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.
This is only a short post to close-off the weekend, though ideally one that is appreciated – notably, because it showcases the fungus Pseudoinonotus dryadeus in its senescent state and the associated pronounced buttressing employed by the host oak (Quercus robur). I don’t know exactly where this was, though it somewhere along the A371 in one of the villages between the border of Dorset and Somerset through to Cheddar (as if that narrows it down!).
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).
Grazing rights on commons must be safeguarded, for these rights are an historical relic of an otherwise aggressively-advancing culture. Indeed, there are a wide range of benefits from grazing, including the ecological, socio-economic and cultural, though the New Forest – and probably many (or all!) other sites where grazing occurs under tree canopies – is also subject to the damage associated with unrestricted grazing.
Certainly, the number of horses within the New Forest, the unrestricted nature of their movement and the lack of safeguarding measures (and probably food) around veteran trees has resulted in some quite substantial (yet currently rather isolated and sporadic) damage to the beech trees. I would expect much of the damage comes during winter, when the horses are searching for food that is not in such great abundance, and luckily (or not!?) I managed to watch a few horses de-barking a fallen limb and the butt of one particular beech tree (whilst another horse was grazing upon the lower branches of holly), in addition to some recent examples of damage on other beech.
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.
Yesterday, as part of our monthly aim of visiting sites across the south east of England, a half-dozen strong group of arboriculturalists made the journey to London’s Greenwich Park – myself included. Indeed, as much of the park consists of deciduous specimens (principally, avenues of Castanea sativa and Aesculus hippocastanum), the park was rather bare in the foliage sense, though such barren canopies did allow us to appreciate the true magnitude of – most notably – some of the veteran sweet chestnuts. The frost-clad ground and crystalline sky provided a similar beauty, and thus we shall begin with one of the most iconic vistas from Greenwich Park – the city skyline.
Of course, we didn’t go there for the view, so let’s get into the main bulk of this account – trees and fungi. There’s no real order to how the below series of images rank, so don’t consider this post a chronological reflection of our trip!
Perhaps the best place in which to start the core section of this post are the huge sweet chestnuts, though we must begin on a rather sombre note. With a species of Phytophthora suspected on site and some of the older individuals exhibiting stunted and chlorotic leaf growth, there is a valid concern for the future of these veterans which is – without doubt – highly concerning. During the winter months, fully appreciating this contemporary issue is difficult, though we did spot some foliage on the floor that was certainly smaller in size than would be typically expected. Alas, this situation should not impact adversely on our admiration of these trees, and should in fact raise attention and draw intrigue to those within the industry and beyond, with an eye to ensuring we continue to care for the current and future populations of veterans. Therefore, promoting the Ancient Tree Forum and their most recent publication on ancient and veteran tree management is critical. And now, for some fine shots of various veterans!
Some of the veteran sweet chestnut we came across were also home to two annual common wood-decay fungi – Fistulina hepatica and Laetiporus sulphureus. Without doubt, the state of the fruiting bodies was not good, though when ravaged by time, wind, rain, frost and sun, to still even have a form is respectable! Certainly, a summer visit would have yielded a much greater haul of these two fungi on the sweet chestnuts, so a summer visit is probably on the cards.
Away from the sweet chestnut, there was a variety of other large trees. Below, I share the ones that were home to fungi, through the identification of fruiting bodies. Absolutely, all trees on site are host to many species of fungi, though fruiting is not necessary in many instances, and it certainly costs the fungus energy to create and sustain. To begin, we’ll take a look at the ever-accomodating mature Robinia pseudoacacia in the park, which didn’t disappoint. In all, the population supported three species of wood-decay polypore, as we will see in the below images.
Steering attention away from false acacias, I now turn towards a focus on the brown-rotting polypore Rigidoporus ulmarius. With both horse chestnut (Aesculus hippocastanum) and beech (Fagus sylvatica) on the site, the chances are that there would have been a few examples of this fungus. Indeed, there were, as we will observe.
Greenwich Park also has a good number of large plane trees (Platanus x hispanica). The most abundant fungus on these trees was massaria (Splanchnonema platani), and there probably wasn’t a plane in the park that didn’t show at least some signs of its presence. However, it was the large plane with Inonotus hispidus that gained much of my eager attention, given I am not often around mature planes with extensive fungal decay.
To round this post off, which has admittedly taken a long time to write, I’ll share some lovely images of a not-so-lovely bird – the parakeet (Psittacula krameri). Plaguing many of London’s parks and beyond, these things produce an utter cacophony and are certainly invasive, though one must admit that they are incredibly photogenic. Below, I share a few examples of where the parakeets were using cavities for shelter.
“The tree is damaging my brick wall!“, they exclaim. “Fell the tree!“, they demand. Frankly, the word “no” would be sufficient, in at least a good portion of cases. After all, there’s an easy engineering solution that not only balances the need for a crack-free wall and the presence of a tree, but also signals ingenuity and a reasoned approach to situation management – the bridging of said wall around the butt of the tree and its immediatly-adjacent root plate. The issue is addressed in various publications, including Tree Roots in the Built Environment, and it is a message that needs to be communicated to homeowners and tree owners alike. More of the below, please!