Biological Problems of Tropical Vegetation * Richard P. Aulie, Department of History of Science and Medicine, Yale University, New Haven, Connecticut Rain forest once covered much of West Africa. In recent years this has been replaced in many areas by savanna and secondary forest. All three vegetation types represent activities of great interest to the biologist. The author is a former high school biology teacher who spent a year in Liberia making these studies. The article demonstrates an excellent ecological study with clear implications for teachers wishing to conduct similar projects. It was wriften in Monrovia, Liberia during 1963-64. Downloaded from http://online.ucpress.edu/abt/article-pdf/27/5/331/21457/4440974.pdf by guest on 29 September 2021 Richness of Vegetation must learn the conditionsof their genesis and If the travelernotices a particularspecies growth, together with the continual changes and wishes to find more like it, he may often occurringamong them. As a British ecologist turn his eyes in vain in every direction.Trees has written, ". the understanding of what of varied forms, dimensionsand colours are happensis fundamentaland the study of what around him, but he rarely sees any one of is preliminaryto it." (5). them repeated (1). The purpose of this article is to present a broad discussionof West African vegetation With these words Alfred Wallace in 1878 types, and to point out some unsolvedbiolog- provideda glimpseof the richnessof tropical ical problems that are involved. The study, vegetation. Although the celebrated English largely ecological and genetic, is based on explorerdid his epoch-makingsurveys in the observationsmade in several forest regions MalayArchipelago and Amazonia, his descrip- of Liberia during the period 1962-64 while tions to a great extent fit what may be found filling a UNESCO teaching appointmentat in Liberia,and in much of West Africa today. the Universityof Liberia (6). This article is One need not have the practiced eye of a aimed at the kind of broad understandingto Wallace, though, to be impressedby the ex- which Waddingtonrecently has applied the uberantvegetation of the tropics. useful term "syntheticbiology," which seeks There is the richness of componentparts; to present a more "coherentpicture of the around600 species of trees have been identi- whole realm of living matter" (7). fied in the Cote d'Ivoirealone (2, 3) and over The need for this approachis now becom- 235 in Liberia (4). There is the richness of ing clear, for it is only in recent years that structure,in which dozens of organismsare West Africa has receivedthe sustainedatten- superimposedone on the other, masking by tion of biologists(8). The famous expeditions seeming disarrayits clear conformitiesof or- of the 19th century,such as those of Charles ganization.To be sure, nature has a horror Darwin,Alexander von Humboldt,and Alfred vacui and rapidlyfills every niche with some- Wallace, turned rather to the forests of the thing green. There is the richnessof dynamic equatorialAmericas and Malaya.As a result, organization.Any changein one part, such as by the beginning of the 20th century there soil, microclimate,or vegetation, results in was an almosttotal ignoranceof West African compensatingadjustments in the others. plantlife. Indeed,so isolatedwas West Africa The tropicallandscape is the richestbiolog- from serious biologicalwork that the phrase, ical environmentof any land mass in the "ceux violent la foret," was often applied to world. It is composedof integratedgroups of those who first traversedthe area early in the communitiesconstantly interactingin space 1900's (9). and time. Indeed, this richness of vegetation There was a good reasonfor this isolation. is an obstacleto its understanding,for a plant Due to the extremelyunhealthy condition of communityis not "understood"if we are con- the climate, as comparedwith other tropical tent only to list the species composing it. regions of the world, West Africa properly After determiningthese constituentunits, we earned the title during the late 19th century 331 332 THEAMERICAN BIOLOGY TEACHER Downloaded from http://online.ucpress.edu/abt/article-pdf/27/5/331/21457/4440974.pdf by guest on 29 September 2021 Fig. 1. Tropical forest profile in Liberia. Area in foreground has been cleared for farming. Note the 'umbrella trees" (Parasolieres). They are Musango cecropoides, and rapidly invade clearings in response to increased light during early stages of succession on Bong Mountain Range. of the "white man's grave." Malaria, dysen- He was followed by M. A. Aubreville, who teries, and dengue fever raised the death rate continues to bring out important publications among soldiers, officials, missionaries, and in which he describes new species and dis- traders to 10% for people between the ages cusses forest populations (14). The Kew gar- of 18 and 50. However, with the widespread dens in London have extensive collections, use of drugs in recent years and access to good and today most of the important species have medical care, disease no longer holds the same been described in print (15). In more recent threat to physical and mental well-being. Las years there has been an increasing interest in Palmas, Paris, and New York are only hours the management of Liberian forests as a val- away by jet. The enervating climate has be- uable national asset, in large measure due to come tolerable and the death rate is around the efforts of the Bureau of Forests of the 10 per 1000, which is considered fairly nor- Liberian Ministry of Agriculture and its mal for the same age group (10, 11). USAID advisers, the German Forestry mis- The great pioneer of scientific exploration sion, one that is engaged in a forest survey, was Auguste Chevalier of the French Acad- and the educational program of the College emy. He conducted extensive surveys of the of Forestry of the University of Liberia, C6te d'Ivoire in 1906-7, and also explored the largely staffed by FAO (16). forests of Liberia in the region of Mount The early explorers distinguished 3 different Nimba. His work marked out the forests as vegetation types. (a) The most prominent, of objects of serious biological inquiry (12, 13). course, is the rain forest, which the French BIOLOGICALPROBLEMS OF TROPICALVEGETATION 333 call "la foret dense," mile on mile of green wilderness blanketing the earth to the horizon. Since time immemorial its canopy of high trees has enclosed an almost complete solitude (Fig. 1). (b) Then, too, the early travelers noticed that abandoned land, once cleared for farming, would, under certain conditions, re- build itself into rain forest. A stage in this rebuilding process, and manifestly quite dif- ferent in character, is secondary forest, often appearing as a labyrinth of tangled under- growth, vines, creepers, and trees. This is Downloaded from http://online.ucpress.edu/abt/article-pdf/27/5/331/21457/4440974.pdf by guest on 29 September 2021 really the "jungle" of travel books and films (Fig. 3). (c) The 3rd area is the park-like savanna (man-made), consisting of isolated trees, often the oil-palm, surrounded by thriv- ing grasses and low-lying shrubs. This partic- ular savanna is man-made, since it occurs wherever there is regular firing of the grasses (Fig. 4). Of course, one cannot always expect to find clear geographical boundaries between these 3 "communities." One may grow accustomed to the sight of palm trees in savanna land- scapes only to come upon them thriving on the edge of secondary forests, wherever con- Fig. 3. Secondary vegetation. Lianas climbing a high tree toward the light. From the "Para Bush" near the ELWA radio station, Monrovia. ditions of light are optimal,and even in small clearings.Then, too, the later, more mature stages of secondaryforest are often indistin- guishablefrom primaryrain forest, which is to be expectedif the formeris a precursorof W.I~ the latter.And one may find remnantsof all 3 in areas that have been cleared for farming. p~~~ As a matter of fact, almost all of the "rain forest" has been affected in one way or an- other by human activities. Even in the finest examplesof maturerain forest one can often find fragmentsof pottery,palm nuts, mounds, and subsurfacelayers of charcoal,all evidence that the forest at one time had been cleared and inhabited(17). A biologist approachingthe study of trop- ical vegetationmay start by collectingplants, gathering into an herbarium collection the greatestnumber of species in the shortestpos- sible time. However, such a collection rarely Fig. 2. Aerial photograph of tropical forest bordering representsa random sampling of the entire Atlantic ocean shown at bottom, near Monrovia, Liberia. Mottled, circular depressions are clearings in the forest geographicrange of a species. Since a biol- used for farming. Note logoon behind sand bar. Large ogist usually collects where he can, he can areas of coastal savanna in lower half. River cuts never be sure he has through forest at top of picture. (Courtesy Hansa-Luftbild sampledall the variation Munster) patterns that exist within a single species. 334 THEAMERICAN BIOLOGY TEACHER caps on the biologist who is interested in as- t F- ' 0 _ 00 ;ji 0 > 0 it N z- ;l i ;: s : certaining broad relationships therein, never- ~~~~~.'.gi.... ' . s ;..... theless this same abundance confers important advantages. Much that is new to biology will doubtless emerge from studies of tropical plant life simply because so little is at present '. ...:' .. ...T ; f - 0 known. Whereas most ecological studies have .Et-E itV,; i: ~~~~~~~~~~........'. !i .;".'.-i been done in temperate climates, the floris- 0:; ; ;;, '.-::0:..E is 'liS4',-~~~~~~~~~~~~~~.-...... ..-..;. ;: ,0:00::;',;'. :::V tically rich communities of the tropics hold : ....',.........'.';,, :_ unrivalled opportunities for the 0 . .;....ls:...B.. x i ..... .... ...|: : biologist, par- ticularly as regards studies of evolution, adap- tations, and succession. Downloaded from http://online.ucpress.edu/abt/article-pdf/27/5/331/21457/4440974.pdf by guest on 29 September 2021 Evolution The floristic richness of the tropics is no Fig.