Fenologia da vegetação e a sua relação com a água e o carbono em ambientes de cerrado no Brasil: influências do uso e cobertura da terra no passado, presente e futuro
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2015-02-02
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Universidade Federal de Goiás
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The Brazilian savanna (known as Cerrado) is an upland biome made up of various
physiognomies, from herbaceous to arboreal. In this work, vegetation greenness (EVI),
precipitation (PPT), and evapotranspiration (ET) data for the 2000 to 2012 period were analyzed
in order to understand the phenology of the major Cerrado natural and anthropic landscapes, as
well as its relation to precipitation, net primary productivity (NPP), biomass, and
evapotranspiration fluxes, according to different land use scenarios. Along the 13 years under
analysis, for all vegetation types the mean wet season duration varied from eight to nine months,
while the growing season lasted seven to eight months. The mean start of the wet and growing
seasons were very close for all land cover types during these 13 years, with the start of the wet
season in August or September (with the exception of 2002 and 2007), and the start of the
growing season in September or October. The mean end of the wet and growing seasons
occurred in April or May and in May or June, respectively. The start, the end, and the duration
of the wet and the growing seasons varied according to rainfall volume and distribution, which
are affected by the El Niño and La Niña phenomena. For example, during El Niño years, the
start of the wet season occurred earlier in August, and the duration of the wet season was longer
than eight months. If followed by a La Niña, the start of the growing season of the vegetation
occurred later in October and the duration of the season was shorter than eight months. In
addition to the rainfall variability (El Niño and La Niña) and the type of vegetation (natural or
anthropic grasslands), the start, the end, and the duration of the wet and growing seasons are
also affected by the spatial variation (latitude and longitude). Considering the spatial variation
of the start of the wet and growing seasons, the beginning was earlier in the southern portion of
the Cerrado biome, in August-September and September-October, and later in the north, in
November-December and October-December, respectively. The end of the season showed the
same behavior, i.e. an earlier end (March-April) in the southern portion for the wet and growing
seasons, while much later in the northern portion (June-July). Regarding the seasonal and
phenological behavior of the different vegetation types, the green-up for all Cerrado
physiognomies started in mid-September to the end of October, at the onset of the rainy season,
reaching peak values from December through January, and a gradual senescence, starting as
early as March or April. The total Cerrado growing season biomass for 2002 was 28 gigatons
of carbon and the evapotranspiration was 1336 gigatons of water. A sample-based response
associated with the area occupied by each vegetation type showed that pasture and cropland
had 52% and 22% less NPP and ET than natural landscapes. The mean growing season
evapotranspiration and biomass for 2002 was 576 Gt of water and 12 Gt of carbon for pasture
and croplands compared to 760 Gt of water and 16 Gt of carbon for the Cerrado natural
vegetation. Considering a modeled future scenario (year 2050), the ET flux from natural
Cerrado vegetation was 394 Gt less than in 2002 and 991 Gt less than in a potential scenario,
characterized with only natural vegetation, while the carbon was eight Gt less than in 2002 and
21 Gt less than in a pre-conversion Cerrado (potential scenario). In 2050, the sum of the pasture
and cropland ET fluxes increased by 405 Gt, relative to 2002, and the carbon by 11 Gt. At last,
the different land use scenarios showed that the deforestation impact until now in the fluxes of
evapotranspiration and in the biomass were greater than the future scenario.
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ARANTES, A. E. Fenologia da vegetação e a sua relação com a água e o carbono em ambientes de cerrado no Brasil: influências do uso e cobertura da terra no passado, presente e futuro. 2015. 84 f. Dissertação (Mestrado em Geografia) - Universidade Federal de Goiás, Goiânia, 2015.