Áreas climático vegetacionais do Brasil segundo os métodos de Thornthwaite e de Mohr

Resumo

The aim of the present paper is twofold: first, to draw a bioclimatic classification of Brazilian territory, and secondly, to establish a correspondence between climatic zones and vegetation complexes. Two systems have been used: Thornthwaite's and Mohr's, and two colored maps derived thereform are included. The conclusions reached are as follows:

1. Moisture is the most important factor, in both the climatic and the edaphic complex, where vegetation determinism is concerned.
2. Thornthwaite's and Mohr's have proved to be the system that bring out more clearly the correlation between climate and vegetation, with greater emphasis upon the share of the determinism of certain vegetation types.
3. The term "vegetation type" has been replaced by vegetation complex, a concept advanced by both Rizzini and Zohary the same year (1963) and applied by them with the same meaning to the vegetation of Brazil and of Iran, to designate a set of various communities occurring in a given ecologically diversified area. These vegetation complexes may usefully be considered to me the major Brazilian phytogeographical units, and are made up of 31 well-defined plant formations. A reference to "cerrado", for instance, is not intended to be restricted to the savannah, but to comprise all the formations which are to be found intermingled with the savannah on the Central Plateau, so that a more adequate designation would be Cerrado Complex or Central Brazil Complex.
4. Thornthwaite's moisture index (Im) has been used to establish moisture zones on the basis of 310 localities scattered all over Brazil and enable 4 general climatic types to be identified. Map 1 shows how these climatic zones are borne out by the 10 vegetation complexes.
5. Mohr's system, which merely takes into account the number 01 dry months in the year, has deserved some preference for tropical regions. Working with the same 310 localities, it has likewise been possible to determine the 4 general climatic areas delimited in Map 2, which may be said on the whole to be in excellent agreement with the vegetation complexes, though it was necessary to make a correction in the caatinga boundary as drawn in the previous map (Rizzini, 1963).
6. Both maps (1 and 2) and the two bioclimatic classifications may be seen to be practically identical. Inasmuch as the two quite distinct criteria lead to the same final result, it would seem wiser to choose the simper, especially as it also shows the dry season.
7. It is suggested that the following bioclimatic (ecological) classification corresponding to Map 2 and founded upon the principles set forth by Mohr (Mohr & Baren, 1951, Ho, 1960) be adopted for Brazil:
8. PERMANENTLY WET AREAS (0-1 dry month per year): No dry season, either meteorologic or ecological. Temperate region (Sonthern Brazil).

• Rio-Grandean Plain Campos (100% between 0 and 1) - Map 2 : X.
• Pinheiral (pinewoods - 95% between 0 and 1) - Map 2 : VIII.

1. HUMID AREAS (0-3 dry months per year): Dry season short, meteorologic, and ineffective owing to the ample soil resources, hydrographic system or position near the sea.

• Amazon Forest (89% between 0 and 3) - Map 2 : I.
• Restinga (offshore bars - 64% between 0 and 3) - Map 2 : VII.
• Upper Rio Branco Campos (data insufficient) - Map 2 : IX.

1. SEASONALLY DRY AREAS (4-5 dry months per year): Dry season fairly long, regular, ecological in general, compensated by edaphic reserves, which may be deep (cerrado) or shalow (forest).

• Cerrado (71% between 4 and 5) - Map 2 : III.
• Atlantic Forest (68% between 4 and 5) - Map 2 : II.
• Meio Norte (Middle North - 50% between 4 and 5) - Map 2 : V.

1. SUBARID-ARID AREAS (6-9 dry months per year): Dry season long, intense, irregular, ecological, uncompensated owing to lack of water storage in shallow or rocky soils, etc. In short, atmospheric and edaphic drought.

• Caatinga (68% between 6 and 9) - Map 2 : IV.
• Pantanal (seasonally inundated floodplain) Map 2 : VI. Transition area, with an intermixture of Chaco, Central and Atlantic Brazilian flora, the first dry and the last two subhumid to humid.

1. The tables included in the text give data on stored groundwater, number of dry months, evapotranspiration, moisture deficiency, etc.
2. It may be concluded that, as many ecologists think, the tropical climate is mainly characterized by the prevalence of a winter dry season lasting from 1 to 9 months.
3. Either method shows that Amazonia (the Hylaea or rainforest) is more humid than the Atlantic Forest; this holds true for the temperate southern zone.
4. It has become evident that the Central Brazilian Savannah (cerrado) thrives under the same climate as the Atlantic Forest, the dry season being generally the same for both. The chief ecological difference between the two vegetation complexes lies in the depth of the soil. 12. Campo limpo and restinga are neither of them so responsive to climate as they are to a particular type of soil; both have a very wide range. It follows that the campo formation inhabHs wet countries for geamorphological reasons.
5. The formations which make up the vegetation complexes may be classified as climatic, edaphic or edaphic-climatic according to the preference they show for a given climate, soil or both together. Some of them, though primarily climatic, can be looked upon as secondarily edaphic whenever they colonize particularly favorable soil under different climates.
6. Examples of climatic formations are the rainforests to which the concept of climax is applicable. Edaphic formations include the campos, the restinga, the swamp forests and the buritizal. Finally, among those that may be taken to be edaphic-climate are the caatinga, the cerrado, the dry forests and the scrubs.
7. The concept of the cerrado as a mesophilous formation is not far wrong; it differs from the mata by living on deep soils that dry up toward the surface, while the mata soils are shallower with plenty of water close to ground level.
8. Besides, there ls a conspicuous difference in the morphology of the underground systems. On the savannah, the trees have a very far-raching root system, exceeding the aerial part. Quite to the contrary, forest trees grow much shorter roots, accompanied by the development o f those aerial supports called buttresses.
9. Forest soil is formed at the expense of the activity of an extremely rich fauna, the animalcules of which are provided with a filmy skin and require an environment permanently saturated with moisture. Seed regeneration also calls for this sort of milieu. The savannah, however, depends upon deep water, surface relations being almost without importance save during the rainy season.
10. In a clay cerrado soil (dark-red latosoil) 49% of water was found at field capacity as compared with 18,4% at wilting point, which gives an available moisture range of 30,6%. Results approaching these were obtained in the Congo under similar conditions. The forest humus from Serra dos Orgãos had a field capacity of 100%, while campo fine sand from Serra do Cipó displayed the following characteristics:

• Field capacity ....................................20,4%.
• Wilting point .....................................3,6%.
• Available water_ ..................................16,8%.

1. Finally attention is drawn to the sharp contrast between Brazilian and African moisture

zones as shown, in both cases by the Thornthwaite method, in Map 1 and Unasilva, 9 (2) : 54.

1955, colored map

            About half of African territory consists of desert (arid climate), which does not exist anywhere in Brazil except for 5 unimportant localities.

            Furthermore, there remains an ample belt of semiarid climate, which means that some two-thirds of the continent may be looked upon as dry, while only a small equatorial region is wet and forested.

            In Brazil there is only one dry semiarid tract, which is known as the caatinga, as opposed to the greater part of the country which enjoys humid climates, 50 per cent even humid to superhumid. The savannah itself ls subhumid-humid.

            It is thus evident that Africa is quite distinct from Brazil as far as water distribution is concerned: the former is only one-third humid, while the latter is humid over nearly the whole country. In wil be seen, therefore, that conditions are excellent in Brazil for establishing a land-use system that is both rational and intensive.