The answer depends on who you ask.
In this article we are going to take a closer look at the difference one tree can make.
I will explore how much carbon dioxide one tree sequesters from the atmosphere and how much oxygen one tree can produce.
I will also provide you the calculations and step-by-step instructions needed to determine these figures for the trees in your own backyard.
I will also break down how much air pollution one tree can remove from the air and how much stormwater runoff one tree can reduce.
Finally, we will explore how much food one tree can produce and the wildlife habitat values of a single tree.
As you will discover, for some, one tree could be the difference between having a beautiful yard or not.
For others, one tree could be the difference between life and death.
What is a Tree? (A Quick Summary)
A tree is a tall woody perennial plant. Like most other plants, trees are primary producers that convert light energy from the sun, water (H2O), and carbon dioxide (CO2) into biomass in a process known as photosynthesis.
Glucose, a simple sugar, is the basic unit of biomass created from photosynthesis. These sugars are then converted into compounds like the polymer cellulose (C6H10O5)n.
Cellulose is the main component of plant cell walls and other plant fibers. Cellulose makes up 50 – 80% of the wood in trees but is also found in its leaves and reproductive structures.
The trunk of the tree makes up about 60% of the biomass of the tree, and another 15% is in the stems.
The leaves account for about 5%, and this is where most of the photosynthesis takes place. Leaves are like the powerhouse of trees, where light energy is converted into sugars. Note that certain trees actually photosynthesize through their green trunks and stems, like Palo Verde (Parkinsonia spp). Others, like aspen, do a significant amount of photosynthesizing through their bark, even in winter. But, for most trees, photosynthesis occurs in leaves.
Finally, about 20% of the tree is its roots, usually completely hidden beneath the soil’s surface. Roots anchor the tree to its location and draw in water and nutrients to nourish it and help it grow.
When many of us think of trees, we may think of the wood, food, or aesthetic values it provides for us. While these economically quantifiable values are important, studies have shown that their non-market values of carbon sequestration and air pollution removal far exceed their commercial values.
Let’s look more in-depth at some of the benefits trees provide for us!
1. How Much Carbon Dioxide (CO2) Can One Tree Remove From the Atmosphere?
How Do Trees Play a Role in CO2 Removal?
Most people now know that trees play a role in removing carbon dioxide (CO2) from our atmosphere. If you are not sure how they do this, take a look back at the photosynthesis diagram above. Then check out this animated image showing carbon cycling through a forest.
CO2 is produced from combustion, the burning of fossil fuels in vehicles and industrial processes, animal respiration (when we breathe, we take in O2 and release CO2 as a waste product), geologic activities (volcanism, weathering, water chemistry), and soil respiration.
The burning of fossil fuels since the industrial revolution has been releasing carbon into the atmosphere much faster than natural processes can cope with it, leading to an increase in atmospheric CO2 concentrations.
Terrestrial plants, of which trees are the most significant, take in about 25% of the carbon emissions we produce by burning fossil fuels, according to scientific research.
Fortunately, for now, an increase in CO2 concentrations in the atmosphere directly leads to an increase in net ecosystem productivity, including photosynthesis and CO2 uptake by plants and trees. It acts as a fertilizer to stimulate growth.
Unfortunately, as CO2 concentrations in the atmosphere rise, temperatures worldwide increase. The increase in carbon uptake by plants becomes limited at higher temperatures.
This means that if we do not slow the rate of warming, we will reach a tipping point. When the temperatures rise too much, our forests will become sources of CO2 instead of sinks.
How CO2 Sequestration is Affected by Species and Ages
There are variations in CO2 uptake between evergreen and deciduous trees, coniferous and broadleaf, young and old, fast-growing and slow-growing, and tropical and temperate trees.
Even within the same category of trees, it varies significantly at the species level and the climate that that species is found in. Take a look at the following chart from scientific studies showing the variation in carbon sequestration for the same species found in different climates.
Now, this does not mean that as temperatures increase, for example, the boreal will become more temperate and sequestration will increase. In fact, the exact opposite will happen. As the boreal forest heats up, there will be massive die-offs since trees there are cold-adapted species that will not thrive in a warmer environment. It is believed that temperate species will be slow to replace the dying boreal forest.
Carbon storage capacity also depends heavily on the mass and density of a tree.
Simply put, the more dense a tree is, the more carbon it can hold.
Then, obviously, the more massive a tree is, the more carbon it holds too. The mass has to do with the species, its age, growth rate, location, and density.
Some people have recommended planting more softwood conifer trees to boost short-term carbon absorption because they grow faster. But that depends entirely on the species. Some conifer trees are slower-growing and among the longest-living organisms on the planet, like Nootka Cypress. Some hardwood trees, like Poplar, are among the fastest-growing trees on the planet, but they do not live long, and when they die, they usually become a carbon source. Blanket recommendations are never a sound solution.
Furthermore, not all trees are suitable for all environments, and not all environments are even suited to trees.
Do Younger Trees Really Sequester More Carbon Than Mature Trees?
It is often said, and I was told years ago, that younger trees, because they are rapidly growing, absorb more CO2 than older trees. But this never really made sense because older trees are so much larger.
Relatively new studies done on more than 400 different tree species have confirmed that the rate of carbon assimilation actually increases continually with age.
Older trees have larger trunks, branches, and a larger leaf surface area. So even though productivity and growth rate do usually decline with age, this is outpaced by the leaf surface area available for photosynthesis.
Another factor that needs to be considered is how long that tree lives. Is it a short-lived species, again like many poplars, or does it live very long, like Douglas Fir or Nootka Cypress? Trees often become a carbon source when it dies, depending on what happens to them, instead of a sink. Short-lived species can become sources that much faster.
If the wood is made into furniture or other long-term storage, then it does not necessarily become a source. Numerous studies have proposed different options for wood storage in wood vaults to allow for long-term carbon storage.
So, depending on what is done with the tree when it dies or is logged, planting short-lived, fast-growing species is not a viable solution to our carbon problem.
The short answer is that diversity is always the key.
Having different species at different ages is the way to maximize CO2 uptake and enhance biodiversity simultaneously.
Calculating the CO2 Sequestered by a Single Tree Using the Easy Method
Scientists have done lots of calculations to find the amount of carbon a tree sequesters each year for all kinds of different species and ages. These calculations vary with different methods used.
The accepted average is usually quoted as 48 lbs of CO2 (or “about 25 kg”) for a single tree per year. Many sources use this number, often quoting it from the Arbor Day Foundation, which used calculations from environmental agencies that used widely accepted scientific research.
You can multiply 48 lbs/year by the number of trees you have to get the total amount of carbon being sequestered from the atmosphere each year.
The home I just moved into currently only has four trees, so
- 48 lbs x 4 trees = 192 lbs CO2 per year
My last home was on 22 acres in the Canadian Rocky Mountains. There we had approximately 2200 trees, using an average of 100 trees per acre.
- 48 lbs x 2200 trees = 105,600 lbs CO2 per year
If you want to find the total carbon sequestered in a certain tree’s lifetime, you can multiply the per-year rate by the age. If your tree is 40 years old, it has sequestered approximately:
- 48 lbs/year x 40 years = 1920 lbs CO2 total
If you want a more accurate calculation of a specific tree, particularly if it is large or small, fast-growing, or just a tree you are curious about, then follow the steps below. I will walk you through calculating the carbon sequestered by an individual tree.
Simple CO2 Sequestration Calculator
How to Accurately Calculate the CO2 Sequestered by a Single Tree
I researched multiple methods online and found some interesting things.
First of all, many calculations are fraught with issues. For instance, some overestimate the dry weight of carbon, and others ignored the mass of the roots and/or leaves. Others underestimated the water weight in trees, and some used the wrong atomic mass of carbon and oxygen. Still, others assumed that you already knew the mass of the tree, which is impossible unless you also know its height, circumference, and density.
So I considered all the factors possible and used the most current scientific research I saw. I also used methods that I felt everyone could follow without needing special tools or a science degree, and I calculated the carbon sequestration for a specific tree.
It may seem complicated at first, but if you follow the steps below, in very little time, you can calculate just how much CO2 is being sequestered by any given tree!
How to Calculate the Weight of a Tree
The first step is to find the weight of your tree. The total weight of the tree is the total weight of the leaves, trunk, branches, and roots. Remember this image:
The weight of a tree is not super easy, but not that difficult either.
- Above-ground Weight = (Volume x Density) + Weight of Leaves
Then you need to factor in the root weight, which is about 20% of a tree’s weight. So the total weight can be calculated as follows:
- Total Weight = ( (Volume x Density) + Weight of Leaves) x 120%
How to Calculate the Volume of a Tree
First, you need to calculate the volume, which is the trickiest part because the volume of a tree (above ground) is calculated using the volume of a cylinder. And to find that, you will need to find its radius and its height:
- Volume = 𝜋r2 H
Of course, this is not perfect because the trunk narrows towards the top, but it also has all those branches. Together, these factors make the cylinder formula as accurate as possible without cutting the entire tree down and weighing it ourselves, which would be problematic, to say the least.
So let’s learn how to find the radius of the tree and its height in a few simple steps.
How to Calculate the Circumference and Radius of a Tree
To find the radius, r, is fairly simple. The radius is half the diameter or half the distance across the tree’s trunk. To find this, you just need to find the circumference because C = 2𝜋r.
The circumference is relatively easy. It is simply the distance around the trunk.
You can take a tape measure and measure the tree’s circumference directly by measuring the distance all the way around the trunk, which by convention is done around breast height (4.5 ft or 1.37 m from the ground’s surface).
I have a Ponderosa Pine tree that I used for the following calculations, where my measured circumference was exactly 6 ft.
I did my circumference in feet rather than inches because I am doing my height in feet, and my density numbers are in lbs /ft3.
If you are using metric density in kg/m3, then be sure to do both radius and height in meters.
Your units MUST be the same, or your calculations will be wrong.
So, for my tree, I can calculate the radius, r, as follows:
- Circumference = 2𝜋r where r = radius, so using some basic algebra, let’s solve for r
- r = C/2𝜋
- r = 6 ft/(2 x 3.14) = 0.955414 ft
How to Calculate the Height of a Tree
Height is a bit more complicated. There is an easy method and several more scientific methods requiring some trigonometry, a tape measure, and a clinometer (measures angles). If you want to learn more about the other methods, check out the American Forests Champion Trees Measuring Guidelines Handbook. It is a handy pdf you can download to your computer.
However, I will assume most of you do not have a clinometer, and I want to keep the mathematical calculations as simple as possible. Fortunately for us, there is a much simpler but still fairly accurate method that has been used for thousands of years to measure height. All you need is a yardstick or a meter stick (metric).
To do the easy method, mark a spot 4 feet up on the tree, which will be the sighting point. Use a ribbon or masking tape, or have someone stand there with their hand at the 4 ft mark.
Next, hold the yardstick up straight in front of you at arm’s length and back away from the tree until that 4 ft mark equals exactly 1” on your yardstick (about 100 feet).
It is very important that you are holding the yardstick straight to ensure accuracy.
Now, without moving yourself or the yardstick, look from the base of the tree to the top of the tree and see how many inches tall the tree is on the yardstick.
Now since 1” = 4 ft, simply multiply the number of inches by four to get how many feet tall your tree is. My pine tree measured 16” on my yardstick. Therefore:
- H = 16“ x 4 ft/” = 64 ft
Now that you have height and radius, you can finish your volume calculation
- Volume = 𝜋r2 H
- Volume = 3.14 x (0.955414 ft)2 x 64 ft = 183.439 ft3
What if You Have a Multi-trunk Tree?
It’s not as hard as you might think. There are a few ways of two ways of doing it. If the trunk splits partway up the tree, then you just measure the circumference below the split and proceed as normal.
If there is one much larger trunk and one to several much smaller trunks, then simply measure the largest trunk. This treats the other trunks like branches.
If it has multiple trunks of equal size from the ground up, then treat them as separate trees. You can measure the volume of one trunk and multiply that by the number of trunks. Keep in mind this may slightly overestimate your volume because a multi-trunk tree will have fewer branches per trunk than a single-trunk tree. But calculating only one trunk of multiple equal size trunks will certainly underestimate it by a lot more.
Now we just need to add the leaves and roots.
How to Calculate the Weight of Leaves
The weight of leaves can be done by collecting a sample of leaves and weighing them, then counting the number of leaves on the tree if it is a small tree.
Or, most of the time, you would count the number of leaves on a branch and multiply that by the number of branches on the tree.
For larger trees like my Ponderosa Pine or any coniferous trees of any reasonable size, counting all the leaves, even on one branch, could be extremely challenging. Sometimes you can find data on the internet about the number of leaves on a coniferous tree of a given size. But what I did was the following.
Ponderosa Pines have needle-like leaves clustered at the ends of the branches. I plucked off one cluster of leaves and counted the number of leaves in it (I saved these for my weight). Then I counted the number of clusters on a branch. Then I counted the number of branches on the tree. The total number of leaves then is:
- Total leaves = 80 leaves/cluster x 260 clusters/branch x 50 branches/tree = 1,040,000
You could do a similar method using the number of leaves on a twig and count the number of twigs on the branch and then multiply both of those by the number of branches on a tree.
Next, I plucked my leaves off the twig and weighed those 80 leaves.
The 80 leaves weighed 0.14 oz / 80 = 0.00175 oz/leaf
- Total weight of leaves = weight/leaf x number of leaves
- Total weight of leaves = 0.00175 oz/leaf x 1,040,000 leaves = 1820 oz
- 1820 oz / 16 oz/lb = 113.75 lbs of leaves (again, everything must be in the same units)
Now, keep in mind coniferous trees usually have much less leaf weight than deciduous trees simply because their leaves are much smaller. Deciduous trees can easily have 200 – 1000 lbs or more, depending on the size of the leaves, the size of the tree, and how many leaves are on the tree.
Also, I know from personal observations that my Ponderosa Pine has less leaf weight than a more typical tree of its size because it lives in a desert. Its leaves are thinner and lighter, medium-sized in length, and there are only two leaves per bundle.
Ponderosa Pines growing in more humid climates have thicker, often longer leaves and typically have 3 (2 – 5) leaves per bundle. But they still would not have the weight a similar-sized deciduous tree might have.
Leaf Weight Calculator
The Final Calculation for the Weight of the Tree
Now remember that:
- Total Weight =( (Volume x Density) + Weight of Leaves) x 120%
For density, we don’t need to calculate this as they are already done for you. This chart at the Engineering Toolbox will give you the density of many common trees. Make sure you use green wood density since we will account for water later. If your tree is not listed here, just google it. Odds are someone has already determined the density for you.
- Total = (183.43949 ft3 x 45 lbs/ft3) + 113.75 lbs) = 8368.527 x 120% = 10,042.23 lbs
Wow, there we have it. My Ponderosa Pine weighs a whopping 10,042.23 lbs or about 5 US tons (4.55 metric tons)!
How to Calculate the Dry Weight of Carbon Stored in a Tree
The dry weight versus water weight of a tree can vary enormously because it depends on seasons, age, and species, as well as the tree’s health and other local environmental factors.
But we can use averages from specific gravity conversion factors, which conveniently works out to 0.5 or 50%. This is what most sources use, and it avoids us having to get the data for each tree species and then factor in the seasonality, climate, health, etc, of our specific tree.
As we learned from our photosynthesis diagram above, trees are not only made of carbon, but they also have abundant oxygen and hydrogen. They also contain nitrogen and much smaller amounts of calcium, potassium, sodium, magnesium, iron, and manganese.
It is often assumed that the dry weight of carbon is 50% of the total dry weight. However, scientific studies have shown that the dry weight of carbon varies between species from about 41.9 – 51.6%, with an overall average we will use of 47.4%.
Now let’s get the dry weight of carbon for my Ponderosa Pine:
- 10,042.232 lbs green weight x 50% dry weight = 5021.116 lbs dry weight
- 5021.116 lbs dry weight x 47.4% carbon = 2380.009 lbs dry weight of carbon
Now to Calculate the CO2 Sequestered by the Tree
You can now take that dry weight of carbon and multiply it by 3.664 to get the carbon dioxide sequestered to produce that carbon in the tree.
Let’s look at this basic chemistry if you want to know where we get that 3.664 conversion factor from.
- Carbon dioxide is made of one carbon atom and two oxygen atoms, as shown in the chemical formula CO2, where subscript 2 denotes two oxygen atoms.
Now, look at a periodic table of elements (this interactive periodic table is my son’s favorite) to get atomic weights.
- The atomic weight of Carbon is 12.011
- The atomic weight of Oxygen is 15.999
Now, the atomic weight of one molecule of CO2 is:
- weight of C + (2 x weight of O) = 12.011 + (2 x 15.999) = 44.009
And the ratio of CO2 sequestered to the dry weight of Carbon is:
- 44.009 / 12.011 = 3.664
Therefore, to determine the total weight of CO2 sequestered, you multiply the dry weight of carbon by 3.664 to give you the total CO2 sequestered to create that dry weight.
My Ponderosa Pine tree had 2380.009 lbs dry weight of carbon, therefore:
- 2380.009 lbs x 3.664 = 8720.35 lbs of CO2 has been sequestered by my tree
If you want to know how much carbon dioxide your tree has sequestered per year, simply divide the total by the age.
From the size of my tree, the growth rate of Ponderosa Pine, the desert environment, and the age of my home, I assume my tree was probably planted not long after the house was built, so let’s say it’s 65 years old:
- 8720.35 lbs / 65 years = 134.16 lbs of CO2 per year
Now, this is more than the average, as you might have already guessed because this is a large, mature tree.
Without showing all the steps this time, here are some examples of other trees I chose of various ages and sizes to give you an idea of the variation between trees:
Notice a few important things:
- Larger, older trees sequester far more carbon than younger trees
- Fast-growing trees like Red Alder, Eucalyptus, and Black Cottonwood sequester relatively large amounts of CO2
- Eucalyptus is particularly good at sequestering CO2 because it grows very large very fast. However, it should not be planted large scale for carbon sequestration because it sometimes becomes highly invasive in areas where it isn’t native.
- Also included is the world’s largest Coast Redwood tree for comparison of what a very massive tree holds and can sequester
- Note that the 30-year-old Sugar Maple is close to the 48 lb average per tree. This is because most of our trees worldwide are much younger than our mature examples.
- Our average from this chart is much greater than the 48 lb average because extreme examples were included to highlight the enhanced capacity of large, mature, and fast-growing trees.
So, to get a more representative average, I took 1000 of my sample of trees but weighted the numbers, so there were many more young trees and average trees and fewer mature trees, and only one of the largest Coast Redwoods in the world.
When I made a more representative group of our sample trees, we get much closer to that average number.
Accurate CO2 Sequestration Calculator
How Much Carbon Would a Yard Full of Trees Sequester?
Well, if our trees were all roughly the same age and we followed the steps to calculate the carbon sequestered for one of them, we could just multiply that by the number of trees in our yard.
However, I currently have two very different types of trees in my yard, and I have two of each. I have two of the same-sized Ponderosa Pines I did my calculations on. I also have two smaller deciduous trees I have yet to identify (it’s winter, and I am unfamiliar with the tree) that are shorter and younger, about the size of our Sugar Maple tree, so I will use those numbers for those two trees.
We find the numbers for the two pines and the two deciduous, then we add them together:
- 8,720.35 lbs CO2 x 2 = 17,440.70 lbs total for my two pines
- 134.16 lbs/yr x 2 = 268.32 lbs/year for my two pines
- 1,550.75 lbs CO2 x 2 = 3,101.50 lbs total for my two deciduous
- 51.69 lbs/yr x 2 = 103.38 lbs/year for my two deciduous
Therefore the trees in my yard sequester:
- 17,440.70 lbs + 3,101.50 lbs = 20,542.20 lbs total CO2
- 268.32 lbs/year + 103.38 lbs/year = 371.70 lbs CO2/year
Note that when I did this calculation above using the 48 lb average, my total was only 192 lbs per year, but that did not take into account I have two pretty average trees, but I also have two large mature pines that sequester much more.
But the average is still good to use. If you have 100 or 1000 trees of various species, ages, and sizes, do you really want to calculate the amount for each tree?
Also, the more trees you have, the more that average usually comes closer to the truth, as you can see from the sample tree charts I made above for 1000 trees.
How Much Carbon Does a Forest Sequester?
Well, that depends on the size and maturity of the forest. Old-growth forests have a lower density of trees per acre, but the trees tend to be much more massive, so they sequester much more on a much longer time scale. Since we have few of those left, let’s look instead at managed forests.
Nowadays, managed forests have 80 – 120 trees per acre, according to a paper from Penn State Extension.
For the sake of simplicity, let’s go with the average of 48 lbs of CO2 and 100 trees per acre:
- 48 lbs CO2 per year/tree x 100 trees/acre = 4800 lbs of CO2 per year/acre
- 10 hectares of forest = 24.71 acres x 4800 lbs/acre = 118,608 lbs CO2 per year
- 100 hectares of forest – 247.1 acres x 4800 lbs/acre = 1,186,080 lbs CO2 per year
How Many Trees Would it Take to Offset Our CO2 Emissions?
That depends entirely on your carbon footprint, a separate series of calculations we won’t get into here.
But let’s look at our average vehicle emissions.
According to the US E.P.A. “A typical passenger vehicle emits about 4.6 metric tons of carbon dioxide per year. This number can vary based on a vehicle’s fuel, fuel economy, and the number of miles driven per year”.
If you convert 4.6 metric tons, it’s the same as 10,141.3 lbs of CO2 per year. That’s a lot of CO2!
If you calculated the actual carbon sequestered by your trees, you can compare it to that number. My current four trees only sequester 371.70 lbs CO2/year which works out to an average of 92.925 lbs CO2/year, so I would need:
- 10,141.3 / 92.925 = 110 of my trees
Or, if you used the average of 48 lbs of CO2 per year per tree, then you would need:
- 10,141.3 / 48 = 212 average trees
Fortunately, there are many more trees than people, and not everyone drives. But there are, of course, numerous other sources of emissions, and some vehicles and modes of transportation produce far more. Also, some people, like me, drive far more than average.
This is why carbon accumulates in the atmosphere faster than our sinks can remove it. And this is why reducing emissions in combination with mitigation by trees is so important.
I plan to purchase my first electric vehicle later this year, and I am going to be installing solar power at my home. The solar power in my home will then be used to power my electric vehicle. I also will be planting multiple drought-resistant trees around my home to reduce the cost of cooling while offsetting my other emissions at the same time.
As always, diversity is the answer. In this case, the diversity of both trees and our approaches will offset our emissions the best.
2. How Much Oxygen (O2) Can One Tree Produce?
Plants Rule the World
I am a homeschool mom, and I have always taught my children that plants rule the world. And if plants rule the world, then trees are the queens and kings of the plant kingdom because of their sheer size and quantity.
Why do they rule the world? Without them, there would be no animal life on this planet, including humans.
Most people are aware of how trees sequester carbon dioxide.
But did you also know that trees and other plants also produce the oxygen that all animal life depends on? We breathe in oxygen and produce carbon dioxide as a waste product.
Trees are the opposite. They take in carbon dioxide and release oxygen as a waste product. The molecule critical to our survival is a waste product produced by plants. Look again at the photosynthetic equation:
Oxygen in the singular O form is highly unstable and quickly combines with another O to create the O2 that animals like us breathe to sustain our lives. This is fortunate because singular oxygen (O) is a very potent and reactive oxidizing element that’s lethal to living organisms.
Ancient earth had very little breathable O2 until the Great Oxygenation Event that occurred 2.33 billion years ago and enabled the evolution of more complex lifeforms. It was believed to be caused by cyanobacteria that photosynthesize and create oxygen as a bioproduct.
Cyanobacteria are believed to be the origin of chloroplasts found in all photosynthetic plants.
Today, trees and plants keep this cycle of life as we know it going.
How Do You Calculate How Much Oxygen Can One Tree Produces?
The answer is not that simple, and there are many different methods used to calculate this, with often very different results.
When trying to find the answer to this question online, you will find multiple sources, all quoting what I consider nonsensical values because they do not explain where they get their numbers from. Some of these include:
- A mature tree produces as much oxygen in a season as 10 people breathe in a year.
- One tree absorbs 48 pounds of carbon dioxide per year and releases enough oxygen to support two human beings
- Two mature trees can provide enough oxygen for a family of four.
- One tree produces nearly 260 pounds of oxygen each year.
- A 100-foot tree, 18” in diameter, produces 6,000 pounds of oxygen
Only the last two even come close to providing actual numbers. But try as I might, I could not find the actual scientific sources of any of those numbers. Just multiple articles saying more or less the same things, and just referencing each other, if at all.
Some sources stated that the 260 lb figure came from Environment Canada, yet I could not find that anywhere on Environment Canada’s website either. I will talk more about that number later.
Oxygen produced is calculated in one of two main ways. You can use either the photosynthetic formula or the Leaf Area Index (LAI). LAI assumes that oxygen emission is proportional to a tree’s leaf mass. Which is not in itself wrong. However, that method is debated, and more challenging to determine than one might think.
For one, it skews the answer highly in favor of deciduous trees, which produce no oxygen while dormant. But it also avoids the issue of annual leaf loss not being accounted for if using the photosynthetic formula.
Another complication with any method is that not all oxygen produced is actually released. Some of it reacts in complex biochemical pathways we will not get into here. And some oxygen is respired by the tree at night or in winter.
So any calculation slightly overestimates the breathable O2 released.
If you want to learn more about some of the complexities, you could start with this measuring the ratio of CO2 efflux to O2 influx in tree stem respiration article.
How Much Oxygen is Produced as a Byproduct of Photosynthesis?
So, to avoid the vague numbers given online and the complexities and debates with the LAI method, let’s use the photosynthetic equation.
To find out how much one tree produces as a byproduct of photosynthesis, we can use the dry weight of carbon in the tree we calculated above. This method assumes that if the tree gains mass, then carbon was sequestered, and this net accumulation of carbon can be correlated to a net production of oxygen.
This method has the simplicity of not needing to actually measure the oxygen released from a tree (a challenging process best done in a controlled environment), not needing to know how much O2 is consumed by the tree, or looking at its health, location, and other complex factors.
So, if you look at the photosynthetic equation, you see that for every six molecules of CO2 consumed, we get six molecules of O2.
Simplifying that, for each carbon atom sequestered, one molecule of breathable O2 is produced.
When we looked at the periodic table for atomic weights, we got:
- Carbon is 12.011
- Oxygen is 15.999
Now we need the atomic weight of one molecule of O2:
- 2 x weight of O = 2 x 15.999 = 31.998
And the ratio of O2 to C is:
- 31.998/12.011 = 2.6641
My Ponderosa Pine sequestered 2,380.009 lbs of carbon. Therefore it has also produced:
- 2,380.009 lbs of C x 2.6641 = 6340.58 lbs of O2
Or, if you want that in a per-year calculation:
- 6340.58 lbs of O2 / 65 years = 97.55 lbs O2 produced per year
Alternatively, you can use the amount and rate of CO2 sequestered and multiply that by the atomic mass ratio of O2 to CO2 as follows:
- O2 / CO2 = 44.009/31.998 = 0.7271
- 8720.353 lbs CO2 sequestered x 0.7271 = 6340.57 lbs of O2
- 134.16 lbs CO2 sequestered per year x 0.7271 = 97.55 lbs O2 produced per year
As you can see, the results are the same (excluding rounding errors).
Let’s look at our example trees to see how much oxygen they produce using this simplified method based on photosynthesis, along with a 1000 tree weighted average as we did with CO2.
A few things to note:
- Larger, older trees produce more oxygen than smaller, younger trees that have fewer leaves for photosynthesis
- Our numbers are less than the vague numbers often quoted on the internet.
- Our 1000-tree average was also smaller than the average of my 13 example trees because that set included several large mature trees. In reality, the world has many, many more small trees than massive mature trees.
Given our calculations and the fact that they likely still overestimate the production of breathable oxygen because it does not account for night or winter respiration and other biochemical processes, it seems that the “260 lbs per year per tree” figure so popular online is extremely unlikely for the majority of the trees on the planet.
Let’s examine that number using basic chemistry. We know O2 production is directly related to CO2 sequestered from the photosynthetic equation (though, in reality, not quite at a 1:1 ratio). Plants do not make O2 in any other way.
So the ratio of CO2 to O2 using atomic mass is:
- 44.009 / 31.998 = 1.3754
- 260 lbs O2 x 1.3754 = 357.60 lbs of CO2
That number comes close to our very large 150-year-old Western Red Cedar. But it should never be used as an average for trees because most tree species on our planet never reach that size no matter how long they live.
So, it seems likely that we can use our 1000 tree averages over a yard, city, or forest of trees to calculate a more realistic oxygen production.
For example, if we had a city park with 20 trees, they would produce, on average:
- 36.78 lbs O2 / yr x 20 = 735.6 lbs per year
Controversy aside, our numbers still show that a significant amount of oxygen is produced each year by every single tree on earth.
Tree O2 Production Calculator
How Much Oxygen Does a Human Consume?
According to NASA, humans require about 2 lbs of oxygen per day to survive or about 730 lbs per year.
So to provide one person with enough oxygen per year, they would need:
- 730 / 210.83 = 3.46 trees based on our biased average
- 730 / 36.78 = 19.84 of our weighted average of 1000 trees
- 730 / 37.59 = 19.42 of our 30-year-old Sugar Maples
- 730 / 332.13 = 2.2 of our 250-year-old English Oaks
- 730 / 925.26 = 0.79 of our 100-year-old Eucalyptus
How Oxygen Production Varies With Species
The amount of oxygen a tree can produce depends on numerous factors like species, location, health, and age.
One important factor is something we already mentioned, the Leaf Area Index. Simply put, the more surface area of leaves, the more oxygen a tree can produce.
The Leaf Area Index is inadequate to explain coniferous trees, however. We know that many coniferous trees grow fairly quickly and sometimes sequester enormous amounts of carbon. Therefore they must produce almost equally enormous amounts of oxygen, as proven by the photosynthetic equation.
Faster-growing trees will produce more oxygen than slower-growing trees. The environment will also affect the growth rate. Poor soils or poor locations will slow the growth and, therefore, oxygen production of that tree.
Trees in warmer climates will produce more oxygen than trees in colder climates. This is because cold weather slows down the rate of photosynthesis and is often the justification given for saying coniferous trees produce less oxygen because the rate is impeded by cold temperatures during the winter.
This inability to make generalizations is emphasized by the fact that if you look up the “best oxygen-producing trees”, you typically get a list that includes True Firs, Douglas Firs, Beech, Spruce, and Maple. Despite the fact that many sources say coniferous trees produce less based on the LAI, they are more than half the species on that list!
This is why we relied instead on the photosynthetic formula. It is simpler, and our results agree with real-world observations. Just remember that all of these numbers are more approximate than our CO2 calculations were, for reasons explained above.
3. How Much Air Pollution Can One Tree Remove From the Air
Trees everywhere help remove thousands of tons of air pollutants each year. But urban trees in streets, parks, and yards throughout our cities provide the greatest benefit where the pollution concentrations are the highest.
Fine particulate matter (PM2.5), ozone (O3), carbon monoxide (CO), sulfur dioxide (SO2), and nitrogen dioxide (NO2) are five of the six primary components of air pollution, according to the CDC. All of these pollutants have significant impacts on human health.
Numerous studies, like those done by Nowak et al., have shown significant reductions in human mortality due to the removal of these pollutants by the trees growing in our cities worldwide.
In New York, for example, it is believed that the trees there prevent 7.6 deaths annually from air pollution.
How Do Trees Remove Air Pollutants?
Trees remove gaseous air pollution by taking it in through their stomata. These are tiny pores in leaf surfaces that allow for gas exchange with the atmosphere. There, the gases diffuse into the intercellular spaces and are retained within the tree.
Some pollutants, like particulate matter, are removed simply by physical interception of the particulates from the air that are then deposited on the tree surfaces. Sometimes they are brought back into the air via wind, while other times, they are deposited in the soil/ground surface below.
Because they are evergreen, conifers provide the best overall reductions of urban air pollution because they remove pollutants all year round.
How Much Air Pollution Can One Tree Remove?
Most studies are done based on tree cover, and individual tree studies look at leaf surface area, which is complicated to determine. This makes it hard to show you how to quantify how much pollution one tree can remove.
However, the USDA Forest Service Research created a tool available online. I used that tool and an urban location in Washington, DC, for my trees and kept the location the same to make some useful comparisons.
Here is my spreadsheet, which includes the 20-year projections provided by the tool that takes into account the age of the tree.
Note a few things:
- Larger trees remove more pollutants than smaller trees
- Fast-growing trees like Balsa and Alder remove more than slower-growing trees
- Coniferous evergreen trees removed more than deciduous trees
- Our 50-year-old Quaking Aspen likely won’t be alive in 20 years, they rarely live past 60, so its 20-year projection is inaccurate.
- We removed the giant Coast Redwood because the tool gave surprisingly low numbers, and realistically, you could never get a tree to grow that size in any city.
I then did another weighted average to include more smaller and average trees than old-growth trees to obtain some useful averages.
Things to Note:
- Our averages on a 1000-tree average are lower, as we would expect, because we have fewer large mature trees and more smaller trees, which is more representative of urban and other treed environments worldwide.
This average could be used to estimate the approximate benefit of a mixed group of trees in an urban environment.
I would not use these numbers for those 2200 trees in the Canadian Rockies I mentioned in the carbon calculations. The air pollution there would be much lower than in an urban area, rendering the numbers meaningless.
However, let’s say we want to calculate the air pollution removed by an urban park in Nashville, Tennessee, USA, or in Lyon, France, with a mixed group of various ages and species of 20 trees. Collectively, they would remove approximately:
- 0.15 oz x 20 = 3 oz CO per year
- 7.46 oz x 20 = 149.2 oz O3 per year
- 1.38 oz x 20 = 27.6 oz NO2 per year
- 0.34 oz x 20 = 6.8 oz SO2 per year
- 0.58 oz x 20 = 11.6 oz PM2.5 per year
How Does Tree Cover Affect Pollution Removal?
As you can see from the spreadsheets, the amount removed by one tree may seem low when you look at the amount of smog and haze seen in cities worldwide. But when you add up all those individual trees, they make an enormous impact on air pollution.
The total tree cover is extremely important.
For example, Nowak found that the amount of PM2.5 removed annually by trees varies significantly between cities. His 2010 studies showed trees removed 4.7 tons of PM2.5 in Syracuse, NY but as much as 64.5 tons in Atlanta, GA, in that year.
The population of Syracuse is approximately ⅓ that of Atlanta, so Atlanta is roughly three times larger, yet Atlanta trees removed 13.7 times more pollutants. Why is that?
Atlanta has more trees, so they remove more pollutants from the air.
Every single tree helps.
Which Trees Are Best For Removing Air Pollution?
Generally speaking, evergreen conifers are better at removing more pollutants annually simply because they are evergreen.
Unfortunately, not all conifers are suited to city environments because many are sensitive to pollution, particularly ozone. Some of the more resistant ones include Pinus sabiniana, Pseudotsuga menziesii, Sequoia sempervirens, Sequoiadendron giganteum, and Cedrus deodara.
Trees like our Silver Birch and our Eucalyptus are also quite good at removing pollutants. But they are not always a solution. Eucalyptus can become quite invasive in areas it is not native to. Silver birch has been introduced worldwide and is sometimes considered invasive.
Some trees are also unsuitable because they emit higher amounts of Volatile Organic Compounds or VOCs, which is in itself a form of air pollution. Deciduous trees tend to emit more than coniferous, and poplars tend to emit the most.
The answer, as always, is diversity and numbers.
Cities should plant many different types of trees, native wherever possible (except maybe poplar), and plant them in large numbers for the cleanest possible air.
4. How Much Stormwater Runoff Can One Tree Reduce?
Trees in all environments play a critical role in flood mitigation worldwide. This is because they intercept rain and prevent or slow surface runoff.
This then increases the lag time between precipitation and the rise of water levels in our creeks and rivers. Increased lag times mean the system can better handle the water, and floods are prevented or at least reduced in severity.
The Importance of a Healthy Riparian Habitat
In addition to the widespread historical draining of our wetlands, removing riparian trees and shrubs are some of the biggest current contributors to the severe flooding that destroys homes, infrastructure, and human lives.
Riparian areas are simply the area between the water and ‘dry land’. They begin at the water’s edge and end around the high water mark where flood waters typically reach. They usually have characteristic trees, shrubs, plants, and grasses that are adapted to seasonal flooding.
Riparian trees slow stormwater runoff and allow time for sediments and contaminants to settle, helping to clean the water simultaneously. They also provide critical habitats for countless species of plants, animals, and insects that normally live in the riparian zone.
When we remove the riparian growth to make way for grass that we grow in parks or on pastureland, for example, we degrade the area for wildlife and ourselves. Lawn and pasture grasses have little ability to slow flood waters. This is different from aquatic grasses found in actual wetlands that do have the ability to slow flood water.
Non-aquatic grassy riparian zones are the most likely to erode, destroying those parks or pastures we created. They also contribute to further flood damage downstream because they have such a poor ability to slow the flood waters compared to riparian trees and shrubs.
The Importance of Trees in Runoff and Rainfall Interception
However, all trees, not just riparian trees, are important in stormwater reduction. Our forests absorb a huge amount of the rainfall we get, so much so that runoff is rare to see in most forests under normal and all but the most extreme rainfall conditions.
The amount of water a tree can intercept from rainfall is directly proportional to its size and the surface area of its leaves. The larger the tree and the more leaves it has, the more rain it can intercept and absorb. Evergreen coniferous trees with small needle-like leaves can still intercept a lot of rainwater because they retain their leaves all year.
In cities, our trees play an even bigger relative role in rainfall interception and runoff prevention. Cities have the poorest absorptive capacity of any ecosystem because the pavement is impermeable and promotes rapid runoff.
The presence of trees there intercepts surface runoff, slowing it down and helping mitigate flood damage.
However, even cities like Atlanta, with their abundant trees, can still have problems with runoff because of the impermeability of pavement.
Take a look at the water on this Atlanta street in the photo below I took in 2021. The green garbage can on the left side of the road signs is actually floating down the street, and the one on the right was until it hit the car it is resting on. Now imagine how bad that rain event could have been without that city’s unusually high 47.9% tree coverage.
How Much Rainwater Can One Tree Intercept and How Much Runoff Can It Prevent
Most studies on rainfall interception for an individual tree are done by taking the amount of falling rain and calculating the amount that reaches the ground through a tree’s canopy. The difference is the amount intercepted.
Since this is difficult to do in the field and impractical for most of us, we will again use numbers from the USDA Forest Research’s itree tool to calculate stormwater interception.
Check out this spreadsheet below I made using numbers from this tool for my example trees, with yearly, 20-year, and 1000-tree average numbers.
Note that the averages of our example trees are higher than our 1000 tree sample, again because our example trees highlight large and mature trees to show their potential. The 1000 tree average is more likely to represent an “average” tree when you look at a large number of trees.
As we did for air pollution, we can take our 1000 tree averages and apply them to that city park with its 20 trees to get the approximate amount of rainfall intercepted, and runoff avoided as follows:
- 190.19 gallons of runoff avoided/tree/year x 20 trees = 3,803.80 gallons of runoff prevented per year by the trees in that park
- 553.16 gallons of rain intercepted/tree/year x 20 trees = 11,063.20 gallons of rain intercepted per year by the trees in that park
These numbers show that the more trees we have, the more stormwater flow is reduced, and the more potential flooding is reduced.
Every single tree, whether riparian, rural, or urban, helps reduce the damage caused by floods.
5. How Much Food Can One Tree Provide
How much food a tree can provide varies even more with species, but also with wild versus cultivated trees.
It is important to consider what kind of food they produce and who consumes it.
This makes it challenging to generalize this across all trees as we did above, and the usability of the results would be debatable. So instead, let’s look at a small selection of trees that produce edible crops.
How Much Fruit Does an Apple Tree Produce – (Malus domestica)
What Are Apples?
An apple is a pome – an accessory fruit where the flesh that you eat is part of an enlarged receptacle or hypanthium from the flower rather than the ovary itself. The carpels of the ovary form the tough inner ‘core’ of the apple, which contains the seeds.
All apples are part of the Malus genus of the Rosaceae family. Most of the apples that we eat are Malus domestica. These were bred from a wild ancestor, Malus sieversii, several thousands of years ago.
We have over 7500 cultivars of domestic apples available today.
While they have hermaphroditic flowers, they are not self-fertile, so you need at least two apple trees to ensure cross-pollination and fruit production.
How Much Fruit Can One Apple Tree Produce?
Apple trees take 3 – 8 years from planting to fruit production, depending on the variety. They generally produce annual crops fairly reliably, but occasional poor years occur.
Mature standard apple trees can produce 90 – 440 lbs of apples each year.
Dwarf cultivars produce 20 – 180 lbs per year, but they fruit earlier, and you can fit multiple dwarf trees in the same space as one standard apple tree.
The average apple weighs 0.33 lbs. Your standard apple tree would produce:
- lbs/lbs/apple = 90lbs/0.33 lbs/apple = 272 to 1333 apples yearly
- dwarf trees produce 60 to 545 apples yearly
If you eat “an apple a day,” then approximately one tree per person in the household should supply you with plenty of apples, depending on the productivity of your tree (but you do need at least two for cross-pollination).
Apples generally store well in cold storage and can also be frozen and dried for snacking in the off-season.
How Much Fruit Does a Mango Tree Produce – (Mangifera indica)
What Are Mangos?
Mangos are technically a drupe. They have an outer skin with a fleshy inside and a stony pit in the middle that contains the seed.
Mangos are large fruit trees of the Anacardiaceae family domesticated in southeast Asia over 4000 years ago.
Mangos are monoecious trees with separate male and female flowers on the same tree. They are self-fertile, so only one tree is required to produce fruit.
A new mango tree takes 4 – 8 years to produce fruit. Newer dwarf varieties like the Glenn Mango can fruit the first year and can be grown in containers in temperate climates and moved indoors in winter.
How Many Mangos Will One Tree Produce?
Mangos are great producers. In some tropical areas, you can get 2 – 3 crops per year, while in more northern subtropical zones, you will get one good crop each year.
One mango tree (excluding dwarfs) can produce 200 – 600 or more mangos per crop, depending on the cultivar and the tree’s age.
Peak production starts around 40 years of age, and they live up to 300 years, so they could produce between 50,000 – 180,000 or more mangos in their lifetime.
If you eat a mango daily and only get one crop per year, one to two mature trees could easily supply one person with an ample supply of mangos.
You can eat them fresh while in season, they can be stored short-term in cold storage, and they can easily be frozen or dried to make delicious snacks for eating throughout the year.
How Much Food Does a Wild Shagbark Hickory Produce – (Carya ovata)
What is a Hickory Nut?
Wild Hickories technically produce a pseudodrupe because their nuts, consisting of a hard outer shell and an inner seed, are encased within an outer husk. Some would consider this a dry drupe. But, in this case, the husk contains involucral bract tissues not found in other dry drupes, therefore, a pseudodrupe. But, for simplicity’s sake, let’s just call it a nut.
Wild hickories provide food for numerous wildlife species. Their nuts are the preferred food choice of squirrels, who will eat them almost exclusively until the supply runs out. They are 5 – 10% of the diet of chipmunks and are also loved by bears, foxes, rabbits, mice, wood ducks, wild turkeys, and other birds.
In North America, hickory leaves are eaten by about 200 native Lepidoptera (moth and butterfly) species and are occasionally browsed by deer and livestock.
Shagbark Hickory is a wild native tree of eastern North America that is also occasionally foraged by humans for its delicious nuts. They are closely related to the Pecan but are rarely cultivated commercially due to their thick shells.
How Much Hickory Nuts Does a Shagbark Hickory Produce?
Shagbark Hickory reaches production around 40 years of age but produces reliably from 60 to 200 years of age and will continue producing until 300 years old.
A productive wild Shagbark Hickory will produce 1.5 – 2 bushels of nuts in a given year, the equivalent of 75 – 100 lbs per tree.
They produce nuts every 1 – 3 years, with few, if any, produced in the intervening years.
A squirrel eats about 1.5 lbs of nuts each week x 52 weeks = 78 lbs per year
So two trees could be enough to keep one squirrel alive, assuming no other food sources and the trees produce crops an average of every two years.
Assuming we ate as much per week as a squirrel, because we also have other food sources, we would need two trees per person to provide us with an ample supply of hickory nuts.
Note that this is a wild tree. Purchasing a Shagbark from a nursery that has been cultivated for nut production or one of the closely related pecan cultivars will produce larger crops. This example was included to show what a wild tree can produce.
How Much Food Does a Pistachio Tree Produce – (Pistacia vera)
What is A Pistachio?
Pistachios are another seed of a drupe, not a botanical nut, but a true drupe.
Pistacia vera is a small tree of the Anacardiaceae family that is native to central and western Asia.
Pistachios have been eaten by humans as far back as 6750 BC and domesticated around 3000 years ago.
They are dioecious plants with separate male and female trees. One male tree can pollinate about 12 female trees. You would need at least one of each sex to produce fruits.
How Much Pistachio Nuts Can One Tree Produce?
Pistachios take 7 – 10 years to reach productive age but can live and produce for 300 years. They produce heavily every other year with smaller crops in the alternate years.
A newly productive pistachio tree produces 15 – 22 lbs of dry nuts per tree, while a mature, productive tree can produce 33 lbs of dry nuts (83 lbs fresh) per tree on average.
Let’s assume you have one mature female tree producing 33 lbs of dry nuts, and you eat 1 oz per day or 365 oz per year. Then that would last you 1.45 years as follows:
- 33 lbs x 16oz/lb = 528 oz
- 528/365 = 1.45 years
However, since they produce heavily every second year but produce a smaller crop every other year, then you could assume that roughly one tree would be required for each person.
If you have a family of four, you could plant four female trees and one male tree.
If you have 12 female trees and one male tree, you would harvest 396 lbs (33 lbs x 12) of nuts every second year! More than enough to feed an entire family and then some!
How Much Food Does a Pine Tree Produce – (Pinus edulis)
What Are Pine Nuts?
All pine trees produce ‘pine nuts,’ which are not nuts at all but actually naked seeds found within pine cones. Some produce bigger seeds than others.
Pinus pinea is the most commonly grown in Europe, along with Pinus siberica in Russia and Pinus koraienis in Asia.
In the USA, the piñon pines Pinus edulis and Pinus monophylla are the most commonly harvested, but they are typically wild-harvested rather than commercially grown.
How Much Pine Nuts Can A Piñon Pine Tree Produce?
Pinus edulis or Piñon starts producing viable crops around 10 years of age when they are 3 – 4 ft tall.
Most pine trees take 2 – 3 years between harvestable crops due to the time it takes from cone production to seed maturation.
According to scientific studies, the average time between commercially harvestable crops of Piñon is 4.1 years, and the average yield per tree is 10 lbs. More is produced by more mature trees, which could easily yield over 20 lbs per tree.
Since they can survive 200 years, they can produce at higher yields for several human generations.
So if we have one Piñon that is only 15 years old, it will produce, on average, 10 lbs of pine nuts every four years.
Pine nuts are healthy and nutritious, and health experts recommend eating 1 oz at least three times per week.
If we consume 3 oz per week x 52 weeks = 156 oz per year.
But each tree only produces an average of 160oz (10 lbs) every four years, so we would need, on average, roughly 4 trees per person to sustain that diet.
Note that these numbers are based on wild production.
If we grew them ourselves and fertilized them each spring, and watered them during drought conditions, we should easily get the higher 20 lbs per tree. We would also likely be able to harvest more reliably every 2 – 3 years since this is the time it takes Pinus edulis cones to mature in ideal conditions. That means 2 trees per person should provide us with an ample supply.
Numerous birds, rodents, and other wildlife also depend heavily on the piñon pine nuts for survival. The Pinyon Jay, in particular, which is currently listed as Vulnerable and is being proposed to be placed on the endangered species list, is entirely dependent on them for survival.
This bird has lost 80% of its population in the last 50 years due mostly to the destruction of Piñon forests. Sadly, these forests are often seen as ‘poor quality land’, resulting in their conversion to more ‘valuable pasture land’.
How Many Coconuts Does a Coconut Palm Produce – (Cocos nucifera)
What Are Coconuts?
Coconuts are part of the Palm Family, which are monocots more closely related to grasses than they are to trees. Nonetheless, we call them trees, and they are beautiful, productive palms that produce delicious coconuts.
Cocos nucifera is the common coconut, the only species of its genus.
Coconuts are not nuts at all, they are a single massive seed of a drupe. They have a thick husk that is usually removed before they are sent to market. We eat the seed’s endosperm inside the hard shell (see diagram above).
Coconut trees not only provide food but also are used for fuel, clothing, and building materials throughout the tropical world.
Coconuts are monoecious, producing separate male and female flowers on the same tree.
Dwarf cultivars are often self-pollinating, but larger varieties tend to be mostly cross-pollinated, so be sure you plant more than one tree to guarantee fruit production.
How Many Coconuts Does a Coconut Palm Tree Produce?
From planting, coconut palms take 6 – 10 years to start producing.
They reach peak production after 15 – 20 years, where they can produce up to 75 coconuts per year but often produce around 30.
They can usually be counted on reliably producing these crops every year.
My son can eat a coconut a week, requiring 52 coconuts a year.
Two trees, which is required for good cross-pollination anyway, would ensure he had a year’s supply of coconuts and delicious coconut water that we drink and put in smoothies.
At room temperature, a coconut will last 4 months or longer in cold storage. Frozen fresh coconut can be stored all year long in a freezer.
6. How Much Wildlife Habitat Can One Tree Provide?
Habitat is extremely difficult and complex to quantify, and explaining that would be an entire long article in itself.
So, instead, let’s talk about what kinds of habitats trees provide and which trees provide the best habitat.
What Kinds of Wildlife Use Trees for Habitat?
Trees provide critical nesting sites for countless bird species worldwide. Arboreal rodents, like squirrels, chipmunks, and voles, also build nests high in the trees made of leaves and twigs, and other natural materials.
Other animals like mice, raccoons, martens, certain squirrels and birds, skunks, and other animals use natural cavities or downed logs for their homes in the trees.
Very large trees like Western Red Cedar, or nowadays, more often the rot-resistant old-growth stumps left behind, provide critical denning sites for bears that may overwinter inside of them.
Numerous Insects and invertebrates use trees as their primary habitat.
Birds, small mammals, beavers, bears, deer, reptiles, and other animals often rely on trees’ fruits, bark, twigs, and leaves as their primary food sources.
Countless insects and invertebrates routinely feed on tree leaves or wood as their primary food and egg-laying sites.
Other creatures, like woodpeckers, feed on the insects living within dead or dying trees.
Birds use trees for roosting sites to rest on long journeys or while searching for prey or food. Other animals use trees for shade from the hot sun or as cover to protect themselves from predators.
Epiphytic plants, mosses, lichens, and fungi rely on living trees to provide habitat.
Numerous other lichens and particularly fungi, rely on dead or dying trees for their habitat.
Ground-dwelling fungi often have symbiotic mycorrhizal relationships with tree roots that are essential to both organisms’ survival.
Quality of Habitat Versus Quantity of Trees
The problem with habitat is it is so much more about quality than it is quantity. Many small trees have much poorer habitat value for much fewer species than a few large trees.
The reason is simple. Imagine a 10-year-old tree; it’s relatively short and has small branches. Only the smallest of birds could nest on a tree like that or use it as shelter. Even then, many small birds still only nest in larger trees. And this small tree would be impossible for a squirrel or a larger bird to nest in, let alone a raccoon or bear.
And the tree species often matters far less than the size/age of the tree. When it comes to habitat, size really does matter.
Another problem with habitat is that of scale. Think about how much land, including the tree it is using, a bear would require for its denning site. Now think about how much land or trees a squirrel or even a simple forest mouse requires. Scale makes a huge difference when you talk about habitat.
What Can Individual Trees Do For Habitat in Urban, Agricultural, or Residential Environments?
Obviously, the lack of trees in residential areas, agricultural fields, or urban areas means there is no habitat at all for tree-dwelling species. So every single tree in those areas, regardless of size, is a critical source of habitat. Even if the tree is very small, given time, it will grow.
With the conversion of so much natural land to urban, residential, or agricultural landscapes, planting trees is more critical than ever.
A single tree in an agricultural landscape provides necessary roosting sites for birds, shade for ground-dwelling animals, and food for insects that other species feed on. It also helps prevent soil erosion, improves soil health, and regulates microclimate, all benefitting the agricultural field. Adding more trees multiplies all of those benefits.
An urban landscape without trees will be mostly void of biodiversity. But an urban landscape rich in trees, particularly native ones, will be much more biodiverse. Urban trees also clean the air, provide shade, regulate the temperature, and provide numerous other benefits. More trees multiply all of those benefits.
Trees in these highly anthropogenic landscapes are equivalent to islands of habitat for terrestrial species living in the middle of an ocean. The more islands we have, the greater the number of habitats and the greater species diversity they can support.
We should all go out and plant a tree, or 10, today!
Why Primary Forest Provides the Best Habitat
Primary forest cover is arguably the most beneficial habitat for the largest number of species. The reason is that large, mature trees develop cavities and other ‘imperfections” depicted in the photos above that create perfect nesting sites for birds, rodents, and sometimes even bears.
Primary forests also contain more standing dead trees known as snags, which are important habitats for insects, fungi, and lichens, which then become food sources for various animals and other insects, creating complex food webs that support more and more diverse species.
Downed logs, or coarse woody debris, also provide critical habitat. Some species require logs in the early stages of decay, while others rely on logs in a much later stage of decay. These logs are homes to rodents, birds, reptiles, amphibians, and more. They are also critical habitats for numerous insects and other invertebrates that themselves become food for other creatures.
Woody debris also plays a critical role in the nutrient cycling of the forest, which can help with the next generation of trees by providing a nutrient-rich environment that will support a greater diversity of trees.
Primary forests also contain better structural diversity due to having trees of wildly different age classes and, therefore, heights and diameters.
Structural diversity is important for creating habitat niches for more organisms.
Second-growth forests and plantations tend to have trees of the same age class and therefore have poor structural diversity.
Increased structural diversity also provides more open gaps in the canopy, which lends itself to more ground cover. More low-growing shrubs and plants in the forest provide additional food sources for a greater number of species, again enhancing biodiversity and species richness.
If you want more information on any of these factors I just described, try this resource here.
Certain Species Will Only Live in Primary Forests
These are known as old-growth-dependant species, and most will go extinct after losing their habitat. Some examples include the Marbled Murrelet, Northern Spotted Owl, Northern Flying Squirrel, and Tree Vole.
There are also numerous lichens, plants, and mosses, many of them epiphytes, that are old-growth dependent and will not survive in second-growth or plantation forests.
Do Secondary Forests and Plantation Forests Provide Habitat?
Since secondary and plantation forests are becoming so predominant in the landscape, we have begun the process of trying to quantify those habitats. This in itself is also fraught with numerous challenges, but if you want to learn more, check out quantifying the biodiversity value of tropical primary, secondary, and plantation forests.
The short answer, though, is yes. Secondary forests and plantation forests can provide habitat for certain species, though they will never replace primary forests for the reasons explained above.
Many opportunistic species can survive and even thrive in these environments. Certain birds, rodents, deer, and reptiles do very well.
Unfortunately, those that do well in heavily altered habitats tend to be the least vulnerable to extinction.
But given the overall reductions in bird, animal, and insect diversity and numbers in the last 50 years, we should take a win wherever we can. Let’s give you some numbers on the staggering losses of diversity.
Since 1970 in the USA and Canada alone, we have lost 3 billion birds, and 1 billion of those have been lost from forests.
According to the World Wildlife Federation, our vertebrate populations, including mammals, animals, fish, reptiles, amphibians, and birds, have declined globally by 69% since 1970. A significant portion of those species also relied on forested habitats.
Insect populations have also been plummeting over the past few decades. I can verify this from personal observations since my childhood. Studies are now predicting that 40% of our world’s currently living insect species will go extinct over the next few decades. Again, many of those are also dependent on trees.
The lesson to take from this is while we can’t have primary forests everywhere anymore, we should try to keep as many mature trees as we can.
We should also manage all of our second-growth and plantation forests with wildlife habitat at the forefront of our consideration.
For instance, when trees die and remain standing or fall, when safety permits, we should leave them where they are to provide additional habitat and diversity.
Finally, Let’s all PLANT MORE TREES everywhere that they used to grow!
Scientific References Used
Here is a list of the scientific resources used in this article. Sources not published in a scientific journal have also occasionally been used but are linked to in the article above and generally will not be included in this list.
- AmericanForests.org American Forests Champion Trees Measuring Guidelines Handbook https://www.americanforests.org/wp-content/uploads/2014/12/AF-Tree-Measuring-Guidelines_LR.pdf
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- What Difference Can One Tree Make?
- What is an Old-Growth Forest and Why are They Important?
- Are Trees a Renewable or Nonrenewable Resource?
Lyrae grew up in the forests of BC, Canada, where she got a BSc. in Environmental Sciences.
Her whole life, she has loved studying plants, from the tiniest flowers to the most massive trees.
She is currently researching native plants of North America and spends her time traveling, hiking, documenting, and writing.
When not researching, she is homeschooling her brilliant autistic son, who travels with her and benefits from a unique hands-on education about the environment around him.