Foreword
The knowledge of the importance of trees is spreading. And that’s important because trees have a large influence on us culturally, socially, and environmentally.
Proper tree care is a cultural issue, it is a social issue, and it is an environmental issue. Trees aren’t just big decorations; tree stewardship is actually in the best interest of everyone, whether they know it or not.
This purpose of this article is to emphasize the importance of preserving old and large trees in urban and residential places. This article aims to present the preservation and prudent care of mature, old, and less-than-perfect trees as climate action.
Intro
In some capacity or another, trees spend their entire lives growing. Trees have one solution to nearly all of their problems: to grow. In a simplified sense, that’s all they can do. And just by living, trees and forests provide incredible ecological services that improve the places where we coexist with them. One of the most significant ones has planetary importance: capturing carbon from the atmosphere.
They spend their entire lives collecting carbon dioxide from the air, through photosynthesis, and transforming it into leaves and wood and flowers. Isn’t that awesome? Think about that; creating wood from light and air, basically.
It has been abundantly clear for years now that trees and forests offer a solution to one of our planet’s needs during this period of accelerated climate change. What’s especially cool is that they don’t require any new invention or engineering; they’re already here, and they’re already at work. Their global numbers are dwindling, though. Global deforestation and global CO2 emissions are both at all time highs (1) (2). This is a bad combination.
This article is written on the assumption that you know why responsible environmental stewardship is important, and are aware of the current global climate crisis and CO2’s role in it.
Keeping large trees around for as long as possible has far reaching benefits, and their sequestration of CO2 might be the farthest reaching one of them. The four sections of this article explore the mismanagement of trees, the consequences of that, and we use data and science to shape a more responsible future of tree care.
Section 1: Mismanagement
Examples from My Neighborhood
There is an active but disconnected effort amongst the majority of run-of-the-mill tree companies and municipalities working against trees. And ergo, against climate action. While mostly unintentional, this negligence reduces the quality of our urban spaces because, when trees are made to come down, we lose the entire list of services they provide. This is a gigantic problem because they’re supposed to be the ones protecting trees, and you can't readily replace old trees.
A significant number of urban and residential trees are taken down each year. These include justifiable removals and predatory ones. Excluding improper logging and land development, the list of tree mismanagement offenders is very long; abuse of land and trees takes place in plenty of major industries, not just tree care. At the very top of the list are municipalities, tree companies, and homeowners themselves. Trees are mismanaged to a point where they are made undesirable, made unsafe, or are the unlucky targets of tree companies on the production hamster wheel.
Check out these examples of large tree mismanagement from both tree “care” companies and municipal sidewalk construction from my neighborhood in Ferndale, Michigan.
Above, the sidewalk contractors hired by Ferndale have done catastrophic damage to this tree’s base. Below is an example of what this damage will likely look like in 10 years on a tree just up the street.
80% of this stump’s crown was dead and it stood above a busy corner, and the tree was in pretty rough shape. Evidence of the same exact damage from the sidewalk installation is present and very obvious. It doesn’t take an arborist to determine what caused this tree to become a hazard.
Yes, some trees should come down for safety reasons. But, when we are prudent with our tree care, we can avoid letting our trees get to the point of being too hazardous in the first place.
Unfortunately, the folks who own the tree pictured below in my neighborhood thought they were hiring someone to care for their oaks, but instead got something far from it.
This pair of oaks were dramatically overpruned. The diameter of one of the living removed branches is ~two feet in diameter. The live-crown-ratio of this tree has been significantly lowered, the center of mass has gone way up, and the accumulated area of now-embolized healthy tissue from the cuts is dramatic. The photosynthetic area has been massively reduced. These huge cuts were made on the trunk, even though they were “properly” cut, it just goes to show how short-sighted the current state of tree care can be. I could go on and on.
In fewer words, each of these example trees is well on its way to being less safe and less healthy, yet the owners think they’ve hired professionals to make the tree safe and healthy. Each of these issues are commonly known practices not to do to trees, yet they are very easy to find in any neighborhood.
Easy to Find
The examples above point to the prevalence of tree mismanagement; each of these examples were in the same neighborhood. Our cities and officials have a responsibility to maintain their trees, and tree “care” companies ought to not make trees worse-off.
Aged-based and size-based tree care practices are well established. Risk assessment technology is very sophisticated and affordable. Unfortunately, the understanding of those concepts are not requisite for being a “tree care company.” Broadly speaking, they’re mostly interested in what keeps big money coming in, and that often means either removal or exploiting the tree in some other way, like overpruning. This problem is exacerbated further by the length of time it takes for tree problems to become obvious—today’s sidewalk installation will be a problem in 10 years, just like in the above example.
The indirect benefit of companies and contractors damaging and killing trees should not cast shade over the direct benefits trees provide. Keeping people working is important; industries are built on making urban places better. That’s supposed to be the point of tree care. And there are ways we can coexist with trees without making them worse off, which we’ll get to soon.
There are many reasons why these failings occur: municipalities are slow to change, and the tree care industry is largely behind on science and generally doesn’t plan for comprehensive long term care. We all need to be more diligent in who we hire, and diligent in our professions. We can all be better.
The first thing we can do to be better is to become aware, and finding a new perspective on trees that is compelling to you is important. If you think about trees long enough, you will see.
Section 2: Flaws in "remove and replace"
Restart
Tree companies use the “remove and replace” pitch to soften the blow when they tell a homeowner they should hire them to cut their tree down. The idea here is once the tree is removed and the stump is ground out, a new tree will be planted in its place. That’s great if the tree really ought to be removed. Not so great if we’re just lining tree company pockets to make our spaces worse off. We shouldn’t look at trees as commodities. They are vital to functional ecosystems, not replaceable lawn decorations.
Plenty of urban trees that are removed aren’t replaced. And while there are endless resources for learning how to plant trees properly, poorly planted trees are more common than properly planted ones. To give credit where credit is due, it isn’t a bad thing to replace removed trees. The graphic below represents tree carbon sequestration when trees are removed.
When trees are removed, the annual sequestering of large amounts of CO2 stops. We are stopping an already functioning carbon collecting machine that’s been online for decades, or even hundreds of years. According to a study from the University of Hamburg, up to 70% of the CO2 sequestered by a tree occurs within the last half of its life, assuming it lives its full natural lifespan (3).
When we zoom out a bit, imagine the accumulation of all of the trees removed for urban development and during urban forest management (or mismanagement). Multiply the above graph by millions. A staggering amount of carbon sequestering has been stopped with the removal of our trees, and continues to do so.
Avoidable Losses
Forests gradually replace themselves with varying ages of trees; this is called forest succession. Ecosystems naturally change over time, and sometimes significant environmental disturbances happen naturally, but it is not the norm in most ecosystems. In our urban spaces, frivolous annihilation of trees contributes to the abrupt and large loss in the global carbon sequestration over time.
A very in depth study of carbon sequestration of large trees in the American pacific northwest claims:
Replacing large diameter trees with seedlings will create a major carbon loss to the atmosphere during harvest and not achieve storage of comparable atmospheric carbon for the indefinite future. (4)
Things don’t look so good either when we take a look at carbon offsetting programs for businesses and corporations. Those programs are rife with justifiable criticisms, and encourage companies to continue their emissions so long as they offset enough (5). “Time and time again, projects are making their money up front, and then failing to live up to the long term promise that encompasses the entirety of their value.” (5)
Replanting each removed tree is not a silver bullet for our climate crisis either. The real answer is to stop our CO2 emissions entirely. And since that probably isn’t happening any time soon, the consequences of removing large trees that collect massive amounts of carbon while emissions continue, seem unmistakable. Every tree counts right now.
Remember, we’re talking about the total CO2 sequestration of each contributing tree together. In our urban and suburban places, each tree is more valuable, not less, because there are fewer of them than now. And guess what, we don’t have to remove trees in order to plant new ones. We can take care of the ones we already have, too.
Section 3: Using Data to Understand Trees
Data is our Friend
When the services trees provide have actual values we can understand, we can make better sense of them.
There are mathematical models for predicting and calculating just how much CO2 trees collect. The inputs for these models are things like crown size and shape, orientation, species, diameter, etc..
Despite being somewhat limited by nature of complexity, they give approximate quantifications of the benefits trees provide. When the benefits are quantified, we can use information to make tree-decisions in our yards and communities, instead of arbitrary statements like “this tree needs to come down”.
How Large Trees Do It
We ran the information on two small trees in my yard through i-Tree’s MyTree model, which was developed by the U.S. Forest Service. The reports this model generates are longer and more detailed than shown below, but we want to zoom-in on carbon sequestration. They also include several other interesting values like rainfall interception and avoided emissions. These models are fascinating to look at, and I recommend you try them out too. They’re totally free and simple to use and interpret.
The tree on the left is a 4” diameter oak sapling planted two years ago, and the tree on the right has a trunk diameter of 29” and is a veteran tree with a partially retrenched crown. This report shows an estimated annual value of carbon sequestration; the larger tree is sequestering more.
While the tree on the right is 7-times larger in diameter, it captures nearly 14-times more carbon annually than the smaller tree on the left.
Any other similar model would show the same trend. And this is intuitive, right? While small trees generally grow at a faster rate than large trees, their total growth is by orders of magnitude less.
Larger trees simply require more CO2 to grow. Each year, the tree’s stems elongate (called primary growth) and the tree puts on an annual ring around its circumference (called secondary growth). In addition to just simply having a larger crown full of more leaves, that increase in total circumference is a major contributor to what causes the total growth to be so much greater in large trees than in small trees.
Think about that: the entire volume of the tree is expanding–and it captures CO2 from the air to make that happen.
Section 4: Care
What Can You Do?
You might say it is a human duty to minimize our negative impacts on the ecosystems we live in. Duh. Trees offer us so many benefits, and we should reciprocate. Doing right by the urban forest is something every homeowner or property owner can do, though it can be a bit challenging when few tree care companies and few municipalities work for trees.
Finding mindful arborists is hard. A good place to start is to ask why they’re an arborist. And when in doubt, get a second, or even a third opinion on something, ask them to explain their plan. It may be a bit more difficult to influence the trees in our cities and towns, though. Local officials who emphasize the environment generally have our better interest in mind.
Presenting alternatives to the current mismanagement of trees in our cities and towns to them is a step towards keeping big trees around as long as possible. We can do these kinds of things by reaching out to our city foresters, planners, and infrastructure offices. If you are someone who practices conservation arboriculture, let your city know you’re a resident.
If you happen to own trees and really want for their wellbeing, I strongly urge you to reach out to a consulting arborist, either before or after you get quotes. Compare what the consultant says with what the tree cutters say. We should interact critically with tree care providers because big trees are simply not replaceable.
Since trees really are a key player in carbon sequestration efforts, that is just one more reason that we should all be concerned about the maintenance and preservation of big trees. A vast amount of tree losses are avoidable.
Modern Arboriculture
It will take some time before conscientious, nuanced, science-driven tree care is the norm. But hopefully this article helps shift the needle a bit towards making it the expectation. Arborist who focus on tree conservation are now using all kinds of data in their practices, making the reliance on guesswork ever-shrinking.
Jeremiah using our tomograph to peer inside of the tree’s base, discovering a small amount of decaying heartwood. This tree is still being managed, and was not condemned thanks to this scan.
Thanks to scientific tools and models, we can better understand what our trees do for us. We don’t have to solve every problem with a chainsaw because tree science has come so far. We can better gauge the risks thanks to the advancement of tree risk assessment technology. And therefore, we can coexist with far more large trees than we currently do. The current standard of tree care in our country is very low, and has been accepted for a very long time. I suspect this is due to a lack of scientific tree care companies, and so people who own trees don’t even know what tree care can actually be.
A pristine and defect-free tree is an unrealistic expectation. It is plainly clear when you spend time in a forest, that no tree is pristine for long. And that’s totally OK, but we ought to not make them worse. Urban and suburban development may have removed most of the forest from around us, but the remaining trees’ biology and importance transcends the context they’re in.
Treating trees as critically significant and complex organisms, instead of lawn ornaments, deepens and enriches our worldview. This perspective adds weight to the decisions we make with our trees. And it should.
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Works Cited
(2) Annual carbon dioxide emissions worldwide from 1940 to 2021
(3) The impact of tree age on biomass growth and carbon accumulation capacity
(4) Large trees dominate carbon storage in forests
Other Sources:
Potential underestimation of biomass carbon in temperate forest