A terrestrial biological community shaped by the regional climate, soil, and disturbance patterns where it is found, usually classified by the growth form of its most abundant plants.
biosphere
The highest level of biological organization, consisting of all living organisms on Earth plus the environments in which they live; the biosphere is located between the lithosphere and the troposphere.
convergence
The evolution of similar growth forms among distantly related species in response to similar selection pressures.
desertification
Degradation of formerly productive land in arid regions resulting in loss of plant cover and acceleration of soil erosion.
hyporheic zone
The portion of the substratum below and adjacent to a stream bed where water movement still occurs, either from the stream or from groundwater moving into the stream.
land use change
The conversion of land from natural to human-disturbed communities for resource extraction, such as agriculture or pastoral land use.
lentic
Of or referring to still water. Compare lotic.
lithosphere
Earth’s surface crust and upper mantle; the layer of Earth that includes the tectonic plates.
littoral zone
The nearshore zone of a lake where the photic zone reaches to the bottom.
lotic
Of or relating to flowing water. Compare lentic.
macrophyte
A rooted aquatic plant.
nekton
Swimming organisms capable of overcoming water currents. Compare plankton.
pelagic zone
The open water zone of a lake or ocean at some distance from the shore.
permafrost
A subsurface soil layer that remains frozen year-round for at least 3 years.
photic zone
The surface layer of a lake or ocean where enough light penetrates to allow photosynthesis.
phytoplankton
Photosynthetic plankton. Compare zooplankton.
plankton
Small, often microscopic organisms that live suspended in water; although many plankton are mobile, none can swim strongly enough to overcome water currents. Compare nekton.
pool
A relatively deep and slowly flowing portion of a stream. Compare riffle.
riffle
A fast-moving portion of a stream. Compare pool.
savanna
A type of community dominated by grasses with intermixed trees and shrubs.
tides
Patterns of rising and falling ocean water generated by the gravitational attraction between Earth and the moon and sun.
