The Tree

by Colin Tudge

  MONOECIOUS Refers to a plant with single-sex flowers, but in which both sexes occur on the same tree. Pines and oaks are among the many monoecious trees.

  MUTUALISM The form of symbiosis in which both partners in the relationship gain net benefit.

  MYCELIUM The total of all the hyphae in a fungus. The mycelium of a single fungus may extend over many acres, and form mycorrhizal relationships with hundreds of trees.

  MYCORRHIZA (pl. MYCORRHIZAE) A symbiotic relationship between fungi and the roots of plants. Many trees, from pines to oaks to acacias (and a great many others) rely heavily or absolutely upon their fungal associates for optimal growth or even for survival.

  N

  NATURAL SELECTION The process that Charles Darwin proposed is the chief adaptive force in evolution. The basic idea is that all creatures have the potential to produce more offspring than the environment can support, and so there is competition, which he also called a “struggle for existence”; that among these offspring there is variation; that, inevitably, some of the variants will be more closely adapted (or “fitted,” as the Victorians tended to say) to the prevailing conditions than others, and so be more likely to survive and leave offspring of their own. Thus as the generations pass, the lineage becomes better and better adapted to the prevailing conditions (until and unless the conditions change).

  NEO-LINNEAN CLASSIFICATION See Linnean classification.

  NICHE A particular conceptual space within a habitat, offering opportunity for exploitation by specialist organisms.

  NITROGEN FIXATION The process by which certain bacteria convert atmospheric nitrogen into soluble ions, notably ammonium, which is further converted to nitrate in the soil and can be used by plants as a macronutrient. Many plants, including many trees, harbor nitrogen-fixing bacteria within special nodules in their roots.

  NUCLEUS The special region of the cell, surrounded by a specialized double membrane, within which the chromosomes (which contain the DNA) reside.

  NUT A fruit that is dry, hard, and indehiscent (meaning it does not split naturally to release the seed inside but must be actively prized open).

  O

  ORDER A taxon smaller than a class and bigger than a family (see Linnean classification).

  ORGANELLE A discrete, specialized structure within a cell, such as a nucleus, chloroplast, or mitochondrion.

  ORGANIC Chemists use the term “organic” to mean any compound containing carbon (or containing carbon, hydrogen, and oxygen, with carbon as the principal component). More generally the term applies to any living material (or at least to material that was formerly alive).

  OSMOSIS The net diffusion of water from a region where the concentration of dissolved materials is low to where the concentration is high.

  OUTCROSSING Fertilization effected between different individuals (as opposed to inbreeding).

  OVARY The enlarged base of the carpel (or the fused bases of adjacent carpels) that forms a chamber that contains the ovule or ovules.

  OVULE The structure within the carpel of a seed plant that contains the female gamete (egg cell) and that matures after fertilization to become the seed.

  P

  PALEOBOTANY The study of ancient plants, generally conducted through the study of plant fossils (including fossil pollen).

  PARALLEL EVOLUTION Sometimes two separate lineages of creatures that live in similar habitats evolve over time in similar ways, so that at any one time in their history each resembles the other. This is parallel evolution.

  PARALLEL VENATION The condition characteristic of monocot plants in which the principal veins in the leaf run roughly in parallel from the leaf base to the tip.

  PARASITE An organism that lives on or within another organism, usually of a different species, and derives nutrient from it. Parasitic relationships always benefit the parasite and do varying degrees of harm to the host. When the host also benefits from the presence of the parasite, the relationship is said to be “mutualistic.” Thus mycorrhizal fungi might be said to be parasitic on the roots of plants, but they also bring great benefit to the plant.

  PATHOGEN Any organism that causes disease in another.

  PHENOTYPE The overall form of an organism. Two or more organisms of similar genotype may nonetheless look or behave differently—which means that although they are genetically similar, they have different phenotypes.

  PHEROMONE A chemical agent that passes from one organism to another and influences the physiology or the behavior of the recipient. Essentially, an airborne (or waterborne) hormone.

  PHLOEM The specialized tissue outside the cambium that contains elongated cells that transfer foods, particularly organic foods such as sugars, around the plant. The phloem forms the inner (living) part of the bark.

  PHOTOPERIODISM The mechanism by which plants respond to day length and so adjust their life cycle to the seasons.

  PHOTOSYNTHESIS The process, mediated by chlorophyll, whereby plants harness the energy of the sun to split molecules of water into hydrogen and oxygen, and then attach the hydrogen to carbon dioxide (from the atmosphere) to form organic materials.

  PHOTOTROPISM The tendency of plants to grow toward or away from light. In general, stems grow toward the light (positive phototropism) and roots grow away from it (negative phototropism).

  PHYLLODE A flat, expanded area of petiole (leaf stalk) or stem that carries out photosynthesis. In some trees, including the coniferous celery pines, leaves have been abandoned in favor of phyllodes.

  PHYLOGENY The term derives from the Greek phylos, meaning “tribe”; so “phylogeny” literally refers to the origin of different taxa. In practice phylogeny has come to refer to the true evolutionary relationships between different taxa. The entire methodology of cladistics is designed to identify these true relationships. Modern, neo-Linnean classification, guided by cladistic principles, is intended to produce a taxonomy firmly rooted in true phylogeny.

  PHYLUM A large taxon of animals, positioned between kingdom and class, and equivalent to “division” in botany (see Linnean classification).

  PHYSIOLOGY The study of all the functions and metabolic processes of living organisms.

  PHYTOCHROME A plant pigment (or collection of pigments) that absorbs red and infrared light and is heavily involved in the mechanism that controls photoperiodism.

  PIGMENT Any chemical that absorbs light of particular wavelengths and reflects what it does not absorb, so that it appears colored. In general, all the many responses of plants to light are mediated by pigments of various kinds.

  POLLEN A small structure produced by conifers and angiosperms, containing the male sex cell.

  POLLEN TUBE When an individual pollen grain lands on the stigma of a flower it germinates to produce a pollen tube that grows down through the tissues of the style to reach the ovule beneath.

  POLLINATION The process by which pollen is transferred from the anther to the stigma.

  POLYPLOID A cell that contains more than two sets of chromosomes; or an organism that is compounded from such cells.

  POPULATION The term is used in various ways. It is best used to describe a group of individuals from the same species, living in the same place at the same time, who interbreed (or may be considered capable of doing so when circumstances permit).

  PREDATOR A creature that preys on another creature. The term is commonly taken to refer to carnivores, which prey on other animals. But herbivores such as giraffes, koalas, and many a caterpillar may be seen as predators of trees.

  PROKARYOTE An organism in which the DNA is not sequestered within a cell nucleus. There are two domains of prokaryotes: the Bacteria and the Archaea. Plants—including trees, of course—belong to the third domain, the Eucaryota, which have eukaryotic cells.

  R

  RADICLE The root of the plant embryo.

  RANK, RANKING In Linnean (or neo-Linnean) classification, “genus” is a higher rank than “species,” “family” is higher than “genus,” and so on all the way up to “dom
ain,” the highest rank (or ranking) of all.

  REACTION WOOD Wood with an abnormal structure that develops in response to particular stresses and strains. It is manifest in trees that lean, as “compression wood” beneath the boughs of conifers, and as “tension wood” above the boughs of angiospermous trees.

  RHIZOME A more or less horizontal underground stem, frequently swollen and serving as a storage organ.

  RNA (RIBONUCLEIC ACID) DNA, ensconced within the nucleus in a eukaryotic cell, provides the code for the construction of proteins. RNA in various forms ferries the information out from the nucleus and into the cytoplasm, where the proteins are put together.

  S

  SAP The fluid within the xylem, which is released when the stem is cut. “Cell sap” is the fluid within individual cells.

  SAPWOOD Outer part of the stem or trunk in which the xylem conducting tissue is still alive and flowing with sap. Sapwood is commonly lighter in color than heartwood, sometimes strikingly so, as in the yew tree and some species of ebony.

  SAVANNAH Grassland with scattered trees.

  SECONDARY GROWTH Growth arising from division of cells of the cambium, which increases the girth of the trunk.

  SHORT-DAY PLANT A plant that will not flower unless first exposed to days that are shorter than some critical day length (or, more accurately, is exposed to nights that are longer than some critical length; see Chapter 11).

  SHRUB A perennial woody plant with several stems arising at or near the ground. The distinction between large shrubs and trees is arbitrary.

  SOFTWOOD A forester’s name for the timber of conifers.

  SPECIES The basic ranking of living creatures; see Linnean classification and discussion in Chapter 2.

  SPORE A cell (usually just a single cell) that is typically diploid, is released from the parent plant, and can then grow directly into a new plant. Thus spores serve as agents of asexual reproduction.

  SPOROPHYTE The generation of the plant that produces spores. In fact, although seed plants are properly called “sporophytes,” they do not produce free-living spores. They produce seeds instead. See Chapter 3.

  STROBILUS A reproductive structure constructed from a number of leaves or scales, commonly arranged in a spiral, as in a cone.

  SUBSPECIES A subdivision of a species; generally synonymous with “race” (see Linnean classification).

  SUBSTRATE Whatever the plant is growing on.

  SUCCESSION In ecology, the sequence of species over time as new land is colonized.

  SUCCULENT Refers to plants that have fleshy leaves or stems, swollen with water.

  SUCKER A sprout arising from the roots that can give rise to a new plant, as in aspens and many willows.

  SYCONIUM Broadly speaking, the fruit of the fig tree. This is not quite accurate, however, since a fruit only becomes a fruit after the ovules within are fertilized. But the term “syconium” also refers to the fleshy inflorescence, even before fertilization.

  SYMBIOSIS Literally means “together life.” Refers to the often close association of different organisms, generally of different species. Although the term is commonly taken to imply mutual benefit, technically it can include parasitism, in which the host organism suffers. Symbiotic relationships from which both (or all) partners benefit are properly called “mutualistic.”

  SYSTEMATICS Essentially synonymous with “taxonomy.”

  T

  TAXON, TAXONOMY “Taxon” literally simply means “group”; and taxonomy is the craft and science of placing creatures into groups—that is, of classification. A taxon (the plural is “taxa”) may be of any grade: so “species” is a taxon; “family” is a taxon; “order” is a taxon; and so on all the way up to “domain.” Ever since Darwin, however, mainstream taxonomists have insisted that a taxon cannot be formally acknowledged as such unless all the creatures within it are literally related to one another—meaning that they all share a common ancestor. Cladists have refined the idea so that no group can nowadays be admitted as a “true” taxon unless it includes all the descendants of a common ancestor, and the ancestor itself, but includes no other creatures that are not part of the lineage.

  TENSION WOOD Reaction wood that develops in response to tension, which develops on the upper side of big branches of dicot trees, on the upper surface of leaning trunks, and in buttress roots (which, in truth, act more like guy ropes than buttresses).

  TETRAPLOID A cell with four sets of chromosomes, or an organism compounded of tetraploid cells.

  TISSUE, TISSUE CULTURE A tissue is any group of cells of similar type and function. (Organs commonly consist of several different kinds of tissue working in concert.) Tissue culture is the craft and science of maintaining tissues in cultures, used both to study cells and, increasingly, as a means of asexual reproduction: whole new trees (of teak, coconuts, and many more) may be grown from cultured cells taken from outstanding (“elite”) trees.

  TOTIPOTENT Cells of embryos, and other specialized cells known as “stem” cells, are able to differentiate to form any of the tissues of the organism. Such cells are said to be “totipotent.”

  TRACE ELEMENT, TRACE MINERAL A chemical element that is essential for nutrition but is required only in very small amounts. For plants, molybdenum and manganese are examples.

  TRACHEID The xylem of conifers is composed of elongated cells known as tracheids (pronounced with three syllables: tray-key-ids).

  TRANSLOCATION The transfer of water or foodstuffs within a plant. (Used more commonly to refer to the transfer of foodstuffs within the phloem.)

  TRANSPIRATION The loss of water from the aerial parts of the plant. Most of the loss occurs through the stomata.

  TRIPLOID A cell with three sets of chromosomes, or an organism with triploid cells. Cultivated bananas are triploid (and sexually sterile). So are the cells of the endosperm of angiosperm seeds.

  TROPHIC Refers to feeding. Thus plants, which synthesize their own food, are “autrotrophs.” The different layers of creatures in a food chain—carnivores eating smaller carnivores eating herbivores eating plants and so on—are referred to as “trophic levels.”

  TROPISM Movement, or more accurately growth, toward or away from an external stimulus.

  TURGID, TURGOR PRESSURE “Turgid” means swollen, as in a cell that has taken up a lot of water so that it presses hard against the cell wall. Herbaceous plants stay upright primarily because of water pressure in their cells, known as “turgor pressure.” The leaves and young shoots of trees are also held in shape by turgor pressure. Herbs and tree leaves wilt when too much water is lost.

  U

  UNICELLULAR An organism with only one body cell.

  V

  VARIETY A subdivision of a species (see Linnean classification).

  VASCULAR, VASCULAR PLANT “Vascular” refers to any part of a plant that contains conducting tissue, either xylem or phloem. Living vascular plants include all land plants except the bryophytes—mosses, liverworts, and hornworts.

  VECTOR Anything that carries anything else. Thus bees are vectors of pollen and fruit bats are vectors of figs (and aphids are vectors of viruses that cause many diseases in plants).

  VEGETATIVE A general term that applies to all parts of the plant apart from those involved in sexual reproduction. “Vegetative reproduction” is reproduction via suckers or rhizomes, or (in cultivation) via cuttings or tissue culture.

  VEIN, VENATION A vein is the conducting and supporting tissue within a leaf, or in other flat structures. “Venation” refers to the pattern of veins within a leaf.

  VESSEL An open-ended tubular cell of the kind that forms the main conducting tissue within the xylem of an angiosperm. (Also used loosely in this book, and strictly speaking inaccurately, to refer to the corresponding structures in conifers, which should be called “tracheids.”)

  W

  WEED Any plant growing in a place where, in the opinion of the botanist, gardener, or forester, it should not be growing. Any plant that the botanist
, gardener, or forester regards as a nuisance.

  WHORL A circle of leaves or flower parts. The basic flower contains four whorls: of sepals, petals, stamens, and carpels.

  WOOD Botanists apply the term “wood” to xylem, especially the xylem that no longer serves to conduct fluids and is solely supportive.

  X

  XYLEM Conducting tissue that carries water (and minerals dissolved in the water).

  Z

  ZYGOTE A cell formed by the fusion of male and female gametes. In effect, a single-celled embryo.

  ACKNOWLEDGMENTS

  OVER THE PAST half century I have had many illuminating conversations with a lot of people who know a great deal about trees, in at least a score of countries in every habitable continent, and it would be too exhausting to mention everyone who has helped me with this book. Over the years, however, I have been particularly informed by Professor E. R. (Bob) Orskov, now at the Macauley Research Station in Aberdeen, on Third World agriculture in general and agroforestry in particular. From China, I have particular cause to thank Professor Hao Xiaojiang, director of the Kunming Institute of Botany in Yunnan, China, who introduced me to the extraordinary collection (including one hundred species of magnolias) in the Botanic Garden of Kunming, and Dr. Ian Hunter, director of the International Network for Bamboo and Rattan, Beijing. In Australia, I spent several excellent days with scientists from CSIRO both in the bush of Western Australia and in the tropical and subtropical forests of Queensland and New South Wales. In New Zealand, Keith Stewart, novelist and columnist, took me to see the kauri forests on the North Island and introduced me to Tane Mahuta.

  For the particular writing of this particular book, I am especially aware of my debt to Professor Jeff Burley, formerly head of forestry at Oxford University, who indeed inspired this whole enterprise (just as he inspired generations of foresters worldwide). Also at Oxford, Dr. Stephen Harris read several of the chapters for me; Dr. Nick Brown helped me on my way with comments about mahogany; Professor Martin Speight provided fine fresh insights into pests; Professor Andrew Smith instructed me in tree physiology; and Dr. Yadvinder Malhi had excellent, original things to say about tropical forests and climate change. At the Royal Botanic Gardens, Kew, I was privileged to be introduced to the latest thinking on conifers by Dr. Aljos Farjon. At EMBRAPA in Belém, I was treated royally and introduced to the realities of Brazilian forestry by Ian Thompson and had particularly illuminating discussions with Dr. Mike Hopkins and Dr. Milton Kanashiro. In Belém, too, from Johan C. Zweede I learned at least a few of the ins and outs of tropical forest commerce. I was introduced to the Cerrado by Professor Carolyn Proença of the University of Brasilia and by Dr. Manual Cláudio da Silva Júnior of Brazil’s forestry department, while José Felipe Ribeiro took my wife and me out into the field to show us ways in which local people can make a much better living from the Cerrado than by growing yet more soybeans. Hugely instructive, too, as well as enjoyable, was our stay with Robin and Binka Le Breton, at Iracambi, who are seeking, among other things, to restore at least some of the sadly depleted Atlantic rain forest. At the Smithsonian Tropical Research Institute in Panama I was prodigiously instructed by Drs. Anthony G. Coates (continental drift), Neal G. Smith (mainly birds), Stanley Heckadon-Moreno (mangroves), Egbert G. Leigh (particularly on the tropical forest on Barro Colorado Island), and Allen Herre (whose extraordinary researches on figs are a key theme in Chapter 13). Boundless gratitude to all of them, and to Beth King for fixing up the entire trip. At the Tropical Agricultural Research and Higher Education Center (CATIE) in Costa Rica, Dr. Bryan Finegan was wonderfully generous with his time and showed, as we stood in the rain, how physically hard as well as magical it can be to carry out research in tropical forests; while Dr. Muhammad Ibrahim introduced me to CATIE’s excellent researches in agroforestry and Dr. Wilberth Philips showed me the local trees. Then to India, and in particular to the vast and extraordinary campus and arboretum of the Forestry Research Institute at Dehra Dun, where I have particular cause to be grateful to FRI’s then director, Dr. Padam Parkash Bhojvaid, for excellent discussions and hospitality (including Christmas dinner with his family), and in particular among his colleagues to Dr. Sas Biswas. In Latvia, I was introduced to the forest (and its beavers) by Ieva Muizniece of the British Council, Anita Upite, editor of Hunting, Angling and Nature, and Monvids Strautins, forester. I am grateful, too, to the British Council in general and to Dr. Gavin Alexander in particular, who arranged some of my most illuminating trips.