752
INTERPRETATION OF COLOUR-INFRARED PHOTOGRAPHS FOR THE ASSESSMENT OF FOREST DECLINE
IN CENTRAL EUROPE
Claus-Peter Gross Norbert Heidingsfeld
Universität Freiburg i. Br.
Abt. Luftbildmessung und Fernerkundung
Werderring 6, D--7800 Frei bürg, FRG
Forstliche Versuchsanstalt
Rheinland-Pfalz, Abt. Waldschutz
Schloss, D-6751 Trippstadt, FRG
ABSTRACT
In addition to the terrestrial assessment of new types of forest decline, the visual interpreta
tion of large-scale Colour Infrared Photographs is a common and powerfull inventory method to
detect and study new types of forest, damage in Central Europe.
The paper summarizes on investigations of an international working team of experts in photo
interpretation which allows to establish standard interpretation keys.
KEY WORDS: Forest Damage, Photointerpretation, Colour-Infrared Photographs, Interpretation Keys
1 TERRESTRIAL FOREST DAMAGE SURVEYS
1.1 Main Symptoms and Assessment Methods
The last decade saw a new type of forest de
cline in many forest regions of Central Eu
rope. The damage is widespread and indepen
dent of 3ite conditions or proximity to in
dustrial centres. The symptoms vary but gen
erally point to air pollution.
Main visible symptoms of the damages are:
progressive loss of needle/leaf, discoloura
tion affecting parts or the whole crown and
also deformation of the crowns. Decreasing
virour makes the afflicted trees prone to
biotic as well as climatic effects. Further
more remarkable decrease of timber increment
can be observed.
The situation is alarming and has led for
estry and research institutes to develop ob
servation and monitoring methods in order to
inventory the extent, distribution and in
crease of the forest, decline. In the Federal
Republic of Germany (FRG), for example, this
need has since 1983 been met by annual ter
restrial inventories. The basis of data col
lection ist a representative field survey
using systematically distributed sample
points tied to a geographic coordinate system
(generally grids of 4 x 4 km). At each point,
a number of sample trees are selected (gen
erally 24 trees) and their crown condition is
assessed every year /16/.
For every single sample tree a visual assess
ment. of defoliation is made in five classes
separated according to needle/leaf loss per
centage as follows /2/, /18/:
Class
Degree of
Percentage of
defoliation
needle/leaf loss
0
not defoliated
0 -
10 %
1
slightly defoliated
> 10 -
25 %
2
moderately defoliated > 25 -
60 %
3
severely defoliated
> 60 -
99 %
4
dead
100 %
Discolouration of the remaining foliage can
additionally be assessed as in the following
4 classes:
Class Discolouration Percentage of
foliage discoloured
0
None
0 -
10
%
1
Slight
> 10 -
25
%
2
Moderate
> 25 -
60
%
3
Severe
>
60
%
