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Kveldssanger

(Arboricultural-styled) 'Fact of the Day'

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I'm posting this one early as it's so bleedin' awesome (and I might be busy tomorrow)!

 

13/08/15. Fact #5.

 

The relationship between plants and mycorrhizae is a complex one. Perhaps one of the more intriguing forms of the relationship is when plants utilise their mycorrhizal networks to communicate (or eavesdrop) with one another. Certain plants, such as the tomato, are able to identify when a 'connected neighbour' has come under attack from a pest or pathogen and subsequently begin preparing for a similar attack themselves. In one study, the tomato plant anticipated attack of a pathogen fungus by elevating levels of resistance to such pathogen fungal attack, simply through the mycorrhizal network shared between the infected host and healthy one.

 

Bean plants have also showed similar behaviour to tomatoes. A study that looked into aphid attack on bean plants identified that healthy neighbours of infected specimens connected by the same mycorrhizal network began to synthesise and emit volatiles that repelled aphids and attracted their parasitoids - even before a single aphid had come into contact with the healthy specimens!

 

As mycorrhizal networks may span large distances, sometimes much greater than distances feasibly covered by airborne signals, the potential benefits for such communication may be significant. Furthermore, such research likely acts as a proxy indicator for trees and their communication methods via mycorrhizal networks (which are perhaps even more complex). Research is however lacking, though I'm sure there's a PhD thesis just waiting to be undertaken for this exact topic.

 

Source: Karban, R. (2015) Plant Sensing & Communication. USA: University of Chicago Press.

Edited by Kveldssanger

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A similar symbiotic relationship is exposed when the acacia tree is predated upon in Africa. Ants colonise these trees in response to the tree rewarding them with a sugar rich nectar-like substance from glands at the petiole.

 

When a Giraffe (or similar) predator begins removing the leaves, the tree releases an agitative hormone that excited the ant and sends them scurrying to the bows to escape it. This is where they find the Giraffe and the set about biting it. Whilst the venom of the ant is relatively mild, in abundance the Giraffe gets a little perturbed and seeks another lush tree. By this time the attacked acacia is emitting an airbourne hormone that tells adjacent acacia that they are being predated upon. This then stimulates the hormone to scatter the ants and so the cycle begins.

 

Now, if I wasn't stuck in some grubby service station motel awaiting a survey tomorrow I could give you the reference but I am pretty sure Perter Thomas, History of the Tree (Part 1) tells the same story (to a fashion)

 

The acacia is not alone, our English Oak carries out a similar response and 'talks' to their friends. You see, I tell people everyday that trees are living, breathing, sensitive creatures and should be respected. One day they may all turn on us and start pumping out CO2 rather than O2 just to p*** us all off!

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For those who are looking to read more about armybloke's comment about acacias and their ant-exciting chemical secretions (as well as the effect of browsing on spinescence), attached are some references.

Symbiotic ants as an alternative defense against giraffe herbivory (1992).pdf

Relaxation of an induced defense after exclusion of herbivores (1998).pdf

Effects of simulated shoot and leaf herbivory on vegetative growth (2001).pdf

Effects of natural and simulated herbivory on spine lengths of Acacia (2003).pdf

Edited by Kveldssanger

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14/08/15. Fact #6.

 

Severing roots out of purpose is hardly ever something that an arborist would find desirable, though it nonetheless occurs rather commonly where construction takes place and also where abatement of nuisance is practiced for terrestrial encroachment of a tree.

 

Current research indicates that the severance of roots is, by-and-large, highly variable. In one instance, root severance may have very little adverse impact on tree stability, though in other cases may weaken a tree by over 20%.

 

Roots that 'guy' a tree (exist uphill of the trunk) or reside on the outer (tension) side of a lean are ultimately far more crucial to the tree than the majority of the remaining root crown. Severing roots may not therefore simply be a case of "no more than 25% of the root crown can be lost", as context is key. If a guying / tension root is severed, the impact upon stability will be far more significant than if a compression root (or even multiple roots) is lost.

 

Statistically (from a survey done on willow oak), when assessing strength loss due to buttress root severance at the base of the trunk, a loss of 50% of the buttress roots will reduce the mechanical required force to move the tree one degree by a third (33%). However, due to the oscillating nature of winds, such a loss in root mass will result in a much higher decline in strength, particularly for larger trees with more wind sail (or where root decay is evident). Interestingly, such a loss can at times be achieved simply by severing a single guying / tension root, which suggests that trenching may be of particularly significant adverse impact to trees in more exposed sites.

 

Additionally, research indicates that severing roots closer than at a radius three-times the trunk diameter is not recommended, as tree stability declines significantly once this threshold is surpassed.

 

Source: Smiley, E. (2009) Root pruning and stability of willow oak. In Watson, G., Costello, L., Scharenbroch, B., & Gilman, E. (eds.) The Landscape Below Ground III. USA: International Society of Arboriculture.

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14/08/15. Fact #6.

 

Severing roots out of purpose is hardly ever something that an arborist would find desirable, though it nonetheless occurs rather commonly where construction takes place and also where abatement of nuisance is practiced for terrestrial encroachment of a tree.

 

Current research indicates that the severance of roots is, by-and-large, highly variable. In one instance, root severance may have very little adverse impact on tree stability, though in other cases may weaken a tree by over 20%.

 

Roots that 'guy' a tree (exist uphill of the trunk) or reside on the outer (tension) side of a lean are ultimately far more crucial to the tree than the majority of the remaining root crown. Severing roots may not therefore simply be a case of "no more than 25% of the root crown can be lost", as context is key. If a guying / tension root is severed, the impact upon stability will be far more significant than if a compression root (or even multiple roots) is lost.

 

Statistically (from a survey done on willow oak), when assessing strength loss due to buttress root severance at the base of the trunk, a loss of 50% of the buttress roots will reduce the mechanical required force to move the tree one degree by a third (33%). However, due to the oscillating nature of winds, such a loss in root mass will result in a much higher decline in strength, particularly for larger trees with more wind sail (or where root decay is evident). Interestingly, such a loss can at times be achieved simply by severing a single guying / tension root, which suggests that trenching may be of particularly significant adverse impact to trees in more exposed sites.

 

Additionally, research indicates that severing roots closer than at a radius three-times the trunk diameter is not recommended, as tree stability declines significantly once this threshold is surpassed.

 

Source: Smiley, E. (2009) Root pruning and stability of willow oak. In Watson, G., Costello, L., Scharenbroch, B., & Gilman, E. (eds.) The Landscape Below Ground III. USA: International Society of Arboriculture.

 

 

Like that one (and particularly timely / relevant right now!)

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15/08/15. Fact #7.

 

The traditional view of mycelial fungi is that the development cycle can be split into two stages: vegetative and reproductive. The former relates to the mycelial spread within the host and the latter the production of sexual or asexual structures that produce spores.

 

However, a more contemporary approach to discerning the development cycle of fungi reveals four distinct stages: arrival, establishment, exploitation, and exit. Such development stages are considered to be triggered by the changing conditions of the substrate (such as drying, cell degradation, etc), as in meeting the changing conditions the fungus must adapt its own behaviour (dubbed 'functional modes') to successfully persist within the host. Curiously, a fungus can compartmentalise itself so that, at different stages of decay within the same host, it adopts a different functional mode.

 

Each mode is briefly described below:

 

(1) Arrival: two known mechanisms exist: arrival as propagules (airborne and seemingly only favourable when localised conditions are optimised at the arrival surface - good supply of nutrients, a good microclimate, and a lack of competitors), or arrival as migratory mycelium (contact of an infected host to a non-infected host, such as with H. annosum and A. mellea).

 

(2) Establishment & exploitation: three principal concepts of this mode are understood: the fungus must successfully gain access to the host and begin to command available resources; the fungus must begin to successfully convert potential energy resources into actual energy sources, and; the fungus must successfully 'wall-off' an area to resist against competitors or the host tree itself, or in turn have a rapid exit strategy (panic fruiting on the wound surface or within the inside of the hollow(ing) host, for example).

 

(3) Exit: in the rawest sense, exit can be achieved either through the formation of reproductive structures or by the outgrowth of mycelium (relating back to the arrival strategies). The efficacy and extent of the exit mode is dictated by two factors: the extent to which resources are re-allocated from the mycelial biomass within the wood structure to the biomass of external structures, and; the effect of the environment on the form these exit structures adopt.

 

At a slight tangent, the r-K continuum further dictates exit strategy, with r-strategists (Deuteromycotina, Zygomycotina) taking a more rapid, economical stance to reproduction (not developing massive or durable exit structures), whilst K-strategists (Ascomycotina, Basidiomycotina) limit commitment of non-reproductive biomass, though also possess greater ability to develop exit structures that persist and are thus durable and do so at more 'fixed' stages. Within the continuum, certain species do however hold the ability to possess more than one mode of exit (such as with F. hepatica and L. sulphureus having the ability to develop either as a basidiospore on primary fruiting structures and as a conidiospore on auxiliary structures).

 

Source: Rayner, A. & Boddy, L. (1988) Chapter 5: Development Cycles. In Fungal Decomposition of Wood: Its Biology and Ecology. UK: John Wiley & Sons.

 

I learned a lot with this one!

Edited by Kveldssanger

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Ah sweet - cheers for that.

 

If anyone has anything to add to anything I say, or even has an update on newer information (some of my books are 10-20 years old and thus there may be some more recent developments) then do say.

 

If there's any desire for a particular type of fact, again let me know.

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A little side-fact that I just came across whilst reading. Thought it best to share for its sheer obscurity.

 

15/08/15. Fact #7.5.

 

When the Ancient Woodland Inventory (of the UK) was being compiled, it was initially done with tracing paper and coloured pens, only later shifting to digital (during the late 1990s, when GIS became readily available). Very quickly it was noticed that errors had crept into the data (for obvious reasons), so these were corrected, though more interestingly the change in true magnetic north from when the sites were mapped by hand to when they were transferred to digital had meant that many of the plotted woodlands did not overlay as precisely as necessary. Only when GIS further advanced (in 2003), allowing for precision mapping that accommodated the change in magnetic north, did the boundaries properly align on the digital version overlaying a recent aerial photo.

 

Source: Goldberg, E. (2015) The UK's Ancient Woodland Inventory and Its Use. In Kirby, K. & Watkins, C. (eds.) Europe's Changing Woods and Forests: From Wildwood to Managed Landscapes. UK: CABI.

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