Nothing much need be added, in light of who is narrating. As a 20-minute long film, it’s something you can readily watch at any point where you have some time going spare. There’s a few good segments on trees, including on ancient trees, deer, deadwood and wood-decay fungi. Really a fascinating watch!
A huge thanks to Burnham Beeches yesterday for hosting some of us for the day and showing us around the site. Below are some of the stand-outs from the day, which I am certain you will all appreciate!
The importance of functional units
As we can see in the below few images of a particularly striking beech pollard, very little of the structure of the tree needs to remain for the tree to persist as a living and functional organism. In this example, only one unit of vascularity supports a very small crown, though the beech is generally without significant fault. It could, potentially, persist in this state for many decades! Certainly, the two natural ‘props’ that support the crowd through a sort of tripod could, in their eventual failure, be the demise of this tree; assuming the functional unit cannot itself adequately support the crown. Depending on the rate of decay of this two ‘props’, this last vascular strip might (if decay is slow) – or might not (if the ‘props’ fail sporadically) – be able to lay down the necessary wood fibres for such mechanical support.
Reduction work on lapsed pollards
There comes a point where one has to make a decision – for what reason is a lapsed pollard being managed? If it is to be managed for the provision of habitat then the major failure of the structure might not be an adverse occurrence (to a degree!), though if the intent is to retain the pollards for as long a period as is at all feasible then it might be necessary to undertake quite extensive reduction work, in order to reduce the mechanical loading upon the old pollard head. As can be seen from the below beech, heavy reduction work has taken place and the crown architecture / good number of ripe buds that remain below the pruning points will hopefully ensure that this lower crown will function very effectively. Of course, where lapsed pollards don’t have this lower growth then a heavy reduction might not even be possible, though where such low growth exists then it does provide for more effective means of management, with regards to reduction work of the crown.
Submerged deadwood for reptiles
A terrapin uses a large section of a mostly-sunken stem for sunbathing, in the centre of a large pond. Indeed, this section of deadwood is an effective tool for the terrapin, which allows it to be exposed to direct sunlight and isolated from potentially aggressive mammals (that includes humans – seriously). Improving the texture and heterogeneity of this aquatic habitat with deadwood is evidently important, therefore!
As some of the old beech pollards are quite literally falling apart, safeguarding their structures against such cataclysmic failure is necessary, if their presence in the landscape is to be retained. For some, this involved reduction work, whilst for others it involves installing props to support either the enture tree or large / heavy parts of its structure. In the below two cases, we can see how props have been installed to stop the trees falling over completely.
As you’d very much expect from a place such as this, wood-decay fungi are found in relative abundance. Beneath, the best examples are shown – this includes less common fungi, which we also came across during the trip; or less common associations, as you’ll see for one particular set of photos!
Fomitopsis pinicola (red-banded polypore)
Along the stem of a beech, this single bracket of a very infrequently found (in the UK, anyway) wood-decay fungus, the red-banded polypore, resides. Adjacent to a colony of Bjerkandera adusta and above extensive swathes of Kretzschmaria deusta, exactly to what degree this fungus has secured the wood substrate is unknown, though the good thing is that it has produced a fruiting body and in sporulating!
Heterobasidion annosum (fomes root rot)
A common fungus but probably not one you see every day on hawthorn! Hidden beneath a branch ridden with Fuscoporia ferra (syn: Phellinus ferreus) and some leaves, a series of fruiting bodies were tucked away comfortably. Fungi love to throw curve-balls!
Ganoderma pfeifferi (bees-wax polypore)
Sadly, the host beech had recently failed, due to the decay caused by this fungus. With respect to the rot induced, the failure was seemingly a brittle one and thus the failure can be attributed to a significant loss of cellulose. The cross-section of the failed region also yielded some glorious ‘rosing’ patterns, which is something that has been seen in other cases of failure as caused by this particular fungus.
Fomes fomentarius (hoof fungus)
Found on both birch and oak, this species isn’t notably abundant in the south of England, where the pathogens Ganoderma australe / resinaceum / pfeifferi (in order of commonality) tend to be better suited. In the two instances shown below, fallen deadwood has provided the resource, which aligns with its colonisation strategy – that of awaiting stress / entire vascular dysfunction of an area or whole tree, before launching wide-scale colonisation activities.
Daedalea quercina (Oak mazegill)
Found quite frequently on dysfunctional wood of oak, this instance has provided the best sight yet of this species. As you can see, an oak monolith is utterly littered with fruiting bodies, which is genuinely a spectacular sight!
Single-celled organisms that may create larger structures as groups in order to reproduce, slime molds, whilst not considered active wood decayers, can be found colonising deadwood (Heilmann-Clausen, 2001). Deadwood of 10-22 years of age, Heilmann-Clausen (2001) alleges, is most optimal for slime molds – at least, for the species observed on the decaying beech logs that featured within the study. This correlates with current understanding of slime molds, which suggests species strongly prefer moist, well-decayed wood.
The presence of wood-decay fungi sporophores, or even simply mycelium within the wood substrate, may also act as a source of energy for slime molds (Ing, 1994). As mycelial networks and their associated sporophores may take some time to develop within deadwood, this may perhaps be a further reason for why slime molds are found in greater abundance on older woody debris. The presence of bacteria, also greater in abundance on older and heavily-decayed wood, may also influence slime mold presence, as bacteria can be utilised as a further source of energy (Heilmann-Clausen, 2001). Lodge (1997) describes some slime molds as “predators of decomposers”. Slime molds may also utilise decaying leaves as a habitat (Ko et al., 2009; Raper, 1941; Raper, 1951; Stephenson, 1989). Therefore, the decaying leaf litter-soil ‘zone’ is another potential niche for slime mold species (Landolt & Stephenson, 1986). Moreover, slime molds may be found upon the bark of living trees (Olive & Stoianovitch, 1973; Stephenson, 1989).
Away from wood, decaying leaves, and soil exclusively, the composition of a forest ecosystem may also have an impact upon slime mold density. Landolt et al. (2006) found that, whilst species diversity did not differ between deciduous-broadleaved and coniferous stands, the broadleaved sites were host to slime mold populations over four times more abundant than coniferous sites. The same study also identified that different species of slime mold would be found at different altitude levels within forests, and suggested different micro-habitats perhaps act as refugia for different slime mold species that may have once colonised greater ranges of forest.
Heilmann-Clausen, J. (2001) A gradient analysis of communities of macrofungi and slime moulds on decaying beech logs. Mycological Research. 105 (5). p575-596.
Ing, B. (1994) Tansley Review No. 62: The phytosociology of myxomycetes. New Phytologist. 126 (2). p175-201.
Ko, T., Stephenson, S., Jeewon, R., Lumyong, S., & Hyde, K. (2009) Molecular diversity of myxomycetes associated with decaying wood and forest floor leaf litter. Mycologia. 101 (5). p592-598.
Landolt, J. & Stephenson, S. (1986) Cellular slime molds in forest soils of southwestern Virginia. Mycologia. 78 (3). p500-502.
Landolt, J., Stephenson, S., & Cavender, J. (2006) Distribution and ecology of dictyostelid cellular slime molds in Great Smoky Mountains National Park. Mycologia. 98 (4). p541-549.
Lodge, D. (1997) Factors related to diversity of decomposer fungi in tropical forests. Biodiversity & Conservation. 6 (5). p681-688.
Olive, L. & Stoianovitch, C. (1974) A cellular slime mold with flagellate cells. Mycologia. 66 (4). p685-690.
Raper, K. (1941) Dictyostelium minutum, a second new species of slime mold from decaying forest leaves. Mycologia. 33 (6). p633-649.
Raper, K. (1951) Isolation, cultivation, and conservation of simple slime molds. The Quarterly Review of Biology. 26 (2). p169-190.
Stephenson, S. (1989) Distribution and ecology of myxomycetes in temperate forests. II. Patterns of occurrence on bark surface of living trees, leaf litter, and dung. Mycologia. 81 (4). p608-621.
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!
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.
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).
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).
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.
The New Forest has no shortage of failed beech, given the fact that most of the beech are mature or veteran in age. Typically, the species of Ganoderma can be found to be devouring the remaining stumps and stems, though sometimes further fungi pop up in the most unexpected of places. In this case, looking inside the significantly-hollowed bole yielded a sight of various sporophores of the fungus Phlebia tremellosa (known commonly as ‘jelly skin’).
Because this species is considered to be generally be saprotrophic, the extensive decay (which appears to be caused principally by a white rot) wasn’t created by this fungus and was likely generated instead by Ganoderma australe and / or Ganoderma resinaceum. However, upon windthrow of the bole, or perhaps even before that time, spores of this fungus germinated upon the wood substrate and have since produced fruiting bodies. Such structures are also kept snugly within a consistently warmer and more humid microclimate, which has probably ensured they have endured the frosts that covered the outside world in the prior weeks.
The extent of attention as to exactly how critical trees are for fish populations is unfortunately not all that significant (in comparison to the study or trees and birds, for example), though this is not necessarily surprising – this is perhaps because fish spend their lives largely under water, and thus their presence is not necessarily recognised to the degree it would be if fish were land-based organisms. However, there is certainly a healthy array of research that has been undertaken into this relationship of trees and fish within the forest ecosystem, as is demonstrated below.
Many undisturbed pools (areas of slow-moving or still water within in rivers and streams) in forests are either created or enhanced by the presence of deadwood (as either driftwood or sunken wood). Such deadwood presence can also raise water levels locally and create a diverse range of aquatic habitats (Hodge & Peterken, 1998) by damming up rivers and streams, and reducing flow velocity (Barbour et al., 2001; Gippel et al., 1996). Large woody debris (including fallen stems and large branches) is particularly critical in this regard, and research has shown that nearly 30% of pools within a stream or river may be created by such woody debris (Mossop & Bradford, 2004).
Other research has, whilst not focussing on large woody debris exclusively, identified that as much as 75% of all pools may be created from submerged woody debris (Robison & Beschta, 1990a). Through the creation of these habitats, fish populations can increase, as their range of viable habitat increases – notably for feeding and spawning (Harvey, 1998). However, because even the largest of woody debris will likely not persist for over 50 years, there is a need for a continuous replenishment if streams and rivers are to retain the presence of deadwood-induced pools (Hyatt & Naiman, 2001). When pools are instead created by wood jams, which are made of small (and sometimes also large) branches and stems clustered together, their average viable retention time may only be between 2-3 years (Lisle, 1986). Again, a need for a constant supply of such deadwood is necessary, and this should obviously mean management practices retain trees that can constantly provide for such woody material (Robison & Beschta, 1990b).
Driftwood may be particularly beneficial for fish populations, as not only will its presence control flow velocity, but also protect its banks from erosion, create waterfalls and pools, and thus provide protection for fish spawning as well as increasing habitat diversity (Gurnell et al., 2002). Additionally, driftwood can provide hiding places for species of fish, assisting either in their predatory pursuits or in evading predation (Crook & Robertson, 1999; Werneyer & Kramer, 2005).
Sunken (or partially submerged) deadwood, for those fish species which are insectivorous, can also be highly valuable (Barbour et al., 2001). The wood’s provision of habitat for invertebrates means there is a potential abundance of prey for such insectivorous fish (O’Connor, 1992). A study into the effects of deforestation on wood input levels into woodland stream environments there unsurprisingly showed how reduced amounts of sunken deadwood led to reduced fish diversity and abundance (Wright & Flecker, 2004). In such wood-void streams, wood-eating fish (such as certain species of catfish, whilst not ‘true’ xylivores) may also suffer (German & Bittong, 2009; Lujan et al., 2011), though the loss of diversity in a stream (or river) environment, both because of reduced wood presence and the faster flow associated with such a lack of wood, may also have wider implications for fish species overall (Lancaster et al., 2001; Shields & Smith, 2002; Tsui et al., 2000); particularly when it is understood that a lack of (large) sunken wood is indicative of a degraded stream (Shields et al., 2006). It is also suggested that sunken wood may aid with orientation for fish (Crook & Robertson, 1999).
Deadwood that has fallen and become (partially) submerged is also beneficial, as previously ascertained, because it creates pools within a stream or river ecosystem. These pools are areas of a stream or river where the flow is potentially very slow, and in the redwood forests of California downed trunks and branches of trees are considered to be crucial for constituent salmon populations (Barbour et al., 2001). Notably, in areas of steeper ground, this fallen deadwood can create tiers of pools, which actually enable salmon (that travel upstream to breed) to ascend up the river with more ease, as the salmon can ‘leap’ from one pool to another, and swim against a current with reduced velocity (which is critical for the enabling of salmon to conserve vital energy). These pools also reduce bankside erosion and catch up to 85% of sediment (which may amass behind a large branch or stem, though perhaps even more significantly amongst larger wood jams comprised of deadwood of varying sizes), ensuring the rate of sedimentation of the stream or river is slow and sustainable (Berg et al., 1998; Smith et al., 1993; Thevenet et al., 1998). This is important for the salmon, as females nest within the clean gravel beds in the riverbed, and any marked rate of sedimentation would prohibit this (Madej & Ozaki, 2009). These nesting sites may also, in fact, be located within close proximity to large pieces of woody debris (Senter & Pasternack, 2011). The very same deadwood can also support plant life, particularly when a large stem has fallen across a river, and therefore the plants growing atop the log can shade the river and keep the water cooler – this is also critical for the salmon, which prefer cooler waters (Welsh et al., 2001).
Across the United States, in the Appalachian Mountains, research by Jones et al. (1999) has also revealed that the reduction in sedimentation created by fallen woody debris is critical for other species of fish (including the rainbow trout Oncorhynchus mykiss), that spawn in sediment-free riffles within the forest areas of the mountains. Furthermore, their research highlighted that deforestation along riparian zones as little as 1km in length can have massive adverse effects upon the quality of habitat for fish, due to the removal of the source of such critical deadwood. The associated re-growth after the felling, whilst still injecting debris into the water courses, cannot match the size of the debris from older-growth stands, and therefore rainbow trout occur less frequently and at lesser densities (Flebbe & Dolloff, 1995). Deforestation also increases the risk of severe flooding and high flow velocity within the Appalachian Mountains, which can both extensively decimate viable habitat for rainbow trout within the ecosystem. In part, this is because such factors eliminate the fauna that occupy the river bed, which the trout almost exclusively predate upon.
Beyond the realm of deadwood, the beneficial impacts of shading by large trees adjacent to such aquatic environments can also improve the suitability of the habitat for fish (Beschta, 1997; Larson & Larson, 1996). Using the redwood forests as an example once again, it has been recognised that large conifers that reside by a water course cast shade and thus reduce maximum temperatures and the risk of thermal pollution (Madej et al., 2006). Such cooler temperatures, much like how deadwood can support plants that shade and cool waters, protects critical nesting locations for female salmon, reduces the subsequent mortality of juvenile salmon, and improves their growth rate.
Beyond California, the cooler waters created through significant (50-80%) canopy shading are equally as important for fish, for similar reasons (Broadmeadow & Nisbet, 2004; Broadmeadow et al., 2011; Swift Jr & Messer, 1971). Such canopy shade may also enable for rivers and streams to support macrophytes (plants growing in or near water), which can act as a food source for some fish species both directly and indirectly. Similarly, they can provide refuge for fish seeking shelter from predators (Pusey & Arthington, 2003). Therefore, retaining riparian trees is mandatory, if viable habitats for fish are to be protected (Young, 2000).
I was forunate to be able to spend some time in the New Forest yesterday, having driven back from Somerset after picking up a microscope (more on that, in due time). When last down there, which was during mid-summer, I spent a few hours sojourning around the Bolderwood / Knightwood Oak ornamental drive, with specific focus upon the myriad of mature and veteran beech pollards that dressed the roadside. One beech, even then, alluded to fungal parasitism, given its dire vigour and evident crown retrenchment (perhaps associated with ground compaction, given its close proximity to a car park and the Knightwood Oak). Therefore, I paid a visit to this beech, with the hope of finding some fungi – and I wasn’t disappointed!
I’ll actually be honest and say this beech is testament to the ability for the species to provide for many wood-decay fungal species. I really don’t think I have ever seen a tree more covered in fruiting bodies of many species than this one, and we’ll run through the suspected species below. First, we’ll look at the tree as a whole, however, and from the first image I don’t think there’s any debate over its poor condition. Granted, with the impending demise of a tree, weak fungal parasites and saprotrophs can enter, and this alludes to the cyclical aspect of energy transfer. In time, this beech will be the food for other plants and trees, though for now it’s fungal food.
With fungi still about in good numbers, not a day goes by when I don’t come across some ephemeral specimens. Below, I showcase two very unique-looking fungi, which are both saprotrophs of wood. It’s likely that – at least, if you’re in the UK – that you have come across both before. If not, then now’s the time to look!
Abortiporus biennis (the blushing rosette)
This dude is weird, and is so impossibly distinctive from other polypores that occur on dead wood (I have seen it on actual stumps and fruiting in grass, where it is feasting on roots below ground after the stump has either rotted away or been ground down) that you don’t even really need a microscope to discern it to the species level. In spite of its common name however, it doesn’t always look like a rosette and can instead adopt a quite obscure morphology where pores are on the upper surface and it stays as a whitish blob (sometimes exuding red liquid – notably when young). Thankfully, when it does achieve its ‘potential’, it becomes a very pretty polypore and releases a white spore that can be found to dust any leaves or blades of grass caught beneath the fruiting bodies.
For ease of understanding what I am on about, I have included both examples below so to illustrate the variability of this fungus. Also note that, when fruiting in grass, the roots it is devouring beneath the surface often leads to the fruiting body protruding out from the ground on a rather long stipe, which I have seen reach lengths of over 10cm.
I have not observed this species in a woodland setting as of yet. Instead, examples have all been limited to urban areas (including parks) where canopy cover is either non-existent or very sparse.
Rhodotus palmatus (the wrinkled peach)
This gilled mushroom is found generally on elm, though can also occur on other hardwoods in the UK. Unfortunately, since Dutch elm disease battered our elm population, it has become a rather uncommon sight amongst the landscape. However, it can still be found, and in this instance I spotted a few of them growing on a cluster of downed elm stems.
This mushroom has a rather pleasant smell, is very soft and moist (almost akin to oysters), and when young has quite the artistic form (as we will see below). The stipe is usually offset, and the cap is a very soft pink (though fades with age, in this example).