Forest ecosystem consist of producers and consumers. Producers are organisms that are capable of producing the energy they require themselves. Green plants are the most significant producers of the forest. They gain their energy from sunlight. They convert this energy to chemical compounds such as sugar during a process known as photosynthesis. Consumers gain their energy by eating other organisms that contain these chemical compounds originating from plants. 


A birch forest during the summer. Birch trees and other green plants convert the energy they receive from sunlight into chemical form. 

Herbivores are consumers that eat plants, whereas predators are consumers that eat other consumers. The forest's producers and consumers form food chains. In these food chains, the energy bound by producers travels from consumer to consumer.

Let's consider an example of a food chain. An oak tree binds energy it gathers from sunlight and converts it into sugars. The tree uses these sugars as its source of energy to grow and develop. However, the leaves of the oak can also be consumed by a butterfly larva. The larva is a consumer that uses the sugars produced by the oak as its food. When the larva metamorphoses into a butterfly, it can become the food of a insect-eating bird. In turn, this bird can become the prey of a larger predator bird. In time, all these organisms will die, and the chemical compounds contained in their bodies will return to the soil to be decomposed by bacteria, fungi, and invertebrates. This is how the energy produced by plants flows through ecosystems. The nutrients contained in dead organisms ultimately return to the soil as they decompose. From there, it is once again accessible to producers.

In summary, food chains consist of 

• producers or green plants.
• 1st degree consumers or herbivores.
• 2nd and 3rd degree consumers that are predators.