4C – Forest ecosystem

Supporting article C: A short example of a forest ecosystem: Canada


Forest Ecosystems of Canada

Ecosystem dynamics
The apparent stillness of a forest belies the ecosystem dynamics at work behind the scenes in a series of interrelated and ongoing processes related to:
• energy input;
• circulation of the elements essential to life: carbon, nitrogen, hydrogen, etc.     (biogeochemical cycles);
• water circulation.

All living organisms need energy to maintain their vital functions and grow. However, the energy in an ecosystem cannot be recycled; it must be constantly renewed.

Energy can only enter an ecosystem through plants. Moreover, barely 1 to 3% of the light that reaches the plants is absorbed via photosynthesis. The rest is lost in the form of heat.

Plants use light to manufacture their own food and tissues (leaves, wood, fruits, etc.). They are called producers or autotrophs: they live on the most basic inorganic (not living) elements, such as carbon dioxide and water, and not by consuming other living organisms.

Every living organism that dwells in an ecosystem depends entirely on the photosynthetic process carried out by plants. The more vigorous its plants, the more dynamic an ecosystem will be.

All animals, insects and micro-organisms are directly or indirectly fed by plants and are called consumers or heterotrophs. For example, a deer eats leaves from a tree and produces waste, which in turn feeds the decomposers. The hunter who eats the deer benefits from the meat that his prey produced from plants. Organic matter thus circulates in the food chain, is transformed, and is ultimately decomposed into basic elements (CO2, water, nitrogen, etc.) that can once again be assimilated by plants.

Throughout this process, the energy that is incorporated by plants into the biomass is liberated through the respiration of autotrophs and heterotrophs, and gradually dissipates as heat.

Water is essential for the circulation of elements through an ecosystem and is one of the necessary components of photosynthesis. Moreover, living organisms are generally made up of 70 to 90% of water.