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Glossary for agroforestry

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

habitat

    1. The immediate environment occupied by an organism.

    2. The natural environment of an organism excluding other living organisms (the biotope). See also site

half sib

    Tree with one parent in common with another (usually the female). See also sib

halophyte

    A plant that is tolerant of high levels of mineral salts in the soil, including sodium chloride; it can withstand salt spray if near the sea.

haploid

    A cell or organism with the gametic chromosome number (1n).

haptotropism

    The growth (movement) of a plant organ as a response to contact or a mechanical stimulus.

hardboard

    Fibreboard. A sheet of material commonly 0.25 cm thick made from pulped wood. 'Exterior grade' is waterproofed.

hardening off

    1. The process by which young seedlings are prepared for transplanting by gradually reducing water, shade or both, and thus causing changes in the leading shoot that renders it more resistant to drought and cold. See also growing on

    2. The treatment of tender plants to enable them to survive a more adverse environment; achieved by, for example, withholding nutrients, lowering temperatures, allowing temporary wilting, and other methods to slow growth rate.

hardiness

    The attribute of a plant that enables it to withstand environmental stresses (drought, frost, exposure to heat, and so on). See also hardening off

hardpan

    1. A cemented (indurated) or hardened soil horizon. This horizon, which may have any texture, is compacted or cemented by iron oxide, silica, organic matter or another substance.

    2. A hardened soil layer in the lower A or B horizon cemented by particles with organic matter, silica, sesquioxides, calcium carbonate or other cementing agents. Hardness or rigidity is maintained when wet or dry, and samples do not disintegrate in water.

hard seed

    Seed with thick and tough testa, which delays water penetration and germination. See also scarification

hardwood

    The timbers from broadleaved, angiosperm trees often, but not always, harder than the timber from conifers (softwoods). They are often, but not always, deciduous (Eucalyptus, for example, are hardwoods).

hardwood cutting

    See cutting

harvest increment

    The increment in the harvested part, or the above-ground biomass, of a woody perennial plant over a stated period. Compare with harvest index, which is often used for seasonal crops and relates to the outcome over the whole life of the crop.

harvest index

    The proportion of the total plant biomass (or more usually the above-ground biomass) produced by a crop species that forms a particular, required (harvestable) plant part; usually expressed as a percentage. The dry weight of the harvested part compared with that of the total above-ground dry weight at harvest.

heading back

    In pruning, removing the apical part of a branch (stem), and so its apical dominance. The result will be to stimulate the growth of lateral branches. See also thinning out

headland

    A strip of unploughed land at the end of a set of furrows or along a fence.

heartwood

    1. The inner of two distinct wood layers in the trunk of many trees. The outer layer, usually lighter and moister, called sapwood, is newly formed wood with some living cells. Inside this ring of sapwood is often a darker, harder, more durable core called heartwood. A striking example of heartwood and sapwood difference is found in Dalbergia melanoxylon, which has light brown sapwood and purple black heartwood; it is often used for craft carving.

    2. The wood in the centre of a tree, no longer in use for conducting water from the roots to the leaves. It is often darker in colour than the outer wood (sapwood) and may contain chemicals that make it more resistant to decay. See also sapwood

hedge

    Bushes or shrubs or trees planted in a row and trimmed. Used to separate one piece of land from another. See also live fence

hedgerow

    A barrier of bushes, shrubs or small trees growing close together in a line. A hedge is similar but pruned. See also live fence

hedgerow intercropping

    See alley cropping

height class

    Any of the intervals into which a range of tree heights may be divided for classification and use.

hemicryptophyte

    Self-supporting plant that is perennial or biennial, herbaceous and with periodic shoot reduced to a remnant shoot that lies relatively flat on the ground surface.

hemi-epiphyte

    Plant that grows by supporting itself on others and that roots in the ground, germinating on other plants first, or that first germinates in the ground, grows up a tree and then disconnects its soil contact (pseudo-liana).

herbaceous

    Not woody, and dying back each season.

herbaceous layer

    Part of the understorey in a forest that consists mainly of non-woody plants (also ground cover, ground layer).

herbaceous perennial

    1. A non-woody plant that continues to grow from year to year.

    2. A plant with soft, succulent stems whose top is killed back by frost in many temperate and colder climates but whose roots and crowns remain alive and develop new top growth when favourable growing conditions return.

herbage

    The vegetative parts of plants. The accumulated plant material (with recognized characteristics) that has accumulated in the above-ground part of a sward. See also grazing

herbicide

    A chemical substance that can kill or suppress the growth of certain plants; a weedkiller. See also contact herbicide, residual herbicide, selective herbicide

herbivore

    Any animal, including insects, that feeds on plant material.

heritability

    1. The proportion of observed variability that is due to heredity, the remainder being due to environmental causes. More strictly, the proportion of observed variability caused by the additive effects of genes.

    2. For a single tree, that portion of the total variance caused by genetic differences among individuals, applicable to data from single trees. For a family, that portion of the total variance caused by differences among families, and applicable only to family means.

    3. In a broad sense, that portion of the total variance caused by genetic factors. In a narrow sense, that portion of the total variance caused by genes with additive effects and most indicative of the superiority that can be transmitted by seed.

heterophyllous

    Having leaves of different shapes on the same plant.

heterosis

    Hybrid vigour exhibited when the mean F1 hybrid phenotype falls outside the range of the parents. In statistical terms, this usually means an increase in some measure over the parents. Usually applied to characters such as size.

heterozygous

    Possessing different alleles at a particular locus on the chromosome. Derived from the union of gametes of dissimilar genotype. A heterozygous individual is called a heterozygote.

heuristic

    An approach to decision making, or investigation, whereby the operator reaches a conclusion with reference to past experience, or inference, sensory, contextual or coherent information. Sometimes where the experimenters find out things for themselves, that is, by trial and error. See also algorithm

hierarchical classification

    A classification in which the classes are ranked. Every individual belongs to a class and every class to a higher ranking class, up to the highest class, which is the totality of all individuals.

hierarchy

    1. A structural relationship in which each unit consists of two or more subunits, the latter being similarly subdivided.

    2. A model of an agricultural system involving units (systems or subsystems) arranged according to increasing scale and complexity, ranging from the plant cell at the lowest and the region or nation at the highest levels.

high-density planting

    Closely planted trees (as in a woodlot) or crops. See also planting density

high forest system

    Silvicultural system that produces forest trees from seedlings rather than from coppice.

hill farming

    Farming in broken terrain where fields are often small and the land is sloping. Soil erosion can often be a major problem.

homegarden

    A land-use form on private lands surrounding individual houses with a definite fence, in which several tree species are cultivated together with annual and perennial crops; often with the inclusion of small livestock. There are many forms of such gardens varying in how intensively they are cultivated and their location with regard to the home, for example, village forest gardens, 'compound gardens', 'kitchen gardens'.

homeostasis

    The maintenance of static or dynamic stability irrespective of external effects.

homozygous

    1. Having like alleles at corresponding loci on homologous (corresponding) chromosomes.

    2. Possessing the same allele at a particular locus. Derived from the union of genetically similar gametes.

horizontal resistance

    Multigenic, partial resistance equally effective against all races of a pathogen. Sometimes called 'field resistance'; distinct from vertical resistance.

household

    A social category that describes a primary social group, who customarily share their domicile and meals. It may or may not consist of family members. The type of household that is predominant in a society is determined by cultural beliefs, values and norms, and is further influenced by economic and political factors.

humid tropics

    The tropical areas with excessive moisture. However, excessive moisture generally occurs only during a certain period of the year, while drought may occur in the same area during another part of the year. The humid tropics are characterized by isothermal conditions, which implies that temperatures in these areas are generally suitable for year-round crop production. Total radiation varies from relatively low values during the wet period to relatively high values in the dry season.

humification

    The process involved in the decomposition of organic matter and leading to the formation of humus.

humus

    1. Organic matter, including lignin, that has reached a more or less stable, advanced stage of decomposition. It is usually characterized by its dark colour, considerable content of nitrogen, a carbon-to-nitrogen ratio approaching 10:1, and by various physical and chemical properties, such as high base-exchange capacity, water absorption and swelling.

    2. The plant and animal residues in the soil that have undergone some appreciable degree of decomposition.

    3. The lower part of the litter layer, consisting principally of amorphous organic matter and located immediately above the A horizon. A complex colloidal mixture. See also soil organic matter

hybrid

    1. Individual derived from seed obtained from natural or artificial fertilization, between plants belonging to different forms, species or genera.

    2. In its simplest form, a first-generation cross between two genetically diverse parents.

    3. Offspring of organisms of dissimilar genotype; often the offspring of a cross between different species.

hydraulic conductivity

    An expression of the readiness with which a liquid such as water flows through a solid such as soil in response to a given potential gradient.

hydromorphic soil

    Soils developed in the presence of excess water.

hydrophyte

    Plant that grows in water or wet soil; opposite of xerophyte; intermediate with mesophyte.

hygrometer

    Instrument for measuring the relative amount of moisture in the atmosphere and for determining the dewpoint.

hypocotyl

    The part of the stem bearing the cotyledons. If the cotyledons are brought above ground, the hypocotyl appears as the aerial part of the plant (epigeal germination). When the germination is hypogeal, both the cotyledon and the hypocotyl remain buried in the soil.

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University of Georgia The Bugwood Network Forestry Images   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
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