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Good morning naturalists!
Welcome to day four of our week on the forces of nature. So far this week we have discovered how forces like water, fire, and humans impact the natural world. Today, we are going to learn what happens after these forces come through. We will learn how nature changes and responds over time to the powerful forces that change it.
Do we look the same for our whole lives? Of course not! We change as we grow up and grow old. Just as people change as they grow, so does nature, although nature usually changes and grows much more slowly than people do. In nature, change over time is called succession. How do you think an ecosystem here in the Ozarks (or in your own hometown) might change as it grows older? What about the living things that live in the forest, would we find the same types of plants or animals in a young forest as in an old one?
Scientists like to split succession in the natural world into two major categories: primary and secondary. Let’s quickly discuss the differences between the two. When a volcano erupts or when a glacier starts to recede, it creates or exposes landscapes that have never been able to support life before. But now these new landscapes can begin to serve as habitat for living things, we call this primary succession. Secondary succession, on the other hand, happens when a disturbance (such as the ones covered earlier this week) impact and possibly even destroy a previously-inhabited area. In order to remember the difference between the two, one of the biggest clues is the presence of solid rock without any soil. Which of these two types of succession do you think is more common on our planet?
No matter what type of succession you’re looking at, the steps the ecosystem takes to grow and mature are fairly similar. Let’s take a look at this page of the ONSC field journal:
Let’s take some time to fill this out together, in order to help us create a sort-of field guide to the different stages of succession we might see around us. Let’s start with a disturbance, as that’s probably the easiest one to identify on the guide. Go ahead and label that section.
Now, we’ll move clockwise around the chart, following the arrows. Imagine a fire or storm has torn down a section of forest, leaving behind only bare soil. If you come back in a month, will you expect full-grown trees to have grown? Probably not. Instead, you will find small plants and fungi growing in this newly-open real estate. Just as the pioneers were among the first people to develop new parts of the country into the systems we have today, pioneer species are the first species to move into an area after it has been disturbed. If you have weeds that like to grow in your yard, chances are that those plants could be considered pioneer species too!
Examples of pioneer species. What plants do you see? What are others that you might find in your community?
Stage one complete, so let’s look at state two! At this time, shrubs, vines, and fast growing, sunlight-loving trees like cedars and pines begin to move in and colonize the forest. These often grow in dense patches, making it difficult for large animals to pass through. It might be hard for deer and coyotes to live in the shrub stage forest, but who would like it more? What animals would thrive in all of those little nooks and crannies?
How does this stage compare to the pioneer stage? Which would be easier for us to pass through?
The first two stages of succession happen fairly quickly; a disturbance that happened when you were born would probably have reached the shrub stage by now. There is a much larger time gap -at least several decades- between the second and third stage. In the third stage, the cedars and pines are now full grown. The slower growing deciduous trees (trees that lose their leaves all at once) like oaks, maples, and hickories begin to colonize the forest. To the untrained eye, this forest can look ancient, but in most parts of the country, this forest is not yet fully-grown. Instead, we have a young forest.
Here at ONSC, our young forest is made of cedar trees that are about 70-75 years old. It’s fun to think that what is old for a human life is young for the life of a forest!
As the forest leaves behind its youth, the oaks, hickories, and other deciduous trees are full grown and well mixed in with the cedars and pines. Ta-da! You now have a mature forest. Once the deciduous trees are fully grown, the forest is now in a somewhat stable state. As individual trees die, others of similar species will take their place. The forest will not change as quickly or as easily as it did when it was still recovering from the disturbance. That being said, it is important to remember that a habitat in any stage of this cycle can become disturbed and move back to step one.
An example of a mature Ozark forest. What do you notice?
Here’s a question for you: How come mature forests are not over-run with grasses, dense shrubs, and cedars? They grow quickly and in large numbers, after all. This is a time to think back to our focus on limiting factors from week four. In this case, the limiting factor for most of these species is sunlight: they simply can’t grow well in dark spaces! Once a well-developed canopy of trees is in place, most of the early-successional plants will wither and die quickly from the lack of light. The slower-growing trees are more well-adapted to the darker conditions below and can take their time growing. This is why a healthy forest will have a mix of every stage. Just as we have many needs to survive, many living things thrive when they have access to several different types of habitats. These edge habitats allow animals to meet several needs quickly. In the end, just as a beautiful quilt is made up of many small pieces of different fabrics brought together in one place, a forest is at its best when it has a high diversity of successional stages.
What successional stages have come together here? What kind of animal would like to live in this place, and how would it use each distinct successional stage?
An important thing to mention is that in different parts of the country (and the planet as well), the species at each stage in the cycle look different. For example, if you live in the Pacific Northwest, your younger forest will have many alder trees, while your older forests will have many more hemlocks. It can be a fun experience to learn about what makes your area unique. If you want to learn more, research the history of your state. What did the first settlers of your area do to make money? If they cut down trees, what trees did they cut? If they farmed, did they have to clean specific plants out of the way? What animals did they see on a regular basis, and what habitats do those animals love? All of this information can give you clues about your area’s successional history. If you are looking to practice scientific writing, this is a great research topic as well.
Change over time doesn’t just happen out in the middle of the woods. Go outside or look out your window all around where you live. Whether you live out in the country or in the middle of a city, write down some changes you see happening around your home. They don’t need to be natural; they can be man made changes like construction or roadwork. Write down the changes you see happening around you. Now keep track of those changes and write them down each day for the next week and see how much has changed in one week’s time. In addition to that, see how many different stages of succession you can spot within a week. If you see any younger stages, ask someone who’s lived in the area for a while what it used to look like!
Since today is Thursday, it’s time for Food For Thought! One of the biggest parts of our on-site programming here at the science center is measuring our students’ food waste. This week, we decided to measure staff food waste! Let’s find out how we did!
Well naturalists, it’s hard to believe we’ve been exploring together for seven weeks! As always, we will have our Find-Out Friday live tomorrow, beginning at 11:00AM CST. Don’t forget, if you have any questions about the forces of nature, or about nature in general send them in to our Facebook page or to Socialmedia@onsc.us.
Also, this is our last call for submissions for our naturalist grab-bag week. If you would like to write about something you love in nature, we will be taking submissions until Saturday, May 16th at 12:00PM CST.
If you enjoyed watching today's lessons and would like to purchase one of our ONSC Virtual Merchandise Packages, which includes an ONSC Program T-shirt and field journal, click to go to our Online Store.
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May 14 & May 28