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Tree Roots and Slope Stability : a Comparison between Pinus Radiata and Kanuka
| Content Provider | Semantic Scholar |
|---|---|
| Author | Ekanayake, Jagath C. Marden, Michael C. Watson, Alan M. Rowan, Donna |
| Copyright Year | 1997 |
| Abstract | Increasingly, in the East Coast region of the North Island of New Zealand stands of indigenous regenerating kanuka (Kunzea ericoides var. ericoides (A.Rich.) J.Thompson) are being felled and replanted with Pinus radiata D.Don. Conversion has occurred predominantly on erosion-prone hillslopes where storm-generated landsliding has been widespread and severe, but data on the relative effectiveness of these two forest species in enhancing slope stability are rare. For kanuka andP. radiata, shear stress-displacement curves for their corresponding potential shear planes were measured at two sites by in situ direct shear tests on soil with and without roots. The contribution of roots to soil strength was first estimated by calculating the difference between the maximum shear stress of the shear stress-displacement curves obtained for soil with and without roots. Results suggested that for individual trees the contribution from the roots to soil strength on a root cross-sectional area per unit shear area basis was independent of species for the two tree species tested. There were, however, significant differences in stand density between these two species. These results were then used to obtain relationships between shear stress and shear displacement at the peak of the shear stress-displacement curve, and between cross-sectional area of roots per unit shear area. Taking the shear strength of the combined soil-root system as the peak value of the shear stress-displacement curve produced from the in situ direct shear tests, a limit equilibrium slope stability analysis method was used to derive the safety factors. A simple model developed using the relationship between the shear strength of the soil-root system, the specific root crosssection area, and slope angle was then used to determine safety factors for typical stand densities of naturally regenerating kanuka for comparison with different P. radiata management regimes at equivalent stages of growth. The model predicted that safety factors for stands of P. radiata in the first 8 years after establishment would be lower than for equivalent-aged stands of fully-stocked regenerating kanuka under similar conditions. However, after 16 years the safety factor for a stand of kanuka would be lower than that for P. radiata at final stocking densities typical of framing and biomass regimes. In areas where vegetation plays a major role in soil conservation and erosion control, the model can be used to compare the stability of forested slopes with different species New Zealand Journal of Forestry Science 27(2): 216-233 (1997) Ekanayake et al.—Pinus radiata and kanuka roots and slope stability 217 and stand densities. However, the model does not take into account the effect of buttressing by mature tree roots. |
| Starting Page | 216 |
| Ending Page | 233 |
| Page Count | 18 |
| File Format | PDF HTM / HTML |
| Volume Number | 27 |
| Alternate Webpage(s) | https://www.scionresearch.com/__data/assets/pdf_file/0017/36260/NZJFS2721997EKANAYAKE216-233.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
