(Arboricultural-styled) 'Fact of the Day'

[daltontrees]

Some very good points you raise there, Jules. I find, from going through the ISA conference proceedings publications (The Landscape Below Ground series and Trees & Building Sites) are a little lacking in terms of background information and setting context. I realise they're overviews of what was presented in spoken word, though I find myself still wanting having read many of the articles.

 

And the ISA has a vested interest in not criticising CTLA even though it has very obvious failings.

[Jon Heuch]

And the ISA has a vested interest in not criticising CTLA even though it has very obvious failings.

 

A simple comment but it's not really a "vested" interest - ISA is one of the members of the CTLA group. The ISA - normally through one individual - have authorship rights so it would be strange to agree the text and then start criticising it. As with any document that has been agreed by a committee, representing several organisations, there are compromises and the achievement is that there is a document at all. The fact that it has developed through several editions reinforces this.

 

However, the problems that the same group are having in order to develop and agree a 10th Edition reflects the array of interests and differing views that can be brought to bear on valuation. As I believe you are a RICS member you will be well aware of these issues. To say that CTLA has obvious failings is a statement of the obvious, just as the Red Book has failings or any other system of valuation has failings especially if you take a different view on any one or more of the assumptions made.

[Jon Heuch]

I seem to have scared everyone off bar Jules, lately! I hope people aren't commenting because they are too busy reading or researching, in place of feeling like their potential comments would be out of place.

 

Comments on the style of stuff I'm putting out are also welcome, and what I write is to help everyone learn - not just myself.

 

I have one comment - who the **** are you?

 

That's said flippantly & jokingly, but the quality, quantity and frequency of your postings are both exceptional and stimulating. Clearly you either do this sort of thing for a living or you don't have a living to make?????

 

with admiration and thanks, but please come out of the closet. Maybe every else knows you but I am just mystified.

[daltontrees]

A simple comment but it's not really a "vested" interest - ISA is one of the members of the CTLA group. The ISA - normally through one individual - have authorship rights so it would be strange to agree the text and then start criticising it. As with any document that has been agreed by a committee, representing several organisations, there are compromises and the achievement is that there is a document at all. The fact that it has developed through several editions reinforces this.

 

However, the problems that the same group are having in order to develop and agree a 10th Edition reflects the array of interests and differing views that can be brought to bear on valuation. As I believe you are a RICS member you will be well aware of these issues. To say that CTLA has obvious failings is a statement of the obvious, just as the Red Book has failings or any other system of valuation has failings especially if you take a different view on any one or more of the assumptions made.

 

That's what I meant, plus it sells the publications and does not endorse any other valuation method.

 

Tree valuation systems, at least all the ones I have seen, share a failing and that is they are weak on published assumptions and limitations, unlike the Red Book which is as exhaustive as one could hope for. So the valuations they produce are inherently vague (that's the best single word I can come up with). I daresay a couple of pedants like us could debate this sort of thing ad nauseam until long after the rest of the world has switched off the lights and gone off to do something, anything, more interesting. I suppose I just wanted to make the point that studies like the Milwaukee one, ambitious and rigorous as they might be, have limitations and if one of those is reliance on CTLA and it has (and had in the earlier editions that must have been used) limitations then the conclusions of the study cannot be extended to other situations with a simple 'therefore'. That and the fundamental tenet of the scientific approach that correlation does not prove consequence.

 

The extreme view is that the trees did not lose value, they never had the value attributed to them because their demise was foreseeable. They might even have been considered financial liabilities. But we tree folk battle with that debate to some extent almost daily.

[Jon Heuch]

it sells the publications and does not endorse any other valuation method.

 

Tree valuation systems, at least all the ones I have seen, share a failing and that is they are weak on published assumptions and limitations, unlike the Red Book which is as exhaustive as one could hope for.

 

Studies like the Milwaukee one, ambitious and rigorous as they might be, have limitations and if one of those is reliance on CTLA ....

 

I agree, the assumptions, limitations etc all need a full explanation in any valuation. The simple statement and re-statement of the number achieved is just misleading.

 

I think you need to give the 9th Edition of CTLA a little acknowledgement as it does recognise "other" valuation methods - Income and Market in particular, but indicates that arborists may not be the best people to use these. As a result the guide provides few details and focuses on the Cost based approach.

 

I think the basic issue is that valuation is full of pitfalls, hurdles and dead-ends and it takes quite a lot of experience and training to make any real sense of things. Mixing arboriculture and environmental valuation has been achieved without the "Valuation for dummies" textbook that should be judged rather similar to "Brain Surgery for beginners" (you can read it but please don't practice it without a bit more experience). Most arbs have been on a single (or possibly two) day course focused on a single valuation method or maybe a few valuation methods. My experience is that arbs don't want to be told how difficult things are, especially in a training course. They want it nice and simple: follow steps A to D and then you have the answer. This has some merits, but also some great big problems.

 

The London i Tree study provides a neat example, containing both a CTLA and a CAVAT "valuation". The journalists and communicators need a headline so what does the AA report: "8 million trees worth £6.1 billion to the capital the wider benefits (ecosystem services) in respect of.." all too predictably the valuation of the ecosystem services is mixed with the "replacement cost" and then for some reason a CAVAT valuation only around 7 times this replacement cost is thrown in. It's a right mess for anyone who wants to use these figures with any credibility!

[Kveldssanger]

Always good to come back to a discussion!

 

RE: magnolia. Longest-surviving flowering (woody?) plant genus, is what I took from the book.

 

And Jon knows who I am, now!

[Kveldssanger]

11/01/2016. Fact #123.

 

The presence of trees on UK urban streets is indicative not only of the state of the economy (a recession was oft marked by a decline in urban tree management and landscaping), but also of the spending priorities associated with maintaining street scenes. This was particularly the case during the early 1800s, when the Industrial Revolution was gaining serious momentum. Not only had a recession (which hit the growing lower class very significantly – the divide between rich and poor was growing ever-larger) in the 1830s struck harshly the horticultural sector, but there was little desire to plant and maintain urban street trees for multiple reasons (including a lack of space, and a lack of interest in ‘providing’ for the poor).

 

During the 1830s-1840s, the advancing industrial age had enticed many rural populations to migrate into cities and, for the first time ever, urban populations (54%) were greater than their rural counterparts (as marked by the 1851 census). This flooding of people into cities, compiled with Irish migrants following the famine in 1845, brought about problems, particularly as such a surge in population was not anticipated. Towns and cities were not ready and thus the infrastructure was not there. In-filling was rife, and any pockets of land in residential areas were used to build houses – such as was the case in Nottingham, where a population of 10,000 swiftly rose to 53,000 and, as a result, many gardens and cherry orchards were destroyed and used to construct homes (for factory workers). Once in-filling was completed, the towns and cities expanded from their perimeters, and were constructed in a similarly property-dense fashion.

 

 

A further issue with such an influx of such people was that they were typically poor (particularly those from Ireland), and thus their presence lead to densely crowded ‘slums’ manifesting. Ironically, the poor, who left (in some cases absolute) poverty in rural areas, were now just as poverty-stricken but instead in an urban area. Unfortunately, these citizens, once surrounded by trees and green space, now lacked that entirely (no back gardens, no public parks, and so on). Additionally, whlst in rural areas they were spread apart over the country, in the cities they were densely crammed together in small back-to-back houses. Tensions between the rich and the poor thus began to rise.

 

As all of this was going on, the well-off (middle class and above) decided it was time to get out of the city and move into the suburbs, and instead commute into the city to work via horse and carriage. Not only were the suburbs cleaner, but they were safer (they may have been gated communities), and actually had space to accommodate trees in communal and private gardens and – perhaps at times – along streets. Such estates within the suburbs (and also the cities) thus began to form, and by 1875 around 150 of these estates existed.

 

 

The curious aspect of the middle class moving out of the city and moving into estates was that the very same middle class began to push for the city areas to have public parks for the working class to be able to utilise. Perhaps the more affluent, who would have had far more say in political matters at the time (particularly with being able to vote), realised that those stuck within the slums deserved a better standard of life (that may have been fuelled, at least partially, by the growing tensions between rich and poor), though even once such public parks were created they were rarely visited by the middle class – they still desired the segregation they achieved by living in the suburbs and gated estates.

 

Following the Industrial Revolution trees progressively, over the course of the remainder of the 1800s, and then over the early to mid 1900s, became more desired (and thus more frequently planted) within urban areas. This has culminated into what we see today – plenty of parks and, for the most part, plenty of urban trees. The author goes into great detail on the years after the Industrial Revolution, though I won’t spoil that as I’d rather you read the book!

 

Source: Johnston, M. (2015) Trees in Towns and Cities – A History of British Urban Arboriculture. UK: Windgather Press.

[Kveldssanger]

12/01/2016. Fact #124.

 

Trees species, such as alder, birch, willow, and poplar, will disperse their seeds via wind. However, just because the seeds are dispersed by wind it does not necessarily mean that they will travel huge distances. In fact, a large percentage of a tree's seed crop will fall within a short distance from the seed tree - perhaps only as far as a few times its height.

 

Despite this, the distance a seed can potentially travel will vary by several orders of magnitude, and therefore seeds do have the capacity to travel huge distances. Storms have been found to enable seeds of poplar to travel up to 30km, maple 4km, scots pine 2km, birch 1.6km, and ash 0.5km. Of course, this really does depend upon the direction and the strength of the wind, and for how long the wind gusts durate for.

 

 

The 'fall velocity' of a seed (as in, the time it takes the seed to fall from the parent tree to the floor in still air) may also be a determining factor in how far a seed may potentially travel. If a seed is heavy (such as an acorn), it will fall to the ground is a few seconds, though for trees that rely on wind dispersing their seed they will usually have much lighter and more aerodynamic seeds. This increases the time it takes for the seed to fall to the floor and thus increases the likelihood of the seed being 'caught' by wind gusts. To give an example, the average 'fall velocity' of Acer platanoides seeds is 107cm per second, whilst Ailanthus altissima seeds fall at 122cm per second. Comparing this to the 'fall velocity' of an acorn, which unfortunately I cannot find (one article seems to be behind a paywall), there would very likely be a marked difference (with the acorn's 'fall velocity' being much greater).

 

In fact, seed dispersal distance increases disproportionately as greater fall distances are reached. In one study, seeds dropped from a height of 61m in wind speeds of 3.1m per second were recorded from 61-975m from the point of fall, whilst seeds dropped from a height of 30.5m in identical wind speeds were recorded no further than 244m away.

 

Now, as even the authors recognise, such distances don't explain how poplar seeds were found 30km away (or even maple at 4km). To answer this, it is suggested that seeds may, in times of very marked wind storms, 'rise' above their release height due to air turbulence and then steadily glide downwards from this higher point (assuming they are not picked up by further turbulence further along, which would increase distance travelled yet further and / or change the direction of travel).

 

Source: Johnson, W., Sharpe, D., DeAngelis, D., Fields, D., & Olson, R. (1981) Modelling Seed Dispersal and Forest Island Dynamics. In Burgess, R. & Sharpe, D. (eds.) Forest Island Dynamics in Man-Dominated Landscapes. Germany: Springer-Verlag.

Edited January 12, 2016 by Kveldssanger

[daltontrees]

[ame]

[/ame]

 

Placky bag 'durates' for 3 minutes. Drop an acorn out of an upper storey window, everyone from Gallileo onwards would guess it will accelerate (at about 10m/s/s) straight down, hindered only by air resistance. Velocity is speed plus direction so the concept of fall velocity is currently not really making sense to my slightly tired brain. Maybe I should read the article, but not tonight.

[Kveldssanger]

The authors made no distinction as to what they meant by fall velocity, though one can presume the study tested velocity in perfect conditions, as I believe the test was done in an elevator shaft. I doubt there'd be any wind in such a place (unless from one of the operators, if they had a dodgy dinner the night before...!!).

 

 

Day off today - got back from my lvl 4 and want to churn out some work on fungi as it's a field I like studying.