New Plant Health Order (2017) – Sweet chestnut blight

A new piece of legislation – entitled Plant Health (Sweet Chestnut Blight) (England) Order 2017 – came into force on 21st February 2017, which relates to the plant pathogen known as sweet chestnut blight (Cryphonectria parasitica).

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Fungal fruiting bodies surrounding a severe canker (left) and a discernible canker developing on a young stem (right). Source: Forestry Commission.

Applying specifically to England, this Order allows for plant health inspectors (typically of the Forestry Commission) to serve a formal Notice on a site deemed (following official confirmation) to be host to the pathogen (“infested area”) and to identify and serve notices upn surrounding land parcels within the “controlled area” (section 3). In such infested sites that have a Notice served upon them, as detailed in section 4, no movement of Castanea sativa or Quercus spp. can take place within or out of such infested areas without the express permission of a plant health inspector – by a similar nature, susceptible Castanea sativa material cannot be moved within our out from the controlled area. However, such materials can pass through the area(s), assuming the materials do not stop within the area (i.e. the materials are not stored within the area and instead road networks within the area are used to transport the materials further afield). Currently, two demarcated zones exist – both in Devon (here and here).

In addition to detailing the powers provided to the plant health inspector and the categorisation of offences committed under the Order (sections 5 and 6), the Order also refers to – in section 7 – the necessity of a review of the Order. Indeed, the first principal report of sweet chestnut blight must be made by 21st February 2022, and reviews must be more routine occurrences that ensure the Order remains contextual and relevant to the situation relating to sweet chestnut blight’s extent in England.

More information can be found on the Forestry Commission’s web page for sweet chestnut blight – see here.

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New Plant Health Order (2017) – Sweet chestnut blight

Ancient Tree Forum summer conference, Epping Forest

A quick heads up that the Ancient Tree Forum summer conference at Epping Forest is now open for bookings at this link. At £50 for the two days it’s certainly worth it, and I can attest to the quality having gone last year to the one in Dorchester.

Expect more additions to this blog next week, though having been very busy lately I haven’t had a chance to get much uploaded!

Ancient Tree Forum summer conference, Epping Forest

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.

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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.

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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!

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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.

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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!

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Fungal foraying in the New Forest

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.

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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).

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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).

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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.

Eurasian jay acorn Quercus
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.

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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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Bednarz, J., Ripper, D., & Radley, P. (2004) Emerging concepts and research directions in the study of cavity-nesting birds: keystone ecological processes. The Condor. 106 (1). p1-4.

Benton, T., Vickery, J., & Wilson, J. (2003) Farmland biodiversity: is habitat heterogeneity the key?. Trends in Ecology & Evolution. 18 (4). p182-188.

Bishop, C., Ng, P., Mineau, P., Quinn, J., & Struger, J. (2000) Effects of pesticide spraying on chick growth, behavior, and parental care in tree swallows (Tachycineta bicolor) nesting in an apple orchard in Ontario, Canada. Environmental Toxicology and Chemistry.  19 (9). p2286-2297.

Ceia, R. & Ramos, J. (2016) Birds as predators of cork and holm oak pests. Agroforestry Systems. 90 (1). p159-176.

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Martin, T. (1985) Selection of second-growth woodlands by frugivorous migrating birds in Panama: an effect of fruit size and plant density?. Journal of Tropical Ecology. 1 (2). p157-170.

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Morelli, F. (2013) Relative importance of marginal vegetation (shrubs, hedgerows, isolated trees) surrogate of HNV farmland for bird species distribution in Central Italy. Ecological Engineering. 57 (1). p261-266.

Nappi, A. & Drapeau, P. (2011) Pre-fire forest conditions and fire severity as determinants of the quality of burned forests for deadwood-dependent species: the case of the black-backed woodpecker. Canadian Journal of Forest Research. 41 (5). p994-1003.

Nappi, A., Drapeau, P., Giroux, J., & Savard, J. (2003) Snag use by foraging black-backed woodpeckers (Picoides arcticus) in a recently burned eastern boreal forest. The Auk. 120 (2). p505-511.

Nappi, A., Drapeau, P., Saint-Germain, M., & Angers, V. (2010) Effect of fire severity on long-term occupancy of burned boreal conifer forests by saproxylic insects and wood-foraging birds. International Journal of Wildland Fire. 19 (4). p500-511.

Newton, I. (2004) The recent declines of farmland bird populations in Britain: an appraisal of causal factors and conservation actions. Ibis. 146 (4). p579-600.

Oppermann, R. (2014) Wood-pastures as examples of European high nature value landscapes. In Hartel, T. & Plieninger, T. (eds.) European wood-pastures in transition: A social-ecological approach. UK: Earthscan.

Orłowski, G. (2008) Roadside hedgerows and trees as factors increasing road mortality of birds: implications for management of roadside vegetation in rural landscapes. Landscape and Urban Planning. 86 (2). p153-161.

Pasinelli, G. (2007) Nest site selection in middle and great spotted woodpeckers Dendrocopos medius & D. major: implications for forest management and conservation. Biodiversity and Conservation. 16 (4). p1283-1298.

Reijnen, R., Foppen, R., Braak, C., & Thissen, J. (1995) The effects of car traffic on breeding bird populations in woodland. III. Reduction of density in relation to the proximity of main roads. Journal of Applied Ecology. 32 (1). p187-202.

Remm, J., Lohmus, A., & Remm, K. (2006) Tree cavities in riverine forests: What determines their occurrence and use by hole-nesting passerines?. Forest Ecology and Management. 221 (1). p267-277.

Riffell, S., Verschuyl, J., Miller, D., & Wigley, T. (2011) Biofuel harvests, coarse woody debris, and biodiversity–a meta-analysis. Forest Ecology and Management. 261 (4). p878-887.

Robinson, S. & Holmes, R. (1984) Effects of plant species and foliage structure on the foraging behavior of forest birds. The Auk. 101 (4). p672-684.

Rudolph, D. & Conner, R. (1991) Cavity tree selection by red-cockaded woodpeckers in relation to tree age. The Wilson Bulletin. 103 (3). p458-467.

Rutz, C. (2008) The establishment of an urban bird population. Journal of Animal Ecology. 77 (5). p1008-1019.

Saab, V., Dudley, J., & Thompson, W. (2004) Factors influencing occupancy of nest cavities in recently burned forests. The Condor. 106 (1). p20-36.

Sanesi, G., Padoa-Schioppa, E., Lorusso, L., Bottoni, L., & Lafortezza, R. (2009) Avian ecological diversity as an indicator of urban forest functionality. Results from two case studies in Northern and southern Italy. Journal of Arboriculture. 35 (2). p80-86.

Savard, J., Clergeau, P., & Mennechez, G. (2000) Biodiversity concepts and urban ecosystems. Landscape and Urban Planning. 48 (3). p131-142.

Schmidt, K. & Whelan, C. (1999) Nest predation on woodland songbirds: when is nest predation density dependent?. Oikos. 87 (1). p65-74.

Sedgley, M. & Griffin, A. (1989) Sexual Reproduction of Tree Crops. UK: Academic Press.

Smith, K. (2007) The utilization of dead wood resources by woodpeckers in Britain. Ibis.  149 (2). p183-192.

Spetich, M., Shifley, S., & Parker, G. (1999) Regional distribution and dynamics of coarse woody debris in Midwestern old-growth forests. Forest Science. 45 (2). p302-313.

Thiollay, J. (2006) Large bird declines with increasing human pressure in savanna woodlands (Burkina Faso). Biodiversity & Conservation. 15 (7). p2085-2108.

Vera, F. (2000) Grazing Ecology and Forest History. UK: CABI Publishing.

Watson, D. (2011) A productivity-based explanation for woodland bird declines: poorer soils yield less food. Emu. 111 (1). p10-18.

Weikel, J. & Hayes, J. (1999) The foraging ecology of cavity-nesting birds in young forests of the northern coast range of Oregon. The Condor. 101 (1). p58-66.

Wheelwright, N. (1993) Fruit size in a tropical tree species: variation, preference by birds, and heritability. Vegetatio. 107 (1). p163-174.

Trees in the ecosystem pt III: Trees & birds

A roadside beech colonised by Ganoderma resinaceum

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!

ganoderma-resinaceum-fagus-sylvatica-roadside-1
To give a sense of context, this is the position of the beech relative to the adjacent road.
ganoderma-resinaceum-fagus-sylvatica-roadside-2
Some rather nice bulging on the main stem, though around the prominent buttress roots we can spot a few sporophores of Ganoderma resinaceum.
ganoderma-resinaceum-fagus-sylvatica-roadside-3
Another fruiting body hides on the other side of the buttress!
ganoderma-resinaceum-fagus-sylvatica-roadside-4
From the damaged bracket atop the one on the right, either we have prior years of fruiting or this bracket was torn off and another one grew in its place earlier during this growing season.
ganoderma-resinaceum-fagus-sylvatica-roadside-5
We can observe how this significant buttress root has likely been produced in response to the white rot associated with the decay incuded by Ganoderma resinaceum.
ganoderma-resinaceum-fagus-sylvatica-roadside-6
And a final picture for good measure!
A roadside beech colonised by Ganoderma resinaceum

Rigidoporus ulmarius acting as a saprotroph

The distinction between a fungal necrotroph (i.e. parasite) and saprotroph is – in the most basic of senses – easy. The former causes the host woody cells to die as the mycelial network metabolises, whereas the latter metabolises woody tissue that has already died / ceased to serve a vascular function. Indeed, this poses an interesting question, by where many fungi on living trees aren’t actually necrotrophs in the truest sense of the word, as they metabolise heartwood that doesn’t serve a function beyond adding structural support to the overall above-ground structure. Consequently, many wood-decay fungi that degrade heartwood, such as Fistulina hepatica, Laetiporus sulphureus and Phaeolus schweinitzii are arguably saprotrophic – even when found on living trees.

Regardless of that entire aspect of fungal ecology (that’s an entire week’s worth of blog posts right there!), the purpose of this post is to share two finds of Rigidoporus ulmarius (the ‘giant elm bracket’) from yesterday. Both were colonising horse chestnut (Aesculus hippocastanum), and specifically dead specimens. For me, it’s an interesting case, as I generally observe this fungus upon living trees, and despite things I have read this is – from recollection – the first time I have seen this fungus on a dead host.

Without further blabbering, I share below the two specimens, which were within 15m of one another. The other horse chestnuts very close by don’t sport outward signs of this fungus, though the localised and elevated inoculum base has probably resulted in all the horse chestnuts acting as hosts for Rigidoporus ulmarius – to varying degrees.

rigidoporus-ulmarius-aesculus-saprotrophic-1rigidoporus-ulmarius-aesculus-saprotrophic-2rigidoporus-ulmarius-aesculus-saprotrophic-3rigidoporus-ulmarius-aesculus-saprotrophic-4rigidoporus-ulmarius-aesculus-saprotrophic-5rigidoporus-ulmarius-aesculus-saprotrophic-6rigidoporus-ulmarius-aesculus-saprotrophic-7rigidoporus-ulmarius-aesculus-saprotrophic-8

Rigidoporus ulmarius acting as a saprotroph

Trees in the ecosystem pt II: Trees & molluscs

Whilst the presence of herbivorous slugs and snails within forest ecosystems has been far from extensively researched in the past – usually because of their low density within forests (Emberton et al., 1996), though high density hotspots may exist in ideal habitat conditions provided by trees that are practicably inaccessible (Cameron & Pokryszko, 2005) – there has been an increased focus on surveying for their presence because of their sometimes unexplained high mortality rates (Hadfield & Miller, 1989), because of deforestation and woodland degradation (Kappes et al., 2009; Schilthuizen et al., 2005), and because molluscs may act as an indicator of ancient woodland (Alexander, 2011). Such research has demonstrated how individual (and groups of) trees are critical for the survival of molluscs, with large expanses of woodland cover (at times, over 1,000ha) being necessary to sustain diverse and healthy populations. This may be because molluscs cannot travel with any degree of pace by themselves, and thus the standard concept of fragmentation and its associated isolation effects will not apply to such species so steadfastly (Kappes et al., 2009). However, more open wooded landscapes, such as wood pastures, can also support molluscs, and notably when such wood pastures have a higher canopy cover; either due to abandonment or a reduction in grazing intensity.

The stumps of trees, or other habitats containing deadwood (including veteran trees and coarse woody debris), may be of great value for molluscs – even, at least in the short-term, where their provision is due to thinning or felling of stands. For example, stumps generated through management regimes can act as an attractive resting and hibernation spot for molluscs (Fondo & Martens, 1998), though where deadwood may exist within floodplain areas, land molluscs may take a preference to standing deadwood in order to avoid flood waters (Kappes et al., 2014). However, the openness created by felling operations, as well as its associated disturbances, will detract from the quality of the landscape (principally through the reduction in humidity), and therefore sheltered and undisturbed deadwood sites are of particular importance to many terrestrial molluscs (Rancka et al., 2015; Remm & Lõhmus, 2016). Thus, the presence of deadwood (such as coarse woody debris, though also standing deadwood) within a damp woodland setting may be highly beneficial for molluscs with regards to resting (Kappes, 2005) – particularly during advanced stages of decay (Stokland et al., 2012). Deadwood may also be beneficial for predaceous snails, where the remains of other organisms can be digested, or living organisms can be predated upon (Kappes et al., 2006).

fallen-deadwood-windthrow-beech
Sites such as this (New Forest, UK) could be very beneficial for molluscs and perhaps most notably as the wood succumbs to white rotting fungi.

However, it is not always the trees themselves that provide molluscs with the ability to travel between isolated patches, or even within the same woodland patch, but other species the woodlands attract – deer and wild boar are but two examples. Molluscs may ‘use’ these mammals to travel vast distances – intentionally or not – thereby enabling for effective dispersal of offspring (Bruinderink et al., 2003). This is particularly critical in terms of genetic diversity, as populations of mollusc may be very similar on a genetic level even across wide distances (Hillis et al., 1991). In addition, slugs may feed upon the sporophores of macrofungi and slime moulds, which are themselves harboured upon a wood substrate or supported by the presence of trees (Keller & Snell, 2002; Rathcke, 1985).

Curiously, it is not just terrestrial land molluscs that benefit from deadwood (Lorion et al., 2009). Deep sea bivalve molluscs may, for instance, bore holes into and lay their eggs within deadwood that has been washed down from rivers and into the ocean, where it has then sunk to a depth of up to 500m (Tyler et al., 2007), or perhaps been provided by a sunken vessel. In addition to this, riverine molluscs may also be drawn to deadwood and be found in particular abundance where a river runs through woodland (Thorp & Belong, 1998). Furthermore, driftwood may transport molluscs across many kilometres of ocean and to new shores, where the molluscs on board can then begin to colonise the new landscape. Not only this, but sunken driftwood harbouring estuarine molluscs has also been linked to such estuarine molluscs becoming fully adapted to marine environments, to depths of 135m (Kano et al., 2013). Interestingly, this research suggests that the versatility of molluscs is not fully understood.

Marine bivalve molluscs may also utilise wood, harvested by humans and then used to construct naval vessels (ships), for transport across vast tracts of ocean. The shipworm (Teredo navalis) is a fantastic example of a marine mollusc that disperses itself via this process, and its destructive presence for such ships it colonised by boring into led to, particularly in the centuries gone by, the hulls of ships being dressed in copper (Grave, 1928). This – and other – shipworms (known as teredo worms), would also colonise upon sunken deadwood (from ships), and other man-made aquatic wooden structures, such as bridges, piers and groynes, causing sometimes irreparable damage (Britton, 1875; Nordstrom et al., 2007; Thompson, 1830).

teredo_navalis_in_a_branch
Damage caused by Teredo navalis to a branch of a tree. Source: Wikimedia.

References

Alexander, K. (2011) A Survey of Ancient Woodland Indicator Molluscs in selected sites on the Isle of Man. [Online] Available at: http://www.manxwt.org.uk/sites/default/files/files/wfom_ancientwoodlandmolluscsurvey2011.pdf

Britton, T. (1875) A Treatise on the Origin, Progress, Prevention, and Cure of Dry Rot in Timber: With Remarks on the Means of Preserving Wood from Destruction by Sea Worms, Beetles, Ants, Etc. UK: E. & F. N. Spon.

Bruinderink, G, van der Sluis, T., Lammertsma, D., Opdam, P., & Pouwels, R. (2003) Designing a coherent ecological network for large mammals in northwestern Europe. Conservation Biology. 17 (2). p549-557.

Cameron, R. & Pokryszko, B. (2005) Estimating the species richness and composition of land mollusc communities: problems, consequences and practical advice. Journal of Conchology. 38 (5). p529-548.

Emberton, K., Pearce, T., & Randalana, R. (1996) Quantitatively sampling land-snail species richness in Madagascan rainforests. Malacologia. 38 (1-2). p203-212.

Fondo, E. & Martens, E. (1998) Effects of mangrove deforestation on macrofaunal densities, Gazi Bay, Kenya. Mangroves and Salt Marshes. 2 (2). p75-83.

Grave, B. (1928) Natural history of shipworm, Teredo navalis, at Woods Hole, Massachusetts. Biological Bulletin. 55 (4). p260-282.

Hadfield, M. & Miller, S. (1989) Demographic studies on Hawaii’s endangered tree snails: Partulina proxima. Pacific Science. 43 (1). p1-16.

Hillis, D., Dixon, M., & Jones, A. (1991) Minimal genetic variation in a morphologically diverse species (Florida tree snail, Liguus fasciatus). Journal of Heredity. 82 (4). p282-286.

Kano, Y., Fukumori, H., Brenzinger, B., & Warén, A. (2013) Driftwood as a vector for the oceanic dispersal of estuarine gastropods (Neritidae) and an evolutionary pathway to the sunken-wood community. Journal of Molluscan Studies. 79 (4). p378-382.

Kappes, H. (2005) Influence of coarse woody debris on the gastropod community of a managed calcareous beech forest in western Europe. Journal of Molluscan Studies. 71 (2). p85-91.

Kappes, H., Jordaens, K., Hendrickx, F., Maelfait, J.P., Lens, L., & Backeljau, T. (2009) Response of snails and slugs to fragmentation of lowland forests in NW Germany. Landscape Ecology. 24 (5). p685-697.

Kappes, H., Kopec D., & Sulikowska-Drozd, A. (2014) Influence of habitat structure and conditions in floodplain forests on mollusc assemblages. Polish Journal of Ecology. 62 (1). p739-750.

Kappes, H., Topp, W., Zach, P., & Kulfan, J. (2006) Coarse woody debris, soil properties and snails (Mollusca: Gastropoda) in European primeval forests of different environmental conditions. European Journal of Soil Biology. 42 (3). p139-146.

Keller, H. & Snell, K. (2002) Feeding activities of slugs on Myxomycetes and macrofungi. Mycologia. 94 (5). p757-760.

Lorion, J., Duperron, S., Gros, O., Cruaud, C., & Samadi, S. (2009) Several deep-sea mussels and their associated symbionts are able to live both on wood and on whale falls. Proceedings of the Royal Society of London B: Biological Sciences. 276 (1654). p177-185.

Nordstrom, K., Lampe, R., & Jackson, N. (2007) Increasing the dynamism of coastal landforms by modifying shore protection methods: examples from the eastern German Baltic Sea Coast. Environmental Conservation. 34 (3). p205-214.

Rancka, B., von Proschwitz, T., Hylander, K. a, & Götmark, F. (2015) Conservation Thinning in Secondary Forest: Negative but Mild Effect on Land Molluscs in Closed-Canopy Mixed Oak Forest in Sweden. PLoS One. 10 (3). p1-17.

Rathcke, B. (1985) Slugs as generalist herbivores: tests of three hypotheses on plant choices. Ecology. 66 (3). p828-836.

Remm, L. & Lõhmus, A. (2016) Semi-naturally managed forests support diverse land snail assemblages in Estonia. Forest Ecology and Management. 363 (1). p159-168.

Schilthuizen, M., Liew, T., Elahan, B., & Lackman‐Ancrenaz, I. (2005) Effects of karst forest degradation on pulmonate and prosobranch land snail communities in Sabah, Malaysian Borneo. Conservation Biology. 19 (3). p949-954.

Stokland, J., Siitonen, J., & Jonsson, B. (2012) Biodiversity in Dead Wood. UK: Cambridge University Press.

Thompson, W. (1830) Observations on the Teredo navalis and Limnoria terebrans, as at Present Existing in Certain Localities of the British Islands. Abstracts of the Papers Printed in the Philosophical Transactions of the Royal Society of London. 3 (1830-1837). p291-292.

Thorp, J. & Delong, M. (1998) In situ experiments on predatory regulation of a bivalve mollusc (Dreissena polymorpha) in the Mississippi and Ohio Rivers. Freshwater Biology. 39 (4). p649-661.

Tyler, P., Young, C., & Dove, F. (2007) Settlement, growth and reproduction in the deep-sea wood-boring bivalve mollusc Xylophaga depalmai. Marine Ecology Progress Series. 343 (1). p151-159.

Trees in the ecosystem pt II: Trees & molluscs