NATURE NOTE Number – 72 July 14, 2023
Thanks for visiting NATURE NOTES. Sometimes I get questions, or see or hear something that gives me an idea for a NATURE NOTE. So here is one in reply to a question that comes up from time to time, mostly from folks in urban or suburban areas. But there are a lot of lessons to be learned from talking about the question.
Our Current topic: Does Ivy kill trees?
This usually involves the common groundcover English ivy that has gotten out of control in a yard, garden or wooded lot near homes. Anyone who has ever had English ivy in their yard knows that it can quickly spread to trees, porch columns, chimneys, walls, lamp posts, and maybe a lazy dog if it sleeps too close to the ivy patch. But I suppose the comments below could apply to other vines.
So let’s think about this situation. If the ivy reaches to the crown of the tree and is so dominant that it actually prevents all sunshine from reaching the leaves of the host tree and prevents photosynthesis from taking place, yes, the tree will eventually die due to the non-production of sugar/energy for the tree. This very seldom occurs, but heavy shading of host tree leaves by the ivy could impair the growth of the tree and make it less able to resist other threats. The ivy will use some moisture and minerals from the same soil that supports the host tree, but that is generally not an impact on a well-rooted tree, as other plants around the tree also compete for that moisture and minerals. It is possible for the weight of the ivy stems and leaves to cause a branch of the tree to break off, or even the entire tree to topple in heavy winds or ice storms. This damage may open the possibility of insects or disease entering the tree and eventually cause further damage or even kill it. The likelihood of the ivy stems “strangling” the tree trunk like a piece of wire around the tree is very remote, as the stem and the trunk are both relatively flexible as they grow, unlike a wire.
So where does this lead us concerning the initial question: Does ivy kill a tree? Based on the above, you might just say “yes”, or you might answer with “yes, but it is a rather indirect death that will take a long time and/or other events have to occur, or you might say “no”. Like many things in nature, a simple “yes” or “no” answer doesn’t work very well. “It depends” is often a handy and correct answer. But this is an excellent question to ask your scouts, because it makes them think about nature and tree growth. It addresses photosynthesis and what is needed for that to take place (sunlight, chlorophyll, carbon dioxide and water); the root system of a tree; the impact of insects and disease on a tree; the impact of weather (wind, ice, snow) on a tree; the impact of an invasive species (like English ivy) and how it can take over native species; and how believing, as many do, that ivy growing on a tree will kill it is not quite correct. But there might be those that say “I have seen a tree almost covered in ivy and it is dead”. Ok. Is there a chance that the tree died from something else, and the opportunistic ivy saw a chance to climb up to the sunlight and really grow? Hmm? Something to consider. You can Google the internet and find various opinions about our question, and how to remove ivy and how not to remove it, and the benefits it provides to wildlife, and on and on. But hopefully you gave the whole question some thought.
As discussed above, this simple question, without a simple answer, is the kind of thing that make folks, like your scouts, think about the workings of nature, and how they can apply what they may already know to figure out answers (like “it depends”) to the endless questions nature can throw your way. Give it a try. Maybe ask the question one night at a scout meeting and ask them to bring their answer next week. It might be the beginning of a good conversation between scouts and parents or teachers about nature. If you have been using NATURE NOTES to help your scouts learn, they may have a better answer than the adults they talk to. Discussion usually provides knowledge to at least one person in the crowd, and often to all. We are just trying to help scouts learn about nature. Discuss it. You might learn something too. And be careful with that lazy old dog sleeping near the ivy.