Today is National Arbor Day – a holiday initiated by J. Sterling Morton right here in my home state of Nebraska. The idea of Arbor Day is to encourage the planting of trees. However, as a prairie ecologist, I spend considerable effort trying to keep trees from taking over the prairies I manage and/or care about.
As a result, I have some mixed feelings about Arbor Day.
A cottonwood tree in a Platte River prairie at sunrise. Beautiful, but not without some impacts on prairie ecology.
I don’t harbor any particular enmity toward trees themselves. In fact, some of my favorite places in Nebraska have fantastic woodlands, including The Nature Conservancy’s Rulo Bluffs Preserve and Niobrara Valley Preserve. I also really like the trees in my yard – especially the one that produces a big crop of pie cherries each year!
On the other hand, I don’t hesitate to use all necessary force to remove trees from grasslands. Why? There are numerous reasons. Here are a few examples:
– The shade from trees changes the microclimate underneath them, suppressing the growth of many prairie plants and favoring others, including some nasty invasive species that can then spread into prairies.
– Trees completely change the habitat structure of a prairie, making it unsuitable for many wildlife species that rely on wide open habitats. As trees and shrubs increase in density, prairie animals are forced out.
– Many grassland birds avoid nesting near woodlands, or even lone trees. There are multiple reasons for this, but a big one is the abundance of predators that hang around in and under trees. A line of trees along the edge of a prairie creates a wide “dead zone” within which very few prairie bird species will nest. In landscapes where most prairies are already small and fragmented, the loss of that additional habitat can have serious consequences.
– Once trees and shrubs become established, they tend to promote the establishment of more. Some spread by rhizomes (underground stems) and all of them are good perch sites for birds, which drop seeds out both ends onto the ground beneath the trees. Once on the ground, shade from the trees reduces the vigor of prairie plants and helps woody seedlings thrive. Dense tree and shrub patches can also become fire proof because their shade prevents grass growth beneath them – and it’s grass that carries fire.
Burning prairie can suppress the encroachment of trees, including eastern red cedars.
Woody plants, including both trees and shrubs, have always been good at invading prairies but, historically, fires and dry climate helped keep them from becoming established across most of the grasslands of the Great Plains. Today, fire suppression, landscape fragmentation, and even changing levels of carbon and nitrogen in the atmosphere are giving trees the upper hand. As a result, my staff and I (ok, mostly my staff nowadays) spend an inordinate amount of time cutting trees down, burning grasslands to kill trees, and treating trees with herbicides.
Can you see why a holiday that promotes tree planting – especially in a grassland state like Nebraska – might make me a little nervous? There’s absolutely nothing wrong with planting trees, but the kind of trees being planted and the location they’re planted in makes all the difference in the world.
If you live near a prairie, here are two important tips to consider as you prepare to celebrate National Arbor Day by planting a tree (or lots of trees).
1. Do some research on the tree species you plant. Some species, such as Siberian elm, Russian olive, Autumn olive, and other non-native trees and shrubs can be very invasive in grasslands, quickly spreading by seed far from the parent tree. A quick internet search using the name of the tree and the word “invasive” will tell you whether or not the tree species you’re considering is one that could cause problems. However, even many native trees can spread into grasslands, so that leads us to…
2. Carefully consider the location of your proposed tree planting. As mentioned earlier, even a single tree, let alone a row along the edge or (heaven forbid!) through the middle of a prairie can wreak havoc on grassland birds and other species. Prairies and their plant and animal inhabitants thrive in wide open habitats; adding trees to those habitats can really mess things up.
By all means, plant trees in your yard, around your farmstead, or in a local park or school. Trees provide shade, habitat, food, and aesthetic beauty to cities, towns, and acreages, and you should feel good about contributing toward those things. However, as you celebrate Arbor Day, please don’t forget about prairies, the plants and wildlife that rely on them, and the hard-working prairie ecologists and land managers trying to conserve them.
So,
Happy Arbor Day!
(please celebrate wisely)
The Prairie Ecologist 
This post really “nailed it”, Chris. Plus, you’ve posted a couple of excellent candidates for “wallpaper” for my computer monitor with the pictures here! (That sunset photo reminds a bit of a certain oil painting we’ve both seen.)
I don’t know if the ADF offers Siberian elm or autumn olive as part of their tree list, but they do have some others that are questionable, e.g. the exotic golden rain tree which is invasive in the southeastern quarter of the US is offered in that region! And we do not know the geographic origin of even their “native” material. (Red oak of Pennsylvania origin may not be suited for the drier and windier conditions of Nebraska, just as a hypothetical example.)
Chris, Thanks for this important reminder that native ecologies don’t lack value if they aren’t a forest. At my church, we are trying to spread this message. The United Church of Christ was encouraging all congregations to plant trees. Here’s an article by the UCC about our efforts to educate our congregation about planting native prairie plants instead, in the same vein as your thoughts: http://www.ucc.org/news/kansas-ucc-stresses.html
Angela,
That sounds like a great idea!
Suzanne
Hi Chris. As I read this I get a grrr in my throat. Don’t panic. I am ready for an Up with Prairie week!!! There is so much hype about “plant more trees, plant more trees”. Oh yes trees are very beneficial in the right place and definitely not non natives. You gave a good outline of where trees are most beneficial but society has no clue as to the value of prairie spaces. The Up With Trees organization sees every blank spot as a place needing trees. Oh Ugh…. Can you tell I am a prairie person?
This is a well taken point. I have stopped giving to the Arbor Day Foundation because of their blanket approach to tree planting with little regard to local ecologies, and the exceedingly poor quality of, and in some cases inappropriate, plant material they offer. A local propagator of local ecotypes is always a better approach to habitat restoration.
Interesting, so there are other issues with this then? Have you contacted them?
Suzanne
A number of years ago there was a short article in Nebraskaland called Kill A Tree For Arbor Day. As someone once said, only God can make a tree but any ecological ignoramous can plant it where it shouldn’t be.
Good post! Forests and trees far too often gobble up the spotlight.
A good reminder on Arbor day. I’ve done battle with buckthorn and maple here in Illinois. I don’t think I’d want a maple even in the city any more.
Nice post Chris, it made me think of the park I used to frequent in Bloomington (area), IL where there is a good section that is filled with some kind of short olive trees. I wonder if they are not managing this park, they also had invasive sweet clover start to come into the prairie a couple of years ago, very unfortunate.
Suzanne
There’s nothing like the smell of eastern redcedar on my saw blade in the morning . . .
Agreed!
All great points Chris. There may come a day when prairie and forest-lovers will both have an abundance of intelligently managed ecosystems to learn from and enjoy. Until that day proper species selection and education are particularly critical to maintaining stable examples of ALL that Nebraska has to offer!
Trees are controlled on the African savanna by big browsers, in particular the African savanna elephant and the black rhinoceros. The decrease in the populations in Namibia has been thoroughly studied. There has been an increase in eye lacerations of cheetahs, from tree branches when they chase after their prey. So the big browsers are needed to control tree growth on the African savannas. What are the equivalents on the American prairies? Elk? Elk were heavily feeding on aspen saplings in Yellowstone National Park, so that was the reason why gray wolves were brought in.
I think trees in prairies will no longer be a problem as soon as people stop using fossil fuels. They will go back to cutting down trees and expand the prairies in the process.
James
I’ve been thinking lately that people who value Prairie might start using language like “our
grasslands and prairies are an important part of our forests.” If someone asks “what do you mean?” Wow! What an opportunity.
Maybe for Arbor Day 2014 the trend could begin for people to plant pocket prairies on their suburban sites. Neighborhood associations remove invasive woody plants from prairies in their towns.
Not too far fetched.
wes
Prairies are not just confined to the Midwest. Western Oregon is famous for its old growth forests, but right in the middle of the Willamette Valley is prairie. Prairie land everywhere is threatened by agriculture.
Awesome image!
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So just how do you think mother nature expanded our existing forests and jungles.All I hear from you folks is that you still think humans are in charge. I respect the knowledge but I can’t for a minute believe we are capable of controlling the natural change. I was taught in 1974 that where I live we were under hundreds of feet of ice. Maybe nature wants to re forest the prairies who are we to decide.
Grant, I hear you. Remember, though, that grassland “reforestation” is happening largely because of decisions humans have made, not because of processes apart from humans. We have made conscious choices to suppress fire and to plant trees throughout formerly grassland landscapes. Both of those actions have led to the much higher (compared to a few hundred years ago) rate of spread of woody species into grasslands. It’s up to us to decide whether or not to preserve some areas of open treeless grassland for the species and natural processes that depend upon that habitat type. There isn’t necessarily a right or wrong choice there – though I’m certainly an advocate for keeping some prairie around. It’s also good to remember that humans have played a major role in North American prairie for as long as it has existed. When the last glaciers receded and spruce forest gave way to grassland, people were here, and they were actively using fire as a landscape management tool – as well as hunting and otherwise impacting the landscape around them. Today, we’ve developed technologies that allow us to have an even stronger impact on the land, but even 5,000 to 10,000 years ago, we had the ability to heavily influence what prairies looked like.
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