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(1) The total elements in an organism's physical surroundings which have a direct bearing on that organism's function and survival. (2) The total of environmental conditions of a specific place that is occupied by an organism, by a population, or a community of interest. (3) The "home" or place where animals live, reproduce, and die. (4) A geographical niche. (5) The natural or native environment of a plant or animal.
Habitat Analysis Unit
An area of land defined by geographic or administrative means and selected as the unit for evaluating the quality of habitat of a species, guild, or other taxon.
Habitat Capability
The capacity of a given area, nearly equivalent to carrying capacity (inapplicable to elk management.) (USFS-2005: The estimated ability of an area, given existing or predicted habitat conditions, to support a wildlife, fish, or plant population. It is measured in terms of potential population numbers(?))
Habitat Capability Model
A model which depicts the relationship of a species to a variety of habitat factors which provide for quantitative predictions of a species response (animal abundance numbers) to habitat change.
Habitat, Critical
Any air, land, or water area including any elements thereof which the Secretary of the Interior, through the Director, U. S. Fish and Wildlife Service or National Marine Fishery Service, has determined is essential to the survival of wild populations of a listed species or to its recovery to a point at which the measures provided pursuant to the Endangered Species Act of 1973(and subsequent Acts) are no longer necessary. Such determinations are published in the Federal Register.
Habitat Diversity
The mix of habitats; or size variety; or numbers of layers present; or number of types; or evenness of stand sizes and shapes by type. Also relative rarity. Not always lack of similarity. Occasionally differences in an area observed over time (instability).
Habitat Effectiveness
Percentage of available habitat that is usable by wildlife (e.g., elk) outside the hunting season. Originating in the road density models as a means of expressing habitat loss associated with open forest roads, it has since been used to express habitat quality, hunting season security, habitat capability, carrying capacity, and several other conditions.
Habitat Management Unit (HMU)
A unit of land approximately 4,000 acres in size, the boundaries of which fall on compartment boundaries, and which contains a mix of habitat types. At least one of these types must be a pond or stream with wetland potential.
Habitat Type
A small unit of land from a few to over 100 acres lying within a given climatic mineralogical zone and supporting a probable sequence of vegetation growing on a unique type of soil material.
Hard Mast
Fruits of oaks, hickories, pines, and beech trees that are important foods of many species of wildlife in the fall and winter.
A property of water that may cause formation of an insoluble residue when used with soap and causing formation of a scale in vessels in which water has been allowed to evaporate. It is primarily due to the presence of calcium and magnesium ions. It is generally expressed in milligrams per liter.
A hardened soil layer in the lower A or in the B horizon caused by cementation of soil particles with organic matter or with materials such as silica or calcium carbonate. The hardness does not change appreciably with changes in moisture content, and pieces of the hard layer do not disintegrate in water.
A broad-leaved flowering tree, usually deciduous, as distinguished from a conifer. Trees belonging to the botanical group of angiosperms; trees such as oaks, maples, ashes, elms. It does not necessarily refer to the hardness of the wood.
As related toEndangered and Threatened Wildlife and Plants, a rule formulated within the National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration (NOAA), Commerce. The final rule (effective on December 8, 1999)defines the term "harm", which is contained in the definition of "take" in the Endangered Species Act (ESA). The purpose of this rulemaking is to clarify the type of actions that may result in a take of a listed species under the ESA. This final rule is not a change in existing law. It provides clear notification to the public that habitat modification or degradation may harm listed species and, therefore, constitutes a take under the ESA as well as ensuring consistency between NMFS and the Fish and Wildlife Service (FWS). This final rule defines the term "harm" to include any act which actually kills or injures fish or wildlife, and emphasizes that such acts may include significant habitat modification or degradation that significantly impairs essential behavioral patterns of fish or wildlife.(Chief, Endangered Species Division, Office of Protected Resources, NMFS, 1315 East-West Highway, Silver Spring, MD 20910. Also contact Chris Mobley, NMFS, 1315 East-West Highway, Silver Spring, MD 20910, phone (301)713-1401 or Garth Griffin, NMFS, 525 NE Oregon St, Suite 500, Portland, OR 97232, phone (503)231-2005.)
Harvest Cutting Method
A means of removing all or part of a stand of timber, either by a single cutting or a series of regeneration cuttings.
A loose term for removing produce (i.e., a merchantable material) from the forest for utilization; cutting, sometimes further initial processing (e.g., with trees, topping and trimming) and extraction (removal from the forest).
Haul Road
Road from pit to loading dock, tipple, ramp, or preparation plant used for transporting mined or other material by truck.
Head of the Hollow (Valley-Fill Method)
A method for surface-mined land in which overburden material from adjacent contour or mountain top mines is placed in compacted layers in narrow, steep-sided hollows so that surface drainage is possible.
The small rivulets that are the source of a stream or river. Mapped as starting at the last crenulation in a contour line below a ridge or crest on a topographic map.
The inner core of a woody stem, wholly composed of nonliving cells and usually differentiated from the outer enveloping layer (sapwood) by its darker color.
Heat Island
A small area in a landscape with air temperatures measurably greater than that of its surroundings. Urban areas form heat islands. The "heat island effect" is an air circulation phenomenon generally found in and around cities. Warm air tends to concentrate in the city's center, probably because of the mass of tall buildings and concentration of paved surface. This warm air rises, carrying with it a burden of pollution. As the polluted air moves up over the city, spreads out, cools, and sinks at the city's periphery, it forms a distinctive ceiling (composed of suspended pollutants) known as a haze hood or dome. Cooler air from the edge of the city flows into the center to replace the rising air and is followed again by cool air from the city's edge. Thus, a self-contained circulatory system is set up that is altered only by a strong wind capable of breaking up the pollution-formed ceiling. Such a heat island, if it becomes stabilized for a sufficient length of time, can create hazardous concentrations of pollutants.
Heavy Metals
Metals having a specific gravity (i.e., weight in comparison to weight of an equal volume of water) of 5.0 or over, and generally toxic in relatively low concentrations to plant and animal life. Such metals can persist in animal tissue and are capable of increasing in concentration as they pass upward through the food chain. Major sources of heavy metal contamination are pesticides, limestone and phosphate fertilizers, manure and sewage sludge, and mine wastes. Examples include lead, mercury, cadmium, and arsenic.
The appearance of browse plants that have been browsed so as to appear artificially clipped. The consistent browsing of terminal buds of browse species causes excessive lateral branching and a reduction in upward growth.
To store young trees prior to plannng by placing them in a trench and covering the roots or rooting portions with soil.
Height, Merchantable
The height of a tree (or length of its trunk) up to which a particular product may be obtained. For example, if the minimum usable diameter of pulpwood sticks is 4 inches, the merchantable height of a straight pine tree would be its height up to a trunk diameter of 4 inches. Note, one must know the product being cut to estimate merchantable height.
Height, Total
The height of a tree from the ground level to the top of its crown.
Any flowering plant except those developing persistent woody stems above ground.
Herbaceous Vegetation
The low-growing, non-woody plants in a forest understory, including grasses (graminoids),wildflowers, and ferns.
Herbs taken collectively, usually used in the same sense as forage, except that it may include material not acceptable to grazing or browsing animals.
Herbicide (Weedicide)
A chemical substance used to prevent, inhibit, or destroy non woody plant growth. If its effectiveness is restricted to a specific plant or type of plant, it is known as a selective herbicide. If its effectiveness covers a broad range of plants, it is considered to be non-selective or broad spectrum. A herbicide is one type of pesticide. In common usage, however, often used interchangeably with the words phytocide (plant killer) and silvicide (tree killer).
An animal that feeds primarily on living plant substances.
Herd Home Range
The area that a social group of ungulates traverses during normal activities. It usually includes the total range for a year.
Differing in kind; not uniform; having qualities which are significantly different throughout; possessed of different characteristics.
Heterotrophic Organism
An organism that is dependent on organic matter for food. In contrast, an autotrophic organism is capable of using inorganic substances as its source of food.
A condition in which an animal's metabolism is purposely slowed to endure prolonged periods of adverse environmental conditions. normally several months at a time.
Hiding Cover, Structural
Vegetation capable of hiding 90 percent of a standing adult elk (or other animal) from the view of a human at a distance equal to or less than 200 feet. As a site-specific vegetative component of security, the quality of hiding cover varies inversely with sight distance.
Hiding Cover, Functional
Hiding cover allows elk to use areas for bedding, foraging, thermal relief, wallowing, and other functions year-round. Hiding cover may contribute to security at any time, but it does not necessarily provide security during the hunting season. Hiding cover is a requisite of elk habitat and a component of security. Hiding cover alone does not provide security during the hunting season.
Classification in which successively lower (i.e., more specific) level units must fit entirely within the separate units delineated by the next higher (i.e., less specific) level in that system. The boundaries of the more specific level units must occur within or coincide with (and not cross) those boundaries delineated for the units of the next less specific level in the classification system.
Hierarchical Structure
Group(s) of things (or persons) arranged in order of rank, grade, and class.
High Grading
Removing the mature, high quality trees from a stand and leaving inferior species and defective trees. "Take the best and leave the rest." Generally regarded as a poor forestry practice.
High Quality Hardwoods
Hardwood trees or stands that will yield high value timber products such as face veneer, knot free lumber, furniture or specialty product stock, or flooring.
The unexcavated face of exposed overburden and coal or ore in an open-pit mine or the face or bank on the uphill side of a contour strip mine excavation.
Hydrologic Information Storage and Retrieval System. A computerized data bank, which provides direct access to streamflow and weather data in a variety of methods and formats. North Carolina State University developed the system.
Histopath Analysis
Determines changes in an organism's tissue structure as a result of some physical (parasitism) or chemical (toxic substance) activity.
Historic and Cultural Sites
Sites associated with the history, tradition or cultural heritage of national, state or local interest and of enough significance to merit preservation or restoration. The location of the feature establishes the site. Recreational activities on these sites center on sight seeing, enjoying and studying the historic or cultural feature. Management is generally limited to activities that would effect such preservation and restoration as may be necessary to protect the features from deterioration and to interpret their significance to the public. Administration is by all levels of public agencies and private landowners who identify, set aside, and manage historic and cultural areas.
Historic Preservation
Protecting, rehabilitating, restoring, and reconstructing districts, sites, buildings, structures, and objects significant in American history, architecture, archeology or culture.
Historical Range of Variahility
The limits of change in composition, structure, and processes of the biological and physical components of an ecosystem resulting from natural variations in the frequency, magnitude, and patterns of natural disturbance and ecological processes characteristic of an area before European settlement. Estimates are made for a specified period of time and include the effects of pre-European settlement human activities.(USFS 1999)
Historic Sites Act (49 Stat. 666)
The Historic Sites Act of 1935 authorizes the programs that are known as the Historic American Buildings Survey, the Historic American Engineering Record, and the National Survey of Historic Sites and Buildings; authorizes the establishment of National Historic Sites and otherwise authorizes the preservation of properties "of national historical or archeological significance"; authorizes the Designation of National Historic Land marks; establishes criminal sanctions for violation of regulations pursuant to the act; authorizes interagency, inter governmental, and interdisciplinary efforts for preserving cultural resources; and other provisions. The U.S. National Park Service administers the program.
Historical Area
Sites and areas which have been Designated as containing important evidence and remains of the life and activities of early settlers and others who used or visited the area or the sites where important events took place. Examples are battlegrounds, remnants of mining camps, old cemeteries, important pioneer roads and trails, and early trading sites.
The doctrine that the universe-including life in all its forms and the inorganic environment -- is correctly seen in terms of interacting wholes that are more than the mere sum of elementary particles.
An attempt to study and master the knowledge and control of entire systems. An emphasis on functional relations between parts and whole; a doctrine in which a whole cannot be expressed as the simple sum of its parts.
(1) An important process or mechanisms of an organism (perhaps biotic community) for regulation (perhaps pre-disposed self-regulation) toward a constant or standard condition. All communities, except possibly the very simplest types, appear to contain regulatory mechanisms that enable them to adjust to the changing conditions of their physical environments. (2) The maintenance of a high degree of uniformity in functions of an organism or interactions of individuals in a population or community under changing environmental conditions. The constant function or status that results from the capabilities of organisms to make compensatory adjustments. (Negative feedback is at work.)
Home Range
The area which an animal uses during its normal actykies, not to be conflised with territory.
Homogeneous Response Unit (Response Unit)
A particular land (or water) unit that is delineated on the assumption that it is sufficiently uniform within its boundaries to respond in a homogeneous manner throughout the area to any set of inputs. That is, any treatment, stimulus, or set of conditions will cause approximately the same reaction, response, or set of outputs when applied to each location within the unit.
Horizon, Soil
A layer of soil approximately parallel to the land surface with more or less welldefined characteristics that have been produced through the operation of soilbuilding processes. 1) A-horizon--The upper horizon of the mineral soil, from which material has been removed by percolating waters. The horizon of eluviation. Commonly divided into a dark colored Al horizon contairnig a relatively high content of organic matter, and light-colored M horizon of maximum leaching, 2) B-Horizon--The horizon of deposition, to which materials have been added by percolating waters, the horizon of illuviation. 3) C-Horizon--The weathered parent material.
Horizontal Diversity
A comparative measure of occurrence and complexity of distribution of cover types over a wide area encompassing different cover types. Stand site, stand configuration, species composition, and a variety of age classes are some variables that make up horizontal diversity in a forested environment.
Hydrologic Unit Code. An eight-digit numeric code which identifies site locations with reference to the definitions of areas shown on U.S. Geological Survey State Hydrologic Unit Maps. The first two digits comprise the regional area defined by the U.S. Water Resources Council (WRC); the second two digits are the subregions as defined by IHRC; the third 2 digits are the National Water Data Network Accounting Units and the last two digits are the cataloging units of the Catalog of Information on Water Data maintained by the Office of Water Data Coordination (OWDC).
Human and Community Development System
A system having actions that help people and communities to help themselves. The system includes activities that provide (1) youth development through working and learning experiences, (2) adult employment and training opportunities through various federal manpower programs, (3) community planning and development information and services for rural areas, and (4) technical forestry assistance for urban areas in the establishment, management, and protection of needed open space and the use of trees and woody shrubs. One of the six "systems" established by the U.S. Forest Service to have a systematic, orderly way to view and evaluate its many diverse but interrelated activities. The Forest Service developed this approach to respond to the mandates of the Forest and Rangeland Renewable Resources Planning Act of 1974. It grouped its various programs into these six "systems," each of which incorporates all the activities concerned with developing and managing a specific resource. The six "systems" are: Land and Water, Timber Resource, Outdoor Recreation and Wilderness, Rangeland Grazing, Wildlife and Fish Habitat, and "Human and Community Development".
Human Community
The spatial or territorial unit in social organization in which members have a psychological cohesiveness or feeling of belonging, one not forced, and without loss of individuality.
Human Resource Unit
A geographic area characterized by particular patterns of cultural lifestyle and economic conditions.
Humus Layer
The top portion of the soil which owes its characteristic features to its content of humus. The humus (brown or black organic molecules, gellatinous, following processing by bacteria, fungi, and soil organisms) may he incorporated or unincorporated in the mineral soil.
Hunt Camp
Area Designated for camping use during a major hunting season (e.g., for deer). Facilities may consist of a parking area and toilet facilities.
Hunter Opportunity
An array of options that allows hunters to choose situations that are personally rewarding. Human activities, hunting regulations, access, time, space, and land management activities influence these options.
Hydraulic Conductivity
The rate at which water moves through aquifer material under a unit hydraulic gradient, expressed as volume per unit time per unit cross section (ft3/day/ft2 or M3/day/M2 reduced to feet per day or meters per day).
A graph showing variation in the water depth in a stream or the volume of water flowing past a point in a stream over a period of time.
Hydrolic Lift
Thge passive movement of water from the lower wetter layers to the upper drier layers of the soil profile via plant root systems. "Inverse lift", the redistribution of water downward, has been observed. Reverse flow of water in lateral roots is a prerequisite for hydraulic lift. (Moreira et al. 2003. Functional ecology 17:573-581
Hydrologic Cycle (Water Cycle)
The circuit of water movement from the atmosphere through various stages or processes on the ground (such as precipitation, interception, runoff, infiltration, percolation, storage) and then back to the atmosphere again by evaporation, and transpiration.
A science dealing with the properties, distribution, and circulation of water, specifically the study of water and its behavior on the surface of land, in the soil and underlying rocks, and in the atmosphere, particularly with respect to evaporation and precipitation.
Stages of ecological succession in a pond environment.
Hygric (Hydric)
A habitat characterized by wet or moist conditions rather than mesic (moderate) or xeric (dry) conditions.
The deep layer of a lake below the thermocline and removed from surface influences such as direct heating by sunlight and aeration by vertical circulation.
Hyporheic Zone
A layer of the landscape; the saturated interstitial [volumes] beneath streams and rivers and into the banks that exchange water with the channel and surface. It contains water of both subsurface and stream channel origin.
Ice Cream Species
An exceptionally palatable species of plant sought and grazed first by livestock and wildlife. Such species are usually over-utilized, even under proper grazing.
Impact Assessment, Environmental
An evaluation and objective prediction of the environmental impacts of a proposed action using a systematic, interdisciplinary approach that integrates social and natural sciences and environmental design arts.

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Last revision January 17, 2000.