Cerrado sensu stricto and cerradão often occur side by side under similar edaphic and topographic conditions. The factors which contribute to the existence of cerradão in this situation are not well established. The objective of the present study was to compare the floristic composition and phytosociology of a Cerrado and cerradão on a dystrophic soil in eastern Mato Grosso and to determine whether higher soil fertility was contributing to the existence of the cerradão. Fifty 10 m×10 m plots were laid out in each vegetation type and a phytosociological survey was conducted of all trees with a minimum diameter of 5 cm at 30 cm above ground level. Soil samples were collected up to a depth of 2 m of soil profiles and from surface layer (0-10 and 10-20 cm) in each area. The two physiognomies showed distinct floristic, structural and phytosociological characteristics. The basal area (21.4 m² ha-1) and the mean heights (6.4 m) of the cerradão were greater than that of the cerrado sensu stricto (14.9 m² ha-1 and 3.7 m). The three most important species were Hirtella glandulosa Spreg., Sclerolobium paniculatum Vog. and Xylopia aromatica (Lam.) Mart. in the cerradão, representing 29% of the total Importance Value (IVI), and Qualea parviflora Mart., Davilla elliptica A. St.-Hil. and Roupala montana Aubl. in the cerrado sensu stricto, representing 21% of the total IVI. The soils of both areas were acid (pH < 5.0) and dystrophic (Ca2+ < 0.4 cmol c kg-1) with high exchangeable aluminium levels (Al3+ > 1.3 cmol c kg-1). The fertility of the soils of the two areas was not different to support the hypothesis that the occurrence of the cerradão was due to the higher fertility of its soil. However, the cerradão soil showed higher percentages of clay than the cerrado soil at all depths up to 2 m, which could result in a higher availability of water throughout the year for the trees. This is an aspect worth investigating in future studies.
Savanna; phytosociology; phytophysiognomy; soil fertility
