Glossary - Agroecology: The Ecology of Sustainable Food Systems - page 374

secondary succession Succession on a site that was pre-
viously occupied by living organisms but that has under-
gone severe disturbance.
seed bank The total seed presence in the soil.
self-pollination The fertilization of the egg of a plant by
its own pollen.
Shannon index A measure of the species diversity of an
ecosystem based on information theory.
short food supply chain A route from production of a
food product to consumption by the consumer that
requires a minimum number of steps.
silicate clay A soil component made up primarily of
microscopic aluminum silicate plates.
silvopastoral system An agroecosystem that combines
trees and livestock grazing.
Simpson index A measure of the species diversity of an
ecosystem based on the concept of dominance.
slope wind Air movement caused by the different heat-
ing and cooling rates of mountain slopes and valleys.
soil creep The movement of large soil particles along
the soil surface by wind.
soil health The overall picture of the soil's ability to
support crop growth without degradation.
soil profile The set of observable horizontal layers in a
vertical cross section of soil.
soil solution The liquid phase of the soil, made up of
water and its dissolved solutes.
solution The process by which soluble minerals in the
regolith are dissolved into water.
specialist A species with a narrow range of environmen-
tal tolerance.
species evenness The degree of heterogeneity in the spa-
tial distribution of species in a community or ecosystem.
species richness The number of different species in a
community or ecosystem.
standing crop The total biomass of plants in an eco-
system at a specific point in time.

stomata The openings on a leaf surface through which
gases enter and leave the internal leaf environment.
succession The process by which one community gives
way to another.
successional mosaic A patchwork of habitats or areas in
different stages of succession.
symbiosis A relationship between different organisms
that live in direct contact.
synthetic variety A crop or horticultural variety pro-
duced through the cross-pollination of a limited number
of parents that cross well and have certain desirable
traits.
tilth The combination of the characteristics of soil crumb
structure, porosity, and ease of tillage.
transgenic A descriptive term applied to organisms
developed by transferring genes from one organism to
another.
transpiration The evaporation of water through the sto-
mata of a plant, which causes a flow of water from the
soil through the plant and into the atmosphere.
transported soil Soil that has been moved to its current
location by environmental forces.
trophic level A location in the hierarchy of feeding rela-
tionships within an ecosystem.
trophic structure The organization of feeding and
energy-transfer relationships that determine the path of
energy flow through a community or ecosystem.
valley wind Air movement that occurs when the heating
of a valley causes warm air to rise up adjacent mountain
slopes.
vernalization The process in which a seed is subjected
to a period of cold, causing changes that allow germina-
tion to occur.
water of hydration Water that is chemically bound to
soil particles.
watershed A portion of the landscape draining to a single
point.