ground or below. When we remove trees that are growing next to others, we change how wind and weather hits the exposed tree. When we dig near trees to alter the grade, add a trail, or place a utility, we physically remove roots and organisms that the trees have relationships with that may be helping the trees gain access to nutrients, water, and air. This can cause stress and change their vigor and ability to respond to weather condi- tions over time. When we drill into a tree or wrap it, we induce physical responses by the tree to seal a wound or develop new sprouts. Sometimes this response may not be successful enough to prevent the development of decay. In addition, these elements and the people using them load the trees in ways they are not adapted to. All these factors can affect how a forest or individual tree responds during a weather event. Good design and man- agement will help managers anticipate any issues and support a long lifespan for the course—and increase the rich- ness of the user’s experience.
Regular monitoring with a plumb line attached to the low side will reveal whether this large elm is subsiding or failing after a storm that caused the tree next to it to fail.
THE WEATHER FACTOR
Since bad weather is inevitable, you should have a plan in place for inspec- tion of your entire property after any se- vere weather event. Strong winds, snow or ice, and heavy rains can all affect the stability of trees, which, in a forest, act as a damping mechanism, shedding and sharing the loads generated by wind and other forces both individually and collectively. Trees adapt their growth to cope with the loads that are normally present in the environment. Unusually high loading events like a strong snow or ice storm with winds ex- ceeding 35 mph will likely cause chang- es in trees, including partial failure. Partial failure means that a tree has par- tially uprooted or that woody parts have been pushed beyond their elastic limits and wood fiber has been damaged but not fractured. Wood pushed beyond its elastic limit will not rebound to its original shape.
Different types of weather events are likely to have subtly different impacts on your trees, so it’s important to under- stand the differences. Ice and snow. By far the most worri- some event would be an ice storm, which is devastating for trees that are not already adapted to an alpine environment where snow and ice loads are more common. Trees in alpine environments are adapted to snow and ice loads, making them more resilient to the effects. But trees in areas where snow and ice storms are less common will not fare as well when the frozen stuff falls from the sky. Ice can build up tremendous loads on trees, leading to whole-tree failure or breakage of large parts. The damage is not always easy to spot, though. I have seen failures occurring weeks after an ice event when cracked and damaged limbs finally let go.
Heavy, wet snow that sits on trees or a warming event where snow buildup gains moisture and thus weight in a thaw can have similar results. To minimize potential damage, some course operators in winter climates remove cables from their trees for the winter, remove decking from bridges and other areas where snow build-up will occur, or hire people to ride the course, clear the cables, and shovel to keep snow loads under control. High wind events that fall outside of a region’s “normal storms” can also cause damage to trees, either by breakage or uprooting. If the weather has been wet and soils are saturated, uprooting can be more likely. Over my years of inspecting challenge courses and zip lines, I’ve realized that connecting trees together with cables and guy systems causes significant
Made with FlippingBook Digital Proposal Creator