Alphonse de Candolle and Why Plants Grow Where They Do
Augustin de Candolle had traveled in Brazil, Indonesia, and northern China, and his observations convinced him of the importance of soil type in determining the way plants are distributed. In 1820 he wrote Essai elementaire de geographie botanique (Elementary essay on botanical geography), in which he elaborated on an idea that Linnaeus had proposed earlier.
Linnaeus—who did not believe that species evolve from earlier species—had maintained that all plants and animals originated from the same particular place. Many scientists then believed that at one time oceans had covered the entire Earth. Linnaeus proposed that plants and animals first appeared on a mountain that was high enough to protrude above the ocean surface, forming an island close to the equator. The mountain provided a variety of living conditions, varying with elevation, and the different species of plants and animals inhabited those parts of the mountainside that best suited their needs. As the waters receded, pairs of animals and plants migrated to the regions of the newly exposed dry land that replicated their original habitats and there they remained, forever unchanging. This meant, according to Linnaeus, that there were two aspects to the study of plant distribution. The first was the “study of stations.” This meant the physical causes for a plant species growing in a particular place or the features that made a locality especially suitable for that plant. The second was the “study of habitations.” This concerned geographical or geological factors that affected the overall range of a plant species. These factors might no longer exist, but they had originally defined the range. Candolle concentrated on what those factors might be and how they might influence distribution. He believed it possible that certain species possessed such a large capacity for dispersal that they could spread from a station to a habitation and eventually achieve a global distribution.
Augustin also taught his son Alphonse (1806–93) plant geography, and Alphonse de Candolle continued his father's work. That work was partly concerned with plant taxonomy, but Alphonse was also keenly interested in plant geography and analyzed in detail the environmental factors, especially temperature, influencing plant distribution. He published his findings in 1855 in his two-volume treatise entitled Geographie botanique raisonnee (Analytical botanical geography). In this work Candolle recognized 20 distinct botanical regions, as well as the distinct floras found on islands. Candolle was a skilled statistician who used statistical techniques to measure the global distribution of vegetation types. This led him to define the types of plants dominating the vegetation in particular types of climatic environment. The climatic environments, determined mainly by temperature, divided the world into latitudinal belts of arctic, temperate, and tropical vegetation. In 1874, in one of the volumes of Prodromus systematis regni vegetabilis (Introduction to a natural classification of the vegetable kingdom), he gave the following names to the resulting vegetation types:
- Hekistotherms—typical of arctic tundra
- Microtherms—typical of cool temperature deciduous forest, cool temperate coniferous forest, and boreal forest—the coniferous forest of subarctic climates that forms a belt across northern North America and Eurasia
- Mesotherms—typical of warm temperate deciduous forests, warm temperate coniferous forests, and Mediterranean climates
- Xerophiles—typical of deserts and grasslands
- Megatherms—typical of tropical rain forest and tropical savanna
It was from Alphonse de Candolle that Charles Darwin learned about plant geography, and they conducted a detailed correspondence on various aspects of plant distribution. Candolle's classification of vegetation types also represented an approach to climate classification, and in 1884 the German meteorologist and climatologist Wladimir Peter Koppen (1846–1940) used Candolle's vegetation types in his first attempt at defining climatic zones. The final version of the Koppen climate classification was published in 1946, after Koppen's death, and it is still the most widely used classification.
Alphonse Louis Pierre Pyrame de Candolle was born in Paris on the night of October 27/28, 1806. In 1816 the family moved to Geneva. Candolle studied law at the University of Geneva, graduating in 1825. For most of his life, starting in 1824 when he was still a student, Candolle continued work commenced by his father. In 1829 Candolle received a degree in law and in 1831 he was appointed an honorary professor at the Academy of Geneva. From 1835 to 1850 Candolle was professor of botany at the University of Geneva and director of the university's botanical garden. He retired from his teaching commitments in 1850 to give more time to research. Candolle devised the first code of botanical nomenclature, which was adopted in 1867 at the International Botanical Congress that Candolle had organized in Paris. He published it in the same year with the title Lois de la nomenclature botanique adoptees par le Congres international de botanique tenu a Paris en aout 1867 (Laws of botanical nomenclature adopted by the International Botanical Congress held in Paris in August 1867). The present International Code of Botanical Nomenclature is its direct descendent.
Candolle was elected to the French Academy of Sciences in 1851, to the Royal Society of London as a foreign member in 1869, and to the National Academy of Sciences of the United States in 1883. He died in Geneva on April 4, 1893.
- Franz Meyen and Vegetation Regions
- Karl Ludwig von Willdenow and the Start of Scientific Plant Geography
- Alexander von Humboldt and the Plants of South America
- Ernest Wilson, Collecting in China and Japan
- The Wardian Case
- Robert Fortune, Collecting in Northern China
- George Forrest, Collecting in Yunnan
- Reginald Farrer and Alpine Plants
- David Douglas in North America and Hawaii