Soils and vegetation relations in areas under desertification in Jatauba county, Pernambuco State, Brazil

Land degradation in semiarid regions is a result of natural processes that call be induced or intensified by mail through the inadequate use of natural resources, resulting in the degradation of vegetation, soil and water resources. Aiming to relate vegetation and soil degradation processes in the Agreste region of Pernambuco State, soil and vegetation in twelve representative plots were characterized as preserved, moderately degraded and degraded environments in the municipality of Jatauba. To study the vegetation, plants were stratified in three layers or height classes: 3 - plants taller than 3.0 m, sampled in the total plot area (2900 7712); 2 - plants with a height between 0.51-3.0 m, sampled in all area of 100 m(2); 1 - plants with height equal to or less than 0.50 m, sampled in 18 miniplots of 25 x 50 cm. Soils were Morphologically characterized in each plot and samples collected from each horizon for physical, chemical and mineralogical analysis. The vegetation of the 2(nd) stratum showed a great decrease in absolute density as a result of soil degradation intensity. Species with highest relative densities were: Neoglaziovia variegata (caroa) and Cordia leucocephala (moleque-duro) in the preserved area; Bromelia laciniosa (macambira), Aspidosperma pyrifolium (pereiro) and Caesalpinia pyramidalis (catingueira), in the moderately degraded area; and C. pyramidalis and Sida galheirensis (malva branca), in the degraded area. The soil Properties of the Planosols that were strongly correlated with the preserved vegetation were the gravel contents in surface horizons, thickness of A + E horizons, and the concentration of organic carbon. The occurrence of soil crusting and erosion, as well as high percentages of exchangeable sodium was observed with greater intensity at the degraded sites covered by more sparse vegetation.