An acid is a substance having a pH of less than 7 when dissolved in water. Ecologists apply the term acidic to plant communities growing in rather acidic and nutrient-poor soils. Acidic soils result from the presence of various inorganic and organic acids.
Related to alluvium or floodplains.
Sediment deposited by flowing streams or rivers in floodplains and streambeds/riverbeds. Different sizes of sediment particles are deposited, depending on the water velocity related to the location within the floodplain.
- Ancient river terrace
A former floodplain terrace, or alluvial landform that is no longer subject to flood events, but is instead in the uplands. At Rock Creek Park, some of the highest hills are topped with coarse sand and smooth stones that appear to have been rounded and polished by turbulent water in past ages. Evidence of marine sediments is lacking, so these terraces are believed to have been formed by flowing fresh water, possibly an ancestral Potomac River.
Synonyms: ancient river terraces
See slope aspect.
A base is a substance having a pH above 7 when dissolved in water. A basic substance is capable of neutralizing acids. Base elements, such as calcium, magnesium, and sodium, are one class of such substances, and are important nutrients for plants. Basic rocks are composed of minerals rich in base elements. Ecologists apply the term basic to plant communities whose presence indicates that the soil contains base elements available in a form plants can use, even if the overall soil pH is not basic.
- Base element
- Base mineral
A rock-forming mineral high in iron, magnesium, and potassium, dark brown or black in color. A common kind of ‘mica’ (a group of soft minerals that tend to occur in flakes or sheets.
Quoted from Stewart, K.G. and M. Roberson. 2007. Exploring the Geology of the Carolinas. UNC Press, Chapel Hill, NC.
Having relatively broad leaves, as opposed to needle-like leaves. Examples of broadleaf evergreen trees or shrubs: American holly, mountain laurel. Examples of broadleaf deciduous trees or shrubs: white oak, pink azalea.
A narrow, continuous ring of growth tissues located just inside the external bark of a tree, that is responsible for transporting water, nutrients and food. As a tree ages, the cambium produces wood (to the inside) and bark (to the outside) causing the tree to grow in width.
The trees whose crowns intercept most of the sunlight in a forest stand. The uppermost layer of a forest. Adapted from Johnson, P.S., S.R. Shifley, and R. Rogers. 2002. The ecology and silviculture of oaks. Chapter 5. Page 194. CABI Publishing, New York.
- Canopy gap
A temporary opening in the forest canopy, caused by the death or toppling over of one or more canopy trees.
To direct the course of a stream through a manmade channel.
Synonyms: channelization channelizations
- Citizen scientist
A citizen scientist is a member of the general public who engages in scientific work, often in collaboration with or under the direction of professional scientists and scientific institutions; an amateur scientist.
Quoted from the Oxford English Dictionary.
Synonyms: Citizen scientists
- Classification code
The unique identifier for each natural community. The classification code is used to identify each natural community in the U.S. National Vegetation Classification and other classification systems. The code is written as "CEGL" followed by a series of numbers. CEGL stands for Community Element Global. For example, the classification code for the Mid-Atlantic Mesic Mixed Hardwood Forest is CEGL006075.
- Clay loam
A system of tree harvesting that removes all the trees in a given area, as opposed to other systems that leave some trees standing. Adapted from Draper, D.L. 2002. Our Environment: A Canadian Perspective, Second edition. Glossary. Nelson, Scarborough, Ontario, Canada.
Describes rock with planes of weakness along which it may split.
Describes colonies of plants that appear to be distinct individuals, but are genetically identical, and interconnected underground by specialized roots. Some types of shrubs in the heath family at Rock Creek Park are clonal. Above ground these plants appear to be distinct individuals, but underground they remain interconnected and are all part of the same plant.
- Coastal Plain
The easternmost stretch of land in the Mid-Atlantic region that lies between the Piedmont and the Atlantic Ocean. This relatively flat land is comprised of layers of unconsolidated sediments and sedimentary rock that get thicker from west to east. The western boundary of the Coastal Plain is the Fall Zone, where it overlaps the Piedmont bedrock in the vicinity of Washington, D.C.
Synonyms: Atlantic Coastal Plain
- Colluvial fan
A blanket of loose stones and soil that moves downslope by a combination of natural processes (frost action, gravity and hillside creep, and slope wash), locally accumulating to considerable thickness on flatter areas (‘benches’ and toeslopes) in the form of ‘colluvial fans.’ At least a few inches of colluvium are present on many slopes in Rock Creek Park.
The simultaneous demand by two or more organisms for limited environmental resources, such as nutrients, living space, or light. Quoted from The American Heritage Science Dictionary. 2005. Houghton Mifflin Company, Boston.
- Competitive advantage
The advantage that a characteristic (or set of characteristics) gives one organism over another in an environment where vital resources such as sunlight, water, nutrients, and space are limited and cannot be shared. For instance, among sun-loving plant species, the ability to grow faster and taller than surrounding plants may be a competitive advantage, giving a plant access to the greatest share of sunlight (and as a consequence, shading the other sun-loving plants, interrupting their growth).
Synonyms: competitive advantages
Curved inward, like the inside surface of a bowl. Describes the shape of land on some slopes, and especially near the base of a hill (toeslope), that tends to collect moisture and fine sediment runoff.
A needleleaf tree that bears cones. A pine tree, for example.
- Conservation status rank
A rating of natural communities and of species that estimates their risk of elimination. Natural communities and species are given a conservation status rank to reflect the fact that while some of them are common across the landscape regionally or globally, others are not. The most rare species risk extinction. The most rare natural communities may be at risk of being severely degraded or even lost in the future unless some conservation measures are taken. (Certain plants and animals that depend on these rarest of natural communities are also at risk of extinction.) NatureServe and its natural heritage member programs have developed a consistent method for evaluating the relative imperilment of species and of natural communities, and assigning each a conservation status rank. The ranking is based on the best available information, and considers a variety of factors such as abundance, distribution, and threats. Rankings of natural communities and species across their global (G) range are as follows:
G1: critically imperiled
G4: apparently secure
G4G5: uncertainty exists as to whether this community is ‘apparently secure,’ or ‘secure’
Synonyms: conservation status G1 G2 G3 G4 G5 G4G5
Curving or bulging outward, like the outside surface of a ball. Describes the shape of land (on some hillsides, for instance) that tends to shed moisture.
- Cut banks
Referring to a plant that sheds leaves at the end of a growing season and regrows them at the beginning of the next growing season. Most deciduous plants bear flowers and have woody stems and, in this region, have broad rather than needlelike leaves. Maples, oaks, and elms are examples of deciduous trees. Compare evergreen. Adapted from The American Heritage Science Dictionary. 2005. Houghton Mifflin Company, Boston.
Living organisms such as bacteria, fungi, ants, and worms, which are able to break down organic matter that is difficult for other organisms to digest. They typically secrete enzymes onto organic matter (dead organisms or animal or plant wastes) and then absorb the breakdown products. Decomposers fulfill a vital role in the ecosystems, returning the constituents of organic matter to the environment as inorganic nutrients that can be used again by plants. See also nutrient cycles. Adapted from Dictionary of Biology. 2004. Fifth edition. Oxford University Press.
The breakdown of dead organisms or animal or plant wastes (organic matter) into inorganic nutrients by the action of decomposers, so that the nutrients can be used again by plants. See also nutrient cycles. Adapted from Dictionary of Biology. 2004. Fifth edition. Oxford University Press.
Debris or litter of biological origin, such as leaf litter, animal waste, or dead organisms. Adapted from Allaby, M. 1994. The Concise Oxford Dictionary of Ecology. Oxford University Press.
- Disturbance intervals
The amount of time that lapses between repeat episodes of a natural disturbance to a plant community. Where, for instance, long intervals between flood events are the norm, the vegetation will look quite different than where flooding occurs more frequently.
(As used here) A redirected section of a stream, either temporary or permanent (usually for construction purposes).
- Dry-site oaks
Oak species that are known for their ability to thrive on nutrient-poor, dry sites. Examples in the Mid-Atlantic region of the U.S. include: chestnut oak, scarlet oak, black oak, and post oak, and to some extent, white oak.
Decaying leaves and branches covering a forest floor. Quoted from The American Heritage Dictionary of the English Language. 2006. Fourth edition. Houghton Mifflin Company, Boston.
- Ecological system
A broad ecological environment in which certain natural communities tend to cluster together. (For instance, the Central Appalachian Stream & Riparian ecological system encompasses all kinds of natural communities that occur along streams in the Central Appalachian region.)
Synonyms: ecological systems
- Edge habitat
A boundary where two or more habitats meet. (For example, where a natural community meets another natural, semi-natural, or non-natural plant community or disturbed area.) Some animal species prefer edge habitats—where a meadow borders a forest, for instance—with access to resources that aren’t found in a single natural community.
Synonyms: edge habitats
- EDRR species
EDRR stands for Early Detection and Rapid Response—a strategy of watchfulness and quick eradication to keep newly-arrived species of weedy non-native invasive plants from getting established on a site. "EDRR species" is a nickname for species that are being targeted for management by this strategy.
A substance whose structure is made up of only a single type of atom. For example, the mineral copper, which is made up of 100 percent the element copper (and no other substances), is known as an element. The ‘periodic table of the elements’ is a layout of all the elements. Adapted from The Mineral & Gemstone Kingdom. Glossary. 2017.
- Energy flow
The flow of energy in an ecosystem from producers to users. Energy on Earth (in most ecosystems) is derived from the sun, which energizes plants to convert inorganic nutrients into plant tissue (photosynthesis); those plants feed (i.e., energize) animals, which feed other animals, etc. There is some loss of energy each time it is transferred—for instance, only a small percentage of sunlight that strikes plants is used by the plant for photosynthesis; and animals can’t digest every particle of plant or animal they consume. A constant input of new energy from sunlight is required to continue the energy flow on Earth; energy is not completely recycled the way nutrients are. See also nutrient cycles and food chain. Adapted from Marietta College Department of Biology and Environmental Science. 2017. Biomes of the World—Ecology Pages. Environmental Biology—Ecosystems.
Having green leaves or needles all year. Evergreen trees lose their leaves individually on an ongoing basis, rather than losing all of them in a short period at the end of a growing season in the manner of deciduous trees. Evergreen plants may be broadleaf or needleleaf. Quoted, in part, from The American Heritage Science Dictionary. 2005. Houghton Mifflin Company, Boston.
Not native to a region; being from another part of the world. “Exotics” can be a synonym for ‘non-native plants.’ See also non-native invasive plant.
Having a landscape position (usually high or open) that heightens the effect of weather (primarily sun and wind, but also lightning, rain, ice) on vegetation. Contrasted with ‘sheltered.’
- Extrusive rock
Lava; magma that cooled rapidly above-ground, producing a fine-grained igneous rock. (Compare intrusive rock.) Adapted from The American Heritage Science Dictionary. 2005. Houghton Mifflin Company, Boston.
Species interactions that benefit at least one of the participants and cause harm to neither. (Stachowicz, J. J. 2001. Mutualism, facilitation, and the structure of ecological communities. BioScience 51: 235-246.)
Synonyms: ecological facilitation
(As used here) A natural process whereby the presence of one organism facilitates or helps another organism to grow. Both organisms may benefit from the interaction, or just one.
- Fall Zone
The Fall Zone (sometimes called the fall line) is the boundary between the Piedmont and the Coastal Plain; often marked by falls and rapids as rivers leave the hard rocks of the Piedmont and step down into the more easily eroded sediments of the Coastal Plain. Quoted from Stewart, K.G. and M. Roberson. 2007. Exploring the Geology of the Carolinas. UNC Press, Chapel Hill, NC.
Synonyms: fall zone Fall Zone fall line
A fracture in the earth which shows evidence of the movement of blocks of rock relative to one another. Earthquakes are the result of shifting along faults (‘fault motion’).
All the different kinds of animals of a particular area.
- Feedback loop-ecology
(As usedhere) A circular chain of cause-and-effect, in which the outcome of some natural processes affect other processes, which in turn affect the original processes.
- Field layer
- Fire suppression
Efforts to control and extinguish fires, usually to prevent loss of human life and property.
Describes plant species characterized by the ability to thrive as a species in spite of (or partly because of) some degree and frequency of fire occurring in the landscape. The means of survival vary considerably. Some fire-adapted species have qualities that make them less vulnerable to light or moderate fire. (Example: the thick bark of chestnut oak.) Other fire-adapted species possess qualities (such as oily sap, or low-hanging dead branches) that make mature specimens more prone to complete destruction by severe fire; but also possess qualities that will give their seeds or stump sprouts a fresh start in the charred forest that results. (Example: mountain laurel, or pitch pine)
- Floodplain dynamics
What happens in the natural interplay between rivers or streams and their floodplains.
- Floodplain terrace
The higher parts of a modern stream valley (farther from the stream channel than the floodway), which may be inundated only infrequently, e.g., a 10-year floodplain, a 25-year floodplain, etc.
That part of a modern floodplain adjacent to the active stream channel, and which is typically inundated annually or more frequently, whenever the stream overflows its banks.
All the different kinds of plants of a particular area.
- Food chain
A series of feeding relationships in which one organism eats another organism, only to be eaten itself by another organism. Organisms such as green plants form the bottom rung of the food chain, since they do not eat other organisms, but instead convert inorganic nutrients (non-living chemicals) into food with energy supplied by sunlight. (See primary production.) The collective interactions of all the food chains in an ecosystem are called a food web (a way of representing the complex system of passing nutrients and energy from producers to users.)
- Food web
See food chain.
Easily crumbled or broken apart into small pieces.
- Frost action
- Gap-phase regeneration
A phase of forest regeneration, during which trees begin to colonize gaps created by fallen trees. Adapted from Allaby, M. 1994. The Concise Oxford Dictionary of Ecology. Oxford University Press. See also canopy gap.
- Geologic substrate
The study of the form and origin of landscapes, and the arrangement of geologic materials and processes on them.
The growth of a seed into a seedling.
- Glenelg loams
Water that percolates down into the earth through permeable layers and cracks until it encounters a layer that water cannot penetrate. There it collects and/or flows horizontally, filling the porous spaces in soil, sediment, and rocks. Groundwater originates from rain and from melting snow and ice and is the source of water for aquifers, springs, and wells. Adapted, in part, from The American Heritage Science Dictionary. 2005. Houghton Mifflin Company, Boston. As it flows, groundwater can re-surface. It often carries with it dissolved base minerals leached from soils and bedrock. See also groundwater discharge, groundwater recharge, water table.
- Groundwater discharge
Groundwater that re-surfaces as seepage, or even as a flowing spring. It may surface in such places as ravines, along the bottoms of hillsides, and in stream or river channels. Where a road or trail has been cut through a hillside of layered rock, you may be able to see groundwater seeping from between the layers of exposed rock for days after a good rain.
- Groundwater processes
The physical, chemical and biological processes that occur in or produce groundwater.
- Groundwater recharge
The process of precipitation replenishing the groundwater supply as rain, melting snow, and melting ice soak into the earth.
- Growing season
The period of the year when climatic conditions are favorable for plant growth. Quoted, in part, from McGraw-Hill Dictionary of Scientific and Technical Terms. 2003. Sixth edition. The McGraw-Hill Companies, Inc, New York. For instance, in this part of the world, generally the time period between the last freeze in the spring and the first frost in the autumn. The growing season can vary by plant species, as different plants have different tolerances for freezing temperatures.
- Hard mast
A term used to describe the hard-shelled fruits of plants such as the seeds of beech and oak. Hard mast is an especially important wildlife food in the fall and winter. It is high in fat content and is available when other plant foods (fleshy fruits and foliage) are not available. Quoted from Algonquin Provincial Park’s Online Learning Centre. 2009. The Science Behind Algonquin’s Animals. Glossary.
- Heath-family shrub
A member of the plant family Ericaceae, made up of mostly shrubs and small trees and including azaleas, rhododendrons, mountain laurel, blueberries, and huckleberries. Botanists sometimes refer to members of this family as ‘heaths.’ Since they usually thrive on acidic soils with few nutrients, they can help indicate soil quality.
Synonyms: heath heath shrub heath shrubs 'heath shrubs'
- Herbaceous plant
Generally any plant which does not produce wood. Grasses, wildflowers, and ferns are all ‘herbs.’ When they die back, their stems die back, too. (This field guide does not restrict the term ‘herb’ to plants valued for flavor, scent, or medicinal qualities.)
Synonyms: Herb herbaceous plants
An animal that feeds chiefly on plants.
The consumption of plants by animals.
A rock-forming mineral rich in iron, magnesium, and calcium. (The common form of amphibole.)
Low hills or mounds. (A term often used for elevated bits of land in wetlands.)
Synonyms: hummocky hummock
- Hydrologic cycle
The continuous process by which water is circulated throughout the Earth and its atmosphere. Also known as the ‘water cycle.’ ’ Adapted from The American Heritage Science Dictionary. 2005. Houghton Mifflin Company, Boston.
The study of water (in all its forms) on the Earth’s surface, in the soil and underlying rocks, and in the atmosphere.
- Ice Age
A period of geological time ending about 10,000 years ago, when continental ice sheets seem to have repeatedly covered the high and mid latitudes of the world’s continents. Occurred during the latter part of what geologists call the Pleistocene epoch.)
- Igneous rock
Rock that crystallized from hot magma. Can include lava (which solidifies after reaching earth’s surface) or intrusive rock (which solidifies before reaching earth’s surface). At Rock Creek Park, most types of igneous rock (except quartz) contain minerals that become valuable plant nutrients as they weather into soil.
- Impermeable surface
Mainly artificial surfaces (e.g., pavements and rooftops, but also compacted earth) that keep water from penetrating into the ground. When the soil is thus sealed, groundwater recharge is eliminated. Sometimes called ‘impervious surfaces.’
An adjective describing a natural or man-made layer that stops rainwater from soaking in or moving through it. Examples of man-made impervious surfaces are rooftops, parking lots, and streets. Examples of natural impervious layers beneath the soil are clay and shale.
A block of rock trapped in another kind of rock.
- Indicator species
- Infertile soil
- Inner Coastal Plain
An invertebrate animal that, as an adult, has 6 segmented legs, a three-part body, compound eyes, and two antennae. Adapted from The American Heritage Science Dictionary. 2005. Houghton Mifflin Company, Boston.
- Intrusive rock
The International Vegetation Classification [of which the U.S. National Vegetation Classification (NVC) is a subset]—a standard used internationally by ecologists to classify (categorize) and map natural communities.
- Kensington Tonalite
One of the major intrusive rock units in the greater D.C. area. Medium to coarse-grained, it includes crystals of light and dark minerals (including quartz and biotite), giving it a granite-like appearance. Named for the village of Kensington, MD.
- Laurel Formation
A type of acidic bedrock at Rock Creek Park, metamorphic in origin, and containing fragments and inclusions of various exotic rocks. Widespread in the eastern Piedmont between D.C. and Baltimore, and named for the town of Laurel, MD. Restricted to the east side of the Rock Creek shear zone.
The process by which soluble parts are dissolved out from rocks, soils, or other matter as water or other liquid passes through slowly. Adapted from The American Heritage Science Dictionary. 2005. Houghton Mifflin Company, Boston.
Synonyms: leaching leached
A long ridge of sand, silt, and clay built up by a river or stream along its banks, especially during floods. Adapted from The American Heritage Science Dictionary. 2005. Houghton Mifflin Company, Boston.
Textural term referring to soil or sediment composed of roughly equal parts of sand (22-52 percent), silt (28-50 percent), and clay (8-27 percent). Sandy loam contains 50-85 percent sand, silt loam contains 50-85 percent silt, while clay loam is defined as having 28-40 percent clay.
Synonyms: loams loamy
- Mafic rock
Rock with significant concentrations of iron and magnesium, making it heavy and dark.
Molten rock underground. Quoted from Stewart, K.G. and M. Roberson. 2007. Exploring the Geology of the Carolinas. UNC Press, Chapel Hill, NC.
- Manor loams
A phenomenon in which large numbers of trees bear a lot of fruit in a particular year despite no seasonal change in temperature or rainfall; this does not occur every year but at intervals of two to 10 years. See also hard mast and soft mast. Adapted from Wisconsin Primate Research Center Library. 2009. Primate Info Net: Primate Factsheets Glossary. University of Wisconsin-Madison.
When said of habitats, mesic means having a moderate or well-balanced supply of moisture. When said of plants, mesic means requiring a moderate or well-balanced supply of moisture.
- Mesic-site oaks
(As used here) Oak species that thrive on mesic sites. Examples at Rock Creek Park include: northern red oak and white oak.
- Metamorphic rock
Synonyms: metamorphic metamorphic rocks
Metamorphism is the process of change when rock is subjected to enough heat and pressure to change the minerals, textures, or structures without melting the rock. Deep burial or stress from fault motion can cause rock to undergo metamorphism, i.e., to metamorphose.
- Metasedimentary rock
Shorthand for metamorphosed sedimentary rock (i.e., metamorphic rock derived from sedimentary rock). Any sedimentary rock, such as shale or sandstone, which has been subjected to enough heat and pressure to change some or all of the minerals, textures, or structures without melting the rock.
Synonyms: metasedimentary rocks metasedimentary
- Metavolcanic rock
Shorthand for metamorphosed volcanic rock (i.e., metamorphic rock derived from volcanic rock). Any rock of volcanic origin which has subsequently been subjected to enough heat and pressure to change some or all of the minerals, textures, or structures without melting the rock.
Synonyms: metavolcanic rocks metavolcanic
Local climatic effects associated with or caused by a specific landform.
A microscopically small organism, such as a bacterium.
- Migrant trap
(As used here) A site where great numbers of migrating birds may stop over for rest during their long flights in spring and fall.
Any naturally occurring inorganic substance with an arrangement of atoms (chemical structure) that can be exact, or can vary within limits. Quartz and feldspar are examples of minerals. Elements that occur naturally as crystals are also considered minerals. A rock is mainly composed of minerals. The terms sand, silt, and clay can refer to specific particle sizes of minerals. Adapted, in part, from The Mineral & Gemstone Kingdom. Glossary.
- Mineral soil
Synonyms: mineral soils
Decomposed organic matter (plant and animal).
Pertaining to a mutually beneficial relationship between plant roots and fungi (plural for fungus). Plants support fungi by providing sugar and a hospitable environment. Fungi support plants by providing increased surface area for water uptake and by selectively absorbing essential minerals. Quoted from Plantlife. 2009.
- Native plant
(As used here) A plant species that occurs naturally in a particular region, and whose presence is not traceable to human actions, either directly or indirectly.
- Natural community
A ‘community’ of native plants that recurs in the landscape with similar species composition and physical structure. Occurrences of a natural community also tend to share characteristic environmental features such as bedrock geology, soil type, and topographic position, and to have natural processes in common such as climate, means of energy flow, nutrient cycling, and water cycling. Each supports certain kinds of wildlife. Adapted from Canada. Ministry of Forests and Range. 2008. Glossary of Forestry Terms in British Columbia, March 2008.
Synonyms: natural communities
- Natural disturbances
Natural events such as fire, severe drought, insect or disease attack, or wind that periodically disrupt natural communities or entire landscapes, impacting them to greater or lesser degrees, for greater or lesser periods of time. See also scale. Adapted from U.S. Forest Service. Cleveland National Forest Land Management Plan, Part 3 – Design Criteria for Southern California National Forests, Appendix L—Glossary (M–R).
- Natural history
A descriptive study of nature, based more on observation than experimentation. It may include elements of biology, geology, climatology, ecology, and more. A ‘naturalist’ is a person who studies natural history.
- Natural process
A process existing in or produced by nature (rather than by the intent of human beings), e.g., evaporation, volcanic activity. Adapted, in part, from WordWebOnline.com. 2017.
Synonyms: natural processes
Describes a non-native species of plant or animal that has permanently established itself in a region by successfully reproducing and living alongside native plants in the wild. Some naturalized plants become aggressive invaders. Adapted, in part, from The American Heritage Science Dictionary. 2005. Houghton Mifflin Company, Boston.
A plant or animal that readily establishes itself in a new region to which it is not native.
Having needle-like leaves, as opposed to broad leaves. Example of a needleleaf evergreen tree: Virginia pine. (Rock Creek Park lacks examples of needleleaf deciduous trees, such as bald cypress or American larch.)
(As used here) A species (plant or animal) that was not historically present naturally in a particular region. Rather, its presence can be traced to human activity, either directly or indirectly. See also non-native invasive plant.
- Non-native invasive plant
A plant species that not only is non-native to a particular region, but also aggressively multiplies or spreads there, becoming a weedy pest and threatening the well-being of native populations of plants.
Synonyms: non-native invasive plants non-native invasive non-native invasives
- Nutrient cycles
The natural recycling of nutrients (chemical elements and molecules) on our planet. Carbon, nitrogen, phosphorus, and even water (hydrogen and oxygen) are just a few of the classic ‘nutrients’ whose pathways of movement are studied. As they are used in living organisms or non-living geological processes, nutrients are never ‘used up,’ but are either released and re-used elsewhere, or are held for long periods of time (such as in rock). Adapted from Marietta College Department of Biology and Environmental Science. 2017. Biomes of the World—Ecology Pages. Environmental Biology—Ecosystems. See also food chains and energy flow.
- Nutrient-rich soil
Soil that is good for plant growth. Sometimes called ‘fertile’ soil, or simply ‘rich.’
(As used here) Chemical elements and molecules, in forms that plants can use. (‘Inorganic nutrients.’) At least sixteen are known to be essential to a plant’s well-being, even if in tiny amounts. Some come directly from carbon dioxide in the air and from water (hydrogen, oxygen, carbon). Others come from soil, dissolved in water (nitrogen, phosphorus, potassium, calcium, sulfur, magnesium, iron, zinc, manganese, copper, and other micro-nutrients). Groundwater dissolves some of these out of soil or bedrock.
The U.S. National Vegetation Classification [a subset of the International Vegetation Classification (IVC)]—a standard used nationwide by ecologists and the federal government to classify (categorize) and map natural communities.
- Organic matter
(As used here) Residue from living organisms (plants and animals) decomposing in the soil, along with living microorganisms.
See rock outcrop.
- Outer Piedmont
- Parent material
Synonyms: parent rock parent rocks parent rocks)
The standard measure of acidity of a substance. On a scale of 1-14, 7 is neutral; anything that tests lower than 7 is technically acidic, and anything higher than 7 is alkaline (or basic). See also acid, acidic, and base, basic.
The process by which a plant makes its own food. Green chlorophyll pigment in the leaves absorbs light energy, which is used to fuel sugar production. A plant ‘photosynthesizes’ during most of its growing season.
The scientific study of the natural features of the Earth’s surface. (Physical geography.) Adapted from The American Heritage Science Dictionary. 2005. Houghton Mifflin Company, Boston. ‘Physiographic regions’ are broad-scale subdivisions based on terrain texture, rock type, and geologic structure and history. Quoted from U.S. Geological Survey. 2000. A Tapestry of Time and Terrain. Near D.C., the three physiographic regions are the Blue Ridge Mountains, the Piedmont, and the Coastal Plain. The Fall Zone separates the latter two.
The land bounded by the Blue Ridge Mountains to the west, and the flatter Atlantic Coastal Plain to the east. This rolling terrain is underlain by solid bedrock, which is thought to be the eroded ‘roots’ of an ancient mountain range.
- Pioneer species
A plant or animal species that colonizes land that has been cleared or somehow severely disturbed. Typically sun-loving, fast-growing species, sometimes thought of as ‘weedy.’ Around the D.C. area, ‘pioneers’ include native plants such as wild blackberries, Virginia pine, tuliptree, and lots of grasses and other herbaceous species. Non-native plants have become some of the most aggressive pioneers in recent decades: Japanese stiltgrass, garlic mustard, Asiatic bittersweet, Japanese honeysuckle, multiflora rose, tree-of-heaven, princess tree, mimosa tree.
- Point bars
Crescent-shaped deposits along meandering streams, on the inside of stream bends. See also cut banks.
- Primary cavity nester
An animal, such as a woodpecker or chickadee, that can make its own tree cavity (hollow) in which to nest. See also secondary cavity nester.
- Primary production
The activity of green plants and algae that produce and store their own energy (food) from sunlight and non-living chemicals, rather than consuming other organisms to meet their energy needs. Primary producers are therefore the base of the food chain.
Any plant structure (such as a bulb, root, etc.) with the capacity to give rise to a new plant, e.g., a seed, a spore, part of the vegetative body capable of independent growth if detached from the parent. Adapted from Biology-Online Dictionary. 2017.
Hard white rock at Rock Creek Park that weathers to an extremely acidic soil. (One of the most common minerals on earth (SiO2).) Quoted from Stewart, K.G. and M. Roberson. 2007. Exploring the Geology of the Carolinas. UNC Press, Chapel Hill, NC.
- Quartz veins
Fractures in rock that are filled with milky white quartz. Quartz veins form when hot silica-rich water moves through cracks; as the water cools, quartz is deposited. Quoted from Stewart, K.G. and M. Roberson. 2007. Exploring the Geology of the Carolinas. UNC Press, Chapel Hill, NC.
- Radio button
Synonyms: radio buttons
A process in rocks that occurs during metamorphism, whereby the structure, but not the composition, of the minerals in a rock is altered due to incredible heat and pressure.
The continuous renewal of a forest stand. Natural regeneration occurs gradually with seeds from the same or adjacent stands or with seeds brought in by wind, birds, or animals, and with stump-sprouting. Adapted from North Carolina Forestry Association. 2017. Forest Management Basics.
(As used here) The process by which an organism breathes or somehow exchanges gases, especially carbon dioxide and oxygen, with the environment. Adapted from The American Heritage Science Dictionary. 2005. Houghton Mifflin Company, Boston.
The microscopically thin biologically active zone of soil and microbes on and around plant roots.
On, near, or related to the banks of a river.
- Rock outcrop
Tiny but gritty particles of rock. In U.S. geology, sand is a size label for rock fragments between about 1/16 mm and 2 mm (about 1/16 inch or less, but gritty). See also cobble, gravel, silt, and clay.
Synonyms: sands sandy
- Sandy loam
Synonyms: sandy loams
A young tree.
The magnitude of a natural process in terms of extent (how large an area affected), or frequency/duration (how frequent the recurrence, or how long the process or impact lasts). Also, the intensity (how severe the impact) of a natural disturbance.
- Seasonal wetlands
(As usedhere) Pools of water that periodically dry up; therefore usually lacking fish. Particularly important habitat to some salamanders, frogs, and toads.
- Secondary cavity nester
An animal, such as a raccoon, bluebird, or wood duck, that is unable to excavate its own tree cavity (hollow) in which to nest, and so uses cavities that other animals or natural processes have created. See also primary cavity nester.
(As used here) Loose particles of varying sizes including bits and pieces of rocks and minerals and organic matter such as shells. Includes sand, silt, and clay. Quoted, in part, from Stewart, K.G. and M. Roberson. 2007. Exploring the Geology of the Carolinas. UNC Press, Chapel Hill, NC.
- Sediment transport
The movement of sediment and the processes that govern their motion. Sediment transport is typically due to a combination of the force of gravity acting on the sediment, and/or the movement of the air, water, or ice in which the sediment is carried. The force of gravity is due to the sloping surface on which the particles are resting. Adapted from Wikipedia contributors, "Sediment transport," Wikipedia, The Free Encyclopedia (accessed November 17, 2009).
- Sedimentary rock
Rock that is formed when organic or inorganic sediments are compressed (or ‘lithified’) into layered solids by the weight of overlying material such as other rocks. It forms at pressures and temperatures that do not destroy fossil remnants. See also igneous rock and metasedimentary rock for contrasts.
Synonyms: sedimentary rocks sedimentary
- Seed bank
Synonyms: Soil seed bank
- Seed dispersal
(As used here) A baby tree or shrub.
- Semi-natural community
A vegetation community that, although largely comprised of native plants, owes its present form to historic human manipulation or severe natural disturbances. It is not considered a long-lasting community, but rather is giving way (or succeeding) to another, more natural community as natural ecological processes take their course over the years. May also be called a ‘successional community.’ See also succession.
Synonyms: semi-natural communities
The aging and deterioration of plants.
Late or delayed in developing or blooming. More specifically, it can refer to a pine cone or other seed case that requires heat from a fire to eventually open and release the seed. Quoted from Natural Resources 743 - Definitions. 2009. University of Wisconsin at Stevens Point.
A fine-grained sedimentary rock, consisting of compacted and hardened clay, silt, or mud. Shale forms in many distinct layers and splits easily into thin sheets or slabs. Quoted from The American Heritage Science Dictionary. 2005. Houghton Mifflin Company, Boston.
- Silt loam
Synonyms: silt loams
- Slope aspect
The direction a hill’s slope faces. (The orientation of a slope relative to the four points of the compass.) E.g., a slope with a northerly aspect faces north.
- Slope position
Refers to where something lies on a slope, e.g., high-slope, mid-slope, or low-slope.
- Slope processes
All processes and events by which the configuration of the slope is changed; especially processes by which rock, surficial materials and soil are transferred downslope under the dominating influence of gravity. Quoted from Canada. Ministry of Forests and Range. 2008. Glossary of Forestry Terms in British Columbia, March 2008.
- Soft mast
Seeds that are covered with fleshy fruit, as in holly berries or blueberries.
- Soil profile
- Soil series
A spike of small flowers growing on a fleshy axis, in plants such as skunk-cabbage and Jack-in-the-pulpit. Usually enclosed in a spathe.
Hooded appendage of a plant such as skunk-cabbage or Jack-in-the-pulpit, which encloses the flowering organ (spadix).
- Spring ephemerals
Any of various woodland wildflowers that appear above ground in early spring, flower and fruit, and die or return underground dormant, within a short two-month period. Quoted from Dictionary.com. 2017. Dictionary.com Unabridged. Random House, Inc.
- Stump sprout
Regrowth of a felled tree by means of a sprout arising from its stump.
Synonyms: stump sprouting
Trees in a forest stand that are overtopped by yet taller trees (the canopy). They may be younger specimens of canopy trees, or they may be naturally smaller or more shade-tolerant species. See also layer.
Synonyms: tree understory
- Succeed to
[as in a forest that is ‘succeeding to’ another forest type] Give way to, become.
The sequence of plant communities that develops in an area after large disturbance, from the initial stages of colonization until a long-standing mature natural community is achieved. Many factors, including climate and changes brought about by the colonizing organisms, influence the nature of a succession. Adapted from Dictionary of Biology. 2004. Fifth edition. Oxford University Press.
- Successional canopy trees
Trees such as tulip poplar and pine that are typically the first to establish themselves on cleared or otherwise severely disturbed land. Sun-loving, fast-germinating species such as these form the canopy in the earliest successional communities in the D.C. area.
- Successional community
- Surficial geology
A surficial geology map shows the distribution of all the loose (unconsolidated) materials such as cobbles, gravel, sand or clay which overlie solid bedrock in an area. The surficial deposits are the product of natural geologic processes such as glacier movement or water movement (such as river flood plains), or are attributed to human activity (such as road-fill or other land-modifying features), and may bear no relation to the bedrock beneath. Adapted in part from Maine Geological Survey. 2017.
- Sykesville Formation
A type of acidic bedrock at Rock Creek Park, metamorphic in origin, similar to the Laurel Formation in appearance and origin, but containing a somewhat different suite of exotic inclusions, some rich in base elements. Widespread in the eastern Piedmont between northern VA and MD, and named for the village of Sykesville, MD. Restricted to the west side of the Rock Creek shear zone.
The nearly flat part at the base of a hill slope. It receives deposits of sediment—fine or coarse—that get transported downslope by gravity or other means.
Medium- to coarse-grained intrusive igneous rock containing certain essential minerals, including at least 20 percent free quartz (acidic). Other mineral content varies widely, resulting in rocks that weather to soils of varying but fairly good fertility for plants at Rock Creek Park.
The contour and shape of the land. Quoted from Stewart, K.G. and M. Roberson. 2007. Exploring the Geology of the Carolinas. UNC Press, Chapel Hill, NC.
The process by which water, drawn up from the ground into a plant’s leaves, evaporates into the air through tiny openings in the leaves called stomata. Part of the water cycle.
A stream or river which flows into a larger stream, river, or lake (and not directly into the ocean).
Cloudiness in water, caused by suspended elements.
- Unconsolidated sediments
- Upland terrace gravel
(As used here) Well-rounded, water-polished stones and sand that were likely deposited by a pre-historic river, but can now be found on some ridgetops in Rock Creek Park. See also ancient river terrace.
- Water cycle
See hydrologic cycle.
- Water table
The level below which the ground is saturated with water.
Natural drainage basin; all the land drained by a river or stream and its tributaries.
The breakdown of rock as it is exposed to weather conditions such as heat, water, ice, or pressure, or to chemicals or biological organisms.
Land areas that are wet enough from surface water or groundwater to be saturated at least a good part of the year. Because of the saturated soils, the plants that grow there are different than those in areas of greater elevation.
The uprooting and overthrowing of trees by the wind. Quoted from Merriam-Webster Online Dictionary. 2017. Merriam-Webster Online.
Term for many different distantly-related animals—most of them invertebrates—which have a soft, long body that is round or flattened and typically lacks legs. Adapted from The American Heritage Science Dictionary. 2005. Houghton Mifflin Company, Boston.
- Wrack line
A linear deposit of leaves, branches, mud, and other debris left behind after floodwaters recede, showing the maximum height of the flood. (Technically applied to the seaweed and marine debris left by high tides, but commonly applied more widely to debris from freshwater flooding.)