What Is Biodiversity?

There are certain words that everyone uses but that are exceedingly difficult to define precisely. Biodiversity is one such word: The term is a contraction of biological diversity, which seems simple enough. Obviously, it means the variety of living organisms that inhabit our planet.

Unfortunately, the apparently simple definition leads to difficulties. If it refers to species, there are more than 24 different definitions for the word “species,” so anyone proposing a scheme to save species from extinction must first decide which definition to use, because an organism that qualifies as a species under one definition may not do so under another. Perhaps, though, biodiversity refers to communities of organisms, but it would clearly be impossible to preserve every ecological community. The concept of evolution by natural selection is founded on the observation that there is considerable variation within any population of a species (however defined). Every individual is different. So perhaps efforts should be directed toward preserving every individual? But this is absurd, because it would mean abolishing death. In the end, the term has to remain vague, and we must accept that a term, describing an idea, may be useful even though it cannot be defined rigorously.

Plants are woven into the culture of almost all human societies. William Shakespeare is believed to have been a keen gardener and certainly he mentioned plants frequently in his plays and sonnets. These references would have been familiar to his audiences, as would the symbolism attached to the different flowers and herbs. New York’s Central Park contains a Shakespeare Garden, displaying only plants that are mentioned in Shakespeare’s works. There are also Shakespeare gardens in Brooklyn, Cleveland, Chicago, San Francisco, Johannesburg, Vienna, and many other cities. In the Middle Ages, the War of Roses, fought for the English throne, was between the houses of Lancaster—the red rose—and York—the white rose. The Tudors symbolized their reign with the Tudor rose, which is partly white and partly red. The flag of Lebanon features a cedar tree—the cedar of Lebanon (Cedrus libani)—and every nation and most states, provinces, counties, and regions within nations have their own symbolic plants.

The loss of a plant with such cultural, historical, or heraldic associations would be tragic. It would be felt as an assault on the culture itself. The protection of local or national heritage is important. Plants do not grow in isolation, however. They live in communities on which they depend, so protecting them requires preserving their communities—in other words, the biodiversity of the area where they are found.

Wild plants are also important for other reasons. Crop plants are descended from wild ancestors, and from time to time plant breeders and geneticists need to revisit those ancestors in search of particular qualities the crop has come to need. This is most commonly resistance to disease, but it might be tolerance of drought, or cold, or of soils contaminated with salt.

It is also possible that in years to come new plants will be domesticated in order to provide food or fiber. At present the world relies on a range of crop plants that may need to be augmented to meet the needs of future generations. The United Nations Food and Agriculture Organization (FAO) monitors the use of wild plants, especially those with the potential for domestication. Should the communities containing these plants disappear, this resource for the future would be lost.

Centuries ago physicians were taught botany because most medicines were derived from herbs cultivated for the purpose. Those medicines are now manufactured chemically on an industrial scale, but pharmaceutical research continues to explore wild plants in search of substances with therapeutic potential. If the wild plants disappear, that opportunity will also be lost.

There are clear aesthetic, cultural, agricultural, and pharmaceutical reasons for preserving natural plant communities. It may be impossible to define biodiversity rigorously, but there can be no doubt of its importance.