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Glossary for agroforestry

Compiled and edited by Peter Huxley and Helen van Houten, International Centre for Research in Agroforestry - 1997

saline soil

    1. A soil containing enough soluble salt (sodium chloride) to reduce its fertility.

    2. A non-alkali soil that contains enough salts to interfere with the growth of most crop plants. Conductivity of the saturated extract is greater than 4 mmhos cm –1, exchangeable sodium percentage is > 15, and the pH is usually > 8.5. See also alkali soil

    3. Soil containing high amounts of the sulphates and chlorides of sodium and calcium. Saline soils occur in hot climates, have a typically uneven surface, show little change down the profile and are low in humus. If the sodium salt is carbonate then the reaction can be around pH 9.0. Highly saline soils can contain as much as 1% of salts in the topsoil (that is, up to 250 t ha–1 in the top 120 cm).


    Concentration of dissolved salts in water (g kg–1) when the organic matter has been oxidized, the carbonate converted into oxides, and the bromine and iodine converted into chlorine. See also alkalinity


    A part of a population, consisting of one or more units selected and examined as representative of the whole.  Because of the variability in biological populations, little information is to be gained by measuring just one individual, so a number aretaken to form a 'sample'. The larger this is, the more closely its characteristics (such as the mean) represent the population. See also representative sample, sampling unit

sampling unit

    An individual plot or quadrat. A collection of many such units, each of which is a different small fragment of the community under study, constitutes a sample.


    1. Particles between 2.00 and 0.05 mm diameter, or one of several separates such as coarse or medium sand; a soil textural class.

    2. Mineral or rock fragments that range in diameter from 2.00 to 0.02 mm in the international system, or 2.00 to 0.05 mm in the USDA system.


    1. Begins with the end of the seedling stage and ends when trees reach 10 cm diameter at breast height (dbh), the crowns are well elevated, and usually many of the lower branches have died. See also pole, saw timber, seedling

    2. A loose term for a young tree no longer a seedling but not yet a pole, that is, a few metres high and 2–3 cm in diameter at breast height (dbh), growing vigorously and without dead bark or more than an occasional dead branch.

    3. A young tree, large enough to be above goat height, but still immature and not producing fruit.

sap shoot

    See coppice shoot


    The outer part of the wood of a trunk, in which the sap flows. See also heartwood

saturation vapour pressure

    Maximum possible partial pressure of water vapour in the air or atmosphere at a given temperature. See also saturation water vapour pressure deficit

saturation water vapourpressure deficit

    The degree of 'dryness' of the atmosphere. The difference between the saturation vapour pressure at the existing temperature and the actual vapour pressure. Also termed 'saturation deficit'.


    A grassland with scattered trees, either as individuals or clumps. Often a transitional type between true grassland and forest. Sometimes spelled 'savannah'.

saw timber

    1. Trees of a size and quality suitable for sawing into timber.

    2. Begins at end of the 'pole' stage when height growth falls off and the period of maximum diameter growth begins. Terminates when trees become overmature and die or are cut. See also pole, seedling roundwood


    Of seeds, the abrasion of the seed coat (or fruit coat) by mechanical, chemical or physical (for example, dry heat) means. Usually needed to improve the germination of hard-seeded species. See also pretreatment


    1. A twig, or portion of a twig, of one plant that is grafted onto the stock of another.

    2. Any unrooted portion of a plant used for grafting or budding onto a rootstock. Shoots of woody plants from which scions are cut are called 'scionwood' or, if approprate, 'budwood'.


    A plant that raises itself above other vegetation in the understorey with the aid of thorns or hooks. See also root climber, twiner


    Preliminary comparison of a large number of treatments to evaluate and eliminate obvious undesirable treatments, as in 'wide range provenance screening trials'.


    A vegetation type that is intermediate between forest, bushland and thicket. It implies a poorly productive area.

seasonal plant

    A plant that flowers and completes its life cycle within the duration of a single wet–dry season combination (in equatorial regions). See also annual plant

secondary forestspecies

    See pioneers

secondary production

    1. The production of biomass (by animals, microorganisms or parasitic plants) through the use of primarily produced plant materials.

    2. The production of biomass by heterotrophic organisms (ones that do not photosynthesize), for example, animals. See also primary production

secondary succession

    A succession initiated by an abiotic or biotic agent or agents after the ground has been cleared of its original vegetation.


    Solid material, mineral or organic, in suspension in transport, or that has been removed from the original site by air, water, gravity, or similar agents.


    See gene bank


    The young plant arising from a germinated seed. Trees progress to the sapling stage. A plant grown as a seedling may retain its taproot, unlike one propagated from a cutting, and hence have a differently structured root system.


    1. A convenience term denoting a group of seeds, or their offspring, which will be considered as a unit in an experiment.

    2. An indefinite quantity of seed having uniform quality produced at a specific location and collected from a single crop.

seed orchard

    A tree plantation established primarily for the production of seed of proven genetic quality.

seed source

    See origin, provenance


    The separation of genes or chromosomes of maternal and paternal origin at meiosis (the division of sexual cells).

selected seed

    Seed attested by a recognized certifying agency to be from progenitors previously selected as superior phenotypes for one or more characteristics but on which tests of inheritance are either pending or lacking.


    1. The plant actually selected.

    2. As artificial selection, the choice by the breeder of individuals for propagation from a population. It may be for one or more desired characteristics and be based on the plant itself (phenotypic) or on progeny or relatives (genotypic).

    3. The choosing of individuals or populations with desirable characteristics to obtain genetic improvement.

selection index

    Choosing parents on the basis of several desirable traits. The desirability of an individual, family or clone is judged according to an index value calculated by considering the heritability and importance of every trait.

selection pressure

    The strength of the tendency to eliminate undesirable genotypes or phenotypes, usually expressed in terms of a selection differential or as the portion of total trees that are selected.

selective cutting

    A system of cutting in which single trees, usually the largest, or small groups of such trees, are removed. See also mechanical thinning

selective herbicide

    1. A herbicide that, if used appropriately, will result in control of some plant species without injury to others.

    2. A herbicide that kills only certain groups of plants, for example, 2,4-D, which kills broadleaf plants but not grasses.

selective thinning

    Removing chosen trees, usually so as to give the maximum benefit to those remaining. See also mechanical thinning


    To place pollen from a male flower on a female flower on the same plant; a plant resulting from such pollination. Self-pollination, hence 'selfing'.

selfed line

    See line, self


    1. Inability to produce seed following self-pollination. Sometimes limited specifically to cases in which the inability is due to a pollen-borne gene that prevents pollen tube growth on a stigma having the same gene.

    2. Genetically controlled physiological hindrance to self- fruitfulness. See also pollinator

self-mulching soil

    1. A soil with a high swelling potential in the surface layers so that it cracks into a granular mulch on drying.

    2. A soil with a naturally formed, well-aggregated surface, which does not crust and seal under the impact of raindrops.


    See self


    Inability to produce seeds following self-pollination.

semi-hardwood cutting

    See cutting


    Deteriorative changes of an organ or whole plant preceding death (organ senescence, whole plant senescence). There can also be 'sequential senescence' (leaves along a branch) and 'synchronous senescence' (all at the same time).

sensitivity analysis

    A method of discovering by how much the estimates used in a model can vary without changing the result.

sequential cropping

    1. A pattern of multicropping in which one crop follows another on the same land without any break (continuous cropping = conntinuous land occupancy) or with a break (intermittent cropping = intermittent land occupancy).

    2. Growing more than one crop on the same piece of land with each seasonal crop component being grown during a different time of the year. See also simultaneous cropping

seral species

    See pioneer


    The culture of silkworms (Bombyx mori) for the production of silk.


    In agroforestry, a beneficial attribute (apart from products) brought about by a particular practice, for example, shelter, soil fertility improvement, soil and water conservation.


    Of a leaf, without a petiole (leaf stalk), that is, borne directly on the stem.

shade-bearing tree

    Tree species that will regenerate in shade so is often large seeded. Also known as 'climax species'. See also pioneers, tree temperament


    The falling off and consequent loss of potentially harvestable foliage or fruits. Also called 'shattering'.

sheet erosion

    1. The gradual and uniform removal of the soil surface by water, without forming gullies or rills. See also gully

    2. Removal of a fairly uniform layer of soil.


    An extended windbreak of living trees and shrubs established and maintained for the protection of farmlands over an area larger than a single farm.

shifting cultivation

    Found mainly in the tropics, especially in humid and subhumid regions. There are different kinds; for example, where a settlement is permanent, but certain fields are fallowed and cropped alternately ('rotational agriculture'). In others, whole settlements move and clear new land once the old is no longer productive. Also called 'swidden' (Old English for a 'burnt clearing'), used more to designate the social group, or 'slash-and-burn', so-called because of the operations undergone. See also slash-and-burn system

short-day plant

    A plant whose development is affected by photoperiod, in particular where a process (for example, flowering) is promoted if the plant is subjected to day lengths below (night lengths above) a critical length.

short shoot

    Where there is shoot dimorphism (two kinds of shoots), these are often specialized shoots with greatly compressed internodes, often bearing leaves and usually flowers; not contributing to the overall architecture of the tree.Sometimes called a 'spur'.


    1. A woody plant that remains low and produces shoots or trunks from the base; not treelike nor with a single bole. A descriptive term not subject to strict definition.

    2. A woody perennial plant differing from a perennial herb by its persistent and woody stem, and from a tree by its low stature and habit of branching from the base.


    An open or closed stand of shrubs up to about 2 m tall.


    A term meaning brother or sister, that is, an individual belonging to the same family. 'Half-sibs' have one parent (usually the seed parent) in common. 'Full-sibs' have seed and pollen parents in common. Hence, sibs are progeny of the same parents derived from different gametes.


    See sib

significance level

    The probability that a statistical test will wrongly reject a true hypothesis, for example, the probability of inferring that there is a difference between treatments when there is, in fact, none. Specifically, a significance level of 5% (or = 0.05) implies that there is only 1 chance in 20 that the test will wrongly indicate a real difference.


    1. Forage preserved in a moist condition and prepared by partial fermentation in an anaerobic (airless) environment in silos. The process is called 'ensilage'.

    2. The animal feedstuff resulting from preserving succulent green crops under anaerobic conditions.


    1. Particles between 0.05 and 0.002 mm diameter, or a soil textural class.

    2. Mineral particles that range in diameter from 0.02 to 0.002 mm in the International System, or 0.05 to 0.002 mm in the USDA system.


    A branch of forestry that is concerned with the methods of raising and growing trees. See also dendrology


    The integration of trees with pasture.

silvopastoral system

    Any agroforestry system that include trees or shrubs and pastures and animals. See also forest grazing


    Growing trees as part of a fish-farming enterprise.

simple bud

    Bud containing either leaf or flower primordia but not both. See also compound bud

simple random sample

    Sample selected in such a way that every individual in the population stands an equal chance of being selected. See also representative sample

simulation model

    Any type of model that is described and investigated (usually with the aid of a computer) so as to imitate the essential features and behaviour of a real system.

simultaneous cropping

    A form of multiple cropping where two or more crops (or trees) are being grown on the same unit of land at the same time. See also concomitant, interpolated and overlapping cropping

single-seed descentbreeding method

    A means of advancing populations while preserving genetic variance for later selection. The method uses less labour and space than the backcross and the bulk breeding methods. A single seed is taken from each plant and used to propagate the population. Eventually, pure lines can be generated from existing lines.


    The procedure of removing surplus seedlings or young plants from the clusters (clumps) or close-planted lines in which they have been sown or transplanted, so as to leave each plant with sufficient space for its future needs.


    1. A site within a plant to which particular materials are translocated and then deposited or utilized. Sinks obtain the materials they need from sources, which produce or elaborate them. A knowledge of source–sink relationships can assist with the understanding of whether the growth and yield of a crop are being driven by demand (for example, millet) or by supply (for example, groundnut).

    2. A state variable outside the system boundary, which is not quantified, to which outputs may go.

sink root

    Or 'sinker root'. A root, other than a tap root, that grows straight downward in the soil.

site class

    A measure of the relative productive capacity of a site for the crop or stand under study, based on volume or height (dominant, co-dominant, or mean) or the maximum mean annual increment that is attainable at a given age. See also yield class

site description

    Description of research site with respect to physical and socioeconomic environments and existing cropping systems.

site index

    In forestry, a particular measure of site class, based on the height of the dominant trees in a stand at an arbitrarily chosen age.

size class

    See diameter class, height class


    In forestry, the vegetation (branches and other woody and leafy debris) left on the forest floor after trees have been felled or trimmed.

slash-and-burn system

    1. A kind of shifting cultivation in high rainfall areas where the cropping period is followed by a fallow period during which grass, herb, bush or tree growth occurs.

    2. A pattern of agriculture in which existing vegetation is cut, stacked and burned to provide space and nutrients for cropping; also called 'swidden' cultivation and shifting cultivation.


    In forestry, cutting back the less tough, competing vegetation, for example, ground cover like bracken. A form of clearing.


    The degree of deviation of a surface from horizontal, measured in a numeric ratio, percentage or degrees.


    The semi-liquid animal waste (faeces and urine) that accumulates where animals are confined with little or no bedding. It can be diluted and spread on grassland or crop fields, but there is a risk of spreading salmonella infection. See also farmyard manure, dung

small animal

    An animal of relatively small stature (as compared, for example, with cattle and horses). Includes ruminants (for example, sheep and goats) and, strictly, also many others:  antelopes, gazelles, porcupines, guinea pigs, rabbits, ostriches, poultry, iguanas, turtles, monitor lizards, honeybees, silkworms, worms. Trees and shrubs may play a part in any production enterprise concerning these.


    Usually a farmer who is relatively resource poor, who cultivates or keeps animals, or both, on only a small piece of land, sometimes only a small plot. These farmers may or may not have access to other common land.

small roundwood

    Normally refers to logs of 7 cm maximum top diameter, over bark.

small ruminant

    Commonly refers to a sheep or a goat.

social forestry

    The planting and tending of trees or shrubs for the well-being and betterment of local communities. See also community forestry


    Factors such as marketing facilities, the land tenure system and credit, which influence the cropping systems of a given area.


    1. A surface layer of matted vegetation held together by the roots, rhizomes and stolons of grasses and other herbs.

    2. A piece of turf lifted from a sward.

sod seeding

    Sowing directly into a sward (grass or grass plus weeds) without prior cultivation.


    A term used in the timber trade to describe the wood of most conifers (gymnosperms), as distinct from the hardwood, broadleaved species (angiosperms).

softwood cutting

    See cutting


    1. The superficial part of the earth's crust resulting from weathering of rocks under the combined effect of living beings and climate.

    2. A dynamic natural body composed of mineral and organic materials and living forms in which plants grow. The collection of natural bodies occupying parts of the earth's surface that support plants and that have properties caused by the integrated effect of climate and living matter acting upon parent material, as conditioned by relief, over periods of time. See also edaphic

soil aeration

    The process by which air in the soil is replenished by air from the atmosphere. In a well-aerated soil, the soil air is similar in composition to the atmosphere above the soil. Poorly aerated soils contain more carbon dioxide and less oxygen. The degree of aeration depends on the soil porosity.

soil amendment

    Any material incorporated into a soil to improve its fertility, long-term chemical or physical status, or stability, such as fertilizers (including slow-release fertilizers, trace elements), organic materials (dung, farmyard manure, compost, straw, bark), sand or peat, lime, gypsum, synthetic resins that improvewater-holding capacity, and so on.

soil bulk density

    Ratio of dry weight of a soil mass to its volume.

soil class

    A group of soils having a definite range in a particular property such as acidity, degree of slope, texture, structure, land capability, degree of erosion, or drainage.

soil classification

    The systematic arrangement of soils into groups or categories on the basis of their characteristics.

soil concretion

    See concretion

soil conservation

    A combination of all management and land-use methods that safeguard the soil against depletion or deterioration (loss of fertility) caused by nature or humans.

soil drainage

    See drainage

soil dry weight

    Weight of solid soil particles when all water has been vapourized after heating the particles to 105°C. See also oven-dry soil

soil fertility

    The quality that enables a soil to provide adequate nutrients in a proper balance for specified plant growth, other factors such as light, moisture, temperature and the physical condition of the soil being favourable.

soil horizon

    A layer of soil approximately parallel to the land surface and differing from adjacent layers in physical, chemical and biological properties or characteristics such as colour, structure, texture, consistency, kinds and numbers of organisms, degree of acidity. Soil may consist of an 'O horizon' (of litter; an 'A horizon' (darkened by organic matter, but from which clay or sesquioxides have been lost); a 'B horizon' (subsoil, with natural ground from the A horizon); and a 'C horizon' (little affected by the biological activities). See also soil profile, subsoil

soil moisture deficit

    The difference between the existing soil water status and that which would obtain at field capacity.

soil organic matter

    Material found in soil derived from living matter. 'Fibric' organic matter is the least decomposed and is mainly fibres; it has low bulk density and a fibre content > 60% of the organic volume. 'Hemic' organic matter is intermediately decomposed; 'sapric' is the most decomposed, with the highest bulk density and the least fibre. Other ways of fractionating soil organic matter (such as into 'labile' and 'stable' fractions) are based on treatment with chemical agents, for example, different strength solutions of potassium permanganate. See also humus, organic matter

soil permeability

    The quality of a soil enabling it to pass air or water. See also soil aeration

soil porosity

    The percentage of the soil (or rock) volume that is not occupied by solid particles, including all pore space filled with air and water. The total porosity includes both 'capillary' and 'non-capillary' porosity (capillary refers to the very small pores).

soil profile

    1. A section of two dimensions extending vertically from the earth's surface so as to expose all the soil horizons and a part of the relatively unaltered underlying material.

    2. A vertical section of the soil from the surface through all its horizons into the parent material.

soil reaction

    Degree of acidity or alkalinity. See also pH

soil structure

    1. The combination or arrangement of primary soil particles into secondary particles, normally larger in size.

    2. The combination and arrangement of primary soil particles, units or  peds. The secondary units are classified on the basis of size, shape and degree of distinctness, such as 'crumbly', 'angular', 'granular', 'platey', 'prismatic', 'columnar', 'blocky'.

soil survey

    The systematic examination, description, classification and mapping of soils in an area.

soil texture

    The relative proportion of the various size groups of individual soil particles. 'Fine fraction' is silt and clay-sized particles < 0.05 mm; 'coarse fraction' is the stone, gravel and sand > 0.05 mm. See also clay, loam, sand, silt

soil water content

    The quantity of water in a soil to a stated depth. It can be expressed as a weight fraction (g g–1) or a volume fraction (g ml–1), so that volume fraction = weight fraction x bulk density. See also available water, water-holding capacity

soil water potential

    A measure of the difference between the free energy state of soil water and that of pure water. Technically it is defined as the amount of work that must be done per unit quantity of water to transport irreversibly and isothermically an infinitesimal quantity of water, at a specified elevation and at atmospheric pressure to the soil (at the point under consideration).

soil water storage

    The water retained in the soil, not draining. Soils with a higher proportion of clays usually retain more water than those with a high content of sand, although it may be less available to plants. See also pF

solar radiation

    See diffuse radiation, direct radiation, global radiation

sole cropping

    Crop cultivar grown in pure stands at normal planting density— monoculture. Synonymous with 'solid planting' and the opposite of intercropping.

solid planting

    See sole cropping


    The slow flow of material on sloping ground, characteristic of, though not confined to regions subjected to alternate periods of freezing and thawing.

solifluction soils

    Found in high altitude areas where alternate thawing and freezing causes the soil surface to heave and move. It is difficult for seedlings to establish on such soils.


    The upper and most weathered part of the soil profile; the A and B horizons. (Plural is 'sola').


    1. A state variable outside the system's boundary, which is not quantified and from which inputs are derived.

    2. In crop physiology, a location within a plant that derives and provides particular substances that are used or deposited elsewhere (to sinks). For example, photosynthethizing leaves are a 'source' for carbon assimilates (carbohydrates) required by developing fruits. See also sink

source-identified seed

    Seed attested by a recognized certifying agency as being from the specific seed source (syn: 'standard seed'). See also certified seed

spatial complementarity

    See complementarity


    1. One or more populations, the individuals of which can interbreed but which, in nature, cannot exchange genes with members belonging to other species. A main category (taxon) of taxonomic classification.

    2. A group of similar organisms, capable of interbreeding and more or less distinctly different in geographic range or morphological characeristics from other species in the same genus. See also subspecies,  superspecies

specific combining ability

    See combining ability

specific leaf area

    Area of a leaf per unit leaf weight; expressed as square decimetres per gram. See also net assimilation rate, relative growth rate

specific leaf volume

    Volume of a leaf per unit weight of that leaf. 'Actual leaf volume' compared with the 'specific leaf volume' will give an indication of the amount of air space that there is in any leaf.

spice garden

    See mixed garden

split plots

    A form of layout for experiments in which levels of different factors are applied to different sized plots (for example `plots' and `subplots').


    A shoot from a dormant bud, often at the base of a tree, or from an exposed root or stump (syn: root sucker, 'stump sprout'). A stump with one or more sprouts is called a stool.


    A short shoot.


    A tree dead at the top as a result of injury, disease, or deficient moisture or nutrients.


    1. Of crops, the number of plants per unit of area that survive and grow; sometimes referred to as the 'plant population'. See also community

    2. In forestry, a community of trees possessing sufficient uniformity of composition, constitution, age, spatial arrangement or condition to be distinguishable from adjacent communities, so forming a silvicultural or management entity.

standard deviation

    A commonly used measure of the variability of a set of data; the square root of the variance of a sample. See also variance

standard error

    A measure of the error in an estimated quantity (mean, correlation or regression coefficient), defined as its standard deviation.

standard seed

    See source-identified seed

standing ground

    A sheltered site with facilities for maintaining young nursery stock (often being grown in containers) prior to the plants being planted out in their final position.

state variable

    In simulation modelling, a variable that characterizes the state of the system and directly determines the processes that bring about changes in the endogenous variables.


    1. Any quantity calculated from data.

    2. The characteristics of a sample in some respect. See also parameter


    1. An organ displaying leaves and also conducting water with mineral salts and food. If the stem is herbaceous, it performs a photosynthetic function as well. The places where the leaves arise from the stem between two successive nodes are called internodes. The stem thus consists mainly of internodes (not present in roots) and bears leaves as well as buds.

    2. An above-ground axis (usually) of a plant, which develops from the epicotyl (seedling stem tissue above the cotelydon) of the embryos, or from a bud of an already existing stem or root.

    3. The principal axis of a plant, carrying all the accessory parts such as the branches, leaves and flowers.


    Rainfall captured by the above-ground parts of a tree that flows down the trunk (stem) to the ground (that is, that which is not retained in the bark, which is the 'bark storage factor'). See also intercepted rainfall, throughfall

stem pitting

    A symptom of viral diseases characterized by depressions on the stem of the plant.


    Inability to produce sound (viable) seeds.


    Practices that relate to the care of the land. Usually implies good practices.


    1. A stochastic situation is one in which a given input leads to a number of possible outputs, each with a probability of occurrence. See also deterministic

    2. Having a probability attached to it. A stochastic process is one in which the next event is probabilistically related to previous events.

stochastic model

    A model in which one or more of the functional relations depend on chance parameters and are hence related to a probability distribution.


    1. Part of a plant, usually consisting of the root system, together with a part of the stem, onto which is grafted a part of another plant. See also grafting, rootstock

    2. The available material kept or gathered for planting.


    An indication of the number of trees in a stand, compared with the desirable number for best growth and management, such as 'well stocked', 'overstocked', 'partially stocked' or 'understocked'. Applies also to domestic animals.

stocking rate

    The number of grazing or browsing animals kept on a unit area of land. Usually expressed as livestock units per unit area. It applies to the potential for maintaining animals; the actual number or the livestock units actually being grazed at any time is the 'stocking density'. See also carrying capacity

stock plant

    A plant kept to conserve a selected genotype, which can be multiplied by one form of vegetative propagation or another. Also known as 'nursery stock'.

stock-scion interaction

    The phenotypic effects of the rootstock on the scion (or occasionally vice versa). Scions perform differently when on one rootstock than if on another rootstock or on their own roots. See also phenotype


    1. A horizontal stem at or below ground surface that gives rise to a new plant at its tip. Less commonly, a shoot that bends to the ground and takes root.

    2. An above-ground prostrate (lying on the surface) stem; may form roots at the nodes that come into contact with the ground. See also rhizome, runner


    1. A living stump capable of producing sprouts. Also used to describe a living stump maintained in order to produce cuttings, layers, and so on; hence'stool bed'.

    2. A cut stump from which coppice shoots spring.

stool bed

    See stool

stool shoot

    See coppice shoot


    1. Removal or suppression of apical buds to stimulate the production of lateral branches.

    2. Removing a shoot apex to slow the growth of a plant or to make it branch, a consequence of the removal of apical dominance.


    The air-dried stalks of cereals after removal of the grain.


    1. A group of similar individuals within a variety.

    2. A group of plants, related by common descent, differing in some aspects from the main body of the species. In forestry the exact content of a strain is less well defined than is that of most other subspecific categories. See also cultivar, provenance


    In ecology, the mechanisms by which an organism's genotype is preserved. See also k-strategy, r-strategy, tree temperament


    1. A pregermination treatment to break dormancy in seed and to promote rapid, uniform germination. The seeds are exposed to moisture at a temperature just above the freezing point (1–5oC) for a specified time.

    2. Arrangement of plants in layers, for example, a stratified canopy in a forest.


    Applied to the crown cover arranged in layers corresponding to species or age classes or to the size of a plant as a 'tree layer', 'shrub layer', 'herb layer'. See also canopy, overstorey, understorey

stratified multistagerandom sample

    Or 'stratified random sample'. See also representative sample


    Environmental stress. The effects on plants of a lack or excess of environmental resources (light, water, nutrients), either singly or combined. 'Water stress' includes soil water and the effects of high saturation water vapour pressure deficits. Unsuitable temperatures (high or low) and frost, as well as the effect of wind, either from direct mechanical damage or as the combined effect of exposure, are also factors.

strip cropping

    1. Growing two or more crops simultaneously in different bands wide enough to permit independent cultivation but narrow enough for the crops to interact agronomically. See also zonal agroforestry system

    2. Growing crops in a systematic arrangement of strips or bands to serve as vegetative barriers to wind and water erosion. See also windstrip, barrier hedge

    3. The practice of growing crops in narrow bands along the contour in an attempt to reduce runoff, thereby preventing erosion or conserving moisture.


    Tall planting stock from which the lower leaves have been removed (stripped) to reduce transpiration losses.


    Generally, the basal portion of certain stiff-stemmed plants, particularly cereals, after the top portion has been harvested. More particularly, that portion of range plants remaining after browsing or grazing is completed. See also stover

stubble mulching

    1. Leaving the 'stubble', that is, the remains of the bottom part of the stalks of a cereal crop (usually after mechanical harvesting), to protect the soil. See also zero tillage

    2. Leaving crop residues in place on or partially incorporated into the soil, after harvest and before and during preparation of the seedbed.


    1. Planting stock in which the shoot and root have been cut back (usually by some 2–3 cm for the shoot and 10–20 cm for the root) to produce an easily transported propagule. See also grubbing out, propagate

    2. The remaining, short part of a stem or branch that has been cut. Often refers to that part of a trunk left after a tree has been coppiced.

    3. To clear an area of tree stumps by grubbing them out.

stump sprout

    See sprout


    In forestry, a subdivision of a compartment, in which there is a difference in the tree crop that makes it suitable for different management treatment.


    One of two or more groups of closely related species that together comprise a genus.


    A subset of a natural or artificial breeding population. Artificial subsets may be developed for different sites or characters. See also variety

subsistence farming

    Growing crops and, where appropriate, keeping animals so as to provide food (cereals, pulses, vegetable and fruits), shelter materials, and possibly other products (fibres, medicinals) for the use of the family. See also cash cropping


    The B horizon of soils with weak profile development. Incorrect although common terminology, inherited from the days when soil was seen only as a ploughed layer, defines it as the soil below plough depth in which roots normally grow. See also soil horizon, B horizon, topsoil


    A geographically localized subdivision of a species, genetically and morphologically distinguishable from other subspecies, described according to taxonomic rules, and given a Latin name. A subspecies tends to be larger than a taxonomic variety but there is no clear distinction between the two. See also cultivar, variety


    Often used to describe any part of a system contributing to the same output as the system itself.


    Following on in order, for example, in ecology when certain species replace others or, as in 'crop succession', where the same or several different types of crop are sown one after the other at suitable times. See also sequestral cropping


    1. A shoot arising from below ground level.

    2. Lateral underground shoot that leaves the roots or rhizome and forms roots itself, making an independent individual plant.

superimposed trial

    A small set of experimental treatments superimposed on a farmer's production plot, or the fields of a cropping pattern trial at a research site, to evaluate the performance of alternative component technologies. These trials are usually managed by the researchers.


    A taxonomic category comprising two or more species deemed to be sufficiently closely related and of such recent evolutionary divergences to comprise a taxonomic category not far above that of species.

surface-active agent

    A substance that, when added to a liquid, affects the physical properties of the liquid surface. Can be used for increasing the wetting properties of sprays and for formulating emulsifiable concentrates and wettable powders.


    1. A basic tool for sociology. Survey procedures produce standard guidelines for the use of tools, such as types of interviews and samples, which are intended to increase the validity and reliability of data.

    2. A systematic method for obtaining quantitative information on characteristics of a large sample (of farms); nearly always done through interviews and measurements (for example, of fields).

    3. An investigation (for example, of farms or individuals) in which the sampling procedure and the measurement process (for example, questionnaire) are fixed in advance and are the same for the whole sample.


    See sustainable development, sustainable land use

sustainable development

    The management and conservation of the natural natural base, and the orientation of technological and institutional change, in such a manner as to ensure the attainment and continued satisfaction of human needs for present and future generations. It conserves land, water, plant and animal genetic resources, is environmentally non-degrading, technically appropriate, economically feasible and socially acceptable.

sustainable land use

    Land use that achieves production sufficient to meet the needs of present and future populations while conserving or enhancing the land resources on which that production depends.

sustained yield

    In forestry, the annual volume of wood products that a forest can produce continuously under a given system.


    1. A grassy surface of a lawn, pasture or playing field, not necessarily a pure stand.

    2. A grassed area composed of short grasses giving a continuous cover, with no trees or shrubs present.


    See shifting cultivation, slash-and-burn system


    Development of a lateral branch without a period of dormancy, that is, contemporaneous with its parent axis; hence sylleptic branch, a branch developed by syllepsis. See also prolepsis

sylvopastoral system

    An agroforestry land-use system for the concurrent production of trees and animals that graze or browse or both.


    One of the partners in a symbiosis.


    A mutually beneficial relationship between two living organisms of different species, living closely together. Fungus and algae that form a lichen, or nitrogen-fixing bacteria living in roots are examples of symbiosis. The individual organisms are called symbionts.


    'Living together'. An association of two different organisms that live attached to each other, or one as a tenant of the other, and contribute to each other's support. See also commensalism


    Occurring in the place; inhabiting the same area. Having overlapping distributions.


    The study of groups of organisms that are associated as a unit. The emphasis may be on the fit of one organism into the system, on the relationships between organisms, or on the whole system as a unit. See also autecology, genecology


    In plant pathology, the concurrent parasitism of a host by two pathogens in which the symptoms or other effects produced are  of greater magnitude than the sum of the effects of each pathogen acting alone.


    'Working together' or 'cooperating'. In biology, where one organism (or organ) acts with another (or others) to achieve greater results than the sum of their efforts as individuals.


    See fertilization


    1. A variety produced by crossing among all of a number of genotypes selected for good combining ability in all possible hybrid combinations, with subsequent maintenance of the variety by open pollination.

    2. In agronomy, a cultivar produced by the combination of selected lines and thereafter propagated as one variety. See also composite variety


    1. An arrangement of components (or subsystems) that process inputs into outputs. Each system consists of boundaries, components, interactions between components, inputs and outputs.

    2. A part of that which can be distinguished from its surrounding environment by either physical or conceptual boundaries. It is composed of interacting parts.

    3. A number of components linked together for some common purpose or function; for example, an 'agricultural system', or an 'agroforestry system'. See also practice

systematic design

    An experimental design laid out with no randomization of treatment plots within a replication, for example, a fan design or a fertilizer trial in which adjacent plots have gradually increasing spacing or rates of application. See also parallel row design

systematic sampling

    A sample consisting of units selected in conformity with some regular pattern, for example, the sample formed from every 10th tree in a row or from the intersections of a regular grid. See also representative sample

Systeme Internationale

    An internationally agreed set of units and procedures consisting of 7 base units (metre, second, kilogram, kelvin, ampere, candela, mole), 2 supplementary units (radian, steradian) and derived units. Commonly called SI units.


    Found throughout the whole plant. As with soil- or leaf-applied herbicides or insecticides that are translocated to all the other parts. See also contact herbicide, translocated herbicide

systems analysis

    The orderly and logical organization of data and information into models, followed by the rigorous testing and exploration of the models necessary for their validation and improvement.

systems approach

    Studying a system as an entity made up of all its components and their interrelationships, together with relationships between the system and its environment.

University of Georgia The Bugwood Network Forestry Images   The Bugwood Network - The University of Georgia
College of Agricultural and Environmental Sciences and Warnell School of Forest Resources
Copyright 2004. All rights reserved.       Page last modified: Wednesday, August 8, 2001
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