Climbing Basics, History and Hazards

Mitch Sangl is shown here climbing stationary- or single-rope technique (SRT). For SRT, you must be certain of two points, the limb in the canopy over which the line runs and the basal anchor where it is attached. All photos courtesy of the author.a

Climbing is still considered a basic skill for arborists, but it is becoming an increasingly rare one. Good climbers are always in demand. With the ability to access trees that are beyond the reach of an aerial lift, they are an asset to any tree company. The mobile, elevating work platforms available these days are nimbler than their predecessors, with the capability to enter spaces impossible in earlier years. There are also the new knuckleboom-mounted grapple saws that provide a safe and efficient means to dismantle trees. But with many trees, whether dismantling or pruning, someone still must climb them.

That someone has a lot of ability, knowledge and skill. A tree company can hire workers and train them to drag brush and safely feed a chipper in a few weeks. In a couple of months, a worker can be a competent aerial-lift operator. But climbing is a skill that takes years to learn, and climbers can spend their entire careers perfecting it.

It is, however, a natural talent. Climbing is in our genes. While there is still some debate on the climbing ability of our ancestors – for example, whether our feet, adapted to walking, are suited for climbing – it appears we once spent a lot of time in trees both for safety and gathering food.

Unassisted climbing is still part of the daily life of peoples around the globe, where climbs of more than 100 feet are made to gather fruit and honey. Studies of these people have found that this climbing is an energy-intensive and high-risk activity where falls from heights above 65 feet are almost always fatal, and even falls from 40 feet are fatal for half the reported incidents. But fatalities are not common. When you are unassisted – no rope, ladders or other aids – you’d better be very sure of your ability.

Unassisted climbing was once the norm for tree workers. The use of a rope did not become common until the early 1900s, and even then there was some resistance toward this new technology. There is a great review of the “old days” of arboriculture in the December 1991 issue of Tree Care Industry Magazine from a collection of writings by one of the pioneers of our industry, Leeman Strout (1888 to 1968). He mentions that a rope tied with bowline-on-a-bight and a boatswain’s or bosun’s chair was still not commonly used by climbers in the 1930s.

The speed at which climbing has evolved since then is astonishing, and it is still evolving at a remarkable rate. Back in the ’70s, the taut-line hitch was the standard friction hitch, as it had been for more than 30 years. Now it seems as if new procedures and gear pop up continuously. This evolution of climbing has increased efficiency and allowed more arborists to join the ranks of climbers or to continue climbing longer into their careers.

But safer? The trend here is not as clear. It may be more of a wash, with just the details of an incident changing rather than a dramatic reduction in incidents. Falls were a major incident back then and still are now. The arboriculture association in the United Kingdom, in 2015, published a tree-work-at-height risk hierarchy, with climbing advised only if an aerial lift cannot reach the canopy and the work cannot be done from the ground.

Climbing can be broken down into three separate activities: ascending, working the canopy and descending. Let us look at the changes in procedures, equipment and incidents for each of these.


Free-climbing, which is climbing without the assistance of a rope, to ascend a tree was a common practice in the 1930s, and it continued into the 1980s. One of the most common climbing procedures was to free-climb the tree using the three points of contact – three extremities holding contacting three different limbs – while having the climbing line trailing behind. The climb sometimes began at the ground, but ladders often were used. Many tree crews were equipped with 30-foot ladders, and these were used to start the climb. Some climbers would just shinny up the trunk if the first branch could be reached within 20 feet or so.

Synthetic, left, and manila rope. A climber could get a firm grip on a three-strand manila rope, but it did not have a lot of strength. A 10-foot fall could cause the line to fail.

The climber continued up the trunk, following a path that led to the highest, centermost part of the tree and to a point where the trunk tapered down to about 4 to 5 inches in diameter. At this point, the climbing line would be passed around the trunk above a branch, usually at least 3 inches in diameter, which would serve as a stop.

The tail of the 1/2-inch manila rope was attached on the two D-rings of the saddle with a knot (we were taught to use two half-hitches), and a taut-line hitch was attached (usually two-up and two-down, but I was taught two-up and one-down, which ran faster) to the line. Now the climber was secured.

An old taut-line system.

Free-climbing may seem reckless, but sitting in the early saddles and advancing the taut-line by body-thrusting was slow and exhausting. Many climbers would use a rope but not a friction hitch. The line would be attached to the saddle and run up through a branch union, then climbers would pull themselves hand over hand on the running part of the rope with their legs wrapped around the trunk or pressed against it.

A few climbers also would be belayed through this process. The line was secured through a Munter’s hitch on a carabiner attached to a line around the trunk and tended to by a groundworker. The groundworker aided the climber by pulling in unison with the climber, but the climber was still doing most of the lifting.

An old safety belt and buck strap.

The first challenge of these two latter choices was getting the line up into the canopy. The “lineman loop,” sometimes called the throw knot, was used to fling a coiled rope over limbs that were only 30 feet from the ground. Higher throws were possible, mostly if the climbing line was installed with a throwline. The small, weighted throw bags we now employ on the throwline were unknown; instead, a larger rubber ball – a lead-cored, black, rubber Arco Pear (13.5 ounce) – was used. This ball was common from the 1950s into the 1970s and even the ’80s. The ball was apt to bounce its way through the branches, like a ball in a pinball machine.

You also threw with your hands, not with a throwline launcher. Still, there were arborists who could fling an early throw ball 50 feet into the canopy of a tree. However, most throws were shorter, and the ascent into the canopy often was done in a series of throws and climbs. At least you could see where your next anchor was located.

Manila rope around the trunk and over a branch union in an MRS setup.

Regardless of the climbing method, the climber was not tied in until the highest point was reached. However, once tied in with the taut-line, the climber would not untie until the work was completed and the climber was back on the ground. As A. Robert Thompson stated in “Rope Knots and Climbing: National Park Service Bulletin,” his 1957 classic, “To release the taut-line hitch before coming out of a tree is an unsafe and ill-
advised practice.”

Now, as then, many fall incidents occurred on the ascent. The data on incidents is not detailed from the earlier days of climbing and is often anecdotal, but we do have some good references, such as Walter C. Kiplinger’s 1938 book, Tree Surgery (Michigan Works Administration, Ann Arbor, Mich.), and Kuemmerling’s 1948 report, “Safety for the Arborist,” in the 24th National Shade Tree Conference proceedings. These authors and others pointed out that the most common fall incidents occurred during the free-climb before the safety line was attached. The falls were often due to a climber putting too much weight on a branch while climbing up. There were a few incidents where the climber just slipped and fell.

Now climbers “shall” be secured at all times while ascending a tree, per current standards. But the climbing line is installed from the ground, so there is no possibility to inspect the anchor close up. It’s 60 to 80 feet in the air, often hidden from view. Our Z133 American National Standards for Arboricultural Operations – Safety Requirements calls for the inspection from the ground, not an easy task, and, if suitable, subjects the anchor to a load approximately twice the weight of the climber.

While climbers are now secured, their security depends on the strength of the tie-in point (TIP). It has to be strong enough not to fail, and sometimes it is not. A common reason for a fall on the ascent these days is when the anchor fails. Typically, the climber ascends for about a third of the way, 20 feet or more, before the failure.

Subjecting the anchor to a load can give a false sense of security. It held, didn’t it? But keep this in mind; the pull test only tells you if the anchor will fail before you climb, not during the climb. And how sure are you that your pulling did not weaken it further?

So, while it’s safer when secured to the line for the ascent, be sure the anchor is secure. In moving-rope technique, or MRT, this means the line should be around the base of the branch or, better yet, over the branch and around the trunk. For stationary-
or single-rope technique (SRT), you must be certain of two points, the limb in the canopy over which the line runs and the basal anchor where it is attached.

Mitch Sangl secures a basal anchor for SRT climbing.

There are many SRT systems. The basic one is a line over a branch and down to a basal anchor, though there are many climbers who prefer a canopy anchor instead. The top point for SRT should be at the branch union, not away from it. The farther out, the less strength. And make sure it is backed up. One reason we placed our climbing line over the branch union and around the trunk was that if, and it was rare, the branch broke, the line would slide down only to the next branch. Never be solely dependent on one branch serving as support. Have the line passing over another branch as a backup.

The basal-anchor knot.

The basal anchor should be low on the trunk but ideally not on the trunk of the same tree. Increasing the line angle from the top to the basal anchor decreases the tension on the top point while increasing it on the basal, but you can inspect the basal to be more certain of its strength. However, one critical consideration. Be certain nothing can come between the top and basal anchor and catch the line. We had one incident where a crew installed the line over a rarely used two-track (road). Unfortunately, a truck came down the road, caught the line and pulled the climber out of the tree.

Working the canopy

There were workers who never tied in, even to work through the canopy. John M. Haller, in his 1957 book, Tree Care (MacMillan Publishing, New York), has a picture of a climber walking out on a limb without being supported by a line. But many climbers had an attachment of some type for working through the tree. This might be as simple as a bosun’s chair, which was described in Millard Blair’s 1937 book, Practical Tree Surgery (Christopher Publishing House, Boston, Massachusetts), as a means of walking out on a limb without subjecting it to your full weight.

The use of a belt was mentioned in the 1934 book by A. D. C. Le Sueur, The Care & Repair of Ornamental Trees (Country Life, London). This is a classic text and contains some insights that were forgotten early on only to become common knowledge later, such as pruning at the collar (the branch ring). Le Sueur was interested in safety, a topic often forgotten in tree books, and discussed the use of a safety belt with the rope, a practice that began to appear among French tree workers around 1900. Later he discussed the introduction of the safety sling (bowline-on-a-bight) from the United States. Le Sueur was critical of the practice of free-climbing, and his comments are worth repeating, “No workman (sic) should have an idea that the use of such a belt is a confusion of cowardice. The use of a safety-belt is a question of common sense.”

The boatswain’s seat or bosun’s chair was gone by the 1940s, though I did find a tree worker still using one in the 1990s. The use of a bowline-on-a-bight also has largely disappeared. I remember back in the early 1970s an older arborist showing how he once did this, but everyone was using arborist saddles by then. The saddle, with its waist and butt straps, was more comfortable to sit back in while sawing through a limb with a Fanno saw.

I recently heard one climbing instructor say, “Don’t call them saddles, saddles are for horses.” The difference between climbing saddles and riding saddles was not that great. You sat in them and hung your saw (climbing) or rifle (horse) scabbard from it. Now, many use a harness system for fall protection and work-positioning (we used plow harnesses for the Belgians on our farm, so I guess harnesses are for horses, too!).

There are (and were) fewer fall incidents while working the canopy than ascending. A common incident in the past was the rope breaking. This occurred when the climber took a long swing or short fall while working through the canopy. Rope choice from the 1900s to the 1950s was simple: manila. Nylon was introduced in the 1960s, but many did not like it, too much stretch. Dacron followed in the 1960s and had less stretch. Still, until the 1970s and even the early 1980s, manila was a common rope choice for climbers.

Fall incidents these days commonly occur when repositioning in MRT systems or switching climbing systems for SRT.

It had a lot of advantages. A climber could get a firm grip on a three-strand manila rope. You also could pull it open and hang something on it while your hands were busy (cigarette, for example). But it did not have a lot of strength. A manila-rope manufacturer at the 1952 National Shade Tree Conference cautioned climbers about taking a fall while on a manila line. A 10-foot fall could cause the line to fail. This is one reason for the rope-breaking incidents; another was the cigarette burning the rope!

Fall incidents these days commonly occur when repositioning in MRT systems or switching climbing systems for SRT. This type of incident was not as common in the earlier days of climbing, as there was only one system and once you were tied in, you stayed that way as you worked your way to the ground.


Few incidents, then and now, occur on the final descent. Interestingly, the most common descending incident has not changed. The climber runs out of line. One of the 1930s incident reports involved a climber who fell when the taut-line hitch drew through the end of the line. While we use different knots, devices and ropes, we have the same result – coming off the end of the line. A bit of advice given back then is still good today, and that is the use of a stopper knot several feet before the end of the line.


Finally, someone might ask, why, with all the improvements in procedures and gear, have we not seen a dramatic reduction in incidents, instead of just a change in the type of incidents? The answer may be simple – we have not changed the arborist. Many incidents start in our head, not in the tree.

The industry needs to focus more effort on safety behavior. TCIA’s Certified Treecare Safety Professional (CTSP) credential is a great step in this direction. Acceptance of risk is a requisite for climbing, but this acceptance does not mean we should not always seek to avoid, eliminate or minimize its hazards.

John Ball, Ph.D., BCMA, CTSP, is a professor of forestry at South Dakota State University in Brookings, South Dakota.

Dr. Ball will be a presenter at the TCI (Tree Care Industry) Virtual Summit 2021, January 13-15. For details of that event, visit

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