Chapter 13. Chapter 13: Forests

What is the three-dimensional structure of a forest...?

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Guiding Question 13.2

What is the three-dimensional structure of a forest, and how are the plant species found there adapted to their level of the forest?

Why You Should Care

Aldo Leopold, considered a father of modern environmental science wrote, “One of the penalties of an ecological education is that one lives alone in a world of wounds.” By this, he meant that, once you know what you’re looking at out in "nature," you’ll unfortunately realize just how messed up most forests and other natural areas are. The three-dimensional structure of a forest is an indicator of its health. For example, a forest with trees of the same species, all uniformly sized, and little woody vegetation (small trees or shrubs) underneath is probably a human-maintained tree plantation grown for paper pulp or lumber. A forest with densely growing shrubby vegetation has probably been disturbed somehow: Road clearing or lumber removing could open up light gaps to allow dense growth of shrubs; invasion by non-native species that can out compete native species; or the overfragmentation by development.

The three dimensional structure of forests is also important to understand if one is to understand energy flow in forest ecosystems and its impact on climate. Similar in concept to the way inefficient energy transfer means fewer organisms at each trophic level (refer back to Infographic 8.2), incomplete light capture at each level of the forest means less total plant biomass but higher photosynthetic efficiency as you travel down through each layer of the forest. In this way, forest plants are able to capture nearly all of the light energy that reaches them through the atmosphere.

Infographic 13.2 Interactive

Match the description to the forest layer or layers:

Question 13.1

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999
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Correct.
Incorrect.

Question 13.2

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Question 13.3

Where plants are most likely least efficient at photosynthesis:

Emergent layer aFyLQOV9P9qF6KzY

Canopy aFyLQOV9P9qF6KzY

Understory 6Tla4sTC7UhhcmHA

Forest floor 6Tla4sTC7UhhcmHA

999
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Correct. This could be said of both the canopy and the emergent layer.
Incorrect. This could be said of both the canopy and the emergent layer.

Question 13.4

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999
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Question 13.5

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Correct.
Incorrect.

Question 13.6

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Correct.
Incorrect.

Question 13.7

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999
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Correct.
Incorrect. Although the emergent layer trees are larger than canopy trees, canopy trees represent the most common size, and would therefore hold the most biomass in the forest.

Question 13.8

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A canopy has come to mean any overhanging covering. Since the leaves at the tops of forest trees interlaces themselves to form an almost continuous cover, the name seems appropriately applied.

Question 13.9

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Since there are few gaps in the canopy, plants in lower layers must be very efficient at capturing light. This is especially true for forest-floor plants if there is an understory. The understory trees and shrubs intercept nearly all of the light that makes it through the canopy, leaving little for plants on the forest floor. Food webs start with producers, so in this case, the canopy trees would be the most productive producers and their leaves and carbohydrates are the entry point of energy into the ecosystem. This probably takes a less direct route than the food webs you are used to seeing. For example, a chain in the web could be: leaves from canopy fall to floor, feed decomposing microbes, which feed predatory nematodes, which feed predatory fungi, which feed fungivorous beetles, which feed songbirds, which feed hawks.