Catena & Thermography
Catena & Thermography
Catena & Thermography
"Treethermography® since 1984"
from homepage
when Dr Catena was in charge of the Remote Sensing Unit of the Italian Health Institute of Rome. 

The thermal camera detects, locates and helps quantify decay/cavities in trees, up to their aerial portions at a height of 20-25m (for greater distances, a telephoto lens is available). The measurement is conducted in a fraction of a second, i.e. the time needed for a black and white or pseudo-colour thermal image or thermogram (TI) of a huge tree portion to appear on the camera screen. The thermal image (TI) can be considered a real "thermal map" of the tree under study, because it only shows the surface temperature distribution, which is generated by the different thermal properties (especially conductivity) of the underlying areas of healthy or decaying tissue. In fact, thermal conductivity in wood is mainly linked to tissue humidity and decreases as the liquid content decreases: that is why, the areas with a cavity (no tissue) or decay (less heat-conveying liquids) have a lower surface temperature than healthy areas. The more the decay, the lower the surface temperature in the area covering it.

An healthy tree

A healthy tree
If the different colour distribution (grey shades) and consequently the colder area are in the collar in contact with the ground, then decay is present in the root area: the affected root sector can be spotted by analysing the relevant TI. This is again interpreted according to the wood thermal conductivity: root decay means lower water absorption from the ground and a decreased water transmission to the vessels in the corresponding trunk section. The thermal camera detects this deficit in liquids at the collar level, because this decreases conductivity and consequently surface-bound heat transmission. After cutting trees affected by severe root decay, it was possible to observe in certain cases that stump decay was not as serious as the thermal difference had shown: at times only a simple decoloration with firm tissue was present (Agr. Ricerca, 2002). However, cavities or severe decay were highlighted by digging 10cm below the ground level. It is impossible to draw up a "temperature difference value/decay" table, but a temperature difference of a few degrees between healthy and decayed areas is certainly indicative of severe decay.
The real-time analysis of a TI thus reliably reveals if the tree is healthy, if it needs (can tolerate) cutting or other remedial actions or has to be felled, because its vitality is not such as to counterbalance the decay present. The number of trees that need treatment or are felled as a precaution is considerably reduced, with significant economic benefits for their owners and landscape and environmental advantages for the community.
The health condition of a tree (presence of decay, residual healthy tissue, vitality, new functional tissue) can be assessed in real time, on the spot, while the tree is being examined from a distance. Most of the apparatuses currently used are invasive, risk damaging the integrity of the tree defences, destroying the defensive barriers produced following scars or infections (Shigo) and spreading possible pathologies (Moore). Moreover, these apparatuses require a crew, aerial platforms, tree-climbers to examine the areas that cannot be reached from the ground, and only provide direct information at a given height or point, which is their biggest limitation.
A healthy Tree

A healthy tree
Many have expressed the view that the densitometer probe, that is commonly used in Italy to assess internal tissue, does not spread potential pathogens, because its pathway is "sterilised" by the high temperature generated as the probe penetrates, but this is in stark contrast with the high liquid content of tissue and a measurement done with a thermal camera while the probe penetrates a holm-oak (unpublished data).

In brief, if the tree is healthy, a uniform surface temperature distribution is present and the TI shows a uniform colouring (in case of colour TI) or a uniform grey shade (in case of black and white TI), but if the colour (grey shade) is not uniform, then decay/cavities may be present. For completeness' sake, it is necessary to mention that limited areas having a warmer temperature for no apparent reason were sometimes spotted: when no rejuvenating tissue and vital tissue formations were found, the hypothesis that heat was emitted because of the initial activity of a fungal or bacterial attack was put forward. Research studies are being carried out to ascertain the cause of this phenomenon. This clearly shows how important it is to learn the technique from expert operators with a long experience in the field, in order to be able to recognise significant data with certainty and to autonomously and safely operate.

The thermal camera doesn't "see inside", like the clinical thermometer that measures human body temperature, and just like an abnormal temperature indicates a disorder that can alter the human body temperature, a surface temperature variation in a tree reveals something inside it that can cause this variation. The area covering decay/cavities is colder than surrounding areas covering healthy tissue, because, as already mentioned, the lack of woody tissue (in the cavity) and/or the reduction in liquids in decayed tissue decrease thermal conductivity in that area, and consequently the quantity of surface-bound heat. Heat is partially produced by the tree metabolism and absorbed from the external environment and then released. It should be considered that wood is a good insulating material but has a certain thermal conductivity anyway. In fact, a research study conducted by Dr. Giorgio Catena and his assistant Lanfranco Palla at the "Small Botanic Garden" of the Institute of Botany of La Sapienza University, Rome, consisted in measuring the internal temperature evolution of a 30cm wide laurel (Laurus nobilis) in various points and at different depths over many months. The results showed that the internal temperature followed the evolution of the external temperature, though with a certain delay: the tree heated up during the day and cooled down at night.

Querqus ilexQuerqus ilexQuerqus ilex

Quercus ilex
Even a   completely   hollow tree, in which Treethermography® - TTH has shown clear vital tissue formations, may not raise concerns for its survival, at least in the short term. The arboriculturist in charge of the measurement will decide when the tree needs to be assessed again (if only visually or with a thermal camera) and the possible remedial actions, according to his experience, and the weather and environmental conditions of the site. When the following thermal assessment is conducted, a precise indication of the tree condition will be obtained by simply comparing the relative TIs showing an increase or decrease in the vital tissue; as a consequence, further decisions will be made with certainty. This practice is supported by the experience acquired by periodically re-analysing trees, some even over a 20-year period.
An expert arboriculturist can immediately suppose the existence of an abnormal situation that needs inspecting, and if necessary, monitoring over time, especially in case of external damage (cracks, indentations, a flat or swollen area on the trunk) or fungal fruiting bodies. However, decay is often at an initial stage or comes from the root system or branch wounds and no fungal bodies are visible, therefore, signs and symptoms are difficult to detect; Treethermography® - TTH points out the physiological function of 
trees, from the roots to the highest branches, in real time, thus revealing an abnormality even at the initial stage or a loss of vitality and small decay. If decay is located in the trunk or branches, its position and size can be assessed; if it is located underground, the severity and root area affected can be deduced: Treethermography® - TTH has so far proved to be the only technologically advanced system that can provide this result in real time.

4-5 thermal images are normally enough to understand the conditions of a whole tree. A quick assessment normally requires 2-3 minutes, while an in-depth analysis (with detailed visual shootings, record of the tree characteristics and details, etc.) less than 10 minutes: this technique requires less time than any other technologically advanced investigation system. Experience has shown that an individual operator can assess even 100 trees a day (San Marcello Pistoiese - PT, Italy, and Via Galvani, Rome, Italy, unpublished data and Via Marzabotto, Bologna, Italy, Agr. Ricerca 2002), if they are grouped together in parkways, parks or gardens, thanks to the light weight (from less than 2kg to about 300g) and the ease of handling of modern thermal cameras. 

Quick investigations

Quick investigations
A non expert assistant to carry apparatuses, number and classify trees, write down the comments dictated by the operator, while the latter conducts the measurements etc. clearly facilitates and accelerates the investigation, while increasing productivity, which is anyway subject to a number of factors: closeness of the sites to assess, tree size and facility to approach individual trees, detailed documentation and quality of the necessary visual images, etc. If it is possible to assess trees onboard a vehicle and/or if only the root systems need examining, productivity clearly and significantly increases.
Quick investigations

Quick investigations
As previously mentioned, TI can reveal functional adaptive tissue due to cambial growth in veteran trees or trees with cavities, thus showing that the tree mechanical integrity is not significantly damaged, despite decayed tissue. Thermal images also contribute to the management of veteran trees: they can show functional, vital, recently formed tissue, before it is otherwise visible. Veteran trees are protected and classified for their landscape value and biodiversity: decayed areas and cavities, in fact, are now appreciated as wildlife habitat, while they were only considered as dangerous in the past. To this end, TI are invaluable, because they highlight this function without harming the tree or the animals that nestle, roost or are hibernated in the cavities.
It is important to observe that Treethermography® - TTH revealed decayed tissue caused by Kretzschmaria (=Ustulina) deusta: this fungus has proved difficult to spot with some of the other systems, and Treethermography has thus become a sensitivity test. The system has also detected pathogens like the plane-tree coloured cancer and Phytophthora spp., before the characteristic wounds produced by the latter were visible on the trunk.

As tree diseases are practically incurable, the only possibility to curtail or prevent damage to people and things resides in the prevention of tree failures, which can be achieved if tissue vitality is known and new functional tissue is spotted. Treethermography® - TTH is the first investigation technique which is not limited to measuring a physical magnitude (resistance to penetration, hardness, electrical conductivity, transmission of sound waves, etc.) in a given point or at a given height, but reveals the condition of the whole tree in real time, thus emphasizing possible reactive growth processes.

The system has been used in all weather conditions, by night and day, in the summer and winter, with temperatures ranging from +2 to +35 °C; it doesn't only work in the Mediterranean environment, but has been also tested in continental environments (United Kingdom, Netherlands and Germany) in the months of June and October.

The main Treethermography® - TTH features include the following:

Celtis australisCeltis australis

Celtis australis
  • real-time detection-location of decay/cavities in trees from the ground and assessment of residual healthy tissue, 
  • detection of decay/cavity in the root system, 
  • real-time assessment of the function of the whole tree from the ground,
  • assessment of the tree vitality and detection of new adaptive functional tissue,
  • assessment of trees as wildlife habitat associated with decayed tissue/cavities,
  • real non invasiveness: no tissue or defence barriers (Shigo) are damaged, no pathogens spread,
  • harmlessness to humans and wildlife,
  • availability of images documenting tree conditions; images can be put in a database and used for comparisons over time,
  • possibility to assess and document the conditions of groups of trees (parkways, parks, woodland, etc.) in real time, thus sparing time and resources.

So far, a few thousand trees of different species, even exotic ones (broadleaved, conifers and palm trees), have been examined and assessed: the findings of Thermal Images or Thermograms (TI) were confirmed in over 300 cases by introducing probes in existing holes or using invasive tools or Picus or after felling the trees deemed dangerous.
At times, comparative tests between Treethermography® - TTH and Picus, Resistograph, Impulse hammer, Fractometer were conducted upon request of specialised firms and both private and public Bodies, with positive results for Thermography in terms of quick assessment and reliable outcomes.


- Shigo, A. L., A New Tree Biology, Shigo and trees Associates, Durham, N.H., 1991 
- Moore, W. M., Outillage pour la Détection des Défauts Internes des Arbres - Le point de vue du praticien - Résultats de 14 ans d’experience, II partie, La Forêt privée, 240, 23-39, 1998   

A textbook on Thermography, dealing with the Infrared radiation and many applications of Thermography to Non Destructive Testing (NDT), even too long to learn about the infrared and Thermography, is: 
- Non Destructive Testing Handbook, 3rd Edition, Vol. 3, Infrared and Thermal Testing, Maldague Xavier P. V. (tech. Ed.), Moore Patrick O. (Ed.), ASNT, 2001, pag. 732



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