Decomposition
The process of mechanically or chemically breaking down dead material.

Ice age
A period of time when large portions of the Earth are covered with glaciers. There have been multiple ice ages in Earth’s history.

Weather
Atmospheric conditions at any given time or place, measured in terms of wind, temperature, humidity, atmospheric pressure, cloudiness, and precipitation. In most places, weather changes from hour to hour, day to day, and season to season.

Boreal
The northernmost broad band of mixed coniferous and deciduous trees that stretches across northern North America, Europe, and Asia.

Density
The number of organisms per unit of space.

Köppen-Trewartha
A classification system for the world’s climates first introduced by German climatologist Wladimir Köppen in 1928 and later modified by American geographer Glen Trewartha. The system divides the world into five major climate regions according to average annual precipitation, average monthly precipitation, and average monthly temperature. Each category is further divided into subcategories according to temperature and precipitation.

Carbon cycle
The circulation of carbon in nature. Plants absorb carbon dioxide from the air; by photosynthesis, they convert it to carbohydrates, giving off oxygen as a byproduct. Animals then eat the plants and return carbon to the air by exhaling and through decay.

Ecological zone
A defined area of land characterized by certain environmental conditions and plant communities.

Latitude
1) It is one of many imaginary lines parallel to the equator. 2) Distance north or south of the equator, measured in degrees.

Carbon flux
The process or rate by which carbon moves from one pool to another.