Trunk reiteration in a Sequoiadendron giganteum

One of the local parks has an absolutely stunning Sequoiadendron giganteum, which I valued (with the Helliwell System) at just under £100,000 in pure amenity value (which I’d say is a conservative estimate – CAVAT would value it much higher, I would suspect). Half way up the main stem however, sits a tree forming within a tree (trunk reiteration). Such a reiteration is really quite awesome, and in their natural range in California such trunk-trunk crotches can support entire mini-ecosystems, and as there may be dozens of these crotches in a single large specimen then one tree can support, in itself, an array of ecosystems (at heights of over 50m above ground). Obviously, the one here isn’t going to do that, though it’s a nice example of trunk reiteration in its earlier stages.

You can see it from here, actually. But this image is really just to give a sense of scale and importance to the tree. It’s literally quite massive.
A zoom-in from the same point as in the first photo.
And here we can really observe the reiterating trunk (half way up on the left). I would love to see how this looks in 50 years time!
Trunk reiteration in a Sequoiadendron giganteum

Improved blog navigation

I have just gone through all of my blog posts and added more categories (and sub-categories), which can be accessed via the side bar (top right). Therefore, particularly for my more scientific posts, there is now a much better means of finding what you want to find (beyond using the search bar). Have a look for yourself, and let me know if you have any thoughts.


Improved blog navigation

Severing roots to put in a fence

Sometimes I just have to wonder why. How does anyone think it’s even remotely a good idea to sever large roots to install a new structure? Surely it’s not even a case of lacking common sense, as it’s got to be instinctual to stop and think “hmm, if I remove this part of this object, will the result be something other than beneficial?”. In this case, the answer would be a resounding yes, and for that reason I’m flabbergasted that the individual still went ahead and sliced off a load of tree roots. Now, we can observe a hazard, whereas before we couldn’t have observed one.

One word: lunacy. We, as professionals, can learn as much as there is to know about trees, but such work can be undone so readily by those who just genuinely don’t exercise thought. A sobering lesson, perhaps, that we need to extend our reach to those who may never think, nor even care, about trees.

…and now let out a massive sigh, and question the sanity of some.
Severing roots to put in a fence

Using an electronic nose to detect decay in tree roots

Following on from my initial post about using electronic noses to pick up decay within a tree (which I suggest you glance over before reading this), I thought I’d visit further literature on the subject but with more of a refined focus. In this instance, we’ll be looking solely at the ability for electronic noses (specifically the PEN3 electronic nose) to detect decay within the rooting environment of trees. As was elucidated to in my previous post, the PEN3 can pick-up decay from root systems in the field setting, though here we can observe how a slightly earlier study fared in terms of its efficacy upon root samples inoculated in the laboratory and stored beneath different types of soil.

Because not all fungi will colonise the root system of a tree, the fungal species chosen in this study were Armillaria mellea, Ganoderma lucidum, and Heterbasidion annosum (a shame that Meripilus giganteus was not included). These three species can be considered principal root-rotters. These fungi were, once cultivated and made into mycelial plugs, brought into contact with healthy root samples (1-3cm in diameter and 2-10cm in length) of adult trees of the species Aesculus hippocastanum, Cedrus deodara, Liquidambar styraciflua, Platanus x hispanica, and Quercus robur. Such roots, complete with fungal inoculum, were then buried beneath sourced urban soils (and also ‘professional’ nursery soils), in order to reflect what soils the PEN3 would need to ‘sense’ through if it were to be applied in the ‘field’, and a period of time was given for the mycelium to begin colonising the root samples and. After a year, the samples were ready for testing. Then, following a set of complex processes that only a three-page methodology could ever fully encapsulate, it was time to look at the results (which are equally as complex, so I’ll do my best to simplify them).

What the researchers found was that the ability for the PEN3 to detect decay in the roots of different tree species by different wood decay fungi, all whilst under different soil types, was quite good (and more notably for urban soils) – see the below graphs. The nose was able to differentiate between healthy and decayed samples of root tissues with a high degree of variance between the two, meaning that there was little to no scope for ‘confusion’ between healthy and decayed root samples. Similarly, it was able to significantly differentiate between the fungal agents causing the decay in certain instances, and particularly in the cases where the fungi-tree relationship would naturally occur in the ‘field’. For example, the nose could identify (but not significantly differentiate between the two) oak roots colonised by A. mellea and G. lucidum – both are natural pathogens of the species. Granted, this trend wasn’t conslusive, as the nose couldn’t differentiate between healthy and A. mellea-infected samples in horse chestnut. The second set of graphs outlines the data collected with regards to differentiating between the decay from different fungal species.

The ability of the PEN3 to discriminate between healthy (green) and infected (blue) tree roots for A. hippocastanum (a), C. deodara (b), L. styracuflua (c), and Q. robur (d).

Under the urban soils, the nose worked more effectively, and this is considered to be because soils also emit their own VOCs, and professional nutrient-rich soils will have a ‘stronger’ emission. However, these professional soils still didn’t stop the PEN3 from identifying whether a root was decayed or healthy.

How the PEN3 differentiated between decay from different fungi (A. mellea [blue], G. lucidum [red], H. annosum [grey], and healthy [green], on the tree species A. hippocastanum (a), C. deodara (b), L. styraciflua (c), P. x hispanica (d), and Q. robur (e).
Evidently, some work is required in ensuring the PEN3 becomes very able to differentiate between the decay from different fungi on different tree species (and under different soils), though even from the graphs above we can see how there is, by-and-large, some degree of differentiation between the readings (as shown by the clusters, which infrequently overlap, but are sometimes close together). The decay from different fungi in Cedrus deodara appears to be particularly well differentiated, whilst decay in Aesculus hippocastanum is less so. Of course, it’s mainly a calibration and sensory game, and if the PEN3 can be accentuated in sensory ability then there’s certainly scope for this to be a very effective field diagnostic test for decay of root systems, and all whilst not having to damage the tree in any manner. Compiled with the more recent results of the PEN3 being able to work in the ‘field’, it’s an interesting piece of technology to keep an eye on.

Source: Baietto, M., Pozzi, L., Wilson, A., & Bassi, D. (2013) Evaluation of a portable MOS electronic nose to detect root rots in shade tree species. Computers and Electronics in Agriculture. 96 (1). p117-125.

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Using an electronic nose to detect decay in tree roots

A walk in the forest – the health benefits

I don’t think that one can question the anecdotal benefits of walking through a woodland or forest. Away from civilization, it’s a time where one can really begin to relax, let the mind shut off from stressors, and let the eyes take in the wonderful sights. I know, from personal experience, that a woodland walk can bring about a state of calm and ‘inner peace’, and I often find myself exploring for hours on end only to realise I’ve been gone for half a day, am slightly lost, and need to walk home before it gets too dark.

Personal journeys aside, there is a growing amount of evidence to state how woodland and forest settings can be used to reduce anxiety, treat (as part of a wider range of things) stress, and maintain a general good state of well-being. In this post, I thought I’d look at a study from Japan that assessed how the practice of ‘Shinrin-yoku’ (‘experiencing the forest’) can impact upon the mental and physical state / well-being of individuals (for this study, this was 12 male university students of 21-23 years of age). The forest in question was an old-growth broadleaved deciduous forest, and the experiment was undertaken in the height of summer.

In order to quantify the benefits of Shinrin-yoku, the 12 men were separated into two groups of six. One group spent the first day in the forest and the other in a nearby city (to enable for comparisons to be drawn), and on the second day the two groups swapped locations. All 12 men stayed in the same hotel, which was located around one hour away from either site (by car). Before leaving for each location, they would have breakfast, and upon return they would have dinner. Once at each location, individuals had their day planned so that they would first spend some time in a rest room on the site, and then go on a leisurely but lone walk (a pre-planned route) within the study area. They would then return for lunch at the rest room on the site, before remaining in the rest room to look at the scenery (by themselves). During each day, all individuals had physiological data collected from them, including blood pressure and pulse rate, before and after each activity (at the hotel for breakfast, at the rest room prior to the walk, after the walk, before looking at the scenery, after looking at the scenery, and back at the hotel for dinner). The men were also asked to rate, on 13-point scales, whether they felt comfortable or uncomfortable, and calm or roused (agitated). They were also asked to rank how refreshed they felt. Again, these subjectivity tests were taken six times each day, for all individuals.

The results of this study are very interesting, as they show that the 12 men almost always preferred the forest experience in a subjective sense, and their physiological measurements backed this up. Benefits were particularly evident after the men had experienced the forest (after the walk and after looking at the scenery from the rest room), though even prior to going on the walk and observing the scenery there were marked benefits (as if the expectation automatically improved an individual’s perception of well-being, and their physiological condition). Below, we’ll look at specific data sets and what they show.

How calm or roused the men felt at each site and at each measurement time. * p<0.05; ** p<0.01

In terms of how calm the men were, one can clearly observe how the forest walk had a significant impact upon their state of mind, which was even more significantly impacted following a period where they individually took in the view from the rest room site. Alarmingly, the men actually felt slightly agitated after observing a city vista. However, we can observe how the impacts on the feeling of calm were largely immediate, as by the evening there was no significant difference between the two data sets. However, the fact that those who experienced the forest felt calmer in the evening than those who experienced the city is interesting, as it is the inverse of the morning’s results, and even prior to the walk’s results.

How comfortable the men felt at each site and at each measurement time. * p<0.05; ** p<0.01

With reference to how comfortable the test subjects felt, we can clearly see how the forest experience (even when not on site, but eating breakfast at the hotel before heading out to the forest) made the men feel significantly more comfortable. The forest walk and scenery were particularly significant in raising the level of comfort within the men, whilst the city walk and scenery actually made them feel very uncomfortable. Following each walk and each observance of scenery in both locations, all men were significantly impacted by the experience, and the benefits and adverse impacts of these experiences have already been mentioned and can be seen in the graph above.

How refreshed the men felt at each site and at each measurement time. * p<0.05; ** p<0.01

Looking at how refreshed the men felt throughout the day, we can again see how the forest experience trumped the city experience. Again, the refreshed state of each individual rose significantly after each experience, and individuals were significantly more refreshed after forest experiences (notably after observing the scenery). We can now see a trend, that observing a forest view from a point of rest is certainly very beneficial, and studies on how hospital recovery time is positively impacted by the view of trees from a window now start to make yet more sense (as mental well-being manifests in the physical form, via blood pressure levels, and on on).

The pulse rate of the men at each site and at each measurement time. * p<0.05; ** p<0.01

Moving onto physiological impacts of a forest experience, we can see how the pulse rate of the men was, on average, lower before and after each forest experience, and also in the evening following the day’s experience. Only prior to the forest visit was pulse rate higher, and perhaps this was down to a form of excitement and / or apprehension (I am only speculating). Interestingly, the pulse rate of the men was quite markedly lower prior to the walk when they were awaiting a walk in the forest, suggesting that even the prospect of walking in a forest is physically calming, though curiously this doesn’t align fully with the men’s subjective feeling of calm prior to a forest walk. Therefore, we can observe perhaps a slight disparity between perception and actual physiological responses from the individuals to the prospect of a forest walk (perhaps, because walking in a city is more of the norm, they were more nonchalant about such a walk?).


The blood pressure of the men at each site and at each measurement time. * p<0.05; ** p<0.01

As for blood pressure, we can once again see how it was lowered in both the top (systolic) and bottom (diastolic) readings. Yet again we can see how the forest walk and observance of forest scenery were beneficial for lowering blood pressure, though this was more significant with the sitting down and watching of the scenery. Perhaps this is to be expected, as walking, which is a physical activity, will raise blood pressure (even slightly). Importantly, this benefit progressed into the evening, where evidently the men were still more relaxed, albeit not significantly so.

So there we have it. Forests are good both physically and mentally! Please, however, bear in mind this is only a study of 12 men of the age 21-23, so it’s by no means a conclusive study, but it’s a useful indicator of how a larger study might turn out. Further to this, it was done in the height of summer in a broadleaved forest of significant age, so we must also accept the marked benefit may also be seasonal (and younger forests, perhaps also coniferous in nature, may elicit a different response). There may also be differing cultural responses, and therefore replications in other areas of the world would also be interesting to see. I’ll let you look over the graphs again so you can form more conclusions for yourselves, though I hope this has been of use for many who are reading this. For me, it certainly aligns with my own experiences from walking through broadleaved woodlands. And I write all this as I overlook miles of fields and woodlands from my bedroom window, which has also had a very calming impact upon me – that is without doubt.

What’s not to love…!

Source: Tsunetsugu, Y., Park, B., Ishii, H., Hirano, H., Kagawa, T., & Miyazaki, Y. (2007) Physiological effects of Shinrin-yoku (taking in the atmosphere of the forest) in an old-growth broadleaf forest in Yamagata Prefecture, Japan. Journal of Physiological Anthropology. 26 (2). p135-142.

A walk in the forest – the health benefits

More books and more reading

And so, the book shelves continue to bulge. These additions are a little different to the more standard tree books, as I’ve taken an interest in understanding more about the traditional and cultural values of trees as of late (plus wanting to learn more about redwoods, before visiting next year). Below is the list of books, and where you can purchase them from (assuming you’re interested).

Links below!

Top rowThe Spirit of Trees (Hageneder, F.); The Olive: Tree of Civilization (Train, J.)

Middle rowThe Redwood Forest (Noss, R.); Coast Redwood: A Natural and Cultural History (Evarts, J. & Popper, M.); From the Redwood Forest (Dunning, J.)

Bottom rowPlants of the Bible and the Quran (Musselman, L.); Tree Wisdom: The Definitive Guidebook (Paterson, J.); Celtic Tree Magic (Forest, D.)

More books and more reading

Trametes gibbosa on a fallen hornbeam (Carpinus betulus)

It’s seemingly the beech that tend to be host to the greatest perennial fungal abundance in Epping Forest, and so whilst looking for fungi on constituent beech trees I came across a fallen hornbeam. On one of the larger stems, I noticed a cluster of fungal brackets, which turned out to be what I strongly consider is ‘the stumpgrinder’ Trametes gibbosa (syn: Pseudotramates gibbosa). Nice to see from a general interest point of view, and also good to see from a mineralisation angle, as this fungus is a very good decomposer of deadwood (hence the name ‘stumpgrinder’). Essentially, this’ll do what a mechanical stumpgrinder does (I suppose like many Trametes species), though in a more ecologically-friendly way and less instantaneously.

Pseudotrametes gibbosa carpinus1
Evidently quite markedly decayed already, if you look closely to the left of the image you can spot the brackets.
Pseudotrametes gibbosa carpinus12
Here they are upon the stem.
Pseudotrametes gibbosa carpinus13
A little closer, so that we can appreciate their morphology and colouration.
Pseudotrametes gibbosa carpinus14
Closer still!
Pseudotrametes gibbosa carpinus15
And the underside reveals the elongated tubes.
Pseudotrametes gibbosa carpinus6
Taking a cross-section, we can also see the pure white inner flesh and the depth of the tube layer.
Trametes gibbosa on a fallen hornbeam (Carpinus betulus)

The benefits of large woody debris for breeding salmon

We may usually think of deadwood as something that benefits terrestrial species (bats, insects, fungi, mammals), though this is not the limit of what organisms may benefit from its presence. Many rivers and streams will, at some point in their existence, run through woodland and adjacent to hegderows, and beyond the beneficial cooling effects of a dappled shade courtesy of a canopy cover, the provisioning of deadwood (coarse woody debris) into the aquatic ecosystem may be of marked benefit for fish. Without question, the exact requirements of a woodland stream or river will vary depending upon constituent species, though by-and-large the presence of deadwood can be considered to be of benefit. The slowing-down of flow to create pools can aid with feeding, can certainly help salmon travelling upstream (in terms of enabling them to expend less energy on reaching egg-laying grounds), and can also reduce the build-up of silt on the stream bed by reducing bank erosion (‘clean’ gravel beds are critical for successful egg-laying). Benefits beyond this absolutely exist, and in this case we’ll be looking at the relationship between Chinook salmon redds (spawn sites) and large woody debris within the stream / river environment in a Californian river.

The study site chosen by the researchers was a 7.7km stretch of the lower Mokelumne River, where around 90% of all the river’s Chinook salmon redds are created. At its source, some 3,000m above sea level, its watershed is dressed with mountainous forests, before flowing westwards through oak woodlands and agricultural fields clad with tree belts and hedgerow. Riparian zones adjacent to the river are around 20m in width, and the constituent trees (alder, cottonwood, oak, walnut, willow, etc) reach heights of up to 25m. The river ends at its confluence with the San Joaquin River. The Mokelumne River is considered to be of medium size, with a channel width ranging from 15-83m (averaging at 31m). The below map gives more of a representation of the river’s location.

The location of the study site in the wider landscape.

Because of the historic management of the river (gravel bed extraction, salmon fishing, and so on), the river had actually been rather degraded up until more recently (management began in the 1960s to repair the degradation). Improvements to the river involved the addition of significant (over 100,000 tonnes) amounts of gravel and cobble (for improving spawning beds), and this has served to markedly increase Chinook salmon populations to the point that over 2,000 redds are created each year (up from only a couple of hundred). A great deal of the gravel augmentation took place in the 500m stretch of river west of the Camanche Dam (this dam sits just to the east of the study site), and was added in a way that made the river bed heterogenous in nature (providing riffles and pools, viable egg-laying sites, and even locations for adult salmon). Boulders were also added, as were large pieces of woody debris. This woody debris was buried in parts by gravel, so not to have the woody debris drift away.

The lower Mokelumne River. Source: Wikimedia Commons.

In this study, a total of 340 pieces (plus nearly 200 more where there we no redds) of large woody debris in the study area were surveyed and mapped (as redds were located nearby), where the average length was 6.9m (give or take 4m), and the average diameter was 23cm (give or take 12cm). The large majority (70%) of the large woody material was oriented in the direction of flow, and only 20% was oriented laterally (and never beyond 6m into the river). A total of 59% of the 340 deadwood pieces were located within the river but no more than 2.5m away from the river margin. The rest resided (at least partially) upon the bank. 65% of the deadwood was at least significantly decayed, and much of the identifiable deadwood was from alder.

In the first 3km of the study site, Chinook salmon utilised an area, 10m in radius, surrounding large woody material located in riffles (to a total of 68% of all redds). In the western 4.7km, this dropped to 44% of all redds. In many instances, these redds were situated downstream from large woody material, and were located in areas where there had been gravel augmentation. Furthermore, most of the redds were found within a 10m margin from the river bank, which is where 90% of all woody debris was also located. In this sense, one can identify how large woody material is certainly important for Chinook salmon redds, and the addition of such woody material to the river ecosystem is likely to have been a marked driver behind why Chinook salmon populations have increased. Reasons are because of, for example, altered flow velocities, increased levels of dissolved oxygen, cooler temperatures, and the shelter (against predators and other female salmon) provided by woody debris for egg-laying females (a larger list is given at the end of the journal article).

By a similar token, the addition of gravel would have provided improved conditions for redd creation by female Chinook salmon, though it is perhaps almost certain that the two, when combined, have the most beneficial impact. In fact, the researchers suggest that the much-increased habitat complexity associated with their presence is of great benefit and therefore, from a river restoration perspective, large woody material should be incorporated into management projects associated with ecosystem rejuvenation.

Source: Senter, A. & Pasternack, G. (2010) Large wood aids spawning Chinook salmon (Oncorhynchus tshawytscha) in marginal habitat on a regulated river in California. River Research and Applications. 27 (5). p550-565.

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The benefits of large woody debris for breeding salmon

Churchyard lime pollards

I was out walking in and around the village where my girlfriend lives yesterday (Easter Friday), after we thought we’d take advantage of the nice weather. After going through some fields and generally seeing just an abundance of dead elm (thank you Dutch elm disease), we finished up by walking back past the village church (not where the dead elm are remembered). Within the grounds sat dozens upon dozens of pollarded lime trees, almost perfectly uniform, and certainly high in amenity value. I confess that they’re probably some of the best pollards I have seen outside of a traditionally-managed wood pasture, and therefore thought some of you may be interested in them as well (granted, I am easily amused, having found joy on numerous occasions in looking at the somewhat vulgar Ganoderma applanatum / Ganoderma australe). The beauty with these limes is that, even during winter, they’re so interesting. A fine example of year-round interest.

A lovely greeting!
Here we can see them from a different angle. The entire periphery of the site is also lined by such limes. It absolutely creates a formal landscape, that fits with the theme of a graveyard (in the nicest sense).
Some fabulous knuckles have formed on the limes. They must be pollarded every few years, one would imagine.
Churchyard lime pollards

Urban soil and mycorrhizal symbiosis – is it always lower?

Associations (symbiosis) with mycorrhizal fungi are necessary for a vast number of tree species, and for those where associations are not necessary for (mainly pioneer species such as willow and birch) then such a lack of association will usually lead to the tree having significantly stunted growth. In this sense, a symbiosis between tree roots and mycorrhizal fungi is very much crucial. Therefore, where associations are lacking of abundance, which may particularly be the case in urban environments (because of soil compaction, construction damage, changing pH levels due to pollution, and so on), trees may markedly suffer. In fact, I have looked at a paper quite recently on such a lack of mycorrhizal symbiosis with fine root hairs in urban locations.

Granted, certain tree species do fare rather well in the urban environment, and therefore it may be the case that these species are able to associate more successfully with mycorrhizal fungi (amongst other reasons). By a similar token, the properties of the fine root mass of trees in urban areas may differ from rural locations, which of course would have implications for mycorrhizal associations. As a means of testing this, the well-known and well-used tree species horse chestnut (Aesculus hippocastanum) was studied across four urban and two rural sites in late autumn in Poznan, Poland, with specific focus upon the extent of arbuscular mycorrhizal colonisation in the trees’ root masses, the properties of the fine rooting masses, and soil chemical properties. The authors note that the horse chestnut is an ideal tree species to use for such a study, because is is well-adapted to the urban environment, and has been cultivated for ornamental planting for many centuries.

Briefly touching upon the actual study sites, the first two urban sites (URB1 & URB2) features horse chestnuts planted in an avenue between 1909-1911. this avenue is 10m wide, and on either side sits some form of public highway. The avenue has always had poor soil conditions, and in 1998 the two URB sites were mulched in an attempt to improve soil conditions. Site URB1 has, since then, received routinely mulch applications, whilst site URB2 hasn’t. The third urban site (URB3) is in the city centre and near a main public highway, within the Henryk Wieniawski Park. This site was planted with horse chestnuts (amongst other species) in 1907 and 1910. URB4 (a closed cemetery in General Jan Henryk Dabrowski Park) consists of many tree species, including horse chestnut, which were planted somewhere between 1830-1930. The two rural locations were both where horse chestnuts were situated in Wielkopolska National Park, which is 20km to the south of Poznan. The two locations were within horse chestnut avenues, bordering agricultural fields, established during 1800-1850, making them some of the oldest horse chestnuts in the region.

The avenue where sites URB1 & URB2 were located. Source: Wikimedia Commons.

With regards to the results, soil analyses identified that lead and copper levels were significantly higher in urban environments, and that elements such as calcium, carbon, magnesium, phosphorus, potassium, and sodium, also varied between all six sites to rather marked extents. No significant difference was found between sites for elements such as nitrogen and sulphur and, overall, the toxicity of urban soils (associated with higher levels of lead, and sodium, in particular) was considered to be only of a low level, and rural sites had a level toxicity as well because of chlorine (associated with fertilisers).

Despite this, the rural sites were shown to be significantly different in soil characteristics to the urban park sites (URB3 & URB4), which were in turn significantly different to the street-side urban sites (URB1 & URB2). Similarly, fine root characteristics of the horse chestnuts studied varied significantly between the rural and urban sites. In sites URB1 & URB2, for example, the fine root biomass was 1.6-2.2x greater, as was fine root length, surface area, and volume. This was very likely because of the mulching undertaken on these sites, which would have, particularly in the case of URB1, consistently improved soil conditions in the upper layer, thereby enabling better fine root growth.

However, fine root tip density was 1.3-1.4x lower in urban sites. Conversely, in rural sites, fine roots were thinner, and specific fine root lengths (the ratio of fine root length and the dry mass of such fine roots), and also specific fine root areas, were greater. This suggests that those horse chestnuts in rural areas, because of the better soil conditions (reduced bulk density and associated soil compaction), had the ability to produce finer rooting masses that could disseminate out into the soil with greater ease. In turn, nutrient and moisture uptake is, theoretically, easier for the tree.

Interestingly, this is where the differences end. In relation to the rate of colonisation by arbuscular mycorrhizal fungi (specifically, vesicles, hyphae, and coils), and even fungal endophytes, there was no significant difference between those horse chestnuts in rural environments and those in urban environments (though urban settings did yield greater abundances of arbuscular mycorrhizae and fungal endophytes, on average – around 1.2x higher for arbuscular mycorrhizae). The horse chestnuts at URB1 & URB2 had the highest abundance of vesicles, for example, and those at URB3 had the highest abundance of hyphae and coils (as shown in the table below). The abundance of vesicles is considered to be because they are most routinely found during late autumn, which coincided with the timing of this study.

Colonisation rates for each site.

Such results are also interesting because they are vastly different to the study I looked at in this blog post, which presented arbuscular mycorrhizal fungi colonisation rates down in the 20% range for urban sites and the 40% range for rural sites for the horse chestnut. Perhaps, the stressors that could impact upon such colonisation rates are not so evident in Poznan, when compared to Ontario, Canada. Additionally, as the horse chestnuts studied here are all very much mature, perhaps their likely longer existence in situ has enabled for a greater rate of mycorrhizal symbiosis.

Furthermore, the authors did note that the horse chestnuts in the rural locations were more extensively defoliated by horse chestnut leaf miner (Cameraria ohridella) and leaf blotch (Guignardia aesculi). Compiled with the fact that agricultural fertilisers would have been applied in the vicinity of the rural horse chestnuts (as known by the high chlorine content of the soils), such factors may have lead to lower colonisation rates by arbuscular mycorrhizal fungi – for the latter factor, there is a vast pool of research outlining how fertilisers adversely impact upon such associations.

In essence, therefore, one can conclude that, at least in this case, urban soils are not poor enough to impact upon mycorrhizal associations with horse chestnut roots. From this, it can be posited that, if urban soils are looked after so that they are not hugely adverse in properties, then they can support similar, or higher) levels of mycorrhizal fungi associations than rural locations. Because such associations are critical for the health of trees, it may enable for urban trees to live healthy lives that are not prematurely terminated by damaging environmental factors. Therefore, focus should be paid to the soil environment, as such an environment may be a key (of perhaps many) to safeguarding our urban tree populations.

Source: Karliński, L., Jagodziński, A., Leski, T., Butkiewicz, P., Brosz, M., & Rudawska, M. (2014). Fine root parameters and mycorrhizal colonization of horse chestnut trees (Aesculus hippocastanum L.) in urban and rural environments. Landscape and Urban Planning. 127 (1). p154-163.

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Urban soil and mycorrhizal symbiosis – is it always lower?