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Lesson 2

A Group of Young Longleaf Pine Trees Growing in a Forest Opening

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Student Information:

If you were to look at the longleaf forest from a bird’s perspective, it would be similar to a big piece of Swiss cheese. Over time, lightning, tornados, and hurricanes create “holes” in the forest by killing trees. It is only through the death of these older trees, that the younger forest can grow.

 

Teacher Information:

A quick glance across the longleaf pine forest may lead one to believe that all the trees are the same size. However, upon closer inspection tightly clustered patches of longleaf pine seedlings will be observed. Young longleaf pine seedlings actually take advantage of the forest openings created by the death of adult (canopy) trees to regenerate. These disturbances occur somewhat regularly. Lightning kills one or two adult trees frequently in the longleaf ecosystem while tornadoes and hurricanes may kill hundreds of trees infrequently. “Forest gaps” is the term that scientists give to these forest openings. This picture shows young longleaf pine trees accumulating in these gaps.

The reason for this phenomenon is twofold. Adult longleaf pine trees drop seeds every few years. However, these living trees are also dropping pine needles every day. Pine needles burn very well. Small longleaf pine seedlings growing amongst all these pine needles have a difficult time becoming established because frequent ground fires sweeping through the forest burn them up. Because there would be less accumulation of pine needles in forest gaps, fires are unable to travel far into the opening—thus giving small seedlings a chance to grow. You will also note how the growth of these seedlings in these gaps appears to follow a “bell-shaped curve.” The death of mature trees means that there is decreased competition and increased resources available for longleaf pine seedlings. Compared to “closed canopy” redwood, Douglas fir, or tropical rain forests, when walking through a longleaf pine forest you will immediately notice how open and sunny it appears. One would think that light would not be a limiting resource for seedlings. However, within these gaps light DOES increase as well as soil moisture and soil nitrogen (all elements needed for longleaf pine seedlings to grow). The farther one travels into the gap, the more of these resources are available. Seedlings in a gap center are getting more sun light, soil moisture and nitrogen than ones growing at the edge—and thus are larger.
 

Some of the longleaf pine seedlings clumped together in this picture are observed in various stages of growth. Some longleaf pine seedlings are in the grass stage. The grass stage is a period when seedlings are not growing much aboveground and instead are putting on a tremendous root system below ground. In this stage, longleaf pine seedlings resemble a clump of grass—hence the name. Longleaf seedlings are very resistant to fire at this stage. Trees may stay in the grass stage for several years until enough resources become available so they can grow in height. Other longleaf pine seedlings pictured are in the rocket stage. This is a stage when rapid height growth occurs in longleaf pine. For the rocket stage to start, excess resources must become available around the seedling. By growing fast, the tree is able to capture more resources then its neighbor, thus giving it an advantage. Also, rapid growth allows the tree to get its top above the frequent fires that move through the woods. Longleaf pine remains somewhat susceptible to fire when they leave the grass stage until they reach about 4 feet in height. Those trees that are stuck somewhere in between the two growth stages are usually thinned out by fire or stressed over limited resources.

 

Key Words and Concepts:

Canopy: A general term used to describe the area at the tops of trees. The term can mean all the treetops in a forest area, or parts of an individual, mature tree that are green. As longleaf pine reaches maturity, this canopy stops growing in height and flattens out – it is not beneficial to be the tallest tree in an environment dominated by lightning. Such a canopy in an old longleaf pine forest is called "flat-topped."

Competition: Two or more individuals attempting to secure finite resources for themselves. Competition can occur with abiotic factors like light, nutrients, living space, water, or biotic factors like mates. For example, a longleaf pine seedling may stay in the grass stage for several years until competition is reduced and resources become available.

Disturbance: Something out of the norm which can cause disruption and can be natural or man-made. These can be large or small in size (scale). In longleaf pine forests, hurricanes, lightning, fire, tornado, and insects are examples of natural disturbances. A man-made example would be logging.

Forest Opening: An opening without trees. A meadow or gap in the tree canopy were extra resources are available (like light, soil moisture, nitrogen, etc.) and fires may not be as intense. Usually these openings are required by certain plant species to regenerate such as the case with longleaf pine seedlings.

Gap: A small opening in the forest canopy caused by the death of one or several trees. The results are an increase in resources such as light, nitrogen, soil moisture reaching the forest floor. A gap is required for young longleaf pine to regenerate.

Grass Stage: The early period in a longleaf pine seedling's life, where it has no aboveground stem. In fact, the tree more resembles a clump of grass rather than a tree. Despite little sign of above-ground growth, the tree is growing an immense root system below-ground that we can't see.

Regeneration: Getting trees back on open land by planting or natural seeding.

Resource: A supply that can be drawn upon when needed. Supplies can be abiotic factors like light, nitrogen, and water or biotic factors such as meat.

Rocket Stage: A period in the life of a longleaf pine seedling when it begins growing very rapidly to get ahead of the next fire that may come through an area.

 

Suggested Activities:

  • Life stages of tree – longleaf pine
  • Graphing activity: Compare average yearly growth of a person to average yearly growth of longleaf pine. When you are 30, how tall will you and the pine be?
  • Demonstrate dormancy by planting seeds and placing them in the dark. Bring the seeds out into the light to watch for growth.
  • Identify living (biotic) and non-living (abiotic) factors that affect animal life
  • Recognize evidence of the sun as the Earth’s major source of energy
  • Describe changes to the earth’s surface caused by natural and man-made forces

Correlations to Course of Study coming soon!

 

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