The rate at which energy is stored by organisms in the form of organic substances which can be used as food materials. (5) The rate of storage of organic matter in tissue by organisms including that used by the organisms in maintaining themselves.
Productivity, Biotic
Growth products and by-products of living organisms (e.g., wood, meat, other plant fibers).
Productivity, Gross Primary
The rate of synthesis of organic material produced by photosynthesis (or chemosynthesis), a rate that includes accumulating organic material in plant tissues.
Productivity, Net-Primary
(1) The amount of organic material produced by biological activity in an area or volume. (2) The total amount of energy stored over a specified period by an organism or organisms.
The capacity of National Forest System lands and their ecological systems to provide the various renewable resources in certain amounts in perpetuity. For the purposes of a Forest Service plan it is an ecological, not an economic, term (36 CFR 219.16).
Productivity, Primary (Basic Productivity)
The rate at which energy is stored, typically as weight change, by the photosynthetic and chemosynthetic activity of producer organisms (chiefly green plants) in the form of organic substances.
Productivity, Secondary
(1) The rate of new biomass addition (weight growth) and storage on plant-eating (herbivorous) animals. (2) The rate of energy storage by consumer organisms.
Productivity, Tertiary
The rate of new biomass addition (weight growth) on meat-eating (i.e., carnivorous) animals.
Profile View
An illustration in which the features coinciding in space with the plane of sectioning are strongly emphasized (usually by thick linework). Features in the background are usually shown with much thinner linework and without any reduction in size in proportion to their increasing distance from the plane of sectioning (as would occur if they were drawn according to the rules of linear perspective). Underground features are seldom shown in "profile" type drawings and there is never any exaggeration of the scale of vertical or horizontal features.
An activity or coordinated, organized combination of activities carried out to meet an objective. Within PPBS it is a major agency endeavor, mission oriented, which fulfills statutory or executive requirements, and which is defined in terms of the principal actions required to achieve a significant end objective.
For the US Forest Service, 2005, it is a sets of activities or projects with specific objectives, defined in terms of specific results and responsibilities for accomplishments designed to pursue desired conditions and objectives in the plan.
Program Budget
A plan that allocates annual funds, work force ceilings, and targets among owner or agency management units.
Program Budget Level
A single, comprehensive integrated program responsive to the agency direction (chief's) that specifies a level of production attainable from a given investment of dollars and other resources. Each budget level represents a complete, full, and independent package within the criteria and constraints identified.
Program Element
A subdivision of a program category typically emphasizing major areas of responsibility which comprise the specific products or categories that contribute to an agency's statutory or executive-directed mission.
Program Planning
A process of identifying objectives, establishing relationships between resource program objectives, evaluating alternative courses of action for attaining objectives, establishing output targets, and projecting costs and personnel requirements. It is based on negotiating and interacting within and among organizational units concerned. The result is a multi-year course of action proposed under a given set of assumptions and constraints.
Program Proposals
A multiyear course of action proposed under a given set of assumptions and constraints.
Programmed Harvest
The part of the potential yield that is planned for harvest in any one year (comparable to annual allowable harvest).
(1) The process of deciding on specific courses of action to be followed in carrying out planning decisions and objectives. It also involves decisions in terms of total inputs required or total costs to be incurred over a period of years as to personnel, material, and financial resources to be applied in carrying out programs. (2) Computer programming, the writing of a computer program in a language such as FORTRAN, BASIC, PASCAL, or C++.
Prohibition Zoning
See Zoning, Prohibition.
An organized effort to achieve an objective identified by location, activities, outputs, effects, and time period and responsibilities for execution.
Project Design
See planning, paradigm, etc. General, and now so diversely used as to be meaningless. Perhaps the phrase includes making the first creative outlines of a project. One meaning: The process of developing specific information necessary to describe the location, timing, activities, outputs, effects, accountability, and control of a project.
Project Planning (Operational Planning)
Types of planning concerned with physical undertakings (such as building a dam). Project planning incorporates a greater range of specific elements than functional planning and, thus, deals with more numerous and diverse parts.
(1) An extrapolation of a series of data to estimate a value beyond the range of the data (usually using a linear or curvilinear model). These are estimates and may not have a time dimension. (2) Similar models may be used to predict future conditions and occurrences. The accuracy of a projection is very dependent on past trends continuing, or upon changing in some known manner. A "projection" differs in a strict sense from a forecast, which is also a prediction of future conditions and occurrences, but is based on an understanding of the system being discussed from current and past data rather than merely continuing and adjusting past trends. There is a distinction but it is imprecise. (3) Projections are conditional forecasts of the future. They are based upon stated assumptions about factors that are expected to influence future conditions. Projections reflect historical development and economic activity as modified by discernible trends determined by analysis of present and past relationships. If there are no changes in the objectives of the people, if limits of resource availability are not reached. If anticipated technology is attained, and if the influence of external forces remains constant, projections could reasonably be expected to chart the future.
The dominion or indefinite right of use or disposition which one may lawfully exercise over particular things or subjects, land, improvements or objects of value to which rights of ownership and control may be acquired. It includes the social relationships of rights and obligations between people over the use of an object. An object in these relationships may be material or nonmaterial, such as a trademark.
Property Rights
The sum total of the rights and legal protection pertaining to property ownership. In the case of real property it embraces the right to quiet enjoyment, the right to sell, mortgage, lease, bequeath, regain possession at the end of a lease, build and remove improvements, and control the property's use within the law.
Removing overburden, core drilling to obtain subsurface samples, constructing roads or any other disturbance of the surface for the purpose of determining the location, quantity or quality of a mineral deposit.
Activity that reduces losses or risks and that tends to maintain basic conditions and values and reduces damages or injury to potential or actual resource outputs of rural lands and resources. It includes insect and disease control, fire protection, and law enforcement. It may include teaching and other human behavioral-change activity.
Protective Element (Fire)
The support element providing protection to forest resources and uses (such as fire suppression).
A statement, which based on such items as budget, policies, and environmental changes, summarizes past performance and forecasts the course of key objectives. These anticipated levels of conditions, uses, and activities and related monitoring performance measures help describe progress towards attainment of desired conditions. A prospectus is usually identified within a plan's Strategy section.
The study of people's use of social and personal space.
Proxy Value
A value assigned to a good or service for evaluation purposes when the good or service is not bought or sold and an established monetary price does not exist.
Public Domain
The territory ceded to the Federal government (U.S.) by the original 13 states, together with subsequent additions by cession, treaty, and purchase.
Public Involvement
The opportunity for feasible participation by citizens in rulemaking, decision making, and land use planning, including public hearings, advisory mechanisms, and such other procedures. It includes informing the public, obtaining early and continuing public participation, and considering the views of interested parties in planning and decision-making processes. It encourages public understanding about and participation in the planning processes. The "public" includes individuals, local, state, regional and national public service organizations and interest groups. It also includes local, state, and Federal agencies that have jurisdiction, special expertise or information to offer relevant to the total planning and implementation picture.

In 2005 it was said to be a Forest Service process designed to broaden the information base upon which agency approvals and decisions are made by: (1) informing the public about Forest Service activities, plans, and decisions and (2) encouraging public understanding about and participation in the planning processes which lead to final decisionmaking.

Public Issue
A subject or question of widespread public discussion or interest regarding management of land and identified through public participation.
Public Land
Land for which the title and control rests with a government -- Federal, state, regional, county, or municipal. Exceptions may need to be studied for lands located on the Outer Continental Shelf; lands held for the benefit of Indians, Aleuts, and Eskimos; and lands where the US retains the mineral interest, but the surface is privately owned. Also any land and interest in land administered by the Secretary of the Interior through the Bureau of Land Management (Federal Land Policy and Management Act of 1976). This includes the mineral estates underlying National Forest System lands.
Public Participation
Activities that include a wide range of public involvement tools and processes, such as collaboration, public meetings, open houses, workshops, and comment periods (36 CFR 219.16).
Public Participation Activities
Meetings, conferences, seminars, workshops, tours, written comments, survey questionnaires, and similar activities designed or held to obtain comments from the general and specific publics.
Planned unit development. See Cluster Development.
Purchaser Credit Road Work
Road work (construction or reconstruction) required of a timber purchaser in timber sale contracts, and paid for with timber receipts.
Put to Bed
The practice of temporarily closing roads between periods of use. This involves removing all drainage structures, re-vegetating the roadbed and drainage ditches, and closing the area to vehicle traffic.
Put-and-grow Trout Stream
A stream that receives hatchery-produced trout less than- harvestable size (up to 7 inches in length). Fingerling trout are generally stocked when growth potential is adequate but natural reproduction is inadequate to support the fishery.
Put-and-take Trout Stream
A stream that receives hatchery-produced trout of a catchable size (typically 7 inches or greater).
Pyramid of Biomass
When the total weight of individuals at successive trophic levels in a food chain is plotted, a gradually sloping pyramid usually results, regardless of the individual size of the producer organisms or consumer organisms, and regardless of whether predators or parasites are considered. This "pyramid of biomass", in effect, gives a picture of the over-all effect of food chain relations for an ecological group as a whole.
Pyramid of Energy
A graphical representation of the rate of energy flow and/or energy productivity at successive trophic levels in a food chain or for a complete biotic community. Of the three types of ecological pyramids, the energy pyramid gives the best overall picture of the functional nature of biotic communities since the number and weight of organisms that can be supported at any level in any situation depend not on the amount of fixed energy present at any one time in the level just below, but rather on the rate at which food is being produced. In contrast the pyramid of numbers and pyramid of biomass, are pictures of the standing states, i.e., organisms present at any one moment, while the energy pyramid is a picture of the rates of passage of food mass through the food chain. Its shape is not affected by variations in the size and metabolic rate of individuals, and, if all sources of energy are considered, the largest numbers will always be at the base because of the second law of thermodynamics.
Pyramid of Numbers (Eltonian Pyramid, Food Pyramid)
A graphic representation of the food chain which indicates the large numbers of producer organisms (i.e., plants) at the base of the food chain, and the progressively decreasing numbers of herbivores (plant eaters) and carnivores (meat eaters) higher up in the food chain. Elton's concept was that in most food chains the number of individuals decreases in each succeeding stage, with large numbers of animals occurring at the base and a few large ones at the top.

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Last revision January 17, 2000.