A Case for Veteran Trees
by Christopher Roddick
Ask any arborist why people hire them and, more often than not, the number one answer is fear. People do love their trees, but most call an arborist because they are afraid of big trees or big branches falling on their houses. While there are many reasons to hire a tree care professional, it’s fear that actually makes people open their wallets.
The fact is, trees do fall over and do hurt people – that’s why tree care is so important. But how afraid should we really be? The odds are much greater that a person will die falling out of bed (about 500 a year in the U.S.) than being killed by a falling tree (fewer than 50). People’s fears don’t always match the likelihood of bad things actually happening, because one of the down sides of having a large brain is also having a vast imagination. The fear of trees is just one of the challenges arborists and land managers face when they seek to preserve larger, older, and sometimes dying trees in the landscape – those we refer to as “veteran trees.”
Assessing the Value of Trees
In the past few years, the term “ecosystem services” has become the latest buzz-term that professionals use to convince people in towns and cities to spend money on green initiatives like tree planting and other programs focused on young trees. Ecosystem services reflect a plant’s direct value to humanity and are a way for us to assess a tree’s ability to do things like reduce storm water runoff, noise, air pollution, and urban heat-island effect.
Planting new trees is a fantastic ambition; the old saying goes that the best time to plant a tree was 20 years ago, and the second best time is today. But it can take 25 to 30 years before a new tree is large enough to start giving a return on ecosystem service investments: the environmental costs associated with growing and planting a tree are far greater than those the tree provides until the tree has reached a certain age, size, and output level. The sad truth is that the survival rate of new plantings in many cities is not great. Studies show that the average life span of a city tree in the U.S. is about 7 to 13 years. On average, suburban trees survive only around 30 years after planting. If cities and towns had better programs to preserve the older trees they already have, they could get even more benefit for the buck when it comes to the environment.
Maximal tree ecosystem services come from larger, older trees with sizeable root and canopy masses. One would think that this alone would be enough to convince people that veteran trees are worth the time and money to protect. But in our over-built, urban/suburban environment, veteran trees are competing for the same precious real estate (both above and below ground) with everyone and everything else. And that makes development another major reason we don’t see many veteran trees in our town and cities.
Oddly enough, tree planting initiatives themselves can sometimes be a culprit in mature tree removal. City officials and builders have a far easier (and sometimes profitable) time removing older trees for development when they are allowed to simply plant multiple new trees to “replace” those chopped down. Unfortunately, given survival rates and the pace of land development, many of those new trees may never reach the point of providing a net ecological benefit, much less equaling the benefits of a mature tree.
So why are these old trees so valuable to our urban areas? We know that most people value historical trees or those with cultural importance – they give us a sense of place and a sense of history – but we are only beginning to understand the importance of veteran trees’ biological complexity and benefit to the environment. Habitat, soil stabilization, carbon sequestration, and air quality improvement are just some of the benefits trees give us, but shade itself may be the most important for those of us in urban areas. Tree shade not only keeps soil temperatures cooler but also cools our homes and streets. As the climate warms, tree shade in cities will become only more important. Mature trees can also raise neighborhood property values, reduce airborne particulate matter, and lower local asthma rates.
Tree shade keeps us happier, healthier, and less stressed on a hot summer day. It can be 10 degrees cooler under the shade of a tree, but that’s not just from the blocked sun. The leaves of a tree are constantly transpiring a fine mist of water pulled up by the roots that then cools and freshens the air. A mature oak can transpire as much as 100 gallons of water a day in this fashion. In addition, tree shade is better ecologically than shade from a building because leaves filter rather than block light, allowing understory plants to grow.
Adopting a New Model for Trees
We may require a new way of thinking about trees in cities in order to properly protect them. The textbook picture of a healthy and safe tree is often quite different from the aesthetic reality of the veteran trees around us. The fact is that even dying trees can be beautiful, in addition to environmentally beneficial, as they die, a process that can take decades or even centuries. As a tree senesces, its decaying wood becomes food for fungi, cavities become homes for birds and animals, and ultimately the whole tree becomes fertile soil for new trees and plants. The roots of veteran and dying trees can use up to 40-60 percent of their photosynthetic byproducts to exude nutrients into the soil, thus enriching the environment for future trees. It’s a magnificent cycle of life, and it would be wonderful to see it take place in more backyards and neighborhood parks.
More and more, we look at trees not as lone organisms but as the heart of “tree-based ecosystems.” Veteran trees provide food, shelter, and oxygen to thousands of organisms, including ourselves. One mature oak tree can supply the bulk of nut forage for many animals like squirrels, deer, raccoons, and even turkeys, if you’re lucky enough to have them living nearby. According to Douglas Tallamy, in his wonderful book Bringing Nature Home, oaks support more species of moths and butterflies than any other tree, thus providing food for all types of birds.
Age Appropriate Care for Trees
Still, the risk of older and dying urban trees causing damage as they fall apart is a reality, but one that can be managed. Too many mature trees are condemned due the lack of understanding of tree biomechanics and true risk of failure. What can we do?
The first step is age appropriate tree care (AATC). From a tree’s juvenile years to its later stages, each phase of life requires its own style of management, one that focuses on the tree’s needs and development at that time. For example, in a tree’s Formative Stage, proper planting and after-care (watering and mulching) are most important. Once the young tree is established, solid structural pruning and training should be the focus. The tree’s Mature Stage should involve less pruning, except for safety, and more protection and monitoring. Protecting the tree’s root zone and maintaining proper soil biology (noninvasively) are also critical for a mature tree. For very old or dying trees, techniques like retrenchment pruning to reduce canopy, cabling and bracing to support limbs, root monitoring, and safety evaluations become important. Many arborists may have some of these skills, but there are situations, like risk evaluations and organic soil work, that require specialists. The care of veteran trees in itself can be a specialization some arborists study and practice, like physicians who specialize in human geriatrics.
In the end, if we want to make our built environments healthier and more ecologically sound, we need a diversity of both tree species and ages. Veteran trees should be preferentially protected and preserved. In order to do so, we will have to convince people of their worth and invest in the resources necessary to care for them. By protecting these titans of ecology, we can bring beauty and environmental health to our landscapes for centuries to come.
About the Author
Christopher Roddick is the Head Arborist and Foreman of Grounds at the Brooklyn Botanic Garden. For over 20 years, he has developed the Garden’s tree care program and established the BBG as a leader in Conservation Arboriculture and veteran tree care. In addition, Chris consults with landscape architects, designers, and private clients on mature tree preservation, tree risk assessments, and tree protection in construction and development sites. He is the author of the Tree Care Primer a guide to care for young, mature, and veteran trees. When he’s not working in Brooklyn, he is often on an expedition, traveling to the Neo-Tropical forests where he conducts canopy research as a climber and project coordinator. Chris may be reached at email@example.com.