Glossary - Afforestation, Reforestation and Forest Restoration in Arid and Semi-arid Tropics - page 251

Carrying capacity The total population that a given ecosystem can support in bal-
ance. Though population in nature is never stable—it always varies cyclically—yet
a mean value between the fluctuations can be said to be the carrying capacity of
that ecosystem. In case of a given piece of land, the naturally occurring density of
trees can be said to be its carrying capacity. It may be worthwhile to note that while
designing spacing between plants in a forest plantation, the carrying capacity should
be kept in view. No matter how many trees may be planted in a hectare of land,
ultimately the number that will survive is determined by the carrying capacity of that
land, unless the land is artificially irrigated and manured.
Cartesian co-ordinates The familiar system of locating a point in space by measur-
ing its distances from two perpendicular axes called the X-axis and the Y-axis. The
position of point is often denoted as ( x , y ) where x and y are the distances measured
along the X-axis and the Y-axis, respectively.
Cation An ion in an electrolyte solution that migrates to the cathode.
Cation-exchange capacity The maximum quantity of total cations that a soil is
capable of holding at a given pH value. It is used as a measure of fertility, nutrient re-
tention capacity, and the capacity to protect groundwater from cation contamination,
and is expressed in the SI unit centimole per kg.
Central nursery A large and permanent nursery with proper infrastructure and
establishment. Such a nursery is well equipped to produce plants of a large number
of species and of different sizes.
Chain and compass The principal equipment used in surveying tracts of land for
afforestation programmes. The chain is made of iron wire links, and is usually of 20 or
30 m length (in case of metric system), and consists of 100 links. The compass is often
the prismatic compass, capable of reading half a degree of angular measurement.
Chainlink fence A fence of heavy steel wire woven to form a diamond-shaped
mesh. The wire is often made of galvanised iron, in diameter from 2 to 3 mm. The
size of mesh cells may range from 5 to 15 cm.
Check dam A structure built on natural water courses, streams or rivulets, to check,
obstruct, or slow down the flow of water. It is meant to prevent water from building
up velocity and thereby carrying heavy charge of silt, thus serving the dual purpose
of preventing soil erosion and improving soil moisture.
Chlorpyriphos A chemical pesticide commonly used to control termites.
Clay Soil consisting of very fine particles, usually hydrous aluminium silicates and
other minerals, characterised by being plastic when moist but hard when dry. Clay is
found in most natural soils in some proportion. It improves water retention capacity
of soil and is the principal source of nutrients for plants. In arid areas, clay is often
available in ponds or tanks and is collected when these run dry. It is one of the three
ingredients of the potting mix used in nurseries. Sand and manure are the other two
ingredients.