Celebrate World Arbor Day with DCZA

Written By: Viktoria Barr, Arbor Specialist

Why Trees Matter

We all know that trees are important, but do you know why trees are important? Aside from providing the oxygen we breathe, trees come with copious amounts of benefits to us as humans, to native wildlife, and to all of the animals that call Denver Zoo Conservation Alliance home. To name a few of these benefits, trees provide shade, food, shelter, and even monetary and medicinal benefits. Without trees, we would not have the everyday items we love like coffee, aspirin, paper, rubber, lumber, and of course, fruit! Trees also regulate our climate, cool our cities, conserve water runoff and erosion, and sequester carbon from the atmosphere. It’s also been shown that trees can relieve stress and provide positive changes in mental health to humans and animals, just by existing in the same space as them.

And so, every year on the last Friday of April (this year, April 25), we celebrate Arbor Day—a day where we can raise awareness about the vitality of trees and encourage sustainable tree planting and care globally and throughout our communities.

The Importance of Long-Term Tree Care

Like yourself, trees in the urban environment need to be cared for after being planted just as you need cared for after you are born. Trees require maintenance throughout their life, like staying hydrated, getting routine haircuts, and making sure they are getting all of their vitamins as they grow up. Imagine how your hair might look if you went five or 10 or 20 years without a haircut—it would probably become quite unruly! It’s very similar for trees. Routine trimming of live branches and the removal of dead limbs is necessary for overall tree health and will reduce the chance of someone becoming injured by falling branches.

The Coexistence Between Healthy Trees, Wildlife and Ecosystems

To properly care for a tree from cradle to grave, there are a few things you must consider.

First, where is the tree going to be planted? Have you selected a tree that is “native” or local to the region in which it will be planted? Picking out trees that are local to the region in which you wish to plant them will benefit you, the trees, and the local wildlife. In Denver, a tree might be able to survive our hot, steppe climate with ample watering, but it would likely be better to select a tree that does not require a lot of watering – which will save you time, money and is much more sustainable in the long term (since Denver does not receive a lot of rainfall).

Additionally, local wildlife has evolved to coexist with localized plant species and typically form mutualistic bonds (meaning both parties benefit). Planting noxious and non-native trees should be avoided, as they can become uncontrollable and take over habitat for native species, potentially becoming invasive if they are not already deemed so (the Tree of Heaven or Ailanthus is a prime example of this).

Additionally, planting “native” or “local” isn’t good just because it’s a popular buzz term. When you plant native and/or localized trees (and shrubs and flowers), local wildlife (pollinators, furry critters, insects, etc.) all benefit because they have formed symbiotic relationships with each other. For example, the Colorado Hairstreak (Hypaurotis crysalus, Colorado’s state insect) is a beautiful purple butterfly that relies solely on the gambel oak tree (Quercus gambelii), which grows here naturally.

You may have noticed that some oaks tend to hold onto their leaves all throughout winter and then drop them when new leaves emerge in the spring—the gambel oak is no exception to this. An adult Hairstreak lays its eggs on a gambel oak leaf in the fall/winter, and then when the caterpillars hatch in the spring, the caterpillars eat the new, young oak leaves. After the caterpillars pupate into adults, they eat sap from the tree. If the oaks were to drop their leaves in the fall/winter, this relationship would not work.

Colorado Hairstreaks will never leave the grove of gambel oak trees where they were hatched, and under ideal conditions, gambel oaks can survive well past 100 years old. This is just one example of how trees benefit our wildlife, but it’s easy to see how important they can be to even one (albeit small) species!

A Simple Way to Celebrate Arbor Day

This Arbor Day, consider taking a walk around the Zoo or your neighborhood and take in all of the benefits that trees provide for us. How many different species of trees can you name while you walk? Do you notice any birds or animals using the trees? Do you come across anything that might not exist without trees (park benches, light poles, books, etc.)? Consider where you might like to see more trees planted—and who might ultimately benefit from them for many decades or centuries to come.