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Glossary for agroforestry Compiled and edited by Peter Huxley and Helen van Houten, International Centre for Research in Agroforestry - 1997 palatable Having a good or at least a tolerable flavour. Some plants, although not poisonous, simply do not taste good and animals avoid them, for example, the leaves of Prosopis juliflora. Others are so highly palatable that establishing the tree can become difficult, for example, Leucaena leucocephala. Hence 'palatability'. See also digestibility palm Member of the Aracaceae (previously Palmae) family, containing over 200 genera and more than 2700 species, many of them economically important for food, fibre, canes, waxes, wood, thatch, and so forth. Typical agroforestry tree. pan coefficient Ratio of evaporation from a large body of water to that measured in an evaporation pan. panmictic unit A local population in which there is completely random mating. panmixia Random mating without restriction. pantropical Throughout the tropics as a whole. That is between latitudes 23°27' north and south. See also neotropics, paleotropics paradigm A pattern or example. A way of thinking and doing; a generally accepted comprehension. parallel row design A type of systematic spacing design in which the area per plant changes in a systematic fashion by varying the between- and within-row spacings with all the rows parallel to one another. See also fan design parameter 1. The characteristics of a population in some respect (literally 'beyond measure'). See also statistic 2. A numerical quantity that specifies a population in respect to some characteristic. parasitism A relationship between two living beings, A and B, where A has a negative effect on B and B a positive effect on A. See also predation parenchyma Thin-walled plant cells with a protoplast (the basic living components). Functions include food storage, photosynthesis (with plastids), wound healing and formation of adventitious structures. parent material 1. The horizon of weathered rock or partly weathered soil material from which the soil is formed. Horizon C of the soil profile. 2. The original state of the soil. The relatively unaltered lower material in which the soil horizons above it have formed. parthenocarpy The formation of fruit without fertilization and without fertile seeds, as in a banana. It includes fruit development stimulated by application of pollen incapable of causing fertilization. Common in some trees. parthenogenesis Development of an organism from a sex cell but without fertilization. particle-size analysis Determination of the various amounts of the different separates in a soil sample, usually by sedimentation, sieving, micrometry or a combinationof these methods. pastoralism A way of life for more or less wandering, animal-keeping peoples. Nomadism strictly applies to a system of using land by moving animals from place to place with no permanent human settlement. In transhumance some form of permanent or semi-permanent settlement exists. pattern analysis 1. Methodology to analyse and display the underlying associations and relationships between sets of attributes. It is aimed at the efficient ordering of data and is non-probabilistic and non-parametric. 2. Assessment of the regularity of an agroecosystem's structure and function, based on established data categories. See also classification, ordination pC A measure of the electrical conductivity of a soil for determination of ions in solution. The electrical conductivity of an aqueous suspension of soil is measured and expressed by the specific conductivity; that is, it uses the reciprocal ohm (or mho or millimho). pC is defined as the co-logarithm of the specific conductivity of soil extracts or suspensions in millimho cm–1. peat 1. Unconsolidated soil material consisting of undecomposed or slightly decomposed organic matter accumulated under conditions of excessive moisture. 2. An accumulation of dead plant material often forming a layer many metres deep. It shows various stages of decomposition and is usually waterlogged. ped A natural unit of soil structure, such as an aggregate, crumb, granule. See also soil structure pedalfer A group of fully leached soils. pedigree breeding A system of breeding in which individual plants are selected in the segregating generations from a cross on the basis of their desirability, judged individually and from their pedigree record (with self-pollinated plants). pedocal A group of incompletely leached soils with free drainage. pedon The smallest volume that can be called 'a soil'. It has three dimensions; it extends downwards to the depth of plant roots or to the lower limit of the genetic soil horizons, and its lateral cross section is roughly hexagonal and ranges from 1 to 10 m in size depending on the variability in the horizon. penetrability With soils, the ease with which a probe can be pushed in. May be expressed in units of distance, speed, force or work, depending on the type of penetrometer used. perched watertable Presence of water in a soil horizon as a result of poor internal drainage, topographic position or an impermeable soil layer. May be permanent or may occur during seasons of high precipitation. percolation The downward movement of water through the soil. Especially the downward flow of water in a saturated or nearly saturated soil. See also infiltration perennial A plant that does not die after flowering but lives from year to year. See also herbaceous perennial, woody perennial periphysis Concerns the transmission to the ramet of effects caused by the environment of the ortet; can be reversible. See also cyclophysis, topophysis permaculture 'Permanent agriculture'. The design and maintenance of sustainable, ecologically favourable, energy efficient agricultural and horticultural systems. The concept includes not only agroforestry but the integration of organic farming principles and intermediate technology, the use of renewable resources and recycling, the exploitation of biodiversity, conservation and habitat protection,as well as social and institutional well-being. It can be applied to urban as well as rural environments. permanent wilting point 1. The amount of water held in the soil when plants remain wilted even though when, for a short period, the aerial parts are kept in a humid atmosphere. Usually taken as 15 atmospheres of tension. 2. The moisture content of soil, on an oven-dry basis at which plants wilt and fail to recover their turgidity when placed in a dark, humid atmosphere. See also air-dry soil, oven-dry soil, wilting point pesticide A substance, inorganic or organic, that kills or suppresses the growth or development of pests (insect pests, fungal pathogens, weeds). pest In the general sense, an insect pest, fungal or viral pathogen, weed, or avian or mammalian pest (birds, rodents). pF The logarithm of the free energy (expressed as a pressure or head in J kg–1) used to express the intensity with which water is held at any particular water content. See also soil-water storage pH A numerical measure of the acidity, or hydrogen ion activity, of a soil. The neutral point is pH 7.0. All pH values below 7.0 are acid and all above are alkaline. A change of one unit in pH value represents a tenfold change in hydrogen-ion concentration. pH represents the `intensity' of acidity, not the total exchangeable hydrogen or 'quantity' of potential acidity. phanerophytes Self-supporting woody plants or herbaceous evergreen perennials that grow taller than 25–50 cm, or whose shoots do not die back periodically to that height limit. phareatic surface The upper surface or zone of saturation. phase change Change from one phase (state) of plant development to another, for example, from juvenile to mature phases. phenology 1. The study of the time of appearance of characteristic periodic phenomena in the life cycle of organisms in nature, for example, flowering or leaf fall in higher plants, especially as influenced by environmental factors such as climatic conditions. 2. The study of the timing of periodic phenomena such as flowering, growth initiation, growth cessation, especially as related to seasonal changes in temperature, photoperiod and similar phenomena. phenophase In phenology, the particular stage in development reached by a plant (organism), for example, germination, the juvenile phase (of a tree), anthesis (flowering). phenotype 1. The visible characters of a plant. The product of a plant's genotype and its environment. 2. The feature(s) of an organism produced by the interaction of the genes of the organism with the environment. Individuals are described on the basis of these features. See also selection 3. Appearance of an individual as contrasted with its genetic makeup or genotype. Also used to designate a group of individuals with similar appearance but not necessarily identical genotypes. 4. An organism as observed, that is, as judged by its visual perceptible characters resulting from the interaction of its genotype with the environment. Similar phenotypes do not necessarily breed alike. phenotypic plasticity In specific terms, the capacity for phenotypic change shown by an individual genotype. An individual plant shows plasticity when its characteristics are altered by environmental influences. See also genetic plasticity, genotype x environment interaction phenotypic selection Choosing trees on the basis of their phenotypic performance. phloem A compound vascular tissue in plants composed of sieve tubes, companion cells, fibres and parenchyma cells. photoperiod A cycle of light and dark intervals, usually with a period of 24 hours. photoperiodism The control of reproductive and vegetative development through the imposition of appropriate sequences of light and dark periods. photorespiration Light-dependent uptake of oxygen and release of newly fixed carbon dioxide from the substrate P-glycollate or glycollate (derived from the photosynthetic carbon reduction cycle). As distinct from 'dark' or 'base' respiration', that is, the breakdown of a hexose sugar (usually glucose) to pyruvic acid with the release of energy through the conversion of adenosine diphosphate (ADP) to adenosine triphospate (ATP). See also C3 plant, C4plant photosynthesis The process of light (photon) capture by green plants and the conversion of atmospheric carbon dioxide to organic compounds. Ultimately the conversion of light energy to chemical energy. See also C3 plant, C4 plant, carbon assimilation photosynthetically active radiation In the electromagnetic spectrum, from 0.4 to 0.7 nanometers wavelength. Equals approximately 45% of the total shortwave radiation received at the earth's surface from the sun (abbreviated PAR). phototropism The growth (movement) of a plant organ as a response to the stimulus of light. phreatophyte A plant drawing its water from subsurface sources, growing mainly along stream courses or where its roots reach the capillary fringe. phyllode See cladode phyllosphere The space immediately adjacent to, and influenced by, a plant leaf. See also rhizosphere phyllotaxy The arrangement of leaves on a stem. phylogeny Racial history and evolution of a group of related organisms. physical determinant One of the important attributes of climate, water and land, such as rainfall, topography and hydrology, that influence configuration and performance of cropping patterns. physical property One of the characteristics, processes or reactions of a soil that are caused by physical terms or equations. Examples of physical properties are bulk density, hydraulic conductivity, pore-size distribution, porosity, water-holding capacity. phytohormone A natural substance produced in small amounts that modulates growth or other plant developmental processes. See also plant growth regulator, auxin phytosanitary certificate A written statement about the health of plant parts made when they are to be exported or imported. Usually in an internationally agreed form indicating field inspection, seed treatments, and so on. phytotoxic Toxic (damaging) to at least some plants. pinching Breaking off the terminal growing point, allowing the axillary buds to start growing. See also apical dominance pioneer A tree species that has a high light requirement for seed germination and seedling establishment and is adapted to grow well in disturbed sites (forest gaps). Typically these species are early flowering and flower and fruit copiously. They do not regenerate in their own shade and may persist as big, old trees over an understorey of mixed species. Also known as 'seral species', 'secondary forest species' and 'forest nomads'. See also tree temperament pitting Planting young trees into prepared holes. plagiotropic branching Of branching, stems that grow only horizontally. See also dimorphic branching, orthotropic branching plagiotropy Gravitational response that produces an oblique or horizontal axis. Hence 'plagiotropic shoot', with the complex of characters resulting from this response: dorsiventral symmetry and horizontal orientation. See also orthotropy plant development Involves both growth and differentiation. Broadly, it refers to the whole series of changes that an organism goes through during its life cycle, but it can refer to individual organs, tissues or cells. plant growth regulator 1. A natural or synthetic substance that acts endogenously at very low concentrations to modulate plant development. 2. An organic compound, other than a plant nutrient, that in small amounts promotes, inhibits or otherwise modifies growth. It can be synthetic or natural (when it is termed a phytohormone). See also growth retardant, growth promoter planting density See plant population planting out The procedure of moving and planting young plants that have been raised in a nursery to the site where they are to be grown next. plant nursery A specially prepared site for germinating seeds and looking after seedlings and young plants under conditions favourable for their growth and development. Facilities for vegetative propagation are also often present. plant nutrient An element essential to plant growth. See also macronutrient, micronutrient plant population The number of plants per unit area. Sometimes referred to as 'plant density 'or 'planting density'. plant succession An orderly process of change in the composition of a plant community until vegetation stabilizes and is in balance with its environment. See also climax plasticity See genetic plasticity, phenotypic plasticity plastochron Time interval between two successive similar events, as in leaf development. Often used in a descriptive sense for its morphological results. plot 1. Any type of experimental material that forms a unit. 2. Usually the smallest experimental unit in a replicated comparative experiment, for example, one replication of one provenance in a trial of many provenances with several replications. See also net plot and gross plot 3. Any small peice of land forming a homogeneous unit for cropping, a primaly land unit. plus tree A phenotypically superior tree not yet proven genetically as an elite tree by progeny testing. pole In forestry, a still-young tree, from the time its lower branches begin to die, up to the time when the rate of height growth begins to slow down and crown expansion becomes marked. See also sapling pollarding Cutting back in more or less systematic fashion the crown of a tree but leaving a main trunk to 1.5 m or so, with the object of harvesting small wood and browse, of producing regrowth beyond the reach of animals or of reducing the shade cast by the crown. See also coppicing pollinator Any plant that pollinates another. In horticulture, a variety or cultivar included where the main fruit tree variety is self-incompatible, so as to ensure cross pollination and proper fertilization so that fruit production occurs. See also self-incompatibility polyploid An individual or a cell having three (triploid), four (tetraploid), five (pentaploid), or more, complete sets of chromosomes instead of two as in diploids. See also amphidiploid, aneuploid, autopolyploid population 1. Statistically, the sum of all the variates of any one kind. The population need not actually exist but the term may refer to the aggregate of all individuals that might have existed under certain specified conditions. 2. Genetically, a group of similar individuals related by descent and so delimited in range by environment or endogenous factors as to be considered a unit. In cross-bred organisms the population is often defined as the interbreeding group. 3. In genetics, a community of individuals that share a common gene pool. In statistics, a hypothetical and infinitely large series of potential observations among which observations actually made constitute a sample. pore-size distribution The volume of the various sizes of pores in a soil, expressed as percentages of the bulk volume (soil plus total pore space). pore space Total space not occupied by soil particles. porosity See soil prorosity porous wood Wood with pores or vessels originating from a continuous cambium layer, featured by nearly all hardwood species. Diffuse porous wood (xylem vessels and fibres from scattered cambia) also occurs, as in palms. See also non-porous wood, ring-porous wood post-emergence After the seedling has emerged from the soil. post-emergent application Application of, for example, a herbicide after the crop has emerged from the soil. In perennial crops it denotes any procedure carried out after the emergence of weeds. See also pre-emergent application practice In agroforestry, a particular use of land involving woody and non-woody plants in some spatial (simultaneous) or temporal (sequential) arrangement. For example, hedgerow, intercropping, homegardens, shifting cultivation. Sometimes referred to as an agroforestry 'technology'. An'agroforestry system' is a specific example of a practice. precision Of an estimate, it is the closeness of agreement to be expected between a succession of independent estimates formed by a repetition of the sampling procedure. preclone Any group of connected shoot-root units formed by a single plant and which has the potential to form a clone by the death or fragmentation of connecting tissue. predation A relationship between living beings A and B where A has a 0,0 effect on B and B a > 0 effect on A; and where the whole of B is taken away. See also parasitism predominant See dominant pre-emergent application Application of, for example, a herbicide when a crop is present but has not emerged from the soil (sometimes applied to weeds: 'pre-weed emergence'). See also post-emergent application pretreatment For seeds, methods of speeding germination for difficult species, for example scarification or treatment with boiling water. pricking out The procedure of transplanting young seedlings from the seedbed, seedbox or container in which they were germinated to a relatively more spacious area or container so as to give them room to grow. primary land unit A basic spatial unit suggested to embrace agriculture, horticulture, forestry and agroforestry. A homogeneous area in which a common species (or species mix) undergoes a common form of management (in agriculture, the plot; in forestry, the compartment). primary production Production of biomass by plants through the processes of photosynthesis and nutrient uptake. 'Net primary production' is this production less losses by respiration. It is often measured only as 'above-ground net primary production' and leaf fall should be accounted for. principal components New variables derived by principal components analysis to describe a body of data. Each is a weighted sum of the 'raw' (as originally measured) variables, or of the centred or standardized variables. principal components analysis A numerical method for ordination of data used either as a multi-variate (statistical) technique or purely for pattern seeking. See also multivariate analysis, pattern analysis procumbent Trailing or lying flat, but not rooting. production The output, for example for an area of land. See also crop productivity, productivity production function In economics, a mathematical expression that describes a production process, showing the relationship between the quantities of inputs employed and outputs produced. Total factor productivity is the sum of all these for the system under consideration. See also production possibility frontiers production possibility frontiers The maximum output obtainable from every possible input combination. See also production function productivity A measure of efficiency relating output of a product to the use of a resource (including time). See also crop productivity, production progeny The offspring of a particular plant or particular combination of one female and one male tree plant or animal. progeny test 1. A test of the value of a genotype based on the performance of its offspring produced in some definite system of mating. 2. Evaluation of parents by comparing the performance of their offspring. Accuracy is usually gained because several to many offspring per parent are evaluated under more controlled conditions than exist for the parent alone. prolepsis Development of a lateral branch only after a period of dormancy as a lateral bud. Hence, 'proleptic branch', a branch developed by prolepsis. See also syllepsis propagate To increase the number of a given plant type. Propagation can be by seed, root sucker, stool, stump, root, stem or leaf cutting, grafting, layering or by micropropagation. propagule 1. A seedling, cutting or graft (especially when small). 2. A part of a plant with the potential for producing a new individual. protandry Maturation of anthers before pistils. See also protogyny protective plants Plants grown to protect crops, soils or land from adverse environmental factors. See also companion crop proteoid root One of thefinely packed lateral roots that can form thick, subsurface mats. Thought to be microbially induced and found in some trees and shrubs of the Proteaceae (for example, Grevillea robusta). protogyny Maturation of pistils before anthers. See also protandry provenance 1. The original geographic source of seed or propagules. See also land race 2. The place in which any stand of trees is growing. The stand may be indigenous or non-indigenous. pruning 1. The process of cutting back growth of plants, including roots, but more particularly, side branches of trees, or the sides and tops of hedges. 2. General term to describe the removal by cutting of buds, stems, or entire branches. See also brushing, form pruning, lift pruning, lopping pseudo-liana See hemi-epiphyte psychrometer An instument used for measuring the water vapour content of the atmosphere; a type of hygrometer. It usually consists of two thermometers with wet and dry bulbs. psyllid A small, hemipteran insect pest that sucks plant sap. The psyllid Heteropsylla cubana has spread around the world from its Central American home to devastate Leucaena leucocephala elswhere. Breeding programmes for resistance using, for example, L. diversifolia, and biological control with hymenopterous insects are now being tried. puddled soil A dense soil often dominated by a single-particle structure, almost impervious to air and water. This condition results from handling a soil when it is in a wet, plastic condition, so that when dried, it becomes hard and cloddy. puddling Destruction of soil structure, reducing porosity and permeability. A dense soil of massive structure, almost impervious to air and water, occurs when wet, plastic soil is worked too much or is trampled by animals. pulses Non-oil-producing, cultivated legumes grown for their edible seeds. pure line In breeding, a strain homozygous at all loci, ordinarily obtained by successive self-fertilizations.
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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 Questions and/or comments to: bugwood@arches.uga.edu |
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