Albedo em cerrado sensu stricto como resposta à variação climática e biológica: conexões com índice de vegetação, estoques de carbono e fluxos de CO2 / Albedo in cerrado sensu stricto as response to climatic and bilogical variation: connections with vegetation index, carbon stocks and fluxes of CO2

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

In this work we analyze the climatic variability influence over a woodland savannah ecosystem at Gleba Pe de Gigante, Santa Rita do Passa Quatro, SP, during the 2001-2007 period. The data collected for this analysis are from a micrometeorological tower located at Vassununga State Park, which was installed under the thematic project called Biosphere- Atmosphere Interaction Phase 2: Savannah and Land Use Change. The physical climate properties used for this analysis were precipitation, air temperature and solar radiation. A theoretical survey for above and below ground biomass was made to characterize the existing carbon stock potential related to the vegetation. The total biomass estimated at grassland savannah was 67.1 Mg.ha-1, at woodland savannah was 185.6 Mg.ha-1 and at dense savannah was 242.7 Mg.ha-1. A relationship between carbon stocks and CO2 fluxes was established where one tone of carbon in woodland savannah absorbs an average of 0.27 KgC.ha-1.day-1 from the atmosphere. The combination of different climate properties and intensities generates different environmental conditions that lead to the vegetation state and its productivity. The main physical parameter considered to evaluate vegetation state was the albedo, which was shared in two spectral bands: visible spectrum (solar albedo) and photosynthetic active radiation (PAR albedo). The seasonal pattern of albedo allows checking that vegetation was strongly conditioned by climatic variability, which dictates the ecosystem functionality rhythm. Generally, precipitation, air temperature and solar radiation vary in a proportional way along the year, providing two different periods related to vegetation status: one period characterized by favorable conditions to vegetal development (October-March) and another by stressing conditions (April-September). Maximum and minimum values for solar albedo at woodland savannah varied, respectively, between 15% (November/December) and 9% (September/October); for PAR albedo, maximum and minimum values varied between 6% (September/October) and 2% (February/March). At annual scale, PAR albedo rose in 2006, after a four years period of falling precipitation rate, between 2003 and 2006. 2006 was the drier year among the others. In 2007, the PAR albedo values were much lower than those calculated for the remaining years, promptly responding to the high precipitation rate observed in the previous rainy season, 2006-2007. Even though a quick response in PAR albedo was noticed due to the recovered water stress in seasonal scale, the albedo pattern in annual scale held a different way: between 2003 and 2006, period characterized by consecutive and negative precipitation rates, vegetation was apparently associated to stable values of PAR albedo, presenting higher values only in 2006. Considering these results, we conclude that the vegetation state is mainly conditioned by precipitation rate, once the air temperature and solar radiation had not presented high variation in the study region. Based on the importance of PAR albedo as a parameter to estimate seasonal vegetation status, a simple linear adjustment according for woodland savannah PAR albedo based on NDVI values was suggested, which explained variance by NDVI was equal to 0.68.

ASSUNTO(S)

savannah fotossíntese senescence cerrado albedo carbon climate pé de gigante albedo clima photosynthesis carbono senescência pé de gigante

ACESSO AO ARTIGO

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