A Vegetação e o uso da terra no Planalto Central
Resumo
By way of introduction to his study on the vegetation and land use of the Planalto Central of Brazil, the author states that he made two field trips to the Planalto, being aided by a botanist on the second one.
Generally speaking, the Planalto is geologically made up two layers: one, the lower, being of folded algonquian crystalline and metamorphic rock and of silurian shales and limestones: the other, the upper one, is made up of more or less horizontal mesozoic sediments, sometimes alternating with effusive volcanic rock. Not all of the elevated areas are mesas; frequently they are formed from a post-cretaceous, probably tertiary, peneplain. This peneplain is capped by a laterite crust known as "canga", which is several meters thick. Due to its porosity, the "canga" protects the peneplain against erosion and permits a subterranean water table, between ten and twenty meters in depth, to exist.
The Planalto has a "savanna" type of climate, as classified by Köppen. In the summer, the equatorial air masses flowing toward the south produce heavy rains from October to March; in the winter, the cold subtropical air masses cause a dry season which lasts from May to September. According to the text books, this dry season is the principal reason for the lack of forests except along the rivers; but the fact is that the vegetation is quite different. Following the classification which has been adopted by the farmers the author divides the vegetation of the Planalto Central into the following types:
First class forest land - This is made up of three layers of vegetation: the highest layer has trees twenty to thirty meters high, losing their leaves during the dry season; the middle one. with smaller leaves, has five to fifteen foot trees; and the lowest layer is made up of sedges and herbs one to two meters high. There are some lanais which connect the different layers.
The trees of the first class forest land are straight and have thin, greyish bark. There are very few with rough bark.
During the dry season, a layer of dry leaves collects on the ground in the forest. This layer makes it much easier for fires to start, these causing great destruction to animal and vegetable life.
First class forest occur in three isolated areas: the Mata da Corda highlands, the Triângulo Mineiro, and the "Mato Grosso" o f Goiás - with 5 000, 18 000, and 20 000 square kilometers respectively. They are related to the occurrence o f fertile soils, these being derived from basic volcanic rock. These three areas can be distinguished on a population map due to the relatively heavy density of the same. Recently they have been subjected to a pioneering movement, except in the Mata da Corda where the system of large land-holdings has been preserved, due to the fact that it is far from any railroad.
Second class forest land - This is also referred to as the "dry forest", as its soil dries out almost completely during the dry season. The soil which predominates here is a sandy clay with an upper layer of humus. The author noticed second class forests in the "Mato Grosso" of Goiás, on the edges of the forest, and on the divides; and in the Trângulo Mineiro, to the east of Tupaciguara at elevations of between 800 and 1,000 meters, on soils derived from red sandstone rich in clay. None was observed in the Mata da Corda.
The second forests frequently occur in drainage basins; at the headwaters of stream, making regular islands of forest; known as "capões". The make-up of this forest is similar to that of the first class forest, but it is not as high as the latter, the highest trees reaching only fifteen to twenty meters. The ceiling foliage is more open, and consequently the undergrowth is richer in grasses and sedges.
During the dry season, about one half of the higher trees of the second class forest Jose their leaves, while in the first class forest this happens in only about ten percent of the cases. Aside from this, most of the trees change their colors, reminding one of a temperate forest in autumn.
The soils of the second class forest are principally utilized as pastures. Land is cheaper than in the first class forest.
In general terms of geography, the tropical American forest which most resembles that of the Planalto Central is that which J. S. Beard classifies as a "semiperennial seasonal forest", on the island of Trinidad.
"Cerradão" - This is a transition type between the "campo cerrado" and the forest. The average height of the trees here is between ten and fifteen meters, as compared to from four to eight in the "cerrado". In the forest, about three percent of the soil is reached by the sun's rays; in the "cerradão" between twenty and thirty percent; and in the "campo cerrado" about eighty or ninety percent. In the "cerradão" there are more grasses than in the forest. About seventy percent of the trees of the "cerradão" are species that are characteristic of the ·•cerrado". Near Goiânia the author noted that the "cerradão" occupies only a few hundred meters, but west of Tupaciguara it consists of many kilometers. The soils of the "cerradão" are very sandy and have a thin layer of humus. When the "cerradão" is burned, vegetation that is different from the original grows up, something which never happens in the "cerrado". The land of the "cerradão" is commonly used for pasture and for the cultivation of rice and pineapples.
"Campo cerrado" - The forest and the grassland ("campo") contain two entirely different sets o f plants. And of the various types of grasslands on the Planalto Central, the most characteristic and the most clearly defined is the "campo cerrado". It has been a problem for plant geographers: Warming considered it a natural climax vegetation, while Lunde and Rawitscher (this one for São Paulo) are of the opinion that it is an altered climax vegetation. Seen from a distance the "cerrado" looks like a forest, but, when one penetrates it, the trees are found to be more widely spaced. It is a transitional development between forest and grassland. It is different from a savanna, but has the appearance of being similar to the so-called Australian scrub. The appearance of the "cerrado" is well known; small, twisted trees with thick bark and a protective layer of cork, and with hairy and leathery leaves; and a dense blanket of grasses one to two meters tall. But that which most attracted the author's attention was the large size of the leaves on certain trees and shrubs of the "cerrado". To the east of the Planalto Central these leaves are smaller. Another fact which also surprised him was that the leaves fall at the end of the dry season in the "campo cerrado", and not at the beginning as is usually the case in the temperate zone.
The author agrees with Warming that fire has a secondary influence on the growth of the "cerrados". It may be able to change the habits of the trees, but certainly would not be able to cause the development of the singularly large leaves on some of them. Another proof that the "cerrado" is an original type of vegetation is the condition of the soil. The soil of the "cerrado" are lacking in humus, sandy, dry, and with colors ranging from grey to red. They are entirely different from the soils of the forest.
What use is to be made of the "cerrado" is a fundamental problem. Until this day. these lands have only been used for grazing, hence their relatively low value. Here, as in Europe, the types of cultures which are most wasteful are carried out only on the more fertile soils; in Brazil rice, sugar cane, and coffee will always be forest land, while manioc, beans, and cotton will be planted on the "cerrado". The author is of the opinion that they would be cultivated if the fires could be stopped, the surface crust broken up, and phosphates applier. But, to do this, a complete change in the agricultural methods would have to be inaugurated.
"Campo sujo" - When the trees get shorter and more widely separated, the "cerrado" becomes a "campo sujo". In terms of general plant geography, this could be called a steppe with scattered shrubs. The "cerrado" and the "campo sujo" generally blend into one another. The "campo sujo" soils appear to be poorer than those o f the "cerrado"; they are generally grey, shallow, stony, and with a thicker surface crust.
"Campo limpo" - The "campo limpo" are the steppes which are to be found on the poorer and drier soils of the Planalto Central. Low bunch grass predominates with here and there. widely spaced, a poorly developed or dwarfed tree.
On his first field trip, the author was of the opinion that the strong winds which occur during the dry season was the principal reason for the existence of the "campo limpo" in the highlands. But later, when he saw the tall forests on the highlands of the Mata da Corda, he abandoned this theory. Today he believes that the lack of water is the principal factor involved.
The "campo limpo" and the "campo sujo" are perhaps inadequate for agriculture and of little value for cattle raising.
The Planalto Central has, then, a great variety of vegetation forms: these relating to the type of soil, the condition of the water table, and the kind of parent rock - not the climate, which is uniform.
Although Köppen and his followers classify the climate of the Planalto Central as being that of a savanna, a natural savanna exists there either rarely or not at all.
Today, after his field trip to the Planalto Central, the author is of the opinion that the "cerrado" is similar to the Australian bush, both having the same appearance and being climax forms. As for the savannas of tropical western Africa, which he at one time considered to be climax, he now believes that they are an altered climax. This alteration was made by a dense agricultural and stock raising population by an abundant fauna of large animals. In tropical South America and Australia, the characteristic of the "cerrado" was maintained due to the fact the primitive populations were sparse
In conclusion. the author states that Brazil, as the largest tropical country in the world, is the best field for studies in "Tropical Geography" and will come to modify the present geographic concepts that have been temperate zone.
