Urban rigging is, essentially, tight-quarters rigging. While you can find this scenario anywhere trees need to be worked on in close proximity to structures, it is nearly the norm in urban environments, from the street trees that have found a way to thrive in their impossibly small curbside planting pits to the backyard big boys that gobble up more resources to expand closer to their fence, concrete, wire, house and utility-pole neighbors (Photo 1). There is no doubt that the city is a harsh and restricting place for a tree. In a place like this, when a tree finally does succumb to the unfavorable abiotic and biotic factors, the task of safely laying its expansive wooden corpse to rest without causing property damage is an undertaking like no other.
When I throw around the term “urban rigging,” this is precisely what I am referring to – a large dead, dying, diseased or structurally unsound tree surrounded by valuable man-made targets. Sometimes things like wires, fences or structures have even been attached to said tree (Photo 2). Often there is no access for any heavy machinery – no crane, no truck-mounted aerial lift, no compact lift and usually no other nearby trees to work with. Those are just some of the above-ground challenges. The installation of pavement, foundations and underground utilities also may have caused damage. If the tree came after the fact, an irregularly shaped root system may have developed. These are very important things to consider when loading a tree with rigging forces.
What is an arborist to do? You have a large expiring or questionable tree in close proximity to the house, utility wires and a fence with a portion of the roots previously cut during excavation. There’s no access to the backyard for large equipment, and circumstances out front are making the use of a crane impossible. The mechanized cavalry isn’t coming. It’s time for plan B. You are going to have to rope-rig this thing down (which is a lot of people’s plan A). Sure, you can probably get away with covering things with layers of plywood and cutting small bits, but eventually you are going to have to rope-rig something.
Rope-rigging in these conditions requires a little bit of a different approach. During the development of our careers, in books, demos and training videos, we are taught to let the rope “run.” By letting the rope that is attached to a rigged piece run, one can dissipate the dynamic forces of the piece’s weight being introduced into the rigging system. This is not just industry folklore. There is real science behind the many well-documented tests conducted by both industry leaders and independent entities, not to mention principles of modern physics. Many findings and articles published by the ISA and TCIA showcase the same things. Letting the rope “run” – or rapidly belaying – reduces dynamic forces.
Unfortunately for the arborist charged with our hypothetical but all-too-common task, there is no room to let the rope “run.” There is nowhere for it to “run” to. Structures are all around, with a landing zone only a fraction of the drip line and often located on one side. We cannot rely on running the rope. We are going to have to get more creative with some of the other lessons we have learned. Since we cannot dissipate forces, we’re going to have to do everything we can to reduce and absorb them.
The use of redirects can have a tremendous impact. By altering the rope angles between multiple rigging points, we not only reduce the amount of force experienced at each point, we change the direction from which this force is being applied. The rope enters the hardware at the rigging point and leaves in a different direction. The resulting direction at which the rigging point experiences that force is at the bisector of the angle the rope creates (Photo 4).
Wood fibers are strongest when loaded, or pulled, vertically, with the grain. If the angles between the redirects can be set in such a way that the bisectors are more in line with the direction of the wood’s fibers, we can bring the forces more into compression, thus maximizing the strength of the system. Essentially, we are reinforcing the tree to be able to more safely absorb force (Photo 5).
Next, adding more rope into the system helps spread some of the forces over a greater surface area. Using ropes and slings with elastic fibers aids in the process as well. Ropes and slings made of these fibers will stretch or elongate a bit when loaded, thus bringing down peak load. On a side note, this elongation should be taken into account, especially in extra tight quarters, as the weight of the piece could cause so much stretch that it ends up allowing the piece to make contact with the targets you are trying to avoid.
Another great way to keep forces down that can also involve adding more rope into the system is using mechanical advantage to lift and lower pieces (Photo 6). Lifting is great, as it keeps the introduction of the weight of a piece mostly static. There are, however, limitations. The tree shape will heavily dictate the usefulness of the technique. A dense canopy may prevent pieces from being cleanly lifted when they run into other branches that could not yet be removed. Canopies with rigging points at too steep an angle or too far away will inevitably result in pieces dropping into the system (Photo 7). It is my opinion that if a piece were to drop into a rigging system after it has been lifted, removing all the slack or stretch from the rope and slings in the process, it could create an unfavorable shock load that the system is less prepared to effectively absorb.
Double-whip rigging adds more rope to the system while increasing lifting power; also, it reduces forces when used solely for lowering (Photo 8). This technique can be used with an overhead rigging point or in a negative rigging situation, where force reduction is of the utmost importance. However, it requires not only more hardware but a longer rope, as you have added an extra distance the rope must travel to get the piece to the ground.
Whether you are lifting pieces or simply rigging them to clear close-proximity objects, you will not be able to rig them brush heavy. You are going to have to either tip-tie, balance-tie or near-balance-tie them. If the rigging point is located at any sort of an angle from the point at which you are tying the piece off, you are going to have to really think about what the butt (and brush) of the piece is going to do when it leaves the cut (Photo 9).
The nature or complexity of the situation will, of course, be dictated by the rope angle to the rigging point, the shape of the piece you are rigging and how it needs to leave the cut to avoid the obstacle. My go-to solution in these trickiest of times is to add a second line, most often as a butt line. The reason the butt-line approach has been a favorite of mine is that it restricts movement of the butt to the distance from the hardware the rope is passing through to the point where the knot is attached.
By keeping this distance as short as possible, you can restrict the distance the butt is allowed to move or gain momentum. This is critical should the butt break off the notch, spear off the cut or flip up if you’ve misjudged the balance of the piece being rigged (Photo 10). Another added bonus, if you are using a midline-attachable piece of hardware for your butt line or are natural-crotching it, is that the rope can be taken out once the piece has come to a stop in the terminal-point line. The butt line can now be converted into a tagline and given to the ground staff to help maneuver the piece into position for processing.
A second line used as a secondary rigging point from above is also a viable option (Photo 11). However, what’s available in the canopy will dictate the possibilities. To me, where this option really shines is during a process I refer to as “drifting.” This occurs when you have a terminal rigging point that will avoid obstacles and land pieces where you want them, but the angle is steep and the distance is far. Where the butt line was used mainly to limit movement, the drift line will be temporarily acting as the terminal rigging point, doing all the work and absorbing most of the forces until the rigged piece has drifted slowly and safely to the intended terminal rigging point. Of course, it takes a very keen eye to properly guestimate distances and see what will happen when swing angles start to close. Any aforementioned techniques should be practiced in a low-risk setting.
If all has gone according to plan, the obstacles you’ve been painstakingly avoiding are still intact and you’re down to trunk wood. Continuing with our no-run scenario makes the situation that much more difficult. “Snubbing” off a negative-rigged piece creates about the most force you can generate. You will have to do the math and build a system that can withstand the greatest possible forces you can generate and then some, something you should be doing when you build any system, rigging or climbing.
Double-whip rigging, as previously mentioned, adds more rope and components to absorb force. Running dual systems accomplishes a similar thing. At some point, however, you are going to run out of height or the trunk itself may not be sound enough to risk applying such forces to it. A negative-rigging system of any design will not be able to keep pieces from hitting ground-based targets (sidewalk, irrigation lines, etc.). In these situations, I’ve had the ground staff create a “crash pad,” basically a nest of pallets, tires, brush or whatever I could get to absorb the impact of bits of wood I’ve had to slab, half or quarter from aloft. Sometimes the hard way is the safe way (Photo 12).
Ideally, you have enough viable redirect points to reinforce a terminal-rigging point that keeps the angles shallow, thus keeping dynamic movement to a bare minimum. The idea is for things to be nearly static. The lower the angles, the less swing. The less swing, the lower the dynamic forces. The lower the dynamic forces, the less stress and strain you’ll be putting on the wood fibers of a compromised tree. In order to achieve this, you may have to move or redirect the terminal rigging point many times (Photo 13). This may sound labor-intensive for the climber or inefficient, but, in my opinion, it is a safer, smarter way to rig, leaving much less to chance and luck. Keeping conditions as static as possible also allows you to remove larger sections in a confident and controlled manner. Once again, what is possible will be dictated by what’s available, what the shape of the tree is and what kind of condition it’s in.
Ultimately, for as much as we know, a tree is an organic structure that can become unpredictable when compromised. However, by using the fundamental principles of rigging in strategic ways to exert maximum control, we can limit movement and limit risk. Rig smart, rig safe.