Recent studies indicate that after protection from human pressures (fire, cattle grazing and agriculture), structural changes occur in the cerrado vegetation, changing open physiognomies into more closed savannas. We analyzed the dynamics of vegetation types along 44 years, at Assis Ecological Station, one of the rare conservation units protecting the cerrado biome in the southeastern São Paulo State, Brazil, with the aim of characterizing and quantifying those changes in space and time. Protected against human pressures since a long time, field observations have shown an upgrade of local cerrado physiognomies, through a successional process whose structural climax can be a forest physiognomy, with a continuous arboreal stratum. The dynamics of the vegetation types was analyzed by using aerial photographs (1962, 1984 and 1994), Quick Bird satellite images (2006) and field surveys. During this 44 years period, field physiognomies were reduced from 23% to less than 1% of the total area studied. In the other extreme, woodland savanna increased from 53% to 91% of the area. Changes did not happen at the same rhythm across the area, and that is apparently correlated to microclimate and edaphyc differences. We believe that field and savannic physiognomies initially existing were mostly maintained due to heavy human pressures, constraining the secondary succession towards an edapho-climatic climax of greater biomass. Confirming the observations of cerrado areas elsewhere, protection against fire, cattle grazing and agriculture allowed the evolution of open vegetation types into more closed ones, tending to be locally extinct the first if new disturbances do not occur. Consequences of these changes related to management strategies, biodiversity conservation and carbon sink are discussed.
Brazilian Savanna; cerrado physiognomies; human pressures; secondary succession; vegetation dynamics
