The wood-wide web – mycorrhizal associations across individuals

It goes without saying that the world of mycorrhizal fungi is so vast and complex that we’re only just beginning to scratch away at the surface of understanding, though this doesn’t mean we haven’t made some very interesting developments over recent decades. For example, we know that trees may use mycorrhizal networks to ‘trade’ resources across a single species and across differing species, as do we know that they will ‘communicate’ to signal neighbours about upcoming defoliation events by insects. However, whilst we understand the concept, we aren’t necessarily in possession of an arsenal of data that can really begin to demonstrate the intricacies of mycorrhizal networks. I feel that this study is one that begins to establish knowledge of such intricacies, and therefore I hope that you find this as brilliant and mind-boggling as I did when I first read it a few months back (and also hopoe I am making sense with what I write!).

The focus of this study was a group of 67 Douglas fir (Pseudotsuga menziesii) of varying ages (courtesy of natural regeneration) in an area of 30m x 30m, and on the manner in which the ectomycorrhizal network of the species Rhizopogon vesiculosus and Rhizopogon vinicolor impacted upon the connectedness of Douglas fir individuals. By a similar token, it looked at the population structure of the two fungal species, across the study site.

In order to obtain data required to draw conclusions from the study aims, samples of soil were taken from four sides of each tree within the plot area (usually within the drip line, though if canopy cover was lacking then obviously not so). This enabled for the authors to theoretically obtain fibrous tree roots from each individual, and analyse the tree roots not only to identify the Douglas fir they were from, but to determine whether the two Rhizopogon species were present within both the root cambium and soil environment and, if so, of what genet they were from. The map below shows the plot area, and the sample locations. From each sample location, arrows are drawn to show what tree’s roots were found at each sample site, and from what Rhizopogon species (and genet) the roots were associated with. If we take, for instance, the upper-most blue-shaded area indicating a Rhizopogon vesiculosus genet, we can see how the genet is connected to many different trees across the site. These trees were thus deemed to be ‘connected’, as they shared an ectomycorrhizal network.

pmenziesiiectomyco
R. vesiculosus genets can be seen in the blue-shaded areas, and R. vinicolor genets in pink-shaded areas. The coloured lines around the shaded areas represent different genets of the two species, and the black dots within are the sample sites. The lines from the black dots show the links to the Douglas firs, which can be seen as the green star-like shapes (larger ones signify larger trees, and there are a total of four ‘cohorts’ marked by different-sized shapes). The arrow marks the Douglas fir most connected to other trees.

In light of the results obtained, which are shown above (visually), the authors identified a total of 56 Douglas firs that were connected with other trees in (largely) the plot area, via the ectomycorrhizal networks created by the two Rhizopogon species (and one fungal genet connected 19 trees!). 45 of the trees were inside the plot area, though a further 11 were outside (and this is why some are plotted outside the sample area). Within the site, 27 ectomycorrhizal genets were also found, of which 14 were from R. vesiculosus and 13 were from R. visicolor. 18 of the genets, 9 from each species, were found to connect at least two trees together. More associations were more frequently found amongst the larger and older individuals, most probably because they had been there longer and their larger rooting environments enabled them to assume more associations with ecotmycorrhizal genets. The table below provides a more detailed breakdown of the genets found and their associated with the different cohorts of Douglas fir.

fungalgenetdfir
A table showing the data obtained from the study.

In terms of the population structure of the mycorrhizae and its impact upon the Douglas firs, the authors found that two trees over 43m apart shared a connection via only two different ectomycorrhizal genets. Their connectedness had to span over more than one genet, as the maximum distance one genet (R. vesiculosus) spanned was around 20m. The ability of R. vesiculosus to span greater spatial distances may also be the reason behind why it was found to connect (10.2), on average, more trees per genet than R. vinicolor (4.4). The most connected tree (at 94 years of age), marked with the arrow in the first image, was considered to be ‘central’ to the overall ectomycorrhizal network, and had a relationship with 11 different ectomycorrhizal genets and 47 other Douglas fir.

A total of 62% of the Douglas fir from Cohort 1 and Cohort 2 were also found to be connected with trees from Cohort 3 and Cohort 4. This means that these younger specimens shared associations with the same fungal genets that older specimens were connected to, which the authors found interesting as it suggested that the fungal species surveyed had Douglas fir hosts that would ensure longevity of its existence within the landscape (as if the fungus has anticipated that, by only colonising older specimens, it could itself cease to exist when its old hosts all die out – succession-planning, if you will). Furthermore, it enables the younger specimens to share an already established inoculum base, from which carbon and water can be provided by the older specimens to aid with establishment. Beneath, a further image shows associations between individual Douglas fir studied during the research.

mycorrdfirassociation
Showing how individual Douglas fir were linked to other individuals, the coloured circles vary in size depending upon tree DBH and colour (from yellow [young] up to dark green [old]) depending upon age. Thicker lines between individuals shows a greater degree ot connection, associated with how many different ectomycorrhizal genets linked them.
What we need to be aware of here is that this study was done over a tiny fragment of Douglas fir forest, and therefore if the associations were extrapolated out over an entire landscape, the connected nature of individuals to others would be absolutely incredible. Not only this, but because two trees were found to be connected at over 40m away, it highlights how the above-ground isolation of individuals in a stand masks the intricately-connected nature of the individuals beneath. Thus, we must really see a forest as a network, in place of individual trees.

The fact that older individuals were found to have many more connections, on average, than younger ones, also highlights the criticality of retaining older specimens in a stand – if only for the benefit of safeguarding ectomycorrhizal networks that aid with younger specimens obtaining required resources for their growth. However, we must also recognise that the mycelial networks of the two Rhizopogon species studied benefit hugely from the older trees, and retaining them is also of benefit to their existence. Targeted felling of large individuals, therefore, could wreak havoc (and rather quickly) upon the entire system, as the stand’s resilience is built upon these (and related) ectomycorrhizal networks that have established and persisted for a long time.

Even if, as the authors suggest, a connection does not provide the young tree with resources, it will still benefit from connecting with a well-established ecotmycorrhizal genet that is itself healthy and fully-functioning as a result of obtaining its carbon from upper-canopy, mature Douglas fir. It does not pay to be isolated from the crowd.

Source: Beiler, K., Durall, D., Simard, S., Maxwell, S., & Kretzer, A. (2010) Architecture of the wood‐wide web: Rhizopogon spp. genets link multiple Douglas‐fir cohorts. New Phytologist. 185 (2). p543-553.

To discuss this, please feel welcome to post below or on Arbtalk.

The wood-wide web – mycorrhizal associations across individuals

Fungal colonisation strategies Pt. III: Specialised opportunism

This strategy sees fungi colonise the sapwood in a living tree by taking advantage of the tree’s physiological stress due, for example, to root dysfunction or drought conditions (Boddy, 2001; Parfitt et al., 2010; Rayner, 1993; Rayner & Boddy, 1988; Schwarze, 2008). Development will be in apparently intact, yet dysfunctional sapwood of areas of the tree which remain uninjured, though decay onset will be timed with desirable conditions within the tree (induced by stress). Single genotypes will usually manifest with distinct speed (up to a few metres per year), and spread extensively, using the xylem as a vector, throughout underlying sections of bark, forming vast decay columns. This therefore entails that such decay fungi are present extensively within the tree (yet not in an overt manner) within its functional sapwood, prior to attack. Onset of decay is likely not observed until the tree suffers localised xylem dysfunction, given the high water content of functional sapwood is undesirable for fungal decay (Baum et al., 2003; Boddy, 2001).

pbetulinusbetula
This mature Betula pendula, whilst still alive, has been aggressively colonised by Piptoporus betulinus, following physiological stress.

Latent invasion may also in fact result from the development and subsequent assimilation of separate fungal mycelia, under the conditions associated with dysfunction. The spores may have spread widely within the sap stream over long periods, initiating only later (following stress in the host) their mycelial development, with subsequent ‘assimilation’ of the many establishing mycelium networks as they coalesce. The consequent decay associated with the assimilation and the host’s inability to defend against the widespread attack by the host may ultimately be very significant (Boddy & Rayner, 1983; Parfitt et al., 2010). Research also suggests that even once sapwood does become dysfunctional, presence of decay may not become overt. Decay may not even begin whatsoever. Further, as many fungal species latently exist within specific hosts, particular conditions may only trigger the onset of decay by one, or a portion of, the fungal species present (Parfitt et al., 2010).

Additionally, such strategists have a high degree of selectivity with regards to their host site and / or species, with branch junctions being a principal location for decay onset (Boddy, 2001; Rayner, 1993). This is perhaps due to the lower side of the branch junction being an inherent weak point within the tree, because the site has low energy reserves – particularly when the branch attached to the parent branch or trunk is dying (Shigo, 1986). An example of a specialised opportunist’s strategy is therefore the entering into a dying branch with sapwood dysfunction, likely induced by the inability to compete with its neighbours for light, waiting at the junction of the dying branch until the spores are incorporated into the heartwood via secondary thickening, and then establishing and beginning the attack (Baum et al., 2003; Chapela & Boddy, 1988a; Chapela & Boddy, 1988b; Oses et al., 2008). Such a colonisation trait can be described as endophytic – this is where a species resides within the host with no adverse impact upon the host until conditions are right for attack (Baum et al., 2003). Such a scenario may even be beneficial in terms of facilitating the “natural pruning” of limbs that become dysfunctional as tree canopies expand (Rayner, 1993).

Under some conditions, certain specialised opportunists may also be able to colonise via active pathogenesis (Rayner, 1993).

References

Baum, S., Sieber, T., Schwarze, F., & Fink, S. (2003) Latent infections of Fomes fomentarius in the xylem of European beech (Fagus sylvatica). Mycological Progress. 2 (2). p141-148.

Boddy, L. (2001) Fungal community ecology and wood decomposition processes in angiosperms: from standing tree to complete decay of coarse woody debris. Ecological Bulletins. 49 (1). p43-56.

Boddy, L. & Rayner, A.. (1983) Origins of decay in living deciduous trees: the role of moisture content and a re-appraisal of the expanded concept of tree decay. New Phytologist. 94 (4). p623-641.

Chapela, I. & Boddy, L. (1988a) Fungal colonization of attached beech branches. I. Early stages of development of fungal communities. New Phytologist. 110 (1). p39-45.

Chapela, I. & Boddy, L. (1988b) Fungal colonization of attached beech branches. II. Spatial and temporal organisation of communities arising from latent invaders in bark and functional sapwood, under different moisture regimes. New Phytologist. 110 (1). p45-57.

Oses, R., Valenzuela, S., Freer, J., Sanfuentes, E., & Rodriguez, J. (2008) Fungal endophytes in xylem of healthy Chilean trees and their possible role in early wood decay. Fungal Diversity. 33 (1). p77-86.

Parfitt, D., Hunt, J., Dockrell, D., Rogers, H., & Boddy, L. (2010) Do all trees carry the seeds of their own destruction? PCR reveals numerous wood decay fungi latently present in sapwood of a wide range of angiosperm trees. Fungal Ecology. 3 (4). p338-346.

Rayner, A. (1993) New avenues for understanding processes of tree decay. Arboricultural Journal. 17 (2). p171-189.

Rayner, A. & Boddy, L. (1988) Fungal Decomposition of Wood: It’s Ecology and Biology. UK: John Wiley & Sons.

Schwarze, F. (2008) Diagnosis and Prognosis of the Development of Wood Decay in Urban Trees. Australia: ENSPEC.

Shigo, A. (1986) A New Tree Biology. USA: Shigo and Trees Associates.

To discuss this, please either leave a comment below or over at Arbtalk.

Fungal colonisation strategies Pt. III: Specialised opportunism

Books acquired this past fortnight

My ever-expanding library has a few more additions. All tree-related, though covering quite a broad range of subjects. The pollard management book was provided very kindly by an individual free-of-charge, which I am massively appreciative of. Having onced-over all of the books (asides from TiT2, which is a CD plus executive summary), they all look like very interesting reads.

If you’re interested in any of the books, I have links below.

Bookpurchases
Links can be found below (from top left to bottom right).

Pollard and Veteran Tree Management II (edited by Helen Read – no link available); The End of Tradition? (edited by Ian Rotherham, Mauro Agnoletti, and Christine Handley); Analysis of the Royal Preserves in Portugal (authored by Cristina Joanaz de Melo); Animals, Man & Treescapes (edited by Ian Rotherham and Christine Handley); Urban Tree Management (edited by Andreas Roloff), and; Trees in Towns II (edited by Chris Britt and Mark Johnston).

Books acquired this past fortnight

Ganoderma sp. on Acer saccharinum – I shouldn’t be so excited!

Both Ganoderma australe and Ganoderma applanatum are so painfully abundant that there’s really little justification in getting head-over-heels excited about their presence. Well, asides from one or two times – and this is such a time!

There are plenty of Acer saccharinum (silver-leaf maple) around the area in which I operate, though I have never seen any fungi on any of them. Until now. Some cracking fruiting bodies of what I suspect is Ganoderma australe, which have colonised and now inhabit the the dead portions of this maple. Whether the fungi entered and caused death or the colonised areas were already dead I cannot say, though the one area not colonised is still alive – this may suggest that the fungi did cause such localised death (following very heavy topping). I doubt very much the fungus was present prior to the heavy pruning, though I may be wrong.

This may very well be a glorious anti-climax for all of you reading this, though I’m still pretty chuffed, and will continue to be until I start finding them all over the place (sod’s law)!

ganodermaacersaccharinum1
Some harsh pruning work here, if it can be called that!
ganodermaacersaccharinum2
On some of the dead limbs, we can observe fungal colonisation.
ganodermaacersaccharinum3
Two small fruiting bodies can be seen on this limb.
ganodermaacersaccharinum4
And a cracker beneath! Note the brown spores, seen on the ivy leaves, identify this as a Ganoderma species.
ganodermaacersaccharinum5
On the opposite side of the tree and on the main stem, this small critter can be seen.
ganodermaacersaccharinum6
Cutting into the flesh of yet another fruiting body reveals a dark brown flesh colour. Perhaps too dark to be Ganoderma applanatum; hence my leaning towards Ganoderma australe.
Ganoderma sp. on Acer saccharinum – I shouldn’t be so excited!

Fungal colonisation strategies Pt. II: Unspecialised opportunism

Such strategists have their spores colonise the (now dysfunctional) sapwood after a wound exposes what would otherwise have been functional sapwood. Such strategists are adapted to a wood environment with high oxygen content and (initially) high moisture levels (Boddy, 2001; Rayner, 1993; Rayner & Boddy, 1988; Schwarze et al., 2000). Cankers may also facilitate the establishment for spores of such strategists, in particular instances (Shigo, 1986).

Sapwood-exposed strategists are typically rapid in colonisation rate, though do not begin to cause decay until the wood dries out (Schwarze et al, 2000); by this point, non-decay-causing organisms have likely already begun to colonise, and may in fact aid with fungal succession and wood degradation (Rayner, 1993; Schwarze et al., 2000; Shigo, 1991). As such, there is a (brief) ‘latent’ period in between infection and decay. During this delay, the fungus will take advantage of readily-available food sources such as sugars, using the energy to fuel its rapid colonisation habit. Such rapid establishment means the tree does not have enough time to properly compartmentalise the attack around the wounded area (Rayner & Boddy, 1988; Schwarze et al., 2000). Some of these strategists also deploy offensive mechanisms to further damage the tree, such as via the secretion of toxins to kill or damage parenchyma cells.

The decay column that manifests following fungal establishment is largely axial in spread, progressing vertically from the wound site with – at least initially – little radial spread. The decayed area will be surrounded by a discoloured margin, where the tree has deposited tyloses, suberin, and phenols, in an attempt to compartmentalise the decay process by shutting down and clogging its vascular tissues (Boddy, 2001; Dujesiefken & Liese, 2015; Shigo, 1991; Weber & Mattheck, 2003). Discolouration and decay extent both vary depending upon the species of fungus and the tree species’ characteristics (intrinsic), as well as the environment in which the host tree resides (extrinsic) (Rayner, 1993; Rayner & Boddy, 1988).

psquamosusaesculus
On this Aesculus x carnea, which has suffered major windthrow within its crown that thus exposed large tracts of sapwood, Polyporus squamosus has colonised.

In certain instances, numerous unspecialised strategists may colonise a tree in different regions, surrounding either the same wound or, if the tree has many wounds, various ones (Boddy, 2000). This can lead to intricate patterns of decay and barrier zones between each different hyphal network, at times with barriers being visibly breached on numerous occasions. Ultimately, it is critical that invading pathogens create and retain their own zones within the wood structure, protecting the hyphal network from both tree defence mechanisms, mycoparasites, and other invading pathogens (Boddy & Rayner, 1983; Shain, 1979; Shigo, 1986).

Furthermore, such strategists possess a wide range of ‘sub-colonisation’ strategies, varying from the ruderal (saprophytic) mold fungi (Hyphomycetes) to the combative (parasitic) Basidiomycetes (Schwarze et al., 2000). Ruderal strategists do not typically degrade wood but merely discolour it, though may initiate decay that may, as already suggested, initiate succession by higher-tier Basidiomycetes of the same site. This is because ruderal strategists tend to enter early, colonise, and exit, before conditions become undesirable (due to lowering nutrient availability, competition from other decay organisms, desiccation of substrate, etc). They are largely non-selective with regards to species preference (Boddy, 2001).

As a partial aside, unspecialised opportunists will also attack incredibly young seedlings. Seedlings, until a certain age (species-specific, in part, though also driven by environmental conditions – may be from 5 days to 2+ weeks), lack the ‘mature’ tissue and resistance to pathogens that established ones have (this occurs when pectin begins to convert to calcium pectate within cell walls). This means seedlings are susceptible to unspecialised opportunists, particularly those within the soil. Depending upon the extent of soil-based inoculum, seedlings may in fact be killed before they even emerge from the soil (high inoculum potential). If the inoculum base is lower, seedlings may instead be killed post-emergence. In such instances, where localised humidity is high due to an abundance of seedlings creating a humid micro-climate and high rainfall (or artificial watering), fungal mycelium may spread across the surface from hypocotyl to hypocotyl – such rapid spread is aided by better aeration when compared to soil aeration (Garrett, 1970). Such a concept is termed ‘damping-off’ disease.

References

Boddy, L. (2000) Interspecific combative interactions between wood-decaying basidiomycetes. FEMS Microbiology Ecology. 31 (3). p185-194.

Boddy, L. (2001) Fungal community ecology and wood decomposition processes in angiosperms: from standing tree to complete decay of coarse woody debris. Ecological Bulletins. 49 (1). p43-56.

Boddy, L. & Rayner, A.. (1983) Origins of decay in living deciduous trees: the role of moisture content and a re-appraisal of the expanded concept of tree decay. New Phytologist. 94 (4). p623-641.

Dujesiefken, D. & Liese, W. (2015) The CODIT Principle: Implications for Best Practices. USA: International Society of Arboriculture.

Garrett, S. (1970) Pathogenic Root-Infecting Fungi. USA: Cambridge University Press.

Mattheck C., Bethge, K., & Weber, K. (2015) The Body Language of Trees: Encyclopedia of Visual Tree Assessment. Germany: Karlsruhe Institute of Technology.

Rayner, A. (1993) New avenues for understanding processes of tree decay. Arboricultural Journal. 17 (2). p171-189.

Rayner, A. & Boddy, L. (1988) Fungal Decomposition of Wood: It’s Ecology and Biology. UK: John Wiley & Sons.

Schwarze, F., Engels, J., & Mattheck, C. (2000) Fungal Strategies of Wood Decay in Trees. UK: Springer.

Shain, L. (1979) Dynamic responses of differentiated sapwood to injury and infection. Phytopathology. 69 (10). p1143-1147.

Shigo, A. (1986) A New Tree Biology. USA: Shigo and Trees Associates.

Shigo, A. (1991) Modern Arboriculture. USA: Shigo and Trees Associates.

Weber, K. & Mattheck, C. (2003) Manual of Wood Decays in Trees. UK: The Arboricultural Association.

To discuss this post, please either post below or do so over on Arbtalk.

Fungal colonisation strategies Pt. II: Unspecialised opportunism

The creation of a mini arboretum

And the earth was without form, and void; and darkness upon the face of the deep…

…and then, trees were planted!

It’s not all too often I am able to really create a lasting collection of trees in an area, though an opportunity came up recently to do just this. I was absolutely delighted to be involved in this project (creating a small arboretum of 20 trees), and the reaction from residents has already been wonderful.

Species selection was limited from the beginning for two reasons: (1) the site is characteristically very wet, and (2) the nursery had sold a lot of this planting year’s stock before this project was planned (from start to finish, it took just three weeks, and began in late January). Regardless, a challenge is good, and I am confident that the final result will be highly impressive.

So what has gone in at this location? Given the nature of the site, a lot of what was planted is tolerant of wetter soils. Alnus glutinosa ‘Imperialis’, Alnus glutinosa ‘Laciniata’, Alnus incana ‘Aurea’, Alnus spaethii, Metasequoia glyptostroboides, Metasequoia glyptostroboides ‘Goldrush’, Populus nigra, Quercus palustris, and Taxodium distichum therefore comprise much of the planting scheme. However, on areas of slightly drier and higher ground Acer buergerianum, Acer rubrum, Juglans regia, Liquidambar styraciflua, Quercus frainetto, Tilia tomentosa ‘Brabant’, Tilia tomentosa ‘Petiolaris’, and Zelkova serrata ‘Green Vase’ have been planted.

I’ll try to keep a tabs on this planting project and share photos of how the trees fare across the coming years, though for now we can simply observe but a few photos of the day of creation. I sincerely hope as many as possible make it into maturity, and really grace the area for future generations who live nearby.

treeplanting1
Here are a few of the trees. Just out of sight is a 16-18cm Liquidambar styraciflua in a 100L bag. That thing was a beast!
treeplanting2
Some of the trees laid out prior to planting.
treeplanting3
One of the dawn redwoods (Metasequoia glyptostroboides) sitting within its planting pit, prior to backfill.
The creation of a mini arboretum

Fungal colonisation strategies Pt. I: Heart rot

There exist four different colonisation strategies of a living tree by wood-decay fungi: heart rot (heartwood-exposed), unspecialised opportunism (sapwood-exposed), specialised opportunism (sapwood-intact), and active pathogenesis (Boddy, 2001; Rayner, 1993; Rayner & Boddy, 1988; Schwarze et al., 2000). Over the coming week or so, I’ll be looking at each strategy. We shall begin with heart rot.

Heart rot

In simple terms, this strategy involves colonisation of heartwood – via an entry point where heartwood becomes exposed – and subsequent decay of such heartwood (or core) of the host, where parenchyma (living) cells are lacking and conditions are very gaseous (Boddy, 2001; Rayner & Boddy, 1988; Schwarze, 2008). Colonisation is considered to be through heartwood-exposed wound surfaces, or alternatively via exposed heartwood from dead or diseased areas of the tree that are old enough to contain heartwood. Entry via such mechanisms can be divided into two distinct segments: top-rot (colonisation originates at the crown and progresses downwards) and butt-rot (colonisation originates at the root collar-butt interface and works upwards). For butt-rots, colonisation can further be divided, with entry being via root-mycelium contact, or by fungal spores (Rayner & Boddy, 1988). Rarely do butt rots cause hollows more than a few feet up into the trunk (Shigo, 1986).

Such strategists are particularly stress-tolerant, predominantly because conditions for decay are initially very unsuitable deep within the heartwood of the host. The lack of oxygen, high levels of carbon dioxide, undesirable moisture levels (particularly if bacterial wetwood is present – this will occur if bacteria are the pioneer invaders of a site, and not fungal pathogens), and abundance of inhibiting compounds (tannins), mean decay will be a very slow process and may take many years to even initiate substantially. Species that adopt this strategy therefore are largely non-combative, very slow with regards to their decay and colonisation of the heartwood, and may well be species-specific; or at least show certain levels of host species-preference (Boddy, 2001; Boddy & Rayner, 1983; Cartwright & Findlay, 1958; Rayner & Boddy, 1988; Shigo, 1986; Weber & Mattheck, 2003). The predominant reason behind such frequently-observed selectivity is suspected to be due to the fact that different species of host possess vastly different characteristics with regards to heartwood formation and properties, and by limiting host preference the fungal species directly reduce their potential fungal competitor range to, in some instance, almost zero (Rayner & Boddy, 1988). Species-specificness ultimately varies between heart rot strategists, therefore; a continuum, of sorts (Rayner & Boddy, 1988). Genus-specific strategists include Fistulina hepatica (Quercus spp.), Phellinus pomaceus (Prunus spp.), and Porodaedalea pini (Pinus spp.), whilst generalist strategists include Armillaria spp. and Heterobasidion annosum. Rayner and Boddy (1988) also note that Laetiporus sulphureus may colonise seemingly unrelated species such as Castanea spp., Quercus spp., Salix spp., and Taxus spp.

fhepaticaweird
This oddly-shaped Fistulina hepatica, a heart rot strategist, was found (by me) at the base of a very mature Quercus robur.

In spite of their largely non-combative ability, both with regards to colonisation of wood and competition against other fungi, their intricate specialisms that have optimised them for heartwood decay enable them to create large individual territories amongst the expansive heartwood extent within their host. Mycoparasites (fungal parasites that predate upon other fungi) may however be a potentially limiting factor, in certain instances, where such fungal parasites establish within the decaying wood zone(s) and attack the wood-decaying fungi present – as may fungal viruses (Badalyan et al., 2004; Boddy, 2000; Boddy & Rayner, 1983; Shigo, 1986).

Research by Highley et al. (1983) also suggests that the lack of difference in performance under low oxygen and high carbon dioxide regime levels for heart rot strategists means they may have evolved to become so specialised by adapting to species-specific heartwood traits (pH, volatiles, extractives, etc) – such as with Laetiporus sulphureus and its ability to tolerate tannin-rich and acetic acid-rich wood, which correlates with the low pH of Quercus spp. heartwood, and its high tannin levels (Hintikka 1969, Hintikka 1971, Rayner & Boddy, 1988).

porodaedaleapini
In this image (taken by me) a mature Pinus nigra, with major storm damage upon its stem, has been colonised by the heart rot strategist Porodaedalea pini.

Heart rot is typically non-fatal for trees (at least, in the direct sense – the tree may die as a result failure induced by the decay), in the sense that it is considered to be more economically destructive to foresters than it is the health and longevity of the tree (Rayner, 1993, Rayner & Boddy, 1988). Because such strategists largely lack the ability to invade intact sapwood, their extent is confined to the heartwood of the host, thereby enabling the tree to continue in its metabolic pursuits without marked hindrance. However, death can be caused when heartrot strategists that are able to attack sapwood (through suspected active pathogenesis – Phellinus pomaceus), for the purpose of creating fruiting bodies (on sites where exposed heartwood does not exist) and for means of continued colonisation (Mattheck et al., 2015; Rayner & Boddy, 1988), do so extensively – to the point that the stem may be girdled, or the sapwood significantly damaged. Such a means of sapwood attack is through the development of a canker, initiated by the creation of a thick mycelial pad, which serves to force bark outwards and thus enable for an exit point (Rayner & Boddy, 1988).

References

Badalyan, S., Innocenti, G., & Garibyan, N. (2004) Interactions between xylotrophic mushrooms and mycoparasitic fungi in dual-culture experiments. Phytopathologia Mediterranea. 43 (1). p44-48.

Boddy, L. (2000) Interspecific combative interactions between wood-decaying basidiomycetes. FEMS Microbiology Ecology. 31 (3). p185-194.

Boddy, L. (2001) Fungal community ecology and wood decomposition processes in angiosperms: from standing tree to complete decay of coarse woody debris. Ecological Bulletins. 49 (1). p43-56.

Boddy, L. & Rayner, A.. (1983) Origins of decay in living deciduous trees: the role of moisture content and a re-appraisal of the expanded concept of tree decay. New Phytologist. 94 (4). p623-641.

Cartwright, K. & Findlay, W. (1958) Decay of Timber and its Prevention. 2nd ed. London: HMSO.

Highley, T., Bar-Lev, S., Kirk, T., & Larsen, M. (1983) Influence of O2 and CO2 on wood decay by heartrot and saprot fungi. Phytopathology. 73 (4). p630-633.

Hintikka, V. (1969) Acetic acid tolerance in wood – the litter decomposing Hymenomycetes. Karstenia. 10 (1). p177-183.

Hintikka, V. (1971) Tolerance of some wood decomposing basidiomycetes to aromatic compounds related to lignin degradation. Karstenia. 12 (1). p46-52.

Mattheck C., Bethge, K., & Weber, K. (2015) The Body Language of Trees: Encyclopedia of Visual Tree Assessment. Germany: Karlsruhe Institute of Technology.

Rayner, A. (1993) New avenues for understanding processes of tree decay. Arboricultural Journal. 17 (2). p171-189.

Rayner, A. & Boddy, L. (1988) Fungal Decomposition of Wood: It’s Ecology and Biology. UK: John Wiley & Sons.

Schwarze, F., Engels, J., & Mattheck, C. (2000) Fungal Strategies of Wood Decay in Trees. UK: Springer.

Shigo, A. (1986) A New Tree Biology. USA: Shigo and Trees Associates.

Weber, K. & Mattheck, C. (2003) Manual of Wood Decays in Trees. UK: The Arboricultural Association.

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Fungal colonisation strategies Pt. I: Heart rot

A hornbeam pollard in a small clearing

During autumn of last year, I visited a site somewhat close to home that was, by-and-large, an old park (that was, at one stage, a private estate). Now, many tracts of the landscape have regenerated, or were simply always retained as woodland, and amongst both landscapes there are plenty of old hornbeam pollards that, in places, are still under active management. The below hornbeam (Carpinus betulus) is no exception, and I am wondering whether the tree has had halo pruning undertaken around it, as it has an uncharacteristically high level of space when compared to the space other trees nearby have.

Anyway, I’m sharing this picture as I really like it. The tree has cracking form, and it displays very successfully the rather alluring character of pollarded trees.

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A beauty!
A hornbeam pollard in a small clearing

Vegetation along urban strees – is it just trees?

I have written a lot about trees in the urban environment, and I can certainly continue to write about them forever more, though when I stumbled upon the study I am to write about below I thought it would be interesting to touch upon vegetation beyond the realm of trees. Of course, the benefits trees provide, and the issues they create, are well understood, and there will always be a torrent of new research articles dealing with their presence in the urban setting. However, I am not aware of such an abundance of research for shrubs and other types of vegetation that may exist within urban environments. This is probably not all too surprising given trees are simply bigger and more noticable than other types of vegetation, though when we work with trees we also will generally work with shrubs, grasses, and so on. Combined, or even exclusively, such vegetation (and the form adopted – formal or ‘wilded’) will impact upon the lives of residents, and understanding exactly how is always going to be vital to their successful incorporation into an urban landscape. In this instance, the residents of two German cities (Berlin and Cologne) are the focus.

In Cologne, the authors asked passers-by (a total of 108 were questioned) on a main arterial road (see the below image) just outside of the inner portion of the city how they perceived roadside vegetation (with regards to what they valued in terms of the functions the vegetation provides), what types of roadside vegetation they knew about and preferred, amongst other related topics (including how they thought vegetation established within the urban environment). The passers-by were stopped and questioned over the course of three weekdays from the morning through to the evening, during summer. All answers were written down either by them, or by the authors. 56% of passers-by who answered the questions were below 30 years of age, and 58% were male.

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This was the site used by the authors for their Cologne study. We can see vegetation occupying different ‘tiers’, with some higher canopy trees with smaller shrubs beneath (some appear to be coniferous, in the foreground).

The Berlin study was somewhat different, and whilst it also was conducted along a similar main arterial road on a summer day (which had wilded vegettion growing along the pathways, below the trees – see the image below), it asked different questions. Principally, the questionnaire provided to the passers-by was standardised, though some open-ended questions did feature. For example, the main bulk of the questionnaire was asking the individuals what type of vegetation cover they thought would work best on the arterial road they were walking down (no vegetation, maintained vegetation, wilded vegetation, or no preference). However, individuals could give reasons as to why they chose the answer they did, and were also asked what they thought about the current ‘wild’ appearance of the roadside vegetation.

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This was the exact location of the Berlin survey. All passers-by who stopped to answer the questions thus, in response to the open-ended question asking for their thoughts on the street’s current view, formed their opinion from this vista.

For the Berlin study, 40% of respondents were beloe 30 years of age, and gender distribution was almost equal. 74% of the individuals lived either near to the street or in an inner city borough of Berlin, and 78% were familiar with the street to some degree.

Results

In Cologne, just over half (52%) of the respondents considered trees to be the main vegetation type that feature along roads. The remaining 48% therefore detailed shrubs, perennials, and grasses – some individuals were specific to the species, as well. Furthermore, a wide array of landscaping features were also identified by the respondents, with flower beds, tree pits, and planting tubs being but three examples. In terms of how the individuals thought the vegetation had become established, the vast majority (87%) considered artificial planting to be the cause (be it through public or private hands). Only 13% suggested that natural regeneration could have led to the street vistas of Cologne.

A great number of the surveyed individuals also valued roadside vegetation as important, and for a variety of reasons (see the below table). Responses ranged from their presence being good for amenity to being beneficial for improving air quality, though most answers related to the vegetaton’s amenity value. So positive were the answers that many had a desire to see a greater amount of roadside vegetation of all types, of which some answers pushed a greater number of ‘wilded’ scenes more akin to a rural and naturalised scene. The reason for this ‘wilded’ desire varied, though answers included for the benefit of insects such as bees, to simpy being more interesting to the eye and making the streets more “lively”.

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This table compares how respondents valued different ecosystem services, across the two cities.

For respondents in Berlin, 48% considered the current ‘wild’ appearance of the street undesirable, and suggested it should be more formal in character (dubbed ‘urban devotees’). Conversely, 43% liked the vegetation as it was (dubbed ‘wilderness enthusiasts’). The remaining 8% did not mind, or were undecided. Therefore, there is certainly a similar mix of individuals who like ‘wilded’ streets and those who don’t. Unspurprisingly, it was the wilderness enthusiasts that most routinely saw the vegetation on the street as greatly improving the landscape’s character, because they considered the street to have a greater association with nature (a total of 40% of all respondents responded in such a manner). On the other hand, the ~30% of individuals who didn’t like the ‘wilded’ vegetation were more frequently from the urban devotee group (and this group cited the poor safety and amenity of the ‘wilded’ area as their reasons for such an opinion). The below table shows the disparity of opinion.

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A breakdown of how urban devotees and wilderness enthusiasts valued the current ‘wilded’ streetside vegetation.

Across both sities, neither age or gender were significant in determining how an individual viewed vegetation cover.

Concluding remarks

From the results detailed, there is no question that there is a wide range of opinion regarding what vegetation types are most valued by individuals, and the form that these vegetation types adopt (formal or ‘wilded’). It is entirely evident that there will always be a significant minority of people who do not appreciate the vegetation cover an urban area possesses, and it is also evident that people will value vegetation presence for different reasons (though mostly, it is for the aesthetic benefit provided – even then, what is considered as aesthetic beauty differs from person to person). Despite this, more vegetation (in general) on streets was in demand.

It is nonetheless curious that a good portion of those surveyed valued ‘wild’ vegetation (particularly in Berlin, and likely because individuals were more routinely exposed to such vegetation cover), though perhaps still considered this ‘wilded’ character as originating from man’s intervention. Only a small selection of respondents understood that the vegetation on streets may also regenerate naturally. By a similar token, the fact that many respondents recognised that trees are not the only type of urabn vegetation cover that may grace street scenes is suggestive of a need to incorporate complex landscaping vistas into urban sites – simply having canopy cover is not ‘enough’, perhaps. At the same time however, the desire of many for safe and formal landscapes may mean that constituent vegetation is maintained to some degree. Perhaps there is scope to have both more formal and ‘wilded’ vegetation types, assuming a street can accomodate such diversity (this requires size and desire).

Source: Weber, F., Kowarik, I., & Säumel, I. (2014) A walk on the wild side: Perceptions of roadside vegetation beyond trees. Urban Forestry & Urban Greening. 13 (2). p205-212.

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Vegetation along urban strees – is it just trees?

A birch growing out of an oak stem!

Not something you see every day, though I know it happens and have been told about alders growing out of hawthorns in a similar manner to this. Really cool, to be honest. The (epiphytic?) birch (Betula pendula) featured in the below images is, every few years, pruned back, so that its chances of surviving in the oak are better. However, as you’ll see below, one wayward root has done something very awesome!

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A birch peering out from behind an oak stem, right…?
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Wrong! It’s growing in the oak stem.
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Here we can see its rooting system, reaching down to where nutrients and moisture are available.
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And one root has gone in search of the ground, it seems. And it has made it. If this birch survives and this oak stem fully decays, perhaps it’ll end up on ‘stilts’?
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Here’s a look at the oak stem, and we can see the root tracking down to the ground from underneath the bark (which has fallen off in places).

 

A birch growing out of an oak stem!