WAHLENBERG, GöRAN (GEORG)

(b. Skarphyttan, Sweden, 1 October 1780; d. Uppsala, Sweden, 22 March 1851), botany.

Wahlenberg began his studies at Uppsala University at the age of twelve under the guidance of a tutor. He soon decided to study medicine and natural history; botany became his major interest, and under Thunberg he acquired a thorough knowledge of plants. In 1806 Wahlenberg received his medical degree, having defended a dissertation on the sites of medically active substances within the plant body. He advanced very slowly in his career, and his financial situation was correspondingly poor for many years. From 1801 he had several positions, all at very low salaries, at the natural history collections of the university; and in 1814 he was promoted to the poorly paid post of botanical demonstrator. By 1828, when Wahlenberg succeeded Thunberg as professor of botany, he had acquired an international reputation and had completed almost all of his botanical work; his interest now centered on homeopathic cures.

Of the greatest importance for Wahlenberg’s scientific development were the many voyages he made during his younger years. In 1799 he traveled to Gotland, in the Baltic Sea, which has remarkable calcareous flora; and he visited Lapland in 1800, 1802, 1807, and 1810. Through these journeys he gained an extensive knowledge of Scandinavian plants and their geographical distribution. In 1811-1814 Wahlenberg traveled in Germany, Switzerland, Austria, and Hungry, comparing the flora of the Alps and the Carpathians with that of the mountains of northern Europe. While visiting Berlin in 1811 he became friends with the botanist C.L. Willdenow and the geologist Leopold von Buch.

Wahlenberg seems to have considered his steadfast defense of the Linnaean tradition in its most limited sense as his most important contribution to botany. His declared ambition was never to alter the limit of a Linnaean species or name and never to abandon the Linnaen sexual system in any detail—however trifling; and his judgment of those whom he considered heretics was severe. his main scientific works were floras, based on his travels, in which he expounded these principles: Gotlands flora (1805-1806), Flora lapponica (1812), Flora Carpathorum principalium (1814), Flora upsaliensis (1820), and Flora suecica (1824-1826; second edition, 1831-1834). He is better known today, however, for the introductions of these floras than for the works themselves. The introductions place him among the pioneers of plant geography, worthy of comparison with Humboldt.

Wahlenberg’s interest in geography dates from early in his career, and his love of cartography is reflected in the beautiful maps included in his works, which he drew. His grographical writings include Geografisk och ekonomisk beskrifning om Kemi lappmark (1804), Berättelse om lappska fjällens höjd och temperatur (1808; also in German, 1812), Röm springkällors temperatur (1811), and De vegetatione et climate in Helvetia septentrionali (1813). Together with his botanical works they constitute his considerable contribution to phytogeography.

A keen observer of the distribution of plants, Wahlenberg made a definitive analysis of the stratification of vegetation on mountains with summits above th snow line and with treeless strat above regions dominated successively by different species of trees. His knowledge of the Alps, Carpathians, and mountains of Lapland enabled him to make comparisons that emphasized both the similarities and the differences in stratification. In Scandinavia, especially in Sweden, Wahlenberg also distinguished the main regions of the lower parts of the country, both those in the north-south succession and those oriented to the east or west according to their distance from or nearness to the coast.

In discussing the causes and circumstances of the differentiation of vegetation, Wahlenberg considered the most important factors to be the influence of climate (temperature and precipitation) and its dependence on latitude, altitude, and nearness to the sea; thus he was aware of oceanic as well as continental floreal elements. According to Wahlenberg the distribution of temperature during the seasons–not the mean annual temperature–was what determined the vegetation of a region. He also indicated the importance of soil temperature, which he measured in springs tht did not freeze in winter,together with its difference from the temperature of the air–a difference varying, for instance, in relation to altitude.

Wahlenberg’s awareness of the influence of climate on vegetation did not preclude his ascribing great importance to the soil. He also considered the complicated relationship between climate and soil, noting, for instane, that certain calcareous plants of the Carpathians could be found in noncalcareous soil of the Alps and Lapland.

Wahlenberg was also conscious of the time factor in phytogeography and maintained that the present distribution of plants is due to migrations occurring at various times and originating from different sites. Many areas were once submerged and consequently were invaded by their present vegetation only after emerging from the water. The distribution in other countries of Swedish plants indicated to Wahlenberg their migration either from the south, over the Danish islands, or from the vast forests of Finland and Siberia to the northeast.

It is difficult to assess Wahlenberg’s true importance. His views on plant history were obviously influenced by Willdenow, who in his Grundriss der Kräuterkinde had stressed mountain regions (considered as former islands on an otherwise submerged earth) as centers of distribution of the plants found in lower regions. Priority for the idea of the influence of climate and geology on vegetation must be shared by Wahlenberg, Humboldt, and Buch. Their ideas, soon disseminated among younger phytogeographers, came to be considered so self-evident that few cared who had introduced them.

Wahlenberg had great difficulty in collaborating with other botanists. Considered odd and egocentric, he went his solitary way, isolated during his last twenty years from botany as well as from others. He never married. No student was allowed to enter the botanical garden, and in winter he forbade skating on the pond. Iron from the skates, he believed, would remain in the water when the pond thawed. His grazing cows would then ingest the iron with their water and thus, according to his homeopathic convictions, render the milk dangerous to drink.

BIBLIOGRAPHY

I. Original Works. There is a complete list of Wahlenberg’s botanical works in T. O. B. N. Krok, Bibliotheca botanica suecana (Uppsala—Stockholm, 1925), 741–745. An MS on phytogeography is in S. Borgman, “Göran Wahlenbergs handskrift ‘Svensk växtgeografi,’” in Svensk botanisk tidskrift, 49 (1955), 337–347. Many letters and MSS are at the library of the University of Uppsala.

II. Secondary Literature. There is a bibliography by E. Wikström in Kungliga Svenska vetenskapsakademiens handlingar (1851), 431–505, with bibliography. See also H. Krook, “Den siste linnean,” in his Angår oss Linné? (Stockholm, 1971), 104–115; and “Den unge Göran Wahlenberg,” in Nationen och hembygden, 8 (1960), 188–211. Futher works are A. Engler, “Die Entwickelug der Pflanzengeographie in den letzten hundert Jahren und weitere Aufgaben derselben,” in Wissenschaftliche Beiträge zum Gedäachtniss der hundertjährigen Wiederkehr des Antritts von Alexander von Humboldt’s Reise nach Amerika (Berlin, 1899), 9–p10, 164; and S. Lindroth, in Kungliga Svenska Vetenskapsakademiens historia II (Stockholm, 1967), 424–429.

Gunnar Eriksson