EFFECT OF GRAZING BY STEERS AND A LONG DROUGHT ON A CAATINGA LIGNEOUS STRATUM IN SEMI-ARID NORTHEAST, BRAZIL

Abstract

A Caatinga vegetation was submitted to various grazing intensities (GI) by steers (1981-84) to verify their effect on ligneous stratum degradation. The study involved four GI: Heavy (1 steer/6.7 ha); Moderate (1 steer/10.0 ha); Light (1 steer/13.3 ha); Exclosure (no grazing). Areas under grazing varied from 40 to 80 ha, whereas exclosure had 20 ha. The research had two replications, occupying a total area of 400 ha. Data of woody species new plants density (NP) were determined annually in 1 m2 plots, and data of shrubs and trees density were determined by Point-Centered Quarter Method in 1982 and in 1984. NP density (Mean = 3.38 plants/m2) was neither affected by GI, nor by years, although it was highest in 1984 (3.83 plants/m2), the rainiest year. Taking into account the eight areas, there was linear relation (P<0.01) between 1982 and 1984 tree densities. There was linear relation between tree density and density of tree species in shrub stages in 1982, but not in 1984, because the drought probably affected shrubs but not trees. There was, for some tree and shrub species, linear relation between adult plant and NP densities. This fact occurred more in 1982. There was in 1983 a very high germination of the tree Tabebuia spongiosa (22.14 seedlings/m2), there being a linear relation (P<0.01) between NP and tree density.