AgroForestryTree Database
Glossary D
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.
dbh
Diameter of tree trunk at breast height. Usually 1.3 m above the ground line.
deciduous See also evergreen, leaf retaining
1. Of leaves, bark, and so forth, falling regularly at the end of a growth 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.
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 See also humus
The processes by which organic matter is broken down.
decussate (of leaves)
Arranged in opposite pairs on the stem, with each pair at 90 degrees to the preceding pair.
defoliant
A chemical which, when applied to a plant, causes leaf fall.
dehiscence (adj. dehiscent; verb dehisce)
The method or act of opening or splitting.
dentate
Having a toothed margin.
denticulate
Having a finely toothed margin.
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.
di-
A prefix meaning two.
dichasium (of inflorescences)
A form of cymose inflorescence with each branch giving rise to two other branches; of monochasium.
dicotyledon See also monocotyledon
One of two subclasses of angiosperms; a plant whose embryo has two cotyledons.
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.
dimorphic branching See also orthotropic, plagiotropic
Where plants posses branches whose growth behaviour is characterized by the ability to grow only either vertically or horizontally as with coffee.
dimorphism (adj. dimorphic)
Having two distinct forms.
dioecious See also monoecious
Pertaining to plant species in which unisexual flowers, the staminate (male) or the pistillate (female), are borne on different individual plants.
diploid
1. Having 2n (or 2 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. of an organism with 2 chromosomes of each kind.
direct sowing
Putting seeds to germinate in the site at which the mature plants are to be grown.
disk
The fleshy outgrowth developed from the receptacle at the base of the ovary or from the stamens surrounding the ovary; it often secretes nectar.
distichous
Arranged in two vertical rows.
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, from or functional processes, possesses the ability to take a larger share of the available environmental resources than would otherwise be the case.
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.
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.
dormancy
A period of quiescence when no apparent growth or development is taking place; a form of growth regulation.
dorsal
In a plant, abaxial (that is, facing away from the stem).
dorsifixed (of anthers) See also basifixed
Attached at the back to the filament.
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.
drupe
Fleshy indehiscent (not regularly opening) fruit with the seed contained in a woody stone.
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