Fine-scale spatial variability of throughfall amount and isotopic composition under a hardwood forest canopy

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Stable isotopes of water can give clues to the physical processes of forest canopy interception. We examined whether fine-scale canopy structure is related to throughfall amount and isotopic variation by intensively quantifying both throughfall and canopy structure in a broadleaf, deciduous forest in Louisiana, USA. Local throughfall amount was correlated with canopy structure quantified as distance to the nearest tree, local crown coverage, and local crown length; isotopic composition was also correlated with the same variables but weakly. Spatial patterns of throughfall amount showed some consistency across storms, but spatial patterns of stable isotopes were much weaker and inconsistent. Spatial autocorrelation was consistent in throughfall amount across events, which suggests fixed controls over patterning of throughfall to the forest floor by the canopy. In contrast, lower spatial and temporal autocorrelation in isotopic composition suggested temporally varying controls over patterning, and that routing through the canopy, intra-storm isotopic variation of rainfall, isotopic exchange, and evaporation interacted to affect the stable isotopic composition. Copyright © 2015 John Wiley & Sons, Ltd.

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