Agroforestry Systems

, Volume 17, Issue 2, pp 119–133 | Cite as

Optical porosity and windspeed reduction by coniferous windbreaks in Southern Ontario

  • A. E. Loeffler
  • A. M. Gordon
  • T. J. Gillespie


Relative windspeed reduction was measured behind nine relatively narrow, homogeneous windbreaks in southern Ontario, Canada to assess whether any characteristics of the windspeed reduction curve could be predicted from optical porosity. The latter was determined for each windbreak using high contrast black and white photographic silhouettes on a computer digitizing system. Minimum windspeeds behind the windbreaks ranged from 29 to 71% of open windspeed; these minima were located 2 to 6 multiples of windbreak height away from the windbreak. Optical porosities of the bottom half of the windbreak ranged from 0 to 31%. Multiple regression of the shelter parameters (location and value of minimum relative windspeed) on the independent variables (optical porosity, open windspeed, surface roughness, approaching wind direction relative to the windbreak, average tree diameter and average tree spacing) showed that the minimum relative windspeed could be predicted from the optical porosity of the bottom half of the windbreak. The results suggest that optical porosity can be used to predict minimum relative windspeeds and may therefore be useful as a guide in the field evaluation of windbreaks.

Key words

windbreaks optical porosities windspeed reduction Ontario/Canada 


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  1. Chepil WS (1945) The transport capacity of the wind. Soil Sci 60: 475–480Google Scholar
  2. Coreco (1986) Image analyzer user's manual. Coreco, Inc, 1986Google Scholar
  3. Hagen LJ and Skidmore EL (1971) Turbulent velocity fluctuations and vertical flow as affected by windbreak porosity. Trans ASAE 14: 634–637Google Scholar
  4. Heisler GM and Dewalle DR (1988) Effects of windbreak structure on wind flow. Agric Ecosystems Environ 22/23: 41–69CrossRefGoogle Scholar
  5. Jacobs AFG (1984) Wind reduction near the surface behind a thin solid fence. Boundary-Layer Meteorol 33: 157–162Google Scholar
  6. Jensen M (1954) Shelter Effect: Investigations into the aerodynamics of shelter and its effects on climate and crops. The Danish Technical Press, Copenhagen, pp 263Google Scholar
  7. Kenney WA (1985) The effect of inter-tree spacing on the porosity of shelterbelts and windbreaks. M.Sc. Thesis, University of Guelph, Guelph, Ontario, pp 58Google Scholar
  8. Kenney WA (1987) A method for estimating windbreak porosity using digitized photographic silhouettes. Agric For Meteorol 39: 91–94CrossRefGoogle Scholar
  9. Klingbeil K, Benndorf D and Grunert F (1982) Aerodynamische Grundlagen für Windschutzpflanzungen: Teil II — Der Einfluss der geometrischen Struktur von Gehölzschutzstreifen auf ihre Schutzwirkung. [Aerodynamic guidelines for windbreaks: Part II — the effect of the geometric structure of windbreaks on their effectiveness.] Z Meteor 32(3): 165–175Google Scholar
  10. Mulhearn PJ and Bradley EF (1977) Secondary flows in the lee of porous shelterbelts. Boundary-Layer Meteorol 12: 75–92CrossRefGoogle Scholar
  11. Naegeli W (1953) Untersuchungen über die Windverhältnisse im Bereich von Schilfrohrwänden [Investigations on the wind conditions in the range of narrow walls of reed.] Mitt. Schweiz. Anst. Forstl. Versuchswesen 29: 213–266Google Scholar
  12. Oke TR (1987) Boundary Layer Climates. Methuen & Co. Ltd, London, UK, pp 435Google Scholar
  13. Panofsky HA and Dutton JA (1984) Atmospheric Turbulence — Models and Methods for Engineering Applications. John Wiley & Sons, New York, pp 397Google Scholar
  14. Plate EJ (1971) The aerodynamics of shelterbelts. Agric Meteorol 8: 203–222CrossRefGoogle Scholar
  15. Raine JK and Stevenson DC (1977) Wind protection by model fences in a simulated atmospheric boundary layer. J Ind Aero 2: 159–180Google Scholar
  16. SAS (1987) SAS User's Guide: Statistics, Version 5 edition. Cary, N.C., SAS Institute Inc, pp 956Google Scholar
  17. SAS (1987) SAS User's Guide: Statistics, Version 5 edition. Cary, N.C., SAS Institute Inc, pp 956Google Scholar
  18. Seginer I (1975) Atmospheric-stability effect on windbreak shelter and drag. Boundary-Layer Meteorol 8: 383–400CrossRefGoogle Scholar
  19. Sturrock JW (1969) Aerodynamic studies of shelterbelts in New Zealand — 1: Low to medium height shelterbelts in Mid-Canterbury. N Z J Sci 12: 754–776Google Scholar
  20. Van Eimeren J, Karschon R, Razumova LA and Robertson GW (1964) Windbreaks and Shelterbelts. World Meteorol. Organization Tech Note No 59, pp 188Google Scholar

Copyright information

© Kluwer Academic Publishers 1992

Authors and Affiliations

  • A. E. Loeffler
    • 1
  • A. M. Gordon
    • 1
  • T. J. Gillespie
    • 2
  1. 1.Department of Environmental BiologyUniversity of GuelphGuelphCanada
  2. 2.Department of Land Resource ScienceUniversity of GuelphGuelphCanada

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