SIGNS OF CHANGE

We live in times of change and the impact of climatic warming can already be seen in many marginal areas. Effects that appear to be directly attributable to climate change are most noticeable in polar and alpine regions with the retreat of glaciers and snow and ice cover regions (Fig. 12.1). Coastal erosion as a result of rising sea levels is also having a noticeable impact. Archaeological rescue excavations of ancient coastal settlement sites exposed by erosion are now numerous. Several Scottish coastal golf courses have had to be redesigned as sections have been totally removed by the advancing sea. A coastal Scottish National Nature Reserve (Tentsmuir) that had been growing steadily seawards for centuries is now in places retreating rapidly by as much as 200 m depth of dunes over the last 20 years, returning sections of the coastline to where they were in the 1920s (Fig. 12.2).

More positive changes include an increase in the number of plant species to be found on the summits of European mountains (see Section 10.7), and an earlier flowering of the vernal flora with an extension of the growing season into the autumn. Northern agriculture is also profiting from the passing of the Little Ice Age in both crop production and length of the grazing season. However, in many parts of the world deleterious changes are taking place which are being aggravated by increasing human disturbance.

Originally entitled The Naming of Plants and the Meanings of Plant Names, this book is in two parts. The first part has been written as an account of the way in which the naming of plants has changed with time and why the changes were necessary. It has not been the writer's intention to dwell upon the more fascinating aspects of common names but rather to progress from these to the situation which exists today, in which the botanical and horticultural names of plants must conform to internationally agreed standards. The aim has been to produce an interesting text which is equally as acceptable to the amateur gardener as to the botanist. The temptation to make this a definitive guide to the International Code of Botanical Nomenclature was resisted since others have done this already and with great clarity. A brief comment on synonymous and illegitimate botanical names and a reference to recent attempts to accommodate the various traits and interests in the naming of cultivated plants was added after the first edition.

The book had its origins in a collection of Latin plant names, and their meanings in English, which continued to grow by the year but which could never be complete. Not all plant names have meaningful translations. Some of the botanical literature gives full citation of plant names (and translations of the names, as well as common names).

It is basic to the collector's art to arrange items into groups. Postage stamps can be arranged by country of origin and then on face value, year of issue, design, colour variation or defects. The arranging process always resolves into a hierarchic set of groups. In the plant kingdom we have a descending hierarchy of groups through Divisions, divided into Classes, divided into Orders, divided into Families, divided into Genera, divided into Species. Subsidiary groupings are possible at each level of this hierarchy and are employed to rationalize the uniformity of relationships within the particular group. Thus, a genus may be divided into a mini-hierarchy of subgenera, divided into sections, divided into series in order to assort the components into groupings of close relatives. All such components would, nevertheless, be members of the one genus.

Early systems of classification were much less sophisticated and were based upon few aspects of plant structure, such as those which suggested signatures, and mainly upon ancient herbal and medicinal concepts. Later systems would reflect advances in man's comprehension of plant structure and function, and employ the morphology and anatomy of reproductive structures as defining features. Groupings such as Natural Orders and Genera had no precise limits or absolute parity, one with another; and genera are still very diverse in size, distribution and the extent to which they have been subdivided.

Man's highly developed constructive curiosity and his capacity for communication are two of the attributes distinguishing him from all other animals. Man alone has sought to understand the whole living world and things beyond his own environment and to pass his knowledge on to others. Consequently, when he discovers or invents something new he also creates a new word, or words, in order to be able to communicate his discovery or invention to others. There are no rules to govern the manner in which such new words are formed other than those of their acceptance and acceptability. This is equally true of the common, or vulgar or vernacular names of plants. Such names present few problems until communication becomes multilingual and the number of plants named becomes excessive. For example, the diuretic dandelion is easily accommodated in European languages. As the lion's tooth, it becomes Lowenzahn, dent de lion, dente di leone. As piss-abed it becomes pissenlit, piscacane, and piscialetto. When further study reveals that there are more than a thousand different kinds of dandelion throughout Europe, the formulation of common names for these is both difficult and unacceptable.

This book is intended for use by botanists, gardeners and others who have an interest in plant names, the manner and rules by which they are formed, their origins and their meanings. The evolution of our current taxonomic system, from its origins in classical Greece to its present situation, is dealt with in the first part. This presents an overview of some major aspects of resolving the earlier unregulated way of naming plants. It goes on to explain how the current system evolved, and the use of Latin as the universal, and often innovative, language for those names. It then treats the naming of cultivated plants, from the wild, produced by hybridization or by sporting, maintained only by vegetative means, in horticulture, agriculture or arboriculture, and perhaps differing only in single small features. These are subject to the botanical rules of nomenclature but also have their own set of international rules for the naming of garden variants. Both Codes (the International Code of Botanical Nomenclature and the International Code of Nomenclature for Cultivated Plants) are explained.

The main body of the book has been considerably enlarged for this edition. It consists of a glossary of over 17,000 names or components of names. Each entry contains an indication of the source from which the name is derived.

There can be no doubt that the diverse approaches to naming garden plants, by common names, by botanical names, by mixtures of botanical and common names, by group names and by fancy names, is no less complex than the former unregulated use of common or vernacular names. The psychology of advertising takes descriptive naming into yet new dimensions. It catches the eye with bargain offers of colourful, vigorous and hardy, large-headed, incurved Chrysanthemum cvs. by referring to them as HARDY FOOTBALL MUMS. Perhaps the director whose appointment was headlined ‘Football Mum appointed to Sainsburys’ hopes that she is also ‘hardy’. However, we are not here concerned with such colloquial names or the ethics of mail-order selling techniques but with the regulation of meaningful names under the Code.

In 1952, the Committee for the Nomenclature of Cultivated Plants of the International Botanical Congress and the International Horticultural Congress in London adopted the International Code of Nomenclature for Cultivated Plants. Sometimes known as the Cultivated Code, it was first published in 1953 and has been revised several times at irregular intervals since then (Trehane, 1995, Brickell et al., 2004). This Code formally introduced the term ‘cultivar’ to encompass all varieties or derivatives of wild plants which are raised under cultivation, and its aim is to ‘promote uniformity and fixity in the naming of agricultural, sylvicultural and horticultural cultivars (varieties)’. The term culton (plural culta) is also proposed as an equivalent of the botanical term taxon.

The rules which now govern the naming and the names of plants really had their beginnings in the views of Augustin P. de Candolle as he expressed them in his Théorie élémentaire de la botanique (1813). There, he advised that plants should have names in Latin (or Latin form but not compounded from different languages), formed according to the rules of Latin grammar and subject to the right of priority for the name given by the discoverer or the first describer. This advice was found inadequate and, in 1862, the International Botanical Congress in London adopted control over agreements on nomenclature. Alphonse Louise de Candolle (1806–1893) drew up four simple ‘Lois’, or laws, which were aimed at resolving what threatened to become a chaotic state of plant nomenclature. The Paris International Botanical Congress of 1867 adopted the Lois, which were:

1. One plant species shall have no more than one name.

2. No two plant species shall share the same name.

3. If a plant has two names, the name which is valid shall be that which was the earliest one to be published after 1753.

4. The author's name shall be cited, after the name of the plant, in order to establish the sense in which the name is used and its priority over other names.

Three centuries before Christ, Aristotle of Stagira (384–322 bc), disciple of Plato, wrote extensively and systematically of all that was then known of the physical and living world. In this monumental task, he laid the foundations of inductive reasoning. When he died, he left his writings and his teaching garden to one of his pupils, Theophrastus of Eresus (c. 370-287 bc), who also took over Aristotle's peripatetic school. Theophrastus' writings on mineralogy and plants totalled 22 treatises, of which nine books of Historia plantarum contain a collection of contemporary knowledge about plants and eight of De causis plantarum are a collection of his own critical observations, a departure from earlier philosophical approaches, and rightly entitle him to be regarded as the father of botany. These works were subsequently translated into Syrian, to Arabic, to Latin and back to Greek. He recognized the distinctions between monocotyledons and dicotyledons, superior and inferior ovaries in flowers, the necessity for pollination and the sexuality of plants but, although he used names for plants of beauty, use or oddity, he did not try to name everything. To the ancients, as to the people of earlier civilizations of Persia and China, plants were distinguished on the basis of their culinary, medicinal and decorative uses – as well as their supposed supernatural properties. For this reason, plants were given a name as well as a description.

Plant life forms and biological spectra

Variation in vascular plant and bryophyte life form

In addition to taxonomic classifications which endeavour to place closely related species in the same family, botanists have for centuries attempted to distinguish particular life forms, any one of which may be adopted by quite unrelated species. The simplest of these is the distinction between woody and herbaceous plants. Raunkiaer (1934) developed the most widely known scientific description of life forms, and then used it to initiate the use of biological spectra to compare different floras. The main feature of this ecologically valuable system is the position of the vegetative perennating buds or persistent stem apices during the cold winter or dry summer forming the unfavourable season of the year. The main life forms shown in Fig. 3.1 form a sequence showing successively greater protection from desiccation, indicating the position of the vegetative buds when the plant is dormant.

It was assumed that the flowering plants evolved when the climate was more uniformly hot and moist than it is now, and that the most primitive life form is represented by the phanerophytes which still dominate tropical vegetation. These large terrestrial plants can grow continually forming stems, often with naked buds, projecting high into the air. Those whose buds are protected from cold or desiccation by bud scales are considered to be more highly evolved.

Producers and consumers

Primary production is undertaken by autotrophs, which in forests are green plants (photoautotrophs) that produce complex compounds from simple raw materials using the energy of light in the process of photosynthesis. Chemoautotrophs do this using the energy of chemical reactions (chemosynthesis), but do not play an important role in woodlands. Heterotrophs, by contrast, consume other organisms and so are dependent on the uptake of energy in organic materials synthesized by these other organisms. Herbivores, carnivores, parasites and decomposers (saprotrophs) are all heterotrophs; they vary in size from microorganisms and insect larvae to elephants and all play important roles in woodland, forest and related ecosystems. The increase in biomass of heterotrophs is known as secondary production. Heterotrophs that exploit autotrophs directly are called herbivores or primary consumers. These are consumed by secondary consumers, the carnivores, and some of these may in turn be eaten by tertiary consumers to form food chains. It is rare for an animal to feed on just one other species, so in reality food chains become a food web, a network of interconnected food chains (see Fig. 1.10). Many of the consumers forming this plant-dependent web influence green plants adversely, often by feeding or trampling. Others are positive, acting as pollinators and dispersers of fruits and seeds, and even more significantly, promoting nutrient cycling (see Section 8.3).

Soils and trees

Soils are often given superficial treatment, and yet without them forests would quickly cease to function. As well as physically supporting plants, soils act as refuse collectors, processing organic waste and thereby recycling nutrients, a major influence on the productivity of forests. Without functioning soils, forests would rapidly be choked with dead wood and other material, and the bulk of nutrients needed by plants and animals would be locked up and unavailable.

Moreover, soil is not simply a loose collection of ‘dirt’, it is a complex mix of living and non-living components, consisting of air (soil gases: typically 25% by volume), water (25%), mineral particles (45%) and organic matter (5%); the last can be subdivided by weight into around 10% organisms, 10% roots and 80% humus. As described further in Chapters 1 and 7, various soil animals, such as earthworms and arthropods and the micro-organisms, including fungi and bacteria, decompose dead material to release nutrients and form the left-over, rather inert black humus of the soil.

Soil takes a long time to form, usually thousands of years, and its quality is one of the most important conditions governing the growth of trees, smaller plants and associated organisms in any site. As Fig. 2.1 demonstrates, soils have distinct morphologies each with a characteristic profile (a sequence of horizontal layers or horizons from ground surface to unaltered bedrock or sediment).

Characteristics of woodlands and forests

Wooded environments

Forests often appear monumental and unchanging. This is, however, mostly an illusion caused by our short human perspective. The earliest green plants possessing both roots and tissues specially adapted for the transmission of water belonged to the Psilopsida, which gave rise to the ferns and fern allies. It is from the ancestors of this group, which arose in the Silurian (c. 440 million years ago), that all trees – both ancient and modern – are ultimately derived (see Fig. 1.1). Amongst the many evolutionary trends found within this group were tendencies towards the production of (a) tall trunks and (b) seeds from which young plants, including trees, could develop relatively rapidly. Tree ferns, cycads, maidenhair trees, conifers, palms and the very large number of broadleaved genera remain in our woodlands and forests to this day (further detail on past forests can be found in Chapter 9). The amount and composition of the world's wooded areas have changed continuously over geological time, sometimes more rapidly than at others, and continue to do so, helped especially now by human activities. This book is mainly concerned with understanding today's forests in that light.

Wooded land currently covers between 30–35% of the world's land surface (depending on what is counted as forest) or around 39–45 million km2.

Plant strategies

Strategic response to competition, disturbance and stress

The concept that living organisms display ecological ‘strategies’ has advanced rapidly in recent years. The r–K continuum of MacArthur and Wilson (1967) made an important early contribution in contrasting the opportunistic r-species (with rapid rates of population growth), which exploit temporary habitats, with the equilibrium K-species of stable habitats in which competitive ability and survival of the individual is more important than population growth. In the same way that differing species of organism have gradually evolved over long periods of time (Darwin, 1859), such strategies arose through the exertion of competitive natural selection upon varied populations in which differences from the previous norm constantly arose. The CSR model of Grime (1974, 1979) – standing for Competitor–Stress tolerator–Ruderal – made an important further advance in adding the stress-tolerators, organisms capable of exploiting continuously unproductive environments or niches. The competitors are equivalent to the K-species and the ruderals (living on disturbed sites) approximate the r-species. This theory also recognizes that in plants there is a separation of the established (adult) and regenerative (juvenile) strategies and they may respond differently to their environment. This theory has been very thoroughly applied over a long period of time in a number of ecosystems, and with the publication of Plant Strategies, Vegetation Processes and Ecosystem Properties (Grime, 2001), is becoming a major tool in the manipulation of vegetation and ecological prediction.