(Arboricultural-styled) 'Fact of the Day'

[David Humphries]

This was in 2014 (probably written a good few months before, maybe even in late 2013), so perhaps the threat was not as evident as it is now. The scope of this was just assessing these two, as even leaf blotch was cut out. No doubt the horse chestnut is being brutalised, and many other tree species as well. Rather depressing, to be honest.

 

Xylella's been on the scientific radar for decades.

 

 

Just not been talked about 'locally' until the last two or three years.

 

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[Kveldssanger]

Indeed. I suppose they didn't consider it pertinent to the discussion, for whatever reason. I have no doubt Glynn knew about it, amd I'm sure he'll write a lot on it in the coming few years!

[David Humphries]

........ I have no doubt Glynn knew about it, amd I'm sure he'll write a lot on it in the coming few years!

 

Probably already has, you two share a monopoly on the word enthusiasm

 

 

 

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[Kveldssanger]

Hahah I love what I do and absolutely love learning more things. What's not to be enthused about!?

[Kveldssanger]

16/03/16. Fact #174.

 

The use of an increment borer to obtain a core sample from a tree may be used for a variety of reasons, including tree ageing, determining past climatic conditions in which the tree has existed through, and ascertaining wood properties (generally associated with establishing internal decay). However, taking a core sample is not without its issues. For instance, around the wound site, the tree will form reaction zones in an attempt to compartmentalise the damage, and such damage may also breach existing reaction and barrier zones established from prior instances of wounding and internal spread of decay. Therefore, there is a theoretical risk of such cored trees suffering from the injury, and potentially having a reduced life expectancy / increased mortality rate because of an increased spread of internal decay.

 

In order to test this theoretical assumption, the authors of this study commissioned a survey of unmanaged Picea abies (Norway spruce) stands in the Scatlè Forest, which lies within the Swiss Alps. In two small segments of this forested area, when the entire forest became protected under Swiss law in 1965, all of the trees were inventoried and many of the spruce (approximately 25%, amounting to 619 spruce) of over 8cm in diameter at breast height were cored. In 2011, the authors re-visited 22 of these trees, and paired them with 22 ‘control’ (un-cored) trees in similar micro-sites within the very near locale (basically, one could say they were paired with a close neighbour). At these study trees, they used sonic tomography (PiCUS Sonic) and electrical resistivity tomography (PiCUS Treetronic) to ascertain internal wood properties, and considered any trees to be decayed only if it had an evidently and extensively decayed heartwood region in both of the PiCUS tests. The tomograms below show, as an example, how the two PiCUS tests outlined trees with decay and trees without decay.

 

The tomograms marked A and B are sonic tomograms (of the same spruce), whilst C and D are electrical resistance tomograms (of another spruce). The top two images are from a spruce considered largely free of decay, whilst the bottom two are considered to be of a spruce that is significantly decayed within the heartwood zone.

 

Following these tests, the authors took samples from ten (five neighbouring pairs) of the trees (six with observable decay and four without observable decay, from the tomograms – the six decayed trees were not necessarily considered to be extensively decayed, however), to determine whether the two fungal heart rot pathogens Heterobasidion annosum and Armillaria sp. were present. These two fungal pathogens are viewed as significant agents of damage, within coniferous stands across Europe. These samples were taken at heights of 1m, the height of the tomograph measurements (around 45-90cm), and at the butt.

 

In light of the data collected, it was found that only four of the 44 Norway spruce had heartwood decay, and just one of these four had been cored in 1965 (just over 9% of trees surveyed were thus deemed to be decayed). Curiously, this is lower than the accepted ‘background rate’ of decay within coniferous stands across Europe, which is considered to be between 15-80% (depending upon the study). The reason for this, it is suggested, is that because the stand is unmanaged, the damage to remaining trees associated with timber extraction has not occurred. This has therefore led to the trees not being wounded to such an extent as conifers in harvested stands would be wounded. Furthermore, because the cores were taken in 1965, it can be said that they are unlikely to have enabled for decay to extend into the region, as if they had increased the risk of decay, then more of the cored trees would have shown up as being decayed with the tomographic surveying. When recognising that Heterobasidion annosum can potentially extend in the stem by 30-40cm a year, and the cores were taken at 40-90cm up the stem in 1965, if there cores would have facilitated in heartwood decay then they would have done so already.

 

From the ten trees cored for living samples of Heterobasidion annosum and Armillaria sp., it was found that 75% were colonised, discoloured, and in six cases observably decayed by either of the fungi. Generally, these decayed trees occupied a space in close proximity to one another, and of these trees, Heterobasidion annosum was observed to be a much more comment (seven trees) agent of decay than Armillaria sp. (one tree). The close proximity of decayed spruce to one another is perhaps not surprising, when one recognises that both fungi can colonise via active pathogenesis (root-to-root contact only, in the case of Heterobasidion annosum). Therefore, it is perhaps more likely that decay is not facilitated by increment coring, but instead root grafts between spruce trees. In addition, because Heterobasidion annosum has a life expectancy of around 40 years, after which it has a high mortality rate (per tree), it seems yet further unlikely that the cores taken in 1965 caused the decay and discolouration in the ten tested trees. It is far more likely, instead, that infection came (long) after, given that 75% of the ten tested trees had living mycelium found in the core samples taken. Not only this, but artificial core inoculation of trees with Heterobasidion annosum has a very low success rate, and therefore in this sense taking core samples is also very rarely going to induce decay by the fungus.

 

To conclude, it can be asserted that increment coring spruce trees is not at all routinely going to induce decay by Heterobasidion annosum or Armillaria sp. Of course, other decay fungi may potentially utilise cores that are not studied here (Phaeolus schweinitzii, for example), and because the PiCUS is not as effective at discerning only slightly decayed wood, the 9% of trees deemed to have extensive heartwood decay (of which only one had been cored) may be a slightly conservative estimate. Further to this, because the sample size was only small, larger-scale studies may be needed to add weighting to the findings contained within this report. Nonetheless, it can hardly be stated that increment coring has massively adverse impacts to tree health, if the results here are anything to go by.

 

Source: Wunder, J., Manusch, C., Queloz, V., Brang, P., Ringwald, V., & Bugmann, H. (2013) Does increment coring enhance tree decay? New insights from tomography assessments. Canadian Journal of Forest Research. 43 (8). p711-718.

[Kveldssanger]

17/03/16. Fact #175.

 

Trees, whether in the urban or rural setting, provide a huge array of ecosystem services. A service that is of particular relevance to human activity is the ability for trees to filter out harmful airborne pollutants, such as ozone and nitrogen oxides. Of course, the ability for a tree to filter such pollutants is determined, to a large degree, by its phenology and morphology, and this phenology and morphology is considered to be influenced by the airborne pollutants themselves (ironically!).

 

In order to add substance to this premise, the authors of this study looked at how ozone, nitrogen dioxide, nitrogen oxides, and particulate matter, influenced the onset of flowering and leaf emergence in the tree species Aesculus hippocastanum (horse chestnut – red dots), Betula pendula (silver birch – white dots), and Corylus avellana (common hazel – yellow dots). For silver birch, the effects of air pollution on leaf morphology were also observed. The study was undertaken, during 2010, in the German city of Munich, and across the urban-rural gradient. The below map shows rather specific site locations.

 

A map of all study locations (dots relate to those mentioned above, though white dots with black dots within are sites where ozone and nitrogen dioxide were measured. In terms of the colours on the map behind: urban (red), forest / pasture (green), arable (yellow), and rivers / lakes (blue).

 

Data relating to air pollution was largely sourced from pre-existing surveys completed across Europe in the early 2000s, though site-specific measurements were taken at some of the sites where silver birch were studied (as marked by the white dots with black dots inside. Therefore, comparisons could be drawn between short- and long-term differences in ozone and nitrogen dioxide concrentrations within the air, and such comparisons could then be related to tree phenology and leaf morphology of silver birch present at those sites.

 

With regards to results that displayed marked significance, for silver birch it was identified that increased long-term ozone levels within the urban landscape very significantly delayed (p<0.01) the onset of flowering, and (to a lesser degree – P<0.05) full flowering, in spring, in addition to the delaying (p<0.05) of the first leaves unfolding. This may very well be because birch are considered sensitive to ozone. However, when rural sites were included with the urban sites, ozone did not significantly delay a silver birch’s phenological timings. The authors remark that this is peculiar, because rural locations tended to have higher ozone levels than urban locations. Therefore, perhaps other factors influence upon the flowering phenology of birch, at the same time. In the short-term however, ozone was not found to be significant at any site, though because ozone levels fluctuate greatly on a daily basis, adverse impacts on phenology may only be discernible over a more elongated time period.

 

For common hazel, nitrogen dioxide, nitrogen oxides, and particulate matter (of varying sizes) within urban sites delayed (p<0.05) full flowering (though moderately-sized particulate matter had a very significant delaying effect – p<0.01), and when rural sites were included nitrogen dioxide, nitrogen oxides, and only the very small particulate matter had the same impact. From these results, it can be suggested that common hazel’s maturing flowers are sensitive to such pollutants (notably nitrogen dioxide and the nitrogen oxides), and more so than young flowers. Because these pollutants are more common in urban locations, it is of little surprise that common hazel within such settings had more of a delay in full flowering.

 

Horse chestnut was observed to have massively delayed (p<0.001) full flowering in both urban and rural locations, where ozone levels were elevated, and also very significantly (p<0.01) delayed flowering onset. The fact this delay spanned across both urban and rural sites is interesting, as unlike birch it suggests that the higher average ozone levels in rural settings does have as much of an impact as ozone from urban settings. The below table outlines this all in greater detail, as well as non-significant results.

 

Degrees of significance: *** (P<0.001), ** (p<0.01), and * (p<0.05). Heading meanings: BBCH 61 (onset of flowering), BBCH 65 (full flowering), BBCH 10 (bud break), and BBCH 11 (first leaves fully unfold). Negative results within the table suggest that flowering and leaf emergence may even be hastened, though not to any significant degree.

 

In terms of how pollution impacted upon leaf morphology of silver birch, no correlations were found in rural sites. In the urban setting, only one result displayed significance, and suggested that an increased amount of airborne nitrogen oxides increase surface leaf area.

 

To conclude, we can certainly observe that airborne pollutants can have a significant effect upon tree phenology, though it is clear that this will vary between species (and that is hardly breaking news). Some tree species may be more sensitive to ozone, for instance, whilst others particulate matter. Concerningly however, this suggests that ecological processes reliant upon tree phenology timing with the phenology of insects, birds, and so on, may be adversely impacted, and notably in urban settings. As the authors remark, the onset of pollination by insects may be stalled, whilst the emergence of insects ready to pollinate is not stalled. Additionally, for species that unfurl their leaves later in settings with elevated levels of certain pollutants, such as silver birch and atmospheric ozone, they may subsequently filter out less of that very same pollutant during their ‘active’ period, which may facilitate in the gradual accumulation of that same pollutant on a local level, which in turn has a progressively stalling impact upon leaf emergence (a negative-feedback loop). On an amenity level, which is not ecologically concerning, but concerning nonetheless (and to a lesser degree), such delayed flowering may also impact upon residents’ perceptions of the changing seasons.

 

An emerging flower of the horse chestnut, in an urban park. How exactly may air pollution have impacted upon the timing of such flower emergence?

 

Source: Jochner, S., Markevych, I., Beck, I., Traidl-Hoffmann, C., Heinrich, J., & Menzel, A. (2015) The effects of short-and long-term air pollutants on plant phenology and leaf characteristics. Environmental Pollution. 206 (1). p382-389.

[Kveldssanger]

19/03/16. Fact #176.

 

Mycorrhizae, both ecto- and endo-mycorrhizal, are for the survival of trees of all ages and species, and exist within the soil wherever there are trees (and other plants). By enabling a tree to uptake additional nutrients (nitrogen, phosophorus, etc) and water, in addition to providing connective networks linking many trees together (and allowing them to trade resources), overall tree health is greatly improved by their presence. Of course, different tree species have different types of associations with different mycorrhizae, and therefore a healthy diversity and abundance of mycorrhizal fungi within a soil environment can support a diversity and abundance of tree species, and vice versa.

 

In the natural woodland setting, such mycorrhizae and trees naturally operate together, in a sort of successional symbiosis, though in a landscape altered by man such a symbiosis can be aggressively severed. Soil disturbance, pollution, and removal, in addition to the clearance of vegetation, can bring with it a mycorrhizal armageddon, and one can surely not therefore expect trees to exist in the same state as they would in an undisturbed and far more natural environment. Perhaps this is one reason why urban trees can be observed to very much struggle, and notably newly-planted trees put into an already much-altered landscape, and the point of this post is to explore one study that investigated whether mycorrhizae were indeed in less abundant in the urban environment of Ontario, Canada.

 

The study looked at a total of 26 tree species, including Acer platanoides (Norway maple), Juglans nigra (black walnut), Quercus palustris (pin oak), and Robinia pseudoacacia (black locust), and assessed, in both rural and urban locations, the amount of association (relative to total root mass) each tree species had with mycorrhizal fungi. For every single of the 26 tree species, ten separate locations were identified – five in urban settings (streets, urban parks) and five in rural ones (including forests) – and soil samples were taken for assessment in a laboratory. For the urban trees, it was largely accepted that they were all transplanted nursery stock. Both ectomycorrhizal and arbuscular (a sub-set of the endomycorrhizae) fungi were studied.

 

Following the examination of soil samples in the lab, it was found that all 26 tree species (in both the urban and rural setting) had associations with arbuscular fungi, whilst 7 also had associations with ectomycorrhizal fungi (and these seven had lower colonisation rates of arbuscular fungi, as a result). However, this is essentially where the similarities end, as trees in rural settings had, by-and-large, a much greater association with mycorrhizae than their urban counterparts. In fact, mycorrhizal associations were 37% and 33% lower (for arbuscular and ectomycorrhizal fungi, respectively) in urban areas when compared to rural areas. We can however see that some trees species had higher colonisation rates of mycorrhizae in the urban location, though this does not extend to many of the tree species studied, and never were these differences statistically significant. Conversely, many were statistically different in favour of rural locations.

 

The data relating to the total colonisation percentage of a tree species’ root mass by arbuscular mycorrhizae. Those marked with * indicate significant difference (p<0.05).

 

Data showing how the tree species also associated with ecotmycorrhizal fungi fared, in terms of percentage colonisation rates of the rooting mass, between urban and rural locations. Again, those marked with a * are significantly different.

 

Evidently, this has implications for urban trees. Without doubt, mycorrhizal associations do occur, though simply not to the same levels, and thus urban trees do not receive the same benefits that rural trees do. Therefore, there may very well be a problem with the infectivity of mycorrhizal fungi within urban settings, and the authors state this may be for a couple of reasons: soil compaction, nutrient content, pH, and pollution. A build-up of aluminium ions in urban soils, for instance, may mean that the pH of the soil is too low for effective associations between tree roots and mycorrhizae, and the poorly aerated conditions around many well-used areas (including construction sites) is also likely to have a very adverse effect.

 

On a landscaping level, problems may also arise with there being a general lack of habitat for the mycorrhizal fungi themselves. Because mycorrhizae largely rely upon trees to either complete, or fully support, their life cycle and existence, the lack of tree species that can provide habitat for these fungi may very well be an issue. Particularly where monocultures are present, soils may be lacking in mycorrhizal diversity, and therefore if other tree species are planted into the monoculture then they may very likely not have available to them those fungal symbionts they require. Even if urban trees are present in the right amounts to support a wide range of mycorrhizae, the stress the trees are experiencing due to other adverse biotic and abiotic factors may limit their ability to provide the nutrients the mycorrhizal fungi require, and therefore there may not be scope for a significant association akin to that of rural locations.

 

This study only goes to demonstrate just another angle in a chapter of a book (that is growing into an encyclopedia of massive proportions) relating to why urban trees will struggle. How can this issue be fixed? I’m sure that can be debated to the ends of the earth. What must be said is that it’s certainly worth considering for when planting tree species and preparing ground for urban developments, amongst the array of other things also worth considering. It makes you wonder how urban trees survive at all, as explained quite brilliantly in .

 

Source: Bainard, L., Klironomos, J., & Gordon, A. (2011) The mycorrhizal status and colonization of 26 tree species growing in urban and rural environments. Mycorrhiza. 21 (2). p91-96.

[Kveldssanger]

20/03/16. Fact #177.

 

I have previously looked at the pros and cons associated with invasive methods of decay detection, and it is clear that wound creation is not something to be desired – in spite of the benefits of assessing wood qualities through the application of, for example, the Resistograph. Granted, issues may – or may not – stem from such wounds created by invasive instruments, and therefore it cannot be said that using invasive technology is always going to be bad, but surely it would be better if a non-invasive method could be used that has a (generally) good degree of accuracy (such as the PiCUS). Even better would it be, if a system can be developed that may be able to ‘learn’ over time.

 

Such a system that is being developed that may fit into this category – of being non-invasive and being able to ‘learn’ in time (as the instrument is used and updated by the manufacturer) – is one that utilises an ‘electronic nose’ to measure the levels of volatile organic compounds (VOCs) being emitted by a tree and any constituent wood-decay fungi.

 

Whilst such a system is still in its infancy, the general gist behind the concept is that all trees, whether healthy or decayed, emit gaseous volatiles. In trees that are ‘suffering’ from decay, a particular mixture of voltailes is emitted. Such a mixture is comprised of volatiles produced by the tree (metabolites, and anti-fungal compounds including terpenes and phenols) and by the wood-decay fungi (metabolites) present within the tree. This very mixture can be recorded by an electronic nose (a sensory device), assuming the concentrations are high enough to be picked up by the instrument. Therefore, by ‘teaching’ an electronic nose to identify particular mixtures of volatiles in the air around a tree (essentially, the instrument will hold an ever-growing databse of gaseous volatiles and mixtures of many), in theory the nose should be able to identify whether the tree is healthy or decayed (and perhaps even to what extent). At present, a few different electronic noses are available, and these include the Aromascan A32S Electronic Nose, the Lybranose 2.1 Electronic Nose, and the PEN3 Electronic Nose.

 

As mentioned, this technology is still in its very early stages (it is only around 10 years old), and even the authors here acknowledge that this research they are undertaking is pioneering. However, they have found that these electronic noses are able to differentiate between healthy wood samples and those that are decayed, where the wood samples are exposed to ambient conditions. When these wood samples are buried under soil, as would be the case with the rooting system of a tree, the PEN3 Electronic Nose still identified those samples which were decayed, though only after a period where the wood has been decaying for at least 12 months (the authors propose that this is because VOCs take longer to ‘build up’ when a soil substrate separates the source of the emissions and the air).

 

Of course, as the above research was done in the laboratory setting, it is easy to question whether the ability of the electronic nose to pick-up wood decay also applies in the field environment. Therefore, the authors took the noses out into the field, and looked at whether the instruments could differentiate between healthy and decayed roots of 60 street trees in Milan (species included Acer negundo, Acer pseudoplatanus, and Aesculus hippocastanum). It was concluded, following field experiments, that the PEN3 Electronic Nose could indeed accurately determine whether a tree root was decayed or healthy, and could even differentiate between the host tree species by the mixture of volatiles being emitted.

 

In the field setting, the electronic nose was placed inside a vacuum cylinder, with a small tube that drew air into the vacuum that the nose could then assess.

 

In light of this field trial, it is clear that the electronic noses have the potential to be very effective, and both at measuring wood decay in the aerial structure of a tree (above ground) and the rooting structure (below ground). The fact that these noses are able to identify decay that is below the ground (and thus not visible) is particularly interesting, as currently there are no effective means of determining whether a root plate is decaying. Hopefully, as this technology is developed further and more aromatic profiles of VOC mixtures are archived, electronic noses may be able to be very accurate (and immediate) in their determination of wood decay, all whilst being non-invasive. And why stop here? A tree that is stressed for other means will also emit a VOC mixture, and therefore the same electronic noses could be used to diagnose other disorders of unlimited scope. This technology may therefore have huge potential.

 

Source: Baietto, M., Aquaro, S., Wilson, A., Pozzi, L., & Bassi, D. (2015) The Use of Gas-Sensor Arrays in the Detection of Bole and Root Decays in Living Trees: Development of a New Non-invasive Method of Sampling and Analysis. Sensors & Transducers. 193 (10). p154-160.

[David Humphries]

17/03/16. Fact #175.

Trees, whether in the urban or rural setting, provide a huge array of ecosystem services........

 

Chris do you subscribe to 'Urban Forestry and Urban Greening' ?

 

There's a study being published soon looking at the effect of Cooling by London's small and medium greenspaces, entitled "The impact of greenspace size on the extent of local nocturnal air temperature cooling in London"

 

I've only seen a manuscript version so far, as we supplied some information on tree populations at one of my sites, but I suspect you will find it very interesting.

 

Keep an eye open for it

 

Monteiro, M.V., Doick, K.J., Handley, P., Peace, A.,The impact of greenspace size on the extent of local nocturnal air temperature cooling in London, Urban Forestry and Urban Greening (2016),

 

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[Kveldssanger]

Chris do you subscribe to 'Urban Forestry and Urban Greening' ?

 

There's a study being published soon looking at the effect of Cooling by London's small and medium greenspaces, entitled "The impact of greenspace size on the extent of local nocturnal air temperature cooling in London"

 

I've only seen a manuscript version so far, as we supplied some information on tree populations at one of my sites, but I suspect you will find it very interesting.

 

Keep an eye open for it

 

Monteiro, M.V., Doick, K.J., Handley, P., Peace, A.,The impact of greenspace size on the extent of local nocturnal air temperature cooling in London, Urban Forestry and Urban Greening (2016),

 

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I 'subscribe' to the open access stuff, hah! 374 EUR p/a is a little too much for me, unfortunately. Some of the articles make it to ResearchGate as well, so I can also nab them there. I have a few articles from more recent ones I am keen on reading, though they're behind the paywall. I suppose I could ask a local university if they can allow me access, perhaps...

 

I shall make a note of that article and hope it comes out as open access, else I'll await a probable article by a journalist on the study.