Posted in Central Ohio, History, Nature, Park review

Cranberry Bog: The World’s Only Floating Island

Previously I’ve pointed out that Jackson Bog and Cedar Bog aren’t really bogs. Now it’s time to look at a nature preserve that really is the bog that it claims to be: Cranberry Bog State Nature Preserve. However it’s not like any other bog in the world since the entire bog is floating in the middle of a lake.

I took this photo while standing on the floating mat of sphagnum moss that makes up Cranberry Bog. I’ve labeled some of the other vegetation that is growing here without the benefit of any dirt.

Here’s what happened. For thousands of years Cranberry Bog was an ordinary bog located in what came to be known as Big Swamp. In 1830 Ohio decided to build a dyke in Big Swamp to create a reservoir of water for our burgeoning canal system. The water inundated the swamp except for a mat of sphagnum moss fifty acre in size. Since Sphagnum moss is buoyant, this large, relatively young mat tore loose from the surrounding moss and floated to the surface. The bottom of the mat was lifted approximately six feet above the floor of the new lake, known as Buckeye Lake. Although the canal system is long gone, the floating island remains. But over the past 82 years it has been gradually shrinking in size and will at some point disappear entirely. Although there originally weren’t any trees on the island, trees have since sprung up on the island’s periphery. During storms strong winds will occasionally blow some trees over. When this happens, the fallen trees break off chunks of the island. The island is also made smaller by waves slapping against its edges and by ice rubbing against it in the winter time. In all the island has decreased in size from 50 acres to a mere 11 acres. Compounding the moss’ difficulties, the alkaline lake water is making the bog less and less acidic, so the sphagnum moss finds itself in an ever-more hostile environment. The only reason the island has lasted this long is because it started out as such a large mat that it created an acid-rich zone in the middle of the alkaline lake, but the ability of the shrinking mat to protect the moss from the surrounding water’s alkalinity is gradually decreasing.

Because the island is such a fragile habitat, Cranberry Bog is only open to the general public once a year. In previous years, the state held a lottery to determine who’d get to visit it. This is the first year that the island was open to anyone who showed up on the designated day. We paid a small fee to ride a pontoon boat to a dock on the island. Both Bob and I were really surprised that this mat of sphagnum moss was able to support such large trees. I’d also been wondering if standing on the island would feel like standing on a boat.. would I feel the island move and bob? No, because the layer of moss is so thick and massive it has a lot of inertia. I also wondered if my feet would sink down into the mat. They did not (we were only allowed to step off the boardwalk at a designated area).

This was taken from our pontoon boat as we approached the island ahead.
Here’s another view of the island from the boat. There’s a little boat in the photo that gives some sense of how large these trees are.
Now we are on the island, and a volunteer guide is showing us what the island is made of: sphagnum moss.
I’m standing on a floating mat of moss here. Although soft, my feet didn’t sink into it.
However if you dig into the mat a little ways, you soon find water.

Since the island is called Cranberry Bog, and I labeled a patch of cranberry plants in the topmost photo. It’s good to look at the top photo to realize how small this “shrub” is. I had thought it would look more shrubby, but Cranberry plants are a low-growing, creeping shrub; they only reach a height of 8 inches or so. Here’s a closer look at the Cranberry plants.

A cranberry stem.

When Freda Detmers did a study of the plants on the island 65 years ago, she was surprised that there were no Northern pitcher plants on the whole island. A Northern pitcher plant is a carnivorous plant that often co-exists with sphagnum moss in bogs. She introduced a single plant to the island then, and there are now more Northern pitcher plants on Cranberry Bog than there are in the rest of Ohio taken as a whole.

These leaves make up the “pitchers” of the Northern Pitcher Plant. The pitcher plants are surrounded by other plant species. In the foreground you are seeing some leaves of a poison sumac shrub. In the background, there are cranberry plants.
The Northern pitcher plants were in bloom while we were there. The flowers sit atop a surprisingly tall stalk.

Here’s how the Northern pitcher plant feeds on insects. The leaves form a “pitcher” that catches rainwater. On the top portion of the leaves, there are downward pointing hairs. If an insect lands here it’s easy to walk down toward the hollow portion of the pitcher, but it is difficult to walk back up against the hairs. Once an insect passes the pitcher’s rim, the leaf surface suddenly turns smooth and glossy, and it becomes difficult for insects to cling to the wall. Once they slip off, they end up drowning in a mixture of rainwater and digestive enzymes.

Looking into the trap. Note the downward hairs near the top of the pitcher, followed by a smooth cavity, and terminated by a pool of yucky-looking liquid.

But that wasn’t the only carnivorous plant on the island! There was a second plant that used an entirely different technique to lure insects to their death: the Round-leaved sundew.

This was a tiny plant that I photographed from the boardwalk with my telephoto lens. Low-growing cranberry shrubs surround it.
The dew-like drops are the trap.

The Round-leaved sundew plant lures insects to it by enticing them with the sweet, drops of liquid that it exudes from its leaves. The catch is that the liquid is very sticky, so if an insects gets close enough to try to eat it, it’s close enough to get stuck to the leaf. The leaf then slowly closes around the insect. Like the pitcher plant above, the leaf of the Round-leaved sundew digests the animal and absorbs needed minerals from it. If you stop to think about it, it makes sense that carnivorous plants might be found in such a setting because it can’t take up minerals via its roots from the earth because there is no earth. However the rest of the vegetable life on the island isn’t carnivorous, so it must be possible for a plant to absorb some minerals from the water.

Here’s a sample of some of the other members of the plant kingdom on the island.

Cinnamon Ferns
Arrow arum
Unbelievable – it’s practically a mini-forest.
Looking off the edge of the moss mat. Most of ground cover in this portion is poison sumac.

Poison sumac is a wetland-loving shrub. Like poison ivy, it has a substance (urushiol) that most people are allergic to. When these plants come in contact with the skin, people typically break out in a blistery, nasty rash. Surprisingly we are the only species that appears to be allergic to urushiol; birds will happily eat the berries produced by both poison ivy and poison sumac. In most of my photos, poison sumac appears to be a short, shrubby plant, but that’s only because most of the ones in my photos are young. As poison sumac matures, it grows up to be a very large shrub.

A field of young, poison sumac shrubs

One of the volunteers with whom I was speaking indicated that it has been extremely difficult to keep the poison sumac from overrunning the island. Because of the fact that the island it made of moss, they can’t use any herbicides. So the only way to get rid of it is to manually cut it down, but that is complicated by the fact that merely touching it will do you harm. She said she was among a group of volunteers who were cutting back a patch of poison sumac, and they were all wearing hazmat suits. However she still had a skin outbreak, apparently somehow touching the outside of her hazmat suit when she was taking it off. And she said that she had taken great care not to touch the outside of the suit. It’s too bad about her allergic reaction, but I think she (and the other volunteers) are to be commended for their service.

By the way when I got home, I was struck by the fact that I didn’t remember seeing any living sphagnum moss. After scouring my photos for a glimpse of some, this is the best I could come up with. The moss in the photo is growing around the base of some cranberry stems and round-leaved sundew. Some of the moss is green, others strands are almost white.

The sphagnum moss responsible for the island is underneath these plants.

Update: Cranberry Bog Day 2014 is scheduled for June 21st with boat tours (small fee) to visit the island. Further info here.

Additional information


Although all visitors are welcome once a year on “Cranberry Bog Day”, it is my understanding that groups can charter a boat to explore the bog on other weekends during the summer. To make arrangements, contact the Greater Buckeye Lake Historical Society. Contact information is posted on this page. The page seems to suggest that individuals can make arrangements for a tour, too, but one of the volunteers seemed to be suggesting that the rest of the tours had to be scheduled as part of a group. So if you want to go as an individual or a couple, double-check with the Historical Society.

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© Deborah Platt, Robert Platt and 2012 to 2021

8 thoughts on “Cranberry Bog: The World’s Only Floating Island

    1. Jill, thanks for stopping by! Do you know how you identify poison sumac in the field? If you lose your footing in a wetland, and you reach out to grab a nearby shrub to steady yourself, that shrub was poison sumac. 😀

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