spectrally-bascd detection, but not necessarily identification, of areas or 
stands containing damage of some type (Olsson 1990 and personal 
communication). Workers (e.g., Wastenson and others, 1987) have not been 
able to use these data to consistently detect or identify trees exhibiting 
substantial needle loss. This result is due to the fact that affected trees tend to 
occur singly and not in groups. Ekstrand's (1988) work with Norway spruce 
in Sweden suggests that use of a geographic information system containing 
current stand histories and other ancillary information in digital form could 
enable satellite-based detection of significant needle loss in certain terrain 
and species mix situations. 
We have concluded that, beyond the aerial photography applications 
mentioned above, significant additional research with both satellite and 
aerially acquired data will be required before additional types of forest 
damage can be detected and then reliably separated from one another using 
this technology in Sweden. 
FINDINGS: COVER TYPE AND COVER TYPE CHANGE 
Clear-Felled Area 
With respect to cover type area and area change estimation, the range of 
near-term applications of remote sensing data are larger. Clear-felled areas, 
given late Spring and Summer Landsat or SPOT satellite data, are readily 
detectable and identifiable in most situations found in Sweden using 
technology available now (e.g., Jaakkola and Hagner 1988, Hame 1988, 
Boresjo 1989, and Olsson and Sohlberg 1989). 
Jaakkola and Hagner, for example, showed that digital Landsat TM and SPOT 
XS scenes from different dates could be used to accurately detect and map 
clear-felled areas down to 0.5 hectare or less in sizx. Olsson and Sohlberg 
(1989) used two spatially registered scenes of SPOT-P digital data (from 
succeeding years) to reliably map clear-felled areas as small as 0.2 hectare 
over ten 5 by 5 kilometer areas in south-central Sweden. The difference 
between the ground surveyed clear-felled area and that obtained from 
interpretation of the digital image was approximately 3 percent — a figure 
which could be reduced further by tuning the procedure (Olsson, personal 
communication). 
Thus, use of remote sensing for clear-felled area estimation is considered a 
strong candidate for early test and evaluation in the Swedish NFI. 
Forest Cover Area Mapping/Estimation 
The next most-developed satellite survey capability of this type is general 
forest cover type mapping and estimation. Jonasson (1987), Jaakkola (1987), 
Hame (1988), Boresjo (1989), and Hagner (1989), among others, have shown 
that cover type, certain cutting classes, and other vegetation or surface- 
related information for Scandinavian conditions is available through the use 
of Landsat TM and SPOT data. Jaakkola and others (1988) present a summary 
of key findings for Landsat TM data in this regard for forestry over a broader 
area in Europe. Medium scale (typically 1:30,000, panchromatic) aerial 
photography for forest type, age, volume, and site class mapping is presently 
being used by at least one government group in Sweden (e.g., Age, 1985). 
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