Environmental arboriculture (Fay, 2002) is characterized by the management of arboreal patrimony influenced by ecologists. It excels in the management of dead wood: preserving, optimizing and maximizing saproxylic habitats (dendromicrohabitats), which are at the core of the biodiversity chain in arboreal ecosystems, hosting fungal, bacterial and invertebrate organisms that participate in the process of wood decay. This specialized know-how comes from an English line of research, both empirical and scientific, largely influenced today by Ted Green, and finding direct application in arboriculture via Neville Fay.
In the management of arboreal patrimony, according to environmental arboriculture, the tree is not the main objective; it is part of it. Paraphrasing Neville Fay (Fay, 2012), when we are observing a tree, we are standing on the tree. It is like looking at a mushroom. The latter is the fruiting body of a vast network of mycelium’s hyphae filaments. In an analogous way, the tree is an organism linked to an immense network of interactions in its ecosystem, in which it acts as an orchestral conductor.
The management of deadwood guided by environmental arboriculture is nowadays more relevant than ever, due to the higher awareness regarding sustainable development. It is largely achieved by the preservation of ancient and veteran trees providing saproxylic habitats which are at the peak of the biodiversity chain in arboreal ecosystems. This is why, environmental arboriculture is also known as conservation arboriculture.
An ancient tree is a mature or senescent tree with unique qualities, providing saproxylic habitats (dendromicrohabitats) to its ecosystem, such as cavities, cracks, and dead wood. A veteran tree, on the other hand, is a tree that may have some of the qualities of an ancient tree, but is not necessarily old. Thus, an ancient tree is a veteran tree, but not the other way around.
Source: The Dead Good Deadwood Blog – What’s so good about deadwood
47 types of dendromicrohabitats have been described as Potential Indicators of Biodiversity in arboreal ecosystems, subdivided in 15 groups and categorized in 7 forms:
1. Cavities
2. Tree injuries
3. Crown deadwood
4. Excrescences
5. Fungal fruiting bodies and slime moulds
6. Epiphytic and epixylic structures
7. Exudates
(Larrieu et al., 2018; Bütler et al., 2020)
Source: Larrieu et al., 2018
The application of environmental arboriculture knowledge to urban arboriculture is distinguished by the optimization, maximization and preservation of such dendromicrohabitats and unmistakably by the implementation of Natural Fracture Pruning (NFP), artificial simulation of natural fractures inflicted by the force exerted by the wind (Fay, 2003).
CORONET CUTS
Coronet cuts are complementary to conventional adequate cuts. They have a proper place in tree pruning practices without conflicting with it.
Source: David Humphries,
Why?
Similar to Natural Target Pruning cuts (NTP) aiming to respect nature and the physiology of the tree, via the simulation of natural pruning (Shigo, 1984, 1991; Stobbe, Dujesiefken and Kleist, 1998; Dujesiefken and Stobbe, 2002; Drénou, 1999), coronet cuts simulate natural fractures that trees may face during strong winds, respecting the course of nature which inflicts accidents on trees and that millions of years of evolution have permitted them to adapt to.
When?
Coronet cuts are complementary to conventional pruning practices. They do NOT replace adequate cuts in the insertion zone of axes, which are proportional to the size of the cut: less than 5 cm in diameter in weak compartmentalizers (e.g. birch, poplar, willow, etc.) and less than 10 cm in diameter in effective compartmentalizers (e.g. beech, elm, honey locust, etc.) (Dujesiefken and Liese, 2008, 2015).
The artificial simulation of natural fractures inflicted by the force exerted by the wind (coronet cuts), has a place of its own without coming into conflict with adequate conventional pruning practices: suppressing dead axes of a diameter greater than the adequate specifications of compartmentalization described by Dujesiefken et al., without affecting the healthy parts, optimizing dendromicrohabitats, leaving trees with a “natural” look, anticipating natural fractures inflicted by the force exerted by the wind on dead branches, that would end up broken in the course of time anyway.
When large diameter decaying or defective axes exceptionally need to be removed or reduced drastically for security reasons, removing them completely all the way to the zone of insertion is detrimental to the healthy tissues remaining. The pruning cut is so large that it’s illusory to expect adequate compartmentalization, regardless of whether the cut is technically traced in the proper way.
“If possible, branches greater than 5 cm in diameter of weak compartmentalizing trees, and [greater] than 10 cm of strong compartmentalizing trees, should only be reduced partially rather than removed completely.” (Dujesiefken and stobbe, 2002)
In this exceptional situation, many arborists insist on making the “adequate” cut, but the attempt goes against science. Dujesiefken et al. studies, which are the most reliable to date regarding pruning cuts, confirm that trees do not adequately compartmentalize wounds when they exceed the maximum indicated pruning cut size. So in these exceptional situations, why affect the healthy parts of the tree? Leaving a stub with a coronet cut may contribute to boost biodiversity, without causing additional trauma to the tree, as if it were a natural accident. In other cases, taking into account the same example, many arborists, aware that there is no point in making the “adequate” cut in the insertion zone exceeding the maximum indicated pruning cut size, do not dare to make a coronet cut and leave a stub with a straight plane heading cut, with no grace whatsoever, speculating that the public will not understand and accept a coronet cut. This is also illusory, people are used to seeing stubs of broken branches and if the coronet cut is well done and simulates natural fractures well, the cut may go unnoticed, which is practically impossible to achieve with a straight plane heading cut in a stub, where on the contrary, the public increasingly sensitive to topping nowadays, automatically identifies it as a desolating and devastating mutilation, with no ecological interest. The artificial simulation of natural fractures, on the other hand, may boost the establishment of saproxylic habitats that in their turn attract birds in search of food and shelter, and small reptiles and mammals complete the chain.
When it comes to senescent trees, dead or broken axes are never replaced (Drénou, 1994, 2011, 2015, 2019; Drénou and Caraglio, 2019). In urban areas, when it becomes necessary to remove potentially dangerous dead wood for security reasons, coronet cuts made without affecting the living parts that remain, ensure a slow and progressive death of the tree without additional trauma that may accelerate its demise.
In regards to stressed trees, going through a transitional reaction phase, in a state of emergency, facing an uppermost crown descent or a retrenchment, no major intervention is preconized (Drénou, 2011, 2015, 2019; Drénou and Caraglio, 2019). If potentially dangerous dead wood must be removed for security reasons, removing the dead axes by leaving stubs with coronet cuts without affecting the remaining healthy parts, respects the integrity of the tree without additional trauma in dead axes that will end up breaking naturally in the course of time, anyway.
Illustration: Stressed tree, Christophe Drénou, 2019
Illustration: Uppermost crown descent, Christophe Drénou, 2019
Source: Vikki Bengtsson, Boadfach Park, Wales
Illustration : Retrenched tree, Christophe Drénou, 2019
Source: David Humphries,
How?
In the 1990s, experiments began using explosives, but they turned out to be too risky and were quickly discarded.
Coronet cuts require arborists to pay attention to natural fractures as much as possible in order to replicate them with fidelity.
Source: Natural fracture, Graham
Even though a coronet cut takes way more time than a conventional cut, the results are impressive and rewarding.
Source: David Humphries,
Making coronet cuts requires intention, extra vigilance and absolute attention since the chain saw has a much higher probability of kickback. Under no circumstances may the coronet cut be achieved without using both hands and placing the back of the holding hand immediately behind the chainsaw break in order to stop the machine right away in case of kickback.
Source: David Humphries,
Bearing in mind that conventional cuts mimic natural pruning and that coronets cuts mimic natural fractures; the real challenge with coronet cuts in urban environments, is daring to implement them without conflicting with current pruning practices.
Source: Coronet cuts over time, David Humphries,
Experimenting and sharing the results has been the vehicle adopted by the community to promote coronet cuts in specialized sites like treebuzz.com.
Source: Coronet cuts over time, David Humphries,
VETERANIZATION
Source: Vikki Bengtsson
In some special areas, when urban trees are relatively homogeneous, without providing major damages or degradation which may restrain the establishment of saproxilic habitats, the application of knowledge in environmental arboriculture encourages sacrificing certain specimens by inflicting artificial injuries, with various tools, in order to accelerate the degradation time of wood decay and thus boost biodiversity. This peculiar, controversial technique, is referred to as veteranization. However it must be perfectly clear, that if it’s erroneously implemented, it may become a double-edged sword. On one hand, it may serve as a key tool to accelerate decay when there are no ancient trees available, contributing to boost, optimize, and maximize biodiversity by permitting the relatively rapid establishment of saproxilic habitats which are at the core of biodiversity, and, on the other hand, it may be a disastrous detrimental tool, if implemented erroneously. Under no pretext may veteranization be implied to insinuate and pretend the replacement of ancient trees by young or adult artificially damaged trees. This argument is a fallacy, ancient trees are IRREPLACEABLE and veteranization is no excuse to deprive arboreal ecosystems of the unique qualities that ancient trees provide; ancient trees are the pick of biodiversity.
Source: Vikki Bengtsson
Source : peninsulaenvironmental.com
Urban deadwood management goes hand in hand with tree risk management. Decisions should not be taken from a purely defensive perspective; above all, they must be reasoned and proportionate. It is imperative to tolerate an acceptable level of risk in order to preserve, optimize, and maximize the benefits and services that urban trees provide to the environment, and our quality of life (Fay, 2007).
This article is a translation of a follow-up proposal by David S. Restrepo addressed to the City of Paris, Trees and Woods Service, Vincennes Wood Division, where coronet cuts are currently an adopted and encouraged practice as a result.
David S. Restrepo, Service de l’arbre et des bois de la Ville de Paris, Division du bois de Vincennes.
Autumn, 2020. v.1.0.0.2020.10.25
Complementary ineluctable information:
https://www.ancienttreeforum.co.uk/
REFERENCES:
Drénou, C., 1999. La taille des arbres d’ornement: du pourquoi au comment. Forêt privée française.
Drénou, C., 2019. Face aux arbres : apprendre à les observer pour les comprendre. Les Éditions Ulmer, Paris.
Dujesiefken, D. and Liese, W., 2008. Das CODIT-Prinzip: von den Bäumen lernen für eine fachgerechte Baumpflege. Haymarket Media.
Dujesiefken, D. and Liese, W., 2015. The CODIT principle. Implications for Best Practices. International Society of Arboriculture.
Fay, N., 2003. Natural fracture pruning techniques and coronet cuts.
Shigo, A. L., 1991. Modern arboriculture: a systems approach to the care of trees and their associates. Shigo and Trees, Associates.
Stobbe H, Dujesiefken D & Kleist G (1998) Die Hamburger Schnittmethode – Grundlagen und neue Erkenntnisse. In: Jahrbuch der Baumpflege 1998 (Eds. D. Dujesiefken & P. Kockerbeck): 184-193. Thalacker Medien, Braunschweig
