Details

Autor(en) / Beteiligte

• Röll, Alexander
• Kang, Tongming
• Hahn, Peter
• Ahongshangbam, Joyson
• Ellsäßer, Florian
• Hendrayanto
• Sharma, Puja
• Wintz, Thorge
• Hölscher, Dirk

Titel

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

Ist Teil von

• Hydrological processes, 2023-12, Vol.37 (12), p.n/a

Ort / Verlag

Hoboken, USA: John Wiley & Sons, Inc

Erscheinungsjahr

2023

Quelle

Wiley-Blackwell Journals

Beschreibungen/Notizen

• 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. For five study plots in Sumatran rainforest, dense point clouds were created from drone missions to assess the relationship between tree transpiration and structural crown metrics. Here, an example of the 3D point cloud workflow for one sample tree (ID 3634) in one study plot (HF2) is depicted. In the processed RGB orthomosaic (left panel), the plot boundaries are delineated (red line) and a given sap flux sample tree is located manually based on data from ground assessments. The crown of each clearly identified sap flux sample tree is then delineated manually (differently coloured shapes). The according crowns (right panel) are extracted from the plot 3D point clouds, are refined manually and are subsequently subjected to different algorithms (e.g., convex hull, alpha25) as the basis for calculating diverse crown metrics.