Seasonal variation in energy balance and canopy conductance for a tropical savanna ecosystem of south central Mato Grosso, Brazil
Seasonal variation in energy balance and canopy conductance for a tropical savanna ecosystem of south central Mato Grosso, Brazil
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DOI：
10.1002/2013jg002472
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发表时间：
2014-01
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影响因子：
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通讯作者：
T. Rodrigues;G. Vourlitis;F. Lobo;R. G. Oliveira;J. Nogueira
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作者：
T. Rodrigues;G. Vourlitis;F. Lobo;R. G. Oliveira;J. Nogueira
热带稀树草原（当地称为塞拉多）占巴西的24%，其特点是气候变化大;然而，能量交换模式知之甚少，特别是混合草原（当地称为坎波苏霍）。我们使用涡度相关来测量混合草地的潜热（Le）和感热（H）通量，并将气象和遥感数据联系起来，以确定对这些通量的控制。我们假设：（1）H和Le的季节性变化会很大，由于降水量的变化;（2）生态系统物候，估计使用增强植被指数（EVI），将是最好的预测季节性变化的Le;和（3）塞拉多，过渡，潮湿的万年青森林将有类似的平均年Le率，尽管塞拉多乐大的季节性变化。我们的数据表明，campo sujo在能量平衡方面表现出很大的季节性波动，这是由降雨驱动的，对降雨脉冲的反应是快速和动态的，特别是在旱季。路径分析表明，EVI的时间变化并没有显着影响乐或Gc，但这是因为所有三个变量（EVI，乐，和Gc）响应类似的地表水可用性的时间变化。与其他热带生态系统相比，潮湿的网站有较高的率在旱季，但类似的利率在雨季时，水不受限制的乐。随着年平均降雨量的增加，由于季节性更强的热带生态系统的旱季水资源限制，每年的平均Le率显着增加。
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 (Le) 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 Le 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 Le; and (3) cerrado, transitional, and humid evergreen forests would have similar rates of average annual Le despite large seasonal variation in cerrado Le. 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 Le or Gc, but this was because all three variables (EVI, Le, and Gc) responded similarly to temporal variations in surface water availability. Compared to other tropical ecosystems, wetter sites had higher rates of Le during the dry season but similar rates during the wet season when water was not limiting. Over annual time periods, average rates of Le increased significantly as average annual rainfall increased, due to dry‐season water limitations in the more seasonal tropical ecosystems.