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| Format: | Artículo Open Access |
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Wiley
2026
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| Online-Zugang: | https://onlinelibrary.wiley.com/doi/10.1002/hyp.70569 |
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Inhaltsangabe:
- Crown Exposure Drives Sap Flow Variability Among Nearly Identical Trees in a Lowland Tropical Rainforest Natalia de Aguiar‐Campos Yoko F. Ishida Will Edwards Susan G. W. Laurance Hydrological Processes ABSTRACT Tropical forest transpiration strongly influences the global hydrological cycle and is often estimated through sap flow measurements. Due to their high diversity and complex canopies, estimates often rely on mean sap flow measured from cohorts of similar trees, although within‐cohort variability remains poorly investigated in tropical forests. We aimed to quantify sap flow variability in a cohort of 10 similarly sized conspecific trees in an Australian tropical rainforest. Over three campaigns (dry, wet, and dry seasons), we measured sap flow simultaneously on north and south stem aspects and at two sapwood depths using heat‐ratio sensors, and estimated crown exposure for each tree. Between the first and second campaigns, a tropical cyclone increased mean crown exposure of the cohort two‐fold. We found that sap flow readings varied up to 14‐fold between trees under the same environmental conditions, decreasing to nine‐fold when within‐tree variation was accounted for. Regardless of aspect or depth, sap flow varied by an average of 52.5% within trees across the study period. Although sapwood depth was a poor predictor of sap flow, averaging across the radial profile decreased within‐tree variation to 34%. Despite similar stem dimensions, crown exposure largely explained variability among and within trees. During the dry seasons, north‐aspect sap flow remained stable, whereas south‐aspect sap flow increased by 44% following cyclone‐induced increases in exposure. In contrast, variation within and across trees was substantially lower during the wet season, presumably due to more uniform soil water availability. These results yield two recommendations to reduce uncertainty in tropical forest transpiration estimates: (i) sap flow should be measured at more than one point (at different aspects and/or depths) to account for the 52.5% difference in readings per tree; and (ii) crown exposure should be incorporated into stratification approaches to reduce within‐cohort sap flow variability. 10.1002/hyp.70569 http://creativecommons.org/licenses/by-nc-nd/4.0/