Glossary for agroforestry

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

validation

1. The process of assessing the accuracy for a given purpose of a simulation model by comparing the model's predictions with independent results.

2. Ground validation is the confirmation of information from satellite imagery or aerial photography. See also ground truth

variability

Absence of uniformity. Quality of differing from the average value. This term is usually used in a general sense and qualified by such words as 'low', 'moderate', and 'high'. For quantitative comparisons, the concept of a variance is used.

variable

1. A quantity able to assume different numerical values. When considering two variables at the same time, one can sometimes be considered the dependent variable and the other the independent variable, for example crop growth (dry matter) and intercepted solar radiation (MJ m–2) respectively.

2. Any quantity or quality likely to show variation from one individual to the next in the same population. See also endogenous variables, exogenous variables, rate variables, state variables

variance

1. In statistics, of a set of observations, the mean of the squared deviations from their mean value.

2. A statistical measure of variability defined in an exact manner. Many types of variances can be calculated, for example within-block variance and within-plot variance among individual plants. Examining the ratios between two calculated variances provides a way of determining if observed differences, or relationships, are large enough to be caused by factors other than chance.

variate

An individual observation or value of any variable.

variation

See variability

variety

1. A taxonomic subdivision of a species based on minor c haracteristics and often an exclusive geographic range, or an assemblage of cultivated individuals of useful and reproduceable character.

2. In taxonomy, variants of a typical species that are not known to occur as distinct populations but appear sporadically in wild stands as single or isolated individuals. See also agronomic variety, cultivar, provenance, strain

vegetative

Not flowering. The stage of development when a plant is producing only roots, stems and leaves, that is, the vegetative organs.

vegetative reproduction

See asexual reproduction

veld

The name given to grasslands in southern Africa. Can be 'winter veld' or 'summer veld' depending on the climatic pattern, the soil and what grass species occur, hence when it can be grazed. Also spelled 'veldt'.

veneer

A product made from round logs of certain trees by turning a log and slicing a continuous sheet from it. This sheet is then cut into lengths and glued to lower quality wood for making panelling, table tops, doors and other products with improved appearance.

vernalization

Exposure of a plant or plant organ to chilling, which subsequently brings about a development phase change (for example, flowering). See also chilling requirement

vertical resistance

Resistance to plant pathogens conferred by specific, identified genes. See also horizontal resistance

viability

1. A measure of the potential for seeds to germinate and grow. A seed of short viability will germinate well only within a short time after harvest. Some tree seeds have long viability and will germinate readily, possibly with pretreatment, long after collection. See also recalcitrant seed, orthodox seed

2. The possession of life.

viable seed

Seeds that will germinate and develop into a plant, given favourable conditions, provided any dormancy that may be present is removed.

village forest garden

Larger than the homegarden, less densely planted and not so well tended. Planted with higher trees and often containing spontaneous species of herbs or lianas.

volume rate

Amount of a liquid applied per unit area. For example, for herbicides: 'high' = > 675 litres ha–1, 'medium' = 226–675 litres ha–1, 'low' = 57–225 litres ha–1, 'very low' = 12–56 litres ha–1, 'ultra-low' = 1–11 litres ha–1.