Here’s a nice one! As I was out surveying, there sat this large roadside beech (Fagus sylvatica) that sported a trio of sporophores of the lacquered bracket (Ganoderma resinaceum). Curiously, this association between host tree and parasitic fungus is a not-so-common one in the present day, in comparison to this fungus upon oak (Quercus robur) – in spite of the lacquered bracket historically being more common on beech than any other tree.
Evidently, judging by the past prunung cuts, an arboriculturist made the decision to manage this beech. Whether or not it was due to the presence of this fungus is something open to speculation, though there’s certainly reason to prune this beech once more for good arboricultural reasons associated with hazard management – notably because of the busy road directly adjacent to the beech. A PiCUS test might be the best investigative route of action here, though that decision remains with the landowner.
I’m sure that you’ll be able to appreciate the issue to do with hazard management, from the pictures below!
I was driving down near to a local tip site early yesterday morning, and passed a line of willow just within the tip site’s boundary. As I was driving very slowly due to the presence of speed bumps, I was able to commit a little more than just a fleeting glance at them all. Towards the end of the line, I could see a downed willow (due to windthrow), and pulled over after spotting a few fungal brackets upon the lower stem. I admit that I suspected a species of the Ganoderma genus, though hadn’t expected it to be Ganoderma resinaceum, as this is usually found on oaks (Quercus). Nonetheless, from the photos, it certainly appears to be the lacquered bracket, both from the morphology of the brackets and the colouration. Unfortunately, as there was a chain link fence between me and the willow, I could only get some shots on my camera by zooming in, so pardon the lack of closeness on the below images.
After driving past this large red oak on multiple occasions, I thought I’d finally park up and have a more in-depth look at it. I’m glad I did, as there is a large (but very decayed) fungal sporophore at the base, within or around a buttress that ends up becoming a sort of girdling root (there are two large roots partially girdling the stem on this tree, as can be seen below). At first, I thought the fungus was a very old Pseudoinonotus dryadeus, though when I found an old remnant of the sporophore a few yards from the tree I noticed it had small segments of the characteristic lacquered appearance of Ganoderma resinaceum. Comparing the tube layer with existing photos I have from other samples, it also appears there are similarities in this regard, as are there similarities with the pore surface on the underside. For this reason, I’m running with Ganoderma resinaceum.
After sounding the tree with a nylon hammer, there was no indication of hollowing, and therefore one can suspect that the decay is well compartmentalised (or not at the stage where wood has become markedly degraded). As Ganoderma resinaceum can however infect principal roots in the location surrounding the stem base (according to literature), perhaps the girdling roots have lead to some localised decay just beneath the surface, from which this fungus has been feeding from. Of course, this is only a suspicion of mine, and I have no means of currently proving that.
In the UK, the plane tree (Platanus x hispanica) has been, and perhaps still is, a very popular choice of tree for urban landscapes. In London, the recent i-Tree report suggested that up to 4% of Inner London’s tree population of 1,587,000 trees are plane (meaning 63,480 are plane trees), though in terms of leaf area is provides as much as 8.9%. In this sense, it’s evidently a tree that is usually found to be quite large, and this landscape dominance makes it a very prominent feature as well as quite a common one (for a larger tree, where feasible planting space is automatically more limited). However, the ability to clonally propagate plane, in addition to the report’s findings that 21% of London’s trees are clones, we can assume that at least 13,331 planes are genetically not unique (perhaps more, as many planes are assumed to the ‘Pyramidalis’ cultivar, though other cultivars may also be found and thus raise the total level of ‘clonal-ness’ amongst plane meta-populations). This presents problems, as such a lack of genetic diversity means pests and diseases can readily sweep through clonal stands, as there is no inherent level of variable resistance in the population. Beyond London, they also feature quite prominantly in some of the new towns, and particularly along main vehicle routes and within urban parks.
Introductory spiel aside, my remarks on pest and disease are quite pertinent to this post, which will look at a recent article published by Tubby & Perez-Sierra in the Arboricultural Journal, which looks into the current status of plane and those pests and diseases that may soon put the species at risk, within the UK. For those that get the print journal (like myself), then you may have already read this, though it’s got some great information and thus is a good one to share with an audience far beyond those who get (or have access to) the journal.
Arguably the most prominent aggressor of plane in recent years is what we know as Massaria (Splanchnonema platani). Despite this fungus being considered a “weak pathogen”, where it will ‘aid’ (in an adverse sense) with twig abscission and cause small cankers upon minor branches, it has been increasingly observed, across central and western Europe, to cause decay and dieback within larger-diameter branches at the upper branch crotch and along the upper side of the branch, and notably in the lower crown where branch diameter is between 100-200mm. The dieback has the potential to cause very wide decay strips, with potentially around 30% of the entirety of a branch’s circumference being damaged by the fungus (which induces a soft rot). Such damage will induce symptoms of decline within the affected branch (which may be highly discernible if the branch is large and bears a lot of foliage), as will cambial dieback create lesions that are evident from above the crotch (a pinkish-orange colour). Failure can occur in as little as three months following on from the onset of decay. Of course, as most plane trees are present within the urban environment in the south east of England (and are generally large in size), which incidentally is also the most densely-populated area of the UK, there is an evident risk to public safety. For this reason (amongst others), the LTOA (London Tree Officers Association) published guidance quite recently on the subject.
Beyond Massaria, which is indeed present within the UK, we can also observe how plane canker (Ceratocystis platani) may be a very possible threat in the near future. Whilst it is a fungus not present within the UK right now, courtesy of transportation over from the US during WWII, it is indeed present on the continent, and ‘uses’ humans as its primary vector across the landscape. In both urban and forest-borne planes, in countries such as France and Switzerland, this fungus causes marked xylem staining (extending up to as much as 2-2.5m a year), thereby induces wilting, and may even cause the death of its host plane tree as a result. Because its spores may remain ‘active’ for long periods of time before finding a host to infect (usually following wounding), chainsaws (and other equipment), boots, and even the transporation of soil may enable it to spread over vast distances. For this reason, infected trees are felled and disposed of on site, and all equipment used is thoroughly cleaned (or replaced) afterwards. Such a rigorous sanitation measure is, unfortunately, necessary, and therefore its emergence in the UK could be very damaging and costly.
Remaining with fungal decayers, Fomitiporia punctata (syn. Phellinus punctatus) also has the potential to significantly infect planes within the UK (it can already be seen colonising some planes in the UK, however). On the continent it may indeed use the plane as a host species, and when it does it creates rather non-distinct sporophores (brown ‘splodges’) that can easily be missed. The fungus causes a very significant white rot of the sapwood and (depending upon host species, false-)heartwood region of its host, and therefore in the urban environment such decay may prove to be significant in terms of the level of risk posed by the host tree.
Similarly, whilst Inonotus hispidus may already be found colonising plane within the UK, a species of the same genus known as Inonotus rickii may be another potential fungal pathogen. Native to the tropics, it is currently in Italy, where it induces a white rot upon its host and may colonise, like Inonotus hispidus, through open wounds. The authors do note, however, that climatic differences between the UK and Italy may mean its emergence in the UK may not be for a fair few years, though it is likely to succeed at some point (and particularly in urban areas where it is warmer, courtesy of the urban heat island effect – and this is where most plane trees reside). Other wood-decay fungi that may use the plane as a host include the resident Ganoderma species (G. australe, G. lipsiense, and G. resinaceum), and also Perenniporia fraxinea.
A type of powdery mildew, with the scientific name of Erysiphe platani, is a further potential pathogen of plane. In fact, it was found in the UK in 1983, though does not appear to be at all significant at this moment in time (if it is even still here – it may have been eradicated?), and is instead far more significant as a pathogen in countries such as Spain. Much like other powdery mildews, it affects the foliage and causes leaf deformation, though may also impact upon the amenity value of infected plane trees. If, like oak mildew, there are also marked impacts to the health of the tree over the long-term, then this powdery mildew of plane may have adverse consequences in that regard as well.
Sticking with the leaf, a more evident problem for plane trees is anthracnose (Apiognomonia veneta). Peronal observation of this leaf pathogen (that over-winters on twigs, where it may blight them during milder years) is that it can be very readily observed in larger plane trees, where it can cause extensive leaf dieback (to the point that members of the public are concerned enough to report it). In younger trees, the entire foliage crown may prematurely be lost, and a second one formed. Such a loss of foliage (in plane trees of all sizes) has an adverse impact upon tree energy levels, and like Cameraria ohridella in horse chestnut, is far more than an amenity problem.
Again upon the leaf, though this time a pest and not a pathogen, the sycamore lace bug (Corythuca ciliata), since 2006, has been a UK problem. Adults will feed on the underside of plane leaves, which will cause the upper surface of the leaf to become minutely-dotted in white. In time, as feeding continues, the leaf may eventually be evidently chlorotic or bronzed, after which time the leaves will prematurely abscise. Again, this is far more than an amenity issue, and heavy infestations of this lace bug can play a role in the death of a plane tree (particularly when combined with other plane pests and pathogens).
From the source article, it is certainly evident that there are many looming (and some already present) threats to the plane tree in the UK. Whilst the plane doesn’t necessarily have as much direct ecological value as many other tree species found in the UK (notably native ones), it does have a substantial impact upon airborne pollutants, and its hardy nature means it can thrive where other trees species may suffer beyond belief. Therefore, if it does begin to succumb more readily to pathogens discussed here, then there may be problems with regards to its longevity and abundance. As many of our plane trees are urban-based, will risk management be a principal driver behind its decline? Only time will tell, though as always, protecting and safeguarding ecosystems from invasive pests and pathogens is absolutely critical and, as an island, the UK is (theoretically) greatly-poised to control the entry of these organisms. Of course, I say theoretically, as a control program is only as effective as its weakest link.
If you’re wondering what on earth was going on with my last post, please rest assured that my little trek wasn’t all in jest. I found plenty of fungi and saw some awesome sights, and over the coming while I shall be sharing the best ‘scores’. Below is one of them, and oddly enough it’s a tree I have walked past so many times, but have never stopped to properly look. Thankfully, that changed today, and I spotted two glorious sporophores of the lacquered bracket Ganoderma resinaceum.
I thought I’d share a little bit on the lacquered bracket, for those that may be interested. An interesting species of Ganoderma, particularly in the way in which is presents itself. Hopefully, for those interested in fungi, this post will be of use.
Frequently found colonising mature Quercus spp. (Mattheck et al., 2015; Rayner & Boddy, 1988; Watson & Green, 2011), though may also be found on other broadleaved species such as Acer pseudoplatanus (Deflorio et al., 2008a), Carpinus betulus (personal observation), Fagus sylvatica (Deflorio et al., 2008a; Schwarze & Baum, 2000), Platanus spp. (Schwarze & Ferner, 2003), and Robinia pseudoacacia (personal observation). Pseudotsuga menziesii may also act as a host (Deflorio et al., 2008a; Deflorio et al., 2008b). In colder areas, it may very rarely be found – even on its preferred hosts (Schwarze & Ferner, 2003).
Entering through exposed heartwood surfaces, Ganoderma resinaceum will typically begin its life as a parasite. However, upon death of the host, it may persist as a saprophyte (Deflorio et al., 2008b; Mattheck et al., 2015). Upon entering into heartwood, it may begin to also colonise sapwood (Watson & Green, 2011).
The type of rot induced by Ganoderma resinaceum is not fully understood, though it is considered to selectively delignify its host (Deflorio et al., 2008a; Mattheck et al., 2015; Rayner & Boddy, 1988; Schwarze & Ferner, 2003; Watson & Green, 2011). Lonsdale (1999) remarks that it may oft be confused with Ganoderma lucidum, making differentiation of rot characteristics between the species difficult, though it is considered that Ganoderma resinaceum induces a more ‘complete’ rot that other Ganoderma species.
Decay is normally confined to the roots and buttress zone (Rayner & Boddy, 1988; Watson & Green, 2011), though may also – albeit rarely – extend further up the stem (Mattheck et al., 2015). The host species may perhaps play a role in the location of the decay, with Quercus spp. usually having rot confined to the roots and butt, whereas in Platanus spp. decay may extend some metres up the stem (Schwarze & Ferner, 2003).
Because Ganoderma resinaceum can spread into sound sapwood (Watson & Green, 2011) by breaching the reaction zone (Schwarze & Ferner, 2003), in addition to the ‘complete’ delignification induced by the mycelium within not only the butt but also the roots (Lonsdale, 1999; Schwarze & Ferner, 2003), there is a potentially high level of risk associated with retention of a specimen with a full crown, where the target area is significant. Ductile fracturing will typically be induced at the root plate or near to the base of the host (Mattheck et al., 2015), when the decay has advanced significantly (Watson & Green, 2011). Schwarze & Ferner (2003) do however note that the extent of decay may be less than where decay has been caused by other Ganoderma species (such as Ganoderma applanatum).
Treatment and prevention
Limiting the severity of pruning operations is likely to reduce the risk of decay by this fungus, though care where working around the base of potential hosts is also important – given the fungus will colonise around the root plate and butt region (Mattheck et al., 2015). If found to be colonising a tree, if the target area includes people and / or property, strong consideration must be given as to at least pruning the tree (even if only a small reduction). Investigations into determining wood strength can be supplemented with the use of a resistograph, ultrasound tomography, or a fractometer (Deflorio et al., 2008a; Mattheck et al., 2015). However, as Ganoderma resinaceum may colonise sapwood very easily when the barrier zone is breached by invasive devices (Schwarze & Ferner, 2003), careful consideration as to what type of decay-detection device that is to be used is mandatory.
Whilst up at Hampstead Heath, the arborists showed me a large (but very heavily pruned, as it sits right by a road) Turkey oak (Quercus cerris) that was host to Ganoderma resinaceum. Certainly some very extensive decay, which has also extended into a buttress root on one side of the tree.
I followed the growth of two Ganoderma resinaceum sporophores at the butt of a mature roadside Quercus robur during the summer just gone, to ascertain rate of growth and the way in which the fungus developed morphologically. The below photos detail its growth from 12th August 2015 to 2nd November 2015.