Friends, the CCI has been talking about the habitat value of dead trees for about four years and when we do, we get THE LOOK! That look says, ‘Who cares about dead trees! They’re dangerous and ugly! And some get bad pests!’ Every point is true, and when we are talking about bad pests, well, the discussion is naturally over. But here’s the most important thing we hope you’ll take from this presentation. It’s actually a simple question we’d like you to ask when facing a decision about removing a dead tree. ‘Does the tree need to be removed completely?’ We are here to suggest why that question is worth asking.
We are sure you already know all the benefits of a mature, healthy tree. But folks, as crazy as it sounds, science suggests that more species of wildlife use a dead tree than a live one. For starters, about 85 types of birds in North America need holes in standing rotting wood in order to raise their families. These guys, woodpeckers, make and eventually vacate many, many cavities. Those cavities benefit over 40 bird species and many small mammals. Woodpeckers are critical to many forest systems.
The great thing about cavities is this. Whether they are made by woodpeckers or by natural causes, they provide other functions such as places to den and to roost. But they are critical for survival in other ways. How? They offer shelter from the elements and safety from predators. This is even true for old hollow logs on the ground. You see, in all phases of its decay, a tree is a virtual time share for critters in urban forests.
Perhaps you can think of a dead tree as a Hilton for insects. So who drops by for Happy Hour? Insectivores of course! They come for the free appetizers. Some court each other and decide to move in! Others decide they don’t want to live there but just store their food. So they find hideaways for berries, prey, seeds and nuts. In California, Acorn Woodpeckers provide the most dramatic example of this.
Have you ever noticed how much animals are like humans? They want to see and be seen. So they seek the best view. Perches on dead trees are just that. Birds use them for hunting and consuming prey. Perches are also ideal for defending territories and for courtship. Fights over these things are a big deal! They determine who has claim to the assets in the territory, who gets the girl and whose genes are passed on.
It’s not easy living in the wild. Survival is critical. So if you’re seeking a place to rest, hide or bring your temperature in check, where do you go? A space behind loose bark, in the split of a trunk, under or inside a log may be perfect. And can you see the camouflage value of these locations? Small prey often hide here as well. So a predator could easily hope that a moth or mouse might practically walk into its mouth!
A dead tree’s legacy doesn’t end there. Haven’t you ever used a fallen log to get across a stream? It’s a great place to fish too! Over time it may even become a nursery for new vegetation. Scientists have written volumes about a log’s benefit to aquatic life, to the quality of stream beds and the management of water flow. By the way, the value of standing dead trees along riparian areas is well supported by science. If you can, please make these trees a priority.
Here’s what’s great! When you retain dying trees you actually enrich the overall habitat. How so? Because a dead tree’s customers are good community volunteers! Some do the job of decomposition. Others pollinate plants. Yet others help to keep down those tree pests that we worry about. But that’s not all. Many transport fungal spores. Directly or indirectly they help the tree fulfill its ultimate destiny…to return nutrients to the soil to support surrounding vegetation.
So what can we do? You’d first want to call an arborist, wouldn’t you? A tree risk assessment might mean some tough choices. Perhaps you could prioritize and select trees 12” or greater in diameter, those with sapwood still intact, and those away from structures and high-use areas. There will be lots to consider. But always begin with the question, “Does the tree need to be removed completely?” The photo on the left indicates the depth of a woodpecker cavity. It is helpful in making some decisions.
Most nesting woodpeckers need less than 18” of rotting wood. Note the hole entrance in the left photo. It was made just below a cut. Keep that in mind even when you consider a tree that has just a small section of heartwood decay. Obviously regular risk assessments may be necessary. The photo on the right shows the number of years this tree has been used. This is a cavity-nesting falcon evaluating the abandoned homes of a woodpecker!
Sometimes an arborist will say that risk of failure can be reduced by shortening the tree and its limbs. The photo on the left shows an ideally managed snag. So the question is how short can you make it? Look at the cavity in the far right photo! Even a small stump or snag 5’ high can be useful to a small bird! Healthy trees sometimes have one dead limb. It does not always pose a high risk. If it’s 6” in diameter or greater, perhaps you can save it by reducing its length. But always leave at least 18.” These small sections add up! They are excellent compromises for the urban forest!
How about putting a sign on the tree? It could change public perception. And how about encouraging naturalists to take their field trip participants to visit a dead tree? Here’s another idea… Graduate students are often looking for projects. The impact of dead wood on habitat quality and diversity can be the subject of scientific study. The results can support urban forest management. All these are ways to “sell” dead trees to park managers and to park visitors.
You already know there’s more than one pathway to education. These methods are what we use to engage all generations, lay and professionals alike. Perhaps you can try some of them. If you are the impatient type, this is not a mission for you! I mean, most people understandably shake their heads with reservation. But since it’s time to wrap up, I want to leave you with a word of encouragement.
Friends, if you’re willing to pioneer new ways of thinking about dying trees you are likely to discover, as we have, that when motivated people sit at the same table, remarkable compromises and innovative ideas emerge. If you’d like to learn more about our work, please write down our website or contact Gillian at this address. Thank you so much for your interest in dead trees!