Picking the right trees for carbon sequestration is a good step to take in creating a Landscape that does more than look pretty.
In this post, we will begin a 3 Part Series showing an ecological mixed landscape bed design by selecting trees to sequester CO2 and support wildlife at a high level.
Let’s start with showing the basic layout of the planting bed.
The Beginning of the Planting Design
We will be planting an island bed that is in a kidney bean shape and is 50′ wide by 32′ deep.
In this planting bed, we will have a shade tree (light green symbol), a shorter understory tree (reddish symbol) and an evergreen tree (dark green symbol).
With just these three trees, it will look something like this:
How to Select the Species to Plant
- Our site will be in Full sun,
- the soil will be a neutral pH loam, with
- average amounts of moisture.
It will be located in McHenry, Illinois (far Northwest suburb of Chicago) in plant hardiness zone 5b.
If this design was done in a different area with different growing conditions, the plants selected might change.
We have three trees to select:
- A shade tree,
- a smaller understory tree, and
- an evergreen (conifer) tree.
Our goals are #1) Trees to benefit Wildlife and #2) Trees for Carbon Sequestration.
We have two tools that will help us select the best species for each tree.
Goal #1 – Supporting Wildlife
Trees provide lots of benefits to wildlife including places to build nests and food in the form of nuts and fruits.
But perhaps the best measure of how trees support wildlife is the number of different species of native caterpillar that feed on the tree’s foliage. It is the best indicator of the value that tree has to the food chain and thus wildlife.
For instance, remember from my last post that 96% of migratory birds raise their young not on berries but instead on insects such as protein-rich caterpillars.
So what are the best trees for this? In my last post, Landscaping for your grandchildren, I linked to a great website from the National Wildlife Federation that gives information local to your zip code.
I will use information that is local to my zip code of 60050 in McHenry, Illinois to get the most accurate list of trees and the numbers of caterpillars they support.
Here are my lists of the Top Eight trees and the number of caterpillars that they support:
- Oaks (Quercus)- 456
- Cherries (Prunus) – 345
- Willow (Salix) – 299
- Birch (Betula) – 274
- Poplars (Populus) – 262
- Maples (Acer) – 255
- Apples (Malus) – 245
- Hickory (Carya) – 231
To pick our shade tree, we can start with that list, but we need to use another tool.
Goal #2 – Picking Trees for Carbon Sequestration
To figure out what trees are best at sequestering carbon, we are going to use a tool called I-Trees Eco, which will allow me to estimate the amount of Carbon dioxide specific species of tree will sequester in a given situation.
All of these numbers assume a 1.5″ caliper tree planted in full sun. A 1.5″ caliper B&B or Containerized tree is small enough that most homeowners can plant these themselves. Smaller trees also establish quicker and start to grow faster than larger trees. Plus they have a lower energy and carbon footprint to produce and transport to your site.
Besides species from the NWF list, I also added a Ginkgo just out of curiosity. It apparently grows SOOOO slow it is poor as a tree for carbon sequestration at least in a home landscape. It is also near useless as a wildlife tree (see Would you want a 70 foot statue in your yard? ).
Selecting the best Shade Tree for Carbon Sequestration and Wildlife for our design…
DRUM Roll, please……………….
Our shade tree will be a Swamp White Oak (Quercus bicolor).
Being an Oak it is not only the best tree to support wildlife (not even considering how happy our neighborhood squirrels and Blue Jays will be with the acorns), but it also is the tops of the trees for Carbon sequestration for a 50 year time period.
It is hardy, drought tolerant and can also take wet conditions. Being a member of the White Oak group, it is also more resistant to oak wilt and other diseases than Red Oaks. It’s also among the fastest growing oaks for the area. This is one of the main reasons it is so good at carbon sequestration. What a great tree.
Swamp White Oak can also live for over 300 years unlike other high CO2 performers like Black Cherry (80-100 year life) or Paper Birch (only 30-40 years in home landscapes). Its total CO2 benefit will be much higher over its lifetime than those two trees.
I was not able to check all species of oaks, and I suspect Chinkapin Oak (Quercus muehlenbergii) would have done pretty well on the CO2 sequestration scales as well, although it does not grow as quickly. It does tolerate high pH soils better than the Swamp White Oak so it would be my choice in those soil types.
Some of those CO2 sequestration numbers look off, for instance…
Why did the very fast Quaking Aspen do so poorly as a tree for CO2 removal?
One reason was the limited branching Aspens put on. A grove of Aspen might very well be a good use of space to sequester carbon dioxide but not a single tree. However, another reason is that Aspen doesn’t typically live for 50 years. In fact, the model had the Aspen stop growing somewhere between 30 and 40 years.
Why did Burr oak, White oak, and the Hickories do so poorly as trees for carbon sequestration?
I think the simple reason is that they grow too darn slow to take in that much CO2 from the atmosphere. My favorite tree, the Shagbark hickory grows pretty narrow as well. That would be another tree where you could plant a grove of trees instead of a single tree, but it still would be nowhere as good as the Swamp White Oak (at least for the 1st 50 years).
In the next post of this 3 part series, we will pick some more great trees for carbon sequestration and wildlife for our design.