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Forest Structure Basics Forest Layers: healy/schmied2012 Emergent --The tallest trees that rise above the canopy. Exposed to stronger sunlight and winds. 1. Canopy – Made of large mature trees. Forms roof of the forest, absorbs over 50% of incoming sunlight. Sometimes called the overstory. 2. Understory - Smaller trees and tall shrubs that tolerate shade. Also area for future canopy trees awaiting the opportunity to grow into the canopy. 3. Shrub Layer – Medium to low lying vegetation (3-7”). Bushes and saplings provide food for many forest animals. In return the animals spread the shrub’s seeds. 4. Herb - Fern Layer – Ground to about 3’. Lowest forest layer with leafy vegetation. Typically the first layer to turn green in spring. Often plants with short life cycles. O A B C 5. Litter or Organic (O) Layer -Dead material from all layers are decomposed here into topsoil. Especially by fungi, also bacteria, and soil invertebrates (worms, insects, & nematodes). Decomposition releases nutrients like NPK for reuse by the forest plants…. Decomposed organic material makes soil spongy, able to filter and hold water better! 6. Topsoil or A Layer - Uppermost soil layer. Dark and rich with organic material. Provides valuable nutrients, including water to forest. 7 & 8. B and C layers. Deeper layers… have more and larger rocks & less organic matter than layers above. Key forest terms Coniferous: Cone-bearing trees, usually with evergreen needle- or scale-like leaves Deciduous: Trees or shrubs that lose their leaves seasonally. Snag: A dead standing tree. Most people consider dead trees as a sign of an unhealthy forest, but snags are actually extremely important for many forest species, from tiny insects to large winged predators (eagles & hawks). Healthy forests have an abundance of snags. Log: A tree that has fallen to the ground. Often called “downed woody debris” and can last over a hundred years on the ground. This debris is home to wildlife and returns nutrients to the soil. Large amounts of downed woody debris are a sign of a healthy forest. There is a regular cycle to the life of a downed tree. First, insects such as beetles invade the tree. Bark beetles chew into the sapwood and carpenter ants carve tunnels for their colonies. The insect pioneers pave the way for the next wave of immigrants: especially fungi, also bacteria, and nematodes. Nematodes are microscopic roundworms that feed on rotting logs. Then predators higher up the food chain such as woodpeckers and salamanders feed upon life in the log. Mushrooms, mosses and lichens feed on the moist, decaying log. The moist environment acts as an oasis for organisms, which feed on the log, accelerating the log’s decomposition.