Image from https://en.wikipedia.org/wiki/Crown_shyness

Student information

MSc thesis subject: Understanding crown shyness from a 3D perspective

Crown shyness refers to the tendency of tree crowns to maintain a small buffer of empty space between neighbouring crowns. This phenomenon is widely familiar to ecologists, but its actual cause, extent, and implication is understudied.

It is believed to be the result of abrasion of tree crowns during their collisions during wind events, but little evidence supports this conclusion.  Collisions between adjacent trees can result in loss of leaf area, touch induced or thigmomorphogenic inhibition of lateral shoot elongation, and in significant damping of wind-induced tree oscillations. Collisions may there- fore affect long-term forest ecology by influencing crown shyness, thereby affecting light foraging and light capture within the canopy.  The extent of the gap may vary by species, height, stand density, slenderness, bole stiffness, wind frequency and intensity, and branch stiffness compared to neighbours.

Until now, studying tree crowns has been very difficult due to the need to climb trees and perform measurements in situ.  New laser ranging technology, however, has brought about a step change in our ability to measure the forest canopy.  This study would represent a significant step forward in understanding a famous but poorly-understood phenomenon.


For this research project, Terrestrial Laser Scanning (TLS) data were acquired along different sites, Guyana, Peru, Indonesia, Ghana. Pre-processing has been done and plots are ready to be further analysed.

You will be in contact with a researcher from University of Oxford for further analysis and research.

Objectives

  • How to process TLS data to create 3D models for crown volume?
  • Assess 3D canopy models to understand crown shyness in tropical forests trees.
  • Evaluate if and how TLS are suitable for understanding crown shyness.

Literature

  • Béland, M., Widlowski, J. & Fournier, R.A. (2014). A model for deriving voxel-level tree leaf area density estimates from ground-based LiDAR. Environmental Modelling & Software, 51, 184–189.
  • Bienert, A., Hess, C., Maas, H.-G. & von Oheimb, G. (2014). A voxel-based technique to estimate the volume of trees from terrestrial laser scanner data. ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, XL-5, 101–106.
  • Brown, P.L., Doley, D. & Keenan, R.J. (2000). Estimating tree crown dimensions using digital analysis of vertical photographs. Agricultural and Forest Meteorology, 100, 199–212.
  • Park, H. & Lim, S. (2010). Voxel-based volume modelling of individual trees using terrestrial laser scanners. M.
  • Seidel, D., Hoffmann, N., Ehbrecht, M., Juchheim, J. & Ammer, C. (2015). How neighborhood affects tree diameter increment – New insights from terrestrial laser scanning and some methodical considerations. Forest Ecology and Management, 336, 119–128.

Requirements

  • Basic understanding of ecological principles.
  • Programming skills (R and/or Python) or desire to learn them.

Output

  • The student is expected to write-up a scientific paper following the standards of international peer-reviewed journals.

Theme(s): Sensing & measuring