Effects of windbreak structure on shelter characteristics
P. R. Bird A C , T. T. Jackson A , G. A. Kearney A and A. Roache BA Department of Primary Industries, Private Bag 105, Hamilton, Vic. 3300, Australia.
B ‘Glenwood’, Hawkesdale, Vic. 3287, Australia.
C Corresponding author. Email: rod.bird@dpi.vic.gov.au
Australian Journal of Experimental Agriculture 47(6) 727-737 https://doi.org/10.1071/EA06086
Submitted: 24 March 2006 Accepted: 18 October 2006 Published: 17 May 2007
Abstract
Eleven windbreaks (Monterey cypress, Monterey pine, tuart, sugar gum, black wattle and mixed native species) were studied in south-west Victoria. Windrun (U) was measured with cup anemometers set above ground (Z) at 1.5 m and 0.5 m (eight windbreaks), 1.5 m (two windbreaks), or 0.5 and 0.25 m (0.95 m mesh). The U pattern (U/U0, where U0 is open windspeed) was: (1) to windward, a shelter effect to at least –3 H, (where H means windbreak height) with a reduction of 20% or more at –1 H and (2) to lee, Xmin (position of minimum windspeed, Umin) from 1–7 H; Umin (minimum U/Uo) varied with windbreak density; and XS (distance where U/U0 is <0.8) varied from 8–25 H. Optical porosity (βO) was 0.16–0.53 compared with 0.24–0.61 for aerodynamic porosity (βA), obtained from the ratio of Umin and U0. βA from present data and calculated for windbreaks of previous studies, showed a curvilinear effect of windbreak porosity (βA, %) on Xmin, but little effect on XS: Xmin (H) = 3.008LnβA – 6.6 (adjusted r2 = 0.33, P < 0.0001, r.s.d. = 1.8); XS (H) = 12.2+ 0.307βA – 0.0047βA2 (adjusted r2 = 0.07, P < 0.08, r.s.d. = 4.1). Effective shelter is best obtained by establishing tall, dense windbreaks and excluding browsing livestock.
Acknowledgements
We acknowledge the following landholders who gave us access to their shelterbelts: G. Hermann, ‘Kanandah’, Cartys Rd, Hamilton; G. Roache, ‘Glenwood’, Hawkesdale; J. Gubbins, ‘Coolana’, Chatsworth; P. Waldron, ‘Willandra’, Melville Forest; R. Jamieson, ‘Bolac Plains’, Woorndoo; R. Dawson, ‘Kooringal’, Hawkesdale; B. Milne, ‘Helm View’, Melville Forest. We also acknowledge the assistance of Kay Aldridge, John Cayley, Keith Cumming and Glenys Downes for technical assistance at various stages of this work. Anne Roache collected data from the Hawkesdale shelterbelts as part of a degree of Bachelor of Agricultural Science with La Trobe University.
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