Does Slacklining Damage Trees?

Outdoor slacklining involves the use of two trees that act as stabilizers at each end of your slackline. You use a ratchet to tighten the slackline around the trunk of each tree until it is tight and snug. As a result you have to be careful to protect the trees in question and avoid damaging them.

Use trees to slackline that have a diameter of at least 12″ (30 cm) at the anchor point. Use tree protection of 80′ (200 cm) in length, 8′ (20 cm) in height and 0.16″ (4 mm) in thickness before attaching the slackline to the trees or you risk damaging the bark and integrity of the tree.

While indoor slacklines for kids can be set up inside the house and sit on a base on the floor with no trees involved, most slacklines are fastened to two trees outdoors.

With damage to the outer bark, trees can be exposed to disease and pests. If you choose a tree that is too small that can’t hold the weight load, you risk breaking the tree and hurting yourself.

Using Trees As Anchors

Humans have long used trees for various purposes. Climbing them for fun as kids. Assembling tree houses in them. Tying ropes around them with an old tire attached for swinging on them. Or using two trees to attach a hammock to. Most of the time at best we might have considered the safety aspect for ourselves, and ensure that whatever we did was safe for our use and for the use of others. We probably didn’t spend too much time considering the effect it had on the tree though.

The general rule of thumb for a safe tree swing is to find a strong branch with at least 8″ diameter (20 cm) that has no cracking or other visible damage. Finding two trees to install a safe slackline between is a bit more complex when you take into account both your safety and that of the trees.

Slackline DIN 79400

You may have heard or read references to DIN standards which have to do with the standardization of products and items around the world. DIN stands for Deutsches Institut für Normung which is German for German Institute for Standardization. Since 1917 the DIN has set technical standards for various items from paper clips to screws to laboratory equipment to lead batteries and tens of thousands of other products so that people and businesses around the world can speak the same language when using various technologies and products to everyone expect the same standard. They even have a standard for slacklining.

DIN 79400 sets out the technical standard for slacklining and more specifically the minimum tree standards that should be adhered to when choosing trees to attach your slackline to.

Minimum Tree Size

Based on DIN 79400, the following minimum requirements should be followed to avoid damaging trees used for slacklining, not to mention for safety purposes, too. You should have:

Tree diameter of at least 12″ (30 cm) at the anchor point. The tree diameter should be increased when you have higher tension and more weight.

Tree protection under the tree sling to prevent damaging the tree bark. This also helps to distribute pressure on the surface of the tree. Many modern slacklining sets will come with a form of tree protection to use underneath the sling and ratchet set.

Slings (ie. a product like TreeSling) which are at least 2″ (5 cm) wide as the larger the width the more the weight is spread out. You should spread the sling out behind the back of the tree to increase its surface area.

Other Considerations

Choose two trees that have no hazards, obstacles or debris that could harm you or inhibit your slacklining. If you view pictures of knowledgeable slackliners you will always see two trees set up with a slackline that are completely free of obstacles such as branches that could get in your way. You should also look for a ground that is even if possible as you will fall from time to time especially if you’re a newbie. The cleaner and more even the ground beneath you, the less likely you will hurt yourself.

Calculating Anchor Loads

So you’ve already found two ideal sized trees but how can you be extra sure that the slackline is safe enough even for your large friends who are heavier than you are? You can calculate your anchor load with an online calculator such as the one at BergFreunde.eu. The page offers a very detailed explanation of how to use the calculator and determine how much load your trees should be able to withstand.

With this sort of calculator you enter the Length of the slackline, Weight of the user, Sag under load, and Slackline type. Once you’ve inputted your numbers, you see the results below that and get an explanation of the figures and terms below that.

I inputted the following information for myself to test the calculator out:

Length of the slackline: 50m

Weight of the user: 71 kg

Sag under load: 0.5m

Slackline type: Longline

Expected force on the anchors: 17.8 kN with static load & 18.6 kN with dynamic load.

If you check the table just below that you’ll see that 10kN equates to a mass of 1000 kg. Since my results of 17.8 kN and 18.6 kN can be rounded up to 20, that would be double the mass being applied to the slackline which equates to 2000 kg at 20 kN.

A further thing to keep in mind is to avoid using trees that cannot withstand a force of around 2200 lbs (1000 kg) at a minimum.

And if all of this math is too much to calculate, go back to the Minimum Tree Size section above and measure your trees instead.

Final Thoughts

An interesting study done by the International Slackline Association called Impact of slings and tree protection on the distribution of pressure was completed in 2017. The study decided to look at the relationship between four key areas:

• Pull forces involved in slacklining.
• Position of the slackline around a wooden pole (mimicking a tree).
• Type of sling used.
• Type of protection used when fastening the slackline to the pole.

The study attempted to figure out how best to reduce pressure from these four factors. The results were summarized as follows:

1. Increase the thickness and quality of tree protection.
2. Increase the width of the sling.
3. Use trees with larger diameters.
4. Keep the forces in your slackline system low.

Source: Slackline International

Conclusion

Slacklining can damage trees if you use the wrong size tree (ie. too small) or if you don’t use a tree protector underneath the slackline before it is fastened to the tree. The outer bark of a tree can be damaged and while it will not be harsh enough to kill a tree in the majority of cases, it certainly does cause damage that can lead to other problems for the tree and quite frankly aesthetically does not look nice.

Choose trees that meet the standards as specific by DIN 79400 shown above for not only the safety of the trees but yourself and your fellow slackliners, too.

As per research conducted by the International Slackline Association, the best way to slackline safely and to also protect the trees can be achieved by increasing the thickness of the tree protection, increasing the width of the sling, using trees with larger diameters and keeping the forces in your slackline low.

Do you wonder if it’s better to slackline in shoes or while barefoot? Check out the article called Is It Better To Slackline Barefoot Or With Shoes?