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Glossary for agroforestry

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

race

    1. A genetic subdivision of a species, with more or less distinct characteristics when grown in a particular environment. Sometimes used to denote a portion of a cline. Differences among races may or may not be adaptive; differences among ecotypes are presumed to be adaptive. Hence, 'race' is a more general term than ecotype.

    2. A genetically and often geographically distinct mating group within a species; also a group of pathogens that infect a given set of plant varieties.

radicle

    The rudimentary root of the embryo.

rainfall

    Atmospheric precipitation occurring as droplets of water (as different from mist or dew). It is characterized by its intensity, duration and seasonal distribution. Measured as a depth of water falling on a level surface (mm); best expressed as the probability of occurrence of stated amounts. See also rainfall distribution, rainfall intensity

rainfall distribution

    The quantity of rain falling at different times of the year. In the tropics, rain may fall over one season only ('monomodal'), or near the equator over two seasons ('bimodal', hence first and second rainy seasons). See also rainfall intensity

rainfall intensity

    1. The rate at which rain is occurring at any given instant, usually expressed in millimetres per hour. 'Maximum rainfall intensity' refers to the rate during any time when the rate is both maximum and uniform. Usually one or more standard time periods, such as 5 or 10 minutes, are specified, and then the term refers to an average rate calculated from the amount that occurred during any such time period, although the rate was not neccessarily uniform.

    2. The amount of rain received per unit of time. Convective tropical storms often have a 'leading edge rate', that is, rainfall at the onset of the storm is greatest; it may be 150–200 mm h–1 or more for a short period. See also rainfall distribution

rainfed farming

    Growing crops or animals under conditions of natural rainfall. Water may be stored in a crop field by bunding, as in lowland rainfed rice, but no water is available from permanent water storage areas.

rainforest

    Generally, a forest that grows in a region of heavy annual precipitation. There are both tropical and temperate rainforests.

rain shadow

    A region (or smaller site, or place) situated on the lee side of a mountain (or obstruction of any kind), where the rainfall is much less than on the windward side.

ramet

    1. An individual member of a clone, descended through vegetative propagation from the ortet.

    2. A propagule.

    3. A unit of a plant with a set of roots and leaves. Ramets are connected by rhizomes or stolons. See also genet

randomness

    Unselected, entirely by chance. Having the property that only the probability of an outcome, not the actual outcome, can be predicted.

range

    1. Land that produces primarily native forage suitable for grazing by livestock; also forest land producing forage. Usually relatively extensive areas of land suitable for grazing but not for cultivation, especially in arid, semi-arid or forested regions. A unit of grazing land used by an integral herd of livestock. The geographical area of occurrence of plants and animals.

    2. The geographical and altitudinal limits within which a taxon occurs.

    3. In statistics, the limits of magnitude (of a set of data).

rangeland

    Land suitable for grazing by domestic livestock. The vegetation consists mostly of native grasses, grasslike plants, forbs, shrubs

rapid rural appraisal

    A methodology in which a multidisciplinary team of researchers uses social science tools for the quick collection of primary data during one or several visits. The research team transforms the primary data into secondary data for assessment and analysis. See also diagnosis and design

rate variable

    A variable that controls the rate at which various responses are generated by various changes in the system's state. Rate variables represent the coefficients of the governing equations describing the dependence of endogenous variables on their controlling state variables.

ratoon

    Sprouting or regrowth from buds or young tillers; crops originating from ratoon growth.

ratoon cropping

    The cultivation of an additional crop from the regrowth or stubble of a main crop after its harvest, thereby avoiding replanting, as with sugarcane, sorghum and rice.

rattan

    A climbing palm (mainly Calamus spp and others in the lepidocaryoid line). Used for making baskets and furniture. See also palm

raw humus

    See mor humus

recalcitrant seed

    The seeds of some species have relatively short viability and cannot be stored in a dry condition or at low (subzero) temperatures. Some such seeds even suffer chilling damage. Examples are seeds of cocoa and rubber. See also orthodox seed

recessive

    The member of a pair of alleles that is not expressed when the other (dominant) member occupies the homologous (corresponding) chromosome.

reciprocal crosses

    Crosses in which the sources of male and female gametes are reversed.

recombination

    1. Formation of new combinations of genes as a result of segregation in crosses between genetically different parents; also the rearrangement of linked genes caused by crossing over.

    2. Obtaining new combinations of genes through crossovers and independent segregation of chromosomes at meiosis (the division of sexual cells).

recommendation domain

    A more or less homogeneous group of farmers with similar circumstances for whom similar recommendations can be made.

recovery rate

    Rate of conversion of roundwood to timber products.

recruiting

    See beating up

recurrent selection

    A method of breeding designed to concentrate favourable genes scattered among a number of individuals by selecting in each generation from among progeny produced by matings of all the selected individuals (or their selfed progeny) of the previous generation.

reforestation

    Replacing forests after felling. See also afforestation

regional system

    A complex, large-scale land unit of utilization that produces and transforms primary products and involves a large service sector. Components of the regional system are natural resources, the agricultural sector, and secondary and tertiary sectors.

registered seed

    The progeny of foundation seed normally grown to produce certified seed. See also foundation seed

reinforcement planting

    See beating up

reiteration

    Development of shoots outside the normal expression of the architectural model of a tree, as a specialized environmental response, but repeating the basic model.

reiterative complex

    The complex of meristems produced by reiteration.

relational diagram

    A diagram used to show the interrelationships of components and processes in a system.

relative growth rate

    At a given instant, the increase in plant material per unit of plant material initially present. Expressed over a period (for example, one week) as a mean relative growth rate in g g–1 day–1. Relative growth rate = net assimilation rate x leaf area ratio. See also absolute growth rate

relative humidity

    The dimensionless ratio of the actual vapour pressure of the air to the saturation vapour pressure, which changes with temperature.

relay cropping

    1. Planting crops between plants or rows of an already established crop during the growing period of the first planted crop(s). One form of overlapping cropping.

    2. The growing of two or more crops on the same field with the planting of the second crop after the first one has already completed development.

replication

    1. The number of times a treatment is repeated in space or time. To halve the standard error, four times the degree of replication is needed, so extraneous variability must also be identified and dealt with.

    2. Applying a treatment or set of treatments more than once to increase the precision of comparisons and to provide an assessment of the variability among experimental units treated alike.

    3. One complete set of all experimental units in a comparative experiment.

representative sample

    1. A sample whose properties accurately reflect those of the population.

    2. A selection of individuals from a population of whom specific characteristics are studied that is large enough to allow statistical treatment and conclusions about the population as a whole. Samples can be 'simple random samples' (a type of sampling unit), 'multistaged random samples' (a series of sampling stages, each with its sampling unit), 'stratified random samples' (where the sampling units are first assigned to strata and these are then randomly sampled) and 'stratified multistage random samples'.

research

    An investigation directed to the discovery of some fact by the careful study of a subject. A course of critical or scientific enquiry. The act of researching, which, in its broadest sense, involves both inductive (algorithmic) reasoning and heuristic convergence.

research strategy

    The allocation of research resources to specific activities to maximize the efficiency and effectiveness of research according to certain specified goals (such as improving the sustainability and availability of food to all sectors of the population).

residual herbicide

    A herbicide applied to the soil that remains active for at least several weeks, but sometimes many years. See also contact herbicide, systemic

residual variation

    The part of the total variation in data that cannot be explained by differences between treatments or blocks or by the effects of other controllable or measurable variables. Also known as covariance or error variance.

resin

    A thick, sticky liquid that comes out of certain trees and later becomes hard. Acacia senegal produces one of the more valuable resins ('gum arabic'), as do Boswellia and Combretum species.

resistance

    The ability of an organism to exclude or overcome, completely or in some degree, the effect of a pathogen or other damaging factor. See also horizontal resistance, vertical resistance

resource capture

    The acquisition by plants of environmental resources, that is, the processes by which plants obtain light, water and nutrients. See also resource capture efficiency

resource capture efficiency

    The measure of the ability of a plant, or more often a plant community, to transform captured resources (light, water, nutrients) to dry matter (or yield). See also light-use efficiency, water-use efficiency

response

    The measured reaction to some treatment, for example, the effect of pruning the on basal area of trees or of thinning on the diameters of branches of the trees remaining.

Rhizobium

    Type of bacterium that has the capacity of both invading the roots of certain species of the Leguminosae and fixing atmospheric nitrogen, which is subsequently used by the host plant.

rhizome

    A horizontal stem growing beneath the soil surface, capable of producing adventitious roots and with nodes having scale leaves subtending axillary buds that may form either rhizome branches or upright shoots. See also stolon

rhizophore

    A leaf-bearing root; a leafless stem with roots.

rhizosphere

    1. The soil surrounding and directly influenced by plant roots.

    2. The soil close to plant roots where there is usually an abundant and specific microbiological population. See also phyllosphere

rhythmic growth

    Growth of an axis determined by a rhythm that results in periodic shoot extension alternating with dormancy. Also known as 'episodic growth'. See also phenology

ribulose biphosphate

    The enzyme ('Rubisco') of the first carboxylation process in C3 plants. See also carbon assimilation

ridge terrace

    A long, low ridge of earth with gently sloping sides and a shallow channel along the upper side, to control erosion by diverting surface runoff across the slope instead of permitting it to flow uninterrupted down the slope. Types of ridge terrace include 'drainage', 'narrow-based', and 'Nichol's' terraces. Contrast with bench terrace. See also broad-based terrace, graded terrace, level terrace.

rill

    A small, intermittent water course with steep sides, usually only a few centimetres deep. See also gully

rill erosion

    1. The formation of rills as a consequence of poor cultivation.

    2. The occurrence of many small channels a few centimetres deep.

ring-barking

    A method of killing trees by removing a ring (strip) of bark right down to, and including, the cambium. Usually done near the bottom of the trunk.

ring-porous wood

    Wood in which the pores of one part of a growth ring are in distinct contrast in size or number (or both) with those of the other part.

riparian forest

    See gallery forest

river basin

    See watershed

riverine

    Along permanent and semi-permanent streams a different environment is created because of the increase in soil moisture. This is termed a riverine environment.

roguing

    Systematic removal of undesired individu als in a population; culling.

root climber

    A plant that raises itself up by means of adventitious roots, which adhere to the plants that support it. See also scrambler, twiner

root hair

    Unicellular, hairlike growth from a root. Functionally important in water and nutrient uptake.

rootstock

    A root-bearing plant or plant part, generally a stem or root, onto which another plant part (the scion) is grafted. Also, the collective roots in a stand, capable of sprouting.

root sucker

    A shoot arising from an adventitious bud in a root. Some plants, like bananas and date palms, reproduce by sending out root suckers, which grow from the mother tree's root system. These can be cut away and planted at another site. Other trees will produce root suckers if their roots are cut some distance from the tree and left exposed (for example, Ocotea usambarensis and Melia volkensii can be propagated in this fashion). See also sprout

root zone

    Layer of the soil interwoven by plant roots. Also called 'rooting zone'.

rotational cropping

    The repetitive cultivation of an ordered succession of crops, or crops and fallow, on the same land. One cycle often takes several years to complete. See also crop succession, sequential cropping

rotational grazing

    Grazing systems in which the pasture is subdivided into a number of enclosures, with at least one more of these than there are groups of animals. The practice of submitting a grazing area to a regular sequence of grazing alternating with rest.

roughage

    The part of animal feed that does not get digested; coarse fodder or browse.

roundwood

    1. Timber or fuelwood prepared in the round state, that is, from felled trees to material trimmed, barked and cross-cut. Logs, transmission poles, pit props and the like are 'round timber'; with fuelwood included, the term is 'roundwood'. See also small roundwood

    2. Timber as harvested, before conversion.

row intercropping

    Growing two or more crops simultaneously, where one or more crops are planted in rows. See also zonal agroforestry system

r-selection

    Selective conditions that favour high reproductive rates at the expense of individual vegetative longevity. An r-strategist is a species adapted to high rates of sexual reproduction at the expense of individual longevity.

Rubisco

    See ribulose biphosphate

ruminant

    An animal that has more than one stomach. The first is called the 'rumen', in which bacterial fermentation takes place, and from which the animal is able to regurgitate ingested food back to the mouth for further chewing ('chewing the cud'). Cattle, antelopes, deer, giraffe, sheep and goats are ruminants. See also small ruminant

runner

    A slender horizontal stem with elongated internodes; it roots at nodes that touch the ground. See also stolon

runoff

    Water, usually from rain, that fails to infiltrate the soil surface and passes out of the plot or field.

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