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Glossary active collection Comprised of accessions that are maintained under conditions of short- or medium-term storage for the purpose of study, distribution, or use. afforestation Establishing trees on ground where they have not pre- viously grown. agroforestry Any land use that combines the growing of food and tree crops. Domestic animals may be included. allele One of two or more alternative forms of a gene, differing in DNA sequence and affecting the functioning of a single gene product (RNA and/or protein). All alleles of a series occupy the same site or locus on a pair of homologous chromosomes. allozyme Differing forms of an enzyme, all produced by the different alleles of a single gene. They can generally be distinguished from one another using electrophoresis. (See also isozyme.) angiosperm Any flowering plant; a plant bearing seeds that develop in an enclosed ovary or carper. apomixis Asexual reproduction in plants in which the sexual organs or related structures are involved, but fertilization does not occur. The resulting seed is vegetatively produced from an unfertilized egg or from somatic cells associated with the female parent base pair A pair of hydrogen-bonded chemical components (one a purine, the other a pyrimidine) that join the component strands of the DNA double helix. biodiversity (biological diversity) The variety and variability among living organisms and the ecological complexes in which they occur. 201

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202 I Glossary biosphere The largest, all-encompassing ecosystem that includes soil, water, and the atmosphere. climax forest The final stage in a forest succession sequence where the species composition remains relatively unchanged as long as climate and physical geography remain the same. collecting The general activity of gathering or acquiring genetic ma- terials (e.g., plants, seeds) for addition to genetic resources collec- tions. (See also sampling.) community A group of ecologically related populations of various species that occur in a particular geographic area at a particular time. conifer A general term referring to trees and shrubs of an order (Coniferales) that consists mostly of evergreen species; a cone- bearing tree such as pine, fir, spruce, or cypress. cryopreservation Maintaining tissues or seeds for the purpose of long- term storage at ultralow temperatures, typically between -150C and -196C; produced by storage above or in liquid nitrogen. deciduous Pertains to those trees that drop their leaves at the end of the growing season, typically during winter. dioecious Pertains to plant species having female and male sex organs on different plants. diploid Possessing twice the number of chromosomes as the number present in reproductive organs such as eggs or the reproductive cells of the pollen grain. The somatic number of chromosomes (2n). ecosystem A community of organisms interacting with one another; the environment in which organisms live and with which they also interact. ecotypic differentiation The process of producing distinct individuals within a species, subspecies, or variety in a given environment that are different morphologically and physiologically from others of the same species in another environment. These so-called ecotypes cross freely with other ecotypes of the same species, subspecies, or variety and can arise from the selective pressures unique to each environment. electrophoresis The differential movement of charged molecules in solution through a porous medium in an electric field. The porous medium can be filter paper, cellulose, or, more frequently, a starch or polyacrylamide gel. electrophoretic analysis A method commonly used to separate proteins and other organic molecules.

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Glossary / 203 endangered In the context of this report, a term that applies to taxa (population, subspecies, species) in danger of extinction and for which survival is unlikely if the causal factors of loss continue. enzyme A large group of proteins produced by living cells that act like catalysts in essential chemical reactions in living tissues. even-age plantation management A practice where all trees of a plantation are of the same or very nearly the same age. exotic A tree growing in an area in which it does not naturally occur. ex situ management The management of planted stands of trees outside of their natural range; the conservation or preservation of trees as seed, pollen, tissue culture, or excised plant parts (e. g., bud cultures). extinct In the context of this report the term refers to taxa (e. g., populations, subspecies, species) not found after repeated searches of known and likely areas. food chain The pathway for energy in a natural community from producers (e.g., plants) to consumers (herbivores and carnivores) to decomposers (e.g., fungi). food web The complex interrelationships among the interconnecting food chains that occur within a community. gene The basic functional unit of inheritance responsible for the heritability of particular traits. gene bank An institution or center that participates in the management of genetic resources, in particular by maintaining ex situ or in situ collections; the term also can refer to a collection of genetic resources rather than the institution holding it. gene flow The movement of genes through or between populations as the result of outcrossing and natural selection. gene pool The totality of genes and their alleles within an interbreeding population. genetic diversity In a group such as a population or species, the possession of a variety of genetic traits that frequently result in differing expressions in different individuals. genetic resources In the context of this report, trees from which the genes needed by breeders and other scientists can be derived. genotype The genetic constitution of an individual or group that may be either expressed or unexpressed, depending on the environ- mental effects of a given location. germplasm collection A collection of many different varieties, species, or subspecies representing a diverse collection of genotypes and, hence, genetic diversity.

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204 / Glossary gymnosperm Woody vascular plants, such as conifers, that produce naked seeds not enclosed by an ovary. habitat The place where an organism is usually found; its natural environment. hermaphroditic Pertaining to an organism or structure that has both male and female reproductive organs. heterozygous Having one or more unlike alleles at corresponding loci of homologous chromosomes. homologous chromosomes Chromosomes that are morphologically similar and pair at the first division of meiosis. homozygous Having like alleles for a particular gene at corresponding loci on homologous chromosomes. hybridization The process of crossing individuals that possess different genetic makeups. inbreeding The intentional or unintentional breeding or crossing of individuals that are more closely related than their parents. in situ management The managing of organisms in their natural state or within their normal range; for trees, this may include such activities as the planting of provenance trials, seed orchards, or conservation stands within a species' natural range. interbreeding In the context of this report, trees that are capable of actual or potential gene exchange through hybridization. isoenzyme (isozyme) Different chemical forms of the same enzyme that can generally be distinguished from one another by electro- phoresis. (See also allozyme.) major genes Genes that make a large contribution to the expressed character, relative to environmental or other modifying influences (e.g., genes for flower color). micropropagation The clonal production of trees or other plants through techniques of in vitro culture of buds, plantlets, or tissues. minimum viable population (MVP) The size below which a population cannot remain stable or increase in number, but will decline and disappear, due either to insufficient reproduction or the genetic consequences of inbreeding. monecious A plant species having female and male sexual organs on the same plant. monotypic In taxonomy, having a taxon represented by one subordi- nate member. A monotypic genus, for example, is one in which there is only a single species (e.g., Ginko biloba). morphometric Referring to the measurement or study of external form. mutualist An organism that participates in a form of symbiosis (mu- tualism) in which both organisms derive benefit from the association.

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Glossary / 205 Nei's measures A measurement of genetic distance developed to estimate the number of DNA codon differences per structural gene locus for proteins and the divergence time between closely related species. It presupposes that the genes are selectively neutral (see E. B. Spiess, Genes in Populations, 2d ed. John Wiley and Sons, New York, 1989~. nitrogen-fixing bacteria Select bacterial species that biologically convert molecular dinitrogen (N2) to molecular forms useable by plants. Outcrossing The breeding of unrelated plants or plants of different genotypes, usually under natural conditions. panmictic population A population in which mating is entirely ran dom. perennial crops Crop plants that are managed to be productive over several years. They include herbaceous perennials that die back annually, such as asparagus; and woody perennials that have stems that may live for many years, such as apples, citrus crops, or mangos. phenotype The sum total of the environmental and genetic (hereditary) influences on a tree; the visible characteristics of a plant. pollen vector The carrier, such as wind or insects, of pollen from one plant or tree to another. pollen-seed vector The carriers or distributors of pollen or seed (e.g., wind, bird, insects). polygenic trait A genetically controlled characteristic that is the product of the combined interactions of numerous genes, each having individually small effects. A species with several to many variable forms. polymorphic population A group of organisms of the same species that occupy a particular geographic area or region. In general, individuals within a population interbreed with one another. progeny testing Determining the genetic characters or evaluating the genotype of an organism based on the performance of its offspring under controlled conditions. provenance Origin or source; for trees, an identifiable region in the natural habitat of a species from where the seed of the trees originally came. provenance testing Growing trees in different provenances to deter mine how they will respond. Exotics are sensitive to the use of the wrong provenance for growth, and they may die, have dieback, or produce an unacceptable form. rare In the context of this report, the term refers to taxa with small

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206 / Glossary world populations that are not currently endangered or vulnerable, but that are at risk of loss. reforestation The introduction of trees on land from which they had previously been removed. sampling In the context of genetic resources, the use of the principles and theory of population genetics and related disciplines to ascertain what and how much collecting is needed to obtain the genetic diversity available in a population. (See also collecting.) seed bank An ex situ managed collection of seeds, usually available for distribution and exchange. seed collection stand Plantations or planted stands managed and maintained for the purpose of producing seed. selection Any natural or artificial process that permits an increase in the proportion of certain genotypes or groups of genotypes in succeeding generations in relation to others. self-pollination (selling) The natural or artificial process of placing pollen grains on a receptive stigma of the same individual. silvipastoral system An agricultural system that combines forestry and the production of domestic animals. species A taxonomic subdivision of the ranking genus. A group of organisms that actually or potentially interbreed and are reproduc- tively isolated from other such groups. stumpage value The value of standing timber if cut. threatened In the context of this report, the term refers to taxa for which the potential for loss exists but for which there is insufficient data to determine whether they are rare, vulnerable, endangered, or extinct. tissue culture A technique for cultivating cells, tissues, or organs of plants in a sterile, synthetic medium; includes the tissues excised from a plant and the culture of pollen or seeds. tree A woody perennial plant typically having a single main stem or trunk. vulnerable In the context of this report, the term refers to taxa believed likely to move into the endangered category in the near future if the causal factors of loss continue.