Reintrodução de espécies nativas em área de caatinga e sua relação com atributos do solo.

Abstract

Anthropic pressure on the vegetation of the semiarid region of Brazil Northeast is widespread, and consists of partial or total removal of shrub and trees to collect firewood and other forest products, or to open new farming areas. This combined with the harsh climate conditions results in environmental degradation. Recovery of such areas is based on the adaptation potential of native trees to the degree of local degradation, and on the chemical, physical and morphological characteristics of the soil. The initial growth of three tree species reintroduced in a deforested overgrazed Caatinga site was evaluated and correlated with its chemical, physical and morphological soil characteristics. Seedlings were produced in plastic bags containing 4L of soil, goat manure and chemical fertilizers. They were transplanted in a 2 m x 2 m grid into 40 cm x 40 cm planting holes in the field, with a depth of 40 cm or less according to soil conditions. Data were collected from the four inner plants of squared-144 m2 plots of a current complete block design experiment carried out in a deforested overgrazed Caatinga site, with five treatments (no tree planting, and planting of Poincianella pyramidalis, Mimosa tenuiflora and Cnidoscolus quercifolius seedlings in pure or intermixed three species stands) and three replications of 36 seedlings. At the moment of the opening of the four central pits of each plot, thickness of A, B and C soil layers was measured, and two soil samples were collected at two soil depth (0-20 and >20 cm), for physical and chemical analyses. Multiple linear regression models were estimated to correlate the seedling length and basal diameter growth observed from February 2009 (5,5 months of age) to October 2010 (25,5 months of age) with the chemical, physical and morphological soil attributes. Growth of P. pyramidalis, M. tenuiflora and C. quercifolius was significant especially in the first growing season. In general, soil P, H+Al, electric conductivity and clay, and pplanting hole area and depth were the variables that more frequently showed a significant effect on seedling growth and participated in the regression models. When recovering degraded Caatinga sites, tree seedlings should be planted into planting holes containing more material of the C soil layer in order to take advantage of its natural fertility.