which error reduction and more localized estimates are desired through this 
approach include the following: 
(1) forest area clear-felled annually; 
(2) forest area thinned on an annual basis and to what degree thinned; 
(3) area by forest type (for the NFI, these types are defined in terms of 
dominant tree species, relative stocking density, and tree size); 
(4) change or exchange of forest area, on an annual basis, in or with other 
than traditional forest land classes, including agricultural land, wetlands, 
mountains, and national park land; 
(5) forest area, on an annual basis, associated with given degrees of 
regeneration success; and 
(6) forest area damaged annually by diseases and pests. 
The Department of Forest Survey has grouped the six estimation areas listed 
above into two categories: (1) remote sensing-aided estimation for 
environmental monitoring (which includes the sixth estimation objective), 
and (2) remote sensing for cover type area and cover type area change 
(which includes the first Five estimation objectives). Environmental 
monitoring, while a technically more difficult problem from the remote 
sensing standpoint, has recently been given a slightly higher priority by 
the Department. 
Another important objective of introducing remote sensing in the Swedish 
NFI is to provide a data type that can enable the effective use of forest 
industry sample plot data with NFI plot data. This will enable further error 
reduction, particularly at the local level, and perhaps expand the kinds of 
estimates available. The use of satellite-acquired digital data will also result 
in the availability of data files containing spatial information. These files 
can consist of category maps, aggregatablc into different class structures 
according to NFI or other user needs. 
FINDINGS: ENVIRONMENTAL MONITORING (TREE DAMAGE) 
Focus on environmental monitoring in this review has been directed to the 
problem of forest tree disease and pest detection and identification. With 
respect to this problem, some specific applications of aerial photography for 
mapping or counting affected trees for a few types of damage could be 
adapted for use in the NFI in the near future. These include the present 
operational use in Sweden of large (approximately 1:2000) scale color 
infrared photography for Norway spruce (Picea abies) and Scotch pine 
(Pinus Sylvestris) needle loss surveys (e.g., Hedlund and Jacobson, 1988, 
Sylvander 1987). Abnormal needle loss is thought to be related to acid rain 
damage in many cases. Based on a study reported by Sylvander (1989), use 
could be made of the same type of photography for inventorying, on a 
sample basis, Gremmeniella abietina fungi damages. Color aerial 
photography of somewhat smaller scale is now being used by private 
companies in Sweden to locate and assess blow-down damage. 
Satellite applications, with the following exception, arc not expected to be 
reliable for application in the near future in the Swedish forest context. The 
exception is the possible use of Landsat TM and SPOT data to enable