Trees infested by bark beetles are often clustered in unevenly dispersed 
groups of highly-variable size, making design of sampling systems to acquire 
reliable data on losses very difficult (Fig. 1). Stratification from aerial 
sketch map surveys has been shown to be an effective base for multi-stage 
surveys designed to estimate bark beetle mortality (Wert and Roettering 1968; 
Heller and Wear 1969). We therefore designed a multi-stage survey system 
which involved use of aerial sketch mapping for stratification, aerial photo- 
graphy for estimation of mortality, and a small ground sample for correcting 
photo estimates and obtaining data on volumes infested and residual green 
stand. 
  
Figure 1.  Ponderosa pine stand in western Montana infested by mountain pine 
beetle. Trees with light colored crowns have been killed.