Características estruturais e dinâmica temporal da composição florística de uma pastagem natural manejada sob diferentes métodos de pastoreio

Abstract

The objective of this study was to evaluate vegetation structure, floristic composition and vegetation dynamics of a natural grassland, during fall and winter seasons, grazed by beef heifers. The experiment was conducted from 03 /13 to 08/ 20, and was divided into six consecutive periods. The treatments were continuous and rotational grazing, with two replications in a completely randomized design with repeated measures over time. The stocking rate was variable, aiming to keep the height of the lower layer between eight and twelve centimeters. The rotational grazing interval was given by the accumulated thermal sum of 375 degree days. Measured variables at the pasture showed no significant difference between the grazing methods (P > 0.06) or interaction treatment x time (P > 0.06). Total herbage mass and average canopy height showed no significant differences between periods (P > 0.23). The upper stratus showed no significant difference (P > 0.29) for forage mass variables, canopy height and density. The herbage mass and height of the lower stratus decreased throughout the experiment (P < 0.02). The percentage of dead material and of leaves in the lower layer did not differ (P > 0.27) between the two periods, with mean values of 54.4% and 27.55% respectively. The stratification of feeding stations for height and forage mass showed an increase in frequency of lower height values and a decrease in greater height values throughout the experiment, with a predominance of stations that can restrict the consumption of forage. There was a reduction in forage mass (P < 0.06) of the functional groups of short grasses, legumes and other herbaceous plants throughout the periods, primarily due to removal by animals. Tall grasses, sub-shrubs and rosulated groups did not change during the surveys (P > 0.1). The grazing method did not alter the structure or dynamics of the vegetation during the study period. Maintaining the recommended height of the lower layer through the stocking adjustment method used was not possible, and a decrease of forage mass consumption by animals occurred.