Post on 07-Jul-2020
transcript
1
Veteran tree risk management via reduction,
nutrition and exclusion
Part 1 – Background Edited by Karyn Szulc (QAA Executive Officer)
Introduction
This article coincides with the development of my most recent QAA Workshop
Advanced Pruning for Veteran trees (scheduled for Cleveland 26/6), which like
this article involves the consideration of reduction, exclusion and nutrition
acting as sustainable risk management strategies over whole tree removal.
In part 3 of this article I also consider the benefits of support as a means to risk
management and look at a solution to Australia’s general resistance to the
installation of fall arrest systems in trees.
Historically the collective tree profession has largely looked at tree removal as
being the only applicable risk management strategy to use for veteran trees (if a
veteran tree can not be pruned to standard it is cut down). Many amongst the
climbing arborist sector will gladly remove a tree with ‘defect’ symptoms using
that as reason for pulling out a chainsaw as a means to abate the risk.
In reality most of the kinds of trees that fail are those that are already falling
apart and are far from being safe to climb at all. In fact it is easier to safely retain
veteran trees at reduced financial cost and gain to the environment (that relies
on trees) by reduction, nutrition and exclusion.
Before we can get serious about managing veteran trees we must recognise how
they naturally adapt to the environment, to the mechanical failure of their
bodies. Veteran tree adaption or optimisation is a process predating the
evolution of people-kind, in our bid to manage trees we surmount tree time with
our time and forget this. We become lost in our perception of the ‘defective’, our
misunderstanding of the process of tree self-optimisation, whilst forgetting to
look at all the trees that have not failed.
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Plant growth & Epicormic/Endocormic growth transition in Trees
A rudimentary glance at the growth of plants tells us that limbs are grown from
immature shoots or buds. Scientifically buds are categorised by location, status,
morphology and function.
Fig 1
Buds are located either at the end of a stem via a terminal bud or at the sides
(lateral or axillary bud) of a stem. Axillary buds are formed at nodes (the base of
leaf axils) and internodal locations on plant stems via adventitious buds.
Adventitious buds are buds (which likewise grow lateral to the parent limb) that
are formed on the trunks and roots of woody plants. When a leader or branch is
damaged or removed (e.g. by people or the environment) and the lateral branch
suppressant hormone auxin (is temporarily lost with the terminal growing
point) adventitious buds (dormant and newly formed) grow producing shoots,
which like axillary buds become woody limbs following incremental secondary
growth.
Fig 2
Epicormic shoots (Camphor laurel)
Axillary buds (which grow from leaf axils with a bud trace) are considered by
most in higher arboricultural education to produce stronger limbs than those
that have grown adventitiously (I would like to see a study explaining why).
Determining whether a limb has grown from an axillary or an adventitious bud is
seldom possible in an advanced age tree. However a limb, which has grown
sufficient increments of wood (into the parent stem) or has a sufficient diameter
in proportion to its height (H/D) is known (by the principles behind VTA) to be
stable in the same way that a limb grown from an axillary bud is stable (held in
place by multi laminations of wood).
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If epicormic (a well established arboricultural term) limbs are born from
adventitious buds, then what do axillary buds grow into?
We have all grown up with the use of the term epicormic, Latin for Upon the
Stem (Epi – Upon, Cormic – Stem), we have all grown up with advice on the
defective nature of epicormic limbs.
So what is the name or term for the opposite of epicormic? This question is
something that has long bugged me since my initial Arboricultural UK (Merrist
Wood) education (90-92).
Following a major report that I prepared for Energex on the 2008 Brisbane Gap
Storm (and past AA article - Ref ETS/Energex 2008 Gap Storm Report –
Aug/Sept edition AA 2009) I invented a new term to both fill the void in (my)
arboricultural understanding and offer explanation for why so many of the
‘epicormic’ branches that I had condemned survived the storm. That term is
Endocormic – Latin for Within the Stem (Endo – Within).
I have been using this term professionally ever since, though it was not until an
AA publication (2012) by Gail Bruce (Arboricultural Journalist) on Scott Hanley's
past QAA Advanced pruning workshop that I saw the term used by another
leading Qld Arboricultural professional.
Though regardless what we humans think, the trees are physically growing and
adapting to the environment via the growth of axillary, adventitious buds,
secondary growth (the laying down of wood increments) and
epicormic/endocormic type advancement.
Fig 3 Fig 4 Epicormic - Latin for ‘upon the stem’ Endocormic – Latin for ‘within the stem’
Fig 5 Fig 6
Fig 5 - Epicormic growth branch break out failure due to insufficient wood
laminations and Fig 6 - Endocormic growth tension failure with sufficient wood
laminations – Note failures caused by hand
Ref ETS/Energex 2008 Gap Storm Report – Aug/Sept edition AA 2009
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Study of many urban-forested city environments will yield numerous examples
of trees that where veteranised by storms or tree loppers that have since
adapted and succeeded.
The pioneers in UK Veteran tree management (Neville Fay - Tree Work
Environmental Practice) have posed that storm damaged trees better adapt to
their veteranisation than flat topped trees (by chainsaw), this has lead to natural
fracture pruning practices being employed in UK conservation arboriculture.
Fig 7 Fig 8 Natural fracture pruning practice (courtesy of Andrew Cowan) now a part of
Conservation Arboriculture UK
We know that topping trees is destructive, that topped trees (by storm or
lopper) are certainly compromised, though do we recognise that many veteran
trees adapt damaged crowns into stable functioning replacements - via the
growth of buds and laminations of wood? Many experienced arborists in
arboriculture agree that there are more veteran trees that adapt and succeed
(for years) following veteranisation than those that fail.
Arboricultural experience shows us that those trees that best adapt to crown
failure are those that lose smaller diameter branches as a means to mitigate
wind force (assuming that crown harmonics – the trees natural ability to diffuse
force flow is overcome). Though there are also numerous trees that lose large
diameter branches and make subsequent crown adaptions that keep them alive
for many years.
Regardless of a trees age its success is driven by vitality, which is driven by its
ability to successfully photosynthesise, draw nutrients (elements) and water.
Where we witness excellent signs of adaption involving the generation of
replacement crowns, wound occlusion, reaction wood development and
compartmentalisation then we know that we either have a healthy tree (health
or vitality is driven by a compatible growing environment) or a vigorous tree
(which is driven by a strong genetic code) to quote Shigo (or both).
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The fact is that the shedding of small diameter branches (25mm<) or even just
leaves, as a means to dissipate wind force is a part of the trees natural success
story. Though we fail to notice the leaf litter, the downed small diameter
branches and the still standing trees after a storm event (favoring observation of
the dramatic – the big and the broken).
The reason that trees easily adapt to light crown failures is simple – 1) due to the
numerous dormant and adventitious buds that are located all over the stems of
young limbs. And 2) because of the ease of adaption that epicormic shoots have
on small diameter branches (subject to some tree species variation – i.e.
Camphor laurel trees produce better epicormic growth from larger diameter
branch stubs) – with the growth of wood laminations they become endocormic
very quickly.
Fig 9
Fig 9 – Refers to a study of any of Britain’s famous 1000 year+ ancient oak trees
(as with this one from Meetings with Remarkable Trees by Thomas Pakenham)
which Illustrates self-optimisation and crown ‘re-configuration’ (via growth of
dormant buds and wood increments) following historical loss perfectly.
In the natural environment trees are generally regarded to have 3 phases to their
lifespan – upward/outward growth, a sustained functional rest (without
significant growth expansion), then a slow downward decline (or retrenchment)
with subsequent generation of a lower/internal crown. However in the urban
forest due to our non-sustainable interaction with the environment (largely
caused by a hard landscape foot-print) and demands for space trees seldom live
beyond the first phase. Yet with arboricultural management (reduction, nutrition
and exclusion) there is no reason why old aged and veteranised trees can’t be
sustainably retained and managed into the final chapter of their lifespans.
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Thanks to the contribution of UK Veteran tree management
researchers/practitioners (Neville Fay, Ted Green, Jill Butler & Andrew Cowan)
we have records such as the 99-year-old photographic history of the Arthur
Clough Oak.
Fig 10
This historic trees adaption (courtesy – Andrew Cowan Arbor Ecology UK) from
a forest to field pasture tree via crown loss - crown retrenchment - dieback and
transition from an epicormic to endocormic crown is well recorded in 5
photographs spanning 1910 to 2009.
Since the 2008 ISAAC Brisbane seminars on Veteran trees (Ted Green, Jill Butler,
David Lonsdale & Andrew Cowan) I have been looking for and finding the same
traits of transition in our Australian veteran trees.
My well-travelled VTA course (VTA an Australian Perspective) covers a large
amount of local photographic data supporting the transition of epicormic to
endocormic (a small sample of them feature in this article).
It sadly is to often that the case of one limb failure that leads to human tragedy
will fuel the felling of hundreds of trees that have no past history or imminent
likelihood of limb failure. Limb failures occur based on stressors in the internal
and external tree environment, naturally the outside environment influences the
trees internal environment. Figs 11 & 12 are photographs of limbs, which have
made the transition.
Fig 11 Fig 12
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Fig 13
Fig 13 is a classic example of a veteran Gum (E. crebra) that has generated a
substitute crown of epicormic branches (already transitioning and restoring
crown harmonics) following a historic crown failure.
Based on my 5.5 years (2007-12) of assessing large Gum tree populations
extending south to north from Central West Brisbane to Tin Can Bay and west to
east from Esk to Bribie Island (the Energex VTA Program) my experience of
epi/endo crowns and limb failure has validated my hypothesis (that trees
transition). The Gums by measure of population, time duration (of appraisal) and
record of electrical outage are considerably more prone to succeeding than they
are failing. Of the Gums that had the most major crown failures in S.E. Qld (with
mechanical constraints or defects) E. grandis and E. signata where the most
common (but still not significant in number).
Fig 14 Fig 15
As with all trees where there is sufficient vitality (resources to grow) and
sufficient diameter (foundation) in proportion to height (stable structure) trees
succeed. Considering the amount of resources that the epicormic branch in Fig
14 (E. tereticornis) must use to generate a sufficiently stable footprint (to
occlude/compartmentalise the severed codominant limb and then to generate
sufficient increments of wood around that limb) then this would be a major feat
on behalf of the tree (though with sufficient vitality not impossible).
Whereas considering the resources and diameter growth necessary for the
epicormic branches in Fig 15 (Cinnamomum camphora) to succeed then failure
is not much of a consideration (unrecorded on Camphor laurel in Toowoomba by
Toowoomba Regional Council).
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Epicormic limb failure is mostly based on branch breakout failure (as with Fig 5)
or failure akin to bifurcation failure, though other factors may influence (fungi
induced wood embrittlement or fungi induced wood softening) but failure is
always based on a lack of diameter to support height or length.
Another major career learning opportunity for me has involved working on the
Camphor laurel lined street Trees of Toowoomba (a small rural City West of
Brisbane), between 1996 to 2001 as a contractor I pruned at least 3 thousand
Street and Park trees. Then in 2003 I was commissioned to prepare a vegetation
management review and report (as a part of a MOU between the Council and the
Utility managers Ergon) on a sustainable approach to managing Toowoomba’s
historic avenues of Camphor laurels.
These trees had been topped at least 5 times in their lifespans going back to the
1930’s, though this as a practice had stopped by the early 90’s, all the Camphor
lined streets are made up of veteranised trees (as with the Brisbane historic
avenues of Camphor laurel). The camphors being vigorous large woody trees
growing in highly fertile volcanic soils (in a cold winter climate) have adapted to
topping and root severence/butress root grinding (due to footpath lifting/trip
hazards) in ways better than any species of tree I have witnessed (bar the
Australian Red Cedar). It was learning from these trees that I first recognised
epicormic to endocormic type crown adaptions.
Figs 16-19 show varying stages of Epicormic to Endocormic transition on
Camphor laurel trees (Anzac Street New Town)
Fig 16 Fig 17
Fig 18 Fig 19
The photographed stages of growth (akin to wood growth associated with lapsed
pollards in the UK) range from 5 to 25 years of the generation of wood
increments over the original epicormic shoots linking into the trees parent
stems.
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Photographs (Figs) 20 – 23 show leaders/limbs which where cut internodally
and grew subsequent epicormic shoots, which generated into replacement limbs.
Fig 20 Fig 21 Fig 22 In Fig 20 we can clearly see the incremental circles of wound wood via the bark
pattern around the end of the occluding remnant (hollow) parent limb. In Figs
21, 22 and 23 we can likewise clearly see the ends of the occluded parent limbs
through the bark of the adapted endocormic branches/replacement leaders.
These epi/endo crown adaption samples are all of Camphor laurel, bar Fig 22
which is Grey Gum (E. propinqua) and are all excellent examples of significant
vigour and vitality.
Fig 23
A study of any one of the hundreds of Toowoomba’s veteran Camphor laurel
trees validates these observations. Contained with-in my VTA presentation I
have numerous other examples of this and similar traits that are unique to
Australia.
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Conclusion
Part 1 of this article sets the stage as the background to the Reduction
component to a 3-part piece, which is a study of the risk management options
that are available to us for veteran trees. The current Australia standard for the
pruning of amenity trees does not cover sustainable veteran tree management
via pruning. In Part 2 of this article I will be posing a well considered, supported
(US, CAN, UK) and trailed approach to advanced pruning for veteran trees. It
must be stated at this point that my promotion of veteran tree management (and
the recognition of transition from Epicormic to Endocormic) does nothing to
take away anything from AS/4373 but adds to it.
Of the Genus and species of tree that I have consistently observed that have
successfully made the transition from Epicormic to Endocormic (without failure
to minimal failure) throughout S.E. Qld – those are Camphor Laurel -
Cinnamomum camphora, Jacaranda - Jacaranda mimosifolia, Chinese elm – Celtis
sinensis, Grey gums - Eucalyptus major, propinqua & biturbinata, Corymbia -
Corymbia citriodora maculata, C. henryi, C. tessallaris, Blood woods – C.
intermedia, C. trachypholia, Brush box - Lophostemon confurtus, Forest red Gum -
Eucalyptus tereticornis, Blue Gum - E. saligna, Iron Barks - E. crebra, E. fibrosa,
White maghogany – E. carnea, E. umbra & E. acmenoides. Perhaps one of the most
dynamic examples I have observed of the transition is with examples of the
Genus Ficus where aerial roots are employed to graft epi/endo crowns to the
parent crown (more epi/endo examples to come in Part 3).
These are off the top of my head, the list goes on. Regardless of tree Genus or
species the reciepe of success for trees that succed in general is vitality. This is
especially so to enable trees the transition of epicormic to stable endocormic
crown structure, it is the arborists job to inspect those unions to determine
stability as part of a risk management plan (the UK - ITMP is covered in part 3).
While I accept that tree species with weaker vigour (gene codes) and poor
vitality will not make the transition (without sucumbing to death or structural
failure), those tree species and trees that do need to be recognised by us as
veteran trees worthy of retention and risk management.
In part 2 of Veteran tree risk management via reduction, nutrition and exclusion
we will explore a financially and environmentally sustainable means to achieving
veteran tree risk management via Reduction. This strategy is by no means a new
one to arboriculture though historically the practice has done more to reduce
tree lifespans than promote them. In my last Arbor Age article I made reference
to the 5/30 rule as a directive to sustainably reduce the crowns of trees. This is
to be explained based on a veteran tree management project and report that I
developed in my last senior arborist role. Knowing the hands on approach that
most arborists have (including me) I generally like to use an actual job to
illustrate the reason behind my articles.
Thanks, with regards to all in arboriculture – Cassian.