Picture putting on a straw hat, sipping your favorite drink, and dazing out at the Florida seashore as a warm wind tugs at your clothes. You lay out your blanket and umbrella, putting on some shades, enjoying how cool you probably look on the down low.
You marvel at the peaceful nature of your surroundings and the drifting sand derived from alluvium parent material, Eolian sand, and marine sediments (Figure 1). Maybe, just maybe, you are also an aspiring soil scientist who loves the spodosol unique to this region as well as the ultisol found along the reaches of the southeastern United States. Or, perhaps, you might even like tortoises. Or, miraculously, maybe you like both.
Figure 1. Eolian sand deposits in Alcúdia Bay.
First of all, what even is spodosol and ultisol? I am glad you asked (or didn’t). Spodosol and ultisol are two of twelve soil orders on our globe. Believe it or not, like animals, soil actually has a taxonomic naming system where order is the least specific and species is the most specific a soil can get.
Figure 2. Here we have an aquod, a type of spodosol common specifically in Florida. Notice the deep leached E horizon (may be albic) and the two spodic B horizons that are much darker. The “h” distinction indicates humus moved down through the soil profile, which is organic material. This happens due to how large the sand particles are and how easily water leaches downward. Spodosol may also have an “s” distinction that stands for sesquioxides and that would indicate presence of Al/Fe oxides.
For simplicity, spodosol is an acidic soil characterized by organic material and aluminum and iron oxides (Figure 2). It is usually very sandy, so it is well drained and has a low water holding capacity due to large particle size. It is characterized by a spodic subsurface diagnostic horizon and often an albic E horizon. What this means is that there is a layer of soil that is extremely light in color due to leaching out of materials and a layer below that is a bit darker in which reddish and brownish materials accumulate. In short, this occurs by a process known as eluviation from the E horizon and illuviation into the B horizon.
Figure 3. Aquults and udults are two types of ultisols common in the Southeastern United States. The reddish subsurface diagnostic horizons indicates translocated clays from a sandier layer above (Bt horizons mean translocated clays). The extremely light layer is an E horizon that experienced this leaching. The darker surface layer is the A horizon that has organic matter. The “p” distinction indicates that the soil was tilled.
Similarly, ultisol is also acidic and can be relatively sandy, but it is different because it is usually a red soil due to clay content (Figure 3). I am sure some of you have listened to country music talking about red Georgia clay or something about how exciting southeastern soil is. This is actually an ultisol, often characterized by a kandic subsurface horizon (great group Kandiudults), which is a horizon in which clay translocates down through a soil profile. In other words, you get a lot of red clay in kandic ultisols and it is super common in the southeastern United States.
So what does this have to do with tortoises?
Let us focus in on gopher tortoises, Gopherus polyphemus, that are a vulnerable regionally threatened or candidate keystone species in the southeastern United States. Averaging 9 to 11 inches in length when fully grown, these herbaceous grazing animals can survive 40 to 60 years in the wild (Figure 4). Although they have such a wide range, their stability in Florida is of particular concern in which the species in endemic to all 67 counties, but populations are in decline.
Figure 4. Gopher tortoise eating its typical herbaceous diet.
Figure 5. Gopher tortoise enjoys his home in a longleaf pine sandhill.
Why are they in decline? Gopher tortoises require soils like Entisols, Ultisols, and Spodosols in order to develop their burrows because sand particles are easier for them to dig through. These soils are found in habitats like longleaf pine sandhills, xeric oak hammocks, pine flatwoods, prairies, and coastal dunes (Figure 5). These dwellings are of high importance for the survival and settlement of the species since the tortoises will spend 80% of their life in their burrows.
However, urban sprawl and unsustainable soil uses are actually depleting the amount of soil we have on Earth (Figure 6). It takes about 100 years to develop 1 inch of soil from natural biogeochemical processes, but practices like till farming and deforestation are making soil much more susceptible to erosion, meanwhile human development is covering these ideal soils with which gopher tortoises may settle. This means that we are making soil slower than we are using it, which is resulting in the endangerment of many species, not just the gopher tortoise.
Figure 6. Till farming can increase soil erosion by loosening the topsoil (A horizon).
Figure 7. A sense of possible niches for animals created by gopher tortoises burrowing.
In fact, gopher tortoise burrows offer a home for over 350 other species including mice, owls, rabbits, frogs, and the locally threatened indigo snakes. Their burrows are incredibly spacious, typically 15 feet long and 6.5 feet deep into the soil profile. Correlatively, if the tortoises cannot burrow due to the loss of available ideal soil, then many other commensal species suffer (Figure 7).
Conservation efforts by the Working Lands for Wildlife (WLFW) partnership with the Natural Resources Conservation Service (NRCS) is breathing new hope into restoration of gopher tortoise and, inevitably, other species’ habitats. Such practices involve prescribed burning, tree planting, and management of invasive plants. The goal is really to restore longleaf pine forests and reduce ideal sandy soil erosion so that gopher tortoises have more options for establishing their homes and, hence, many other species will benefit.
Just like how we mentioned how prairie dogs digging holes in the landscape in the Great Plains region substantially changes flora and fauna, gopher tortoises are no different. Who knew ditches and soil are so important to sustaining the animals of our world?
I have always wondered how soil works and what it is made of. Dirt has become a basic element in the English language, in the same way that metal, air and fire have. Those generalizations always made me ponder the origins of those classifications. I knew that soil had various sources for its composition, but I didn’t realize it took so long to make. What are the conditions required to make soil?
I think it would be interesting for you to do a blog on the soil at Penn State and how the weather, people, and animals affect its quality and quantity. For example, whenever it snows a lot and the snow melts, a lot of the previously upkept and good-looking yards look a little shabby. It would be cool to learn about how much the snow affects the ground beneath the veneer-like grass.
Hey Douglas, I would be happy to give a soil morphology overview for the Penn State area. Hopefully I don’t put you to sleep doing so, but I will try my best next week to make that interesting. Also, notice how in the blog I strictly used the word “soil.” Believe it or not, you will offend a soil morphologist using the word “dirt” and the reason for that is that dirt can be formed by manmade procedures and often upsets a soil profile. Soil is actually formed by climate, organisms, relief (topography), parent material (like how I mentioned Eolian sand and such), and time in a process known as pedogenesis. I can explain that more later and I will admit I only know so much, but I’ll do my best!
THIS TURTLE IS SO ADORABLE!!!!!!!! I never knew that it takes 100 YEARS for soil to form naturally. It really pains me to learn also that human activity is destroying these soils faster than they are formed (wow, what a surprise Yuki) and turtle habitats are getting destroyed because of it. It also makes me sad that I didn’t know that this species of turtles was almost (or already is) endangered. I imagine there are thousands, possibly millions of species that are endangered but we just don’t know about. I hope conservation efforts extend to those less known animals too (not just pandas and elephants and tigers, though they are very cute and popular). Also, I just learned today that turtle shells are actually modified turtle ribs. I guess it makes sense morphologically, but I thought they were like cool add-on structures. Oh well, turtles are still cute anyways, and I hope this turtle won’t go extinct because of human activity!
Turtles and soil?! Wow, I guess you learn something new every day. It’s so weird for me to consider turtles in the wild outside of a rainforest or a beach climate; I guess the stereotypes got me stuck thinking in one way about them. However, I’m not surprised that they’re also endangered due to human activity and that it’s a combination of our practices on soil and how we handle natural disasters that are causing this disruption. I know that you mentioned that gopher turtles can only live with certain types of soil, but what happens when the pH of that soil changes? I’m just curious because I know acid rain and runoff largely contribute to the acidification of substances on earth, and it would be cool to see how that ties into this topic. Either way, turtles still rock and they continue to fascinate me the more I learn about different species!
Hey Joseph, so fun fact is that most of those soils are actually already pretty acidic! The reason for that is to actually form some of the horizons in ultisol and spodosol, you need a decent amount of rain to make particles leach downward. It would actually be super bad if it did not rain as frequently or the rain got a higher pH (more basic) because that would change the soil profile! I am not certain this would affect the tortoises as much, but it would very much affect the other species that use its burrow as a home. Smaller organisms like earthworms and bacteria are heavily affected by pH.