Amelanchier

We've seen these before somewhere on a thread by Bundle2. I appreciate the design aims but doubt the Y and Z rig systems are effective. The Y seems intended to distribute the energy created by the roll of the limb? You could achieve this with less equipment by bracing before the union... I can't see the Z rig functioning at all. It creates a pivot central to the sytem which acts on the limbs between points A & C (or B & D), problem is - the limb is attached to the tree and can't rotate around that axis. Pointless IMO.

I don't see why anyone should be writing a spec that just includes a percentage without explaining it. It takes seconds to describe works accurately - I suspect people either; can't be bothered, don't know what they're doing or expect to get the work, Honestly, if you're going to use a percentage - state what it's a percentage of! Otherwise you might as well say "cut off not too much and not too little." I use the metres from the outer limit of the crown method and often specify a maximum cut diameter as well. Of course, I'm not going to climb the tree with a set of callipers but it communicates my expectations. Everyone can be on the same page. I've often thought we should spec what's going to be left of the tree rather than whats coming off. The cut diameter is part of that but maybe something like; Undertake a crown reduction by the removal of no more than 2m of the outermost canopy back to suitable secondary growth points, leaving minimum crown dimensions of 8m radial spread and 18m overall height at any one point. Resulting pruning cuts must not exceed 150mm in diameter. That took 20 odd seconds to write, its not hard. Just a tiny bit more effort (more so on large numbers of trees!) I know people like a flexible spec so they can make their own judgements when climbing and react to the pruning points - fair enough, there is room for leeway but it fundamentally ties down what the hell is going to happen to the tree.

Furthermore, you wouldn't want to fall onto a static line...

Yale blaze is a CE-EN1891 Type-B rope as opposed to most 13mm parallel core XTC etc which are CE-EN1891 Type-A. There was some minor grumblings by rope geeks when Blaze was brought over here and marketed as an arb rope as the testing process never examined Type B in trees. Something to do with the friction coefficient between the two sheaths when travelling over a rough large radius like a branch IIRC. Yawn.

Uh huh yep the oldest branches are often near the bottom which provides a short carb pathway to the roots, which is why crown lifting is bad for veterans and why stem and basal epi is more important than most CS units give it credit for. We know that. My point is that an aesthetic rule does not necessarily correlate to a phsyiological rule. Hence the willow example. The same could be said for trees with a low wide habit such as Persian Ironwood. Take a third off the bottom and you've removed quite a bit of foliage.

I don't think there is a definition of forestry in planning law Here is the act you referred to: http://www.opsi.gov.uk/acts/acts1962/pdf/ukpga_19620038_en.pdf Which defines Agriculture in S221 as: "agriculture" includes 'horticulture, fruit growing, seed growing, dairy farming, 'the breeding and keeping of livestock (including any creature kept for the production of food, wool, skins or fur, or for the purpose of its use in the farming of land), the use of land as grazing land, meadow land, osier land, market gardens and nursery grounds, and the use of land for woodlands where that use is ancillary to the farming of land for other agricultural purposes, and "agricultural" shall be construed accordingly;" One might suppose that if its not defined in their local plan /development framework policies they would grab a dictionary? "the science of planting and taking care of large areas of trees"

I agree with you on a point of aesthetics, but I can't see that a visual proportion based rule of thumb has any relation to the carb transfer of the vascular system. Of course this aesthetic rule should be applied with caution to some species especially those with a weeping habit. Its entirely possible to keep your visual balance and remove all but a handful of branches at the top with your average weeping willow...

Interesting enough (or more likely not) I've been re-reading the draft revision for BS3998 as part of a plan to future proof my reports etc. The section on lifting includes this excerpt: "9.7.1 General Crown lifting should if possible be phased over a number of years, with a view to providing some opportunity for physiological and mechanical adaptation to the resulting wounding and branch removal. Crown lifting should be avoided or minimized in mature or old trees if possible, since it can increase the probability of stem failure. If it cannot be avoided, it should preferably involve the removal of secondary branches or branch shortening rather than branch removal, provided that the desired clearance can thereby be achieved. The choice of these options should take account of factors including the size, growth potential, branching habit and shade tolerance of the tree. NOTE 1 If crown lifting involves the removal of branches which form a substantial proportion of the lower crown of a mature or old tree, the resulting wounds on the main stem are likely to become the seat of extensive decay, which could eventually lead to mechanical failure. Failure could also become likely in the short term, since branch removal can cause an immediate impairment of mechanical properties. Crown lifting that involves the cutting back of branches to the main stem should preferably not result in the removal of more than 15% of the live crown height and, unless the objectives change, should not be followed by further crown lifting (except in the case of a young tree undergoing formative pruning, see 9.5), which would increase the effect of wounding on the main stem and the impairment of mechanical properties. NOTE 2 For example, if the stem of a 20 m high tree is branch-free to a height of 5 m, it could be crown lifted to a height of 7.25 m." Useful? So assuming our imaginary Euc is has a current clearance of 10ft we could lift it by another 9ft before we start to instigate problems... To answer the OP question - I'd recommend a lift. Reducing Eucs is like running on the spot.

I'll try to find a comprehensive example in the QTRA forum and post it here.

Fine questions. The first I'd suggest is only answerable by Mr Ellison. I ain't got a clue! Very interesting though - I'd guess he'd point the finger at the HSE and Helliwell? The second question is bigger, and as I'm an infrequent user i've only ever used the system on up to 600 significant trees on any one site. In that instance, I broadly categorised target zones based on sampling pedestrian / vehicular usage. That allowed me to systematically prioritise works for the client - I didn't bother working beyond the basic calculations (the wheel of fate hama!). I don't think we need to have an calculation for total risk, outside of hypothetical circumstances its rare that any one target is threatened by more than say, 10 -15 trees at a given moment. Static targets don't meet a lot of trees and mobile targets stay under a tree for perhaps 10 seconds at most? Really with QTRA should be looking at this the other way round - rather than how likely is the failure; how likely is the target being in the wrong place at the wrong time? And because a target is not likely to be exposed beyond their own little 'risk bubble' the effects of tree population matter less... You can see I'm not a full time advocate right!

Just for wider understanding. From the ISA Journal of Arboriculture Vol 31:Number 2 March 2005 by Mike Ellison. "Acceptable Risk. We are constantly exposed to and accept or reject risks of varying degrees. For example, if we desire the convenience of electric lighting, we must accept that, having implemented control measures such as insulation, there is a low risk of electrocution; this is an everyday risk taken and accepted by millions of people. When evaluating tree-failure hazards, two types of risk must be considered. We must consider the person upon whom a risk is imposed as with the neighbour of a tree owner, and the person who accepts some degree of risk in return for a benefit, such as a tree owner or visitor to a woodland or forest. Having considered The British Medical Association Guide "Living with Risk" (Henderson 1987) and with particular reference to the conclusion "few people would commit their own resources to reduce an annual risk of death that was already as low as 1/10,000", Helliwell (1990) suggests that 1/10,000 might be a suitable figure to start with as the limit of acceptable risk. Furthermore, "For members of the public who have a risk imposed on them 'in the wider interest' HSE (Health and Safety Executive) would set this limit at 1/10,000 per annum" (Health and Safety Executive 1996). In the management of trees, a property owner or manager might adopt the 1/10,000 limit of acceptable risk or choose to operate to a higher or lower level."

Ok then. I'll bite - hook, line, sinker and copy of Angling Times. With QTRA we generally use a 1 / 10,000 threshold. Although this is a guide and the threshold should be discussed with the client. IIRC its based upon the HSE's ALARP principle and other funky documentation that I can't currently recall, essentially that there is little practical gain in trying to reduce risks to above 1 /10,000.

Aaahh, a true can of worms. Acceptable to whom?

Ha indeed! Fair bit easier... I get a little fuzzy with the scientific notation on my calc, 3.1e06 and all that. I was out with the prediction then? 1:1.53 is more likely than 1:1.58?!? The only problem I ever really had with the QTRA system was referring to the probabilities in the 1/10, 1/100 format - I'd always dealt with probabilities in decimal.

Fraid so (last time I checked - it might have expired!). I don't get as much use out of as I would like though.

One of the golden rules of stats is junk in = junk out. QTRA doesn't try to get it spot on - just as accurate as is 'reasonable' for the given circumstances. Remember we're trying to determine the neccessity of works with a systematic approach. We're not trying to be spot on to 5 decimal places. Provided the working is shown, its just an extension of a professional judgement.

So you can understand why no-one has offered to answer the 1/10,000 question! But it will be somewhere between 1:1 and 1:1.53.

Well lets make the numbers more accessible then (slightly). Lets use 10 trees planted in a circle with a risk of 1/10 (they are uber-fubar) with an imaginary war memorial in the centre (fairly static unless a group of students spots it). So is the cumulative risk to the memorial greater than the individual risk of 1/10? So we need to work out what the cumulative likihood of the event is, one way of doing it is to multiply the odds of it not happening 9/10 x 9/10 x 9/10 x 9/10 x 9/10 x 9/10 x 9/10 x 9/10 x 9/10 x 9/10 = 3,486,784,401 / 10,000,000,000 of no damage to the memorial, or; 6,513,215,599 / 10,000,000,000 of damage to the memorial which = 1:1.53 which is certainly less that 1/10 but not quite 1/1.

No it isn't. You can survey the average density of trees per hectare, and determine the speed at which the average target walks along a particular footpath. You can then for any given moment work out the number of trees within falling distance (perhaps two tree heights) of the path that present a hazard and the average exposure time to the average tree. Sometimes - its just not worth it though.

Presumably, your point is based upon the cumulative probability being more likely than the individual probability. Much in the same way as rolling more dice gives a better probability of obtaining at least one six. The thing is, the target is not going to be within falling distance of all 10,000 trees at once...

I think the clock should roll over and he should start again at 0.

When I was in your position, I did the LANTRA PTI first! It's worth noting that its the only qualification that exists that assesses your ability to inspect, diagnose and specify recommedations. (Perhaps also the PD Arb in a roundabout way?) Indeed, given the fact that such an assessment exists - I wonder if it would not be 'reasonable' in the eyes of the law to expect you to have undertaken and passed it prior to inspecting trees? Maybe, maybe not...

Don't go there...

Despite most people suggesting the LANTRA PTI?