This study examines the evolution of grass and shrub vegetation in six rangelands used by cattle and sheep in the 'Sierra de Guara' Natural Park. A preliminary characterisation of brush vegetation was conducted in the first year of study, which shows large diversity in some sites, even within plots. This evolution was compared in grazed areas and in fenced plots (non-grazed) close to each other. During a single grazing period, the amount of grass in grazed areas was reduced and the relation between green and dead fractions was maintained, whereas in non-grazed areas there was a build-up of grasses with a greater proportion of dead material, which implies lower nutritional value for the animals and risk of environment degradation.