期刊
JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES
卷 119, 期 1, 页码 1-13出版社
AMER GEOPHYSICAL UNION
DOI: 10.1002/2013JG002472
关键词
canopy conductance; decoupling factor; latent heat flux; sensible heat flux; cerrado
资金
- Universidade Federal de Mato Grosso (UFMT)
- Programa de Pos Graduacao em Fisica Ambiental (PPGFA) IF/UFMT
- Grupo de Ecofisiologia Vegetal (GPEV)
- Coordenacao de Aperfeicoamento de Pessoal do Ensino Superior (CAPES)
- U.S. National Science Foundation-Office of International Science and Engineering (NSF-OISE)
- Projeto Ciencia sem Fronteira (Science Without Border) [120/2012 CAPES/CNPQ]
Tropical savanna (locally known as cerrado) composes 24% of Brazil and is characterized by high climatic variation; however, patterns of energy exchange are poorly understood, especially for mixed grasslands (locally known as campo sujo). We used eddy covariance to measure latent (L-e) and sensible (H) heat flux of a mixed grassland and linked meteorological and remote sensing data to determine the controls on these fluxes. We hypothesized that (1) seasonal variations in H and L-e would be large due to variations in precipitation; (2) ecosystem phenology, estimated using the enhanced vegetation index (EVI), would be the best predictor of seasonal variation in L-e; and (3) cerrado, transitional, and humid evergreen forests would have similar rates of average annual L-e despite large seasonal variation in cerrado L-e. Our data suggest that campo sujo exhibits large seasonal fluctuations in energy balance that are driven by rainfall and that responses to rainfall pulses are rapid and dynamic, especially during the dry season. Path analysis indicated that temporal variations in the EVI did not significantly affect L-e or G(c), but this was because all three variables (EVI, L-e, and G(c)) responded similarly to temporal variations in surface water availability. Compared to other tropical ecosystems, wetter sites had higher rates of L-e during the dry season but similar rates during the wet season when water was not limiting. Over annual time periods, average rates of L-e increased significantly as average annual rainfall increased, due to dry-season water limitations in the more seasonal tropical ecosystems.
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