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Wind Engineering risk to forest trees - an experimental and numerical study


Department of Civil Engineering

, Saturday, October 31, 2020 Funded PhD Project (European/UK Students Only)

About the Project

Strong winds can result in tree uprooting (windthrow, the most common one) and/or breakage (windsnap) causing considerable damage and leading to major financial losses for forest owners. The annual loss to the forest industry due to windthrow is estimated at approximately €1.3 million [1].

The current approach to understanding and managing these factors in Ireland follows a two-pronged approach. Firstly, attention is focused on the management of tree stability through cultivation techniques aimed at promoting tree stability [8,9], and secondly, via an empirical model which relates tree stability to site factors and wind induced forces to predict the probability or occurrence of windthrow [9,11]. But these methods have limitations in that they have been developed based on general wind conditions and represent endemic windthrow in forest stands. Therefore, their usefulness to quantify the effects of severe winds and storms (i.e. catastrophic windthrow) is more limited.

Hence, considerable uncertainty exists within climate change scenarios of increased frequency and severity of winter storms and their likely effects on Irish forest and whether new/different management approaches are required [12] and the influence of forest design to mitigate windthrow (e.g. minimising brown edges, direction of cultivation, etc.). New methods need to be developed which incorporate the characteristics of wind and root anchorage in response to soils characteristics which allows a greater understanding of the potential effects of catastrophic windthrow.

The research will combine the expertise of wind and geotechnical engineers as well as practicing biologists, arboriculturist, foresters from Ireland in order to investigate windthrow/windsnap in trees. An idealised numerical model of the tree will be developed covering both the stem and root system [15,16]. Previous work on crops has shown that it is the latter which is key to understanding the issue and as such, a physical model will also be developed which will enable calibration of the numerical model.

The research aims to use innovative methods to include wind as including physical testing in a wind tunnel to simulate different windspeeds and directions and a variety of turbulent conditions with tree models in order to predicted realistic windthrow/windsnap velocities for different soils and as a function of tree height. Combined with the numerical modelling, the aim is to provide insight on the terminal height of trees in response to wind loading and the influence of forest design on the vulnerability of forests to windthrow.

Funding Notes

Funding is secured at EU/Home rate. International students are welcome to apply as long as they can cover the overseas fees.

References

[1] (https://www.teagasc.ie/crops/forestry/research/reducing-windthrow-losses-in-farm-forestry/). Last accessed 8th June 2019.
[8] Hendrick, E. 1989. The effect of cultivation method on the growth abd root anchorage of Sitka spruce. Irish Forestry 46.
[10] Ni Dhubhain, A., Walshe, J., Bulfin, M., Keane, M and Mills, P (2001) The initial development of a windthrow risk model for Sitka spruce in Ireland. Forestry, Vol. 74, No.2, 161 – 170.
[11] Ni Dhubhain, A., , Bulfin, M., Keane, M and Mills, P., Walshe, J. (2009) The development and validation of a windthrow probability model for Sitka spruce in Ireland. Irish Forestry, Vol. 66, 51 – 74.
[12] Ni Dhubhain, A., Farrelly, N. 2018. Understanding and managing windthrow. COFORD Connects silviculture/Management note No. 23. COFORD, Dublin.
[13] Gonzalez, G.F. 2017. The influence of thinning on tree stabiloity in Sitka spruce. MSc thesis, UCD, May 2017.
[14] Pivato, D., Dupont, S., Brunet, Y. 2014. A simple tree swaying model for forest motion in windstorm conditions. Trees 28: 281-293.
[16] Rodgers, M., McHale,J., and Mulqueen, J. 2006. Stability of Sitka spruce on mole-drained and ploughed surface water gley soil. Irish Forestry 63.
[18] Gardiner, B.A., Stacey, G.R., Belcher, R.E. and Wood, C.J. 1997 Field and wind tunnel assessments of the implications of respacing and thinning for tree stability. Forestry 70(3), 455 234–252.

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