Glossary

ASPECT: The direction a particular slope is facing.

BLUFF FACE: The sloping portion of a high bank (see Illustration 1 at right).

Illustration 1: Elements of a bluff

BLUFF RETREAT: The rate at which a bluff or shoreline is eroding as a result of surface erosion and/or mass soil movements. Used by some regulatory agencies to guide setback requirements.

BLUFF TOE: The base of a bluff where it meets the beach (see Illustration 1 at right).

BRANCH WHORLS: The circular growth of branches around the same point on the trunk of a conifer.

BROAD-LEAVED: Having flat leaves rather than needles as conifers do.

BUFFER: A protective strip of vegetated land.

CLEAR-CUT: A timber harvest method that removes all the trees on an area in one operation.

CONIFER: A cone-bearing tree with needles rather than leaves (i.e., pines, firs, hemlocks).

CREST: Upper edge or margin of a shoreline bluff (see Illustration 1 at right).

CROWN CANOPY: The branches and foliage of a tree.

DEBRIS AVALANCHE: A form of landslide where a water-saturated upper soil layer and the vegetation growing on it slides over an underlying less permeable subsoil creating a relatively shallow, narrow slide scar, usually two to three feet deep and 15 to 30 feet wide.

DECIDUOUS: Losing leaves or needles in the fall.

EARTHFLOW: A rapid mass movement of a flowing assemblage of saturated soil, vegetation, and associated debris.

EROSION: The wearing away of land by action of wind or water.

EVAPORATION: The process whereby moisture is turned to water vapor and removed from a surface. Rate increases as humidity decreases.

EVAPOTRANSPIRATION: The loss of water through a plant's leaves or needles from the body of the plant due to evaporation and transpiration.

EVERGREEN: A plant that retains its needles or leaves for more than one growing season.

EXOTIC PLANT: A plant that has been introduced into a region where it is not normally found.

FLORA: The plants of a region.

GLACIAL TILL: Term commonly used to emphasize glacial origin. See Till.

GROUNDWATER: Water within the pores between soil particles. Usually a permanent groundwater table is evident. This is a source of water for wells and springs. If water percolating through the soil encounters barriers such as clay or hardpan before reaching the permanent groundwater table, a perched water table may form.

HARDPAN: A hard, impervious layer of soil (often clay-rich), or iron-oxide cemented material. In Puget Sound the term is commonly used by drillers and contractors to describe glacial till.

HERBACEOUS: Non-woody plants such as ferns, nettles, and foxglove.

HORIZON: One of a particular layer of soil (e.g., the organic-rich "a" horizon) as used in soil science.

HYDROLOGY: (In the context of this guide) Refers to the properties, distribution, discharge, re-charge, and movement of surface and sub-surface water.

IMPERMEABLE: Unable to permit water or roots to move through freely (see Impervious Surface).

IMPERVIOUS SURFACE: A soil or surface through which water, air, or roots penetrate slowly or very little (that is, concrete, compacted soil).Illustration 8: Interdependent Grouping

INTERDEPENDENT: A group of plants that by growing together protect each other from disturbance by wind, erosion, or other natural processes. Shallow rooted trees will often remain windfirm because they form a wide, spreading root mat. (See Illustration 8 at right.)

JACKSTRAWED: A group of trees that has lost firm rooting through wind, land movement, or excessively wet soils and appears chaotic or no longer oriented toward the light.

LANDSLIDE: The downhill movement of a mass of soil or rock, usually wet or saturated, that results in episodic erosion. (Sometimes simply referred to as "slide," but also including falling or flowing masses as well.)

MASS SOIL MOVEMENT:See Landslide.

NATURAL LANDSCAPE ELEMENTS: Natural watercourses, topography, hydrology, and vegetation that comprise a particular site.

NON-NATIVE PLANT: See Exotic Plant.

OVERSTORY: The portion of a plant community that forms the upper-most crown cover or canopy.

PERCHED WATER: Groundwater that accumulates over an impervious soil layer from rainfall or other sources that finds release on bluff faces. Perched water is released on bluff faces as seeps or springs.

PIONEER SPECIES: Plants that colonize disturbed sites after land clearing, logging, fire, or landslides. They are normally replaced over time by other species. Alder, willow, and fireweed are common examples.

PLANT COMMUNITY: An inter-related and interdependent assemblage of vegetation having structural and species diversity (i.e., Western red cedar, Western hemlock, salal, Oregon grape, Evergreen huckleberry, Sword fern, mosses, and lichens).

REGENERATION: 1) The process by which an area is restocked with plants. 2) Young trees, either naturally seeded or planted.

SEEPS: See Perched Water.

SHEAR STRENGTH: A measure of the ability of a soil to resist forces that tend to separate it from its position on a slope and cause it to move.

SILVICS: The study of life history and general characteristics of forest trees and stands in relation to environmental factors.

SLOPE: The inclination of the land surface from the horizontal. Percentage of slope is the vertical distance divided by the horizontal distance, multiplied by 100. Slope is also measured in degrees (90 degrees being vertical) or as a ratio. A 100% slope would be 45 degrees or 1:1.

SOIL COMPACTION: Reduction of the total pore space in a soil. Results in a soil that retains less water and resists root penetration. Soils with high clay content are more easily compacted than sandy soils.

SOIL CREEP: A process of slow, downslope movement over a long period of time.

SOIL HORIZON: See Horizon.

SOIL SLUMP: A deep-seated mass movement of soil. The mass moves down and rotates, leaving a concave depression above.

STRATA: A layer of soil or rock.

STRATIGRAPHY: The sequence or order of rock or soil layers in a geologic formation.

SUCCESSION: The process of replacing one plant community with another over time (that is, alder to Douglas-fir to Western hemlock).

SUCCESSIONAL SPECIES: The plant species that comprise a plant community in a given successional stage (for example, early successional species are alder, willow and Bitter cherry).

SURFACE WATER: Rain, snowmelt, lawn sprinkling, or other additions to the soil surface. Also refers to lakes and streams (in contrast to groundwater).

THINNING: Tree removal in a forest stand that reduces tree density and numbers in a given area. Most discussions of thinning stress increased growth and yield of timber.

TILL: Unstratified glacial drift consisting of unsorted, intermixed clay, sand, gravel, rock, and boulders. Generally well-cemented and impermeable.

TOE OF SLOPE: See Bluff Toe.

TOPOGRAPHY: The physical features of a surface area including relative elevations and the position of natural and human-made features.

TRANSPIRATION: The process by which water vapor is lost to the atmosphere from living plants.

TREE FAILURE: A tree or portion of a tree that collapses as the result of some structural weakness such as root rot, dead branches, mechanical wounds, or other causes.

UNCONSOLIDATED MATERIALS: Geologic materials such as sand, gravels, and mixed sediments whose particles are loose and uncemented.

UNDERCUTTING: The removal of material at the base of a steep slope or cliff by the erosive action of waves, running or seeping water, or windblown sand.

UNDERMINED ROOTS: Roots that are not firmly anchored due to soil removal or loss, beneath and/or around them. Can affect both live and dead trees or stumps.

UNDERSTORY: Trees or other plants that tolerate reduced-light conditions and normally grow beneath the overstory.

UPLANDS: The tops of bluff areas usually developed for home sites.

WATER TABLE: The level at which soil and/or rock is saturated with water. Can be seasonal. Water table can be altered by changes in hydrology.

WINDTHROW: Trees blown over by the wind. Often caused by thinning or adjacent clearing.

 

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