The impact of resistograph on tree decay
Pr A. Toussaint, Pr J-P. Baudoin : Unit of tropical crop husbandry and Horticulture, FUSAGx
Dr B. Campanella, Pr R. Paul : Laboratory for environmental Toxicology, FUSAGx
With the financial support of the Walloon Region (Ir J-C. Gobeaux, Director)
1. The case : 280 limes (Tilia cordata and T. europea) were drastically pruned in 1992
In 2002, an experimentation was started to test the efficiency of several soil treatments in increasing vitality. It was
also necessary to assess problems of wounds and cavities. Numerous 10 years old wounds are now presenting rots and
cavities. Another important problem is the infection of old injuries by decay fungi (Ganoderma sp. and Ustilina sp.). In
the frame of stability diagnostic, resistograph was used to precisely measure the extension of decay. After trees were
cut down, it became evident that the intrusive measurement allowed the discolored zone to progress. In regional
administration services, recent tendency is to use resistograph systematically to detect problems in street trees. This
could have consequences on tree-rot fungi relationships.
2. Decaying tree was firstly pointed
out following two clear symptoms:
3. In July 2003, six
measurements were realised
with Resistograph IML-Rési
F-400 at trunk base and 120
cm. Data were processed
according to a method
described previously
(Campanella et al., 2003).
Following the localization of 60 cm
weakened zones in the 6
directions, an estimation of
fungus extension in the trunk
was presented to local
authorities to traduce the risk
associated with this tree.
• The crown heterogeneity (figure 1).
One half of branches are dying.
• The presence of heart rot fruit
body (Ganoderma sp.) at trunk
base (figure 2) and 120 cm (old
bark wound).
Position of decaying branches
matched with the presence of fruit
bodies and dead bark.
3
2
4
1
5
Figure 1: in july 2003, a lime showing crown asymmetry and severe
leaf symptoms.
6
65 cm
Figure 3: visualization of resistograph results (green: healthy wood, orange: weakened wood, red: amorphous wood
or cavity). Hypothesized extension of fungus at the trunk base (pink) and its real observed extent in november
(pink+red).
Figure 2: fruit body found at the trunk base (12 cm large).
4. After tree cutting down (November
2003), two major observations were
made:
• The extension of the discolored zone
and the fungus is more important than
postulated after resistograph
measurements (figure 3). It is
particularly true in the direction of
measurements 1,2 and 3. This could
partly be due to heart rot progress
during 4 months (figure 4).
3
2
5. Two wood samples were taken to
describe the extent of reaction zone in
the 3 dimensions (figure 5 and 6).
Polyphenol accumulations were also
visible under microscope (figure 7).
This accumulation occurs in vessels
as well as parenchymatic rays. No
trace of fungus was identified in
discolored zone.
• The impact of measurements 2 and 3
are visible. Locally, where news injuries
occured, discolored zone is more
extended.
Figure 5: longitudinal (left) and tangential (right) vue of the discoloured
zone and the ancien drilling trace from sample 3. I : 1 cm.
Figure 6: longitudinal (left) and tangential (right) vue of the discoloured
zone and the ancien drilling trace from sample 2. I : 1 cm.
References:
Campanella, B., A. Toussaint, et al. (2003).
"Amélioration de l'interprétation des données fournies
par le résistographe pour la gestion d'arbres d'alignement.
1 : le cas du tilleul." Arbres et Sciences 9.
Shigo, A. (1989). Tree pruning: a worldwide photo guide
for the proper pruning of trees. Durham.
Figure 7: microscopic vue of polyphenol accumulation in wood vessels
and parenchymatic rays.
Figure 4: visualization of the real extension of heart rot at the trunk base and directions
corresponding to measurements 2 and 3 (figure 3). The extent of discolored zone
(reaction zone) is visualised between the green and the blue line.
d
e
b
a
c
a= longitudinal extension
b = radial extension
c = longitudinal extension at b/2 level
d = radial extension without drilling
a
b
c
d
e
b/d
Sample 2
5,1 cm
10,1 cm
1,9 cm
2,5 cm
0,5 cm
404%
Sample 3
6,7 cm
8,4 cm
2,0 cm
2,0 cm
0,7 cm
420%
6. Dimensions of the neoformed reaction zone are slightly
different between the two samples (table 1).
Compartmentation is more efficient in the tangential
direction (e) than in the longitudinal one (a, c), which is
consistent with CODIT model (Shigo, 1989). In this
particular case, the extent of reaction zone is 4 fold
increased after drilling. It must also be mentioned that wall
4 of the CODIT model has been broken by the fungus.
Table 1: extension of discoloured zone and comparison of its progress
with and without drilling trace (b/d).
e = tangeantial extension at b/2 level
Fig. 8: schematic representation of parameters used to describe discolored zone in the three dimensions.
Conclusion:
In this particular case, resistograph was useful to complete diagnostic and demonstrate the importance of decay. Nevertheless, intrusive measurement could have consequences on fungus
developpement. After 4 months, reaction zone has normally developed around the hole. Even if fungus has not been detected in the hole, its progress will certainly be easier as wood structure has
been broken down and oxygen is present. It is then important to know that the use of resistograph could accelerate the process. Moreover, the even more common practice of systematic
resistograph use should be avoided as some trees showing cavities could be remained in place if the decay was efficiently contained. Systematic measurements realised in cities could accelerate the
decay of street trees.