Post 5 - Structual Layers

To transport water, trees have special cells, called xylem, that line up in a ring of long tubes to link the roots to the leaves. Through evaporation, sunlight pulls water from the leaves, creating pressure on one end like someone sucking through a straw. The xylem tissue uses this pressure to suck water up from the roots. But the leaves aren't just consuming water. They are busy using sunlight and water to make sugar in a process known as photosynthesis. Other transport cells, called phloem, carry this carbohydrate-rich food to the growing parts of the tree. Just like in the rest of the forest, the different parts of the tree interact to keep it alive.

How do you think the different layers of the forest, from the plants on the ground to the trees in the canopy, interact?

Think back to our discussion on succession on the first post. Remember how sunlight influences the structure of a forest? While some plants need it, others can grow with very little. The tallest trees in the forest, which compose the canopy, catch up to 75 percent of the light that comes from the sun. In this forest, the canopy contains Douglas-firs, which need sun to grow, and western hemlocks, which can grow in shade or sun. Below them, slower growing, shade tolerant species make up the understory. These trees catch most of the remaining light, leaving little for the shrub layer of smaller plants beneath them. On the forest floor you will see many varieties of mosses, fungi, low-growing plants and decomposing dead matter. These complex layers interact to form a diverse old-growth forest. Look high and low to see if you can define all of these layers.

We know layers exist above the forest floor, but do you think anything lives below in the soil?

Click on the pictures below to enlarge them.