Sunday, August 16, 2015

Eastern Prickly Pear Cactus

If someone says the word "cactus," what do you think of? Deserts? Heat? Stark, sandy landscapes? Ohio probably never crossed your mind, and why should it? There's no cacti in Ohio...right? If you thought that, you'll probably be very surprised to learn that Ohio does indeed have a species of native cactus.

Sandy Spring Cemetery
I was down in Adams County last week to do some exploring, and I decided to visit the cemetery pictured above. This is Sandy Spring Cemetery, a small cemetery that lies on the Ohio River. Cemeteries are often very important places in the botanical world. As humans expand into an area, they have a nasty habit of destroying all of the native ecosystems during development. Cemeteries face a different kind of alteration. When creating a cemetery, graves are dug and sometimes the native flora is mowed and grass is planted in its place. Sometimes cemeteries become abandoned and are not maintained. Since the soil composition wasn't altered (farmed, removed, eroded, etc.), seed banks still exist, and the original flora might recolonize the area. An example of this is Bigelow Cemetery in Madison County, now a state nature preserve. Bigelow Cemetery was a pioneer cemetery in the Darby Plains, an extensive prairie system in western Ohio. Although most of the Darby Plains were plowed and ultimately destroyed, Bigelow Cemetery was never plowed. It is one of, if not the only, place in Ohio where original, unplowed prairie remains. Had it not been a cemetery, it would have been turned to farmland like the rest of the prairie. Sandy Spring Cemetery is another such instance of a cemetery saving a special area, and I'll get to that later.

Eastern Prickly Pear Ohio
My reason for visiting the cemetery was to see the native Eastern Prickly Pear, Opuntia humifusa, pictured above. It can be found in the Oak Openings region of northwest Ohio and in certain places in southern Ohio. The Eastern Prickly Pear prefers dry, sandy soils and full sunlight exposure. This is why it can be found at the sandy Oak Openings. The Oak Openings region is essentially left-over beaches (hence all the sand) from a long-gone lake called Lake Warren. It's a different story along the Ohio River though. The Eastern Prickly Pear makes its home here in the very rare Ohio River sand terrace habitat.

If we look at satellite imagery, we can get a better idea as to how one of these sand terraces forms. This is a closeup of the section of the Ohio River in question. Ohio is the landmass to the north of the river (where Sandy Spring Cemetery is located), while Kentucky is the landmass to the south. I have outlined two sand terraces in red. To understand how these formed, we have to understand how rivers affect the land through erosion and deposition processes. Above you can see a "meander," otherwise known as a river bend. When flowing water comes to the start of a bend, the majority of the energy goes straight into the bank. This erodes that bank, creating what is called a Cut Bank. A cut bank is essentially just a very steep bank. Now, on the side opposite of the cut bank is what is called the Point Bar. While cut banks are formed through erosional processes, point bars are formed through depositional processes. When the water hits the cut bank, it erodes particles of soil and rock. The water then essentially ricochets off the cut bank toward the opposite side of the river. By this point it has lost some momentum, and the now-slower water deposits some of the soil/rock material it had previously picked up. To see a visual representation of this process, go to this link. This process repeats over and over, slowly eating away at one side of the river while depositing sand on the opposite side. Eventually you get sand terraces like the one above. As you can tell by the agricultural fields, the sand terraces are flat.

Right below the top layer of plants is sand that is a result of thousands of years of buildup from river deposition.
Sadly, being flat has led to this habitat's destruction. Early settlers traveled primarily by river and lived primarily by rivers. As settlers moved westward via the Ohio River in the 1800's, they passed mile after mile of the forested Appalachian foothills. These large, steep hills were unsuited for farming. The settlers were looking for a flat area to farm, as a farm would be their main source of food and goods. When settlers came across these flat sand terraces, they decided to stop and try to set up their homestead. Now, well-drained, dry, and sandy soil isn't the best for farming, but when the alternative is to keep floating down the river for who knows how long, you take your chances. As these sand terraces were developed into farmland and small towns, the unique habitat was slowly destroyed, and with it the unique plant community that called it home. Nowadays original sand terrace habitat is rare, and as a result many of the dry, sandy-soil-loving plants are too.

Range map courtesy of the Biota of North America Program (BONAP).
The Eastern Prickly Pear is a wide-ranging cactus found throughout much of the eastern United States. It is rare in many of its northern locations, including Ohio where it is state-listed as Potentially Threatened. One reason is the destruction of proper habitat (like the development of sand terraces). Another reason is the removal of wild plants from a wild population. People like to have these as a yard plant, and some will simply go to a wild population and transfer those plants to their yard, reducing the individuals in that population.

There are records from a total of 19 counties here in Ohio, although only 13 of those counties have records from after 1980. It appears to be disappearing from the southern counties that are away from the Ohio and Scioto Rivers, although the lack of records from the past 35+ years might simply reflect a lack of effort to keep tabs on those populations. You should look for this species in well-drained sandy soils that are exposed to sunlight.

Eastern Prickly Pear Ohio
Of course, it wouldn't be a post about a cactus without talking about their infamous defenses. The Eastern Prickly Pear employs two different types of defense against a would-be herbivore. The first, and most obvious, are spines. These spines are actually modified leaves, although the cells in spines are dead instead of living like a normal leaf. These spines grow out of a dark bump on the cactus called the areole. The other line of defense are glochids. Glochids are tiny hair-like spines that also grow from the areoles. Unlike the spines, these glochids break off very easy and readily irritate the skin. I personally found this out after touching one of the cacti to get a better look. The rest of the day I kept pulling out tiny glochids that had embedded themselves in my hand. You can see these glochids in the photo above; look for the red clusters protruding from the areoles. There are hundreds of glochids in each cluster.

Eastern Prickly Pear Ohio
Cacti, as a whole, are strange. They're plants, but they really don't look or act like other "normal" plants. They are extremely modified and have many adaptations that allow them to live in dry or drought-prone areas. Most species, including the Eastern Prickly Pear, are succulents, meaning they have thick, fleshy pads that are used to store water. Since they lack photosynthetic leaves, all photosynthetic processes occur in the enlarged stem. They also employ a special water-saving process during photosynthesis called Crassulacean acid metabolism, better known as CAM photosynthesis. Those are only a few of the many adaptations. Of course, Ohio isn't quite like the deserts of the Southwest or South America, but the Prickly Pear uses these adaptations not to simply survive in an area, but to exploit a hard to grow in area. As I've previously mentioned, this species prefers sandy soils. This isn't the easiest type of soil to grow in. Any rainfall will simply seep out of the sand instead of remaining easily accessible like most soils. As a result, these soils are very dry. Add in full sunlight, and you have a very hard place for a plant to live in. The Eastern Prickly Pear, with its water-saving adaptations, can easily take advantage of this type of habitat and thrive, instead of facing intense competition in a more forgiving environment.

Eastern Prickly Pear Ohio
If you look at the bottom of this photo, you can see some of the prickly pear individuals nestled among the other plants. The hills in the background are actually in Kentucky. Those hills are the cut banks from the Ohio River. The rest of the ground you see is part of the flat sand terrace.

I'm currently finishing up this summer's lab work. This upcoming Saturday I move back into the dorms at Ohio University and start classes on that Monday. I plan on trying to get out one or two more posts this week since I have a few days of "rest" before dealing with the craziness of moving in and starting classes. Thanks for reading!

4 comments:

  1. Thanks for a great post. I love how you tell the story of plants in relation to the history of a place. You have a gift for understanding and being able to educate others. Good luck at school this year!

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    1. Hello Stacy! Thanks so much for the kind words!

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  2. Great in depth post Kyle, you have a new follower/fan.

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