Fungal succession and wood decay in living trees – a seminar report (Part II)

See Part I here.

The second part of this cluster of blog posts is one the first of the duo of talks presented by Lynne Boddy. Lynne is a well-known mycologist and researcher and thus, as regards wood-decay fungi, is a good authority from which we can all learn a substantial amount. For a fungi enthusiast such as myself, learning about fungi from one of the best is, in and of itself, very exciting. However, the information presented was equally as exciting, which I shall run through below.

As a slight aside, please watch out for her new book, which is currently being written and should be finished later this year, currently entitled Fungi in Trees. This book will be aimed at the arboriculturist. Lynne is also planning to re-write Fungal Decomposition of Wood, which was a magnum opus co-authored with Alan Rayner.

Fungi invading trees

Primarily, we must accept one core tenet of wood decay: the anatomy of wood has a massive impact upon mycelial networks that sojourn through the wood substrate and selectively metabolise woody cells and their deposits as they go. Indeed, in an ideal world, fungi would gun right for the ray parenchyma, which are incredibly nutritious living cells. However, these cells are very challenging to get to, by virtue of their ‘aliveness’ – living cells in good condition are not easily devoured. Further to this, the sapwood also offers a great for invading fungi, though again – because of the high moisture condition meaning the environment is largely anaerobic (fungi are aerobes and require oxygen to metabolise) – this part of the wood structure is not easily accessed. Of course, the vascular wilts have a better time invading sapwood that is functional, though many fungi will have to bide their time or arrive opportunistically onto and into dysfunctional sapwood if they are to have any means of success in acquiring the treasures within. Thus, is recognising that such living (i.e. conductive and functional) areas of wood are likely just beyond the reach of many fungi, wood-decayers will typically resort to the back-up food source: non-functional xylem vessels within the heartwood or ripewood.

The heart rotters

Now, in accepting this, we come on to perhaps the broadest cohort of wood-decay fungi in living and standing trees (fallen trees have their dysfunctional sapwood metabolised like ravens engulfing a fresh meal) we know of: the heart rotters. These fungi will enter the central wood (i.e. ‘the heart’) through exposed areas of this central column by either sufficiently deep root, stem or branch injury – ultimately, there generally needs to be a continuity of viable ‘heart’ substrate, if any significant degree of colonisation is to take place. Where continuity doesn’t exist, or the fungus finds itself limited to only a certain area, the only manner in which is will typically be able to continue existing is by (1) exiting and finding another host or (2) biding its time and waiting for currently functional sapwood to become incorporated into the heartwood or ripewood, in which it can then spread into – assuming the tree doesn’t lay down defensive barriers that cannot be breached, in order to protect its sapwood, which is in itself a pursuit undertaken to safeguard and hence sustain the high-moisture content of its sapwood (contrary to Shigo’s model, which infers compartmentalisation is largely there with the end in mind of prohibiting fungal succession into the wood). When we look at the ripewood of beech (Fagus sylvatica), we can observe this phenomenon very well – a rosy-coloured ripewood (red heart) with lots of separation lines between instances of decay successions. Ganoderma australe, Ganoderma pfeifferi and Ganoderma resinaceum will afford the most acutely observable examples of this, given their ability to breach such zones by metabolising the phenolic deposits laid down by the tree (this touches upon the idea of a fifth wall in the CODIT model, which will be discussed more later on).

An old Laetiporus sp. on yew (Taxus baccata).

By virtue of the heartwood or ripewood being the least inhospitable (heartwood, in particular, is still often disgustingly harsh, as regards its environment), we can observe immediately some species-specific associations. For instance, the dyer’s mazegill (Phaeolus schweinitzii) will frequent gymnospermous hosts, such as the cedars (Cedrus spp.) and pines (Pinus spp.), whilst chicken of the woods (Laetiporus spp. – often L. sulphureus, though by all means not always, as we will see) will be found often on oak (Quercus spp.), sweet chestnut (Castanea sativa) and yew (Taxus baccata) – it can, indeed, be found on other hosts, as well. On the face value of things, these three tree species have seemingly little in common, though all three have extractive-rich heartwood that this genus can metabolise effectively. In terms of why the genus is referred to and not the exact species, Lynne is of the stance that what we term ‘chicken of the woods’ and default to as L. sulphureus is actually a variety of different species each with their own specialisations – perhaps even down to a specific host tree species (notably for yew, where the chicken species is most pertinently viewed as being a different one).

From a tree management perspective, Lynne then addressed the importance of the heart rotters – what is their impact? Put simply, they change the way in which we view the tree from a safety perspective; as in, when fruiting bodies of heart rotters are identified, if the tree is standing and there exists a target, management considerations are routinely entertained and sometimes the tree is felled. Additionally to this, however, we have other things to appreciate:

• heart rotters do a great job at recycling nutrients, which can then be re-assimilated by the tree when they are uptaken back through its roots (including adventitious aerial roots) or the mycorrhizal fungi the roots associate with
• the wood qualities produced by heart rotters are ideal as habitat for saproxylic insects and nesting birds

The heart of this beech has been hollowed-out by decay fungi. In the process, before its failure, what conditions did this decay provide for insects and, crucially, what habitat does it provide now?

Latent colonisers

Considered the specialised opportunists, such fungi are present within the sapwood or bark, as propagules (thick-walled resting spores known as chlamydospores). Biding their time until conditions are right, wherein the sapwood becomes dysfunctional through means such as wounding or drought (causing embolism), they are perhaps most acutely observed in the years after drought years where they can trigger the formation of strip cankers and resultant reaction growth by the tree (see the below photo). Thus, this year, in the UK, is one to watch out for, as regards such fungi (it might also explain why Kretzschmaria deusta was so abundant this year, given Ascomycetes love dry conditions, which prevailed last summer).

A strip canker in beech caused by the latent fungus Biscogniauxia nummularia that has induced reaction growth, which can be seen cross-sectionally in the bottom right image).

At this point, a delegate enquired as to whether Massaria disease of plane (Splanchnonema platani), as an Ascomycete, could be prevailing in urban conditions recently, because of dry conditions (such as London, where it was been very severe these past few years but prior to that un-noticed). Discussions continued and Frank Rinn interjected to add his thoughts:

• massaria progresses quickly in dry conditions
• recent dry summers have allowed for massaria to thus progress very rapidly (killing branches in as little as three months)
• the lowering of water tables in cities for the construction of basement levels of buildings has meant that plane trees can no longer tap into groundwater supplies
• mature plane trees afford the best conditions for massaria; notably lower lateral branches, which are shaded from the rest of the crown and thus may be most prone to stress
• there have been reports since 1903 from Croatia where large plane trees have shed branches and the massaria fungus was termed the “branch-cleaning fungus”
• conditions are collectively ideal for massaria to become prevalent, as they stand

Reverting back to latent fungi, Lynne then mentioned that she considers fungi to be latent across a broad variety of trees. For example, the coal fungus (Daldinia concentrica), whilst found most often on ash (Fraxinus excelsior) can be isolated from the sapwood of a great range of different broadleaved tree species in the UK. It is, indeed, only when specific conditions arise that are preferable for this fungus that it begins to create mycelial networks – such conditions might not arise in particular trees, or may arise only after conditions suitable for other fungi have arisen and thus D. concentrica then has no capacity to colonise the substrate. Hence, ash remains the core host of this species, in the current climate. However, for the jelly ear fungus (Auricularia auricula-judae), which is also a latent fungus within the vascular system, having been found largely solely on elder (Sambucus nigra) in the 1950s, it is now found on over 20 host species – this marks a huge increase in host range, prompted perhaps by changing climatic conditions.

Wall V

The CODIT model, offered to us by Shigo, details four walls – as can be seen here. As mentioned by Frank Rinn, Shigo himself was considering the possibility of a fifth wall, though this never ‘made it into’ the model. However, Lynne argues that there is the potential for a fifth one, which hearkens back to what was discussed above, as regards rot within the heart of beech wood).

Specifically, whilst the barrier zone (fourth wall) is a zone laid down at the time of wounding by the vascular cambium, the dynamic responses by the tree that occur in real-time as fungal decay advances constitutes a distinction from this initial barrier. Indeed, as decay advances, living cells within the heartwood or ripewood (they do exist; though through mechanisms not fully appreciated, but thought to be associated with the rays running radially through the wood), in addition to the functional sapwood, will, in order to protect the sapwood and keeps its high-moisture quality intact, will plug woody cells beyond the current zone of decay with extractives and phenolic compounds – this will occur within the sapwood most often, though may also be able to occur in the heartwood around the regions where pockets of living cells exist. This response resultantly produces incredibly dense zones of wood that afford the tree’s sapwood a means of protection, which it would otherwise lack, assuming the barrier zone (Wall IV) failed to contain fungal decay. Of course, if this fifth wall fails, another will form, and so on and so forth.

See the myriad of demarcations across this cross-section of a beech that failed from decay by Ganoderma pfeifferi, which suggest a dynamic fifth wall being effective.

Perhaps we will see this idea discussed more in Lynne’s re-write of Fungal Decomposition of Wood.

Fungal succession

When a tree decays, the fungi that initiated the decay process will not end it. This is because, much like all other ecosystems, as an environment changes those organisms that are best-placed to utilise it change as well. In this sense, fungi are no different – they succeed into a dynamic and ever-altering substrate (wood). Such a phenomenon can be so readily observed when walking into any woodland, when comparing the fungi on standing trees and those in early stages of decay and those much more heavily decomposed. In instances where an entire tree falls and stays largely intact, succession can be most acutely observed, as Lynne detailed with a little help from Ted Green and some research students.

The tree in question, a mature beech, failed and was left, in sections, for ease of its movement into an accessible place, to decay. Along the beech, it was found, through analysis of the wood in the laboratory and by presence of fruiting bodies, different fungi were observed colonising different parts at different stages of decay (as shown below). Such an observation does seem readily apparent, though to have it confirmed through scientific means affords us with an understanding that is more concrete than merely the anecdotal. Indeed, whilst Trametes gibbosa was not isolated from this beech, the presence of Bjerkandera adusta infers that, at some point in the future, T. gibbosa will be found – it parasitises upon the mycelium B. adusta, before then colonising the wood substrate itself. We are, in a sense, therefore, witnessing fungal warfare.

The different fungi found at different parts of the beech at different stages of the decay process (open in a new tab to see this in a slightly larger size).

Delving further into the notion of fungal warfare, what is essentially meant is chemical warfare. Fungi synthesise and secrete enzymes, which they use principally to degrade wood, though that can also be used to defend territory or attack other fungi. The result of any fungal battle can be one of four things:

• deadlock, whereby neither fungi gains any ground against the competing fungus
• replacement, whereby one fungus loses its territory entirely by the other
• partial replacement, whereby one fungus loses of some its territory to the other
• mutual replacement, whereby the fungi essentially ‘trade’ places with one another and neither gains any net ground

So how does one determine the outcome of any such skirmish, you ask? Unfortunately, there are so many variables in play that even pitting two fungi against one another in a laboratory is only going to give a slight allusion to what really occurs, though there does nonetheless exist a limited hierarchy of combativeness from which we can assume who the victor will be, under most circumstances (see here at 25:09 timestamp).

Of course, even in assessing this we still have so many caveats to throw in. For example, where moisture conditions are drier because the wood is more exposed, Ascomycetes (i.e. Hypoxylon spp.) will have a better time in securing more wood substrate, as they operate effectively under dry conditions. Indeed, the wood qualities of the substrate itself will even play a role – did the tree uptake pollutants during its life or is it exposed to such pollutants currently, for example. More crucially, if a dead piece of wood (or entire tree) is standing and has thus been subject to relatively dry and exposed conditions suddenly falls to the woodland floor, those fungi reigning when the tree was standing will likely succumb to wood-decay fungi adapted to higher moisture levels and cooler more stable conditions.

The next part of this series will be a brief one on bacteria in wood, as discussed again by Lynne Boddy. I hope to have that written up in the coming few days.

Fistulina hepatica’s anamorphic version: Confistulina

Having been informed earlier by a friend that they have an article coming out soon in the journal Field Mycology and having then read the article, I considered it important to build on the information and photos shared in the manner I am most familiar: ramblings. I do not want to spoil the article so please do source the article yourself, though as a form of executive summary, this fungus, Confistulina hepatica, is the anamorphic (asexual) stage of the fungus Fistulina hepatica (beefsteak), which is common on oak and sweet chestnut. I have found it once on beech, though it generally sticks to the first two hosts. This anamorphic stage produces asexual spore, which adorn the fruiting body’s outer portion in abundance. The reason for its emergence is not known, though it might be weather-related. More information is absolutely required from across its host range – not just England!

Disclaimer: The older finds, because I didn’t know what I was looking at, are quite poor photographs. A huge shame, but alas!

Disclaimer 2: I suspect many of these are the anamorphic stage Confistulina hepatica, though none were confirmed so please do not assume they all are. This blog post is simply to begin building a knowledge base that builds of the limited resource pool of present.

The first oak that I’ll share is perhaps one of the more interesting of the bunch because, two years in a row (2015 and 2016), the outwardly anamorphic fruiting body appeared in the same location; albeit, in 2015, the fruiting body was larger. Nonetheless, it infers that, in a crude manner, the same mycelial colony has done the same thing two years in succession. Unfortunately, during 2015, I didn’t get a shot of the whole tree so the location of the arrow points to the 2016 occurrence. However, from the positioning of the ivy, we can see the location is the same.

The arrow points to the location, which is on the southern side of the tree right at the base.

The 2015 version in its rotten glory!

The fruiting body sports what looks like burns, in addition to exuding a tar-coloured liquid alongside the more routinely observed reddish exudations common to young fruiting bodies.

A closer look at the darker liquid from the 2015 version.

And a puncture wound (so it appears) in the fruiting body.

And the smaller 2016 emergence!

Again, we can see the darker liquid exudations. The morphology is also somewhat similar.

Closer still on the 2016 find.

The next series of shots were taken on my mobile phone back in 2015 and again from oak. Once more, the adornment of the fruiting body with exudations, of which some are darker, can be observed. 2016 saw the fungus return, with a vengeance, and in a different position, again, an anamorphic fruiting body.

Yes, this oak has been hammered. Poor tree! (2015)

At the base we can see the fruiting body.

Oozing everywhere!

Looks like something out of Alien, quite honestly!

2016 checking in. What a load of rubbish!

Further round the tree (note that the 2015 location was to the right) sits an anamorphic fruiting body.

A close(ish) look.

Closer still.

And closer yet further.

From here, we go to another 2015 find. This time, the fruiting body was a little elevated on the oak and evidently emanating from an area of burring / accumulation of dormant buds beneath the bark surface. This one quickly became senescent after perhaps a week so whether it’s Confistulina or not is tough to say – I include photos of both times I visited it. It did not reappear in 2016.

The first visit to this fungus, which was very small – maybe 5cm across.

A closer look.

A week later it had senesced.

The remainder of the photos take us into 2016 and most (but not all!) are taken with a better camera, which is good! First, we venture down to the New Forest and look at a well-decayed oak log, upon which a cluster of fruiting bodies sit atop the log.

Yes, yes, this photo was taken with a potato.

A very odd form but once again we can see the tarry liquid.

A side profile. Looks like a toe!

Yep, definitely a toe – a wrangled one, at that.

The next series are taken a month apart (late August and late September). What’s curious with this one is that we can see two anamorphic fruiting bodies and, come September, Laetiporus sulphureus fruiting directly alongside. The host, as can be seen, is oak, which is in a hedgerow of oak and ash.

Fading light caused the blur!

At the base we can see a dueo of fruiting bodies.

The first…

…and the gruesome second.

A month later a wild chicken appeared!

Two, in fact. Here we see the beefsteak and chicken side-by-side.

And here it’s in the distant murk.

Now, we move to a curious case of two fruiting bodies next to one another, again on oak, where one became a teleomorph and the other an anamorph. Why? Who knows. Very interesting, however, as I am sure you can appreciate.

An oak pollard by a swing. Look at the old pollard head.

A duo forming.

Looking pretty similar. Now watch…

…they change! No longer are they twins.

Exactly why this happened is a mystery though I’d really like to know – anamorph left) and teleomorph (right).

A side profile for comparison with the earlier one taken from the same position.

In October of 2016, I came across this majestic oak in a field. On a buttress root was what appeared to be an anamorphic fruiting body of Fistulina hepatica, which we can observe below.

Yup – majestic.

Also majestic??? (not sure!!)

Eh, nope. A bit more ugly, to be fair. Has the outward character of an anamorph though please don’t assume it is (wasn’t confirmed via microscopy).

Lastly, here’s one I suspect on sweet chestnut. I didn’t return to check how it did, though this year I’ll certainly keep more of an eye out and be more thorough in my inspections of the samples! Please share any examples you might have found of this, too – it’s important we build up a knowledge base.

A lovely old coppice stool.

Here sits the sample.

Whether this is or is not is tough to say, though it does resemble an anamorphic stage somewhat.

Interesting cases of wood-decay fungi

I have been absurdly busy so haven’t been blessed with the time to get some blogging in, though I have been graced with thirty minutes of time this evening so without any further utterings we’ll delve right into the good stuff – trees and fungi (in my usual frenetic and incoherent manner). Plus, listening to some early Hawkwind has really got me in the mood to do something useful!

The cases are all from an absolutely splendid park down in Maidstone – Mote Park. Honestly, if you live anywhere near there, do pay it a visit and explore as much as you can (it’s massive!). The sheer abundance of mature and veteran trees provides for a magnificent display of fungi and, so I am told, there is a need to record the saproxylic insects on site on the many monoliths and moribund trees.

To kick this post off, I take you to a very interesting case of Pseudoinonotus dryadeus on oak – three of them, all of which are within 8-10m of one another and share a crown. All fruitings of the fungus are historic though its presence on all three trees makes for some tempting considerations – namely, the synchronicity of fruiting (are they similar genotypes?) and the means of colonisation (spore or something else?). Indeed, I can only infer some sort of fungal mysticism or sorcery in positing both aspects for consideration (there is no proof of either, per se), though it did make me think. Perhaps it will make you readers think as well! (!?)

The recipients of the Manchurian Candidate!

Exhibit one!

At the base (to the left).

Quite an old bracket but a bracket nonetheless. Lovely buttressing, too.

Exhibit two. More brackets and more buttressing.

Shame these got yanked off, too.

Exhibit three! SOme glorious buttressing here, yet again. Thus the fungus gets its common name: the Eiffel Tower fungus.

Old, dead (not really but who cares for semantecs?) but not forgotten.

And then…and then…more Pseudoinonotus dryadeus – literally 100 yards down the same path. Oh how Mote Park delivers! This example also really does demonstrate the magnificent buttressing induced by its decay on oak, as you’ll see.

Would you then believe it? Essentially opposite (no joke) were two colossal beech trees fenced-off (as if that ever stopped me??!) that, as anyone who has seen mature or veteran beech buttressing all over the place like egg whites pour out of a broken egg when broken too aggressively (nice analogy? – likely not), drew me in. Was I disappointed? Not at all! Ganoderma australe and Meripilus giganteus all over the option.

Good cop (right) bad cop (left) – something something pun something something copper beech and tell better jokes

The copper beech to the right with roots all over the option.

Ganoderma australe and Meripilus giganteus – dual decay. Decay squared? That raises a good thought – is decay by more than one fungus simply a cumulative issue or instead a geometric or even negatory issue (i.e. is decay of two types ‘less serious’ than from one only)? Question galore and no answer. Someone ask an expert!

Merip (foreground) and Gano (background). Also plenty of blades of grass for the monocot enthusiasts who stumbled across this blog because I wrote the word monocot.

Ganodeerma australe being illuminated by a sunburst.

The diddy little brackets further up the stem weren’t blessed with sun.

And between some more buttresses there were some more Ganodermas.

Onto the plain old beech now. Exquisite buttressing here!

Did someone say fungi?

Nope – nothing to see here.

Nor is there anything to see here. I’m just tired of writing captions!

Oh look, finally. Something. Some nice husks. Probably some Ascomycetes on them (Xylaria carpophila).

To finish up, because I’m getting tired and I am up early tomorrow, here’s something to sit on whilst you ponder the plethora of ultimate questions spewed forth from my mind with little restraint – a dryad saddle. The host? Not sure – lots of ash about though one can never rule out sycamore (unless you’re in the middle of a Douglas fir plantation?). These had actually already over-matured, which means you can see dryad saddle (i.e Cerioporus squamosus – named, prior to that, Polyporus squamosus) out there if you look!

Ganoderma australe on larch (Larix decidua)

An interesting relationship going on here, which has been confirmed as Ganoderma australe colonising a larch specimen through microscopic analysis by a professional mycologist. This particular larch is wonderfully clad with ivy, though is still alive (just!). I came across this approximately a week ago and was quick to get it assessed, given the rarity of the relationship.

Not much to add here, besides reiterating it being a very infrequent occurrence – if at all recorded before and subsequently confirmed, in the UK. Cool, eh!

A trip to Aldenham Country Park – trees and fungi

With the weather remaining fair, in spite of the onerous musings spouted from the verbal orifices of the meteorological office, getting out at the weekend to explore new sites is still very much on the cards. Today, a group of us went over to Aldenham Country Park in north-west London, to search for interesting fungi on trees; as if a weekend would yield any other result!

We started the day by doing something socially reprehensible: bringing in fungi collections for display. As the below photos show, my collection is growing in extent, though is dwarfed in literal size by another collection, which essentially involves monster brackets that are, in some cases, still clinging to the very substrate that provided them with their life.

My collection, consisting of fruiting bodies of fungi including the genus Ganoderma (top left), the genus Trametes (bottom left), Fomes fomentarius (top middle), the genus Phellinus (bottom right) and Coriolopsis gallica (bottom right).

Another collection, set up almost like a demonstration of the solar system (with the Perenniporia fraxinea on the poplar being the sun, of course!), including Fomes fomentarius (a monster one), Daedalea quercina and, as stated, the Perenniporia fraxinea on the poplar wood.

Before sharing some finds from today, it’s almost important to share some images of more cross-sectional decay as caused by Ganoderma pfeifferi. For those of you with a memory that stretches back beyond a mere seven days, you might recall a recent post I made showing a decay cross-section on a failed beech. Below, we see how the fungus’ activity within a branch stub of a beech has resulted in zonal decay, which is somewhat comparable to the other example shared recently – particularly, with regards to the rosing pattern.

A tiny Ganoderma pfeifferi within the opening of a branch stub wound on beech.

The cross-section of decay produced by the fungus.

And so, on with the walk we did, quite early on we wandered past an old poplar stump with some quite extensive Rigidoporus ulmarius decay. Indeed, as is quite routine with this fungus, the internal hollow was clad aplenty with small brackets, whilst the outside sported a much more sizeable fruiting body still in an active phase of its existence. Evidently, a new hymenium has recently been laid down, suggesting that this fungus is soon ready to begin producing spore for the coming season.

Rigidoporus ulmarius acting as a saprotroph on this senescent stump.

Quite a nice one, actually! Good morphology.

Looking inside the hollow, not only can we see that it is used as a bin, but also to house many small fruiting bodies of this fungus.

Very soon after this sighting, a fallen poplar log with Oxyporus populinus was discovered. I admit to only having seen this fungus twice, of which this find was one, so for me this was particularly exciting. In fact, the single fruiting body was rather massive and easily discernible by the quite brilliant tube layers separated by narrow bands of mycelium. Almost directly adjacent to this was a fruiting body of Ganoderma applanatum, as could be determined morphologically by the very thin cuticle atop the bracket (that is crushed easily and cuts very easily) and the extensive damage to the fruiting body, as caused by the yellow flat-footed fly Agathomyia wankowiczii.

A poplar log hides amongst ivy.

On one of the cut ends sits this large fruiting body of the fungus Oxyporus populinus.

The demarcations between each growth spurt are incredibly distinct, in this fungus.

A fruiting body of Ganoderma applanatum also sat nearby, on the same log.

Underneath, we can see the distinct gall structures caused by the yellow flat-footed fly.

We can also see the internal damage caused by the fly, as it develops into its adult form and leaves to lay eggs elsewhere. The very thin upper cuticle can also be seen, which is thicker on Ganoderma australe.

Following the sighting of copious amounts of Daedaleopsis confragosa, our attention was then drawn to a rather sorry-looking beech tree over a well-used footpath. Upon close inspection, both Kretzschmaria deusta and the rhizomorphs of Armillaria mellea could be found, which certainly puts the longevity of this beech as is into doubt. To be honest, in all likelihood it’ll be monolithed, in order to still provide habitat but with the risk removed.

It even leans over the footpath!

Both the anamorphic stage of Kretzschmaria deusta and cambial necrosis caused by Armillaria mellea can be seen, in this image.

Not looking good for this beech!

Around the proverbial corner (it was more like a ten minute trundle) from this beech stood a massive stump of an old poplar. In its prime, this would have been a tree operating on beast-mode, though is now far more modest in size. However, to make up for its literal demise, it now is host to the fungus Trametes gibbosa, which can be seen around one of the two stems.

A fortress of nettles guards this poplar stump.

Too bad they can’t defend against a zoom lens and / or walking boots and jeans!

Some fresh brackets adorn the opposite side of the stump.

Quite pretty, to be honest!

Delightfully, this stump also housed a bird nest, which I found only by pure chance when noticing what looked like chocolate mini-eggs! Tucked away impossibly well within a bark crevice was a small robin’s nest (I think), complete with four eggs. Hopefully, this stump will offer enough privacy to enable the chicks to develop well and not get picked-off by predators.

The arrow shows where the nest is, as it’d otherwise be impossible to see!

There were four eggs in this tiny nest. Such a great place for shelter and quite absurd that I came across it!

Once we had come across yet more Daedaleopsis confragosa, which I was busy photographing, a friend spotted a single Sarcoscypha coccinea (scarlet elf cup). Somehow, this is the first time I have seen this fungus and I can understand why it’s such a popular one! An absolute gem.

Cheeky! Hiding away under nettles. Almost doesn’t want to be discovered…

Nature’s very own satellite dish!

And then came something I found very interesting: my first ever sighting of the fungus of willow known as Phellinus igniarius. Upon what was either a crack willow or white willow, a few fruiting bodies had grown and the decay had since led to failure of an upper limb, which has since been cut up and left on the ground. The resulting abundance of fruiting bodies on both the tree and sawn logs is a testamenrt to the extensive colonisation of this fungus within the host. The largest bracket, which was a casulaty of the failure, in fact did not senesce and instead reiterated its growth so that the hymenium and tube layer re-grew at an angle perfectly parallel with the ground (known as geotropism / gravitropsim).

A willow not unlike any other willow – battered by the elements.

Oh but wait – a fungus! Surely it’s a Ganoderma…

…nope!

As we shall see by what is on the floor, upon these logs…

…Phellinus igniarius! Surprise! (assuming you didn’t read the text and look only at the pictures)

Quite a significant number of new sporophores are forming, following the fragmentation of this limb.

Around an old branch tear sits a single fruiting body, however.

Not unlike a young Fomes fomentarius, really!

And the main bracket has not perished!

Using flash photography (literally), we can see the white spore print beneath the reiterated growth, following the change in orientation of this bracket.

To round off, I share a diabolically grotesque example of Ganoderma resinaceum upon Turkey oak. Enough to challenge the gargoyle statues of various catacombs (in both video games and real life, if there exist any!) for the prize of what’s the most vile in appearance, and we’re not talking about the Turkey oak here, this fungus is clearly a shadow of its former self. Nonetheless, it is important we can still identify them in such aberrant form, if we are to appropriate diagnose issues and enact management regimes. Thus, as a sort of encore, I present to you…

Nice enough tree, eh!

But what is that at the base!?

Uhh………??

Yeah; uhhh…….?

Ganoderma resinaceum!

Wood-decay fungi in the Antarctic Peninsula

No, this title is not a click-baiting one – it’s wholly serious!

Courtesy of some recent research undertaken by scientists on Deception Island, which is an actively volcanic island in the archipelago that forms the South Shetland Islands, we now have a fascinating glimpse of the fungal activity that can be found upon the abanonded 19th and early to middle 20th century timber-framed buildings found upon the island’s shores. Indeed, with 57% of the island being covered by glaciers, these buildings were built along the coastline and were used for research and European whaling purposes (Whalers Bay), up until the Chileans departed from Pendulum Cove in 1967. Nowadays, it’s a tourist area for those that quite fancy spending large sums exploring such a desolate island, as well as a research base for Spanish and Argentinian scientists.

Decaying timbers on the island. Source: The Planet D.

As regards to prior research on the historic timber buildings upon the island, research has uncovered fungal decomposition of the timber by Ascomycete fungi, thereby inferring some timber has begun to degrade via a soft rot. However, brown and whit rot fungi had not previously been identified on the island to any marked degree (one fruiting Pholiota sp. sample was found on the wood of a buried whaling vessel in 1967), and thus this research sought to ascertain whether fungal diversity was more appreciable than previously understood. At this point, it is also worth noting that some Asocmycetous fungi are indigenous to the island (such as Cadophora spp.), being found as saprotrophs on the plants growing freely on the island. Moreover, the research enabled for an insightful look into fungal ecology in a location where soil temperature range from below freezing to as high as 90°C.

Using two sites on the island where such timber-framed buildings could be found, which were Whalers Bay and Pendulum Cove (see the below image for rather precise locations), very small wood fragments from the timber-framed buildings (largerly made of Pinus spp. and Picea spp. timbers, though also Betula spp.) were sampled (188 from Whalers Bay and 30 from Pendulum Cove) and taken back to the laboratory under sterile conditions for assessment in a growth medium comprised principally of malt extract agar. Following the placement of the samples within the agar for a few weeks and the subsequent transfer of growing mycelium into pure cultures, genetic analysis was undertaken to ascertain what fungi were present within the wood samples.

The two research locations used for the study (as denoted by the red arrows).

In total, 326 isolates were found from the total 218 sampled wood fragments. Indeed, as was probably expected, the large majority (79%) of the isolated were of Ascomycete fungi from 53 different taxa that were causing a soft rot. However, quite interestingly, 15% of samples (equating to 11 different taxa) were from the Basidiomycetes division and a few (6%) also belonged to the Zygomycota.

From the Basidiomycetes, which are probably more well-known to those who read this blog, 18% of isolates were from the genus Pholiota. Indeed, this genus is a frequently identified one in the UK and further afield, and the genetic analysis revealed that one particular clade of the genus was of the species Pholiota multicingulata, which was found exclusively at the Pendulum Cove site where the Chilean undertook their scientific research up until the late 1960s. Found across the South Pacific and notably in New Zealand, its presence in the Antarctic Peninsula is considered to be as a consequence of infected timbers brought over by the Chileans.

Other common wood-decay Basidiomycetes known to arboriculturists included Coprinellus micaceus and Coniophora puteana, though only one sample of each was identified from genetic analysis – both considered to have been introduced by the Europeans during whaling escapades. Postia pelliculosa, a brown rot fungus of gymnospermous wood, was also identified – as was Jaapia argillacea, which is a rare fungus within Europe and thus its finding at Whalers Bay presented the authors with some surprise.

A group of caps of the fungus Pholiota multicingulata growing on deadwood. Source: Mushroom Observer.

With reference to the other fungal genera and species found, species from the genus Cadophora wthe most abundant and amounted to 20% of all identified fungal samples. Furthermore, Hypochniciellium species accounted for 13% of the total sample count and Phialocephala 7%. Pholiota, as a genus, contributed only to 4% of the total number of records. Importantly, it was also found that many of the historic timbers were extensively decayed by the same fungi at both sites, inferring potentially a long-standing decay arising from a fungal metapopulation on the island. Decayed timbers were found most observably around the locations where the timber was in contact with the soil, perhaps due to a higher moiture content within the wood facilitating for more effective hyphal ingression into the timbers and the localised warming of soils because of volcanic activity. At the Chilean base, white rots of the sampled timbers were found only just beneath the soil surface, with brown and soft rots being identified on timber from both sites in wood exposed to ambient conditions.

As alluded to within the preceding text, it is highly probable that the fungal isolates from the two sites were introduced alongside human migration to Deception Island. Certainly, there have been plenty of opportunities for spores to be deposited on the island, given the whaling and research activities over the past two centuries. Importantly, the current phenomenon of tourism to the island will facilitate potentially in the emergence of new fungal species, which makes future research prospects exciting as the inherent isolation of the site would have rendered it almost impossible for exotic fungi to have otherwise arrived on site and – assuming they had – there would have been no timber for them to colonise. In this respect, the research undertaken on this island outlines a very critical biosecurity risk: human migration.

A further aspect of interest from the results is that native Ascomycetous fungi to the island, which were found to be acting saprotrophically on native plants, broadened their host range to that of the exotic timbers introduced. Thus, the notion of fungal adaptation alongside a change in the potential inoculum base is given credence, which can again be related to current issues with fungal pathogens of trees within Europe and further afield.

Source: Held, B. & Blanchette, R. (2017) Deception Island, Antarctica, harbors a diverse assemblage of wood decay fungi. Fungal Biology. 121 (2). p145-157.

Some fungal finds from the week

Some say it’s written in the stars, though the only experience I have had with braille is from select old Nintendo games from the 1990s and early 2000s (revealing my age a little here!). Others say it’s just annoying. I’d probably agree with the latter! Regardless, here we have it: more pictures of fungi on trees.

As always, I keep my eye out for some interesting finds. This week has been pretty decent on the fungal side of things, though given the time of year only the perennial polypores are really observable – asides from the odd Flammulina velutipes / elastica and some enterprising Pleurotus species. Nonetheless, for the sake of showcasing unique finds and for educational purposes, here are a few species of polypore and some common agarics.

Firstly, we have a rather cool deck of Ganoderma resinaceum brackets around a rather pronounced buttress on an oak (Quercus robur). The fruiting between the two buttress roots is likely indicative of good reaction growth that is well-compartmentalised, which in turn infers respectable and probably sound (i.e. free of appreciable decay) buttressing from which the oak is supporting itself. We then have some shots of a rather aberrant duo of Trametes gibbosa on what is probably an old sycamore (Acer pseudoplatanus) stump, some Kretzschmaria deusta on (again!) sycamore, Ganoderma australe on a fallen ash (Fraxinus excelsior) and finally some Flammulina sp. and Pleutorus ostreatus on a very decayed stump of an unknown deciduous broadleaved species.

Trees in the ecosystem pt IV: Trees & arthropods

The arthropods are vast in terms of species, and include ants, beetles, butterflies, mites, moths, spiders, and so on. Therefore, covering the entire spectrum of arthropods in this section is impractical, though the general provisioning by trees will be outlined and species will be used to illustrate given examples.

Many arthropods are considered to be saproxylic in nature – they principally utilise dead woody material (both standing and fallen, in both dead and living trees) as habitat, for at least part of their life cycle, though they may also rely upon fungal sporophores associated with the presence of deadwood, as is to be detailed below (Gibb et al., 2006; Harding & Rose, 1986; Komonen et al., 2000). Of all the saproxylic arthropods, beetles are perhaps the most significant in terms of the proportion occupied of total saproxylic species worldwide (Müller et al., 2010), though saproxylic flies also feature in great numerical abundance (Falk, 2014; Harding & Rose, 1986).

Beetles may be either generalist or specialist in nature (on either broadleaved or coniferous hosts), and they will normally require a host with an abundance of deadwood (or large sections of coarse woody debris) usually over 7.5cm in diameter that resides within an area typically not heavily shaded (Müller et al., 2010; Siitonen & Ranius, 2015). This may be, in part, due to many beetle species (in their adult stage) requiring nectar from herbaceous plants, which would be lacking in woodland with significant canopy closure (Falk, 2014; Siitonen & Ranius, 2015). This means that veteran trees amongst wood pasture and parklands (including in urban areas) may be particularly suitable (Bergmeier & Roellig, 2014; Harding & Rose, 1986; Ramírez-Hernández et al., 2014; Jonsell, 2012; Jørgensen & Quelch, 2014), though this is not at all a steadfast rule as species may also be found abundantly in (perhaps more open) woodland, and particularly where there are large amounts of veteran trees and deadwood – around 60 cubic metres per hectare, according to Müller et al. (2010). Granted, they are found particularly in older (mature to veteran) trees, including within cavities that possess wood mould, water-filled rot holes, dead bark, exposed wood, sap flows, fruiting bodies (of fungi and slime moulds), mycelia of fungi, dead branches, and dead roots (Carpaneto et al., 2010; Falk, 2014; Harding & Rose, 1986; Siitonen & Ranius, 2015; Stokland et al., 2012). Beetle species may also not necessarily associate preferentially with a species (or group of species), but with the conditions aforementioned that are present within a tree (Harding & Rose, 1986; Jonsell, 2012). At times, preferable conditions may be an infrequent as one veteran tree in every hundred (Harding & Rose, 1986).

A veteran oak tree that is of prime habitat for a variety of organisms.

Despite this, species preference is observed. For broadleaved obligates, heavier shade may be more necessary, and in such instances there is a closer affinity of the beetles with fungal mycelium. Because fungi tend to produce more mycelium in cooler and more humid conditions (though this does, of course, vary with the species), the broadleaved obligates may therefore be found normally in greater abundance where conditions are more suited to fungal growth, and their presence may thus be associated with a canopy openness of as little as 20% (Bässler et al., 2010; Müller et al., 2010). This is, of course, not a steadfast rule, and many open wood pastures may support a great abundance of saproxylic beetles (Harding & Rose, 1986).

It is also important to recognise that many species of saproxylic beetle are reliant upon particular stages of the wood decay process. For instance, species that require fresh phloem tissue will only be able to colonise briefly in the first few summers following on from the death of the phloem tissue (Falk, 2014). Other species require significantly-decayed wood in a particular micro-climate, and even of a particular tree species (Harding & Rose, 1986). There also exist intricate associations between species of fungi and saproxylic insects. Inonotus hispidus, which is usually found upon ash, is the habitat for Triplax russica and Orchesia micans, whilst the coal fungus (Daldinia concentrica), also oft found upon the deadwood of ash (Fraxinus excelsior), is the main provider of habitat for Platyrhinus resinosus (Falk, 2014). The birch polypore (Fomitopsis betulina) is also host to numerous species of Coleoptera (Harding & Rose, 1986); as is the polypore Fomitopsis pinicola (Jonsson & Nordlander, 2006; Komonen, 2003; Komonen et al., 2000). This means that these species may be found where there is a suitable population of the fungus’ host species, where sporophores are present and will likely fruit again in the future, across numerous trees, and for many years. Most beetle species rely on oak more so than other tree species however, as oak generally lives for much longer and thus provides a wider array of different micro-habitats, and possesses increased compositional complexity as a result (Harding & Rose, 1986; Siitonen & Ranius, 2015).

A fruiting body of Inonotus hispidus on apple (Malus sp.). This fungus not only creates habitat in the wood that it degrades but also is a direct habitat through its sporophore.

Therefore, the loss of suitable habitat through active management programmes (including logging, and felling trees for safety reasons in urban areas) will have a very adverse impact upon saproxylic beetles, though also certain species of moth, and even species associated with saproxylic insects, including parasitic wasps, solitary wasps (which use beetle bore holes for habitat), and predatory Coleoptera (Harding & Rose, 1986; Komonen et al., 2000). Curiously, research by Carpaneto et al. (2010) concluded that trees that were ranked as the most evidently ‘hazardous’ were host to the most saproxylic beetle species, and their removal would therefore have a drastic impact upon local populations. Similarly, fragmentation of woodland patches suitable for saproxylic populations has led to a decline in the meta-populations (Grove, 2002; Komonen et al., 2000), as has deadwood removal in a managed site itself (Gibb et al., 2006). Interestingly, though not surprisingly, ‘deadwood fragmentation’ also has an adverse impact upon saproxylic insect populations (Schiegg, 2000).

Both ants and termites also benefit from the presence of deadwood. With regards to both, nests will usually form at the base of a tree or at an area where there is at least moderate decay – enough to support a viable population (Jones et al., 2003; Shigo, 1986; Stokland et al., 2012). Ants and termites both follow CODIT (compartmentalisation of damage in trees) patterns in relation to how their nests progress, and thus their territory will increase as fungal decay propagates further into the host. Ants will not feed on the decaying wood of the host however, and will simply use the decaying site as a nesting area. Conversely, termites will feast upon decayed wood and essentially control (perhaps by slowing down) the spread of fungal decay in a manner that provides as much longevity of the host as possible for a viable nesting site (Shigo, 1986). In tropical rainforests, termites are in fact considered to be one of the principal means of wood decomposition (Mori et al., 2014), and thus the provisioning of deadwood habitat is absolutely critical. Without decaying wood within trees therefore, ants and particularly termites will lack a potential habitat, and thus where a stand is actively managed populations may be markedly reduced (Donovan et al., 2007; Eggleton et al., 1995). Of course, termites are not necessarily to be desired when they are invading the wood structure of a property, and therefore deadwood is not universally beneficial (Esenther & Beal, 1979; Morales-Ramos & Rojas, 2001) – at least, when human properties are involved.

Ecologically beneficial? Yes. Economically beneficial? No. Termites can – and do – damage timber-frames buildings, as is the case here. Source: Pestec.

The presence of deadwood may also be beneficial for ground-nesting and leaf-litter dwelling spiders, which can utilise downed woody debris (particularly pieces with only slight decay) for both nesting and foraging (Varady-Szabo & Buddle, 2006). In fact, research by Buddle (2001) suggested that such spiders may more routinely utilise downed woody material when compared to elevated woody material (dead branches and telephone poles) because of the greater array of associated micro-habitats, and particularly at certain life stages – such as during egg-laying, for females (Koch et al., 2010). Furthermore, as fallen woody debris can help to retain leaf litter (or even facilitate in the build-up leaf litter), spider populations are more abundant and more diverse in sites where such woody debris is present (Castro & Wise, 2010). Therefore, where woodlands are managed and areas are clear-cut, spider populations may be markedly reduced in terms of the diversity of species. However, generalist species may benefit from the amount of cut stumps (Pearce et al., 2004). Curiously, Koch et al. (2010) suggest that spiders may perhaps benefit from woodland clearance, because the vigorous re-growth of trees and the higher light availability to the woodland floor (promoting herbaceous plant growth) increases the abundance of potential prey. Despite this, old-growth species will suffer (Buddle & Shorthouse, 2008), and thus the population structure of spider populations may dramatically change.

Soil mites are a further group that benefit from coarse woody debris, though also from hollows and holes throughout the basal region of a tree (including water-filled cavities), and from fungal sporophores and hyphae associated with wood decay (Fashing, 1998; Johnston & Crossley, 1993). Typically, termites will use fungi and insects found within the wood as a food source, and the wood structure itself will provide for an array of niche micro-habitats that are critical at different life stages of a mite. Certain mite species are obligates that associate with coarse woody debris exclusively, and may in fact only be associated with certain species’ woody debris. Additionally, mites may utilise woody debris and hollows within trees to parasitise upon other species using the ‘resource’, with both lizards and snakes being parasitised by mites following their frequenting of such resources. Beetles may also be parasitised, though the mite in such an instance may use the beetle as a means of entry into woody debris (Norton, 1980).

It is not just deadwood that arthropods will utilise, however. Foliage, both alive and abscised, is also of use (Falk, 2014). For example, the ermine moth (Yponomeutidae) will rely upon the living foliage of a host tree as a food source, and the bird cherry ermine moth (Yponomeuta evonymella) is one example of this. During late spring, larvae will fully defoliate their host Prunus padus, before pupating, emerging, and then laying eggs upon the shoots ready for the following year (Leather & Bland, 1999). Many other moth species will, during their larval stage, also behave in such a manner and thus defoliate their host – either entirely, or in part (Herrick & Gansner, 1987). Other species may alternatively have larvae mine into the leaf and feed upon the tissues within (Thalmann et al., 2003), such as horse chestnut leaf miner (Cameraria ohridella). Flies, including the holly leaf-miner (Phytomyza ilicis), will also mine leaves in a similar fashion (Owen, 1978). Ultimately however, the same purpose is served – the insect uses the living tissues of a leaf to complete its life cycle, and fuel further generations.

Bird cherry ermine moth having defoliated an entire tree. Source: Wikimedia.

Fallen leaf litter, as briefly touched upon earlier when discussing spiders, may also be of marked benefit to many arthropods. Ants, beetles, and spiders are but three examples of groups that will utilise leaf litter as a means of habitat (Apigian et al., 2006). Beetles will, for instance, rely upon leaf litter to attract potential prey, though also to provide niche micro-climates that remain relatively stable in terms of humidity, light availability, and temperature (Haila & Niemelä, 1999). Their abundance may, according to Molnár et al., (2001) be greatest at forest edges, perhaps because prey is most abundant at these edge sites (Magura, 2002). Of course, this does not mean that edges created through artificial means will necessarily improve beetle populations, as research has shown that there are few ‘edge specialists’ and therefore populations usually will go into decline where there has been significant disturbance. Unless management mimics natural mortality events of forest trees, then constituent beetle populations may thus suffer adversely (Niemelä et al., 2007).

With regards to ants, Belshaw & Bolton (1993) suggest that management practices may not necessarily impact upon ant populations, though if there is a decline in leaf litter cover then ants associated with leaf litter presence may go into – perhaps only temporary (until leaf litter accumulations once again reach desirable levels) – decline (Woodcock et al., 2011). For example, logging within a stand may reduce leaf litter abundance for some years (Vasconcelos et al., 2000), as may (to a much lesser extent) controlled burning (Apigian et al., 2006; Vasconcelos et al., 2009), though in time (up to 10 years) leaf litter may once again reach a depth suitable to support a wide variety of ant species. However, the conversion of forest stands into plantations may be one driver behind more permanently falling ant populations (Fayle et al., 2010), as may habitat fragmentation (Carvalho & Vasconcelos, 1999) – particularly when forest patches are fragmented by vast monoculture plantations of tree or crop (Brühl et al., 2003). The conversion of Iberian wood pastures to eucalyptus plantations is one real world example of such a practice (Bergmeier & Roellig, 2014).

Also of benefit to many arthropods are nectar and pollen. Bees, beetles, butterflies, and hoverflies will, for instance, use nectar from flowers as a food source (Dick et al., 2003; Kay et al., 1984), and generally (but not always) a nectar source will lack significant specificity in terms of the insect species attracted (Karban, 2015). Despite this, different chemicals secreted by different flowers, and the toxicity of certain nectar sources to particular insects, means certain tree species may only be visited by certain insect species (Adler, 2000; Rasmont et al., 2005). Tree diversity may therefore be key to sustaining healthy insect populations (Holl, 1995), and where species may prefer to frequent herbaceous plant species the presence of a diverse woodland canopy above may still be very influential (Kitahara et al., 2008). This may be because a diverse array of woody plant species increases the diversity of herbaceous species. At times, pollen may also be a reward, as may (more rarely) a flower’s scent. Karban (2015) remarks that all are collectively dubbed as ‘floral rewards’.

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Fungal foraying in the New Forest

Both a friend and I had the pleasure of trecking around parts of the New Forest with a well-respected mycologist at the weekend. As you can very well imagine, we came across a wide variety of fungi – notably corticioids and polypores. Unfortunately, the poor light levels rendered getting decent photos of corticioids quite tricky (many were on standing hosts), so beyond some rather frequent Amylostereum laevigatum, Byssomerulius corium, Cylindrobasidium evolvens, Schizopora paradoxa and Vuilleminia comedens (which themselves were tricky to get good photos of) there weren’t many other opportunities. Regretfully, I therefore share below some images of poroid fungi and some larger Ascomycetes, though I hope you can nonetheless appreciate the finds!

We’ll start with a really cool find and a find that is my first for the species – the candlesnuff fungus, though not the stereotypical one! In this case, we have the candlesnuff of beech husks, known as Xylaria carpophila. As is evident in the species epithet, it likes to munch away on seed husks. Unlike its companion, it’s also much more slender and harder to spot. Your best shot is to peer into the leaf layer on the forest floor and hunt for some white hairs emerging from between leaves and from exposed husks.

We now move on to some splendid examples of Kretzschmaria deusta, in both its anamorphic and teleomorphic state. The first set of shots is showing ‘kretz’ tucked neatly within a very tight compresion fork of a large beech, with cambial dieback stretching quite far up the insides of the stems. Certainly a site for future failure! The following images show anamorphic fruiting bodies upon / ajacent to Ganoderma australe (again on beech – note that we were also told that Ganoderma applanatum is genuinely rare in the New Forest, with most finds being Ganoderma australe) and then on the underside of a very decayed beech log and finally a failed end. As both my friend and I remarked, this trip changes our perspective on the fungus, and we now recognise it as an important species in the effective decomposition of decaying wood from – or upon – dead (parts of) the host tree.

Moving towards the Basidiomycetes, the first set of photos to share is of Ganoderma pfeifferi on – you guessed it – beech! Honestly, this tree species is superb for fungi and probably the best of all native trees as regards to diversity and abundance. Some of the brackets on this beech has at least 20 sets of ‘growths’, suggesting they could be up to 20 years old!

Rather similar to the Gano is this duo of Fomes fomentarius. On a large dysfunctional lateral of a beech (who would have guessed…!?) that has subsided to the ground, we can see the two sporophores hiding amongst brash.

To round off (as I’m running out of time to write this post after a busy day at work!) I also share some Phellinus ferreus (now known as Fuscoporia ferrea). I won’t even bother noting the host as you’ll know already, and in both cases the sporophores are upon dead parts fallen from the host. Do note that the fungus also occurs on attached but dysfunctional (i.e. dead) parts of living hosts of species other than beech, too!

Trees in the ecosystem pt III: Trees & birds

Trees, and more specifically groups of trees, are of significant importance to avifauna. Their provisioning of food, either directly (fruits, nuts, blossom) or indirectly (attracting insects and other types of prey), in addition to their ability to act as a nesting site, roosting site, or otherwise, makes tree presence absolutely crucial to a successful and healthy bird population. Of course, different bird species will respond favourably to different tree species and stand structures, and this – amongst other aspects – is discussed below.

As alluded to above, the structure of a woodland stand will have a marked impact upon bird species present within a site. For example, active coppice woodlands will provide habitat to bird species not frequently (if at all) found in old-growth stands or even coppice of over 11-12 years since the last cycle (Fuller & Green, 1999), though wood pastures, forest glades, and even agricultural fields bordering woodland may provide niche habitat for particular birds, of which many may be associated with grasslands and the transitional zone (ecotone) between grassland and woodland (Costa et al., 2014; Hartel et al., 2014; Hinsley et al., 2015) – including the nightingale (Luscinia megarhynchos) and the chiffchaff (Phylloscopus collybita), in the UK.

A nightingale perched upon a tree branch. Source: Wikimedia.

Stand structure will also impact upon the growth of young chicks, with some species growing better in older stands and others in younger stands (Hinsley et al., 2002). This is due to some bird species feeding up in the crown of a tree, whilst others forage near to ground level. For ground foraging birds, there will likely be a lack food sources available, where canopy closure has occurred; as will there be a lack of ground-cover for nesting (Fuller & Green, 1999). Similar conditions can however be created by grazing mammals, with deer being a notable example in the UK and North America (Gill & Fuller, 2007; McShea & Rappole, 2000). Furthermore, ground-nesting and ground-foraging birds are also more sensitive to disturbance, and therefore their presence may also be limited in high-traffic areas and locations where predators (and herbivores – including deer and other grazing animals) are found in abundance (Ford et al., 2001; Fuller, 2001; Martin & McIntyre, 2007; Schmidt & Whelan, 1999). Vehicular traffic may also be an issue, and notably when a woodland site runs adjacent to a busy road (Reijnen et al., 1995). Research has therefore suggested that established woodland sites, free of major disturbance and possessing greater structural diversity than succeeding woodlands or coppiced woodlands, will provide for a greater array of bird species (Gil-Tena et al., 2007; Hinsley et al., 2009), though even amongst structurally similar habitats the species composition of a site may have a marked impact upon bird species diversity (Arnold, 1988).

In fact, a greater mix of tree species may bolster bird diversity, as was demonstrated by Díaz (2006) when bird species in pinewoods and oakwoods were found to be lower than in a stand containing both species. By a similar token, species composition may impact upon bird species that forage amongst foliage for arthropods and other food sources. Investigations by Robinson & Holmes (1984), for instance, demonstrated that the distribution of foliage within the crown of a tree will impact upon the foraging ability of particular birds; as will, but only at times, the size (and other characteristics) of foliage. Similarly, as particular tree species will attract certain arthropods, the species composition of a stand will impact upon the constituent bird species and their abundance. Thus, a mosaic of habitats that is mainly – but not at all exclusively – mature and mixed woodland may be most preferable if seeking to attract many species of bird. Such woodland need not be extensive in canopy cover however, as wood pastures attract such an abundance of insects that insectivorous birds can be found in great abundance, assuming the land is not treated with pesticides (Ceia & Ramos, 2016).

Building upon the concept of stand structure, the presence of standing deadwood is also important for birds. Whilst cycles of management are beneficial for some species, those that rely on old-growth stands with minimal management intervention are heavily reliant upon standing deadwood as a source of habitat (Drapeau et al., 2009). Those species which nest within recently-dead snags (or dead portions of living trees), including the woodpecker (Smith, 2007) – though also many species of secondary (successional) cavity-nesting species – will far more readily be found in stands of significant age that contain tracts of large (over 30cm DBH) potential habitat (Bednarz et al., 2004; Remm et al., 2006). Granted, not all standing deadwood is equal. For example, in the forests of British Columbia, USA, woodpeckers will preferentially frequent trembling aspen (Populus tremuloides), to the point that 95% of all cavity nests are found within this species – even in spite of its limited abundance within forest stands (Martin et al., 2004). Similarly, forest edge standing deadwood may be more preferable for some cavity-nesting birds (Remm et al., 2006), and at times standing deadwood created through recent forest fires may be most suitable (Nappi & Drapeau, 2011; Saab et al., 2004). Therefore, post-fire salvage logging may be detrimental to cavity-nesting birds (Hutto & Gallo, 2006). It should however be noted that not all cavity-nesting birds will create their own cavities from sites of decaying wood, and may instead use natural cavities that have formed at the branch junctions of snags (Remm et al., 2006).

A parakeet making this cavity within a large branch of London plane its nesting site. Source: Authoor, 2017.

The benefits of standing deadwood extend beyond the mere provisioning of viable nesting sites, however. They also act as suitable feeding platforms for many bird species, again including the woodpecker. In particular, decaying snags with lower wood densities will provide the suitable conditions for foraging (Farris et al., 2004; Weikel & Hayes, 1999). This is because such decaying snags attract saproxylic insects, which are viable sources of food for birds (Drapeau et al., 2009). However, this does not necessarily mean that such snags should be extensively degraded, as research has also suggested that snags with only some deterioration (through fungal decay and fire damage) are optimal for foraging (Nappi et al., 2003; Nappi et al., 2010). Without question, larger snags will normally provide for greater foraging potential, and not only because of the greater diversity of foraging site types (small branches, large branches, and the stem), but also because of the greater surface area upon which birds (including woodpeckers) may forage (Smith, 2007). By a similar token, snags can also be used for perching and communicating (Lohr et al., 2002), which could be of advantage to predatory birds and breeding birds, respectively.

Coarse woody debris (fallen deadwood) upon the woodland floor can also be of use to bird species. Lohr et al. (2002) identify such downed woody debris as being important for foraging, perching, and communicating; albeit at a generally lesser rate than standing deadwood (snags), though not always (Spetich et al., 1999). Understorey bird species may also utilise downed stems for nesting. Where coarse woody debris is removed therefore, bird species diversity and population abundance will almost certainly suffer (Riffell et al., 2011).

A bird that has used these Ganoderma brackets, which themselves reside between two buttress root of horse chestnut, as a nesting site. Source: Author, 2016.

Of course, it is not only standing (snags) and fallen deadwood (coarse woody debris) that are of benefit, but also the decaying wood of living trees. Typically, it will be trees with more extensive internal decay and thus thinner strips of functional sapwood that will be more preferable to cavity-nesting birds (Losin et al., 2006). However, it is the larger individuals within a stand that will again be more readily frequented, with research by Conner et al. (1994) finding that the red-cockaded woodpecker (Leuconotopicus borealis) requires decaying heartwood of 15cm in diameter (or greater) to form a viable nesting site. Such extensive and suitable heartwood can usually only be found in older trees (Hooper et al., 1991), which therefore outlines the importance of conserving old-growth stands and retaining mature individuals during harvesting operations. In fact, red-cockaded woodpeckers will seek-out older trees wherever possible, because of the greater heartwood extent found within such trees (Rudolph & Conner, 1991).

Furthermore, akin to standing deadwood, not all trees are equal in their provisioning of viable habitat for cavity-nesting birds. Certain bird species may favour particular trees that are being decayed by specific heart-rotting fungi. Using the red-cockaded woodpecker as an example again, it is understood that Pinus spp. being decayed by the heart rot fungus Porodaedalea pini (syn: Phellinus pini) are highly desirable sites for nesting for the species (Jackson & Jackson, 2004). Similarly, the great spotted woodpecker (Dendrocopos major) will commonly frequent large oaks complete with large tracts of decaying heartwood and fungal sporophores (Pasinelli, 2007).

Birds may also utilise the tree’s flower (florivore), fruit (frugivore), and seed crops (granivore), as a source of food. In fact, birds are considered the most significant dispersal agent of a tree’s fruit and seed crops, which is testament to the important relationship birds and trees have in this regard (Howe & Primack, 1975; Sedgley & Griffin, 1989). Certain birds are even associated largely with specific tree species, such as how the Eurasian jay’s (Garrulus glandarius) main food source is the acorn of the oak (Quercus spp.) (Vera, 2000). Open-grown mature trees may typically harbour the greatest crops (Green, 2007), and parklands, pastures (Galindo-González et al., 2000), savannas (Dean et al., 1999), and even gardens and orchards (Genghini et al., 2006; Herzog et al., 2005) may be home to many such trees.

A jay proudly carrying an acorn. Source: Phil Winter.

Unfortunately, pressure on these environments, be it in the form of grazing, chemical applications (particularly in orchards), or simply human activities, has led to declines in constituent bird populations, in some instances (Bishop et al., 2000; Elliott et al., 1994; Thiollay, 2006), though historically orchards amongst extensively-grazed wood pasture were highly valuable for bird species, which would feed upon the abundance of insects (Barnes & Williamson, 2011; Oppermann, 2014). Beyond the open-grown tree however, copses, woodlands, and great vast forests all have the ability to harbour birds, courtesy of their crops. Secondary and regenerating stands may perhaps provide for the greatest abundance and diversity of food for birds, given that the greater light levels provide suitable conditions for a wider range of plant and tree species that flower and subsequently produce fruits (Martin, 1985).

Additionally, the better light conditions mean such fruiting species are likely to be healthier and produce bigger and more plentiful fruits, which is of importance to foraging birds that seek out proteins, fats and carbohydrates from tree crops (Sedgley & Griffin, 1989) and insects attracted to flowers. One example of this would be how the plentiful silver birch (Betula pendula) stands, in Belfairs Wood (Essex, UK) during the 1970s, over-masted quite significantly and consequently attracted very large numbers of redpoll and finch (Carduelis spp.), which all foraged eagerly for the seed. By-and-large, as birds will seek-out fruits and seeds that are larger than average and in healthy supply upon a tree (Foster, 1990; Wheelwright, 1993), it is perhaps not surprising that such regenerating stands are highly desirable. Granted, closed-canopy and late-successional stands also harbour tree crops (including the acorns of Quercus spp. and keys of Fraxinus spp.) that are of huge value to birds (Greig-Smith & Wilson, 1985; Koenig & Heck, 1988). However, the poor soils (nutritionally and hydrologically) of many mature woodlands adjacent to agricultural landscapes had led to – at least in Australia – declines in fruit and seed crops and, as a result, bird population density (Watson, 2011).

Moving away from the woodland and forest stands, though not entirely returning to open-grown trees, we can observe how trees within field hedgerows can be of huge benefit to birds, as can trees within agricultural windbreaks. Benefit may come in the form of landscape connectivity, where hedgerows and windbreaks act as corridors connecting woodland patches to one-another (Davies & Pullin, 2007; Harvey, 2000; Leon & Harvey, 2006; Morelli, 2013), though they may also be used – albeit perhaps less frequently now, courtesy of increased hedgerow management (at least, in the UK) – as nesting sites and foraging sites (Benton et al., 2003; Netwon, 2004). Grass buffers either side of the hedgerow may aid with suitability for birds, as may the presence of a greater number of large trees within a hedgerow (Hinsley & Bellamy, 2000; Herzog et al., 2005).

Within urban environments, the presence of trees and hedgerows adjacent to busy roads can however have a negative impact upon birds, by increasing mortality rates (usually associated with birds flying out into oncoming traffic). Research by Orłowski (2008) concludes as such. Of course, the presence of trees is also of benefit, much like within farmland hedgerows. Urban street trees, and also those within gardens, can improve landscape connectivity, allowing for bird species to travel between more significant areas of tree cover found in parklands and urban woodlands (Sanesi et al., 2009). In particular, connectivity to older parks with remnant woodland fragments will support a greater diversity of bird species (Fernández‐Juricic, 2000). The advent of large coniferous tree (and hedge) planting in many urban areas, courtesy of the planting of the cypress and other conifers (including Chamaecyparia lawsoniana, Cupressus macrocarpa, and x Cupressocyparis leylandii), has also led to an increase in resident bird populations and primarily because of the over-winter shelter such coniferous tree species provide (Jokimäki & Suhonen, 1998; Melles et al., 2003; Rutz, 2008; Savard et al., 2000). Furthermore, sheltered trees within the urban landscape that have abundant fruit and seed crops can be of huge benefit to birds, by providing essential food sources in an otherwise somewhat undesirable landscape. For such reasons, urban parks and woodlands may potentially provide the best conditions for certain feeding birds, though large gardens complete with dense vegetation may also be of great importance. Tree-lined streets may also be critical, and notably so if trees are large, have dense crowns, and have an edible fruit or seed crop.

Large leyland cypress specimens inter-planted with poplar cultivars offer suitable nesting sites in this harsh industrial zone. Source: Author, 2016.

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