DISCUSSION 



These procedures may not be applied to esti- 

 mate mortality rates for larch. Larch is deciduous 

 and thus year of mortality cannot be estimated by 

 the foliage retention characteristics described 

 here. Larch killed prior to the time photos are 

 taken but showing no signs of needle discolora- 

 tion, or trees killed after photos are taken, will drop 

 their needles prior to the next growing season. 

 Such trees will not fit the characteristics of 1 -year 

 mortality trees on either current-year photographs 

 or on those taken the following year, and thus will 

 never be counted as mortality trees. Similar prob- 

 lems exist if this approach is applied to other 

 deciduous species. Larch mortality dating is fur- 

 ther complicated by the defoliation of larch by 

 larch casebearer. Such trees may be difficult to 

 distinguish from larch that have died during the 

 current growing season. 



The description of a dead tree may also impose 

 limitations on the use of these procedures. A tree 

 that has died in the past year is identified by its 

 brightly discolored foliage and by the retention of 

 the majority of this foliage. Trees that die slowly (a 

 few branches each year) will never fall into this 

 category and thus will never be classified as 

 current mortality. This is not a problem unique to 

 photo identification of current mortality. It is dif- 

 ficult to determine when such a tree is to be 

 considered dead, even when the tree is observed 

 on the ground. 



In spite of these limitations, I decidedthat 1-year 

 mortality could be dated and that species could be 

 assigned to green trees and to 1-year mortality 

 trees on 1:1600 and 1:2400 scale photography 

 with acceptable accuracy. A procedure was de- 

 signed for sampling mortality for the Northern 

 Region that uses a quarter mile strip (eight frames) 

 of 70 mm true color aerial photography at a 1 :2400 

 scale as the basic sampling unit. This scale was 

 selected for practical reasons. With the plane, 

 camera, and lens available to the Region, 1 :2400 

 was the maximum scale that could be obtained. 



Although a reduction in interpretation accuracy 

 occurred when the scale was reduced from 



1 :1 600 to 1 :2400, 1 felt that with proper training of 

 interpreters, the 1:2400 scale would provide 

 acceptable results. The sampling design, estima- 

 tion procedures, and photo interpretation guide- 

 lines are described in detail in two companion 

 publications (Hamilton, 1 and Croft, Heller, and 

 Hamilton 2 ). 



PUBLICATIONS CITED 



Heller, R. C, G. E. Doverspike, and R. C. Aldrich. 

 1964. Identification of tree species on large 

 scale panchromatic and color aerial photo- 

 graphs. USDA For. Serv. Agric. Handbook 261 , 

 1 7 p. Washington, D.C. 



Keen, F. P. 



1955. The rate of natural falling of beetle-killed 

 ponderosa pine snags. J. For. 53:720-723. 

 Miller, J. M., and F. P. Keen. 



1960. Biology and control of the western pine 

 beetle. USDA Misc. Publ. 800, 381 p. Washing- 

 ton, D.C. 

 Sayn-Wittgenstein, L. 



1 960. Recognition of tree species on air photo- 

 graphs by crown characteristics. Can. Dep. 

 For., For. Res. Div. Tech. Note No. 96, 56 p. 

 Stage, Albert R., and Jack R. Alley. 



1 972. An inventory design using stand examina- 

 tions for planning and programming timber 

 management. USDA For. Serv. Res. Pap. INT- 

 126, 17 p. Intermt. For. and Range Exp. Stn., 

 Ogden, Utah. 



1 Hamilton, David A., Jr. 1980. Sampling and 

 estimation of mortality using large scale aerial 

 photography. Review draft. Manuscript on file at 

 Intermountain Forest and Range Experiment Sta- 

 tion, Moscow, Idaho, 26 p. 



2 Croft, Frank C, Robert C. Heller, and David A. 

 Hamilton, Jr. 1 980. How to interpret tree mortality 

 on large scale color aerial photographs. Review 

 draft. Manuscript on file at Intermountain Forest 

 and Range Experiment Station, Moscow, Idaho, 

 29 p. 



8 



