Flora and life-form spectrum in an area of deciduous thorn woodland (caatinga) in northeastern, Brazil

摘要

Caatinga, a deciduous thorny woodland vegetation, is encountered in the semi-arid region of northeastern Brazil. In view of the importance of the herbaceous component of caatinga plant communities, a characterization of the flora of the Nao Me Deixes Reserve in Ceara State, Brazil (4°49′34″S, 38°59′09″W, at 210m a.s.l.) was undertaken. The reserve has 300ha of caatinga vegetation, including dense tree steppe and open tree steppe. The mean annual rainfall is 732.8 mm, concentrated between February and May (78%). The flora was surveyed at monthly intervals between February 2000 and June 2001. We encountered 133 species belonging to 47 families. The herbaceous/woody ratio was 1.4. Based on field observations, the life-form spectrum was characterized according Raunkiaer's system, and compared with his normal spectrum. The life-form spectrum observed was: therophytes (42.9%), phanerophytes (26.3%), camaephytes (15.8%), hemicryptophytes (12.8%), and cryptophytes (2.3%). Previous data on the caatinga herbaceous flora, as well as the present study, indicate that the floristic richness of this biome has been underestimated, and that the herbaceous/woody proportion varies according to its physiognomy and water status.