Ecology Part 3 – Ecological Succession

Ecology Part 3 – Ecological Succession


Hi, this is Mr. Judd; and this avalanche pass. It’s a really neat spot in the High Peaks of the Adirondacks where an avalanche took out the entire side of a mountain and displaced and layed all of the vegetation down at the bottom. in ecological terms, we call this a disturbance. A disturbance is anything that disrupts an ecosystem. The topic of today is ecological succession which the term that means an ecosystem grows back and comes back after a disturbance. An avalanches isn’t the only type of disturbance. There are lots of others like tornadoes, floods, hurricanes, forest fires lots of others you can think of. This is a really neat picture that was taken after a forest fire. You can see the charred trunks of the trees that still remained. A photographer came back over a number of years to see what happens. So here is year two. Here is year three. Here is year four. You can see that the ecosystem is starting to recover. Plants are coming back. That is ecological succession. The first type I want to talk about is secondary succession. In this example we are starting with a mature forest. It gets burned and everything is destroyed. Nothing is left but soil after the disturbance. In step five, you can see some grasses and some weeds started to grow back. In step six some bushes and some evergreen trees start to arrive; they get bigger in step seven. And then in step eight we are back to our original state. And that original state is called a climax community. A climax community is any group of species that live in an area and be self -sustaining over a long period of time. So, here in New York State our climax community is mostly beech and maple trees. And in other parts of the world were they have different climate it’s a different set of organisms that make up the climax community. Primary succession is actually a more difficult type of succession. This is a picture I took in Iceland, and this back here is a glacier. And over time it has receded and melted. In its wake, it has left nothing but rock – barren rock. It is a very difficult place for any organism to grow. The ones that can a pretty neat, like this one. This green crust is actually a living things, it is called lichen. It is a combination of a fungus an algae. They can grow directly on bare rock. Some other things that can grow directly of rock are the mosses. These organisms are considered pioneers or pioneer organisms. They are the first organsisms that can start ecological succession on bare rock. This will eventually form soil And then regular succession will proceed until a climax community is eventually established. The difference here is that primary starts on rock, and secondary starts on soil. The last type of succession I want to talk about is pond succession, and here we are going to start off with an open pond. In this situation, the erosion of soil will lay sedement down at the bottom of the pond, and over time that pond will fill in with greater and greater amounts of sedement. and you can see that the community around the pond is also changing. in this example you can see it is almost filled and at the end it’s completely filled in. And you have, once again, a climax community that includes full grown trees and no pond where once a pond did exist. So that is ecological succession, and I hope that was helpful.

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