American Geographical Society

Studien Zur Klima- und Vegetationskunde der Tropen by Wilhelm Lauer; Rolf-DiedrichSchmidt; Rudolf Schröder; Carl TrollReview by: James J. ParsonsGeographical Review, Vol. 44, No. 3 (Jul., 1954), pp. 468-469Published by: American Geographical SocietyStable URL: http://www.jstor.org/stable/212087 .

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468 THE GEOGRAPHICAL REVIEW

ration and the water balance in an area of the world where few data are available, an area whose importance in all future political, economic, and social plans is still much of an unknown quantity because of the lack of such information.-J. R. MATHER

STUDIEN ZUR KLIMA- UND VEGETATIONSKUNDE DER TROPEN. By WILHELM LAUER, ROLF-DIEDRICH SCHMIDT, RUDOLF SCHR6DER, and CARL TROLL.

I82 pp.; maps, diagrs., tables, bibliogrs. Botrtmer Geogr. Abhandl., No. 9, 1952.

This volume brings together four new studies relating to climate and vegetation in the tropics that have come out of the Geographisches Institut at Bonn.

Within the tropics, where vegetation is particularly sensitive to water balance, the length and intensity of the dry season are perhaps of greater significance than total annual rainfall. Wilhelm Lauer's "Humide und arideJahreszeiten in Afrika und Suidamerika und ihre Beziehung zu den Vegetationsgiirteln" is an interesting attempt to apply the ratio of wet to dry months as a criterion for delineating the major vegetation regions of the two great tropical continents. Using De Martonne's "index of aridity," i = R/(T + io), in which the index of 20 is taken as the boundary between wet and dry months, Lauer has mapped the distribution of the number of wet (humid) and dry (arid) months on a single large folded map by means of Isohygrornetieti (lines delimiting areas with the same number of wet months during the year). This is essentially a climatologic study, and the analysis of the relationship of natural vegetation to these isohygromenen is brief; the impressive in- fluence of man and fire on tropical vegetation is referred to in but a single paragraph. Yet, by confining himself to readily available data on monthly rainfall distribution, the author has brought out some relationships that might not otherwise have been apparent and has produced a map that will be useful in further studies into the causes of the distribution of forest and savanna in the warm, wet lands of the world. The much larger area with more than six wet months in tropical South America as compared with tropical Africa is sug- gested to be related to the much greater extent of deciduous miombo-type savanna forest in Africa. It is paradoxical that trees appear to be a more conspicuous feature of "dry savanna" (five-six wet months) than of "wet savanna" (seven-eight wet months). The vast "dry savanna" of southern and eastern Africa is for the most part highland (the Cw of K6ppen); the extensive cainpos and llanios of South America are "wet savanna." This study contains a valuable bibliography of German sources on tropical plant geography and a tabular collation of the terminology used by the various authors who have worked on tropical vegetation classifications. The extratropical areas, though included on the maps, are not discussed in the text.

Parenthetically it may be noted that another recent study, edited by F. H. Schmidt andJ. H. A. Ferguson (Rainfall Types Based on Wet and Dry Period Ratios for Indonesia with Western New Guinea, Kernenteriati Perhuibiuigan Djaivatan Meteorologi dant Geofisik Verhatdeliizgeii No. 42, Jakarta, 1952) provides a somewhat comparable climatic map of part of tropical Southeast Asia. Here, however, wet months are defined as those with more than ioo millimeters of rainfall, dry months as those with less than 60 millimeters. Instead of using average monthly values, the authors have taken the average of the actual number of wet and dry months year by year, a cumbersome but important refinement, particu- larly for areas in which year-to-year variations are conspicuous.

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GEOGRAPHICAL REVIEWS 469

In "Die Niederschlagsverteilung im andinen Kolumbien," R. D. Schmidt has used the published government climatologic data through I937, available to him in Germany dur- ing World War II, to compile the most detailed rainfall maps of Colombia yet published. Unfortunately, he had no opportunity to collect in the field the rather numerous and often more reliable precipitation records available from private sources, nor did he have access to the published I938-1944 climatic summary. Using data for the I23 stations for which he had records of three years' duration or more, Schmidt has mapped the average annual rainfall and the average monthly rainfall for February, May, July, and October on five well-constructed maps that fold out in a single long sheet for easy comparison. The arid Guajira peninsula and the Orinoco-Amazon lowlands of eastern Colombia are not in- cluded. In view of the extraordinary diversity of climate and topography in Colombia, the interpolation of isohyets is at best a risky business. It has been done with care, how- ever, though there are one too many dry pockets in the Cordillera Occidental, between the rain-shadow valleys of Dagua and Dabeiba in an area on the Pacific-facing slope of the Farallones de Citara the reviewer knows from experience to be one of abundant year- round precipitation and dripping montane forest. Rudolf Schr6der's map of average an- nual temperature in Colombia in "Die Verteilung der mittleren Lufttemperatur in Kolumbien," which nicely supplements the precipitation study, inevitably mirrors the topographic map to a considerable extent. The highest average annual temperatures are in the upper Magdalena Valley (Girardot 3I.8? C.). The raininess of the Pacific Coast apparently accounts for the lower temperatures there as compared with the drier Caribbean littoral.

"Die Lokalwinde der Tropengebirge und ihr Einfluss auf Niederschlag und Vegeta- tion" is based chiefly on field notes taken in South America and Africa between I926 and I937. With numerous local examples, described and mapped in detail, he shows the effect on the distribution of vegetation of the well-developed compensation winds associated with the sharp but dissected eastern face of the Andes of Bolivia and Peru and the African highlands from the Cape to the Red Sea. There are case studies of several dry highland rain-shadow valleys (Trockentinseln) and the even drier deep and windy gorges (Dlurch- briichst ler, Winidpjorteni) with which they are frequently associated and of the rain- drenched windward crests of the highlands where ascending daytime density winds are reinforced by strong convection currents. For the theoretical explanation of these phe- nomena, the author turns especially to the works of A. Wagner. The rather extraordinary intensity of the mountain and valley winds that seem to develop within the tropics is shown to be closely related to the high diversity of vegetation types.-JAMES J. PARSONS

THE VEGETATION OF BRITISH GUIANA: A Preliminary Review. By D. B. FANSHIAWE. 96 pp.; maps, diagrs., ills., bibliogr. Imiperial Forestry Itnst. Paper No. 29.

University of Oxford, I952. ios. 934 x 6Y4 inches.

Fanshawe's analysis of the vegetation of British Guiana may not attract much attention, since that British colony is remote and fairly small. Even students of South America will probably do no more than give the book a brief glance. But its significance is far greater than appears on the surface, and for at least two reasons: (i) the study of vegetation is in- creasingly recognized as a basic necessity for intelligent land use; and (2) Fanshawe's man-

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