New research project: How effective are natives for erosion control in hill country?
Blog post.
Raphael Spiekermann and Tom Mackay-Smith
11/5/20243 min read
We are teaming up with Peter Nowell and the Healthy Waters and Flood Resilience team at Auckland Council for an exciting new 2-year project.
A big question when using natives is how effective they are at stabilising slopes compared to exotics such as poplars?
To date, no study has compared the root structure of mature, widely-spaced natives with exotics in silvopastoral systems in New Zealand.
The project has three aims:
1. Compare the root systems of kānuka, tōtara, and poplar on two soil types in the Auckland Region
This involves digging 1 m x 1 m trenches around each tree and counting the number of roots at 4 distances from the trunk (1.5, 2.5, 3.5, and 4.5 m).
We will also measure root strength using a device called a root pullout machine.
We then use the data collected from the field to assess how much each species reduces the probability of landslides under various densities (40, 60, 80, and 100 stems/ha) and rainfall events.
2. Work with expert slope stability modellers from Switzerland (Prof. Schwarz, University of Bern, and Dr. Feiko van Zadelhoff) to input this data into the SlideForMap model
This model creates maps that tells us where landslides are more likely to occur:
3. The final aim is to create an idealized silvopasture design based on the results
We will consider various factors for the design, such as each species' ability to reduce landslides, cost of planting, estimated income from carbon credits, and other benefits to the farm.
References
Ngo, H. M., Van Zadelhoff, F. B., Gasparini, I., Plaschy, J., Flepp, G., Dorren, L., Phillips, C., Giadrossich, F., & Schwarz, M. (2023). Analysis of Poplar’s (Populus nigra ita.) Root Systems for Quantifying Bio-Engineering Measures in New Zealand Pastoral Hill Country. Forests, 14(6), 1240. https://doi.org/10.3390/f14061240
Spiekermann, R. I., Van Zadelhoff, F., Schindler, J., Smith, H., Phillips, C., & Schwarz, M. (2023). Comparing physical and statistical landslide susceptibility models at the scale of individual trees. Geomorphology, 440, 108870. https://doi.org/10.1016/j.geomorph.2023.108870
Mackay-Smith, T. H., Spiekermann, R. I., Richards, D. R., Harcourt, N., & Burkitt, L. L. (2024). An integrative approach to silvopastoral system design: Perspectives, potentials and principles. New Zealand Journal of Agricultural Research, 1–41. https://doi.org/10.1080/00288233.2023.2298922
