The following is a list of terms for which students have, over the years, requested definitions. The definitions themselves have been developed in part by students in classes at the University of New Hampshire. You may also download this list as a Word document.

A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
Above-ground Net Primary Production (ANPP) - Net production of plant biomass above ground only, excluding roots.

Acacia - Shrubs or small trees often associated with symbiotic nitrogen fixation. An important part of the woodlands are of the Serengeti, found in the wetter northern and western areas. Susceptible to being knocked down by elephants.

Actinomycetes -A group of filamentous bacteria that exhibit traits intermediate between simple bacteria and true fungi.

Active Nutrients Uptake -Active transport of elements from soil solution into roots through protien channels across membranes. Requires energy, so places a demand on carbohydrate resources of the plant.

Aerodynamic Roughness - This describes how an object (e.g. a leaf) or a structure (e.g. a canopy) interacts with the atmosphere. The more irregular the surface, the greater the aerodynamic roughness and the greater the turbulence in the air flow over that surface. In canopies, greater aerodynamic roughness leads to greater mixing of air down through the canopy.

Affinity - In terms of plant physiology, generally an expression of the potential rate of nutrient uptake by roots. A high affinity process takes up nutrients rapidly when concentrations are high, a low affinity process is more effective at acquiring nutrients when concentrations are low.

Aggrade - Build; to build up as in the increase the nutrient storage within an ecosystem.

Aggrading Phase - A stage in ecosystem development, where the rate of plant biomass accumulation increases and losses of limiting nutrients approach zero.

Agroforestry - Permanent agriculture using either woody plants for crop production or a combination of woody and herbaceous vegetation that is designed to mimic the structure and function of natural systems.

Albedo - The fraction of electromagnetic radiation reflected back into space after striking a surface (and therefore not affecting temperature of the atmosphere). The average albedo of the earth to sunlight is about 30%, the result of a combination of many different surfaces and the ability of each surface to reflect electromagnetic radiation. Water at noon has an albedo of 5%, fresh snow about 80%, and deciduous forest - 20%.

Allelopathy - The production and exudation of compounds harmful to other species or their function.

Alpha Diversity - The number of species per small, local area.

Ambient - The surrounding environment; designating or pertaining to the immediate surroundings, as in ambient temperature.

Amorphous - Materials that lack adequate crystal orientation to diffract x-rays.

Apical Bud - The bud at the growing tip of a branch or stem.

Apparency Theory - suggests that quantitative inhibitors will predominate n species that are long-lived or occur in high densities over large areas. Alternatively, rare species, or those that are important for only short periods during the development of the plant community, gain a measure of defense by being hard ot find.

Arbuscles - Sac-like structures associated with endomycorrhizae, that penetrate into plant cells.

Arthropod - Any of numerous animals of the phylum Arthropodia including: insects, crustaceans, arachnids, and myriapods; that are characterized by a chitinous exoskeleton and a segmented body to which jointed appendages are articulated in pairs.

Asymptote - The upper or lower bound to a relationship that is approached continuously, but never reached. Photosynthetic response curves approach Amax asymptotically.

Asymptotic - Describing a reaction or activity that approaches, but never reaches, a given value - the asymptote.

Atmospheric Deposition - Inputs to ecosystems from the atmosphere through precipitation, dry deposition, and cloud deposition. Generally does not include direct uptake of gases such as ozone.

Atoll - A coral island consisting of a reef surrounding a lagoon.

Attenuation - Reduction in intensity over space or time, such as the attenuation of light down through a canopy.

Autotrophs - Organisms which supply their own energy - primary producers (plants)

Axiomatic - Fundamental fact upon which other concepts are constructed.

Base Saturation - The fraction of cation exchange sites that are occupied by nutrient cations (e.g. calcium, magnesium, potassium, ammonium), or not occupied by acid cations (aluminum, hydrogen).

Beta Diversity - Change in species composition across a landscape from one area to another.

Biocide - A substance, such as a pesticide or an antibiotic, that is capable of destroying living organisms. Heavy metals present in soil organic mass interfere with important biochemical reactions, thus acting as general biocides.

Biomass - The mass of biologically produced materials in a defined component of an ecosystem. Can be applied to the mass of both live organisms (live biomass) and detritus formed from dead materials (dead biomass or necromass).

Boreal Forest - Northern forest characterized by evergreen conifers and long winters. Found in the northern parts of North America, Europe, and Asia.

Browse - (noun) Leaves and twigs of certain woody species which are consumed by mammalian herbivores. (verb) To eat leaves and twigs of woody species.

Caliche - A cement-like layer of deposited calcium carbonate found usually in subsoils in desert climates.

CAM - See Crassulacean Acid Metabolism

Canopy Phenology - The Timing of leaf production and loss

Carbon cost-nutrient gain ratio - A unitless measure of efficiency, expressing the photosynthetic cost expended per unit of acquired nutrient. Very few measurements of this ratio are available.

Carbon quality - Determined by the types of bonds in decaying organic matter and the amount of useable energy released by decay. Simple carbohydrates and amino acids have high carbon quality. Lignin and suberin have low carbon quality.

Carbon/Nutrient Balance Theory - Species can shift from C to N based defense compounds depending on the relative availability of C and N to plants.

Carbon-Use Efficiency - measurement of the ratio of nitrogen uptake by microbes per unit carbon processed

Carboxyl - The univalent radical, COOH-, the functional group characteristic of all organic acids.

Carboxylation - is the process that fixes carbon dioxide in plants

Catena - The topographic position of soils across a hill slope, usually related to changes in soil drainage classes as well as soil depth, texture and nutrient availability.

Cation - A positively charged ion.

Cation Exchange Capacity - The total quantity of positively charged ions which can be held on soil colloid surfaces by relatively weak electrostatic forces; the total negative charge on soil colloids.

Cation Pump Species - Species which take up relatively large amounts of nutrient cations, have high concentrations in tissues and create cation-rich upper soil horizons.

Caveat - A warning or caution.

Cellulose - A complex carbohydrate, (C6H10O5), that is composed of glucose units, forms the main constituent of the cell wall in most plants, and is important in the manufacture of numerous products; such as paper, textiles, pharmaceuticals, and explosives.

Chaparral - A type of plant community occupying regions with a semi-arid (often Mediterranean) climate and dominated by a mix of evergreen and drought-deciduous shrubs.

Chelation - Chemical binding of metals by organic compounds. Especially important in soil chemistry and the formation of Spodosols. Decreases the chemical reactivity and increases the mobility of iron and aluminum in soils.

Chinampas - A sustainable agricultural practice that was used in Pre-Columbian Meso-America and continues to be used today. Agricultural plots are surrounded by ditches in which water, sediments and nutrient run-off accumulate. Contents of ditches are periodically piled back on the plots. This preserves nutrient content and increases the organic matter content of soils.

Chitin - A nitrogen-rich compounds found as a structural material in the exoskeletons of insects and in fungal hyphae

Chlorosis - The loss of chlorophyll resulting in a yellowing of normally green foliage, often as a result of disease or nutrient deficiency.

Climax - the end-stage of a series orderly changes in species composition called succession.

Closed Cycle - A closed system, cycle, or process is one in which inputs and outputs of mass or energy are small relative to the system's content. For example, many terrestrial ecosystems have closed nitrogen cycles because inputs (precipitation, fixation, etc.) and outputs (leaching of nitrate, denitrification, etc.) are only a small fraction of the nitrogen stored in plant biomass and soil organic matter. See Open Cycle.

Colloids - In soils, small particles with very high surface-to-volume ratios formed by the combination of organic and mineral materials. Surface characteristics of soil colloids determine the physical and chemical characteristics of soils.

Compensation Point - The light intensity at which respiratory loss equals photosynthetic gains in leaves - when net photosynthesis is zero.

Condensation - In the context of the formation of soil organic matter, the chemical combination of smaller molecules to form larger, more amorphous ones. For example, proteins and tannins can condense to form larger molecules which are highly resistant to decomposition.

Conductance - The degree to which leaves are open to the atmosphere. The inverse of resistance. Gas exchange in leaves is a product of conductance times the concentration gradient between the atmosphere and internal leaf spaces.

Conduction - the transmission of energy through material as a function of the gradient in temperature from one side to the other and the material's ability to conduct heat.

Continental climate - a climate with pronounced weather extremes due to the minimal effects of moderating marine air masses, as experienced in the circumpolar taiga.

Convection - The loss of energy from a heated surface by the warming of adjacent air that then is removed by turbulent air flow.

Correlation - A statistical description of the relationship between two variables.

Crassulacean Acid Metabolism (CAM) - A process for minimizing transpiration by taking up CO2 at night and closing the stomates during the day. At night, stomates are open, CO2 enters and is fixed into a C4 acid and stored. During the day, sunlight is used to convert the acid to carbohydrate.

Critical Load - The level of deposition above which substantial negative changes in ecosystem state or function would occur.

Crown fires - Forest fires that reach into the crowns of the dominant trees, burning live foliage, branches, and stems, as well as the forest floor. Crown fires are much hotter than are surface fires and can kill a large proportion of the dominant trees in the system.

Cumulative Leaf Area Index - The total surface area of leaves per unit of ground area computed from the top of the canopy to a specified depth (height above the ground).

Cutin - Waxy, water-repellent substance present in the outer waxy layer in plant leaves which reduces evaporation and protects leaf surfaces.

Dark Respiration - Loss of CO2 by plants at night.

Decadent - In forests, slow growth due to overstocking, nutrient limitations, or other conditions.

Deciduous - Plant for vegetation type that loses all leaves at some point in the year.

Decomposition - The biochemical processes by which litter is transformed into soil organic matter. Occurs through the production of enzymes by the microbial community that break chemical bonds formed during the construction of plant tissues.

Degree Days - A cumulative measure of temperature calculated as the mean daily temperature minus an index temperature (often 0c) summed over a month or year.

Denitrification - The transformation of nitrate (NO3) into gaseous forms of nitrogen, especially nitrogen gas (N2). Nitrous oxide (N2O) and nitric oxide (NO) are also produced. Inhibited in the presence of oxygen.

Density Fractionation - A method of separating soil organic matter based on its degree of sorption to mineral material by flotation in fluid of known bulk density. Colloids with little organic matter will have a greater bulk density than pure organics or organic-rich colloids. The former will sink in the fluid, and the latter will float.

Dentrification - Anaerobic process by which nitrate is reduced to nitrous oxide (N2O) and dinitrogen gas (N2).

Depletion Zone - Areas in soils directly around active root or mycorrhizal tissues in which available nutrients have been depleted by uptake.

Desorption - The opposite of sorption (see definition below).

Differentiation - The process by which a cell uses its resources to produce alternative products; in the context of physiological theories of herbivore inhibition and general theories of nutrient cycling, differentiation is used to explain the alternative allocation of plant resources to production versus herbivore defense.

Diffuse Radiation - Energy reflected off clouds, water vapor, and atmospheric gases and particles. In contrast to direct beam radiation, does not create a shadow. A major form of energy input to

Direct Nutrient Cycling - Uptake of nutrients in organic form, such as nitrogen in the form of simple amino acids.

Dolomite - A mineral found in broad layers as a compact limestone. Contains both calcium and magnesium carbonates

Down-regulation - Physiological adjustments in photosynthetic capacity to match the ability of plants to use the carbon-fixed.

Drought Stress Indicator - The ratio of actual evapotranspiration divided by potential evapotranspiration suggests the extent to which photosynthesis is limited by water stress.

Ecophysiology - the study of the interactions between the physiological processes of living organisms and their environment.

Ecotones - Areas of mixed vegetation that grade into other vegetation types as environmental factors change continuously across the landscape.

Ectomycorrhizae - A form of root-fungal symbiosis. The fungus forms large mats called the Hartig net over the infected root tips. Hyphae penetrate the outer cell layers and extend into the soil, forming a bridge for nutrient transport. Ectomycorrhizae can survive in the soil outside the symbiosis (facultative symbionts) and are thought to increase the uptake of ammonium and organic forms of N.

Eddy Covariance - A method to determine the net CO2 exchange of an ecosystem by the repeated, rapid and simultaneous measurement of CO2 concentration and three dimensional wind speed at a point above the ecosystem canopy.

Efflux - Flux of water, elements or gases out of an ecosystem, or ecosystem component (e.g. soils).

End Product Inhibition - Reduction in the rate of a process because of the accumulation of the end product of that reaction.

Endomycorrhizae - See vesicular arbuscular mycorrhizae (VAM).

Enigma - A puzzling or inexplicable occurrence or situation

Epiphyte - an organism that grows upon another organism, but is not parasitic. Some epiphytes have specialized roots to prevent water loss. Examples of growth forms that can be epiphytes include orchids and mosses.

Episodic- occurring sporadically

Epoch - A period in time marked by particular events and features.

Evaporite - a combination of elements (calcium carbonate, salt, etc.) deposited in subsoils of arid climates as a result of water evaporation. The area of the deposit is usually at the base of the wetting front.

Evapotranspiration - The sum of water lost to the atmosphere by evaporation from the soil surface (evaporation) and through plant tissues (transpiration). Actual evapotranspiration (AET) is often compared with Potential evapotranspiration (PET) to determine the degree of water stress on plants.

Exponential - increasing or decreasing at an increasing rate

Extracellular Enzymes - (in soil microbes) digestive enzymes secreted by microbes into soil solution to breakdown (break chemical bonds) of fresh litter and soil organic matter.

Exude - Emit through small openings, in ecosystems, usually refers to root exudation, the release of a variety of organic compounds into the rhizosphere.

Fallow - Land left unseeded during a growing season or plowed but left unseeded.

Fire Frequency - the amount of times a fire will return to a particular spot.

Fire Intensity - How hot, and how long a fire burns in one location or place.

Fire Ladder - Understory vegetation that creates a path by which a surface fire can travel up into the crown of a forest.

Fire Regime - The frequency, intensity and type of fires, which occur in an ecosystem.

Fixed Charge Clays - In general, 2:1 clays that have a net negative charge that is not changed rapidly by the pH or chemistry of the soil solution. Negative charge results from isomorphic substitution.

Fodder - Feed for livestock, especially coarsely chopped hay or straw.

Fractionation - The result of discrimination against one isotope of an element during a process. Generally, reactions discriminate against the heavier isotope so that the heavier isotope becomes more abundant in the residual material and less abundant in the product of the reaction.

Fugitive Strategy- This regeneration strategy is dependent on light seeds able to travel relatively long distances to disturbed sites (openings) favorable for resource demanding species.

Fundamental Niche - The portion of a set of resource gradients (e.g. light, temperature, nutrient availability) in which an organism can survive in the absence of competition (see also Realized Niche).

Fungal Hyphae - Very fine filaments produced within soils by fungi through which exchanges of nutrients and organic products occur.

Gap Phase Replacement - A species whose continuous presence in a forest community depends on the regular occurrence of openings, whose timing (occurrence) does not surpass its longevity (life span). Species that move into open canopy spaces caused by the death or blowdown of a large individual tree.

Giant Cylinder Method - An experimental design in which an entire section of a tropical forest was enclosed in a large plastic cylinder for the measurement of CO2 exchange with the atmosphere.

Gibbsite - A mineral dominated by oxides of aluminum formed as a product of laterization in

Glucose - 1. A monosaccharide sugar, C6H12O6, occurring widely in most plant and animal tissue. It is the principal circulating sugar in the blood and the major energy source of the body.

Gradient - Any continuos change in an environmental parameter over some distance or over time.

Grazing - the ingestion of grass by herbivore mammals.

Ground Fire - Generally a slow burning fire that effectively consumes accumulated surface organic matter and can burn below ground (disappear) and reappear at another location.

Growth/Differentiation Theory - The conversion of simple carbohydrates and amino acids in plants into new growth cells or into specialized cell constituents, including herbivore defense compounds, that differentiate cell functions.

Half-Saturation Concentration - Generally used as part of the Michaelis-Menten uptake equation, or with photosynthetic response curves. The concentration of nutrients or intensity of light at which nutrient or CO2 uptake is one half of the maximum rate.

Hartig net - Large mats of hyphae produced by ectomychorrhizae that sheath the infected root tips.

Hematite - A mineral dominated by oxides of iron. Accumulates in E horizons in tropical soils

Hemicellulose - Polymers consisting of several different basic sugar units combined into both straight and branched chains

Herbivory - the consumption of live tissue by animals

Heterocyclic Compounds - phenolics combined with amino groups

Heterotrophs - Organisms that require organic compounds produced by others as an energy source.

Hi-grading - The selective removal of trees which are the most valuable due to species or growth form. This practice can degrade the stand or lead to local to regional extinction of preferred species, and is of particular concern in the American Tropics.

Histosol - One of the great soil groups. Histosols consist of an organic soil layer over rock or permafrost.

Hole in the Pipe Theory - A theory which predicts that a measurable fraction of nitrogen is outgassed as nitrous oxide and nitric oxide during the processes of nitrification and denitrification.

Holocellulose Lignin Quotient (HLQ) - The ratio of cellulose to cellulose + lignin; the higher the lignin content relative to cellulose (i.e. the lower the HLQ), the slower the decomposition occurs.

Homeostasis Hypothesis - According to the homeostasis hypothesis, an ecosystem that undergoes a disturbance will demonstrate increased productivity due to greater resource availability. This increase in productivity following disturbance is considered an effective strategy of ecosystem stability.

Homeostatic - Tendency of a system to maintain internal stability, owing to the coordinated response of its parts to any stimulus tending to disturb its normal condition.

Humin - portion of soil organic matter left over after separation by alkali and acid solutions. Considered highly polymerized with high molecular weights high carbon content, low oxygen and low exchange capacity.

Humus - A complex and amorphous form of organic matter in ecosystems characterized by high molecular weight polymers with high content of phenolic rings & side chains; low C:N, and low cellulose/hemicellulose content compared to plants. Litter decays and becomes humus (also called soil organic matter).

Hydrocarbon - Any of numerous organic compounds, such as benzene and methane, that contain only carbon and hydrogen.

Hyphae - The threadlike elements of the mycelium in fungi

Immobilization - Mineral nutrients that are taken up by an organism or one group of organisms and are therefore made unavailable to other organisms.

Immobilization-mineralization - phases of the litter decomposition process; immobilization is the increase of nutrient's amount; while mineralization is the complementary phase beginning when carbon quality declines to the point that nutrient availability is no longer limiting to microbial activity.

Insular - of or pertaining to an island; isolated.

Ion Depletion Zone - See Depletion Zone.

Ion Exchange Capacity- The total ionic charge that can be held in a soil. The number of positively or negatively charged sites in a soil body (see Cation Exchange Capacity).

Irruption - A swift, sudden increase in a population due to alterations in food webs through the introduction or removal of species, or to stagnation of a dominant species.

Island Biogeography Theory- Theory that explains the decrease in the number of species with decreasing island size and increasing distance from the mainland.

Isoelectric point- the pH at which the surface of a clay particle changes from a net positive to a net negative charge .

Isomorphic Substitution - One form of chemical modification in 2:1 layer clays, where a cation of higher valence is replaced with another of lower valence between the major structural layers of the clay, creating a net negative charge (a cation exchange site).

Isotherm - Sorption isotherms describe the quantity of an element or ion that will be sorbed onto soil surfaces at a given concentration of the ion in solution.

Isotopes - Atoms of the same element which differ in atomic weight. Divided into two groups - stable and unstable (or radioactive).

k - In models of the light environment in canopies, the extinction coefficient translating LAI into light interception or attenuation.

Lacustrine - Pertaining to a lake or aquatic system.

LAI - Leaf Area Index or the total leaf surface area per unit ground area.

Laterization - In soils, the preferential dissolution and leaching of silicon from iron-aluminum silicates and the accumulation of clays rich in iron and aluminum oxides in the E horizon. Occurs under hot and humid tropical and semi-tropical conditions.

Lava - Magma which has reached the surface through a volcanic eruption. The term is most commonly applied to streams of liquid rock that flow from a crater or fissure. It also refers to a cooled and solidified rock.

Lessivage - The formation and leaching of clays. Primarily the leaching of clay-sized particles down through the soil profile. Occurs mainly under moderate climatic conditions in non-acid soils. Clay fraction dominated by 2:1 clays.

Lignin - Compound in plants that contains unsaturated carbon-carbon bonds, one of the slowest compounds to decay and yields almost no net energy gain to microbes during decomposition; due to the large amounts of energy required to initiate its decomposition. Makes wood woody since it is found on and around cellulose in the cell wall to provide rigidity and strength.

Litter - Senescent plant material. Also the uppermost slightly decayed layer of organic matter on the forest floor.

Loam - A soil composed of a mixture of sand, clay, silt, and organic matter.

Loess - Wind deposited dust; generally thought to be formed by fine dust particles which settled out of pools of glacial melt as the glaciers retreated and was then blown by the wind after evaporation of the shallow glacial melt water bodies.

Lyotrophic Series - A sequence expressing the relative affinity of different cations for cation exchange sites in soils. Ions with higher charge density in the hydrated state (e.g. H+, Al+++) are higher on the lyotropic series than monovalent cations (e.g. K+, NH4+).

Lysimeter - A small plastic tube with a porous ceramic cup at the bottom and a rubber stopper on top. A lysimeter is used to collect water samples from soil.

Macronutrients - Elements taken up in the largest quantities by plants. Generally used as components of important structural or metabolic molecules (i.e. carbohydrates, proteins, chlorophyll, DNA, RNA, etc.), as coenzymes, or to control ionic balances.

Marine Aerosols - Particles evaporated from wind blown sea foam and spray.

Mass Balance - The concept of mass balance is based on the physical principle of conservation of mass. Mass balance is used to estimate a flux within a system that cannot be easily and directly measured, or to check the accuracy of a measured budget.

Matric Potential - A force between water and soil surfaces - soils retain water against pull of gravity because of tendency for liquid water to adhere to particle surfaces.

Melanization - Enrichment of mineral soil with organic matter. Can result from the mixing of organic and mineral horizons by animals or the deep and concentrated growth of roots.

Mesocosm Experiments - Experiments utilizing small and intact samples of a system grown in a manipulated or controlled environment (i.e. the Biosphere II Project).

Microbes - a minute life form; a microorganism, especially bacteria and fungi in soils.

Microbial Carbon Use Efficiency - The fraction of carbon processed by microbes that becomes cell biomass. The rest is converted to CO2.

Micronutrients - Elements required by plants, but in taken up in smaller quantities than the macronutrients. These are used as components of less common molecules or as coenzymes.

Mineralization - The conversion of an element from an organic combination to an inorganic form, as a result of microbial decomposition.

Minirhizotron - A small glass tubes inserted into the soil and coupled with miniaturized camera systems to directly observe root distributions and dynamics.

Monoculture - The management of a large area so that only a single species is grown there. Can apply to forestry of agriculture.

Monospecific- single species

Muskeg - Fragile home for an abundance of plants that thrive in wet, acidic soil. They are composed of decomposing materials at various stages. The water level are close to the surface and can be very deep. Muskegs can form on steep slopes due to the ability of moss to hold water.

Mycorrhizae - The symbiotic association of fungi with the roots.

Mycorrhizal Fungi - Fungi involved in symbiotic associations with plant roots.

Myrica - A widely dispersed genus of shrubs and trees, usually with aromatic foliage. It includes the bayberry or wax myrtle, the sweet gale, and the North American sweet fern. Many species develop root symbiosis for the fixation of nitrogen.

Myrica Faya - Nitrogen fixing species introduced to the Hawaiian Islands; could change the pattern of N & OM accumulation on the Island by vegetating previously uninhabited areas.

Net Ecosystem Exchange (NEE) - The net exchange of CO2 into or out of an ecosystem. The net carbon movement between an ecosystem and the atmosphere. This is the balance between gross photosynthesis and total ecosystem respiration and can be measured directly by the eddy covariance method.

Net Ecosystem Production (NEP)- The total carbon balance of an ecosystem. This differs from NEE by exchanges of carbon compounds other than CO2 with the atmosphere or the hydrosphere (e.g. volatilization of isoprene, leaching of DOC to groundwater).

Net Immobilization - The biotic or abiotic accumulation of nutrients in litter during the decomposition process. Immobilized nutrients are in organically bound forms that are unavailable for plant use.

Net Mineralization - The net release of nutrients during decomposition. Both net immobilization and net mineralization describe the balance between gross mineralization and immobilization.

Net Photosynthesis - Total carbon fixed by plants (gross photosynthesis) minus leaf respiration.

Net Primary Production (NPP) - The production of new biomass by plants; equal to gross photosynthesis minus all plant respiration.

Niche - See Fundamental Niche and Realized Niche.

Niche Packing - The division of environmental gradients by different species. The number of species in a community can be determined in part by how finely they divide resource gradients.

Niche Theory - A general theory describing the co-occurrence of species by their distribution along environmental, resource or disturbance gradients. Species occupying the same physical space must partition resources in different ways.

Nitrification - The oxidation of ammonium to nitrate.

Nitrify - To oxidize ammonium to nitrate.

Nutrient Balance - A measurement of the inputs and outputs of nutrients (carbon, nitrogen, calcium, phosphorous, etc.) in and out of an ecosystem.

Nutrient Depletion Zone - See Depletion Zone.

Nutrient Quality - the nutrient content, and the ease with which those nutrients can be made

Nutrient Use Efficiency - The mass of nutrient required to produce a given quantity of biomass. In practice, this is the inverse of the concentration at senescence or when a tissue is shed by the plant.

Nutrients - Elements required for metabolic function.

Obligate Symbionts- An organism that cannot function unless combined with another organism. Many VA mycorrhizae are thought to be obligate symbionts.

Occlusion - A term used to describe the process by which amorphous soil constituents (usually sesquioxides) encase nutrients yielding them unavailable for plant uptake.

Open Cycle - An open system, cycle, or process is one in which inputs and outputs of mass or energy are large relative to the system's content. For example, many terrestrial ecosystems have open water cycles because inputs (precipitation, etc.) and outputs (evaporation, etc.) are greater than storage (soil water content). See Closed Cycle.

Orographic - In particular the lifting of air masses over large land masses (i.e. mountains) producing increased precipitation on the windward side and decreased precipitation (a rain shadow effect) on the leeward side.

Osmotic Potential - The reduction of free energy of water due to solute/water interactions. Plant cells in leaves maintain turgor by creating osmotic potentials that are more negative than the physical potential resulting from evaporation from leaf cell surfaces.

Oxide - Combination of an element or mineral with oxygen.

Ozone - (O3) reactive gas formed in the troposphere by a complex set of reactions involving NOX, partially oxidized hydrocarbons and oxygen in the presence of sunlight.

Palatable - Edible; consumable as food. Palatability is a function of both texture and indigestible compound content.

Palisade Cells - In leaves of C3 plants, columnar cells arranged near the upper surface containing chloroplasts that carry out photosynthesis.

Paradigm - An example, model, outstandingly clear or typical example

Passive Nutrient Uptake - Nutrients that move into roots without active uptake. Can occur with water uptake, or in response to electrochemical gradients.

Percent Base Saturation - See Base Saturation.

Periodicity - The return time between repeating cycles, as in peak population numbers of an organism.

Permafrost - Perennially frozen subsoil also known as pergelisol.

Permanent Wilting Point - See Wilting Point.

Perturbation - The act of throwing into great disorder, to disturb.

Phenology - The timing of leaf production and loss in an ecosystem - the seasonality of that system.

Phosphatase Enzymes - Enzymes produced by microbes and also by plant roots that catalyze the

Photosynthate - The first products of photosynthesis - simple carbohydrates.

Photosynthetic Capacity - The maximum rate of photosynthesis that will occur under optimal environmental conditions. Generally realted to leaf nitrogen content.

Phreatic - Noting or pertaining to ground water.

Pitch - Highly flammable resins, in both litter and live biomass, of coastal plain pines; promote rather than inhibit combustion.

Plate Tectonics - The movement of the ocean floor which drives the slow migration of continents over the Earth's surface, and a recycling of crustal material through subduction under continents and re-emergence in areas of sea floor spreading.

Podzolization - Process of soil formation common in cool, humid and acidic conditions. Involves the preferential dissolution and leaching of iron and aluminum in conjunction with organic matter from the upper mineral soil horizon (E) which becomes enriched in silicon oxides. Iron, aluminum and organic matter are precipitated in the lower mineral soil (B horizon). A thick forest floor often accumulates over podzolic soils.

Polymer - A compound made of many smaller, repeating units (monomers). Proteins are polymers of amino acid monomers that contain upwards of 10,000 amino acid units.

Precision Farming - The application of scientific understanding of nutrient cycling and hydrology to intensive management of crop production systems with the intention of reducing chemical inputs and pollution generation.

Predator Swamping - See Swamping.

Primary Minerals - Minerals that are chemically unchanged from the original parent material (i.e. they are not chemically weathered).

Primary Pollutants - formed as the direct result of combustion (e.g. NOx, SO2, CO2).

Primary Production - See Net Primary Production.

Q10 Value - The slope of the exponential increase in respiration with increasing temperature; the proportional increase in rate with a 10 degree C increase in temperature. A Q10 of 2 means a doubling of respiration with every 10oC increase in temperature.

Qualitative Inhibitor - Toxins which are effective in small concentrations, but do not affect all herbivores; C and N based inhibitors to protect plants from herbivory. Generally used by short-lived, rare species of rich habitats.

Quantitative Inhibitor - Generalized feeding inhibitors which affect basic energy gain from digestion. Often occur in high concentrations (examples: lignin, cellulose). Generally used by long-lived and dominant species.

Quantum Yield - the efficiency with which incoming light is converted to carbohydrates within a leaf.

Rain Shadow - A region in the lee of mountains that receives less rainfall than the region windward of the mountains.

Realized Niche - A subset of the fundamental niche. That portion of a set of resource gradients (e.g. light, temperature, nutrient availability) in which an organism can survive in the presence of competition, or that portion actually occupied.

Redundancy - In terms of species present in ecosystems, redundancy means that more than one species can carry out a process in a specific way.

Relative Humidity - The amount of water vapor in the air expressed as a percentage of the maximum amount that the air could hold at a given temperature.

Reorganization Phase - A phase in ecosystem development in which disturbance reduces plant uptake and a pulse loss of nutrients occurs, until the vegetation reestablishes itself.

Residence time - The mean period of time that a unit of material remains in a reservoir. It is calculated as the inverse of the turnover rate, or as the quantity in the reservoir divided by inputs or outputs.

Resilience - The opposite of resistance. Resilient systems show a large response to disturbance, but return to initial conditions more rapidly.

Resistance - Resistant systems show relatively little response to disturbance, but may take longer to return to their initial condition.

Resource Availability Theory - Site quality and leaf longevity, rather than apparency determine which type of herbivore inhibitors are produced. Rich sites result in shorter leaf lifespans, increasing value of short-lived qualitative defense compounds.

Resource islands - Enriched microenvironments such as those surrounding plants in semi-arid environments which trap wind born sediments, increasing soil nutrient and water holding capacity.

Respiration - The reverse of photosynthesis; the oxidation of organic compounds with a release of energy used by plants, animal, and microbes to drive their own life processes.

Retranslocation - The withdrawal of nutrients from leaves as they senesce.

Rhizosphere - Zone of soil adjacent to plant roots where microbial populations and actions differ from bulk soil.

Rinderpest - A disease affecting wild and domestic cattle which was responsible for drastic decreases in wildebeest and buffalo populations in central Africa in late 1800's.

Rotation Length - In forest management, the frequency at which harvests occur.

Rumen - The complex digestive organ in ungulates which maintains populations of microorganisms which aid in the digestive process.

Samara - A generally one-seeded, winged fruit that causes seeds to whirl in the air, increasing suspension time and dispersal distance.

Saprotrophs - Organisms that use dead organic matter as an energy substrate.

Secondary Minerals - Minerals formed as products of weathering; derived from primary minerals.

Secondary Pollutants - Pollutants which form from the reaction between primary pollutants and water and other compounds present in the atmosphere.

Sedge - Any rush-like or grass-like plants of the genus Carex, growing in wet places.

Selection Cutting - In forest management, the removal of only selected trees from a stand; intended to minimize disturbance and allow management of species composition.

Senescence - The process of aging, decline or mortality in plants. Leaves senesce before being shed as litter.

Senescent - Plants, or parts of plants, that have completed their life cycle and have ceased to function.

Serotinous Cones - cones that are fire resistant and do not open and shed seed in the same year that they are grown; scales of the cone are bound together by a resin-like substance that softens only at high temperatures accompanying fires. Cones can remain closed and viable on a tree for up to 25 years.

Silage - Fodder prepared by storing and fermenting green forage plants in a silo.

Sinks and Sources - In plants, a sink is a tissue with a high demand for nutrients or carbohydrates. A source is a tissue that has a large supply. Roots are sources for nutrients and sinks for carbohydrates. The reverse holds for leaves. Stems and flowers would be sinks for both.

Slash - The stems and branches left behind by logging operations. This debris returns nutrients to the soil through decomposition, but also has the potential to feed fires.

Soil Colloids - See Colloid.

Soil Organic Matter - See humus

Sorbed - a process by which minerals are retained on the surface of soil particles. This is based on strong surface complexation reactions. Related to the removal of ions from a soil solution resulting in a surface charge balance alteration.

Sorption - The retention of water or chemicals on surfaces.

Sorption Isotherms - A relationship between the concentration of an ion in solution, and the total quantity of that ion that can be sorbed onto soil particles.

Space-for time Substitution - A method that facilitates studies concerned with temporal trends that are impossible to witness in one human life-span. This method examines sites that vary in time since the last disturbance. This approach assumes that the sites only differ in time since disturbance and no other underlying factors unrelated to time.

Species Equitability - Way of defining biodiversity by the number of species present and the importance of each (i.e. total number of individuals or total biomass per species).

Specific Leaf Area - Leaf area/gram leaf mass.

Sphagnum - Any of a genus of mosses that grow in wet acid areas, where there remains become compacted with other plant debris to form peat.

Stability - Many definitions have been offered - none have been universally accepted.

Stagnation - Reduced vigor.

Starches - Complex carbohydrate formed as a polymer of glucose. A means of storing energy for later use.

Static Measure - A one-time measurement of extractable or available nutrients in soils.

Stem-only Harvesting - In forestry, a practice that removes only the low-nutrient-content stems and leaves the high-nutrient branches and leaves on the site to decompose; minimizes the removal of nutrients.

Sterols - Waxy colorless organic solids containing an alcohol group.

Stilt-Rooted - A characteristic of a tree that has germinated on top of an old root mass of a fallen tree, and subsequently sent roots down into the soil to establish itself. As a result, as the fallen tree decomposes and erodes away, the newly established tree is left with exposed roots.

Strontium - A soft, silvery, easily oxidized metallic element that ignites spontaneously in air when finely divided. Strontium is used in pyrotechnic compounds and various alloys. Atomic number 38; atomic weight 87.62; melting point 769 º C; boiling point 1,384 º C; specific gravity 2.54; valence 2. Commonly used in ecosystem nutrient cycling studies as a tracer or surrogate for Calcium.

Suberin - A hydrophobic, slowly decomposing compound in roots composed of both phenolics and hydrocarbons.

Suberized - Fine roots in which suberin has been produced as a secondary wall compound. These roots become dark brown and less flexible.

Succession - Progressive, directional change in the structure of a community.

Successional Models - Successional models emphasize the self correcting mechanisms that tend to move a disturbed system back toward an equilibrium condition. These models are assumed to be driven by negative feedbacks.

Sun Flecks - Small, localized areas where sunlight passes through the canopy and reaches the ground as full, direct sunlight

Surface Fires - Wildfires that burn in the understory of forests, killing shrubs and saplings, but not the canopy trees. Fires often have a short return interval.

Swamping - The synchronized appearance and disappearance of prey. Related to herding, migration or synchronous reproduction, this reduces overall predation. Can apply to animals or seeds.

Symbiosis - A combination of organisms which is beneficial to both (e.g. mycorrhizae).

Synchronous - simultaneous

Synchronous Canopy Senescence - When the leaves fall at once, or within a short period of time.

Synergism (Synergy) - The interaction of elements that when combined produce a total affect that is greater than the sum of the individual contributions.

Systems Analysis - A method of describing and understanding complex interactions among large numbers of processes or components in a generalized way. The focus is on identifying the fundamental units of a system and defining how they interact rather than the internal processes of each unit.

Taiga - Forested area, also known as boreal, which is characterized by cold winters, and short growing season. Located in the higher latitudes of the northern hemisphere. Taiga areas often experience permafrost.

Tannin - Low molecular weight polyphenolics which serve as herbivore inhibitors in plants, and have been used in tanning of leather, production of inks and as astringents.

Terpenoids - Volatile unsaturated hydrocarbons produced by plants (eg. ponderosa pine and other dry forest and shrubland ecosystems) that may chemically inhibit both mineralization and nitrification; may be destroyed by fire.

Territoriality - A social interaction among animals that structures spatial distribution and can reduce reproduction.

Throughfall - Water dropping to the soil surface after passing over canopy leaves.

Tillering - To put forth new shoots from the root or around the bottom of the original stalk.

Tillers - root extensions that allow a plant to invade a new area

Truncated Succession - Theory which states that the progression of an ecosystem to late seral or climax stages is interrupted by repeated disturbances. As a result, climax types are rarely encountered in nature. A good example of this is frequent fire that kills hardwoods in the pine forests of the Atlantic Coastal Plain.

Tuff - Volcanic rock made up of very small fragments compacted.

Turgor - Opposite of wilt. Full of water to the point of remaining rigid (or turgid - swollen or distended).

Turnover Rate - The ratio of inputs to, or outputs from, an ecosystem component divided by the content (stock) of that component. For example the turnover rates of carbon in soils is total litter C inputs divided by total soil organic carbon.

Ubiquitous - being or seeming to be everywhere at the same time

Ungulate - generally, any hoofed mammal. Although the term is no longer used in formal classification, it is still widely applied to a diverse group of placental mammals that are characterized as hoofed, herbivorous quadrupeds.

Vapor Pressure Deficit (VPD) - The difference between the amount of water vapor the atmosphere can hold at a given temperature and the amount actually present. VPD is inversely related to relative humidity.

Vegetative Reproduction - Asexual plant reproduction where plants are formed not from seeds, but from specialized structures of the root, stem or leaf. This is usually accomplished by means of horizontal stems or roots (eg. runners) which allow the plant to spread over a wider area.

Vesicular Arbuscular Mycorrhizae (VAM) - a specialized type of endomycorrhizal fungi having root-like vesicles and sac-like arbuscles which characterize the fungal tissue. They are obligate symbionts, growing actively only in combination with plant roots. The hyphae grow within plant cells and penetrate out through root surfaces into the soil and are associated with increased uptake of nutrients, especially phosphorous.

Volatile Organic Compounds - Low molecular weight compounds produced by plants that can be emitted in gaseous form to the atmosphere. In plants and the ecosystem can serve as stress indicators, chemical by products, or allelopathic compounds.

Volatilization - loss to the atmosphere in gaseous form

Volcanic Island - Islands formed by the emergence of a building volcano above the surface of the ocean.

Water Potential - the free energy of water, or its capacity to do work. Pure water in liquid form at 20 degrees C and atmospheric pressure is defined as having a water potential of zero. Water moves from soil to plant to atmosphere along gradients from high (less negative) to low (more negative) water potential. Matric, physical and osmotic potential are all components of water potential in soil-plant-atmosphere systems.

Water Use Efficiency (WUE) - The ratio of carbon fixed through photosynthesis to the amount of water lost through transpiration.

Weathering - The process by which geological substrates are converted into soils; involves both physical and chemical alteration of the substrate.

Wilting Point - Lowest soil water potential at which plants can extract water. Generally described as -1.5 MPa, but varies for different species.

Zero point of charge - See Isolelectric Point.

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