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Botany

Plants that migrate

Cerrado shares over half its species of trees with the Atlantic Rain Forest and the Amazon Forest

Do not think any more that the sucupira-preta (Bowdichia virgilioides), a tree with a thick bark full of cracks, white or purple flowers and up to 20 meters in height, is a species typical of the Cerrado, however abundant it is in this kind of vegetation of Brazil’s central region. The sucupira-preta is merely there, like the majority of the other species of trees and shrubs of the Cerrado. Only 41% of the trees found in this vegetation, marked by grassy fields and trees of a small or medium size, with twisted trunks covered with bark and thick leaves, are exclusive to it. This ecosystem, which once occupied about 2 million square kilometers, or almost 25% of the national territory, shares the other species of trees with another two neighboring ecosystems, the Atlantic Rain Forest and the Amazon Forest, according to a study coordinated by Raimundo Paulo Barros Henriques, from the University of Brasilia (UnB), carried out in conjunction with specialists from Embrapa-Cerrados, one of the divisions of the Brazilian Agricultural Research Corporation.

In this work, published in the Brazilian Botany Magazine, Henrique assessed the species of trees and shrubs from 12 localities of the Cerrado stricto sensu – its most characteristic form -, located in areas as distinct as Pedra Caída, in Maranhão; the Chapada dos Guimarães, in Mato Grosso; Araxá, in Minas Gerais; and Botucatu, in São Paulo. Of the 290 species of trees identified, only 119 were exclusive to the Cerrado. The other 171 also occur in the Atlantic Rain Forest, which extends to the east, or in the Amazon Forest, to the north – actually, 130 are both part of the flora of the Cerrado and of the Atlantic vegetation, 4 are in the Cerrado and in Amazonia, and 37 appear in these three forest formations.

Why are some of these species to be found in environments so different as the Cerrado, hot and dry, or the Amazon Forest, with extremely high humidity? It was possibly a very slow migration, arising from variations in climate over thousand of years. Studies about the dispersion of pollen grains and spores indicate that in the last 60,000 years the climate of the region of the present-day Cerrado alternated drier and hotter periods with others more humid and cold. This makes it probable that the increase in humidity created an environment favorable for the dissemination of species like the copaíba (Copaifera langsdorfii), a tree up to 35 meters in height found also in the Atlantic Rain Forest, or like the canela-parda (Nectandra cuspidata) or cajá-mirim (Spondias lutea), which likewise live in the Amazon Forest.

Henriques also found that the proportion of species of trees and shrubs from the Amazon Forest decreases progressively as the distance increases between the area studied and the Amazon. Then the number of species from the Atlantic Rain Forest found in the Cerrado grows with the distance until it reaches a maximum at about 600 kilometers from the boundary between these two ecosystems and then decreases. Another conclusion of the study is that the variety of species shared between the Cerrado and the Atlantic Rain Forest is greater in the areas in which the contours of the Cerrado are higher, at an altitude of from 800 to 1,000 meters.

At least three factors help one to understand why the variety of species found in the Cerrado and in the Atlantic Rain Forest (130) is so much greater than the number of species that occur in the Cerrado and in Amazonia (4). The Amazonian vegetation is probably more sensitive to the colder and drier climate of the Cerrado than the plants from the forests close to the Atlantic. The soil, poor in nutrients, is also unfavorable to the growth of the vegetation of the Amazon Forest. Furthermore, the trees and shrubs from the Atlantic Rain Forest are more resistant than those from the Amazon to the clearing by fire, frequent in the Cerrado. This study may assist in the preservation of the more threatened species. “Part of the biodiversity of the Atlantic Rain Forest, now almost completely decimated, still exists in the Cerrado”, comments Henriques. “This makes it more important to conserve this ecosystem.”

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