A notion related to the amounts of toxic chemicals and other stressors in the environment, to the frequency and intensity of disturbances, and to their effects on humans, other species, ecosystems, and economies.

An event of relatively acidic surface water that can occur in the springtime when the snowpack melts quickly but the ground is still frozen.

The cultivation of trees in plantations, typically using relatively intensive management practices.

A quantitative estimate of the rates of nutrient input and output for an ecosystem, as well as the quantities present and transferred within the system.

Forces associated with crustal movements and related geological processes that cause structural deformations of rocks and minerals.

The deliberate breeding of species to enhance traits that are viewed as desirable by humans.

The gaseous envelope surrounding the Earth, held in place by gravity.

Litter and other organic debris lying on top of the mineral soil of a forest.

A spatial integration of ecological communities over a large marine area.

Grass-dominated ecosystems occurring in temperate regions with an annual precipitation of 25�60 cm per year; sufficient to prevent desert from developing but insufficient to support forest.