As you gaze towards the SW side of the Ridge and Valley Trail at Ruffner Mountain Nature Preserve in the vicinity of GZ, you will see several trees that appear to be growing out of the rocks along this ridge.
While we know that trees cannot actually grow out of bare rock, they can begin to grow from small amounts of soil and debris that collect in pockets of the rock. Over time the tree may grow well enough to send roots into the rock itself, causing the rock to split and making it appear that the tree has sprung from within the rock instead of from its surface.
The change in community structure observed over time is known as ecological succession. When the succession begins in an area that is previously unoccupied or unchanged by other species, the process is known as primary succession.
The role of geology in the stages in ecological succession:
Birmingham, more than most cities, is founded on rock. Its rapid growth stemmed from the earth below it, which held iron ore, coal, and limestone — all the key components needed to make iron and create an industrial power.
The region’s complex geology has also shaped the ecosystems of the area. As different kinds of rocks weather, they produce different soils, which support different types of plants and different animals that depend on them. For example, the limestone bedrock at Ruffner Mountain Nature Center creates calcium-rich, low-acid soils that host plants like American Basswood, Slippery Elm, and Shumard Oak, while the sandstone glades at Moss Rock Preserve are home to unusual species like Nuttall’s Rayless Goldenrod, Pineweed, and Prickly Pear Cactus. In other areas at Ruffner, hematite is evidenced in the soil. The name hematite is derived from the Greek word for blood because hematite can be red, as in rouge, a powdered form of hematite. The color of hematite lends it well in use as a pigment.
The sheer variety of rocks crammed together in our area creates many options for ecological diversity.
But where do these different rocks come from? In Birmingham, all are sedimentary rocks formed hundreds of millions ago. Rivers carried sediments to seas, and the weight of those seas compressed those sediments and altered their chemistry, with the result being new rock. Beach sand became sandstone, mud became shale, reefs became limestone, and swamp muck with its thick deposits of dead plants became coal. In fact, if you look closely, you can find the fossils of swamp plants and tiny sea creatures in rocks all around the metro area.
The changes that take place during any form of succession depend on a variety of environmental factors, such as the amount of moisture, temperature, and wind. One possible scenario for primary succession might begin with the appearance of simple plants, such as lichens and mosses. Such plants are able to spring up in tiny cracks in the rocks in which water and dissolved minerals collect.
When these pioneer plants die, they decompose and begin to form soil in which other, more complex plants can begin to grow. The second stage of plants might consists of grasses, herbs, and small shrubs. A characteristic of these plants is that they devote a great deal of energy producing huge numbers of seeds. They may live only one year, and spend the greatest part of their energy to ensuring that offspring will arise the following year. Species of this kind are known as opportunist species. Grasses are a common example of opportunist species.
Plants that make up the early stages of succession also die, decompose, and contribute to the growing layer of soil. This process takes place over hundreds or thousands of years, however. Eventually, the soil is able to support more complex plants, such as larger shrubs and small trees. These plants gradually take over from earlier communities since they are taller, have more leaves, and can capture more sunlight that was originally captured by simpler plants.
In the final stages of succession, taller trees begin to grow. They, in turn, block out the sunlight needed by smaller trees and replace them. The final stage of ecological succession is known as a climax community.
To log this find, answer the following questions and send the answers to the cache owner:
1) Why does it appear that trees are growing out of these rocks?
2) How long ago do you think that the rocks seen here were formed? What type of rocks are they?
3) Do you see evidence of coal in this area?
4) Can you see evidence of hematite in this area?
5) What is responsible for the different types of soils which support different types of plants and different animals that depend on them?
(Optional) Include with your log entry a photo of a tree that appears to be growing from rocks in this area.