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Glossary for agroforestry

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

damping off

    A term used to describe the action of parasitic soil fungi, which cause rotting of seedlings before or soon after germination. This can sometimes be avoided by adding sand to the soil mixture to improve drainage, thus preventing the fungi from multiplying rapidly, or by using fungicides. Eucalypts and pine species are particularly susceptible to damping off.

data matrix

    1. A numerical table in which each column lists all the observations on one sampling unit (or quadrat) and each row lists the values of one of the observed variables in all quadrats.

    2. A rectangular table of data.

day degree

    See degree day

day neutral

    Plants whose phasic changes are unaffected by daylength or night length.

deciduous

    1. Of leaves, bark, and so forth, falling regularly at the end of a growth period, or in the tropics, prior to one.

    2. Of a leaf, falling at the end of one season of growth or life. Of a perennial plant, losing its leaves (or a proportion of them) at the end of a season's growth. See also evergreen, leaf-retaining

deciduous forest

    A forest composed of trees that shed their leaves at some season of the year. In tropical areas trees may lose their leaves during the hot season to conserve moisture. Trees of a deciduous forest in cool areas shed their leaves during the autumn to protect themselves against the cold and frost of winter. Deciduous forests produce valuable hardwood timber, such as teak and mahogany from the tropics, and oak and beech from the cooler areas.

decomposition

    The processes by which organic matter is broken down. See also humus

decumbent

    Having prostrate or creeping stems with upturned tips.

deductive

    Reasoning from the general to the particular (the opposite of inductive).

defoliant

    A chemical which, when applied to a plant, causes leaf fall.

degree day

    Algebraic difference in degrees between the mean temperature of a given day and a reference or base temperature. For a given period the algebraic sum of the degree days. See also cumulative temperature, thermal duration, thermal time

degrees of freedom

    The number of independent comparisons that can be made in a set of data.

demography

    The study or measurement of particular characteristics of a population. Used for human popuations primarily, but sometimes borrowed to refer to the characteristics (such as age) of populations of leaves, for example.

dendrogram

    A diagram showing the relationships produced by classification.

dendrology

    The study of trees, that is, a knowledge of the taxonomy, systematic relationships and field recognition of tree species. See also silviculture

dendrometer

    A device for measuring the diameter of the trunk or branch of a tree.

denitrification

    1. The biological reduction of nitrate to molecular nitrogen or the oxides of nitrogen, resulting in the loss of nitrogen into the atmosphere, and therefore undesirable in agriculture.

    2. The biochemical reduction of nitrate or nitrite to gaseous nitrogen, either as molecular N or as an oxide of N.

densitometry

    The measurement of density. Wood density, for example, is normally measured in kg m–3. Density may be measured by indirect methods, for example, using beta or x-ray analysis.

dependent variable

    See variable

desiccant

    A compound that promotes loss of moisture (for example, from plant tissues). Silica gel or anhydrous CuO are examples.

determinate

    Of a stem, when continuing growth is stopped by the abortion or permanent dormancy of the apical bud. Of an inflorescence, when the terminal flower opens first and thereby arrests axis prolongation (for example, a cyme, a flat-topped inflorescence).

determinate growth

    A pattern of development in which the apical meristem differentiates into flowers, terminating the production of additional leaves and stems.

deterministic

    A deterministic situation is one in which given inputs lead to predictable outputs. See also stochastic

deterministic model

    A non-stochastic model, in the sense that no random variables are recognized. Exact relationships are postulated, and the output is predicted by the input with complete certainty.

detritus

    Matter produced by the wearing away of exposed surfaces.

development

    For plants, the sequence of events that bring about full sexual maturity, leading to flowering and fruiting. See also plant development

dew point

    The temperature at which a given mixture of air and water vapour will reach 100% relative humidity, or at which condensation will begin.

diagnosis and design

    A methodology developed by ICRAF that plans how to implement research and development projects for land-use systems that incorporate agroforestry—D&D for short. See also rapid rural appraisal

diagnostic factor

    1. A variable, which may be a land quality, a land characteristic, or a function of several such, that has an understood influence on the output from, or the required inputs to, a specified kind of land use, and which serves as a basis for assessment.

    2. Any variable that provides evidence as to how a certain outcome has arisen from an original set of circumstances.

diameter at breast height

    The diameter of a tree at 1.3 m (4.5 feet) above average ground level; dbh for short. Additional abbreviations o.b. and i.b. designate whether the diameter refers to measurements over or inside the bark.

diameter class

    Any of the intervals into which a range of diameters, for example, of tree stems or logs, may be divided for classification and use.

dibble

    To make a hole in the soil with a small pointed stick or something similar.

differentiation

    1. The changes a cell or tissue undergoes during growth that result in a specialized form and function (for example, flowers and flowering).

    2. Of an axis, morphological specialization either as sequential expression of meristematic specialization or growth correlation (for example, from orthotropic to plagiotropic shoots).

    3. Qualitative differences that occur in a plant during development, for example, change from juvenile to mature stages of vegetative growth and form, or change from the vegetative to the reproductive stage.

diffuse radiation

    Radiant energy propagating in many different directions through a given small volume of space; contrasted with direct radiation. Commonly used to describe the incoming radiation not coming directly from the sun. See also global radiation

digestibility

    The degree to which animal feed is assimilated in the digestive tract. Even when browse or fodder are palatable, that is, the animal is willing to ingest it, it may have very varying degrees of digestibility, depending on such factors as its protein and carbohydrate balance; the form and nature of its constituent proteins, carbohydrates and fats; and its fibre content. Anti-metabolites such as polyphenols may slow down digestibility or even harm the animal. All this varies with species and season.

digestible crude protein

    The difference between the crude protein in the feedstuff and that found in the faeces.

digestible energy

    The energy an animal obtains from feed, estimated from a digestibility trial by calculating the difference between the energy of the faeces and urine output and the animal's food intake over a period. See also gross energy value

dimorphic branching

    Where plants possess branches whose growth behaviour is characterized by the ability to grow only either vertically (orthotropic) or horizontally (plagiotropic) as with coffee.

dioecious

    Pertaining to plant species in which unisexual flowers, the staminate (male) or the pistillate (female), are borne on different individual plants. See also monoecious

diploid

    1. Having 2n (or two sets) of homologous (the same) chromosomes. Pertaining to the chromosome number in the vegetative rather than the gametic tissue. In the latter sense it is proper to speak of the vegetative tissue of a 4n or 6n plant as 'diploid', as differentiated from the haploid gametes.

    2. An organism with two chromosomes of each kind.

diploid parthenogenesis

    A type of apomixis in which a seed develops from a gametic (egg) cell. The seed may be 1n or 2n according to whether or not chromosome doubling occurs. It occurs most frequently in seeds bearing two or more embryos or showing other germination abnormalities. See also parthenogenesis

direct drilling

    Sowing seed into soil that has not been previously cultivated in any way in the immediate past.

directed application

    Where the herbicide is directed towards the ground or weeds to avoid or minimize contact with the crop.

direct radiation

    Incoming solar radiation received, without deflection or scattering, from the sun. See also diffuse radiation, global radiation

direct sowing

    Putting seeds to germinate in the site at which the mature plants are to be grown.

discontinuous variable

    A measured characteristic in which distinct classes (for example, dead versus alive) are easily recognizable. See also continuous variable

discounting

    The process of finding the present worth of a future amount. The present worth is determined by multiplying the future amount by the expression 1 + (1 + i) to the power n when i = the discount rate (internal rate) and n = the year.

discount rate

    Rate used for comparing investment projects, by reducing forecast revenue and cost flows back to the present, to give the net present value (NPV).

discrimination

    The precise size of a unit that a particular method can differentiate.

disgenic

    Practices or occurrences that bring about deterioration of the germplasm, for example, where the best individuals are harvested leaving only poorer ones. See also eugenic

disinfectant

    1. A physical or chemical agent that frees a plant, organ or tissue from infection, for example, from bacterial contamination.

    2. An agent that kills or inactivates pathogens in the environment on the surface of a plant organ before the infection process begins.

distribution-free method

    In statistics; See non-parametric method

diversion

    A channel with a supporting ridge on the lower side constructed across the slope to intercept runoff and minimize erosion, e.g. a `cut-off drain'.

divisive classification

    The process of classifying data points by first dividing the whole swarm of points into classes, then redividing some or all of these classes into subclasses, and so on. A form of clustering.

dominance

    In genetics, intra-allelic interaction such that one allele manifests itself more or less, when heterozygous, over its alternative allele.

dominant

    In forestry, an individual or species in the upper layers of the canopy.

dominant plant

    In intercropping, the species or individual plant that, by virtue of its stature, form or functional processes, possesses the ability to take a larger share of the available environmental resources than would otherwise be the case. See also dominated plant

dominant species

    In forestry, dominance occurs when considering the relative basal area of a species to the total basal area of all species in the stratum. The species having the highest relative basal area is considered the dominant species (syn: predominant).

dominant tree

    1. A conspicuous tree in a forest, much larger than neighbouring trees in its vicinity.

    2. Tree with crown extending above the general level of the crown cover and receiving full light from above and partly from the sides; larger than the average trees in the stand, and with crown well developed but possibly somewhat crowded on the sides.

dominated plant

    In intercropping, a species or individual plant that by virtue of its stature, form or functional abilities finds itself with a smaller share of available environmental resources than would otherwise be the case. See also dominant plant

dormancy

    A period of quiescence when no apparent growth or development is taking place; a form of growth regulation.

double working

    Type of graft in which the graft combination contains an interstock or intermediate stem piece grafted between the scion and the stock.

drainage

    1. The frequency and duration of periods when the soil is free of saturation with water.

    2. That part of the water in the soil that passes through to deeper layers, that is, past the root zone, and eventually to the water table.

drainage basin

    See watershed

drift

    Group of trees of one species planted among another species to create a mixed wood. The group may be elliptical in shape but preferably is irregular, longer than it is wide and varying in size to give a natural appearance. See also genetic drift

drip irrigation

    See trickle irrigation

driving function

    See exogenous variable

drupe

    Fleshy indehiscent (not regularly opening) fruit with the seed contained in a woody stone.

dry farming

    A method of farming in arid and semi-arid areas without using irrigation, the land being treated so as to conserve moisture. The technique consists of cultivating a given area in alternate years, allowing moisture to be stored in the fallow year. Moisture losses are reduced by producing a mulch and removing weeds. Usually alternate narrow strips are cultivated in an attempt to reduce erosion in the fallow year. Dry farming methods are employed in the drier regions of India, Russia, Canada and Australia.

dry matter to solar radiation ratio

    See light-use efficiency

dry matter to transpiration ratio

    The increase in dry weight of a plant stand as a ratio of the cumulative total of the water it has transpired over a stated period. See also water-use ratio

duff

    The more-or-less firm organic layer in forests. It consists of fallen vegetative matter in the process of decomposition, including everything from pure humus below to the litter on the surface. A general, non-specific term.

dung

    The faeces of animals rotted or not. See also farmyard manure

dwarfing

    The reduction or inhibition of height in certain plants caused by genetic, chemical or other physiological factors acting through, for example, rootstocks.

dynamic model

    A model that portrays time-dependent processes (as differentiated from static or time-invariant systems), time being an irreversible, independent variable.

dysgenic

    Detrimental to the genetic quality of a population, as when harvesting the best trees from a stand, leaving the poorer phenotypes to be parents of the next generation. See also eugenic

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College of Agricultural and Environmental Sciences and Warnell School of Forest Resources
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