river, is located between 46° 30° - 47° 00° N and
137° 30" - 138° 30° E in the northeastern coastal
area of Russia. In this area, forests of fir-spruce are
widely distributed. (Fig. 1)
3. MATERIALS AND METHODS
In this study, satellite data obtained in October
1983, October 1986, October 1989 and September
1991 from LANDSAT/MSS were used. Based on
the result of an on-site survey, the areas where forest
decline had occurred were detected on the satellite
image. The observation periods are concentrated in
and around October because the leaves of broadleaf
trees and larches that are widely distributed in this
area fall completely by this time of the year, which
means that confirmation of the distribution status of
fir-spruce forests to investigate forest decline is
easier.
4. RESULTS AND DISCUSSION
Fig.2 through Fig.5 show the LANDSAT/MSS
images of the study area. These images were obtained
in 1983, 1986, 1989 and 1991, respectively. The areas
encircled by white line represent the areas where
forest decline and deforestation occurred. Figs. 6 show
recent changes in the area of the forests in which the
forest decline occurred.
Decline in the tree vigor began in the early 1983.
Decline in the tree vigor further progressed upstream
in 1986 and 1989, and by 1991, almost all of the fir-
spruce forests in this area died. The images show that
the area of declined forest is expanding from the right
section to the left section in the images.
The mechanism causing this forest decline has
yet to be clarified, but a research team at the Biology
and Pedology Institute of the Russian Academy of
Science suggested that a strong dry stress may be one
of the causes. Although this region goes through an
——€A^———A—————————
extremely dry period from winter through spring every
year and many forest fires occur during this period,
the only time a dry stress stronger than usual might
have occurred is the time of the large forest fire
occurred in 1987 in the Heilongjiang Province of
China.
However, it is difficult to conclude that forest
decline progressed very rapidly during the period from
1986 through 1989, from the changes in the
distribution of forest decline shown in Figs. 2 through
5 and the changes in the area of declined forests
shown in Fig.6. This suggest that forest decline is
caused by not only strong dry stress but other factors
and mechanisms. Because, if the main reason of forest
decline was strong dry stress, forest decline area
increased exponentially. Therefore further studies
must be conducted to identify these factors and
mechanisms and investigate the degree of contribution
of each factor.
km?
300
200 p
e
©
<< Tg
100
0
83 86 89 91
Year
Fig.6 Changes in the Area of Declined Forest
Intemational Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 721
