4 1 10 concept and applications Zorkoczy, P. Additional Author Hornung,M and Skeffington,R.A Additional Author mixed material London Institute of Terrestrial Ecology 1993 Walker,J.C Additional Author Luehrmann, Arthur Additional Author Peckham, Herbert Additional Author mixed material New York McGraw- Hill Book Company 1969 Boyce,S.G Additional Author Shafquat Ali Additional Author mixed material North Carolina USDA Forest Service 1979 USDA Additional Author Naeem ahsan Additional Author mixed material Washington,D.C USDA Forest Service 1980