xtremetrees said:
Its the hollow trees that scare me the most.I'm not really sure why I'm still alive because of them really. But then I think of beetle killed pines over the power lines. One year we cut over 1000 of which all were over the powerlines, we'd go back a week later and the trees we hadn't cut failed at the base.I met my first free climber on that job. Yep he never used a rope in fact refused to learn ropes at all and they called him cowboy fer real. At least you know a pine tree is pretty dead when it looses its cones-needles-bark mostly in that order--but with hollow trees you just never know how dead they are because the trees grown around the hollow spot. I think a cylinder of growth is pretty strong thou.
I pay close attention from the ground up looking for hollow spots. I'll even circle the tree to look for hollow spots that I dont see going up.
I wish more tree folks would price dead trees high. I'll price them so high I dont get them and pray tell for another tree. Dead trees their booggery. I would'nt do a tree this dead again, but I'm older and wiser and I'mma live for another tree if I pass um by.
A cylinder of growth IS pretty strong, and in hazardous tree assessment there’s a formula for determining strength loss in a tree by measuring the ratio of strong wood to the decay column. Obviously, this formula is a general rule of thumb under ideal conditions, and common sense and the ability to assess other factors that may affect strength loss must be considered, such as:
If the tree is dead, or if more than 50% of major limbs are dead with a history of decline, species of tree, proximity of decay to main branch crotches (especially V-crotches), leaning trees, basal cavities, size and density of the crown (sail effect), how protected the tree is from wind, girdling roots, root decay, and any other factors that may adversely affect the tree’s structural integrity.
The F. A. Bartlett Tree Expert Co. uses a 33% strength loss threshold to determine whether a tree is hazardous and thus should be removed. For hardwoods you can usually drill into the tree with an 1/8-inch drill to determine the amount of sound wood. But with softwoods the transition between sound and rotten wood is more difficult to ascertain, and an increment borer, auger drill, or shigometer is preferred. Since the decay isn’t usually uniform, multiple sites should be drilled, and the resulting thicknesses of sound wood are averaged.
The formula for a tree without a basal cavity is:
(diameter of decay column)^3 / (diameter of stem)^3 x 100
So, for instance if you drill a few holes in a 15-inch Sugar Maple (with no open cavities) and the average sound wood is 2.5 inches thick, then the strength loss percentage is 29.6,
(10 x 10 x 10) divided by (15 x 15 x 15)
and since 29.6% has not exceeded the threshold of 33%, the tree is NOT considered a hazard tree.
Of course, other factors that affect the tree’s structural integrity (as above) must be taken into account as well. There is also a variation of this strength loss formula for trees with open cavities.
Anyway, to me this illustrates, as xtremetrees noted, that a “cylinder of growth is pretty strong.” But having done storm damage work, I’ve come to believe that the more you know your individual trees – how strong the wood is, how shallow-rooted they are, what kind of abiotic and biotic stresses are specific to that particular species of tree, etc. – the better off you are at assessing whether a tree’s going to fail or not.
And then of course there’s always that nagging unpredictability factor. How many times have we just stood back and looked at a downed tree and said, “now what the heck made that tree fall?”