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Glossary of Terms Used in Agroecology

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 

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abiotic factor A non-living component of the environment, such as soil, nutrients, light, fire, or moisture.

adaptation (1) Any aspect of an organism or its parts that is of value in allowing the organism to withstand the conditions of the environment. (2) The evolutionary process by which a species’ genome and phenotypic characteristics change over time in response to changes in the environment.

agroecology The science of applying ecological concepts and principles to the design and management of sustainable agroecosystems.

agroecosystem An agricultural system understood as an ecosystem.

agroforestry The practice of including trees in crop- or animal-production agroecosystems.

allelopathy An interference interaction in which a plant releases into the environment a compound that inhibits or stimulates the growth or development of other plants.

alluvium Soil that has been transported to its present location by water flow (alluvial soil).

alpha diversity The variety of species in a particular location in one community or agroecosystem.

amensalism An inter-organism interaction in which one organism negatively impacts another organism without receiving any direct benefit itself.

aquaculture the production of food and feed using aquatic agroecosystems.

autotroph An organism that satisfies its need for organic food molecules by using the energy of the sun, or of the oxidation of inorganic substances, to convert inorganic molecules into organic molecules.  Green plants are autotrophs.


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beneficial insects  Beneficial insects are predators, parasites, or competitors of insect pests, helping to regulate pest populations without harm to crops.

beneficials see beneficial insect

beta diversity The difference in the assemblage of species from one location or habitat to another nearby location or habitat, or from one part of an agroecosystem to another.

biogeochemical cycle The manner in which the atoms of an element critical to life (such as carbon, nitrogen, or phosphorus) move from the bodies of living organisms to the physical environment and back again.

biogeochemistry The study of biogeochemical cycling.

biological nitrogen fixation The fixation, by bacterial cells, of atmospheric Nitrogen gas into organic compounds useful for life.  Nitrogen-fixing bacteria exist in the soil and in association and symbiosis with plants or fungi.

biomass The mass of all the organic matter in a given system at a given point in time.

biotic factor An aspect of the environment related to organisms or their interactions.

boundary layer A layer of air saturated with water vapor (from transpiration) that forms next to a leaf surface when there is no air movement.

buffer zone A less-intensively-managed and less-disturbed area at the margins of an agroecosystem that protects the adjacent natural system from the potential negative impacts of agricultural activities and management.

bulk density The mass of soil per unit of volume.


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C3 pathway The most common metabolic pathway for photosynthetic carbon fixation in plants.

A metabolic pathway for photosynthetic carbon fixation that is common in tropical plants that have high rates of growth and photsynthesis and are adapted to high temperatures, high light intensity, low CO2 concentrations and low water availability. C4 metabolism is especially common in grass species.

CAM (Crassulacean Acid Metabolism), a metabolic pathway adapation of certain plants that allows them to take up CO2 at night instead of during the day, greatly reducing transpirational water loss during photosynthesis. This type of metabolism is common in xerophytes.

capillary water The water that fills the micropores of the soil and is held to soil particles with a force between 0.3 and 31 bars of suction. Much of this water (that portion held to particles with less than 15 bars of suction) is readily available to plant roots.

carbonaceous  Rich in carbon.

carbon dioxide compensation point The concentration of carbon dioxide in a plant’s chloroplasts below which the amount of photosynthate produced fails to compensate for the amount of amount of photosynthate used in respiration.

carbon fixation The part of the photosynthetic process in which carbon atoms are extracted from atmospheric carbon dioxide and used to make simple organic compounds that eventually become glucose.

carbon partitioning The manner in which a plant allocates to different plant parts the photosynthate it produces.

catabatic warming The process that occurs when a large air mass expands after having been forced over a mountain range and becomes warmer and dryer as a result of the expansion.

cation exchange capacity (CEC) A measurement of a soil’s ability to bind positively charged ions (cations), which include many important nutrients.  Depends on the amount and type of clay and the amount and humification of organic matter in soil.  Most of the major cation nutrients are held in soil by CEC (calcium, magnesium, potassium).

cellulose The chief component of the cell walls of plants, composed of a long chain of repeating glucose units.  Cellulose can only be digested by bacteria, which often grow symbiotically in the guts of animals like ruminants and termites.

chelation A reaction between a metallic ion and an organic compound that removes the metallic ion from solution.  Chelation is a natural reaction in most soils and is enhanced by organic matter, especially humus.  Chelation is similar to cation exchange, except that it usually is more stable in holding ions.  Most of the trace cation nutrients are held in soil by chelation (copper, iron, manganese).

chromosome Genetic material, composed largely of DNA and protein in the nucleus of cells.

climax In classical ecological theory, the end point of the successional process; today, we refer instead to the stage of maturity reached when successional development shifts to dynamic change around an equilibrium point.

C:N ratio The ratio of carbon to nitrogen in a material.   The decomposition of materials is regulated in part by this ratio, so materials with different C:N ratios are usually mixed to improve decomposition rates in composting. The C:N ratio for optimal biological activity is about 25:1, with higher values being nitrogen limited and lower values being carbon limited. The average C:N ratio for soils is about 10:1.

clone An individual produced asexually from the tissues, cells, or genome of another individual. A clone is genetically identical to the individual from which it was derived.

cold air drainage The flow of cold air down a slope at night, when re-radiation of heat (and therefore cooling of air) occurs more rapidly at higher elevations.

colluvium Soil that has been transported to its present location by the actions of gravity.

commensalism An inter-organism interaction in which one organism is aided by the interaction and the other is neither benefited nor harmed.

community All the organisms living together in a particular location.

Community Supported Agriculture (CSA) A nationwide movement linking local consumers and farmers into communities.  Typical CSA's consist of a group of consumer shareholders that pay a sum in advance in exchange for a regular selection (weekly, biweekly) of in-season crops produced by a farm. 

compensating factor A factor of the environment that overcomes, eliminates, or modifies the impact of another factor.

competition An interaction in which two organisms remove from the environment a limited resource that both require, and both organisms are harmed in the process. Competition can occur between members of the same species and between members of different species.

composite A plant in the Compositae (Asteraceae) family.

compost mixed decayed and decaying organic matter with available nutrients useful for fertilizer.

composting the management of organic materials to produce compost.

consumer An organism that ingests other organisms (or their parts or products) to obtain its food energy.

continental influence The climatic effect of being distant from the moderating effects of a large body of water.

Coriolis effect The deflection of air currents in atmospheric circulation cells due to the rotation of the earth.

cross-pollination The fertilization of a flower by pollen from the flower of another individual of the same species.

CSA see Community Supported Agriculture

cultural energy inputs Forms of energy used in agricultural production that come from sources controlled or provided by humans.

cytosterility A genetically-controlled condition of male sterility in the breeding line of a self-pollinating crop variety. A breeding line with cytosterility is used as the seed-producing parental line in the production of hybrid seed.


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dark reactions The processes of photosynthesis that do not require light; specifically, the carbon-fixing and sugar-synthesizing processes of the Calvin cycle.

decomposer A fungal or bacterial organism that obtains its nutrients and food energy by breaking down dead organic and fecal matter and absorbing some of its nutrient content.

decomposition The process by which materials are broken down into simpler compounds by decomposers.  

density-dependent Directly linked to population density. This term is usually used to describe growth-limiting feedback mechanisms in a population of organisms.

density-independent Not directly linked to population density. This term is usually used to describe growth-limiting feedback mechanisms in a population of organisms.

detritivore An organism that feeds on dead organic and fecal matter.

dew point The temperature at which relative humidity reaches 100% and water vapor is able to condense into water droplets. The dew point varies depending on the absolute water vapor content of the air.

directed selection The process of controlling genetic change in domesticated plants through manipulation of the plants’ environment and their breeding process.

disturbance An event or short-term process that alters a community or ecosystem by changing the relative population levels of at least some of the component species.

diversity (1) The number or variety of species in a location, community, ecosystem, or agroecosystem. (2) The degree of heterogeneity of the biotic components of an ecosystem or agroecosystem (see ecological diversity).

DNA (Deoxyribonucleic acid) The primary genetic material of life, containing two nucleotide chains in a double-helix.

domestication The process of altering, through directed selection, the genetic makeup of a species so as to increase the species’ usefulness to humans.

dominant species The species with the greatest impact on both the biotic and abiotic components of its community.

dynamic equilibrium A condition characterized by an overall balance in the processes of change in an ecosystem, made possible by the system’s resiliency, and resulting in relative stability of structure and function despite constant change and small-scale disturbance.


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easily available water That portion of water held in the soil that can be readily absorbed by plant roots—usually capillary water between 0.3 and 15 bars of suction.

ecological diversity The degree of heterogeneity of an ecosystem’s or agroecosystem’s species makeup, genetic potential, vertical spatial structure, horizontal spatial structure, trophic structure, ecological functioning, and change over time.

ecological energy inputs Forms of energy used in agricultural production that come directly from the sun.

ecological niche An organism’s place and function in the environment, defined by its utilization of resources.

ecosystem A functional system of complementary relations between living organisms and their environment within a certain physical area.

ecotone A zone of gradual transition between two distinct ecosystems, communities, or habitats.

ecotype A population of a species that differs genetically from other populations of the same species because local conditions have selected for certain unique physiological or morphological characteristics.

edaphic of the soil, or influenced by the soil.   For example, some edaphic factors that influence soil organisms are pH, organic matter content, and hydrology.

edge effect The phenomenon of an edge community, or ecotone, having greater ecological diversity than the neighboring communities.

emergent property A characteristic of a system that derives from the interaction of its parts and is not observable or inherent in the parts considered separately.

environmental complex The composite of all the individual factors of the environment acting and interacting in concert.

environmental resistance The genetically-based ability of an organism to withstand stresses, threats, or limiting factors in the environment.

eolian soil Soil that has been transported to its current location by the actions of wind (aeolian is an acceptable alternative spelling).

epiphyll A plant that uses the leaf of another plant for support, but that draws no nutrients from the host plant.

epiphyte A plant that uses the trunk or stem of another plant for support, but that draws no nutrients from the host plant.

evapotranspiration All forms of evaporation of liquid water from the earth’s surface, including the evaporation of bodies of water and soil moisture and the evaporation from leaf surfaces that occurs as part of transpiration.


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FAO see Food and Agriculture Organization.

field capacity The amount of water the soil can hold once gravitational water has drained away; this water is mostly capillary water held to soil particles with at least 0.3 bars of suction.

Food and Agriculture Organization The United Nations organization dedicated to agriculture.

food demand  The amount of food needed to support a given population or individual for a given amount of time.

food system  The interconnected meta-system of agroecosystems, their economic, social, cultural, and technological support systems, and systems of food distribution and consumption.

food security  Can be defined as the "state in which all persons obtain a nutritionally adequate, culturally acceptable diet at all times through local non-emergency sources."

forb   A non-grass, herbaceous species (generally legumes and composites)


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gene The basic unit of inheritance comprising a specific sequence of nucleotides on a DNA chain that has a specific function and occupies a specific locus on a chromosome.

gene flow The exchange of genetic factors within and between populations by interbreeding or migration.

generalist A species that tolerates a broad range of environmental conditions; a generalist has a broad ecological niche.

genetic engineering Transfer, by biotechnological methods, of genetic material from one organism to another.

genetic erosion The loss of genetic diversity in domesticated organisms that has resulted from human reliance on a few genetically uniform varieties of food crop plants and animals.

genetic vulnerability The susceptibility of genetically uniform crops to damage or destruction caused by outbreaks of a disease or pest or unusually poor weather conditions or climatic change.

genotype An organism’s genetic information, considered as a whole.

geographic information system (GIS) A computer-based system for managing and analyzing spatially-referenced data.   Examples include land-use, topographic and soils data.

GIS see geographic information system

glacial soil Soil that has been transported to its current location by the movement of glaciers.

gravitational water That portion of water in the soil not held strongly enough by adhesion to soil particles to resist the downward pull of gravity.

green manure Organic matter added to the soil when a cover crop (often leguminous) is tilled in.

gross primary productivity The rate of conversion of solar energy into biomass in an ecosystem.


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habitat The particular environment, characterized by a specific set of environmental conditions, in which a given species occurs.

hardening Subjecting a seedling or plant to cooler temperatures in order to increase its resistance to more extreme cold.

herbaceous Non-woody.

herbivore An animal that feeds exclusively or mainly on plants. Herbivores convert plant biomass into animal biomass.

heterosis The production of an exceptionally vigorous and/or productive hybrid progeny from a directed cross between two pure-breeding plant lines.

heterotroph An organism that consumes other organisms to meet its energy needs.

horizons Visually distinguishable layers in the soil profile.

host An organism that provides food or shelter for another organism.

host-specificity The extent to which a parasite is restricted in the host species it can use.

humification The decomposition or metabolization of organic material in the soil into humus.

humus The fraction of organic matter in the soil resulting from decomposition and mineralization of organic material.

hybrid vigor The production of an exceptionally vigorous and/or productive hybrid progeny from a directed cross between two pure-breeding plant lines. A synonym for heterosis.

hydration The addition of water molecules to a mineral’s chemical structure.

hydrological cycle The process encompassing the evaporation of water from the earth’s surface, its condensation in the atmosphere, and its return to the surface through precipitation.

hydrolog  The properties, distribution, and circulation of water.

hydrolysis Replacement of cations in the structure of a silicate mineral with hydrogen ions, resulting in the decomposition of the mineral.

hydrophyte A plant that is adapted to grow in water or very wet environments.

hydroxide clay A mineral component of the soil without definite crystalline structure composed of hydrated iron and aluminum oxides.

hygroscopic water The moisture that is held the most tightly to soil particles, usually with more than 31 bars of suction; it can remain in soil after oven drying.


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importance value A measure of a species’ presence in an ecosystem or community—such as number of individuals, biomass, or productivity—that can be used to determine the species’ contribution to the diversity of the system.

inoculum The initial organism or organisms that establish a new colony or population; breeding stock.   The term is commonly applied to the application of small amounts of microrganisms to establish new populations in soils or composts, for example, Rhizobium bacteria are commonly applied as an inoculum to legume seeds at planting time.

insolation The conversion, at the earth’s surface, of short wave solar energy into long wave heat energy.

intermediate disturbance hypothesis The theory that diversity and productivity in natural ecosystems are highest when moderate disturbance occurs periodically but not too frequently.

intercropping Planting more than one crop in a field using a regular pattern that interleaves each crop in some pattern.  A form of polyculture.

interspecific competition Competition for resources among individuals of different species.

intraspecific competition Competition for resources among individuals of the same species.

inversion The sandwiching of a layer of warm air between two layers of cold air in a valley.

Integrated Pest ManagementPest control using an array of complementary approaches including natural predators, parasites, pest-resistant varieties, pesticides, and other biological and environmental control practices.

IPM see Integrated Pest Management.


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K-strategist A species that lives in conditions where mortality is density-dependent; a typical K-strategist has a relatively long lifespan and invests a relatively large amount of energy in each of the few offspring it produces.


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landrace A locally-adapted strain of a species bred through traditional methods of directed selection.  Also called farmer varieties.

landscape ecology The study of environmental factors and interactions at a scale that encompasses more than one ecosystem at a time.

Land Utilization Type (LUT): A kind of land use described or defined in a degree of detail greater than that of a major kind of land use. In the context of irrigated agriculture, a land utilization type refers to a crop, crop combination or cropping system with specified irrigation and management methods in a defined technical and socio-economic setting.  In the context of rainfed agriculture, a land utilization type refers to a crop, crop combination or cropping system with a specified technical and socio-economic setting. A land utilization type in forestry consists of a technical specifications in a given physical, economic and social setting.  Defined by FAO.

leaf-area index A measure of leaf cover above a certain area of ground, given by the ratio of total leaf surface area to ground surface area.

legume A plant in the Leguminosae (Fabaceae) family.   Most species in this family can fix nitrogen.

light compensation point The level of light intensity needed for a plant to produce an amount of photosynthate equal to the amount it uses for respiration.

light reactions The components of photosynthesis in which light energy is converted into chemical energy in the form of ATP and NADPH.

lignin an amorphous polymer related to cellulose that cements cell walls, helping them stay rigid.  Lignin is highly resistant to decomposition.

limiting nutrient A nutrient not present in the soil in sufficient quantity to support optimal plant growth.

living mulch A cover crop that is interplanted with the primary crop(s) during the growing season.

lodging The flattening of a crop plant or crop stand by strong wind, usually involving uprooting or stem breakage.


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macronutrient A nutrient plants need in large quantities; the macronutrients include carbon, nitrogen, oxygen, phosphorus, sulfur, and water.

maritime influence The moderating effect of a nearby large body of water, such as an ocean, on the weather and climate of an area.

mass selection The traditional method of directed selection, in which seed is collected from those individuals in a population that show one or more desirable traits and then used for planting the next crop.

mesophyte A plant that is adapted to environments that are neither very dry nor very wet.  Compare with xerophyte and hydrophyte.

microclimate The environmental conditions in the immediate vicinity of an organism.

micronutrient A nutrient necessary for plant survival but needed in relatively small quantities.

mineralization The process by which organic residues in the soil are broken down to release mineral nutrients that can be utilized by plants.

mountain wind The downslope movement of air at night that occurs as the upper slopes of a mountain cool more rapidly than those below.

multiple cropping The cultivation of two or more crops in succession or with some overlap in the same field within one year.  Double-cropping of rice after wheat is an example.  When crops overlap in time, multiple cropping is a form of polyculture.

mutualism An interaction in which two organisms impact each other positively; neither is as successful in the absence of the interaction.

mycorrhizae Symbiotic fungal connections with plant roots through which a fungal organism provides water and nutrients to a plant and the plant provides sugars to the fungi.


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natural selection The process by which adaptive traits increase in frequency in a population due to the differential reproductive success of the individuals that possess the traits.

net primary productivity (NPP) The difference between the rate of conversion of solar energy into biomass in an ecosystem and the rate at which energy is used to maintain the producers of the system.

NGO see non-governmental organization

niche amplitude The size or range of one or more of the dimensions of the multidimensional space encompassed by a particular species’ niche. The niche amplitude of a generalist species is larger than that of a specialist species.

niche breadth Essentially a synonym for niche amplitude.

niche diversity Differences in the resource-use patterns of similar species that allow them to coexist successfully in the same environment.

niche see ecological niche.

non-governmental organization (NGO) An organization that is not part of a government.  Private foundations and development organizations are examples.

nucleotideA subunit of DNA or RNA molecules, part of the genetic code.


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open pollination The natural dispersal of pollen among all the members of a cross-pollinating crop population, resulting in the maximum degree of genetic mixing and diversity.

organic agriculture Systems of agricultural production that do not use any synthetic chemical inputs.

organic matter  Material containing molecules based on Carbon, usually referring to soil organic matter.

organism An individual of a species.

overyielding The production of a yield by an intercrop that is larger than the yield produced by planting the component crops in monoculture on an equivalent area of land.

oxidation The loss of electrons from an atom that accompanies the change from a reduced to an oxidized state.


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parasite An organism that uses another organism for food and thus harms the other organism.

parasitism An interaction in which one organism feeds on another organism, harming (but generally not killing) it.

parasitoid A parasite that feeds on predators or other parasites.

patchiness A measurement of the diversity of successional stages present in a specific area.

patchy landscape A landscape with a diversity of successional stages or habitat types.

percolation Water movement through the soil due to the pull of gravity.

permanent wilting point The level of soil moisture below which a plant wilts and is unable to recover.

pH The logarithm of the reciprocal of the concentration of hydrogen ions in a medium, like water or soil (log10{1/[H+]}).  pH values range from 0 to 14, giving the relative acidity or alkalinity of a medium, with a pH of 7 being neutral, and lower values being acidic, higher values, alkaline

phenotype The physical expression of the genotype; an organism’s physical characteristics.

photoperiod The total number of hours of daylight.

photorespiration The energetically-wasteful substitution of oxygen for carbon dioxide in the dark reactions of photosynthesis, which occurs when plant stomata close and carbon dioxide concentration declines.

photosynthate The simple-sugar end products of photosynthesis.

polyploid Having three or more times the haploid number of chromosomes.

polyculture Cropping systems in which different crop species are grown in mixtures in the same field at the same time.

population A group of individuals of the same species that live in the same geographic region.

potential niche The maximum possible distribution of a species in the environment.

predation An interaction in which one organism kills and consumes another.

predator An animal that consumes other animals to satisfy its nutritive requirements.

prescribed burn A fire set and controlled by humans to achieve some management objective, such as improving pasture in grazing systems.

prevailing winds The general wind patterns characteristic of broad latitudinal belts on the earth’s surface.

primary production The amount of light energy converted into plant biomass in a system.

primary succession Ecological succession on a site that was not previously occupied by living organisms.

producer An organism that converts solar energy into biomass.

production Harvest output or yield.

productivity index A measure of the amount of biomass invested in the harvested product in relation to the total amount of standing biomass present in the rest of the system.

productivity The ecological processes and structures in an agroecosystem that enable production.

protein A compound formed from a chain of amino acids.   Proteins are present in all living things, and are used for enzymes, hormones and other essential molecules.

protocooperation An interaction in which both organisms are benefited if the interaction occurs, but neither are harmed if it does not occur.


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r-strategist A species that exists in relatively harsh environmental conditions and whose mortality is generally determined by density-independent factors; an r-strategist allocates more energy to reproduction than to growth.

rainfed agroecosystem A farming system in which crop water needs are met by natural precipitation.

realized niche The actual distribution of an organism in the environment (compare with potential niche).

reference man A standard "human unit" for populations, based on the food consumption requirements of a "standard human", most often a male of a certain age and occupation (a holdover, perhaps, but useful for some purposes).  Reference man units, also called "refman" units, are used by nutritionists to estimate the food demand of populations, to account for differing food demand between individuals (babies versus adults, etc.).  Refman units should be used with caution, because some segments of the population, such as pregnant women and developing children, can have specific nutritional demands that cannot be standardized properly by this method.   

regolith The layer or mantle of unconsolidated material (soil and mineral subsoil) between the soil surface and the solid bedrock of the earth below.

relative humidity The ratio of the actual water content of the air to the amount of water the air is capable of holding at a particular temperature.

relative rate of light transmission The percentage of the total incident light at the canopy of a system that reaches the ground.

relay cropping Cropping systems in which two or more crops are grown in sequence in the same field in the same year, with little or no overlap in time.  Not a true form of polyculture because very little interspecies interaction usually occurs in these systems.

renewable resources  Resources that are capable of being regenerated or replaced by ecological processes on a time scale relevant to their use.  These resources, such as biomass or energy from animal traction, are contrasted with non-renewable resources, such as fossil fuels and mined products.

residual soil Soil formed at its current location.

response A physiological change in a plant that is induced by an outside, usually environmental, condition.

Rhizobium A genus of heterotrophic soil bacteria capable of forming symbiotic nodules on the roots of legume plants to fix atmospheric nitrogen.

ruminant An animal with a multiple stomach (polygastric) system of digestion capable of digesting cellulose.


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safe site A specific location that provides the environmental conditions necessary for seed germination and initial growth of the seedling.

saltation The transport of small soil particles just above the soil surface by wind.

saturation point The level of light intensity at which photosynthetic pigments are completely stimulated and unable to make use of additional light.

secondary succession Succession on a site that was previously occupied by living organisms but that has undergone severe disturbance.

seed bank The total seed presence in the soil.

self-pollination The fertilization of the egg of a plant by its own pollen.

Shannon index A measure of the species diversity of an ecosystem based on information theory.

shifting cultivation Farming systems that alternate periods of annual cropping with extended fallow periods.  "Slash and burn" systems of shifting cultivation use fire to clear fallow areas for cropping.

silicate clay A soil component made up primarily of microscopic aluminum silicate plates.

Simpson index A measure of the species diversity of an ecosystem based on the concept of dominance.

slash and burn A type of shifting cultivation that uses fire to clear fallow areas for cropping.

slope wind Air movement caused by the different heating and cooling rates of mountain slopes and valleys.

soil creep The movement of large soil particles along the soil surface by wind.

soil health The capacity of a soil to function within ecosystem boundaries to sustain biological productivity, maintain environmental quality, and promote plant and animal health.  Often used synonymously with soil quality.  

soil profile The set of observable horizontal layers in a vertical cross section of soil.

soil quality Used synonymously with soil health.

soil solution The liquid phase of the soil, made up of water and its dissolved solutes.

solution The process by which soluble minerals in the regolith are dissolved into water.

specialist A species with a narrow range of environmental tolerance.

species evenness The degree of heterogeneity in the spatial distribution of species in a community or ecosystem.

species richness The number of different species in a community or ecosystem.

stakeholders All parties who will be affected by the results of planning decisions.

standing crop The total biomass of plants in an ecosystem at a specific point in time.

stomata The openings on a leaf surface through which gases enter and leave the internal leaf environment.

succession The process by which one community gives way to another.

successional mosaic A patchwork of habitats or areas in different stages of succession.

symbiosis A relationship between different organisms that live in direct contact.

synthetic variety A crop or horticultural variety produced through the cross-pollination of a limited number of parents that cross well and have certain desirable traits.

Swidden agriculture same as shifting cultivation


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thermophilic Thermophilic ("heat loving") organisms grow well under high temperature conditions.  Thermophilic composting is the management of the composting process to maintain high temperature conditions, favoring the destruction of disease-causing organisms.

tilth The combination of the characteristics of soil crumb structure, porosity, and ease of tillage.

transpiration The evaporation of water through the stomata of a plant, which causes a flow of water from the soil through the plant and into the atmosphere.

transported soil Soil that has been moved to its current location by environmental forces.

trophic level A location in the hierarchy of feeding relationships within an ecosystem.

trophic structure The organization of feeding and energy-transfer relationships that determine the path of energy flow through a community or ecosystem.


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Vavilov centers of domestication Areas of the world where crop plants are believed to be originally domesticated from their wild relatives.  Named after the Russian scientist: N.I. Vavilov.

valley wind Air movement that occurs when the heating of a valley causes warm air to rise up adjacent mountain slopes.

vermicomposting Composting systems based on intensive management of worms, usually in specialized containers.

vernalization The process in which a seed is subjected to a period of cold, causing changes that allow germination to occur.


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water of hydration Water that is chemically bound to soil particles.


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xerophyte A plant that is adapted to growing under very dry conditions and extended droughts.


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