Dinâmica espaço-temporal (1962-2006) das fitofisionomias em unidade de conservação do Cerrado no sudeste do Brasil

Abstract

-(Spatial and temporal dynamics of Cerrado vegetation types in a protected area, southeastern Brazil). Recent studies indicate that after protection from human pressures (fi re, 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, fi eld 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 fi eld surveys. During this 44 years period, fi eld 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 fi eld 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. Confi rming the observations of cerrado areas elsewhere, protection against fi re, cattle grazing and agriculture allowed the evolution of open vegetation types into more closed ones, tending to be locally extinct the fi rst if new disturbances do not occur. Consequences of these changes related to management strategies, biodiversity conservation and carbon sink are discussed.Key words -Brazilian Savanna, cerrado physiognomies, human pressures, secondary succession, vegetation dynamics RESUMO -(Dinâmica espaço-temporal das fi tofi sionomias em unidade de conservação do Cerrado no sudeste do Brasil). Estudos recentes indicam que em áreas de Cerrado protegidas das atividades antrópicas ocorre uma evolução estrutural de fi tofi sionomias abertas para outras mais fechadas, com tendência ao desaparecimento das primeiras. Analisou-se a dinâmica das fi sionomias do Cerrado ao longo de 44 anos, na Estação Ecológica de Assis, SP, uma das poucas unidades de conservação do bioma no sudeste do Brasil, com o objetivo de caracterizar e quantifi car possíveis tranformações fi sionômicas no tempo e no espaço. Protegida de pressões antrópicas por longo tempo, observações de campo têm indicado um adensamento da vegetação em toda a área, rumo a um clímax de estrutura fl orestal. Para realizar este estudo foram utilizadas aerofotos (1962, 1984 e 1994), imagens "QuickBird" (2006) e reconhecimento de campo. Durante o período compreendido por este estudo, a área ocupada pelas fi sionomias campestres foi reduzida...

Vascular flora in dry-shrub and wet grassland Cerrado seven years after a fire, Federal District, Brazil

“…In areas of savanna woodland (cerradão), cerrado sensu stricto, "campo cerrado" and shrub savanna (campo sujo), the absence of fires caused a significant increase in the number of woody species, with open areas showing the highest values, that is, the absence of disturbances allowed the settlement and regeneration of the woody component (Moreira 2000). After 44 years of protection from fire, the main change observed with satellite images in vegetation cover at the Assis Ecological Station, an area of Cerrado in southeastern Brazil, was the continuous thickening of vegetation, with open grassland areas being gradually occupied by closed cerrado physiognomies (Pinheiro and Durigan 2009). Protected since 1959, with the suppression of fire since 2004 in that area the wet grassland had its area reduced to one fourth of the initial extent, losing ground to the cerrado sensu stricto and riparian forests (Pinheiro and Durigan 2009).…”

“…After 44 years of protection from fire, the main change observed with satellite images in vegetation cover at the Assis Ecological Station, an area of Cerrado in southeastern Brazil, was the continuous thickening of vegetation, with open grassland areas being gradually occupied by closed cerrado physiognomies (Pinheiro and Durigan 2009). Protected since 1959, with the suppression of fire since 2004 in that area the wet grassland had its area reduced to one fourth of the initial extent, losing ground to the cerrado sensu stricto and riparian forests (Pinheiro and Durigan 2009). Apparently, in the ALF wet grassland these patterns described by Moreira (2000) and Pinheiro and Durigan (2009) can also be verified, whereby the exclusion of fire for seven years has encouraged the growth and settlement of phanerophytes and chamaephytes (woody component ) and resulted in changes in the landscape due to the density of these shrubs.…”

Relações solo-vegetação na estruturação de comunidades de cerrado sensu stricto no sul de Minas Gerais, Brasil

“…Da mesma forma, espera-se que a dinâmica sucessional para os cerrado sobre Argissolos seja a mesma descrita para áreas de transição cerrado-floresta sobre solos arenosos da Amazônia (Oliveira-Filho & Ratter 2002), onde o estádio clímax da vegetação seja o Cerradão. Essa pesquisa indica que em áreas de ecótono cerrado-floresta da província florística sudeste, nos solos com maiores teores de argila, fertilidade e capacidade de retenção de água, o comportamento da vegetação climáxica seja o mesmo observado por Pinheiro & Durigan (2009), no qual o cerrado sensu stricto conservado tornou-se um Cerradão. Por fim, os cerrados do sul e sudoeste de Minas Gerais comprovam a afirmativa de Bridgewater et al (2004), na qual os esforços para conservação do Cerrado devem considerar cada província florística em separado.…”

Woody encroachment and its consequences on hydrological processes in the savannah

“…Since 1959, cattle were excluded and the vegetation has been protected from fire [29]. The protected vegetation has changed in structure over the last few decades, with a remarkable increase in biomass after fire suppression, detected by aerial photographs and satellite images from 1962 to 2006 [31]. Grasslands with no trees covered 21.3% of the area in 1962, but did not exist in 2006, while the cerradão (forest-type vegetation) expanded from 53 to 91.4% of the protected area in the same time period.…”

“…[30,33]). Fire suppression or decreasing fire frequency have been reported as the main explanation for woody encroachment in Cerrado vegetation across Brazil [29][30][31][32][33]64], with frequent fires, regardless of season, been shown to reduce woody biomass [65]. Changes over time in density and TBA in our study differed: TBA increased in the cerradão plots at similar rates as those of the cerrado stricto sensu, but density stabilized around 2000 ind ha 21 , corresponding to a basal area around 23 m 2 ha 21 , and after that, mortality equalled recruitment, resulting in no significant changes in density over 5 years.…”