Transpiration on the rebound in lowland Sumatra

Röll, Alexander; Niu, Furong; Meijide, Ana; Ahongshangbam, Joyson; Ehbrecht, Martin; Guillaume, Thomas; Gunawan, Dodo; Hardanto, Afik; Hendrayanto, Hendrayanto; Hertel, Dietrich; Kotowska, Martyna M.; Kreft, Holger; Kuzyakov, Yakov; Leuschner, Christoph; Nomura, Miki; Polle, Andrea; Rembold, Katja; Sahner, Josephine; Seidel, Dominik; Zemp, Delphine Clara; Knohl, Alexander; Hölscher, Dirk

doi:10.1016/j.agrformet.2019.04.017

Cited by 37 publications

(50 citation statements)

References 85 publications

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“…One may have expected that E t at riparian sites is higher than at upland sites. However, a previous sap flux-based study at the same four upland plots showed no indications of soil water limitation of tree water use, in 2013 and 2014 (non-ENSO years) [39]. Further in accordance with our results, rubber and oil palm plantations in the lowlands of Sumatra had lower E t at riparian sites than at upland sites [11].…”

Section: Discussionsupporting

confidence: 92%

“…However, these relationships still need further exploration. In accordance with our results, several previous studies also explained variability in tree water use with crown or leaf area metrics [39,[60][61][62]. Further studies from related ecological fields have also pointed to the high potential of using drone-derived crown metrics as predictors and scalars, e.g., for above ground biomass and canopy biomass [63].…”

Section: Discussionsupporting

confidence: 91%

“…To assess tree water use, we measured sap flux with thermal dissipation probes (TDP) [38]. We selected one upland plot (HF2) and all four riparian plots (HFr1, HFr2, HFr3, HFr4) for these measurements; the remaining three upland plots had already been measured in a previous sap flux study [39]. The three plots not studied with sap flux methods served as independent tests for stand-scale transpiration derived from two different methods.…”

Section: Sap Flux Measurementsmentioning

confidence: 99%

“…In each plot, 15 trees were equipped with two TDP sensors each, with the exception of HFr1, where only 12 trees were equipped due to a lack of sap flux instrumentation, as this plot was measured at the end of the field campaign. Installation of sap flux sensors and calculation of sap flux density (J S , g cm −2 h −1 ) followed the methods described in [39] for lowland rainforest in the same region; therein, the original Granier's [38] equation for deriving J S was applied. Night time zero-flux conditions, as described in Oishi et al [40], were met during the early morning hours.…”

Section: Sap Flux Measurementsmentioning

confidence: 99%

“…Night time zero-flux conditions, as described in Oishi et al [40], were met during the early morning hours. Tree-level water use was derived by considering the water conductive area (A C , cm 2 ) of trees and radial sap flux patterns measured by the heat field deformation technique [39].…”

Section: Sap Flux Measurementsmentioning

confidence: 99%

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Airborne Tree Crown Detection for Predicting Spatial Heterogeneity of Canopy Transpiration in a Tropical Rainforest

et al. 2020

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Tropical rainforests comprise complex 3D structures and encompass heterogeneous site conditions; their transpiration contributes to climate regulation. The objectives of our study were to test the relationship between tree water use and crown metrics and to predict spatial variability of canopy transpiration across sites. In a lowland rainforest of Sumatra, we measured tree water use with sap flux techniques and simultaneously assessed crown metrics with drone-based photogrammetry. We observed a close linear relationship between individual tree water use and crown surface area (R2 = 0.76, n = 42 trees). Uncertainties in predicting stand-level canopy transpiration were much lower using tree crown metrics than the more conventionally used stem diameter. 3D canopy segmentation analyses in combination with the tree crown–water use relationship predict substantial spatial heterogeneity in canopy transpiration. Among our eight study plots, there was a more than two-fold difference, with lower transpiration at riparian than at upland sites. In conclusion, we regard drone-based canopy segmentation and crown metrics to be very useful tools for the scaling of transpiration from tree- to stand-level. Our results indicate substantial spatial variation in crown packing and thus canopy transpiration of tropical rainforests.

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Section: Discussionsupporting

confidence: 92%

Section: Discussionsupporting

confidence: 91%

Section: Sap Flux Measurementsmentioning

confidence: 99%

Section: Sap Flux Measurementsmentioning

confidence: 99%

Section: Sap Flux Measurementsmentioning

confidence: 99%

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Airborne Tree Crown Detection for Predicting Spatial Heterogeneity of Canopy Transpiration in a Tropical Rainforest

et al. 2020

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Combining UAV thermography, point cloud analysis and machine learning for assessing small‐scale evapotranspiration patterns in a tropical rainforest

Cortés‐Molino,

Valdés‐Uribe,

Ellsäßer

et al. 2023

Ecohydrology

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Microclimate and vegetation structure control evapotranspiration (ET) from land surfaces at stand and landscape scales. Tropical rainforests are among the most diverse and complex terrestrial ecosystems, harbouring vast plant and animal species throughout their dense multistory canopy. They contribute substantially to global precipitation through their high ET. However, there is little information about ET influences at very small spatial scales under given climatic conditions. In a tropical rainforest on Sumatra, we studied the relationship between pixel‐level ET as derived from high‐resolution (~10 cm), near‐surface thermography from an unmanned aerial vehicle (UAV) and canopy structure as derived from red–green–blue (RGB) image and three‐dimensional (3D) point cloud analyses. The 16 derived potential predictors encompassed vegetation height, height variability, vegetation density and reflectance variables. Using regression models, several of the studied variables had a significant linear relationship with ET, but the explained variance was only marginal. However, applying a random forest algorithm including forward feature selection and target oriented cross validation explained substantial parts of the pixel‐level variance in ET (R2 = 0.56–0.65), thus indicating multiple non‐linear relationships with interactions among predictor variables. Therein, green leaf index, leaf area density and vegetation height were often the most important variables for the prediction outcome, but their sequence varied among the four study plots. Overall, combining canopy structure variables derived from RGB photogrammetry explained relatively large parts of spatial ET variations. Our study thus indicates the large potential of combining UAV‐based thermography and photogrammetry techniques with machine learning approaches to better understand ET but also suggests that more work remains to be done in explaining ET patterns at very small spatial scales.

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Complex canopy structures control tree transpiration: A study based on 3D modelling in a tropical rainforest

Röll,

Kang,

Hahn

et al. 2023

Hydrological Processes

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Tropical rainforests are rich in tree species and comprise complex canopy structures. Transpiration by forest trees is a major hydrological flux which contributes to climate regulation. We explored the role of forest canopy structure on tree transpiration in a tropical rainforest on Sumatra, Indonesia. Drone‐based photogrammetry and the structure from motion technique were used to compute high‐resolution 3D point clouds and derive forest and tree structural variables. Transpiration of differently sized and vertically positioned trees was assessed with sap flux measurements. Per‐tree transpiration rates increased linearly with several variables related to crown dimension and were further enhanced by top‐heavy crown shape, dense leafage and increasing canopy openness as assessed with the gap light index. Under given environmental conditions, the two variables crown volume and top‐heaviness explained 74% of the observed variance in per‐tree transpiration. Transpiration rates per unit crown dimension were highest for small crowns, decreased non‐linearly with increasing crown dimension and were little affected by other analysed structural variables. Our study underlines the potential of 3D point cloud analyses for accurately determining the structure of complex forest canopies and thus better understanding and predicting transpiration rates of differently positioned trees.

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Transpiration on the rebound in lowland Sumatra

Cited by 37 publications

References 85 publications

Airborne Tree Crown Detection for Predicting Spatial Heterogeneity of Canopy Transpiration in a Tropical Rainforest

Airborne Tree Crown Detection for Predicting Spatial Heterogeneity of Canopy Transpiration in a Tropical Rainforest

Combining UAV thermography, point cloud analysis and machine learning for assessing small‐scale evapotranspiration patterns in a tropical rainforest

Complex canopy structures control tree transpiration: A study based on 3D modelling in a tropical rainforest

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