Geobotany is the science behind dealing with the relationship between specific plant species and the substrata they find nourishment from. In order to gain a better and more thorough understanding of geobotany, I was assigned to read Jane Forsyth’s “Geobotany“. While reading I was given a few questions to keep in mind, below are my thoughts.
The geology of Ohio can be separated neatly into two parts, western and eastern, each having unique physical properties and topography that characterizes each. First, the western part of Ohio is supported by limestone, an extremely durable stone that is nonresistant to humid climates. Around 200 million years ago, the limestone began to erode, leaving the western Ohio landscape flattened. On the other hand, the eastern part of Ohio is underlain by sandstone, which is also supported by shale. Erosion of the sandstone occurred from water seeping between crevices in the natural cement holding the grains together. This process can take a long time, however, this is not the case for the shale. Shale is much less resistant, leaving the landscape with low plains everywhere that was not protected by sandstone. This resulted in the eastern side of Ohio having more deep valleys and higher land than the western side.
Although extreme in contrast, the difference in rocks is easily explained. In Ohio, the original horizontal sequence went limestone, shale, and then sandstone. This stratum was gently tilted into an arc, a result of erosion, which exposed the oldest rocks at the crest. In the west, this was limestone and left the landscape flattened. In the east, this was sandstone, and due to its durability, was not eroded away completely and instead left sandstone hills. The river that prompted this erosion was the same for each side of Ohio. Teays River, along with its many tributaries and contemporaries continued to erode the land undisturbed until the advancement of the glaciers of the Ice Age began.
These glaciers are called Pleistocene glaciers and they continued their way across Ohio slowly due to the steep-sided sandstone hills of the east. However, in the west, the glaciers met little resistance from the limestone plains and their track continued as far as northern Kentucky, as shown below.
When glaciers move across the surface of the landscape, they typically leave behind till, or unsorted glacial sediment. Tills were deposited continuously, covering most of Ohio. Looking at the composition of the till can reveal the nature of geologic materials which the glacier moved over. For example, in western Ohio, the glacial till is made up of lime and clay, products of the glacial grinding against the limestone. In eastern Ohio, the till contains very little lime and clay until you go near the sandstone hills, which then the till has a higher lime and clay concentration than anywhere else in eastern Ohio.
The material makeup of till has a major influence on the basic substrates available to plants. Looking at western Ohio first, the substrate is limey and clayey, thus providing poor soil, high in lime, poorly drained, and aerated. This means that water does not soak into the soil very quickly and oxygen is not available during wet periods. However, the supply of plant nutrients is bountiful. Now looking east, the substrate is very acidic and low-nutrient due to the exposed sandstone bedrock. Moisture is available as sandstone structures lessen in number at low elevations, providing humidity. The shale that lies under the sandstone also offers an acidic, low-nutrient substrate. The difference is that the shale is impermeable, allowing water runoff to rehydrate the substrate during dry spells.
Some examples of plants that prefer limey soil or limestone substrate include:
- American Beech, Fagus grandifolia
- Burr Oak, Quercus macrocarpa
- Ohio Goldenrod, Solidago ohioensis
- Silver Maple, Acer saccharinum
- Hackberry, Celtis occidentalis
Some examples of plants that prefer the sandstone hills of eastern Ohio
- Eastern Hemlock, Tsuga canadensis
- Shagbark Hickory, Carya ovata
- American Beech, Fagus grandifolia
- Chestnut Oak, Quercus prinus
- White Ash, Fraxinus americana
Some examples of plants that prefer the high-lime and clay-rich substrates of western Ohio
- Ohio Buckeye, Aesculus glabra
- Blackgum, Nyssa sylvatica
- Eastern Redcedar. Juniperus virginiana
- Sassafras, Sassafras albidum
- Winterberry, Ilex verticillata
Next, I’ll compare specific plants to gain a better understanding of how different substrates affect plant diversity. First is Eastern Hemlock, which achieves its best growth when in moist, acidic, rich, and well-drained soils. This is why Hemlocks are mostly limited to eastern Ohio, as they match these requirements. Sweet Buckeye has similar preferences, however, they tend to favor acidic, loamy, sandy, wet, and clay soil, which is best offered by the western side of Ohio. Similarly to hemlocks or sweet buckeyes, rhododendrons do well in acidic soil, requiring a very acidic pH.
One of the locations we stopped at on our field trip was the Cedar Bog Nature Preserve, which is the first nature preserve in Ohio. Cedar Bog is a relic of the Ice Age when glaciers advanced over Ohio. The landscape was carved by the Teays River and it filled Cedar Bog with sand, limestone, and gravel that hold an enormous amount of water. The groundwater rises to the surface, allowing specialist plants to grow there. However, the name Cedar Bog may be a little misleading as it isn’t really a bog, but a fen. Although they both contain water, bogs are typically enclosed depressions filled with rain water while fens have a steady supply of groundwater. Fens occur on flat areas or depressions of glacial outwash or when glaciers retreat. Fens are known for being biodiversity hotspots, with their nutrient-rich, moist soil that allows for a large variety of plant life and thus, wildlife too.
While at Cedar Bog, each of us was given a scavenger hunt assignment. I received the challenge of finding two different types of nuts. My first find was near the picnic tables and parking lot, under a black walnut tree. I have a few black walnut trees at home and always had to pick up the walnuts from the front yard as a chore so I felt sure in my identification of these nuts as black walnut nuts. The nuts themselves are known for being one of the best-tasting tree nuts, being used for snacking, baking and cooking. It is also one of the most expensive nuts on the market. In addition, they can help reduce the risk of cancer, heart disease, and diabetes!
The second nut I found had a spikey outside with a shiny brown inside. As someone who lived in Morrill freshman year, right outside the Buckeye grove, I was able to quickly identify this as a buckeye nut. One of their key features, the spikey “outside” of the nut is a kind of defense mechanism to keep animals from eating their nuts. However, even if they get past the first defense, the buckeyes have something else up their sleeves. Buckeyes are not edible, even for most animals. Squirrels are said to be the only animals able to eat the buckeye without any negative effects.
Because Cedar Bog has such a large variety of plants, some of them are specialist species that can only live in those very specific conditions that Cedar Bog provides. Each of these plants has a coefficient of conservatism, ranging from 0 to 10 as an estimate which a species’ relationship with the high-quality natural community that predates settlement. The first species is Swamp Birch or Betula pumila, which has a CC of 10, meaning it has a “narrow range of ecological tolerances that exhibit relatively high degrees of fidelity of a narrow range of habitat requirements”.
The second plant is the Hophornbeam or Ostrya virginiana. This plant has a CC of 5, meaning that it has an “intermediate range of ecological tolerances that typify a stable phase of some native community but persist under some disturbance”.
The last plant is Dog rose or Rosa canina. This plant has a CC of 0 meaning it has “a wide range of ecological tolerances. Often these are opportunistic invaders of natural areas or native taxa that are typically part of a ruderal community”.
Thank you for reading!